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Magpick user manual

1. 4 6 8 10 12 ee eS ee ee ee pit M Moe Bao KYRENIA TN B e Lie IG EA 6e eee ede UE 4 6 8 10 12 Inital depth 10 m Xm Inital depth 0 5 m Xm 4 6 8 10 12 14 de OE TAE hive E sa me E aha tea 40 o A O E O E A la R E E E he wy enis ETEN EA er 4 6 8 10 12 14 Xm inital depth 5 m 4 8 10 14 I AN E10 e tee Brin Le Ed bbedeejeee ghia A b Cen Ub s pecus c A A SEEEN ETE 4 6 8 10 12 14 Xm Synthetic field 4 6 8 10 12 14 N meyer ates LM ME D eee A PENES 4 6 8 10 12 14 Figure 34 5 attempts to find a dipole 84 Tutorial Tutorial 3 A solution based on profile data So far we have used only an interpolated magnetic map to find the position of the dipole Generally speaking this map is not always true If the spacing between data points is large the interpolation procedure fills in the cells in between These interpolated values may not reflect the real behavior of the magnetic field However these values will be used in case of grid based interpretation As you already know MagPick allows you to read profile data It also can use the profile data for finding magnetic dipoles To investigate this do the following Load file bomb grd Go to Profiles Load list and select file bomb bot 1st 19 profiles line are loaded Redraw the picture t
2. uN Then you specify width of the pen O means 1 pixel pen other values show pen width in physical units of your map The line coordinates follow They can be as many segments as you need A pair occupies a separate string Points If you choose to highlight some specific locations you use points To plot them prepare the file 19 Basic operation of MagPick POINTS 12 UTM 5 5 10 RED Point num 1 UTM 10 10 10 BLACK Point num 2 First line of the file has a magic word POINTS and the annotation font size in points This line should be always the same font size can vary Then each line describes one point The first word could be UTM or GEO X and Y coordinates in the same system as data are follow The third number is the size of the mark on the screen in pixels Zero size produces no mark The color name can be chosen from the set above The rest of the string is optional text which appears near the mark The mark itself has a shape of with the hot spot in the centre Polygons This allows you to draw filled polygons to obscure part on the picture The file has exactly the same format as the line file MagPick joints first and last point of each line to make a closed polygon Specify the color you you wish The pen width should be zero to fill in required area only Clip MagPick does not do real clipping as PostScript does Do not
3. Linear transformation parameters scale and offset h Type of export DXF and BNA only Includes segments points or both Figure 10 Export picks as DAT file Export results can be loaded into MagPick if you export them as Magpick points or Magpick lines These represent the internal MagPick format for additional drawings on top of a magnetic map In the first case middle of the picks gets exported in the second case picks as lines You can choose the color and size of annotation for these elements 3 4 Automatic pick Besides manual anomaly selection MagPick has a tool for automatic finding of pair maximum minimum This feature is experimental and will be improved in future Presently is is available under Edit Auto pick The selection algorithm is fairly simple and uses the following steps 1 2 Find all points which are local minimums and maximums Create pairs maximum minimum The number of these pairs can be fairly large each max imum can be matched with each minimum To reduce number of possible pairs the following user defined restrictions apply see figure 1 1 e Two points can be treated as a pair if the distance between them is in the user defined range e Two points can be treated as a pair if the field difference between is in the user defined range 24 Basic operation of MagPick Northern hemishpere 60 60 angle range Azimuth min 150 00 Azimuth max
4. L E L L m E E L L L E E E al gt E L L a m Original data a Filtered data Figure 16 Illustration of data filtering Squares represent original data and circles the result of filter ing All data points inside one grid cell are replaced with one point Refer to figure 16 to understand how data filtering works It affects data points inside one grid cell of a new map All these points are replaced with one point located in the middle of the cell The following are options for data value e Simple average of all data points inside cell is calculated and assigned to the middle of the cell e Median value of all data points inside cell is calculated and assigned to the middle of the cell This might be better when data has considerable spikes e Point nearest to the middle of the cell is taken other points inside the cell are ignored This procedure greatly reduces amount of data being triangulated Note that this idea is similar to the blockmean program from GMT package 3 4 1 2 Gridding with splines This feature employs a method developed by Smith and Wessel 3 which is an enhanced modification of the minimum curvature algorithm It allows the user to control interpolation using the tension pa rameter ranging between 0 and 1 Tension set to zero gives a pure minimum curvature solution which can have undesirable oscillations Tension set to one delivers a harmonic solution n
5. In case you did a false pick you can remove it by choosing Edit Delete pick option The cursor is changed to remind you that you are removing the pick Move it to the centre of the pick and press left button If you are close enough the pick disappears To remove all picks use Edit Delete all picks You will be prompted to save picks in the file if you do not want them to be saved simply press Cancel 3 3 2 Pick export Magpick provides some tools to export picks into external formats such as X Y Z dat file Autocad DXF format Atlas BNA format and in a couple of internal magpick formats to be drawn on top of a magnetic map See Drawing and clipping on top of the map All these are available under Files Export pick menu During the export to DAT BNA and DXF pick positions can be trans formed two ways e Linear transformation along X Y axis can be applied This includes scaling and offset e Inverse UTM transformation can be applied see Universal Transverse Mercator Gauss Kruger in MagPick This result can be presented in geodetical latitude and longitude while MagPick works with Northing and Easting Figure shows sequence of dialog boxes for exporting dat files It is important to check if the UTM transformation is used it may be not what you want to keep old and exported data in the same coordinate system Option Degrees and minutes and Degrees min and sec makes sense only if your data was loaded in MagPick using L
6. Linear The dialog box is very similar to one for smoothing There are few controls e Choose what to transform All profile data active profile s or if there are two valid markers on the same profile between marks can be chosen e Choose the color for transformed curve The result of scaling will be displayed on the same axis till you Accept transformation e Enter data scale a and data bias b These are the most important parameters Please do not enter a 0 it will turn all readings into a constant If you want just add a DC offset enter a and b equal to DC offset you want e n case of multi channel data transformation is applied to one channel at a time Enter the channel number under Channel to apply In many cases only one channel this value is 1 After you press Ok button 7 4 is displayed on the same axis as 75 4 This gives you a chance to check that everything is right After you satisfied with the result you can replace the original data with new data Go to Edit Accept and pick what you need This dialog also is used to accept smoothed data If you don t need transformation result go to Edit Discard If you want to restore original data after you did Accept use Edit Reload The original values will be restored from file and result of transformation will be discarded To make a change permanent you must save the profile File Save You will need to construct a new profile list file or use Simple load to
7. e The results of inversion were presented as an electronic table worksheet Some simple forms of manipulation such as deletion reading undoing etc were implemented e Additional information in the form of lines polygons annotated points clips can be drawn on the top of the magnetic map e Presentation of the field by annotated contours was developed History and features of Magpick e Option to load initial profile measurements and plot their geometrical positions on the top of the map was added The profile graph view was was developed The observed magnetic field can be viewed as set of linear graphs such as T x T y T I and T p Here T field x y planar coordinates of observed points distance along profile p projection of the profile on given line e Inversion based on profile data was implemented This means that all or part of profiles cross ing a given window can be used to estimate the position of the magnetic source Calculated and observed curves are plotted to see the quality of the solution e Point marking on graph map profile view was added The mark on the profile automatically appears on the map view and vise versa Thus the space location of interesting points can be easily found e Printing previewing on postscript printer was implemented MagPick was then used to process data of Hamburg harbor area which was collected during summer autumn of 1997 Some places were examined by divers i
8. triangulation grid cell size 9 history IGRF coefficients file use for inversion use for reduction to the pole installation 6 MS windows 8 inverse problem inversion automatic batch 61 grid data mass estimation profile data output format result worksheets theoretical basis layback calculations locating of magnetic objects 8 magnetic line magnetic properties estimation makefile Unix map color color illuminated dummy information shaded relief simple color zooming map appearance 9 map data limits map resolution 9 mass estimation netCDF format 8 9 INDEX palette gradient gradient editor uniform pick picks automatic delete all delete one export export into BNA export into DAT export into DXF export into magpick lines export into magpick points export with inverse UTM export with linear transform file structure 23 rectangular show crosses simple snap to grid Potential field transformations potential field transformations gradients ill posed problem solution pseudogravity reduction to the pole upward continue 51 printing profile marker accept transformation result activate browse cutting ends cutting parts 40 data data loading data operations data smoothing 41 data transformations description list file direction discard transformation result easy load handlin
9. 210 00 N Distance min 0 000 Distance max 4 000 Field diff min 100 000 Field diff max Remove all old picks Southtern hemishpere mag field A aBuei ploy XEN UIN distance I Min max distance range Figure 11 Setting parameters for automatic anomaly selection picking e Two points can be treated as a pair if the azimuth from maximum to minimum is in the user defined range For example in northern hemisphere anomalies should have mini mums located north from maximum therefore the azimuth range should permit only this selection e A pair is accepted if its field value in the middle point is in between the end values Note that still after all these limits one point can participate in the different pairs To resolve ambiguity pairs are sorted in accordance of difference between their maximum and minimum fields The sorted list is scanned to create unique pairs To use this feature go to Edit Auto pick select angle distance and field ranges if you want to remove all existing picks made by hand or results of previous auto pick check Remove all old picks Press Ok Depening on size of the map and its complexity the operation will take different times to complete If you checked Remove all old picks you are prompted to save old picks before MagPick removes them As a result you get many anomalies selected It is recom
10. 220 5 To plot stack we need to convert field values into distance Data gets divided by that value ha Plot stack profiles Datasets to draw Data scale 5 0000 Preferred direction 30 00 Type End points Fixed direction azimuth 45 00 Fill type Positive Fill color 6 Positive sides of the plot will gravitate to that direction unless Use fixed direction is checked clockwise from north 7 Requestto use fixed direction for positive parts of the data 8 Fixed direction azimuth clockwise from north 9 Which part of plot to fill 10 Choose fill color here 13 Middle line approximation 12 Clip range to produce stack plot simple average or linear by least squares of clip range are cut drawn as and set their parameters 11 If checked all data values out k Enable stack annotations flat lines Figure 3 Stack profile parameters 1 Show profile direction To see how data was taken MagPick will show your profile direction estimated from the samples order in the file note that if your file has time reversed it would be opposite Check this box to see the profile direction 2 Interval between signs Interval in pixels to place the sign gt displaying profile direction Distance is taken along the line This value can not be less then 20 pixels If less then 20 very dense marks appear Recommended is
11. If this is on then the fields in 8 are unaccessible if not checked then the fields in 7 are inactive 31 Basic operation of MagPick 6 Grids Here you can specify the coordinate meshes Check Draw X grid and Draw Y grid and enter steps for the grids Alternatively you can check X autogrid and Y autogrid to let MagPick select the steps 7 Canvas size If 5 is on the picture always fits in the specified size in pixels If 5 is off size is chosen automatically to satisfy scale factors 8 Scales Scales for coordinates in physical units per display units pixels Adjust to find a value that works best If 5 is on the program sets these values automatically This may be the best way to get initial values It could be good initial values to start with Next important menu item is File Browse If this item has been chosen the modaless dialog box pops on the screen In this box you can choose any profile from the list you wish to see As soon as you click the mouse the picture is updated The active profile is highlighted on the map view as well You can navigate to the next or previous profile by using the using the buttons marked lt lt and gt gt If you want to see only part of the multi set data click on SubSet A dialog box appears for you to disable or enable plotting of the specific sensor It should be noted that Profile Browser dialog box has a different functionality in profile view and profile inversion view wind
12. To make life better set the coordinate grid with steps of 2 x 2 meters Ok Now where is the object is really located There are minimums and maximums on the map in front of you Simple theory predicts that object somewhere in between on the line which connects these two points say half a way So we can now locate it Go to Edit Simple pick Cursor becomes Go where you think maximum is click the left button Now the dashed line is started at that point and follows the mouse Go where you think minimum is Click again A solid black line segment appears This is the magnetic pick Perfect The middle of that line is probably where bomb is Now it s time to explain some points in the Common parameters dialog box if you check Snap to grid then start and end points of the pick are snapped to the middle of nearest grid cell If you have worked with Corel Draw or Surfer this should sound familiar If it is not checked they stay where you set them Check box Show crosses enables you to draw small oblique crosses at the end of the pick Try these two features to see how it works To see the cells better you can zoom into part of the map Note that when you do picks they appear in all widows which represent the same magnetic map Certainly you can save and use this information 2 More advanced Rectangular pick The action we just have taken with a simple pick has a problem We used our eyes to find where maximum and minimum were locate
13. accordance of the minimum and maximum of the data It means that the profiles of a different length and amplitude will always occupy the same area on the screen It is difficult to compare them but you see all the features of each profile This mode is recommended for zooming because you always can easily undo it 2 Fixed scale Here scales i e how many pixels per nT in the vertical direction and how pixels per meter in the horizontal direction are fixed and size of canvas is adjusted to these scales This way you see all the profiles with the same resolution and you are able to feel space and field span In some cases if you set your scales for a short profile and then load a long one it can lead to a noticeable memory consumption This mode is not recommended if you zoom profiles Zoom automatically changes scales and limits therefore when you undo zoom it can create a very large picture Following is a full explanation of all the controls for the Profile view parameters dialog box For large profile sets some time can be needed to find profile you pick 30 Basic operation of MagPick jl DX asmosa A limits Xmin 11084 39 Xmax 112789 Data limits F Draw X grid xgrid 10 0 1 X autoarid 7 Draw T grid Tgrid To o l T autogrid Ok Cancel E Profile view parameters Profile graph layout Figure 14 Profile view parameters 1 Field limits Top
14. list is not saved when you exit MagPick Therefore you should load the clip file again when you start MagPick next time 36 Profile data transformations 100 200 300 400 X km Figure 17 Result of grid clipping Draw polygon then go to Operations Clip grid 4 4 Clip the grid Clipping the grid does not create an additional file If you are doing clipping in the zoom window the area you see in this window is affected Therefore you must save the grid file if you want to use it in the future The following is the procedure to do a real grid clipping Operations is next e Go to Edit Polygon The mouse changes its shape to the pen Draw a polygon the left button adds a node to the polygon the right button removes latest node To close the polygon click on its first point To draw a new polygon go to Edit Polygon one more time existing polygon will be erased e Go to Operations Clip grid Choose the part you want to be blank inside or outside polygon Press OK e The program clips the grid in the current window and in the all windows which share the same data array MagPick redraws picture automatically Please note that there is no Undo operation This means you should be careful and probably save the grid also before clipping The clipping result is displayed on figure 17 To blank the data magpick uses the value 1 70141e38 in MS Windows version and 1 e35 in the Unix version 5 Profile data tr
15. of the file if you want to keep this file before you call Preview again 4 Grid operations Magpick allows you to create and modify grid data loaded in a variety of ways which are available under Operations These features are under development and will be extended in the future 4 1 Making grid out of profile data After the profile data has been loaded a regular grid map can be created There are two methods available gridding with tension by 3 or by triangulation with linear interpolation 4 There are a few places where gridding procedure can be started Originally it was located in profile view under Files Interpolate grid but because of obscurity it also available under map view Profiles Interpolate grid Here is a basic sequence of operations to make and view a grid e Start MagPick and load profile data Use the profile list or Easy profile load see 3 5 2 Note that you can load few profile lists or use easy load few times by appending new profile data to dat tat is already loaded After you complete this operation MagPick maintains the profile data internally e If your primary goal is to make a map go to Profiles Interpolate grid and pick the interpola tion method you prefer Spline or Triangulate e Fill in the interpolation parameters and start interpolation e After interpolation completed Magpick will save the map into a file and automatically load the newly calculated map into current map view or crea
16. 1 Press Ok and go to profile browser Go thru profiles again Dou you see a difference Data is always presented in the same scale therefore it is easy to recognize large and small anomalies Check shrink again You can have as many profile windows as you wish Just go to File New to create them 5 Add another file to the profile list We have file g 858g dat which is worth looking at Create new empty grid view we need it just to access File Profiles Simple Load Select g 858g dat now Choose split by LINE and data as BOTTOM RDG Press Ok and press Ok again Answer Yes to Append to previous profile list The total number of profiles loaded is 102 now Create a new profile view the old one does not know you loaded new data Now you have both second one has very large numbers as X Y coordinates This creates a some problem that we will describe later You can browse two files with profile data now You can have as many files as you need 6 Saving file list for future use What happens if you have 200 files Add them all one by one every time you need to load in formation No When you go to File Profiles Simple Load you have a check box Save as profile list If this box is checked MagPick will ask you to save the list of your profiles into a separate file For example load g 858g dat Check the box press Ok enter file name g 858g 1st Now exit MagPick and start it again Go to File Profiles Load list Select file g 858g 1s
17. 4 Dragging method details Here you can find a brief description of the method used to calculate the position of the fish being dragged behind the boat Text below refers to figure 22 Goal Let s consider the object magnetometer fish being dragged behind the boat with constant and known tow cable length The boat is equipped with GPS receiver and therefore its position is known The task is to provide a reasonable approximation for the magnetometer fish position based on GPS readings and the cable length Solution This solution is an approximation and does not take into account a 3 D configuration depth and some physical effects like friction Nevertheless it gives reasonable behavior even if ship makes a turn We assume that we know the position of the ship A and the magnetometer fish at time fo N see fig as well as the cable length At time t we know the position of the ship B but do not know position of the fish M To find the fish position we draw a stright line NB between the old fish position N and new ship position B Then we use a straight line from B to N and place the fish at a cable length distance behind the ship on the line New point M is the estimated position of the fish time t 46 Profile data transformations Figure 22 Calculating magnetometer offset with dragging Shift along profile 250m to the right 20 m Drag profile 250m to the right 20 m 3250 3500 3750 4000 4250 4500 475
18. RGB colors in MagPick to AutoCAD pens a standard AutoCAD palette is used In some cases it might result in different color in AutoCAD as compared with MagPick However most af the colors are transferred without distortions Each string in this list represent a separate layer Press Properties button to set each layer s parameters N Press here to enter drawing title and X and Y axis titles Select grid label format Regardless of drawing system labels can be in short or full UTM of Lat Lon T DXF export elements Hp Contour map Titles Drawings to export Coordinate grid Profile lines Profile Stack Inversion results Picks Polygon amp direction t Marks Drawings selected for output Properties Transformation setup DXF Decimal ja Grid labels format t file name Browse export dxf Ok Cancel Typically magpick operates in short UTM coordinates However drawing can be presented in full UTM or Lat Lon Press this button to set false Northing and Easting or and inverse UTM parameters Internal position representation in the DXF file Recommended 2 for drawings in UTM and 9 for drawings in Lat Lon Press this button to select name of output file Figure 30 DXF export dialog DXF export is available in the grid window under File Picture export DXF Look at figure
19. Shaded relief and color illumination Data multiplied by this value before Ok E shade is calculated You may need to try different ones to find the best Figure 7 Map drawing mode dialog MagPick supports two coloring schemes uniform palette and gradient palette In the first case the palette is defined by all its colors Total number of colors can not exceed 255 There are a set of built in palettes which are available in Magpick In the second case the palette is based on a relative small number of color nodes each with its own color and data value Color for the intermediate data values are interpolated Gradient palettes can be saved or loaded from a file and some set of build in gradient palettes are available as well Ufiform pallete dialog box Grdient color dialog You can choose from number of pre defined color palettes by moving this slider And see sample here You can create delete change color and data value for the nodes Nodes are clickable by mouse and can be draged There is also pre defined set of palettes Click right button to see the menu There are different menus for node and space between nodes FF Equalize colors Cancel Requare magpick to do color equalization So each color occupies approximately the same space on the map Figure 8 Uniform and gradient palette setup MagPick has a flexible tool to deal with
20. The user can enable transformation while preparing the DXF file The typical case is to have the DXF drawing in full UTM coordinates while internal MagPick picture is in short UTM just add Northing and Easting values Another case could be when the user wants to have a drawing in latitude and longitude To use this feature the user can press Transformation setup button This allows the program to transform coordinates in two ways e Linear transformation Xmagpick Ymagpick coordinates are transformed as Xdrawing Xscale X X mag pick Xof fset and Y drawing Y scale X Y magpick xs Yof fset For typical short to full UTM trans formation Xscale Yscale 1 e Inverse UTM transformation This should be enabled only if the user wants to present a draw ing in Latitude and Longitude Attention should be paid to set correct UTM parameters If both linear and inverse UTM transformations are requested program first performs linear and then inverse UTM Note that false Northing and Easting are parts of UTM parameters see figure 24 66 Export to the CAD Note that the text and arrow size should be set in the MagPick coordinate system The program recalculates sizes in the transformed system automatically To specify general title of the plot and axis titles press Titles Remove any text if you don t want titles All titles are plotted on the same layer as coordinate grid with slightly increased text hight Grid labels format controls
21. Yanovsky Magnetism of Earth Leningrad 1978 2 F Goltzman Physical experiment and statistical conclusions Leningrad 1982 3 Smith W H E and P Wessel Gridding with continuos curvature splines in tension Geophis cis vol 55 pp 293 305 1990 4 Watson D F ACORD Automatic contouring of raw data Computers amp Geosciences 8 97 101 1982 5 IAGA Working Group V 8 1995 International Geomagnetic Reference Field 1995 revision Submitted to EOS Trans Am Geophys Un Geophysics Geophys J Int J Geomag Geo electr Phys Earth Planet Int and others 6 Snyder J P 1982 Map projections used by the U S Geological Survey U S Geological Survey Bulletin 1532 313 p 7 Richard J Blakely Potential Theory in Gravity and Magnetic Applications Cambridge Univer sity Press 1995 414 p 93 Index additional drawings clipping color names lines order points polygons autoscale 9 color scale 9 compilation Unix 7 contour lines isolines 9 contours automatic levels color custom 12 fast 12 interval 12 labels min and max total 11 contours isolines 11 coordinate mesh 9 color show 11 step dipole DXF export from magpick using in magpick export CAD systems DXF forward problem grid clipping grid 37 creating path 36 data filtering operations preparation save 94 spline gridding supported formats
