Levelling—tie line levelling (G13)
Contents
1. Top Library Help Top 1 q Back gt Launch the Levelling Tool Start the Project Manager Navigate to the directory install_path sample_data guided_tours intrepid datasets From the Levelling Menu launch Tie Line levelling The INTREPID Levelling tool window appears Open the input dataset and field From the File menu choose Specify Input The Select Database chooser appears Select the dataset albury DIR and choose Open The Select Signal Field chooser appears Select magdigrf from the list of dataset fields and choose OK Specify the output field name From the File menu choose Specify Output The Save Levelled Signal chooser appears Click in the Enter New Field Name text box and delete Zout Now type magdloop for the new field name Choose OK Reconstruct the flights as before Find the crossover points as before Select the levelling correction type From the Corrections menu select Loop Closure INTREPID calculates the required network adjustment using the loop closure method This process is very quick Apply the levelling adjustments to the data and create the output field Choose Apply Corrections The button is located at the bottom of the Levelling tool window The Apply Save dialog box appears Under Choose Corrections to Apply check the LevelLoop box Now choose Apply When completed an information box appears telling you that the process is finished INTREPID produces a report file called level2. t T a t 3 a See t ate i 4 Delete List T T a T 25 _ 4 Load List F AO a R H cee eet fof foose oe a i ve List n R if H 5997 5 ie z H A H All flights for Tie fi t t t 3 t gt f 5997 5 7 H One flight for Tie T K i ee ee T Zr p Ly t r H J Display tie graph b R p t a Choose OK to dismiss the Information box Now select the most eastern tieline in the survey The Current Crossover report updates to display information about the crossover point you have selected From the Tie Line menu select Show List Your list of ties should now contain two lines 174071 and 174091 Choose OK to dismiss the Information box Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 8 Library Help Top 4 Back gt From the Tie Line menu select Complete List Now select Show List You should now have a list of ties which includes all of the tie lines in your survey Choose OK to dismiss the Information box List of Ties 174071 000000 174091 000000 174041 000000 176051 000000 176031 000000 174081 000000 176041 000000 174061 000000 8 Select the levelling correction type From the Corrections menu select Polynomial levelling The Select weighting method parameter box appears For this magnetic survey choose All weights 1 and choose OK 9 Ent
3. Line levelling The INTREPID Levelling tool appears gt g X A eh To L e Ey scp poircig Tol File Dataset Editing Display Levelling Gridding Filtering Mapping Gravity Radiometrics Interpretation Utilities Betas Help File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Style Help urrent Folder D test_data FulT Tie Line Levelling yd mapprint Decorrugation le Last Modified Size File type level A E Microlevelling a _mitre ers 04 12 2012 1 47 48 PM 123MB Intrepid Grid File i z ia_mitre_continued_140 ers 07 12 2012 3 46 34 PM 8 2MB Intrepid Grid File di microlevel Multi Survey Level d S ja _SRTM_subset_SAD69_SUTM24 04 12 2012 2 12 13 PM 20MB Intrepid Grid File edi ae i Marine Split te 340_0 ers 11 12 2012 3 57 09 PM 1KB Intrepid Grid Fie Hdim PE FE Complete _6576_0 ers 07 12 2012 3 45 15 PM 15 5MB Intrepid Grid File sue re yi S F falcon _test job 19 08 2010 3 46 29 PM 693B Intrepid job file i J aoa TH o2_diff31 ers 28 06 2012 4 36 14 PM 21MB Intrepid Grid Fie 750 0 i j i proiit edtor HISTORY 15 02 2012 3 57 24 AM 19KB Intrepid History File Tie gradient i b PEE terrain rpt 15 02 2012 4 02 19 AM 8KB Intrepid Report File Misclosure Ny a A Z Taz FA ers 28 06 2012 4 35 44 PM LOMB Intrepid Grid Fie Beta value E split_cruise ay bh oma tet WIN32 des log 11 12 2012 3 57 23 PM 425KB LogFie Long E ast 5 wormE_processing rpt 11 1
4. Top Library Help Top lt 4 Back gt When you are finished choose OK on the FID Factor and date style dialog box INTREPID sorts the dataset according to date and time This operation takes a few seconds When it 1s completed a report appears on the right hand side of the Levelling tool window showing the number of acquisition lines tie lines and flights that make up the dataset Sg EJ Intrepid ProLevelling Tool cate ongitude East _____ fete atitud e N orth Use xover Acq Lines 649 Tie Lines 6 No Flights 5 No xowers Diff Sum Output Changes Only Levelling produces a detailed flight reconstruction report as part of the prolevelling rpt file Find the crossover points Choose Find Crossovers The button is located at the bottom of the Levelling tool window The Choose Filter dialog box appears For magnetic survey data there is usually no need to apply a filter before finding the crossovers as the signal has been despiked already Choose the default None setting Choose OK The Search radius for Gradient chooser appears Choose the default Ignore setting This option is only relevant for XY positional error analysis Choose OK INTREPID calculates and displays the c