22. above steps with different initial parameters the interpreter can get an idea how stable estimation procedure is and what are reasonable estimations and their errors If results are close to each other procedure is stable and location can be estimated If not the interpreter may re select or even abandon the area as non interpretable After a number of inversions it is possible to discard all or part of the results obtained in a given window To do that go to Inverse Remove results Here there is a list with locations obtained in the particular window To remove select all or part and press Ok The work sheet and map views are altered to reflect new results table To find magnetic dipoles information about the Earth s magnetic field and orientation of the local coordinate system has to be provided These values have to be filled in using the Inversion parameters dialog box To understand what they mean refer to figure 29 Here is complete list of inversion parameters e Main field inclination Inclination of Earth s magnetic field in the geographical system angle I of figure 29 Main field declination Declination of Earth s magnetic field in the geographical system angle D of figure 29 Positive to the East Azimuth of X axis Azimuth of you local X axis angle A of figure In case your local X coincide with geographical east A 90 Positive to the East Total magnetic field Magnitude of T on figure 29
23. again You can interrupt your work save your picks and resume it later You might be interested in looking at the pick out file with an editor probably notedad Each string in this file represents a pick I will not explain all the fields in that string see the complete manual for that but here is what s important e Last number is always 0 000 you do not need it e Two numbers before the trailing 0 000 horizontal X and Y position of the middle of the pick You are probably interested in this point 5 Notes about picking It s a tedious process if you have a large field You generally should not work with the whole map at once Instead zoom into different places to see them better pick anomalies there the close the zoom window and go to the next place Certainly you should cover the area gradually say west to east and north to south In some cases if shape of an anomaly is complicated a rectangular pick is not what you need you have to go with a simple pick The result of your picking is a table with X Y Z locations you want to check with digging or diving The pick file also holds the minimum and maximum values for the field at the pick s ends You can use these values to classify your points MagPick also offers automatic picking See main manual for this option You should inspect results of automatic picking before accepting them 6 Pick export MagPick allows converting picks into its internal drawing f
24. and bottom of the view in nT If 3 is checked program automatically chooses these values based on the data 2 Horizontal axis limits Left and right limits of the view in m If 3 is checked program auto matically chooses these values based on data Because X axis can represent different variables 1 e X Y distance along profile projection be careful in choosing them When you change the type of axis box 3 is automatically checked and new limits appear 3 Data limits If these checkboxes are checked data limits always will be taken 4 Type of X axis Depending on where you created profile view there are two to four choices here a X Y profile inversion view created from map view without additional axis b Along profile X Y profile view created from map view without additional axis c Along profile X Y Along pointer profile view created from map view with additional axis In this case the direction of axis is fixed after creation of profile view even you have changed it on the map view profile view will still operate with an old one This happens because the profile view is actually an independed window opposite to profile inversion view d X Y Along pointer the profile inversion view which is a child of the map view with an additional axis direction In this case if you change the pointer direction the profile graphs are updated automatically 5 Shrink to canvas It sets the method to shrink to canvas see above
25. and number2 is the string number where data profile ends Here is an example of such a file 1_74 dat bl_east dat BLUE RED 1 1 2 h 0 3 75_151 dat bl_east dat BLUE RED 1 1 2 h 0 3 152 228 dat bl_east dat BLUE RED 1 1 2 h 0 3 229_304 dat bl_east dat BLUE RED 1 1 2 h 0 3 305_379 dat bl_east dat BLUE RED 1 1 2 h 0 3 380_454 dat bl_east dat BLUE RED 1 1 2 h 0 3 3 5 2 Easy profile load Having described profile list file in detail now we present a quick way to load profile data file with a column structure Here is a step by step description what to do e Go to File Profiles Simple load e Dialog box 12 appears on the screen Enter False Easting and False Northing before picking any data files you also can use individual values for different data files Note that the usage of false Northing and Easting is recommended in the case of full UTM coordinates if they are not truncated to the short form otherwise loss of accuracy will occur e Press Add button and then pick the data file The bottom part of picture 12 appears 27 Basic operation of MagPick File already prepared for load Load X Y Z profiles t SPLIT 8 XFALSE 0 00 YFALSE 0 00 data misha projects magpick tutor g 858m dat Delete all Fi Pi Save as profile list False Easting 0 00 Ok Cancel Note fasie easting and northing are to be added to your posit
26. as well as the local minimum and maximum of the data In some cases you can choose use MagPick for profile processing only You must always load a grid to create the map view and see locations of profiles You may want to create a dummy grid which has following format DUMMY 100 100 62740 63200 33130 33820 9366 12 17963 5 1 Ujse the magic word gt DUMMY so program can recognize the file 2 Numbers of columns and rows of an empty grid 3 Minimum and maximum X coordinates 4 Minimum and maximum Y coordinates 5 Minimum and maximum of the dummy field It should be noted that in this case the program creates a real array i e allocates memory there fore you should not choose large numbers for rows and columns In case of a dummy grid you might find it useful to check out the Snap to grid option in the Settings dialog box MagPick can create dummy grid for you internally After you load profile information just create grid view with File New menu Program will show profile map faking underlying map internally There is no need for dummy file in this case 18 Basic operation of MagPick 3 2 Drawing and clipping on top of the map Magpick vector formats lines polygons points clip area Magpick allows you to plot some additional information above your magnetic field It can be useful to navigate inside the area Choose menu Edit Drawings dialog box appears which allows you to append drawing
27. confuse this type of clip ping with grid clipping Grid clipping changes the data this feature draws a white polygon of complex shape to simulate clipping of the picture The clip file itself has the simplest for mat it s just two columns of the numbers The first pair of numbers should coincide with the last pair to have a closed path The order of points is very important The points should go clockwise see figure D 1 data boundary magpick drawing to simulate clip Figure 9 Clipping polygon Here numbers inside the contour the show order in which the clip path must be specified Note that you should start with minimum Y value Italic text shows the nodes which MagPick uses to simulate clip Shaded area is white polygon drawn to simulate the clip Normally we assume only one clip for a map 20 Basic operation of MagPick The order of points is not so important for screen clipping but for postscript output it is crucial The order of drawings in the list is important MagPick does drawing in the following order 1 Color map 2 Contours if need 3 Profiles if loaded and required 4 All drawings in the order they appear in the list It means the clip will affect only graphics which are listed before clip itself plus the colored map and isolines 5 Coordinate mesh and additional text if need 3 2 20 Bringing an AutoCAD DXF drawing into Magpick In many cases users can have their maps in Auto
28. currently active it becomes inactive and vise versa In the case when the map window does not have a child window the profile you pick becomes active and the current active profile is deactivated In that last case the program operates with a global list of profiles in the first case it operates with a local copy of part of the list e Set marker Put a special mark on active profile There are two kinds of the marks see figure 13 and they can be two marks of any kind only When you click first time marker 1 appears When you do it second time marker 2 Third time you click marker 1 is removed from its location and set in the new place and so on Any marker is set in the nearest profile sample and appears on the both views profile and map view Thus the location of specific points can be easily found A Y Global profile view markers A Y Local profile inversion markers Figure 13 Profile markers 3 5 4 Parameters of the profile view Profile view and profile inversion view have menus types different from the map view The most complicated item is Parameters Settings When you invoke Parameters Settings dialog box shown on figure l4 appears on the screen You you can specify all necessary information to make the most convenient view of profile infor mation It is important to understand that profile view can work in two modes 1 Shrink to canvas In this mode the drawing area has a fixed size and the profile is scaled in
29. e t is time to work on the inversion itself Make a pick on the map view It will serve as initial location for the magnetic dipole Go to nverse Run in the profile inversion view Here is a dialog very similar to the one we already had for the map inversion Change Positions file and Output file Press Start iterations wait till the discrepancy stabilizes and press cancel You can see a new location of the dipole on magnetic as cross x and number You can inspect the results with a workshee First worksheet column shows P if this is result of profile inversion The grid based inversion is shown with G On the profile inversion view you can the see result of calculations as dashed lines See figure 35 50000 49800 50000 49800 49600 49400 49200 49600 49400 49200 T nT 49000 48800 48600 49000 48800 48600 48400 48200 48400 48200 _ 48000 6 7 8 9 10 11 12 13 14 observed synthetic 48000 Figure 35 Inversion of profile data Now we can work with the profile inversion as we did it with the map inversion Note that nothing prohibits as from applying the map inversion The results come to the same worksheet but it has G in first column Set the initial position depth in the different places of the map and try to invert the data by profile inversion You may note that MagPick reports depth about 0 6m Take a guess why Hint what was the separation between top and bo
30. endian computers becomes incompatible if you use this format to exchange data It corresponds to SURFER binary grid format up to version 6 e NetCDF This is binary format based on NetCDF library It is machine independent and com patible with GMT system 3 All these formats can be read and written by MagPick Therefore if you are using only MagPick and only a certain type of computer it is not important which format you use Regarding space SURFER ASCI wastes maximum and NetCDF minimum After you have selected the format MagPick saves the grid file 4 3 Create clip path This function allows you to create a file which can be used as a clip to trim the picture on the screen No grid modification is involved and therefore no grid saving is necessary The sequence of operation is next e Go to Edit Polygon Mouse changes its shape to the pen Draw the polygon The left mouse button adds a node to the polygon the right button removes latest node To close polygon hit its first point To draw a new polygon go to Edit Polygon one more time existing polygon will be erased e Go to Operations Save clip Pick the file name you want Press OK e After the file has been saved go to Options Drawings and press button Add Choose file the type Clip Pick the file you have just created Press Ok and press Ok once more to close the dialog e To reflect clip redraw the picture Edit Redraw Please note that Additional drawings
31. file and enter name g 858m grd This is where the result of the interpola tion will be stored as a grid file Advanced read article Smith and Wessel Geophysics 3 293 305 1990 to learn more about this interpolation method Press Ok and wait until the program completes interpolation You are seeing the progress dialog Gridding is working which shows the iteration number and discrepancy for the current step It can take from several minutes to complete interpolation 75 Tutorial 3 View interpolated map Go now to File New and choose Grid view The empty window appears Check Options Size set X and Y sizes as 1 Then check Options Settings Here is what to do next e Check Autoscale e Check Show x grid and Show y grid Set X Y as 10 e Uncheck Snap to grid and Contours we do not need this checked for now e Check Show profiles in the configuration dialog Profile plot parameters uncheck Show profile direction and Plot stack profile press OK Check Color map in configuration dialog Color map draw mode set Drawing mode as Simple color map and press OK e Press Change palette select Uniform choose number 33 and check Equalize colors We are ready now to load our file Please note that your are free to adjust settings above anytime after the file is loaded We did it now just to insure proper initial appearance of the picture Now go to File Open and pick g 858m grd You have two windows on the screen now
32. file igrf dat from the site as soon as it becomes available Dialog 25 shows how the IGRF model can be used It gets called from Inversion IGRF model You should enter the data and geographical position The main magnetic field changes from point to point smoothly therefore the high precision of position and date is not required It is acceptable if you are in the 25 km range and within a few month from your place and date of measurements you can check how the field changes by entering different positions and dates The western longitude and southern latitude should have a negative sign As soon as you entered these values press Calculate 50 Potential field transformations button and read the results If you want to use result for an inversion have these values automatically appear in inversion dialog box check Accept parameters for inversion MagPick will store the last calculated values These values also affect reduction to the pole group This is list of typical problems you may encounter e The date you entered is out of model scope 1900 2005 presently Obtain a new file igrf dat and replace the old one e The program can not find file igrf dat Make sure this file is exists in the same subdirectory as the MagPick executable Make sure you call MagPick with the full path or its location is listed in system PATH variable 8 Potential field transformations In many cases the total field anomaly can be treated as a p
33. files Currently there are four types of information which can plotted 1 Lines You should prepare a file which has a special format Here is an example gt UTM GREY 0 0 0 10 10 gt UIM RED 0 1 10 10 20 0 Each line segment starts with the sign gt that makes file compatible with GMT system The word UTM indicates that the data is in meters GEO indicates that they are longitude and latitude In latter case MagPick will use the UTM projection before plotting the data Then you can choose the color of the line from a fixed number of names UJ AQUAMARINE BLACK BLUE UE VIOLET BROWN CADET BLUE CORAL CORNFLOWER BLUE CYAN DARK GREY DARK GREEN DARK OLIVE GREEN DARK ORCHID DARK SLATE BLUE DARK SLATE GREY DARK TURQUOISE DIM GREY FIREBRICK FOREST GREEN GOLD GOLDENROD GREY GREEN GREEN YELLOW INDIAN RED KHAKI LIGHT BLUE LIGHT GREY LIGHT STEEL BLUE LIME GREEN MAGENTA MAROON MEDIUM AQUAMARINE MEDIUM BLUE MEDIUM FOREST GREEN MEDIUM GOLDENROD MEDIUM ORCHID MEDIUM SEA GREEN MEDIUM SLATE BLUE MEDIUM SPRING GREEN MEDIUM TURQUOISE MEDIUM VIOLET RED MIDNIGHT BLUE NAVY ORANGE ORANGE RED ORCHID PALE GREEN PINK PLUM PURPLE RED SALMON SEA GREEN SIENNA SKY BLUE SLATE BLUE SPRING GREEN STEEL BLUE TAN THISTLE TURQUOISE VIOLET VIOLET RED WHEAT WHITE YELLOW YELLOW GREEN I
34. initial guess and magnetization magnetic field can be calculated The discrepancy between observed and calculated field can be expanded into the Taylor s series truncated to the linear terms and written as the following equation OT x0 0 20 2 bd f T O xo yo zo obs calc T xo yo zo where Goyo correction of the position and Tao 1s the field calculated at the point of initial guess Then the new improved position can be found as is the matrix of partial derivatives of T at the point of the initial guess dd is the T 70 0 The magnetization vector has to be estimated again using a new position The process has to be repeated till the discrepancy between the observed and calculated field becomes small and stable 10 3 Estimation of susceptibility and remanent magnetisation For mass estimation susceptibility and remanent magnetization of the body must be known They can be estimated if at least two sets of data with different orientations of the object were measured For each orientation total magnetization of the body can be estimated as it is described above It means two vectors J and J are know Both of them have an induced and remanent part yl gt 7l J VKF hearth JremVIi rem p gt 22 J vKFRearim JremVhizem Here ri is the unit vector along the remanent part which has to satisfy oe oon PI Together with norm conditions we have 8 equations and 8 variables K Jre can be solved as the fo
35. of background function estimated on each iteration After calculation finishes the results appear on the screen and are stored into the special list If you have opened a worksheet window see below a new line is added to the worksheet All map windows are updated automatically o show horizontal coordinates of the found targets 57 Estimation of magnetic sources 9 2 Magnetic modelling based on profile data Magnetic modelling based on profile data is similar to the inversion based on maps but has some significant differences 1 The start of inversion is possible only from the Profile inversion all profiles in current win dow window Only activated profiles and subsets of profiles and therefore visible inside win dow are used for interpretation It could easily happen that many profiles cross a given win dow The interpreter should decide which profiles are suitable for inversion and select them To make this happen new item is added to the map view menu Edit Pick profile Activate this menu item move the mouse cursor to some profile and click left button Profile is deactivated or activated and therefore all subsets disappear from profile view window If Browser dialog box is opened list selection is altered too 2 Depending on on discretization interval along the profile number of data points used in the pro file inversion could considerably exceed number of data points used for map based inversion Therefore the
36. resolution Show which columns hold X Y positions and field If file has a header its fields displayed If not just only the column numbers Pick colors for active and inactive state of profile Press OK to accept A new Strings appears in the list which tells MagPick how to treat this file Use Add button to add as many files as you want Note that you can pick the same file but with different columns After you picked all data files you can check Save as profile list You will be prompted to save 28 Basic operation of MagPick result of your work as profile list file It means when you need to load this information next time you just pick this file directly menu File Profiles Load list without going through all these steps again e After processing of all the profiles the program reports how many profile lines you have If some profile data has been loaded already it asks would you like to erase it from the memory or just append new data You may be requested to close some profile views if you have them on the screen If after profile loading go to File New you have a choice make profile or map view In the case of map view MagPick will create a dummy grid to display positions of your profiles If you only need the stack plot then you don t need to perform any other actions To prepare interpolate grid data go to Profiles Interpolate and pick a method New map window created automatically see 4 1 3 5 3 Operat
37. safely removed and a work sheet window automatically altered If a window has been closed the only way to remove the results is to do it directly in the work sheet window 9 3 Magpick worksheet results of inversions For convenient storage and presentation of the inversion results MagPick maintains special object work sheet electronic table This object is global Only one copy exists during a session and all the inversion results are appended in it The work sheet can be saved or loaded from file In case you are about to quit MagPick without saving of modified work sheet you are warned and allowed to save it The work sheet file has a column structure Here is the meaning of the columns 1 Type of results letter G for grid results or letter P for profile results 59 Estimation of magnetic sources 10 11 12 13 14 15 16 17 X coordinate of the dipole Y coordinate of the dipole Z coordinate of the dipole attempt to estimate mass root one see below attempt to estimate mass root two see below accuracy of the fitting of the total magnetization during mass estimation X coordinate of low left corner of the window where inversion has been made Y coordinate of low left corner of the window where inversion has been made X coordinate of upper right corner of the window where inversion has been made Y coordinate of upper right corner of the window where inversion has been m
38. see below Nevertheless MagPick will always give two values for the mass which correspond two roots in a square equation In case the equation can not be solved the value of extremum of the quadratic function replaces both roots and a message is printed on the console Unix version In the last case a predicted value of J can be calculated and compared with the MagPick estimation The relative difference in arrears in the column Discr 9 5 Automatic estimation of magnetic sources You should note that the estimation procedure requires good deal of manual work It involves selec tion of the area of interest setting pick s by hand or by some simple procedures as rectangular pick or even autopick running estimation and inspection of results This should be repeated for all points of interest To avoid this MagPick has a simplified routine which allows it to interpret all anomalies at once It should be noted that the results of such an interpretations are still to be inspected The procedure is available under Inversion Run batch Its parameters are identical to the previous one described in the inversion but instead of treating all data in the window MagPick does the following e Goes pick by pick For each pick it selects only the data around it e Applies inversion for this pick Inspects a misfit If it is more than user specified value result is rejected if less than user specified value result is appended into worksheet e Repea
39. should be checked e Entity headers should be checked Then press button Specify and check PEN NUMBER under Components All other boxes ENTITY NAME LAYER NAME LINETYPE NAME should not be checked e Under Data Formatting select Move to 0 Draw to 1 Now you can produce the XYZ file by pressing Save or Save as Here is an example of output 70 0 95 39 125 00 1 96 06 130 00 1 95 00 131 00 21 Basic operation of MagPick 1 90 00 134 35 70 0 104 71 125 00 1 105 00 125 99 Here 70 denotes the AutoCAD pen number and strings that follow are line segments 0 means moving in the position with pen up 1 with pen down You can use this file in MagPick directly just select it with line option 3 2 3 Using ArcInfo TM shape files in magpick If shape files are available they can be used in MagPick however a conversion is required There is a command line program shipped with MagPick called shp2mpick or shp2mpick exe under MS Windows This program converts linear features from shape files into a MagPick line file see above Both shx and shp files must be placed in the same folder Then program can be called as shp2mpick exe shp file color thickness GEO UTM output file here shp file is the name of shape file extension shp color is color name might be RED BLACK see a l for full list thickness is line width GEO or UTM denotes coordinate system output file is a MagPick line
40. should be loaded into a new map view to compare with observed field You can change file name by means of Change button Difference The residual grid is equal to the observed minus the calculated It is worth to make new map view and load it to see how it looks like You can change file name by means of Change button Start iterations This button starts the inversion procedure Remember that if you choose the wrong parameters for instance you started the inversion for all your map and all potential sources the calculation can be endless Then you will have to stop it During inversion the program prints results of each iteration on the screen Unix systems only Here is an example of such output N 11 Discrep 52 47 Lin 4 97e 03 Non lin 2 42e 01 lev 49729 32 1 2 4 5 N 11 Current iteration number Discrep 52 47 Current discrepancy for given iteration nT This number has to be reduced dur ing calculation But in some cases program can not perform optimisation i e solve inversion problem Then this number can increase or oscillate Lin 4 97e 03 Ratio between minimum and maximum singular values for linear step of in version Small numbers about machine epsilon 1 e 7 show that a problem mathematically ill posed It can occur in case of large number of sources or their improper initial locations Non lin 2 42e 01 The same as above but for non linear step Has the same meaning lev 49729 32 Constant part
41. therefore it s direction will coincide with the direction of the Earth s magnetic field This tutorial presents a numerical illustration of the procedure As an example a field from a rectangular object with only induced magnetization has been calculated see a on figure 38 Then 91 Tutorial Field at point with declination 30 Inclination 70 degrees Field on pole declination 0 Inclination 90 degrees 20 40 60 80 100 120 20 40 60 80 100 120 120 pop oda iva d a EE dansa E dag oce testis eet pie de Ea Nea ta d ie te ta 1120 100 once Me npe 100 100p eI e mie Wesce 1100 Figure 38 Reduction to the pole this field was reduced to the magnetic pole plate b of the same figure As you can see the anomaly has now a perfect symmetric form Goal Illustrate how reduction to the pole works with perfect model conditions Files for that lesson we take file i 70_d30 grd under on_pole subdirectory 1 Load data file Start magpick go to File Open and pick file i70_d30 grd Adjust size and color scale as needed 2 Make reduction Go to Operations Reduction to the pole Reduction dialog appears on the screen Here set next e Main field declination D 30 degrees e Main field inclination I 70 degrees e Declination of magnetization 30 degrees e Inclination of magnetization 70 degrees e Azimuth of local X axis 90 degrees e Check box Use reduction to the pole N
42. therefore two points are needed to estimate loca tion e Advanced magnetic picking The user selects regions where minimum and maximum are and program automatically finds their exact positions e The removal option erases picks that has been made This first version of MagPick was ready about one week after initial design began It was used to pick more then 1000 magnetic anomalies on map of Hamburg airport area Sophisticated options such as fitting of observed magnetic field by model source were requested shortly These new features were implemented in the framework of MagPick in the autumn of 1996 and Hamburg airport data was reprocessed Each place of interest the user could automatically estimate positions of sources which were represented by set of uniform magnetized spheres To check quality a synthetic magnetic field was calculated and compared with the observed one At the same time attempt was made to estimate the mass of the sources The problem of mass estimation is quite complex A knowledge of susceptibility K and remanent magnetization J is required but these values have a very wide range for ordinary iron Further development of MagPick was resumed in November January of 1997 1998 Many new features were implemented e Regional magnetic field was taken into account as linear function of coordinates This allowed usage of the program directly on measured magnetic field without subtracting the Earth s main field
43. time of computation might increase 3 Instead of relative depth real depth is used This means each point of profile involved in the inversion is taken with its z coordinate It allows usage of the data obtained at different elevations With other side it means that all z values are measured relatively to some pre defined system In the case of GPS heights they are geodetic elevations 4 Because of the above reasons the initial depth of the source has to be specified carefully to avoid choosing it above the data 5 In some cases the Z values have considerable noise and can not be used directly for interpreta tion In such a case smoothing of elevations is required To start a profile based inversion a set of profiles have to be loaded into the program see above Then the interpreter can view the magnetic maps if available or browse profiles as T dist graphs The aim is visual selection of potential places were sources might be located When such a place is selected by map view or by means marker facilities on the profile view the interpreter does zoom in surroundings and creates new map window This last window is used as a parent for profile inversion window After the profile inversion is opened the interpreter can view all profiles crossed and select a subset of them Very often the interpreter has to change decimation of data to get all available points into the inversion All these options can be reached in Browser
44. to accept it or not Basically there are two types of criteria e What is the difference between the observed and calculated field Which features of the observed field we can see as well the in calculated one What is numerical difference These are the questions which should be answered Therefore it is important to inspect the observed and calculated fields e How stable is the solution What happens if you completely change the initial location and depth of the source Do you still get similar numbers You should investigate this empirically Here are five attempts with a completely different initial position and depth of the source see figure 34 Table 2 shows initial depth of the source and estimated X Y Z locations Z initail X Y Z J total mass 1 8 51 10 23 1 93 85x 10 266 0 1 8 51 10 23 1 93 8 5x 10 266 1 10 8 51 10 23 1 93 85x 10 266 1 5 8 51 10 23 1 93 85x 10 266 0 0 5 8 51 10 23 1 93 85x 10 266 0 Table 1 Results of different attempts to find a dipole You can manipulate this data testing the results Delete your pick change mode to Simple pick make the pick somewhere else Then start the inversion Change initial depth as well You will find that this estimation is pretty stable Of course there are some ways to confuse MagPick on this data for example set the initial depth as zero 83 Inital depth 1 m Inital depth 1 m
45. to see the picture undistorted you must choose sizes like 1 x 1 2 x 2 3 x 3 Do not choose sizes where X cell and Y cell are different If your real grid cell size is 2 5 x 5 meters the undistorted picture will appear if your choose 1 x 2 2 x 4 etc Note that unfortunately not every grid cell size can be viewed undistorted Therefore grid your data preferably with equal steps along X and Y Now go back to the 1 x 1 size 69 Tutorial 4 Zoom a picture We just have learned how to zoom all the picture Very often all what we need is to see some part of the big map Here is how you can do it e Go t Edit Zoom the mouse cursor changes its shape e Press the left button and drag release the button Part of the map appears in a new window Note that if auroscale on zoom is checked when old window is active the color scale in this new window automatically adjusts to the local in the window minimum and maximum of the data Therefore you have your full color scale in a narrower range and can see your data better This new window can be zoomed again and again There is no limit on the zoom number Unfortunately MagPick has some problems with zooming near the borders 5 Change data color mapping Go to Common parameters again Here we will learn how to change the color scale The Autoscale box is checked now The two grayed numbers above it are minimum and maxi mum values of your data Uncheck it The fields above becom
46. user marks or A which can be up or down arrows To perform cutting the user must place marks on the appropriate place and call Edit Cut The operations are applied to all data channels if there are more than one Terms before and after used below to denote distances from the beginning of the profile It is strongly recommended to use this feature when the profile is plotted as a function of distance plot mode Along profile For example you might be confused if your profile is going north south and plotted as function of Y Then when you cut the beginning of the profile the northern part is getting cut not southern part with small Y In case of error call Edit Reload This reloads your profile data from hard disk and restores the initial profile configuration After profile being cut you have to redraw the map view if you have one to see any new profile location Here are four possible profile cut operations e Cut from the start of the line to the UP marker If UP marker is set the program removes all data from the beginning of the line untill the UP mark and redraws a profile view If plot mode is Along profile it also shifts the data in the view because now the profile has a new starting point e Cut part after UP marker to the end of the line If the UP marker is set then all data after it gets removed and the profile view is updated e Cut outside UP and DOWN markers This is the sum of two previous operations UP and DOWN ma
47. we should constrain the area we are going to work with Go to zoom Edit Zoom Zoom the area from the bottom left corner 4 4 to upper right corner 14 16 You have now a second window where we will do our operations e Now use the rectangular pick Edit Rectangular pick Show maximum area then min imum area The pick appears in the screen The middle point of this pick is the initial location of the dipole The mathematical solution needs to be given some initial geomet rical position which includes X Y Z e Go to nverse Run Here you have to fill in the table Specify Man filed inclination declination and azimuth of X axis latter is 90 degrees because X axis is going west east Enter total magnetic field and Susceptibility Remanent Let Margin space be 0 Number of iterations 4000 some big number Limit to stop equal zero Now important parameter is Initial depth Set it as 5 meters You should not set Density and J scale now Make sure Induced only and Linear only are unchecked Set Grid type as GS ASCII grd This is a well known Surfer ASCII grid format Now change file names Set Position file to be position dat Calculated grid this is where synthetic field from the source is written to be calc grd and Difference ob served field minus calculated diff grd Set Object type as Dipole s You are done here Press Start iterations e You will see a small progress window with Iteration number and Discrepancy Discrep an
48. 0 5000 3250 3500 3750 4000 4250 4500 4750 5000 B750 exceed ee es rantes Pe Pera ca m Ponce a oa sn EG acne ceea tee 5750 5750 ess iaa a bereep eend incdus Esse sense ntes anim Mh pin aaa Pise dd Idle UST DES ZEN GRUT QOO MT oe 7051900 Eo aa A iii a P EE ti RUTAS ow LOST 2 gt gt 5250 die poe Pesce ie Reeecc deete Bev 44 5250 5250 ie ne Pee Be D CES Bee nee A TEE dei i es a eee 5000 5000 cose foem tek AE ont d ionii aice Dese aa teal e 3250 3500 3750 4000 4250 4500 4750 5000 3250 3500 3750 4000 4250 4500 4750 5000 m m Figure 23 Example of calculating magnetometer offset with simple shift and dragging It can happen that distance BM is greater than BN if ship does a sharp turn In that case the position of the fish is not changed literally fish should sink in this case These calculations are repeated for each GPS point Method explained above assumes that the fish position at time t is known but in general we do not know this Therefore to start the calculation process we need to find the initial fish position Different techniques might be employed for locating the position The easiest one follows use the initial part of the recorded path to find direction of motion by approximating these positions with a stright line using the least squares method and count the cable length along this line This gives a reasonable estimation for the initial fish position When the initial position is selected the dr
49. 1 0000e 01 You may need to try with different parameters Upward continued file name Press button for browser File with continued field data misha projects magpick upward grd File with original continued File with difference original minus continued field Will reperesent residual anomalies data misha projects magpick org up ard Add files to the history list If this box is checked then output files Format SURFER BINARY are added to the history list for easy access Set output format here Figure 26 Upward continuation dialog 8 2 Synthetic horizontal and vertical gradients As you saw above the potential field can be upward continued and therefore a vertical gradient also can be calculated Magpick allows you do to this operation as well as a calculation of horizontal gradients This option is available under Operations Gradients Here you can choose the type of gradient vertical horizontal or absolute value of horizontal gradient For a horizontal gradient you have to enter the direction positive clockwise from your Y axis Because these operations can be numerically unstable you have an option of simultaneous upward continuation to cope with possible noise increase Again you may need several attempts to find the best result 8 3 Reduction to the magnetic pole and pseudo gravity transformation It was shown see for reference t
50. 1 Export to the AutoCAD TM and compatible software via DXF file Magpick is capable of preparinf an ASCII DXF file which can include the following elements e Coordinate grid with axis annotation and general title The default font is used and the grid steps are the same as on the screen Grid labels can be formated in meters or in degrees minutes and seconds e Magnetic field contour map as lines contour plot option The slow contour method is rec ommended because it allows inclusion of labels However the fast contouring method can be used e Profile XY positions with direction pointers e Profile stack plot 64 Export to the CAD e User s picks results of inversion polygon and pointer e Additional drawings such as lines polygons and points However clip is not included All of the above elements reside on different AutoCAD layers Properties of each layer such as name color and line style are user selectable Each drawing can have its color defined by layer or directly thus allowing the AutoCAD user to change the color of all drawings on the layer at once The DXF file is in compliance with DXF 2 5 specification and works with the following CAD sys tems Autocad release 12 and 13 ItelliCAD from CADopia AutoDesk Volo View Express viewer for DXF and DWG files TurboCAD 2D and FastCad DWG DXF viewer The DXF file does not contain any AutoCAD variables only line style and layers definition tables and entities To match
51. 100 200 pixels 3 Plot stack profile This box should be checked if you wish to see a stacked plot If not checked the rest of the controls in this window are disabled 4 Datasets to draw Each profile file can have several datasets inside Thus the word profile does not mean a sequence of X Y Z field values but X Y Zi field were i is the dataset num ber You can select which data set you wish to see as a stack plot 5 Data scale Data has to be scaled to be plotted together with coordinates This value is needed to scale data to the length units MagPick divides the data value by this value before stack profile plotting It converts data units mostly nT to length unist meters This requires a good understanding of how magpick handles profile data In many cases the data set number is just 1 13 Basic operation of MagPick 10 11 12 13 You may need to experiment with it to obtain the best plot Preferred direction This controls where positive parts of the anomalies will gravitate if positive anomaly direction defined by one of the three methods described below is between 90 90 from this direction it is mapped If it is not that it gets flipped before plotting If Use fixed direction is not selected then MagPick estimates direction of data plotting based on perpendicular to the track If the positive anomaly is between 90 90 degrees range from Preferred direction it is plotted it not i
52. 30 It presents the DXF export dialog box Each layer is represented by the string in the list box Star means that the layer is selected for output The absence of means that the corresponding layer won t be included in the drawing To edit each layers properties select them in the list box and push the button Properties The dialog box shown on figure 31 is displayed Here the user can alter the following elements e Enable or disable layer If the layer is disabled its definition and all entities are omitted in the DXF file If layer is enabled but there are no entities if user did not request to draw them in Common parameters dialog 1 then the layer is presented in DXF table but there are to entities If the layer is enabled and its entities are drawn in MagPick then they also are drawn in the DXF file e Layer name MagPick will assign names itself however the user can change them Do not enter same name for different layers e Line style MagPick uses the following convention to code line style digitl digit2 where digit is length of the line dash If digit gt O then line is drawn pen down if digit lt 0 the 65 Export to the CAD Entities are not included in DXF file if not checked ER includes layer in the drawing Line style for the layer Example 5 2 means 5 units draw and 2 units pen up No spaces in this string allowed Set layer line width currently not working Use colo
53. 7 80 deg Declination 351 84 deg Other important parameters are Azimuth of X axis 90 Number of iterations 4000 big enough Limit to stop 0 Initial depth is very important parameter Set as 5 for instance Change files as you need but this is not important now 89 Tutorial 1d adus Buneoo edid Jo pesn Byep ju 01 uoB Apog v NX ve 000 0 08 868Z EO EZLS 35414 Jojeoipui sse Boug 8 as SuoisJeAu enuenbes ic gi re DE ani JO synse ylim 1eeug 9 10 9186 b 46 81 LPSSOE L6 8528 OL 9OLZ LG 8EBS sag z ZA eX LA LX LO 3LZO Z _borase3 tb L t5S8L BEbZOE 627573 8Z BEL Z 78585 d LO BbpEZ Z bO a0z b L 8881 80940 GO LSZTS sL essz l0 8595 d Z LO 80b0 Z bOras8s b E IL pSEZOE ZV SC9 66 6E2Z 14 658S d E pee 9 duuis se paluasaid Uoneoo edid jenu s p ep Jay seu 185 E ZLZGE Lt v3 d L na HY 06 Q8 02 09 05 Oti DE 024 01 0 01 02 0E Qe OSA 095 0251 J peuop prey pevelnoleo A PIIoS pieu peuesao N g ul umoys erep ajjoid ojd 0 uoroeurq S8 1J01d xoeis yM pu Awwnp 10d dew 10 09 OU maia deN MOPUIM UOISJOAU 9 lJOJd 1 yum pereroossy z 00Z8 0018 X 0008 0065 suondOo esiau p ad esiBAu siajaueJed p a Finding pipe location with MagPick 90 Figure 37 Tutorial Set Object type as Pipe and press Obje
54. CAD TM format Magpick is not capable of reading directly neither DWG nor DXF formats however some simple steps and using third party software allows a DXF drawing to be brought into MagPick relatively simple To use this option the user should download DXF2XYZ program available from GuthCAD http www guthcad com au freestuff htm for free This tool working under MS Windows only allows the transfer of AutoCAD DXF files into a simple form of ASCII file Please note that the program can be used for free but not redistributed Also see its license for industrial usage The problem with this program is it can not handle AutoCAD text and ellipses The user can give up text or use a Lisp utility to convert text into polylines inside AutoCAD To do so XSHP LSP lisp program can be used available for free You can download it for example from http www acad co uk freesoft font Note that program requires ASCII font file TXT SHP in the same folder as the binary font file TXT SHX If you don t have an ASCII file you can use the utility SHX2SHP which is available from the same place to produce one Follow standard AutoCAD instructions to load the Lisp program Then select all text in the draw ing and call XSHP It might be slow but program will finally convert all you text into polylines it may not convert text inside Acad blocks Save result as DXF file Now start DXF2X YZ and pick your DXF file Use next settings inside DXF2X YZ e Ignore Z 2D
55. Field graph as function of distance or time 4 average value magnetic field distance along profile or time 4 b Stack plot with average middle line UL 7 7 7 Northing profile position e Easting c Stack plot with linear middle line Northing 2 b YW profile position Easting Figure 4 Different methods of creating stack profile plot simple average is used A better way is use the linear approximation for the background as in the example on plate c 14 Stack labels After a stack plot map is plotted it might be difficult to find what the anomaly values were To make it easy magpick can automatically draw dimension lines on minimum and maximum points Press this button to call the stack labels dialog and set the parameters of this feature See figure 5 for an example of stack labeling To label a stack plot MagPick searches for segments where the field is above or below middle line For each segment it calculates extremum point If extremum value is more than the user set limit MagPick draws a dimension line with annotation This can be a value above the middle line relative or an absolute value or both However if there is not enough space to accommodate the label it won t be printed The user can disable this feature by unchecking the box Use stack plot labels to select labeling threshold set type of annotation its color text hight and label suffix see figure 6 THe
56. It can be or All profiles Active profile or Between marks The latter is available if both marks are set on active profile e Then chose the color to plot shifted positions This allows you to preview the result of trans formation and compare it with the original positions Note that the stack is not plotted if you have a shift preview it may obscure all the picture e Finally specify the shifts along X and Y axis Units are the same as original position informa tion After you press the Ok button the program redraws a current map view any other maps you have to redraw by hand You now have a chance to compare the result of transformation with the original track If you want to repeat it you just do it again The previous result will be automatically discarded To accept changes go to Profiles Accept All original profile data is replaced with the transformed data only for profiles where you did transformations You must save the profile data or the result will be lost after you exit MagPick To discard transformation results go to Profiles Discard The grid view will be redrawn and transformed part will disappear 5 3 2 Spline smooth Similar to the profile data profile X Y positions also can be smoothed with a cubic spline A good example of this is when you are plotting a stack profile of magnetic data with the field plot per pendicular to the track If the GPS Global Positioning System has been used to acquire position inform
57. MAGPICK magnetic map amp profile processing User Guide Mikhail Tchernychev 16 02 98 Last revised 07 26 01 Contents 1 History and features of Magpick 4 LI Version 1 0 1996 1998 ami pom in moto A A 4 1 2 Version 2 0 1998 1999 1 2 uo AA AA A AA a wR A 3 6 2 1 System requirements vo 4a mos xx X 3 E EA REE AAA AA 6 Mei Ross e Sebeeu deeded Dita ate 4 Re 4XxESex43 7 E ee eee A RARA Aa 8 3 Basic operation of magpick 8 5 1 Magpick as map grid VIeWer s ss ce ee e e aa aa X 0x X X Rx 9 RS 9 32 Drawing and clipping on top of the map o 19 3 2 1 Magpick vector formats lines polygons points clip area 19 3 2 2 Bringing an AutoCAD DXF drawing into MagpicK 21 3 2 3 Using ArcInfo TM shape files in magpick 22 CACERES 22 3 3 1 Simple pick gon echae aran SER PERS ES ii 22 3 3 2 PICE export oa ja ce om XO a eR eRe eh eRe ee eS 23 35 4 Automatic pick 4 424 b 444 ono dk ox HA 3 ROO GEER SSE SE EEA 24 3 5 Profile information loading and viewing 2 000008 25 3 5 1 Profile loading se e kee RAO See POR See SH SH RRES 25 3 5 2 Easy profile load x 6 a oh oe RO RO Oe AR OR i xx ook eed 27 NAAA Ai 29 3 9 4 Parameters of the profile view e e ow RR RR UR ee EU 30 A s aod so Bde we i rcd Bah eS we OH EUER OG POR Ko Ho eS 32 33 4 1 Making grid out of profile data cc 33 4 1 1 Triangulation with
58. Shrink to canvas is responsible for the display method If it is checked then Y size and X size vertical and horizontal sizes of the canvas stay constant when you change your profile The profile data gets scaled to these fixed sizes If it is not checked then 7 scale and X scale parameters are used to find the appropriate size of the canvas to accommodate the data In this last case vertical and horizontal scales of the data stay constant when you change profiles You can see difference between them in the same scale Set Y size as 500 and X size as 1000 Notice this is how we can zoom data We also can zoom data the same way we did for maps Go to Edit Zoom Then press the left button and drag mouse to select area Instead of creating new window graphs are zoomed in the same window To unzoom just go to Edit Redraw This kind of zooming works best when shrink is checked 13 Tutorial 4 Browsing profile data There were 51 lines but we see just only one To see other lines go to File Browse The moda less dialog window appears with all your lines with string numbers from the file Press but tons gt gt and lt lt picture will change Fast sequencing of these buttons can cause crash under X windows You also can select data directly from the list box by mouse Now we will show how shrink works select first line and go to Parameters Settings Uncheck shrink to canvas and set T scale as 1 and X scale as 0
59. Susceptibility cgs Susceptibility per volume This value can be used for mass estimation It is supposed to be known 55 Estimation of magnetic sources Depth Figure 29 Coordinate system Remanent gauss Remanent magnetisation per volume Used for mass estimation Elevation For grid inversion all data points should have the same Z coordinate You can in troduce this value here Note that you should then set initial depth of dipoles correctly Z axis goes down Margin space If you wish you can use only part of the window in the estimation by setting appropriate margin Number of iterations The limit for the iterations program to perform inversion Estimation is stopped after the iteration counter exceeds this value Limit to stop After each iteration MagPick calculates the discrepancy between observed and synthetic field If there is a difference in these values taken on two sequential iterations less then this limit estimation procedure stops Initial depth Initial depth for the whole dipoles Sometimes the estimation procedure can be sensitive to value for instance it can put dipoles above observation level In that case take a new value and repeat Density If you want a mass estimation the density value is needed For instance if suscep tibility is in CGS units and remanent magnetisation in gauss and you want to have mass in kilograms it should be the mass of one cubic centimeter in kilograms J sc
60. a gradient palette see figure 8 but uniform palette has the advantage ability of color equalization The goal of equalization is constructing of image where 17 Basic operation of MagPick single color occupies the same area as each other Equalization provides an enhanced color image and even small details can be seen immediately To invoke these options click on Change palette button in the Common parameters dialog box You will be prompted for the type of palette you are going to use Then end up with either dialog figure 8 You can zoom part of the window if you wish To do so choose Edit Zoom You will see that the mouse cursor has a shape of a magnifying glass Press the left button and drag the mouse around area you would like to zoom After you release the mouse button a new window with the selected region appears on the screen It can be zoomed again It is important to understand that all windows created by zoom share the same array map of data Several arrays can be opened at the same time If you decide to close all windows initial window and zoom window of given array choose File Close All If you have closed parent window you will not be able to see the full map again The only way to get back is to load the file again To receive short information about data in the window choose Options Info menu Here you can see the geometrical locations of the corners of the grid and the number of columns and rows
61. a magnetic response from shallow objects Theoretically the field also can be continued downwards untill the continuation level does not cross any field sources However it has been proved that this operation is unstable It greatly magnifies existing noise and makes the field unusable To cope with this problem relaxation regularization can be used This may help but only to certain extent Magpick uses very simple kind of Tikhnonov regularization In the spectral domain upward con tinuation can be written as s u v F u v s u v x f u v gt F u v oa x f u v here f u v is the spectrum of the field to be transformed F u v is the spectrum of transformed upward or downward continued field s u v is the spectrum of the transformation and amp the small regularization parameter You should try several values of amp to find a best for your case start with small vales like 107 51 Potential field transformations The field in the current grid view can be upward continued by calling the Operations Upward continuation menu If function is called for zoom window only data in zoom window is used not the whole grid The next dialog box appears on the screen see figure 26 Elevation to continue field Positive up negative down Elevation positive up negative down 0 500 For downward continuation regularization is needed Check this box and enter parameter Require regularization Parameter
62. ade Inclination of the total magnetization vector in the geographical system degree Declination of the total magnetization vector in the geographical system degree positive to the east Magnitude of total magnetization possibly divided by scaling factor X component of magnetization vector in the local system cgs units Y component of magnetization vector in the local system cgs units Z component of magnetization vector in the local system cgs units Some simple operations are available in the work sheet All of them can be reached by window menu or popup menu right mouse button Here they are Load Load file content into the work sheet Previous content will be lost Save Save work sheet content into the file You are encouraged to do it periodically during the session Delete Delete current row normally highlighted but not necessary Program re numerates all the targets and updates map views Undo Undo last deletion Up to 50 undo calls are available 60 Implementation of inversion 9 4 Option of mass estimation In case of known K Jrem and a given vector of total magnetisation an attempt to estimate the mass of the body can be made MagPick does it automatically after each inversion One should understand that mass estimations can be incorrect in many cases due to the difference between assumed and real magnetic properties of the object In some cases the problem can not be solved mathematically
63. agging method can be used After short distance influence of initial position becomes negligible Potential problems It should be noted that this method is not designed to work with sharp turns It does not take into account the depth of the fish if fish is deep then horizontal distance is less than 47 5750 5500 5250 5000 UTM Gauss Kruger transformation the total cable length Another problem is that the GPS normally is not mounted at the same point where tow winch is therefore the effective cable length should include distance thr GPS to winch offset Simple geometry calculations should be used to estimate errors introduced by these sources for each particular configuration Figure 23 shows two different offset calculation methods They are based on real GPS data which represents a ship turn after it passed the Golden Gate Bridge in San Francisco Bay the data was converted into short UTM MagPick was used to calculate the offset with a hypothetical cable length 250 m and an offset to the right 20 m offset was taken after dragging has been used The left pane represents the result of shift along a GPS track and the right represents a result of the dragging method 6 UTM Gauss Kruger transformation in magpick MagPick is supposed to work with local projected magnetic data Usage of geodetic coordinates is possible but depreciated Instead the user should project his or her data into the UTM Universe Transverse Mercat