5. it takes considerable effort to verify the correct workings of the 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 2 Library Help Top Library Help Top lt 4 Back gt algorithms when expressed in a more general form So we have changed the game when it comes to levelling capabilities Just you might not have realised this In particular the geophysical field gradient conventions East North UP etc have to be properly brought to account for vector and tensor operations At V5 0 INTREPID we also add GOOGLE protobuf syntax for the batch task files INTREPID would recommend a training course be undertaken by groups with innovative geophysical hardware wishing to try out this tool It maybe that some issues will emerge as what you are attempting to do has never been done before This Guided Tour covers the process of tie line levelling using two different methods The first is the method of polynomial approximations which involves fitting a polynomial curve to the intersection errors along a flight traverse or tie as a function of time The second is the method of loop closure which uses standard geodetic surveying procedures to adjust the network of closed loops formed by the intersections of lines and ties Quick review Airborne surveys are typically flown in a grid pattern designed to give duplicate measurements at the intersection points crossovers of t
6. will contain significant artifacts It is important that these be removed before any meaningful analysis or interpretation of the data can be undertaken otherwise you maybe mislead For instance if the aeroplane flew low over a tin shed or a pipeline and there is a BLIP from that source this is not geologically significant However in general it is not practical to measure enough physical parameters such that the data can be processed consistently and predictably by different processors Therefore the success of the levelling methods do depend on the judgement of the data processor The INTREPID Level tool allows you to perform several standard corrections on magnetic radiometric FTG FALCON airborne gravity and digital elevation data e Aircraft heading effects e Parallax corrections Time synchronisation and subtraction of diurnal gt GRF removal e Network adjustment using either polynomial or loop closure methods The Pro version of this Levelling Tool has a similar look and feel to the original standard tool The extra functionality uses gradient and tensor data in the engine room of the separately written library This compeletely re written version of the tool is now what ships as standard The aim in the rewrite was to add support for clever or innovative geophysoical observations to each and every levelling process upgrading them away from just working for scalar signal measures As this is a walk on the wild side
7. 2 2012 3 57 04 PM 1KB Intrepid Report File di subsection A i Lat North FE wormtemp ers 07 12 2012 3 45 17 PM 1 0 MB Intrepid Grid File fi J Survey_Distance_Calculator Elevation fp tensor aia M Use xover dk aurizonia aps h Acq Lines sd Tie Lines di geomodeller No Flights Hdi No Xovers aJ JoBs Diff Sum H Comet_Area1_Example v Output Changes Only 4 ComplexTensors drape_corrections Find Crossovers 4 falcon 250 000 Apply Corrections di hagar CrossOver Corrections J hagar _old interpolate mega J model_demo fy teck_Jawnhil vampeval jy Wijns_Mauritania 250 000 x 500 0 750 0 ia jl vhbge Status Line Save As Zoom In Ji visual Zoom Out fH Jy wiener E E i worms_test C Query 4 geomodeller C Zoom Rectangle I geothermal 2 Open the input dataset and field From the File menu choose Specify Input The Select Database chooser appears Select the dataset albury DIR and choose Open The Select Signal Field chooser appears Select magdigrf from the list of dataset fields and choose OK Intrepid Prolevelling Tool File Corrections Display Tie Manager Specify Input Specify Output Specity Report Load cross overs 22 amp Save cCross owers a Leg hob i mt mE ay b L ede bB R Specify Basestation b a s Sawe Options Wizard for Easy Levelling Edit Database Aliases Reconstruct flights e Curt Libra