64. al points fall into one grid cell only one will be taken or some combination of points This is recommended because if data has duplicated points there will be a problem the program even can crash Set Method as Average value and Format as GS ASCII e Finally change the file name to g 858mt grd where t stands for triangulated This is a bit faster than spline interpolation We end up with a file g 858mt grd on the disk Now again go to File New and select Grid view In the empty window you can check settings in Options Settings and Options Size or go directly to open and pick file y 858mt grd you do not need to close your old map view Compare these two pictures 6 Draw stack profile Up till now we could see the profile data in a separate window Now we will combine the profile information with a map to see them simultaneously In the map view go to Options Settings Click two times on Show profiles till window Profile plot parameters appears on the screen Inside this dialog 77 Tutorial e Check Show profile direction and set each 200 pixels This will allow MagPick to show the direction in which the profile was taken by arrows each 200 pixels along the line The direction is defined by the data order in the original file and therefore will be opposite to the real direction in the case of G 858 data because this device reverses order of magnetic readings e Check Plot stack profiles This means you want the fe
65. ale In many cases the mass estimation will fail MagPick estimates the total magnetic moment of the dipole in cgs units anyway Because it is known that 1 ton of iron has dipole moment in range 10 10 cgs a rough method of mass estimation can be applied Just put the appropriate scale factor and Jora will be in the mass units Induced only If you guess that the body can have only induced magnetisation check this box It is means instead of three components of magnetic moment the program estimates only one because the direction is known Mass estimation becomes trivial then 56 Estimation of magnetic sources Linear solution only In some cases you can presume that you know the source location and you wish to find only magnetisation Then check this box The program will not do iterations because the problem is linear Grid type This is the format of output synthetic grid file There are two choices Golden Software ASCII grid and netCDF binary grid The last one only is needed if you work with GMT cartographic system Position file Besides appending results of estimation to the worksheet the program saves the position in the file which has a format compatible with the pick file i e it can be loaded into MagPick as a new pick file This feature is obsolete The file is overwritten after each inver sion To keep the original file change name by means of the Change button Calculated grid Synthetic field after calculation
66. ansformations This section describes the MagPick features which allow to modify loaded profile data It includes the following 1 Saving profile data Certainly profiles must be saved if any transformation has been used Note that new profile list or Simple load menu call might be necessary in order to load saved data into program next time 37 Profile data transformations You can save only the only profile parts inside the polygon This allows to cut unnecessary sections of the data to be removed Profile cutting These operations can be used to remove part of the active profile It is based on user marks Profile data smoothing A simple cubic spline can be used to smooth data magnetic field along the profile Profile position shifts Any or all profiles can be shifted with constant offsets along X and Y axis Profile position smoothing Any or all profile positions can be smoothed with some type of cubic spline Profile position recalculations based on the profile direction This includes position shift along and perpendicular to the track Dragging recalculations can be used for repositioning It is simple simulation of the object being towed behind the vessel There are some note worthy facts about the way profile data is handled in MagPick e All data is stored as floating numbers 4 bytes This may lead to loss of accuracy if you are operating with large numbers Typical examples are full UTM co
67. ar to the profile The latter is positive to the right if you look along the track and negative to the left To apply a perpendicular shift the program finds a normal vector at every point of the path e To transform first point of the track program needs to find a direction of motion at the beginning of the line To do so it uses first part of the track being approximated to a straight line The distance used for such an approximation is entered under the Distance to find direction This value also used to find a direction at every point of the line This value can not be zero e Finally chose the color to plot the transformed positions This selection allows you to preview the result and compare it with the original positions Note that the stack is not plotted it may obscure all the picture After you press the Ok button the program redraws the current map view any other maps you have to redraw by hand You now have a chance to compare the result with the original track If you want to repeat you just do it again The previous result will be automatically discarded To accept changes go to Profiles Accept All the original profile data is replaced with transformed data of course only for profiles where you did transformations You must save the profile data or the result will be lost after you exit MagPick To discard the transformation results go to Profiles Discard A grid view will be redrawn and the transformed part disappears 5 3
68. at Lon not recommended or you do inverse UTM transformation on the output In addition to UTM transform you can apply a simple linear scaling and shift Exporting DXF and BNA formats are similar except you have less choice in what you can export You can export end or middle points or picks as line segments or both Please note that the results of a DAT DXF and BNA export are not loadable back to Magpick 23 Basic operation of MagPick Export fields Y minimum Z minimum X middle Y middle Z middle Format Decimals Positions after dot g Transformations setup Cancel If checked inverse UTM will _be applied before export Check UTM parameters if you want this feature Linear scaling will be used if after UTM transformation this box is checked It takes effect you wish to export min max or middle Select here which elements of the pick point or all of them Select format decimals degrees and minutes or degrees minutes and seconds Choose number of digits after dot calls this dialog Press this button to see if inverse UTM transformation and scaling are set Note check it anyway gt E Inverse UTM on output _ UTM parameters Linear scaling on output X scale 1 000000 X offset 0 000000 Y scale 1 000000 Y offset 0 000000 Export type Segments E Ok Cancel
69. ation chances are that the path is not a smooth curve individual data points jump around If you use such a path to prepare magnetic field stack plot it will result in an erratic picture After a certain degree of smoothing the positions remain almost the same but path becomes much smoother and therefore can be used as a base line for a stack plot 44 Profile data transformations It should be noted here that MagPick actually constructs two splines X n and Y n where X and Y are positions and n is a fiducial number Each curv e X n and Y n gets smoothed individually The results are combined into X Y pairs which represent smoothed positions It would be better if the program were using time instead of the fiducial number n using of n implies that position data have fixed sample rate Usage of the fiducial number instead of time could result in unacceptable results when data has long position gaps Smoothed curve will spread the positions points over these gaps thus covering them almost equidistantly The rule of thumb is next Position smoothing works well when a time interval between data points is constant or almost constant To smooth position data follow the next steps e After profile data is loaded and map a grid view created go to Profiles Smooth XY A dialog identical to data smooth dialog appears on the screen e Choose what you want to smooth It can be or All profiles or Active profile or Between marks The latter i
70. ature added to the map e Set Datasets to draw 1 In many cases it will be 1 so do not change this value e Set Data scale 100 MagPick has to transfer data values to position values to plot stack profiles and therefore it has to scale data values To do this MagPick divides data values to the number you have just entered To increase the span of the anomalies on the final plot you decrease this number and vise versa For example 50 will increase anomaly span 2 times e Select Type as Fixed direction This means that positive anomalies will be drawn to the direction specified clock wise Enter 90 degrees as Fixed direction azimuth Other choices are End points and Normal to path End points selection means that two end points of each line are used to calculate the stack profile azimuth Normal to path selection means that at every point the stack profile plot is perpendicular to the path Preferred direction is the azimuth to where positive parts of the anomalies will gravitate This is useful when you have parallel lines taken in two opposite directions and you want the positive part of the anomaly to be drawn on the same side of the XY line e Choose Fill type positive and fill color you like Say green e Do not check Clip stack plot for now This feature allows clipping values on the stack plot which are bigger or less then certain limits Press Ok and to close dialog and then close Common parameters too You can see now a
71. ce or tab separated columns can be loaded into Mag Pick You will be able to inspect the data as linear graphs elongated along local X Y or profile direction itself After this lesson you should be able to use MagPick as a simple viewer for profile data Files We need files g 858m dat and g 858g dat which were generously provided by Paul Kot These are result of an export from Magmap Geometrics program and represent magnetic data ac quired with G 858 hand held magnetometer Two different techniques were used for positioning ground marks file g 858m dat and differential GPS receiver g 858g dat Therefore positions in first file are in some local coordinate system but in second file they are in California grid 1 Loading one profile data from one file Start MagPick go to File Profiles Simple Load Press button Add and choose file g 858m dat This file has a header string with names of the columns therefore you can see the number of the column and its name if the file does not have this header only the column numbers show up We need to decide which columns represent X Y and magnetic field File has 9 columns These are X Y TOP RDG magnetic field for top sensor BOTTOM RDG for bottom sensor VRT GRAD difference between them TIME DATE LINE logical line assigned by operator and MARK X is the x axis and Y is y axis Select them in the list boxes X and Y Now we have to select the data Let s take a bottom reading sele
72. cks except autoscale and possibly wraping e Shaded relief This produces a picture as it would be if your data presents a surface shaded by a light source The light source parameters azimuth and elevation degrees can be set 10 Basic operation of MagPick 6 10 11 12 13 as well You also have to set the Data scale in many cases value 1 10 is ok but you might try different ones to find the best value You should use the Uniform palette for this kind of plot e Color illuminated map A simple color map can be combined with the effects of shaded relief It may look very impressive especially for topography data Change palette Calls the dialog box which allows you to choose the type of color mapping Uniform or Gradient Uniform is defined as a pre defined color scale spectra The data gets simply mapped into that color scale You can choose type of palette you like 0 41 and if Equalize colors is checked MagPick will apply non linear color mapping based on the data distribution This is particularly useful when the data has spikes It allows you to see details better The gradient method gives you much more control on coloring but does not work with color equalization When you choose this option you can use the color scale editor to compose the best palette Show crosses If checked picks are shown as black lines with two small crosses at the ends Show profiles If profiles are loaded they are n
73. controls 1 Field direction Some constant angle value which is used for simple picking see below Basic operation of MagPick 2 Minimum and maximum Constant angle to be added to pick values of the field Data is not important 13 Plot coordinate meshes for X and Y Coordinate mesh steps ji for X and Y 11 Allow you to select color for coordinate mesh J i If checked picks are snapped to the grid nodes set contour isolines mapped in this range LES Common parameters Data min 223 85 Field direction Oooo 0 0000 gt T Show x grid p so Data max 353 52 l Show y grid Y 50 J Autoscale Y wrap cel siab Grid color Color map Change palette 1 Snap togrid Show profiles J7 Show crosses Contours 3 If this is checked minimun and maximum are taken from the data 4 If this is checked color is wrapping data repeats itself when out of range how to draw color map calls dialog box 5 Allows you to specify J 6 Calls dialog to choose color sheme 9 Call dialog box to plot parameters 8 Set profile stack plot parameters calls dialog box the picks 7 Show small crosses at the ends of Figure 1 Common parameters dialog box Data min Data max User defined limit
74. ct BOTTOM_RDG 4 in list box Data The profile view on the map as XY curve can be active if selected by operator and being viewed in a separate window or inactive not selected and not viewed It is makes sense to have different colors for these two conditions Names of the colors you can change under Active color and Inactive color Let it be RED active and BLUE inactive Press Ok Create the profile description dialog closes and you can see that a new string appears in the list box 12 Tutorial Press Ok Profile data is being loaded as X Y magnetic field Finally MagPick reports 1 profile loaded If you are familiar with magnetic survey design this may seem strange File g 858m dat has 51 lines The problem is you did not tell MagPick how to distinguish data between lines We will now go over how to correct this problem Loading several profiles lines from one data file Go again to File Profiles Simple Load press Add and choose file g 858m dat You see the Split Here you can specify how MagPick is going to recognize end of individual line It can do it automatically by finding gaps in your position data Select Distance and specify the length of the gap under Distance enter field to use this feature If data file has a special column to mark line change MagPick can use this column for line separation Change in content of this column indicates line change For example to mark line 1 you can have 0 in line col
75. ct specific Here set Number of pipe segments as 1 and check Use infinite approximation This corresponds to the case b from figure 36 Press Ok and press Start iterations Now the program is calculating Watch the progress indicator 8 The last two numbers arethe most important They are the current depth and discrepancy The last one should decrease Wait till it finishes For pipe inversion you normally do not have to press Cancel As soon as it is done a new dotted lines appear in profile inversion window This is the graph of calculated field You can compare it with observed one If the fit is good you can keep this result If not it is better to remove result of alst estimation and try again for example with different initial depth 6 Results of inversion For dipoles you can see results of inversion in the worksheet There is another different from dipoles worksheet for pipes Go to Inverse Worksheet Pipes window with results appears on the screen 6 on figure 37 Once opened it can not be closed The pipe worksheet supports the same set of operations as the dipole worksheet loading saving from file deletion of the raw undo deletion export as DXF or BLN format The results of inversion is also shown on the map view as e where 5 denotes estimation number the same as row number in worksheet It is shown on figure 37 as 7 When you remove the row from the worksheet it is automatically removed from t
76. cy value is decreasing When it stops decreasing for these data it is about 3 6 press cancel You have just found the magnetic source To get mass estimated correctly locate file magpick ini or magpick on Unix systems and make sure that string TronDensity is set to 0 0078 82 Tutorial MagPick shows the horizontal position of your dipole as sign with a number To see it better zoom to the central part of the map and turn off the color map You can see that it was not placed not on the middle of the pick but close e There is another form of data representation called the worksheet Go to Inverse Work sheet Dipoles You will now se a table with one row which represents the location of the source you have just found e Inspect the synthetic field Create a new empty grid view and load file calc grd This file was created during calculation You may need turn on the color map for that view Compare the observed and calculated fields e Inspect the difference observed minus the calculated If the case is a good fit it look like random picture Again create a new veiw and load file diff grd You have done well The magnetic source a very dangerous one in this case was located The real position was X 8 5m Y 10m and Z 2m Compare these values with X Y Z in the worksheet on your screen Stability of the solution We were able to find magnetic source but how stable is this solution What should be the criteria
77. d MagPick can do it for you so you do not have to stare at screen This is the procedure e Go to Edit Rectangular pick The cursor changes its shape Now go to point 6 12 Look at the bottom of the main window to read coordinates Note that it says First Press left button and drag the mouse down and left up to point 10 8 Release mouse You have just showed MagPick the area to search for maximum field e Move the mouse and look at the status line It now says Second This means you have to show MagPick the second area where the minimum is located Go to point 6 14 and repeat the operation drag to point 10 10 As soon as you have released the mouse button MagPick connects the maximum point in the first area and the minimum point in the second You may note that this pick differs from what you did by hand e Important You must show the maximum area first and minimum second Areas can over lap 3 Removing the pick Consider we did a pick by mistake and we want to get rid of it Go to Edit Delete pick then move mouse to the middle of the pick you want do delete click the left button It s gone Remove all picks you have done and make a new clean one 80 Tutorial 4 Saving and loading of pick file We certainly want to keep this information Go to File Save pick and select a file say pick out Press Ok Save Exit MagPick start it again and load the file bomb grd Go to File Open pick and select pick out We have it
78. d to the pole and pseudo gravity fields know the direction inclination and declination of the object s magnetization which is generally unknown In some cases you can assume that objects have only induced magnetization and use the IGRF model to find it in this case the direction of magnetization coincides with direction of Earth s magnetic field Different objects also can have different directions of magnetization Because of this and other reasons do not expect that a transformed picture will be fairly simple Some anomalies could be transformed some not Reduction to the pole also might be an unstable operation on the equator see 7 for details Similar to the reduction to the pole the magnetic field can be reduced to the different direction of magnetic Earth s magnetic field and magnetization reduction to the pole just a special case of such a transformation In this case you should enter explicit directions of new field and magnetization All operations listed above could increase noise To cope with this the option of simultaneous upward continuation which acts as low pass filter is provided Use zero elevation to disable this option These transformations are available under Operations Reduction to the pole and Operations Pseudo gravity Figure 28 shows the dialog box where transformation parameters are set pseudo gravity dialog box is similar 1 Enter inclination and declination of the Earth s magnetic field f
79. data misha projects magpick t grd NS Set file name for result Set format for output file pa Filter data prior triangulation to remove duplicate points and reduce total number of points for triangulation Figure 15 Gridding profile data with triangulation 4 1 1 Triangulation with linear interpolation One of the primary methods employed by MagPick to interpolate a map from scattered points profile data is triangulation that follows by linear interpolation inside triangles MagPick uses the method described in 4 to build a Delauney triangulation network Then each triangle is used to find inter polated field values into regular grid cells This method works well in case of relatively uniform distribution of data points However results may not look good if there are only a few profile lines separated by considerable distance Also note that grid nodes outside the triangulation network do not get any field value attached Thus the method provides some natural clipping of the data Potential problems arise when data set has duplicate data points or points too close to each other Triangulation may fail or the program even crush in that case Because of that it is recommended to process data with a filter before building a triangulation network 34 Grid operations E m L L E gt a
80. dialog box The next most important step is choosing the initial positions of the sources It is done exactly the same way as in the case of grid based inversion by means of picks on the map Note that it is possible you do not have a real grid and must use a dummy grid implicitly created by MagPick or loaded from dummy grid file It might be very useful to uncheck Snap to grid to allow picks to be located anywhere After the profile selection is made the estimation procedure can be started Choose Inverse Run Dialog box similar to the one in the case of grid inversion appears on the screen Here is the difference e Smooth Z parameter Checkbox and value In case you have noisy Z values it is possible to apply a simple method of spline smoothing If you need it check it on The normal value for a smoothing parameter is 1 e 5 less parameters give more smoothed curves Normally changes of orders required to feel a difference 58 Estimation of magnetic sources e Average data depth This value is for information only Program calculates the average elevation of all the data points to get an idea about the possible initial source depth specified by the interpreter Initial depth should be bigger than the average depth It is possible that in the case of improper initial depth during iterations the program can move sources above the observation level Change the initial depth and repeat calculation in that case e Induced only Linea
81. e highlighted profiles get saved When working with a global profile list only one profile can be active at a time All profiles in the window allows you to have more than one active profile e Save between the marks You can set user marks at specific profile points There can be only two user marks at a time and their shape is different if you are working with global sign or local sign A profile list If a polygon has been drawn on top of magnetic map you have two more choices e All inside polygon This means only profile parts inside polygon will be saved e Active inside polygon Only active profiles are will be saved and only the parts inside the polygon will be saved Figure 19 illustrates how this feature might be used to cut profile ends and produce new set of profiles 5 2 Profile data data operations These operations are used to change profile data not their positions They include simple profile editing by cutting part of the profile and data smoothing with cubic spline Latter there can be used as low pass or high pass filters 39 Profile data transformations Figure 19 Profile cutting by saving an active inside the polygon Active profiles are red inactive profiles are blue Function All profiles in the window has been used While loading profiles back they become split by distance 5 2 1 Cutting profile parts These operations are applied to the active profile and based on
82. e available Set the minimum to 1500 and maximum to 2000 All the colored range now is mapped to 1500 2500 and you can see only the top of the moun tain All that is less then 1500 is mapped with blue All that is more that 2500 is mapped with red Intermediate colors are in between blue and red Now lets look at another kind of mapping Say we set range 0 500 All what above is or below this range will be wrapped to this range Therefore the value 510 will appear as 10 and value 1010 too This method is useful for viewing of magnetic maps which have some points with extremely high values MagPick employs this method using the Wrap color scale check box Set minimum value as 0 and maximum as 500 check the box press Ok and see what happens It looks now as a rainbow The data going up in color changes from blue to red When it reaches 500 it becomes blue again and so on Now uncheck this box and check Autoscale again 6 Color palette MagPick implements two methods of color mapping linear and gradient Linear means that the color range simply gets mapped to your data range There are 41 pre defined palettes in MagPick To see them all go to Common parameters and press Change palette Choose Uni form set palette number you like see how the picture changes after you pressed Ok in Com mon parameters dialog Mapping of data into color is linear if Equalize colors box is unchecked and non linear based on your data distributio
83. e color scale saving and loading from file and much more Color equalization method allows visualization of maps with maximum color contrast Currently the feature is available with a uniform palette This allows a color map to be produced where each color occupies an equal space greatly increasing map resolution Visit http imina soest hawaii edu gmt No information was found forbidding usage of GMT code Installation A new kind of coloring color wrapping was added to the program This provides a color wrap around certain range for example if range O 500 then the data point 501 is colored the same as 1 etc It visualizes the map in the greater detail Shaded relief mapping was implemented with a user selectable position of light source Illuminated map presentation was added the color map shaded in accordance with the light position Map drawing speed was increased Easy profile loading does not require hand preparation of profile list file is now available One data file now can hold more then one survey line Program splits file into the lines during loading Stack plot was added on top of magnetic map Progress indicators were added to most time consuming operations such as data loading color equalization map and profile drawing Configuration file was re written to be more user readable than it was before The set of tutorials in this manual has been added Documentation has been imp
84. e position of the mouse cursor in Lat Lon To utilize this feature go to Options Status line Here you choose the format of the coordinates in the status line for example if your data already are Lat Lon you can use degrees minutes seconds and if data in UTM apply inverse projection Check Inverse UTM This means that every mouse location position is projected back to geodetic and formatted accordingly e Pick export For example when you need the final locations of your picks you can obtain them in the geodetic system applying inverse UTM during the export The UTM transformation setup can be called directly from the export dialog box 49 Earth s magnetic field model IGRF e DXF export to AutoCAD You can apply the inverse UTM transformation during export to obtain drawing in geodetic coordinates It is recommeded you save the current projection parameters button Save in UTM setup dialog box and keep this file with the data Each time you are working with the data load this file again button Load in UTM setup For a good reference on UTM and other projections see 6 There are a lot of references on the Internet for example http www cnde iastate edu staff swormley gps gps html http everest hunter cuny edu mp Note for users in the Southern hemisphere by convention we should add 10 000 000 m to UTM northing for points located south from equator Magpick does not do it To do so you should reflect that addition
85. e taken into account to find the real sensor position This problem is complicated and may have different solutions based on the price paid the system including usage of acoustic underwater positioning systems gyro compass on board or complex cable dynamics calculations Magpick provides two the simplest ones 1 a simple shift along the recorded GPS track 2 using simple approximation of tow system with dragging technique Neither method takes into account possible difference between ship heading based on position information and the real ship heading which can be obtained with gyro or magnetic compass Both methods are available under Profiles Drag profiles s in map grid view The profile data should be loaded There is no option between marks The transformation is applied to the entire line of data or to all lines To proceed with transformation perform the following 45 Profile data transformations e After profile data is loaded and map grid view created go to Profiles Drag profile s e Choose the item you want to drag It can be or All profiles or Active profile e Specify shifting method It can be Drag profile or Shift along profile In the first case the program simply moves the data points along the track in second case it uses the dragging method e You might check the button Apply transformation in reverse order This is useful if your data has a reversed order in the file e Enter shifts along and perpendicul
86. ector measurements these values have to be projected on direction of the Earth s magnetic field Considering D declination of the Earth s field and J inclination formula for full field can be written as T XcoslcosD Ycos sinD ZsinI Note that vector J can has an arbitrary direction and value Thus to solve the forward task in the general case three geometrical and three amplitude parameters should be known for each dipole The magnetic moment can be considered as a sum of induced and remanent magnetization In this case we know these values per volume J can be expressed as J VKF earth Jremviirem 105 K magnetic susceptibility per volume cgs units F magnitude of Earth s magnetic field nT Nearth unit vector in parallel to the Earth field Jrem remanent magnetisation of the sphere gauss Tirem unit vector parallel to direction of remanent magnetisation v volume of the body cm In the case all distances are measured in cm then x in cgs units Jrem in gauss and J in nTesla 10 2 Basic inversion To estimate position and magnitude of the source we have to model the observed magnetic field Mathematically it means that function N y TAPETE yc rudis i 0 has to be minimized Here is T observed magnetic field T points of observations total number N in case of the grid interpretation they are nodes of grid in case of profile interpretation they are points of actual measurements T expression
87. ed to use pair of points with known UTM geodetic coordinates to check your setup before going to work with whole data set Knowledge of the central meridian or zone number is one of the problems using the UTM system Six degree zones start at 180W and go to 180E Magpick allows you to find a zone central meridian based on your data The following shows how to proceed e Check Set central meridian from first sample e Go to UTM calculator and enter Latitude and Longitude of your location e Press Lon Lat gt UTM Read Northing Easting UTM zone and central meridian The central meridian value in UTM setup dialog is updated automatically 48 UTM Gauss Kruger transformation Allows you to save and load projection parameters from file Set of ellipsoid names to choose It is recommended to keep this from Major axis and flattening are file with the data changed when you change ellipsoid to reflect your choice Ellipsoid s parameters If you choose Ellipsoid name WGS 84 1984 User defined you can enter these values Major axis m 5378137 00000 If checked central meridian will be Flattening 298 25722 taken from first Lat Lon sample UTM calculator will show zone and C M Warning if you do inverse transform only Y Get central meridian from 1 st sample do not check this box Central meridian degrees 123 00 Base projection parameters cen
88. eg 90 0 Co 2 Note Use zero elevation to avoid continuation File with transformed field Add files to the history list Format NetCDF data misha projects magpick pseudo grd carei Figure 28 Reduction to the pole dialog in magpick 5 You need this group if the results of your calculations are unstable Apply some upward con tinuation as a low pass filter it may help 9 Estimation of magnetic sources Along with the simple magnetic picking facilities MagPick has an internal option of magnetic mod elling Presently it supports only three kinds of sources uniform magnetised sphere magnetic dipole magnetized line and uniform infinite current power line It is possible to find a few sources simultaneously in case of dipoles or power lines Parameters that need to be estimated for each dipole are three components of the total magnetic moment of the body and three parameters X Y Z of its geometrical location In addition a simple function to fit background field can be found Because of it method can be applied directly to the measured field without calculation of the residual field In general searching of the magnetic dipoles is an iterative process which requires knowledge of their initial positions MagPick uses the locations of the middle points of the simple picks as initial locations All picks done in the current map view are involved in the estimation If user does not
89. erates with short form of UTM projection proper UTM parameters should be set to allow program conversion from longitude and latitude to Northing and Easting See the full manual for complete set of features and format description 12 4 Detecting of magnetic bodies Goal MagPick was no originally designed as a visualization tool but rather as an instrument for locating of magnetized objects This tutorial shows how you can use MagPick as alocating tool do it This introduction section is very simple it explains why MagPick is called MagPick Files As an example we will use the magnetic field of a real bomb from World War II GP 500 ISS UK General Purpose 500 Libs excavated out of Kuhwerder hafen Hamburg Germany in September 1997 Its mass is 226 5 kilograms the field was measured with G 858 magnetometer two sensors top and bottom on grid 17 x 20meters Susceptibility was estimated as 0 87 cgs and remnant magnetization as 0 24 gauss we will not discuss here how it was done see rest of the manual for that Files we need are located in subdirectory bomb 79 Tutorial 1 Simple pick of magnetic object Start MagPick and load file bomb grd It has just 35 x 41 cells go to Options Size and set the size of X Y cells as 10 Now you can see it better If you turn off the color equalization Go to Options Settings and then Change Palette Uniform and uncheck Equalize color you are seeing a classical field from a magnetic dipole
90. file Note that all lines in that file have the same color The core for this program was provided by Sol Katz skatz blm gov 3 3 Simple picking of magnetic anomalies 3 3 1 Simple pick Magpick provides two basic options to select specific points on the grid Note that these simple picks have important value they are used as initial positions for searching of magnetised spheres or lines inversion Picks can be saved into and loaded from a separate file Because the simple interpretation of magnetic filed assumes that the source is in between local minimum and maximum of the field the pick consists of two points There are two ways of picking e Simple pick Go to Edit Simple pick for the window where you decide picking The mouse cursor will change its shape to Now move cursor to some point and click left button A ribbon dashed line appears after pointer Move mouse in the second point and click the left button again A black line segment with small crosses at the ends if need see figure 1 is drawn on the screen If the checkbox Snap to grid is checked on the ends of the pick are always in the centres of the grid cells It may not allow to set pick where you want if grid has low resolution In that case check it off e Square picking when magpick helps you to find local extremum Go to Edit Rectangular pick the mouse cursor changes its shape to reflect your choice When square picking is used there are two things that m
91. g in magpick 95 linear data transformation list file examples 27 list file format Middle line approximation 15 operations with positions plot parameters position drag position shift 44 position spline smooth 44 position transformations project on direction resolution save active inside polygon 39 all inside polygon between marks save active save all 39 set mark short UTM show stack plot stack plot clipping stack plot direction stack plot fill color stack plot fill type stack plot labeling stack plot scale two kinds of views start MS windows Unix SURFER format tutorial 68 finding magnetic bodies 79 finding magnetic dipoles 81 finding pipe lines 87 reduction to the pole 91 view grids map 68 view map AND profile data 74 view profile data 72 Universe Transverse Mercator UTM UTM central meridian INDEX data preparation pick export Southern hemisphere status line 49 UTM calulator version view many profiles 9 map 9 map grid one profile 9 profile all view parameters fixed scale mouse functions shrink to canvas profile inversion profile view worksheet wrap color scale 10 wxWin library version 96
92. hat total field anomalies can be reduced to anomalies on the magnetic pole if the direction of the Earth s magnetic field and the direction of object magnetization are known Figure 27 shows the relation between the field measured at the middle magnetic latitude a at the magnetic pole b and the gravity field c from the same object Curve a has a complex shape and the real location of the object is somewhere between minimum and maximum The actual location depends on the Earth s field inclination and declination as well as magnetization direction of the object On the magnetic pole b the Earth s field is directed downwards Induced magnetization is directed downwards too In this case b the main maximum of the field located right above the object Thus the horizontal location can be easily found Plate c shows the gravity field from the same object It is similar to field on the magnetic pole but does not have side minimums Theoretically when you apply reduction to the pole transformation all the specific maximum minimum shapes of the anomalies should change into simple ones However to do so you must 52 Potential field transformations Field Observed magnetic field Transformed to the pole magnetic field Pseudo gravity field OS S f oy Poy m PA i ES Distance Play onouSeui s yu ES P c ay ES NM E a b c Figure 27 Relation between observed reduce
93. he map view too 7 Estimating stability I strongly encourage you to try different estimations with a different initial location depth This way you can get an idea how real your estimation is If the program ends up with the approximately the same numbers this means everything is Ok If not you might conclude that you are unable to find this object perhaps this object is not a pipe This is also a possible result You may note that the estimation procedure here is less stable than one for the dipole If you set the initial location far from real and or with weird initial depth procedure is likely to fail Conclusions Hopefully you have learned how pipe parameters can be estimated using MagPick I would like to stress that this feature has not been in wide use It appears much less stable than the dipole estimation I would recommend to use it only when there is a clear field picture as presented in this tutorial 12 7 Reduction to the pole Preface It is a well known fact that the total magnetic field measured at a arbitrary latitude and longitude can be reduced to the field measured on the magnetic pole To do this kind of transfor mation the user should know the magnetic inclination and declination at the point of measurements use IGRF model to find it Also the direction of the body s magnetization is needed This last value may not be known however in some cases it can implied that the body has only induced magnetiza tion and
94. heet and from the map Re numerates dipoles e Undo Operation opposite to delete Restores eventually removed row e Export Export worksheet content into form readable by other software Presently there are two choices Atlas Boundary and AutoCAD dxf files 12 6 Finding magnetic pipes Preface Some elongated magnetic objects like metallic pipes can be approximated with a simple source such as magnetized material line This line is infinitely thin and has a magnetic momentum This kind of source can be infinitely long or may have a finite length It is certainly not a real pipe but at the distances much greater than the pipe diameter it provides a good approximation MagPick employs this model for locating of pipes or similar objects Practice shows that this kind of object rarely can be considered as infinitely long therefore a simple infinite length approximation won t work Things are even worse most of the magnetic field observed from pipe sources are due to the section joints not from the linear part of the pipe To cope with this problem MagPick provides several user selectable modifications of search see figure e A Simple segment with uniform magnetization To be estimated geometrical location in X OY plan we assume constant depth for all segment and 3 components of magnetization Jx Jy Jz e B Simple segment with uniform magnetization and infinite ends In addition to the properties of the central segment properties of infi
95. how labels are printed The user can choose decimal degrees degrees and minutes or degrees minutes and seconds The latter two make sense if Inverse UTM is enabled in Grid labels dialog Regardless of which one is choosen the drawing coordinate system labels can be presented in UTM or latitude and longitude Figure 32 shows a contour plot exported into a DXF file To obtain the contour labels slow contours should be used see 2 MagPick uses the text hight defined for the layer and fits labels into the space defined in the contour dialog box refiso Due to this operation labels have different sizes the most obvious example is contour OnT Figure 32 Example of DXF contour plot On figure B3 you can see result of export for stack plot If you are viewing this manual with Adobe Acrobat zoom into the picture to see small details This drawing also includes line file magenta see Drawing and clipping on top of the map 1 67 Tutorial Latitude Figure 33 DXF stack plot with magpick 12 Tutorial 12 1 View grid files with MagPick Goal Show how grid information presented in SURFER ASCII format can be loaded and viewed with MagPick After this lesson you should be able to load grid data into the program adjust size of the view pick appropriate color scheme and the coordinate mesh You will learn how to zoom parts of your map to see details with Magpick Files for that lesson we take file helens2 grd which comes
96. icular useful feature if the data is presented in full UTM format To decrease overhead MagPick uses floats 4 byte words to store all values Therefore loss of accuracy for full UTM coordinates is possible Use false Northing and Easting to avoid this loss Note that these field are also optional 3 Name of the profile file with a path if it is not in the current directory 4 Color name for plotting inactive profiles on top of magnetic map 5 Color name for active profiles 6 Number of data sets in the current file One file can contain more than one profile for a multi array magnetometer system for instance 7 Decimation While reading the program can take only part of the data each 10th sample for instance It increases the speed of loading and all subsequent operations In most cases decimated data still has enough resolution to represent geometrical position of profiles and field graphs If then one decided to load all points it is possible to accomplish it inside MagPick 8 Sequences of four numbers X Y Z T for each data set Thus the total number will be the number of data sets x 4 The Z axis goes down as normal in geophysics In case you do not 26 Basic operation of MagPick have Z in the file you can specify a constant value by typing expression h value instead of number of Z column Here value is desired Z Next information is optional and reflects features of an off shore magnetometer array It allows y
97. ilable under MS systems nowdays for free Probably one of the ways might be loading a few lines with Easy profile load and saving them as a profile list Such a list can be used then as a template This manual starts with a descpiption of the profile list file format hard part Users who want it fast can read Easy profile load 3 5 2 Each line of the file consists of description of information loaded from one data file Description fields are separated with one or more spaces Here is the format of the line 1 It may contain or may not words SPLIT NN Here is SPLIT all capital letters key which indicates that data set has to be split into lines NN could be an integer number with out or real number with In first case it is treated as column in the file which has line number Any character string can serve as a line number MagPick assumes that the new line starts when a string changes In the second case with the value is treated as a distance be tween adjusted points to break data into separate lines If the distance between points is more than the current value new than a line starts Note that this field is optional 2 It may or may not contain the words XFALSEZNNI and YFALSEZNN 2 Values NNI and NN2 are false Northing and Easting values to be added to X Y coordinates in the file Note that they must be negative if you want to reduce for example full UTM coordinates to short ones This is a part
98. in False northig 7 Earth s magnetic field model IGRF To estimate location and amplitude of the magnetic sources parameters of the main Earth s magnetic field see also figure 29 should be known International geomagnetic reference field normally provides these values It allows you to find the main magnetic field parameters for any point on the Earth between years 1900 and 2005 This model will be extended in future as new observations which are conducted all over the planet become available Enter date as decimal number Date decimal year Enter longtitude and latitude as Geodetical longtitude 9 0000000 decimal numbers Geodetical latitude 53 0000000 Enter elevation in meters In many Elevation m f0 cases 0 is good enough J Attention Lon Lat in decimal degrees Press this button to calculate Calculate parameters of the Earth s main EE magnetic field Inclination deg B7 90 aia ete Cem Read here the results Pees Esp Inclination deep angle Total field nT 49874 41 Declination and absolute value nT Accept parameters for inversion It you wish to keep these parameters and use them for inversion purposes check k Cancel EET this button Figure 25 IGRF model in magpick Magpick has an embedded IGRF model and an external file with coefficients igrf dat The model was obtained from http www ngdc noaa gov The user may need to get a new
99. ings of the program which can be altered by different dialogs This file is written right after magpick exits If file is not found all defaults are assumed If start is successful you will see a small window with a menu under Uxnix X does not support MDI interface or an empty multi document window MDI window under MS Windows This is the root window of MagPick which remains unchanged during the session Uxnix Besides this root window you can have as many additional windows as you wish These windows are called views The current version of MagPick allows you to have three types of views 1 Map view This is a 2 D coloured or black and white map of the grid with additional informa tion if desired This view is independent from all other windows 2 Profile browser view If a set of profiles is loaded into the program you can browse each one of them as 2 D linear graph This view might be linked or not with map views s 3 Profile inversion view You can see all or part of the profiles which cross the parent map view This view dependents on the parent map view Only one profile inversion view is allowed for a given map view The last views are unaccessible before the profiles are loaded This means that when the program opens you are able to create only the map view When you choose New item a new empty window with the same menu appears on the screen If the profiles were loaded then by choosing New you can the type of view y
100. ion with profiles on the map After loading a new object appears in the program list of the profiles This enables plotting of geometrical positions on the maps if this feature is enabled see figure I viewing of the profile data as linear graphs and allows putting marks on them Each profile can be in an active and inactive state This is shown by color An active profile is shown in the profile view window if any and highlighted on the map When you choose New in any window a small dialog box appears which allows choosing the type of view you want Depending on where you choose New in map window or in root window of the program there will be two or three choices They are e Grid view Create a normal window for map displaying That is the same as without profile loading If profile data is loaded at time map created MagPick creates a fake empty grid to allow viewing of their positions e Profile view This allows to see profiles as linear graphs one by one There are four possible types of presentation as T X T Y T d T p Where X and Y is local coordinates d distance along profile always starting from zero and p projection on user defined axis The last type of graph is possible when the profile view is opened from map view window with plotted direction of a new axis If there are several data sets in one profile file they are shown by curves of different colors All profile view windows share the same data global l
101. ions Attention Set before adding data into list Add picks a file and calls this dialog t checked you will be propmted to save configurations a ist Set which samples to load each each 2nd 3d 5th etc Create profile description Fie you are working with nom 1 Name g 8589 dat 1 m Select splitting mode No split NM split by distance or split by line Split 8 LINE Distance 10 00 Decimation Enter Distance if you are using split by distance E Xx 1X v 2 Data 3 TOP nad Show columns where are your X Y and field If file has header Active color RED N it is displayed Inactive color BLUE Set color names for active and inactive profiles Ok Cancel Figure 12 Easy profile loading Set the method to split into lines or No split if entire file represents just one line If you choose Distance then a new line is started when the distance between two points is more than this value If you choose any file columns than it will be used as a line indicator If the string in that column changes a new line is started Enter the Distance value if you are splitting data by distance Enter Decimation This would allow to load just only part of the data For example if decima tion is equal 2 only each second point gets loaded Note that you can get all points later within MagPick increase the
102. ist of profiles When you are working with one window the results can appear on all the map windows e All profiles in the window Profile inversion Show all profiles which cross the parent map window in the limits of the window The same types of presentation are possible Opposite to profile view program does a local copies of profiles and makes all profiles active This means that they can be viewed simultaneously on the same coordinate axis As its name implies this type of view provides an inversion You can have only one profile inversion window opened for each map window Operations with the global profile list will not be reflected on it After profile loading the bottom items of the Edit menu of map view become available They allow basic operations e Direction Create a local axis on map view Show the beginning of the axis click left mouse button show direction and click again An arrow is drawn on the screen Then you create a profile inversion view window you are able to view profiles projected on this axis You can dynamically alter the profile view by pointing new axis 29 Basic operation of MagPick e Pick profile Making profile active inactive Show the profile and click the left button If mouse pointer is close enough to the profile line profile is highlighted and profile views if any updated If a map window has a child profile inversion window this action reflects only on the child If the profile was
103. ith Automatic you can choose the total number of contours used to plot a picture Min Max Minimum and maximum values for contour lines 11 Basic operation of MagPick 10 11 12 1 Method of choosing intervals If fixed contour values are taken from list d if automatic data interval divided per Total to obtain contour values Total number of contours if Automatic is checked if Fixed values has no effect IF x Fixed values Automatic Total 25 6 List of contour values Gets updated when orton you press Calculate X Can be read from file p 3 Enter here min and max D Min 100 00 contour values Max 100 00 WT i N Mm Z 4 Enter here contour interval 7 Read contour values Interval 1 00 C from file only 1 st column gets read Calculate Isolines intervals won t be 5 Press this button to update updated till you press it 94 00 1 8 Allow you to set color Read from file for contours one for l color Cancel all of them eS 9 Uses fast method to contour data but o qx pr Decimals 0 without label EO SS ime between labels map units 30 00 10 Enables contour annotations only for slow drawing Fast drawing no labels available 11 Places after dot for annotations S on 12Space for annotation For example below it may be abou
104. latest Magpick versions provide considerable improvements in map viewing It includes two new kinds of data mapping Shaded relief and Color illuminated map Both involve some simple shading calculations which the make map naev a better contrast To use them click on Color map check box in Common parameters dialog box You may need to click twice to call Color map draw mode dialog Here you have next choices see figure 7 1 Drawing mode Choose the type of the map you want to draw The possible choices are 3Magpick calculates average or linear approximation for each profile line separately It leads to the breaks in the stack plot if continuous line was divided to the set of sub lines 15 Basic operation of MagPick Stack profile labeling 6010 6020 6030 6040 6050 6060 6070 6080 6090 6100 2940 2940 2930 2930 2920 2920 2910 2910 2900 2900 Y m 2890 2890 2880 2880 2870 2870 JE 6010 6020 6030 6040 6050 6060 6070 6080 6090 6100 Xm Figure 5 An Example of stack labeling Both realtive and absolute values are printed actual mag pick output How to annotate realtive amplitude absolute value or both Check this box to enable stack labels E ER Stack plot labels Y Use stack plot labels How to label EAS Label limit 10 000 Text hight 3 000 Digits o Add text to Batalupiss Aj nil Color Ed annotation Do not label max and
105. limits and enter Xmin 100 and Xmax 100 Now the horizontal axis extends from 100 to 100 m Constraining data used for locating We definitely do not want use all data presented in the map window for location of a single pipe To restrict the data do the following Under map window go to Edit Polygon then go with the mouse to the point 5800 2800 approximately Click the left button Draw a polygon as it is shown on figure 37 4 Close polygon by hitting the first point one more time If you clicked the left button by mistake the last node can be removed by a right click Choosing Edit Polygon removes current polygon completely As soon as you draw the polygon your profile inversion window changes too It shows only data inside the polygon try for example to draw very narrow polygon and see what happens Defining initial pipe location in XOY plan For a non linear inversion we have to define the initial location of the object In MagPick Simple pick serves for this Go ahead and set the pick as it is shown on 37 5 for the first try you even can set it close to anomalies Opposite to the dipole inversion pipe inversion allows just only one pipe at once for dipoles you can have several of them estimated simultaneously Profile based inversion Now we are almost done In the profile inversion window go to Inverse Run Here you should enter Earth s field parameters Total Intensity 35178 03 nT Inclination 3