8. INTREPID User Manual Levelling tie line levelling G13 1 Library Help Top 4 Back gt Levelling tie line levelling G13 Top After correcting our data for the EKarth s regional field the Geomagnetic Reference Field or GRF we can now proceed to further processing of our airborne magnetic survey data We want to remove any remaining data artifacts which are not geological in origin but are the result of the acquisition procedure This process is generally referred to as levelling In this tutorial we use the INTREPID Level tool to perform the next step in our processing sequence which is a type of network adjustment commonly referred to as tie line levelling Context of this guided tour Overview Library Help Top In the context of your data processing cycle tie line levelling follows the magnetic diurnal correction and GRF removal This Guided Tour assumes you have already completed the Introduction to the Spreadsheet Editor G04 removed the GRF component G12 and have a diurnally GRF corrected field in your dataset ready for further processing Our aim in processing aeromagnetic data is to produce a time independent map of local anomalies with the Earth s regional magnetic field removed and with artifacts caused by errors in the acquisition process removed There are several sources of error in a typical airborne magnetic survey If these sources of error are not removed during processing the data
9. dividual traverse lines to the levelled tie lines e INTREPID levels tie lines to the levelled traverse lines Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 9 Library Help Top Library Help Top lt 4 Back gt 10 Examine the drift curves and apply the polynomial fitting process The TIE LINES drift curve graph appears Choose NEXT The drift curve for the Principal tie line 174041 appears Misclosure errors are plotted along the Y axis of the graph Time is plotted along the X axis The red squares represent the misclosure errors for the crossover points along the line The black line is the polynomial curve fit to the misclosure errors j V Y AutoScale 0 8 units c Polynomial Order Piecewise Window Smoothing Length 3 APPLY Change the Polynomial Order parameter to 3 then select APPLY Observe how the drift curve changes shape Note If you change any of the Polynomial Order Piecewise Window or Smoothing Length parameters and select APPLY INTREPID recalculates and replots the drift curve for the current line or flight Reset the parameter for the Polynomial Order to 1 The parameters should now be set as Polynomial Order 1 Piecewise Window 9 Smoothing Length 3 When you are finished choose OK INTREPID calculates drift curves for all the tie lines This process is very quick Th
10. e FLIGHTS drift curve display box appears Choose NEXT The drift curve graph for Flight 25 appears Change the Piecewise Window to 29 then select APPLY Observe how the drift curve takes on a smoother shape as the piecewise window size increases Set the parameters as follows Polynomial Order 1 Piecewise Window 29 Smoothing Length 3 Choose OK What does this Information box indicate INTREPID has found two flights that it cannot correct The reason for this is that those flights consist only of tie lines Since at this stage INTREPID is using levelled tie lines to adjust whole flights of data if a flight consists only of tie lines there cannot be any crossover points Therefore no correction is possible for these flights Information ERROR Ao correction possible For Flight line 24 a0 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 10 Library Help Top Library Help Top lt 4 Back gt Note This is not really an Error as such it is simply alerting to you to an unusual data condition Choose OK on the Information box and INTREPID proceeds normally INTREPID calculates drift curves for only those flights which contain traverse lines This process 1s very quick The TRAVERSES drift curve display box appears Set the parameters as follows Polynomial Order 1 Piecewise Window 9 Smoothing Length 3 Choose OK INTREPID calculates drift curves f
11. er parameters for the polynomial correction Quick review Drift curves are approximated by fitting polynomials to the intersection errors The method works better if the polynomials are fitted to a smaller section of the data called a piecewise window and then moved along the data rather than trying to fit a polynomial curve to the entire dataset The user can control the width of the piecewise window The ends of the polynomial curves are smoothed to improve the fit at the ends of traverse and tie lines The user can control the smoothing length Restrictions apply on the maximum order of the fitted piecewise polynomial The user can control the order of correction function The Select defaults for polynomial box appears Set the following parameter values Smoothing length 3 Order of correction function 1 unctions and width of piecewise window Width of piecewise window 9 V Level flights assuming that tie lines are correct rre WV Level acquisition lines assuming that the tie lines are corret Check the box alongside Level flights assuming evel tie lines assuming that acquisition lines are correct that tie lines are correct When you have finished adjusting the parameters choose OK Quick review The tie line levelling process consists of four basic stages e INTREPID levels all tie lines to the Principal tie line e INTREPID levels whole flights of data to the levelled tie lines e INTREPID levels in