106. linear interpolation 34 A E ni 35 pros ea ae dia 36 4 3 Create clip pal arca a a 909 9 36 peros idear A A dd da Sau 37 37 5 1 Saving and re loading profile data o o 38 Ea e a Wo dob E a ud 39 5 2 1 Cutting profile parts x x ok RR RR a n e RSE ES 40 SP 41 9 SM E SR AR E RA 43 Lear 44 5 3 1 Simple shift uno eR ORE a 44 ches dokoak Por dodo p Sob xd 4 xU Sd 44 Lite ede ed wed wad eed ex xe 45 C4 eR ORE EHR i de EER EEE SERS SRE ER 46 6 UTM Gauss Kruger transformation in magpick 7 Earth s magnetic field model IGRF Potential field transformations 8 1 Upward continuation ge Seedy a Sok A Sore koe ER Se Se e woe HS 8 2 Synthetic horizontal and vertical gradients cc 8 3 Reduction to the magnetic pole and pseudo gravity transformation 9 Estimation of magnetic sources 9 1 Magnetic modelling based on grid data o a 9 2 Magnetic modelling based on profile data o 9 3 Magpick worksheet results ofinversions cc 9 4 Option of Mass estimation 2 0 sse 9 5 Automatic estimation of magnetic sources ee 10 Implementation of the inversion in magpick 10 1 Solution of forward probleM o e e eee eee 10 2 Basicinverston 4 4 2669 RaoekakEGeErd e i de ta edi da 10 3 Estimation of susceptibility and remanent magnetisation 10 4 Mass estimati
107. llowing D This system m ae ae 5Here and below multiplier 105 is included into Jrem 63 Export to the CAD P 2v J i Noah A d earth 1 3 E Jrem sane v2K2 2yk J Tiearth V The periods in the equations denote scalar multiplication This is the way susceptibility and remanent magnetisation can be estimated 10 4 Mass estimation Given the total magnetization of the sphere K and J em one could estimate the mass or volume of the body The following system must be solved J VKFR earth T JremV rem Here is the same norm condition as above ii em 1 There are 4 equations and 4 variables have to be estimated These are volume of the body v and three components of the remanent vector direction This equation can be reduced to x2 J2 Jr 2KU fearn J 0 This is a square equation for v and can have positive or negative roots It also may not have any roots In the case when there are no roots the v value which coincides with extremum might be taken as an approximation of the root It is clear that negative roots do not have physical meaning It has to be made clear that this approach does not provide a good mass estimation for all cases This is due to possible large variations in the magnetic properties of the different metalic objects In the case of two positive roots no assumption can be made which one is correct 11 Export to the CAD and other graphic programs 11
108. load the data next time 43 Profile data transformations 5 3 Profile position operations Magpick also allows set of simple position operations which can be useful to alter or correct profile positions These operations are available in map grid view under Profiles If there is no profile information loaded all the menu items are disabled They become available after a profile is read from the disk All position transformation is first previewed by the user The transformed is path plotted on the same map with a different color If the user satisfied with the transformation he should replace the original positions with transformed position and save unfer different profile file name There is no undo after this point However profile data can be reloaded from the file and original positions re stored Use Profile view to do this If you do several transformations sequentially you should commit changes replace original with transformation result after each transformation For example you shifted the profile along X and Y then you smoothed the profile If there was no Accept command issued after the shift operation then the smoothing would be applied to the original positions not to the shifted 5 3 1 Simple shift This very simple function adds the shifts dX and dY parallel to the coordinate axis It is available under Profiles Shift XY After you call this menus item you should proceed as follows e Choose what you want to shift
109. makefile xt and likely end up with the file magpick xt which is executable version of the program Basic operation of MagPick 2 3 MS Windows installation If you have the magpick exe file the only problem you may have is with ct13d32 dll library At least two versions for Win95 and NT exist You will need to find the right one for your platform The next step is copying of this file into a windows system directory probably C WINNTNSYSTEM32 under NT and C WINDOWSNSYSTEM for 95 98 like systems Please note this file can not reside in the same place as magpick exe After files are in place everything should run Later versions of magpick also have a setup program based on Install Shield 5 0 free edition 3 Basic operation of magpick Here is some basic ideas behind MagPick MagPick works with information that can be presented as a grid files in SURFER ASCII BIN and NetCDF format and with information presented as set of profiles simple ASCII files with space tab separated The grid information is compulsory it provides schene for presenting profile data Some additional data like road a map costline can be loaded on top of the grid data too Loading of grid data is not complex All you need is file in the format which can be read by MagPick Loading of the profile data is more compilcated You should a prepare profile description file to begin with Alternatively MagPick can prepare this file for you but you ll ha
110. map overlaid with the stack plot Do it one more time filling in negative anomalies To see the stack profile plot better you may want to get rid of the color map To do so Op tions Settings and uncheck Color map Press Ok This raises an interesting question In some cases you are not able to produce a quality magnetic map but still want to operate with profiles This means we need the views we discussed in this section The background for these views is the map To resolve this situation MagPick creates a fake map to serve as a background which is never displayed For instance you could load profile data without loading the map Then go to File New and select Grid MagPick shows positions of the profiles using dummy map Alternatively you could load any other map to serve as a background It is common to load bathymetry map in marine surveys and display stack profiles on top of it Advanced feature how to add something on top of magnetic map In many cases we need to see some geometrical topographical information on top of the magnetic field This paragraph is a hint how you can do it Additional information comes in wide variety of formats like USGS DLG AutoCAD DFX DLG ArcInfo files etc It is beyond MagPick s abilities to support all this world of digital data Instead MagPick offers its own but very simple format for external features It is your responsibility to transfer your data into this format For example there is a wa
111. mend that you inspect results before going to magnetic source estimation it also can be done automatically for all anomalies by Inverse Run batch Magpick may place some picks incorrectly and you should correct them 3 5 Profile information loading and viewing 3 5 1 Profile loading Besides map processing MagPick allows loading of the profile data The input can be any ASCII file s which has column organisation At a minimum the file should have three columns X Y 25 Basic operation of MagPick coordinates of the point and a value of the magnetic field To make loading and processing faster the data can be decimated during reading To enable profile features you have to prepare a special file with file names and column numbers or use the Easy profile load feature The latter greatly simplifies access to profile information but has limited application for example each file can have only one data set if you need several data sets then you need to read the file two or more times What you use for profile loding depends on the format of your data and your expirience with a computer For example people with little expirience using Unix tools and with a task to process thousands of profile lines not unusual case with marine magnetic surveys may find it easier to write a simple script This would create a MagPick profile list file Users familiar with Microsoft Excel should assemble such a list manually Aslo all Unix tools are ava
112. minimum values less then this limit Enter number of digits after dot for labels Set text high in distance units if plot in meters this value in meters too Select label s color Figure 6 Stack label dialog e No color map Do not draw it at all e Simple color map There are no 3D effects here just plain color image e Shaded relief Black and white shaded surface It allows you to see some details better e Color illuminated map Similar to above but colored 2 Light source parameters To draw shaded maps you must specify parameters of the light source such as its azimuth and elevation above horizon both in degrees Results are shown on the sun icon 4 3 Data scale Before the shade calculations take effect the data may need to be multiplied by some scale factor to improve the result This control sets this value You may need to try it few times to find the best setting 16 Basic operation of MagPick 1 Possible picture modes 4 Icon shows your current light No color map parameters Simple color map Shaded relief black and white Color illuminated map Drawing mode Color illuminated map 2 Parameters for Shaded relief and color illuminated maps 43 Light azimuth from north and light elevation in degrees Light azimuth degrees Light elevation degrees A 38 P Data scale 1 00000 3 Data scale for
113. n Fill type At your request part of the plot can be filled with a color Here you can specify part of the anomaly to fill positive negative or No fill It is also possible to plot only filled parts of the field select Positive no line or Negative no line Fill color Invokes the color chooser dialog box which allows you to define the fill color Clip stack plot In some cases big spikes for example the plot can be contaminated with data you do not want to see To avoid this you can clip the stack plot All values out of range will be plotted parallel to the track line Min Max Enter clip values here for the plot if you would like it to be clipped Middle line approximation To prepare a stack plot the program first must estimate which values are plotted on the right part of the path and which are on the left Total Earth s magnetic field is always positive and therefore should be transformed to make it suitable for such a presentation The simplest way to calculate the average value for the profile and subtract it from the field thus producing positive and negative anomalies However this method would lead to unacceptable results if field has a regional trend For example a slow increase from West to East see figure 4 Plate a shows a magnetic field as distance along the profile or time There are few anomalies with a linear increasing background Plate b shows what one can get if a 14 Basic operation of MagPick a
114. n if Equalize colors box is checked This last method provides a col oring where each color occupies the same area on the screen as any other color Therefore the picture is much richer Try for example with palette 34 Use with color equalization and without See the difference 70 Tutorial A second method gradient palette gives you more control on the color you wish to have It does not provide color equalization Go to Change palette Gradient You are seeing the gradient palette with control points You are free to move these points change their colors and values with a mouse Press the right mouse button to see a menu There is a pre defined set of palettes for your convenience For example choose Land and Sea and then choose Revert colors The gray is large To reduce it move the second from the top color point up You can move other points as well to provide the same interval for each color Press Ok now and see what happens 7 Advanced mapping techniques The mapping methods include shaded relief and illuminated color map The last may as good for magnetic data than for topography It takes a considerable time to calculate and plot the picture Let s start with shaded relief I assume that helens2 grd is loaded Go to Options Settings press Change palette and make sure thatUniform has been set Now click on Colored map check box You should click once or twice to invoke dialog box responsible for mapping Choose Shaded
115. n most of the cases the magnetic source was found around 30cm in the plane from the predicted point Thus MagPick was proven to be a good tool for magnetic interpretation 1 2 Version 2 0 1998 1999 During this period MagPick was not used extensively The most significant use was designing a pipe inversion This was requested by Geometrics in spring 1998 This kind of magnetic source is more difficult for interpretation than magnetic dipole It appeared that pipe locating is far more ambiguous It is also more difficult for interpreter to deal with Here is some other improvements which were done that time e Magpick now can interpolate data from profiles to rectangular grid therefore there is no need for additional interpolation program Currently two methods are available gridding with ten sion borrowed from GMT software and triangulation with interpolation see and 4 e For pipe and dipole profile based estimation data can be constrained by polygon drawn by user This presently does not work for dipole fitting based on map data e Some improvements were done for map presentation and the number of available map views were significantly increased including A fast but not accurate contour drawing algorithm was brought into MagPick Set of uniform palettes is directly available and viewable with MagPick A new kind of color scheme gradient palette was implemented This control allows easy manipulation of th
116. ne press Ok and one more to close Common parameters You should see stack profile plot now 2 Profile inversion window If you try to start an inversion procedure from the map window then the map data will be used in this case it does not make sense because there is no real map data If you start it from All 88 Tutorial profiles in the window then the profile data is used This is what we want All profiles window is a counterpart to the map window There is just only one allowed per one map window Look at figure There is a map window on the right side of the screen and a profile inversion window on the left side From a map window go to File New and select Profile inversion A new window pops on the screen and all your profile lines in the map window become red You are now seeing all the profile data in your map window as graphs T x To adjust view do the following e In the map window go to Edit Direction Draw direction as it is shown on 37 3 Click first point move to the second and click again Arrow is drawn e In the profile inversion window go to Parameters Settings choose type Along pointer and press Ok Now you are able to see all anomalies from pipe at the same place They were projected on direction you have shown e Change range for profile inversion view If you draw an arrow like it is on figure B7 then in the profile inversion window go to Parameters Settings uncheck here for Xmin Xmax Data
117. nite ends must be estimated too This way we try to model a situation with final segment included into long pipe e C Equidistant parts with different magnetic properties Magpick divides the pipe on number of segments with different magnetic properties and tries to find Jy Jy Jz for each segment Number of segments are defined by the user This should be used to model the case when just a few 1 or 2 survey lines cross over each pipe segment e D Equidistant parts with different magnetic properties and infinite ends The same as above but plus Jy Jy Jz to be estimated into infinite ends 87 Tutorial A simple piece with uniform magnetization B simple piece with uniform magnetization and infinite ends equidistant parts with different magnetic properties D lt gt lt gt 1 2 3 equidistant parts with different magnetic properties andinfinite ends Figure 36 Modification of pipe model Similar to a magnetic dipole case the pipe determination can be based on gridded magnetic data or on profile measurements Because of asymmetry of the object we would recommend primary usage of profile data Interpolated grided magnetic data can contain considerable errors for this kind of a magnetic signature this is of course function of area coverage Goal Based on a simple example we will learn how MagPick can be used to find the location of the pipe segment We will use case B based on profile data Files unde
118. ns there will be a gap in the contour of 1000 units to fit annotation text Press Ok In the current program version the progress indicator is not clear for this kind of drawing you have to wait about 1 5 minutes to have job done for Pentium 200 MHz PC 9 Printing your map 71 Tutorial Magpick printing capabilities are limited They allow you to have at least a hard copy of what you did The printed picture will always be fitted to your paper Therefore it is impossible to choose the exact scale you want this may be be changed in future versions Here is how to print Go to Options Title to set X Y titles Y title never appears under MS Windows and general text above the plot Also choose the font size in 1 72 inch units I recommend something like 10 you may pick different values depending on results Press close Now go to Preview A blank page will appear on the screen this is one of the problems to be solved This is acceptable press Print setup your printer if need page orientation size etc Press Ok The job is going to be printed Take the page from the printer when it is ready MagPick produces big print jobs mostly under MS Windows You should have enough mem ory to spool it For the task you just did helens2 grd with contours it used 11 8 MB Questions e How to make magpick do not plot any color map 12 2 Load profile information into MagPick Goal Show how the profile data file with spa
119. o EOS Trans Am Geophys Un Geophysics Geophys J Int J Geomag Geoelectr Phys Earth Planet Int and others MagPick includes IGRF model for easy computation of Earth s magnetic field elements MagPick is capable of estimating of total magnetic moment of the object Dependence between magnetic properties and mass is quite complex and based on remanent magnetization J em and sus ceptibility K The last two values vary even for one kind of material Nevertheless MagPick tries to find mass based on these two values but results are not so good in many cases because of wide range for J rem and xK This task is non unique it has two solutions So do not pay too much attention when you see some weird values for mass during MagPick operation Goal We will learn how to find the position and magnetization of the point source s if we have a map of magnetic field Files Use the file bomb grd from previous lesson We need parameters of the magnetic field for Hamburg Germany 7 5 4 49011 nT D 0 1 I 68 3 Here D denotes declination J denotes inclination Parameters of the object Jen 0 24cgs Kx 0 87gauss mass 226 5kg 1 Estimation based on magnetic map e Start MagPick and load file bomb grd Adjust the color and size to see teh picture better say set X Y cell sizes as 10 pixels You are now seeing a typical dipole anomaly right in in the middle of the window In real life there are another objects near by therefore
120. o maximum and minimum except data points Tension equal 0 25 is used to reduce oscillations and generally recom mended for potential fields such as gravity or magnetic The value of 0 35 is for steep topographic data The method also allows the user to constrain a solution with fixed values interpolated data points can not be out of pre defined range or with data minimum and maximum values An unconstrained solution is also possible The method is iterative and convergence limit and total number of iterations can be entered The program stops iterations when the maximum absolute change in any grid node is less than the convergence limit The program also will stop if the total number of iterations is exceeded 35 Grid operations 4 2 Save grid There is no need to save a grid created by MagPick because it gets saved during its creation However MagPick provides a set of operations on existing grids After each operation has been used the result should be saved into a file First if you wish to keep any change you did with a grid you should save it Go to File Save and pick the file name you want to use Then MagPick asks about the format for the grid file There are three possible formats e SURFER ASCII This is an ASCII grid format from Golden Software It is compatible with SURFER and machine independent because it is ASCII e SURFER BINARY The same as above but binary It is NOT machine independent little en dian and big
121. o see the profile lines Now go again with the zoom and enlarge area with corners 4 4 14 16 as we did before In a new window go to New and choose All profiles in the window Note that all profile lines in your map window become red This means that you are seeing all these lines simultaneously in the profile window not one by one as we did in the Profile view and this new window has the word nversion in its title Adjust the profile view parameters Go to Parameters Settings and set Type Along Y data were taken along Y You are looking at a classic dipole field Let s work with this now Go to File Browser you can see that all lines are selected Press the button Deselect All Now view window is empty Select some lines from the list You see that you are able to select more than one line When you click on an already selected line it gets unselected Some explanation should be done at this point This new profile window we are work ing with now is the counterpart of the map window from what we called New Profile inversion Only one such window can be opened per one map view window This profile inversion window has some extended properties It can display more than one profile it shows the data as function of direction and it can use the profile data for inversion Press Deselect All now Go to the magnetic map window choose Edit Pick profile pick several profiles which cross the magnetic anomaly Check that you can see them on
122. of the magnetic field from M magnetic dipoles Generally the problem is non linear but can be divided in two steps a linear step to find J and a non linear step to estimate positions The flow of execution is the next First fix the positions of dipoles and estimate J Then fix J and improve the positions and so on Thus J are linear parameters and can be found in one step by inversion of the matrix AJ T 62 Implementation of inversion In the case of one dipole A is the matrix 3 x N where N is number of data points and T is data itself Columns of A have meaning of the magnetic field calculated from the dipole with a unit magnetic moment sequentially along X Y Z axis This task is overdetermined and J can be found by simple least squares method MagPick uses this in the modification of the singular value decomposition In most cases there is a significant background regional field in the observed field which can disturb or even completely destroy the solution To avoid that linear function can be fit simultaneously with estimation of J T Ax By C or in the case of a profile based interpretation where Z values are important T x Ax By C Dz E2 There is total of 3 x M 3 or 3 x M 5 variables for the linear step which does not require iterations and can be solved at once To estimate position of the dipole the non linear problem has to be solved MagPick employs the simple Newton s method to estimate xo yo zo Given an
123. ommon parameters dialog available under Options Settings menu We proceed as folows call this dialog change something replot picture by pressing Ok Call Options Settings check Show x grid and Show y grid Set X and Y values as 2000 these are meters I believe Press Ok Now we have coordinate mesh Look at the status bar in the main window at the bottom You will see a string which starts with the word First and then 3 numbers These numbers are X Y and Z data values in the cell where the mouse cursor currently is When you move the mouse these numbers are changing You can check correctness of the coordinate mesh with a mouse this way You may note that these values are not exactly the same as mesh labels This is due to the finite size of one cell which occupies now exactly one pixel on the screen Now we would like to change this for example each pixel should occupy area of 3 x 3 pixels on the screen Therefore the picture will be increased 3 times Go to Options Size set X cell and Y cell sizes as 3 and answer Yes to the question which appears The picture is larger You can scroll it with scroll bars these are not always correct under Windows but here is a trick hold right mouse button and drag A bit more go to Option Size and set X cell size as 5 and Y cell size as 1 Press Ok Notice the difference An important lesson can be learn here if your grid cell size in the file is 5 x 5 meters in order
124. on cosas errar ed bed eed m 9 99 a 11 Export to the CAD and other graphic programs 11 1 Export to the AutoCAD TM and compatible software via DXF file 12 Tutorial rro TORTE pi dd apa an d auem e ahs Paces ai aaa bee oh kg o a E ui d 12 5 Finding magnetic dipoles 3 e 646688 ee bee Ree HOE HEH HE RR 12 5 Finding magnetic pipes lt 2 see se oe R sWxSE SRESRESERY SE ES 12 7 Reduction to the pole 443 xxx 48 244446226 d pa e 244 A 13 Acknowledgments i 48 50 51 51 52 52 54 55 58 59 61 61 61 61 62 63 64 64 64 68 68 72 74 19 81 87 91 93 94 History and features of Magpick 1 History and features of Magpick 1 1 Version 1 0 1996 1998 Development of MagPick was started in the spring 1996 The initial idea was to provide an interpreter with a simple tool which could perform basic operations such as e View a magnetic map with dynamic adjustment of a color scale in accordance with minimum and maximum grid data Narrowing the data interval could also be accomplished if desired e Zoom of the different parts of the map and present them in separate windows automatic change of the color scale to fit data range in the particular window e Simplify magnetic picking This was accomplished by allowing the user to select two points with a mouse and store them in the file In many cases location of magnetic body is between minimum and maximum of magnetic field
125. one with profile data and another a magnetic map with blue vertical lines which shows profiles position 4 Simple profile map interaction Go now to the profile view and change horizontal axis Parameters Settings then Type Along Y You can see a field that was taken along Y Note that the right profile line on the map view is highlighted by red This is the same line we see in the profile view window Again in the profile view go to File Browse in Profile browser dialog press button marked gt gt You can see that a red line on the map view is moving to the left and field in the profile view window changes You know exactly which profile you are looking at Now in the map view go to Edit Pick profile cursor changes its shape Point cursor on some line and click left button The line you are pointing at becomes red and picture in the profile view window changes as well This is the way you can directly inspect profile information by picking the line you want to see from your map You do not need Profile browser dialog close it for now The next step shows how you can tie points on the profile with points on the map You perform it by setting markers on the map which in turn appear in the profile view or by settings markers on the profile view which automatically appear on the map There are two pre defined markers arrow up and down When you set the marker first time it shows it as arrow up when you do it second time it shows it as arrow do
126. or projection or any other suitable projection UTM is supported by MagPick internally False northing and easting should be introduced to avoid large numbers MagPick stores the position as single precision numbers allows double the amount of data loadable into program The full UTM form as well as geodetic would lead to lost of accuracy The following is an example of the data processing e Prepare your data in the form X Y field columns with northing easting and data Northings and easting may be in full or short form If they are full you should apply false northing and easting during profile reading e Make sure of the UTM parameters you are using This includes false northing and easting It is better if you write them in a file and keep with the data e After the profile is loaded make a grid This grid will be related to the local short UTM system e Set up UTM transformation in MagPick exactly the same way as you used for the initial pro jection Go to Options Utm setup and proceed Figure 24 shows the UTM setup dialog in Magpick You should specify an ellipsoid name di rectly enter the ellipsoid parameters if your ellipsoid is not listed central meridian scale factor normally 0 9996 for UTM 1 for Gauss Kruger and false northing and easting For your conve nience an easy check UTM calculator is provided Using this tool you can convert Lon Lat coordi nates to Northing and Easting and vise versa It is recommend
127. or your area If you do not know go to Inverse IGRF model and calculate it you need to know geographical coordinates of your place To use calculated parameters check Accept parameters for inversion and MagPick will use them when ever possible 2 Here is a similar set of parameters but for magnetization We recommend to start with the same values as with the Earth s magnetic field this implies induced magnetization only 3 The Azimuth of you local X axis It is 90 if it points East 4 Check this box if you want reduction to the pole and the four fields below will be filled in automatically If you want to recalculate field to the new directions you should not check box enter desired directions directly 53 Estimation of magnetic sources SRA Reduction to pole A Main field declination D degrees 30 00000 Main field inclination D degrees 70 00000 Declination of magnetization deg 30 00000 Inclination of magnetization deg 70 00000 Azimuth of local X axis deg 30 00000 D positive to East negative to West A positive to east negative to West positive down negative up Note Use IGRF mode to find main magnetic field p F Use reduction to pole New field declination D degrees 0 0 New field inclination I degrees 90 0 Elevation up down 0 000 New declination of mag deg 0 0 Regularization Parameter 0 0000e 00 New inclination of mag d
128. ordinates or a full magnetic field while looking for anomalies less then 0 05 nT In the magnetic field this is negligible but you could note difference after saving data with MagPick It is not recommended to use full UTM use false northing and easting to reduce the accuracy requirement There are two profile views in MagPick One is simple Profile view where you can see one profile at a time This kind of view operates with the common profile list Therefore changes of this view could be seen on each other view If you do All profiles in the window from the map view Profile inversion in older magpick versions MagPick duplicates all profiles which are inside current map view Note that only one All profiles in the window can be opened at a time for one map view When you close this window the data is not copied back into the main profile list Therefore you should save profiles before closing this window if you did modify them MagPick will usually warn you about it Profile operations can affect profile views and the map views For example if you cut part between marks using the profile view you need to update redraw map view by calling Redraw function Also you should know that the profile data can be loaded with a different resolution decima tion For example only each 5th data point could be loaded Any transformation you do in MagPick affects only the loaded points not all the points in the original file 5 1 Saving and re loading p
129. ormally drawn above the magnetic field In some cases the can completely obscure the picture Check it off to avoid drawing This checkbox calls as well Profile plot parameters dialog which controls the stack plot if you need it see below Isolines If checked the contour plot is drawn on top of the magnetic map When you check it an additional dialog pops on the screen to specify plot parameters see below for details Snap to grid The program shows only positions of the centre of the cell where mouse pointer is default This way picking is limited only by centres of the nodes of the grid To avoid this check box off Grid color allows changing the coordinate mesh color Show X Y grid If checked the coordinate mesh will be drawn on top of the map Mesh steps This were intervals for coordinate meshes are entered Here is a description of the isolines contour plot parameters dialog box see figure 2 i 3 Fixed values Automatic To draw isolines you can choose pre defined levels or you can set the total number of isolines In latter case levels are chosen automatically in accordance with minimum and maximum data values in the window and the Total number of lines contours Thus if Automatic is checked then you do not have to think about range of your data Contours can have odd level values If you choose Automatic then all controls labeled with a on figure 2 do not affect the plot appearnce Total If you go w
130. ormat for usage as a base map Pick can be also saved in SURFER dat format or exported in a very primitive form of AutoCAD DXF file No guarantee your software will read it If it will you might have to scale the picks to fit them on existing maps 12 5 Finding magnetic dipoles Preface Many local magnetic bodies can be approximated with a simple model uniformly magne tized sphere magnetic dipole This simple source has only six parameters to be estimated by the interpreter these are X Y Z location of the center and Jy J and J components of magnetization vector MagPick does not consider the dipole as one which has only induced magnetization in this case J would be parallel to the direction of the Earth s magnetic field It includes remanent mag netization into consideration and therefore total magnetization is represented by an arbitrary vector J Modern magnetometers measure total field which is the projection of an object s own magnetic field into direction of the Earth s field Therefore for proper parameter estimation we should know direction and value of the Earth s magnetic field in the area we are working in There are some models and tables which can be used to find these values The well known IGRF program is one of them IGRF stands on International Geomagnetic Reference Field see for example IAGA Working Group 81 Tutorial V 8 1995 International Geomagnetic Reference Field 1995 revision Submitted t
131. ote than all for values below this check box are filled in automatically e Set elevation and regularization parameter to 0 e Press button File with transformed field and pick folder and name for output file Let s name is on_pole grd If you want this name to appear in the history list check Add files to the history list Set format up with Format control e Press Ok button to start calculation Progress bar on the screen show the process 92 Tutorial 3 View results As soon as a calculation is completed you have two choices go to the Files Recent files and pick you file if you checkedAdd files to the history list or simply open a new window and load the calculated file Examine the result of calculation in a new window Exercises Try to recalculate this field with different directions of the magnetic field and magne tization To do so uncheck Use reduction to the pole button and enter for example new declinations and inclinations as zero case of magnetic equator and see what you get 13 Acknowledgments I thank everyone who participated in this project by using or testing MagPick My many thanks to Dr Jannis Makris and Rainer Kasig from the University of Hamburg who has inspired this program My special thank you to Dr Dennis Wilkison my boss at Geometrics who sacrificed his spare time checking and editing this manual Without his effort this software would never been released to the public References 1 B
132. otential field which allows the use of some standard transformations These are upward downward continuation pole reduction decomposi tion of the total field into its components All these transformations are based on the Fast Fourue Transform FFT and are available in MagPick To learn more about the theory of these transformation please see 7 Due to the nature of an FFT transformation you can get a considerable side effect if your grid has a small number of cells or if you have a considerable gradient across your area Attention All these transformations are working with anomalous magnetic field NOT with the total magnetic field measured by the total field magnetometer Before using of any of these transfor mations you should subtract average field value of IGRF predicted value from your data 8 1 Upward continuation Because of the potential nature of the gravity and magnetic field they can be calculated at any el evation above and in some cases below the level of measurements That is if there are no gravity or magnetic sources between these two levels This procedure is called upward continuation of po tential field It is generally a useful and physically meaningful filtering operation It allows you to smooth the field and eliminate small anomalies from the near surface objects Subtracting the upward continued field from the original field reduces the influence of the deep objects therefore reducing the regional trend stressing
133. ou to calculate the GPS heights of the sensors if GPS hight of antenna and depth of the array are known To take advantage of this feature print A at the end of the string and then troughout the space column number in the data file where the GPS hight is and then the antenna hight above sea level in meters If MagPick finds an A it uses the following expression for Z coordinates for all datasets 1 N L heps hantenna N Zi i 0 Where N is number of sets This expression recalculates all elevations into the geodetic system Then MagPick changes sign to reflect downward direction of Z Here is an example of such a file data_23_09_97 mag_p02_23_09_97_filt dat BLUE RED 4 20 27 28 3 1 29 30 7 5 31 32 11 9 33 34 14 12 A 44 5 2 data_23_09_97 mag_p03_23_09_97 filt dat BLUE RED 4 20 27 28 3 1 29 30 7 5 31 32 11 9 33 34 14 12 A 44 5 2 data_23_09_97 mag_p04_23_09_97_filt dat BLUE RED 4 20 27 28 3 1 29 30 7 5 31 32 11 9 33 34 14 12 A 44 5 2 data_23_09_97 mag_p05_23_09_97 filt dat BLUE RED 4 20 27 28 3 1 29 30 7 5 31 32 11 9 33 34 14 12 A 44 5 2 While loading progress indicator appears on the screen You can stop loading if you want When it finishes the total number of loaded profiles is shown It is possible to have a slightly different format when you need to load several profiles from one data file Here the first column can have the following format number1_number2 Here number is the string number where profile data starts
134. ou want In the following sections a discussion is developed in detail for each mode of operation 3 1 Magpick as map grid viewer Just after the start of MagPick go to New and request a new window Then click Open and you can choose netCDF or SURFER ASCII or binary grid file to load into window After the loading is completed which take time depending upon size of the file you end up with a colored map on the screen Alternatively you can click Open point directly If you choose this option in the root menu a new window is created automatically You can change size of the window and therefore resolution by means of Options Size item Here you are able to choose three values horizontal size of one grid cell on the screen in pixels vertical and zoom factor when you are zooming in part of the map Be careful large sizes can consume all the memory of the computer You may find Autoscale on zoom is useful It means when you create new window by zooming part of the old window color scale into this new window will be choosen in accordance with local minimum and maximum This may allow you see fine details in the view This kind of color zooming is very useful The first view you see may not be what you want To adjust color scale mesh lines contours ap pearance and other items you should go to Options Settings and work in Common parameters dialog box You can see it on figure I Here is full explanation of all the
135. ows In profile view it is just a simple chooser You can see only one profile at once Accordingly only one line can be selected in the listbox Profile inversion view has more functionality you can select all or none of the profiles crossing the parent map window and you can select subsets in these profiles Only graphs plotted on the profile inversion view window are used for inversion A good practice is to change profile decimation before the inversion if there was any decimation during initial load Each point should be loaded This task can be accomplished by the Resolution button The profile view window allows same basic operation with a mouse All these facilities are avail able under menu Edit e Set marker Put a mark on the given line Move the mouse to the place and click left button A mark appears on the screen for the type of mark see figure 13 Markers can be set on curves only and only at the data node The program chooses the nearest node and places the mark If decimation is large the actual mark position and the mouse position can differ considerably e Zoom You can zoom part of the window in the same way as for map views but the zoomed part replaces the content of the view This can be done several times If you work in Shrink to canvas mode then you can return to the state before zooming just by calling Settings and pressing Ok or use Redraw In case you are in the scale mode it is more tricky You should set
136. pick any points the inversion procedure can not be started 54 Estimation of magnetic sources 9 1 Magnetic modelling based on grid data With a magnetic map loaded into the one of the map views the process of inversion involve following steps 1 Interpreter visually analyses all areas and makes a decision about the approximate number of dipoles The interpreter decides where to start and how to proceed through the area Part by part the interpreter selects subwindows by means of the zoom facility The aim is to get a subarea with one or more clear magnetic anomalies Subwindows also can be zoomed into if needed The interpreter does one or more simple picks to hit approximate locations of the magnetic dipoles Then nverse Run is invoked inversion parameters are set see description below and the program does iterations During this step the user interface is blocked and the inter preter has to wait until it finishes After inversion has been completed the results appear in the work sheet table and are plotted on the top of all maps with numbers For inversion based on the grid sign is used The interpreter analyses the results and decides whether or not to repeat inversion with different parameters The interpreter can open output grids with synthetic and residual fields to estimate quality Then initial depth susceptibility etc can be changed and Run step is repeated By repeating the
137. r solution only not implemented for profile inversion e Output file Instead of creating calculated and observed grids the program writes an ASCII file file with that information It stores the calculated field inside the profile structure This means you are seeing the calculated field immediately after calculation This information disappears if you repeat calculation or close profile inversion window During the calculation itself the program posts on the screen the same messages as in the case of a grid based inversion Unix version After the program finishes it creates an ASCII file with the following structure e Line sign P space and name of the file e For all datasets activated in this file trough two empty lines six columns of numbers X coordinate Y coordinate Original Z coordinate Smoothed Z coordinate Original magnetic field Nn A WO N e Calculated magnetic field e Next line with and name of the file This file can be used for further presentation or processing It is overwritten for each inversion In order to save data you have to change its name before the next inversion starts It is possible that there were many inversions done in the particular window Until the window is closed the program keeps track of all of them open Inversion Remove results and you will see the beginning of the line for each inversion that belongs to the window Thus unnecessary results might be
138. r tutor pipe Find here file dummy grd line1 5 dat lines 1st and file field txt The last one holds the parameters of the Earth s magnetic field for a place where data was taken File lines lst is a ready list to load into MagPick 1 Start MagPick and load all information Start MagPick Before doing anything else go to Options Settings and make sure that Color map and Contours are not checked We are not going to use the map in this tutorial We will load the dummy grid it is worth checking file dummy grd with the ASCII editor Set coordinate grid steps to 100 m for X and Y Press Ok Now go to File Open and pick file dummy grd An empty grid appears on the screen The size might be to small Go to Options Size and set X cell Y cell as 5 and enlarge window to see whole area This is our empty map Now go to File Profiles Load list Select file lines 1st MagPick reports that 6 profiles were loaded in this case each profile is represented by its own file Press Ok You can now redraw the picture Edit Redraw If this is not what you wanted go to Options Settings click on Show profiles to invoke profile configuration dialog Here check Plot stack profiles enter Datasets to draw 1 enter Data scale 10 this is value magnetic field divided by before plotting Check as well Use fixed direction and enter Fixed direction azimuth 55 Choose Fill type Positive fill the color you like and uncheck Clip stack plot We are do
139. ram will annotate contours Note that it works only when slow method of drawing is used Decimals This provides selection of the decimal point you wish for annotations For the mag netic field it is normally zero Distance between labels map units This controls how labels are drawn Program counts distance along each contour line when this value exceeds the limits it places a label You should specify this distance in your XY units 12 Basic operation of MagPick 13 Label length map units To place annotation text the program makes a gap in the contour line Text is scaled to fit into this gap This is were you set gap size and therefore inderectly the label size too You can plot profile lines with optional stack plot on top of the magnetic map Here is descrip tion of the dialog box which controls the profile plot parameters This gets called from Common plot parameters dialog box by clicking on the Show profiles check button see figure B 1 Show direction of profile with sign gt Direction 2 Interval between signs gt Distance is is defined by order of readings in the input file taken along profile 4 Each profile file can have 5 Profile plot parameters multiple datasets Here you can define which one you wish to plot as stack for simple load it should be always 1 3 Request to draw k profile plot od X stack proffe piot A Show profile direction each 20 pixels
140. re generally quite complex and might be improved by tuning parameters in the interpolation box You can try for example different values for Tension Tension 0 corresponds to a minimum curvature solution and the value 1 gives a harmonic solution Reasonable values are about 0 25 0 8 But there is another way of interpolation as well We can triangulate data points and then do linear interpolation inside triangles to find data value for each grid point MagPick provides this way also You will see how it can be done In the profile view window go to File Interpolate grid Triangulate The dialog box Triangu lation parameters appears on the screen This dialog has many parameters Here is what to do next e Under X parameters check Data limits This means that the horizontal extent of your grid will be taken in accordance with minimum and maximum values of X coordinate in the data e Under X parameters set interval 0 25 This is your grid cell size along X axis in the grid we are going to interpolate e Under Y parameters check Data limits This means that vertical extent of your grid will be taken in accordance with minimum and maximum values of Y coordinate in the data e Under Y parameters set interval 0 25 This is your grid cell size along the Y axis in the grid we are going to interpolate e Check box Filter data recommended This means that before triangulation the number of your data points will be reduced If a few of initi
141. relief and set light azimuth 315 elevation 25 see as sun is rotating Set data scale as 5 This last value will be different for your real data and you have to try few numbers to find the best value You can see now a black and white steel picture with shadows Now go to the same place and set Color illuminated map Press Change palette and set Uniform 34 Press Ok See how long it takes now But you end up with a nice view Try the same with gradient land and sea palette as it was shown above 8 Make your map nice add contours isolines The simplest way to do it is go to Options settings and invoke contours dialog box by clicking on isolines check box Here check Automatic Total 50 Fast drawing This means that your data interval will be divided into 50 contours Fast drawing means that no labels are available for the contours but drawing is somewhat faster I found this useful in some cases for a mag netic field If you have a lot of lines it can give a clearer picture than shaded relief or color map Press Ok See what happens Now for a slower way but with labels go to the contours menu as before check Fixed values type Min 0 Max 2500 Interval 100 Press Calculate See that levels 0 100 200 2500 are created Now uncheck Fast drawing and check Label contours Set the distance between labels as 4000 This means you want your lines annotated every 4000 units along the contour Set label length as 1000 This mea
142. rkers must belong to the same line Then program counts points from the start of the line and removes all data before first mark and all data after second mark The mark order is irrelevant either UP or DOWN marks can go first 40 Profile data transformations e Cut between UP and DOWN markers This is different from the previous operation in that it acts between the marks Important Data gets removed not interpolated After you have saved the profile it has less data points then the original one it also can have a gap and can be splitted into two profiles if you load it with a split by distance Cut from start of the line to the UP marker Cut part after UP marker to the end of the line direction of profile direction of profile Cut outside UP and DOWN markers Cut between UP and DOWN markers z z gt direction of profile direction of profile Figure 20 Different profile cutting modes Figure 20Jillustrates possible cutting operations 5 2 2 Data smoothing MagPick allows simple data transformations such as smoothing using a cubic spline Data is consid ered to be a function of a fiducial number n first point of the line has number 0 next 1 etc Note this usage is internal there is no view which shows T n most similar is view T distance but this is not the same T n gets approximated with a cubic smoothing spline with the smoothing param eter Large parameter values provide an interpolating spline t
143. rofile data Profile data can be saved by calling File Save menu item in the profile views or by calling File Profiles Save in the map views Remember that if Profile inversion or All profiles in the window is used the operation will be applied only to the profiles in current view After the menu item is called a user should choose name of the file to save the data The next dialog appears on the screen and gives the following choices 38 Profile data transformations What to save All profiles How to save As XYZ Line numbers Simple line nu Decimals after dot for X Y E Decimals after dot for T 3 Choose what to save All profiles Active profile s or part between marks If polygon is present also save active inside polygon or all inside polygon Save as XYZ one channel after another for multi channel data files or with new columns for additional channels Assign line numbers No line numbers Simple line number or create line numbers from file name Number of digits after dot for field and position information Figure 18 Save profile parameters dialog e Save all profiles This means that profile data is saved If you are operating with the global profile list all loaded data is saved If you are working with All profiles in the window profile inversion view then only profiles crossing parent map window are saved e Save active profiles Only activ
144. roved Numerous bug fixes After all these changes were assigned version number 2 0 2 Installation MagPick is using the wxWin multi platform library and therefore exists in two forms Uxnix Linux and MS Windows NT 95 98 Uxnix like systems require compilation Binary is available for MS Windows platform 2 1 System requirements MagPick is C program which works under the Uxnix operating system The current version was developed and used under Linux Uxnix clone for PC s and the gcc compiler version 2 7 2 and above was used It is necessary to have X11 running because MagPick is a full windows client It is linked to the following X11 common libraries libXaw so libXmu so libXext so libXt so libICE so libX11 so libXpm so Selection of the system libraries can be different for another operating systems for Solaris2 x for instance Installation MagPick employs netcdf library to read grid netCDF files Library is freely available A copy of the latest released version of netCDF software can be obtained using a WWW browser or anonymous FTP from ftp ftp unidata ucar edu pub netcdf netcdf tar Z Follow the instructions to install netCDF library on your machine To implement a graphics user interface GUI magpick uses wx Win C library version 1 6x which can be found on http web ukonline co uk julian smart wxwin There are different implementations of wxWin are available Libraries can be based on s
145. rs defined in magpick instead of color by layer Layer s name Assigned by magpick but can be changed by the user F DXF layer Profile lines hb Enable layer Name PROFILES Line style fil Text arrow size 1 Line width ol J Color 4 Use magpick colors Ok Cancel Color for the layer Figure 31 DXF layer properties pen moves without drawing the line Example 5 2 produces line 2 meter gaps each 5 meters Spaces are not allowed in the line style definition e Text arrow size In some cases these values overwrite the values defined in MagPick For ex ample the program uses the size defined here to label grid lines or draw profile direction arrows However the stack label text and arrow sizes are defined in 5 e Line width Presently not used e Color Default color for the layer If the User magpick colors box is not checked all layer entities have color by layer e User MagPick colors If this box is not checked all layer entities have color by layer If checked then the color is defined explicitely for each entity Magpick works in the short form of UTM projection Therefore all sizes above line style text and arrow are in meters If user requests transformation for example inverse UTM to present drawing in latitude and longitude see below these values are still in meters program will automatically recalculate appropriate sizes in degrees
146. s available if both marks are set on active profile e Specify a smoothing parameter Remember that the smaller values provide more smoothing Value 107 is good to start with Smoothing may fail if this parameter is too small less then 19 295 e Then chose a color to plot the smoothed positions This allows you to preview result of smooth ing and compare it with original positions Note that a stack is not plotted if you have a smooth preview it may obscure all the picture After you press the Ok button the program redraws the current map view any other map views you have to redraw by hand You have now chance to compare the smoothing result with original track If you want to repeat it just do it again Previous results will be automatically discarded To accept changes go to Profiles Accept All original profile data is replaced with transformed data of course only for profiles where you did transformations You must save the profile data or the result will be lost after you exit MagPick To discard the transformation results go to Profiles Discard The grid view will be redrawn and the transformed part disappears 5 3 3 Shift dragging along profile Typical marine magnetometer systems consist of a GPS receiver mounted on the ship and a magne tometer fish being dragged behind It is clear that the magnetometer position is not the same as GPS antenna position The distance between antenna and tow winch and tow cable length must b
147. s for plotting of the grid data Unless autoscale is checked color palette is scaled to that range all data above Data max is drawn with maximum color all data below Data min is drawn with minimum color This parameters has no effect if autoscale is checked Data min Data max have different meaning if you choose Wrap color scale Autoscale If checked the color palette is scaled to the real minimum and maximum of the data in the current window Note only the data into window is used to determine min and max Wrap color scale This provides a color scale wrapping and the ability to see fine details in the map It works like this say your data is in the range from 0 to 2000 You have set Data min 0 and Data max 200 This means that all the available color scale gets mapped into this range Now what happens when we need to map cell with value 201 It gets mapped the same way as a cell with value 1 And so on The map obtained in this way has ambiguous colors but allows more structure to be viewed Color map This controls the appearance of the color map or disables the color map com pletely This control is marked as it means when you click on it to check an additional configuration dialog box appears In this dialog box you can choose several modes to draw a color map These are choices you have e No color map Simple does not draw it at all e Simple color map Each data value is mapped into a color without any tri
148. scale factors back as they were before zooming e Remove This item is present only in the profile inversion view In case you have too many profiles on your screen you may deactivate them interactively and therefore deselect them in the Profile Browser list This way you remove all subsets from the screen To remove just only part of them use Profile Browser dialog 3 6 Printing MagPick has printing facilities which are implemented thought the Preview menu for all types of views To make a printout simply open Preview A separate window with a page pops on the 32 Grid operations screen and you can see a preliminary plot This view is not exactly the same you will get on paper To make sure print it to the postscript file and view it with Ghostscript Note that MagPick always scales the plot to fit the given paper size In Print setup dialog box you are able to choose the printer file paper type and portrait or landscape mode Landscape mode is not shown in the preview but the printout is correct Each view window has the menu Title where you can set some additional features of the plot such as axis annotations common plot header and font size All these items have default values if you do not call Title for given window Caveat If you are printing to the file you may encounter a problem When you open Preview the second time your first postscript file is truncated to about 100 bytes To avoid this change name
149. t False Easting and False Northing are zero Press OK The file save dialog pops on the screen Enter the file name g 858m 1st Press OK MagPick indicates that 51 profiles lines were loaded Press OK You have read all your data into MagPick Loaded grid data Go to File New and choose Profile view in the dialog What you see now was discussed above Go to File Interpolate grid Splines The dialog box Interpolation parameters with many fields appears on the screen Here what to do next Under X parameters check Data limits This means that the horizontal extent of your grid will be taken in accordance with minimum and maximum values of the X coordinate in the data Under X parameters set an interval 0 25 This is your grid cell size along the X axis in the grid we are going to interpolate Under Y parameters check Data limits This means that the vertical extent of your grid will be taken in accordance with minimum and maximum values of Y coordinate in the data Under Y parameters set interval 0 25 This is your grid cell size along the Y axis in the grid we are going to interpolate Set Low constrain as by min data value and High constrain as by max data value This means that the interpolated grid can not have values less or more than initial data set Set Tension as 0 25 and Format as GS ASCII the last means Golden Software ASCII Set Iterations to 250 It should be enough for most cases Set Convergence limit 0 Press Output
150. t The result will be the same as with a simple load but we do not need to go through all the pevious steps again You also can create profile list file by hand using you favorite ASCII editor small shell script or your program Note that profile list file gives you more control on data loading For example MagPick can accept few data sets in one file but this feature can accessed only using profile lists 12 3 Putting things together map and profile data Goal MagPick is designed to work with two types of data map grid data and profile data Here we will be given profile data as initial information We will grid the data by MagPick Then we will load the created map into MagPick to see them together For a better understanding of the field structure we will present the profile data as a stack plot on top of the magnetic map Some optional learning material is included here to show how any geometrical information can be included in the view After completion of this part you should be familiar with the creation of magnetic maps using MagPick Files File g 858m dat is the only one we need here 1 Load profile data 74 Tutorial Start MagPick Go to File Profiles Simple Load Press the button Add and choose file g 858m dat Set the following Split 8 LINE X 1X Y 2X Data 4 BOTTON RDG Active color RED Inactive color BLUE Press Ok A new string appears in the list box Check the button Save as profile list Check tha
151. t 30 m Text is scaled to fit into this gap Label length map units 7 00 13 Controls contour labeling Distance along the contour to insert label V For example if you area is 1000 x 1000 m you may wich set it as 200m J These items have no effectif Automatic is checked Figure 2 Isoline parameters dialog box Interval Interval between contours Data levels are distributed uniformly between Min and Max with this interval Calculate After you entered Min Max Interval their values have no effect till you press Calculate Program calculates new levels you can see them in list box Contours Isolines Current list of levels for contour plot It can be calculated or loaded from file Read from file If you use custom selection of the levels you have to prepare ASCII file with desired values Only the first column of such a file will be read rest of the string is not significant Results are displayed in the Contours Color The default contour color is black Press the Color to access the color dialog box and select another color All contours are drawn with same color Fast drawing If this is checked a fast but not accurate algorithm is used to draw isolines 2D version of marching cubes This does not allow labels but speed is much greater It is recommended recommend to check this box in all cases when labels are not required Label isolines If this control is checked the prog
152. t gets flipped before plotting Please note that this method requires a smooth enough track line which is not always available especially for data acquired with GPS Fixed direction is taken clockwise from north Type This allows to select method for finding plot direction for the anomalies Choices are Normal to path Fixed direction and End points If Normal to path is selected then field is plotted perpendicular to the path at every point Preferred direction value is used to distinguish between positive and negative anomalies This method requires a smooth enough track line which is not always available especially for data acquired with GPS Small irregularities in the positions result in big spikes on stack plot If Fixed direction is selected then positive anomalies are simply plotted in that direction and negative ones are plotted in opposite direction Angle is taken clockwise from North End points works similar but direction is found by the program based on end points of the line In latter case Preferred direction is important it allows proper handling of lines doing in opposite directions example lines going North South and South North if preferred direction 1s 0 then positive anomalies on adjacent lines are plotted in opposite directions preferred direction should be 0 or 90 Both Fixed direction and End points do not depend on quality of GPS track Fixed direction azimuth Value which defines fixed directio
153. tandard toolkits motif xview OpenLoolk or Athena widget set Xt In general magpick could be compiled for any of these platforms but a working version described here is compiled with wx Xt libraries version 166d Follow the instructions to install wxWin library During configuration make sure that the usage of Xlib is enabled You will need wxgrid library which is part of wxWin A nicer view of worksheet can be obtained obtain with a patch from ftp ftp aiai ed ac uk pub packages wxwin contrib wxgridd wxgrid_d tgz It is worth checking your installation using test demo programs that comes together with the library When you have all these libraries and gcc C compiler installed you can start the compilation ofMagPick 2 2 Compilation Make a subdirectory and unpack file magpick tgz with gzip and tar programs Edit the file make file xt to match you site configuration You will need to change the next variables in the makefile xt e WXDIR points the root of your wx Win installation e INC points include files folder s If your netcdf library is not in the system place set its include path too e THISDIR is current location where sources are e LDFLAGS linker flags where all libraries can be found This should be the path to wxWin and netcdf libraries e LDLIBS Selection of the libraries If wxWin on your system requires additional libraries you should alter this list After altering the makefile you can type make f
154. te new view if interpolation has been started from main menu e Adjust the view parameters e If you want first see the profile locations and possibly a stack profile plot go first to File New and pick Grid view The program will create an empty fake grid just to have a base to display profiles You can start interpolation from that window also e If you want to examine profile data and possibly modify it go to File New and pick Profile view Adjust the orientation along X or Y axis in the case of data collected with Geometrics G 858 magnetmeter you should choose Y You also can start the interpolation from the profile 33 Grid operations view under File Interpolate grid However a new grid won t be automatically loaded if you start interpolation here Keep in mind that there is no need to save the interpolated grid because it has been saved already However you might do it if you did some transformations or simply want to change the grid file format Enter grid steps Along X Y If don t know limits Enter X Y limits of a new grid liae check here and data limits are used 7 Triangulation Parameters f X parameters X min o 00 X max 200 00 F Data limits Interval Y parameters min 0 37 Y max 99 64 F Data limits Interval gt F Filter data recommended Method Average value Format NetCDF gt Output file
155. the profile inversion view On the magnetic map go to Edit Direction Point the mouse somewhere in the middle of map window Click left button move mouse approximately 45 north east and click left button again The arrow sign is now on the map Now go to the profile inversion view and set Parameters Settings Type along pointer See how the picture changes You are now seeing projection of your data on a direction you have shown on the map view Zero is where arrow on the map view starts it is marked by small o Now go to the map view and show another direction do the same as for first arrow The profile inversion veiw updates automatically to reflect a new horizontal axis Return now to Type Along Y In many cases we need to constrain the data we are going to use for an inversion For the map view we did it by zooming part of the map For the profile view we have a more flexible way Select Edit Polygon in the map view menu now Go approximately to point 85 Tutorial 6 5 6 and click Then go to 6 5 14 click 10 5 14 click 10 5 6 click and again 6 5 6 click We have drawn a polygon in this case a rectangle Check the profile inversion view now The data is cut Only this piece would be used for the inversion If you pointed polygon vertex by mistake you can undo this operation by clicking right button If you need to get rid of the existig polygon just go to Edit Polygon one more time The polygon contour will disappear
156. thed values by selecting File Accept menu There are four choices here you can replace all profiles only active profile you can take just the smoothing result or the difference original data minus the smoothed data e If for some reason you want do discard the smoothed curve go to Edit Discard menu The smoothed curve will be erased e After you smooth data and replaced original data you should save the profile data or results will be lost after you exit the program If you saved data with smoothed curve still on the screen then there is an additional column in the file called T calc This is result of the smoothing 5 2 3 Linear data transformation Data smoothing represents a type of advanced transformation However MagPick has a simpler abil ity linear data transformation Every profile reading can be transformed with the linear formula Thew 4 X Tola b Here 7 q denotes the original profile reading a is the scale and b is the bias of transformation Threw is the transformed field value The function can be applied to all data to active profiles or to the part of an active profile between markers It might be useful when the data needs to be calibrated with a known coefficients or when some of the data was collected with a DC offset The latter can happen if part of the magnetic data was collected at a different time with different Earth s main field Linear transformation is available from the profile view window under Edit
157. thing of the original values with following substraction of smoothed values from the original can stress local anomalies 49550 49540 49530 49520 49510 Magnetic field nT 49500 49490 49480 49470 Original data Smoothed 6800 6900 7000 i 7100 7200 7300 7400 X coordinate m Figure 21 Data smoothing with cubic spline To smooth profile data use the following e Create a profile view simple Profile view or All profiles in the window kind of view Then go to Edit Smooth e Smooth profile data dialog appears on the screen Here you can enter the next values 1 What to smooth you can apply the operation to all profiles currently active profile s or if there are two valid marks on the active profile the part between them can be smoothed 2 Enter the smoothing parameter which controls the smoothing degree Smaller values pro vide more smoothing 3 Choose the color with which the smoothed curve is to be plotted e After you press Ok MagPick will proceed with the operation This process can take different time depending on how many profiles and points you use In the end profile the view gets updated showing the smoothing result e If you are not satisfied with the result you can repeat the smoothing again The result of the previous operation is discarded 42 Profile data transformations e If you are satisfied then you can replace the original values with smoo
158. tral N meridian and scale factor 5 Scale factor 0 9996 for UTM 0 993600 False Northing m 0 00 False northing and easting to be added Note that if you want to cut Resto 00N coordinates these values should be negative Note Nortnihg and Easting are added to projected values Load Save UTM calculator Longtitude 123 30 0 Ok cene latitude 31 10 14 5 Lon Lat format deg min sec Enter here Lat Lon of the point to be projected follow format specification for example if Northing 3448627 03 format deg min sec enter 3 numbers separated Easting 452351 82 by spaces or read here result of UTM gt Lon Lat Zone 10 Central meridian 123W D Read here UTM coordinates or enter UTM ERE UTM gt Lon Lat to be transformed in meters For inverse transformation make sure that central meridian is correct This invokes particular forward or inverse projection Figure 24 UTM setup and UTM calculator in magpick Note that the UTM calculator is a modaless dialog box It means that you can do changes in the main UTM setup dialog without closing UTM calculator Besides the UTM calculator MagPick uses the UTM transformation in the next places this might be extended in the future e The status line coordinates of the mouse position inverse UTM is used This means you can see th
159. ts these steps for every pick As you see this method does not allow you to estimate a few magnetic sources simultaneously 10 Implementation of the inversion in magpick To find magnetic sources MagPick uses a simple form of inversion based on a model represented by set of dipoles Mathematical expressions for the field produced by such a source are well known and have a simple form This allows one to construct an effective inversion algorithm Here is the outline of some basic features of forward and inverse problems as they have been implemented inside MagPick It is important to understand that MagPick does not take into account demagnetisation effects which can have significant value in case of iron objects 10 1 Solution of forward problem It is known that a magnetic field can be expressed as a combination of second derivatives of the gravity potential Which in the case of uniform magnetized sphere of unit mass has the following simplest form 1 y x xo y yo z zo V 6l Implementation of inversion Here xo yo zo are coordinates of the center of the sphere and x y z are coordinates of the obser vation point If the sphere has a magnetic moment with components Jx Jy Jz magnetic field can be expressed as X Vady VJ Vd Z Verdi Voy Vd where Vyy denotes the partial derivatives of potential X Y Z are horizontal and vertical compo nents of the magnetic field In case of full v
160. ttom sensor You can note as well that when you set initial depth to less than 0 6 the process does not converge This is because it s less thanthe real depth of the object It is recommended to start with the initial depth which is more thanthe conceivable depth of the magnetic source In general inversion based on profile data is less stable than inversion based on a map It depends on profile distribution in space For example if you are trying to find the position of a source which is aside from your profiles it might be unstable The case when the source is between your profiles is much better 86 Tutorial 4 Worksheet operation Results of the inversion are displayed in the worksheet window Only one such a window for example for dipoles exist and once you have opened this window you can not close it it hides if you close it MagPick worksheet window is not the same type as a worksheet in Surfer or Excel It allows only some basic operations which are listed here All functions are available by window menu and by pop up window right mouse button e Left mouse button highlights current row e Open Load Load file into the worksheet The file should be a space or tab separated set of columns You may need to redraw to see loaded data e Save Saves worksheet content into simple ASCII file When you have a large project it is recommended that you save your data from time to time e Delete Removes current row from works
161. umn to mark line 2 1 and to mark line 3 0 again Go to Split and select LINE Press Ok and press Ok once more A question appears Append to previous profile list The problem is that we already have load some profile data Now MagPick wants to know do we need keep the data in memory or discard it Answer No and the old profile will be taken out Please note for future if any views of old profile data are currently opened MagPick will not discard old data The loading operation will fail until you close all profile windows Now MagPick shows that it has loaded the 51 profile Press Ok Viewing of profile data Go to File New and choose Profile view in the dialog box You will see just an empty screen with a red vertical line on the right side This is because by default MagPick shows your data as T x here T denotes the data x x axis But lines in g 858m dat are elongated along Y To the change view to T y go to Parameters Settings and select Type Along Y list box at the left bottom corner of the dialog Press Ok Now you can see correct graph of the data as function of x axis The status bar at the bottom of the window shows the type of view T y It also shows Y and T values at the current mouse location Go to Parameters Settings again and set Type Along profile Now the horizontal axis shows the distance along the line line may not be straight This distance is always positive and starts with 0 Checkbox
162. ust be done in the right order first show the area where maximum is then show where minimum is located Point the mouse in the corner press left button and drag The ribbon box will show your choice When the appropriate point is reached release mouse Do the same to the minimum point MagPick will search for the maximum point in the area you showed first Then it will find the minimum point in the area you showed second and draw a pick between these points 22 Basic operation of MagPick Picks can be saved into the file or loaded by File Open pick and File Save pick If you try to exit the program or load new picks without saving of the previous picks a warning appears and you are given opportunity to save the job In case you have duplicated picks in the file secondary copies are discarded during loading The pick file itself is an ASCII file with a simple structure Each pick is represented by one string Here is the format of the string 1 3 numbers X Y and the field for end of the pick where the maximum value of the field is 2 3 numbers X Y and the field for end of the pick where the minimum value of the field is 3 Local azimuth to minimum second point from maximum first point plus Field direction value see figure 1 4 Horizontal distance between picks 5 Two numbers coordinate of the middle point of the pick 6 One number always 0 000 This was implemented for compatibility with some software
163. ve less control You do not have to load the map data to be able to load the profile data As soon as the profile data is loaded it can be interpolated to create a grid file loadable into MagPick You can set marks picks everywhere on magnetic map These picks might represent places you consider to be interesting Picks can be saved into file and loaded again You can delete a pick you don t like Picks can be exported into some formats readable by SURFER and AutoCAD The name of the program MagPick was given because of this feature You can estimate the location of magnetic sources To do this some approximations should be used Presently MagPick allows two kinds of sources Magnetic dipole which is good for a local magnetic source s and magnetic line which fits objects like pipes You can find a geometrical location and an amplitude of the source and in some cases its mass Results of estimations are viewed as worksheets and can be saved orloaded from files as well as exported Under Uxnix start magpick with command line magpick xt or under MS windows with in this case you also can start it from Windows Explorer or create shortcut to desctop magpick exe Basic operation of MagPick MagPick first tries to read the file magpick ini from the MS Windows directory windows 95 98 or from user profile directory Windows NT Under Uxnix like systems MagPick reads the file magpick from user home directory These files hold sett
164. with the standard SURFER distribution if you are using SURFER 7 convert this file in ASCII grid or SURFER 6 binary format using SURFER 1 Check initial state Start magpick from Windows explorer shortcut or command prompt this does not make any difference Go to Options Size Make sure that X size cell and Y size cell are set to 1 These 68 Tutorial are hight and width in pixels of one cell of your grid data on the screen Let Zoom be something like 2 or 4 and check autoscale on zoom Press OK Go to Options Settings Common parameters dialog pops on the screen Uncheck here all check boxes except Autoscale and Colored map Note that when you check Colored map another dialog appears In this dialog select Drawing mode Simple color map and press Ok Press button Change palette choose Uniform press Ok The uniform palette preview appears make sure that the palette number is 34 and the Equalize colors dialog box is checked Press Ok to close this box and once more to close Common parameters You are now ready to load the data Pick and load the file Inspect result Go to File Open and pick file helens2 grd After reading and color equalization a colored map appears on the screen Check what was loaded Go to Options Info You can see all the geometrical parameters of the loaded grid Change geometrical parameters of the view Let s play with it a little to learn how it works Our main tool will be C
165. wn When you do it the third time the first arrow up goes away and a new arrow up appears in the new place and so on Try the following next e In the profile view window go to Edit Set marker The cursor changes its shape to go to some point on the curve and click left button Arrow up arrears on the curve note that the marker can be set only in at the location where you actually have X Y Z data Inspect the red line on the magnetic map You will find the arrow up there e In the map window go to Edit Set marker cursor changes its shape and it becomes Point its center to some place on the red line the profile you are seeing in the profile window Click the left button The sign arrow down appears on the map Go to the profile view and find the same mark there 76 Tutorial e Repeat the above operations several times to become familiar with it Note that at some extreme points in the profile view you may not see some types of markers Zoom to part of the map window where markers are located See that they appear on all map views Note that in the map view you can set markers on an active profile line only They do not go away from this line when you change lines 5 Another approach to grid profile data You can see from the map we have just interpolated that some anomalies appear as wide points on the profiles They do not look realistic This is a property of the interpolation method the interpolation problems a
166. y how to transfer 78 Tutorial essentially any picture presented as PostScript file into MagPick representation this is not easy involves outputting some simple form of PostScript and then parsing it and scaling with your own shell script But here is just a simple example which does not involve the transformation questions Do next e With your favorite ASCII editor in many cases it will be the ugly program called notepad create a new file say line dat e in this file type UTM GRAY 5 10 10 10 7 70 7 70 1 TOL O c5 co CO The sign gt should be in first position and you have to press the cartridge return after last string Save this file e In the map view go to Options Drawings press the button Add select Type of the file Lines press OK select your file 1ine dat Then press OK once more e You should redraw the picture in order for the changes to take effect Go to Edit Redraw A fat grey rectangle appears at the left bottom corner of your map e It s probably too fat Use your editor in 1ine dat again and change gt UTM GRAY 5 to gt UTM GREEN 0 Save file Redraw the map This way you can virtually present any vector information on top of the magnetic map Key word UTM stands for UTM projection This means that coordinates in the file are expressed in UTM Other keyword is GEO which means that position are represented by longitude and latitude Because MagPick normally op
167. ypical values like 1 10 100 or more while small values typically 1074 or less give a smoothed curve The latter is of interest because it works as a low pass filter MagPick provides a view of both original and the smoothed curve a typical result of a smoothing is shown on figure PT As soon as the user is satisfied with the result he should commit changes and replace the original values with smoothed ones There are two choices the original curve gets replaced with a smoothed one which is an equivalent to low pass filter or the original curve is replaced with the difference of the original curve minus the smoothed one thus providing high pass filter Smoothing also can be applied to the part of the curve between marks In this case the value of the smoothing parameter is specified by the user It is related to the middle of the interval The ends of the interval have high smoothing values which essentially give an interpolating spline then parameter decreases by the Gaussian law to the middle of the interval Therefore the middle gets smoothed ends stay similar to original values thus discontinuity at the ends is not introduced 4 Profile data transformations One typical smoothing usage is stressing of the high frequency component on the stack profile plots The stack profile feature itself can exclude the linear part from plotting However in some cases the geological part of the field behaves as a higher degree function The smoo

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