12. he tie and traverse lines Traverse lines give the primary data coverage Tie lines provide control data at the crossovers Tie line levelling uses the differences in the traverse tie data at the intersection points also called misclosure errors to systematically reduce the errors over the whole survey INTREPID has the convention of storing a cross over dataset that mimics the original survey topology but consists of estimates of the signal and its gradients at the cross overs points together with each possible correction contribution from the various errors As it is a standard database all the other tools can be used to examins the state Location of sample data for Guided Tours We provide two complete sets of sample datasets one in INTREPID format and one in Geosoft format INTREPID works equally well with both formats When you want to open a dataset navigate to the directory containing the required data format Where install_pathis the path of your INTREPID installation the project directories for the Guided Tours sample data are install_path sample_data guided_tours intrepid_ datasets and install_path sample_data guided_tours geosoft_datasets For example if INTREPID is installed in C Program Files Intrepid Intrepid4 5 nnn then you can find the INTREPID format sample data at C Program Files Intrepid Intrepid4 5 nnn sample_data guided_tours intrepid_ datasets This is the default location for the sample data If you have
13. installed INTREPID normally the data resides there If you have installed INTREPID elsewhere the exercises will work just as well Just use the appropriate pathnames For more information about installing the sample data see Sample datasets installing locating naming in INTREPID Guided Tours Introduction G01 For a more detailed description of INTREPID datasets see Introduction to the INTREPID database G20 For even more detail see INTREPID database file and 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 3 Library Help Top 4 Back gt data structures R05 Location of sample data for CookBooks Right next to the Guided tours data is a rich set of more exotic geophysics datasets and grids already prepared for the cookbook training sessions A casual user might also gain some trial and error insights into the capbilities of the software just by testing the Project Manger s ability to preview and describe the attributes of each of the cookbook datasets Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 4 Library Help Top 4 Back gt Steps to follow Tie line levelling using polynomial approximations 1 Launch the Levelling Tool Start the Project Manager Navigate to the directory install_path sample_data guided_tours intrepid datasets From the Levelling Menu launch Tie
14. l errors that flow into the components due to aircraft poor attitude measurements INTREPID uses the 4 cardinal flying directions to gather part survey statistics for vectors and tensors as a basis for making simple Heading corrections Q Can Ido an altitude drape correction A New to this version is support for doing continuation of any supported signal from an observed drape to a required drape flying height V5 0 goes further in this regard by using spatial indexing and truncated Fourier series in another novel algorithm Library Help Top 2012 Intrepid Geophysics 4 Back gt
15. ling rpt Choose OK on the information box You have now completed the tie line levelling correction At this point you should have a new tie line corrected field in your dataset called magdloop Exit from the tool To exit from the Levelling tool choose Quit from the File menu The Please Choose chooser appears INTREPID gives you the option of saving the crossover points to an INTREPID point dataset Choose No Do you really want to quit choose Yes The levelling rpt file opens in Notepad You can examine this report file if you wish and exit from 1t when you are finished 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 13 Library Help Top 4 Back gt Further things to consider Which method is quicker to run loop closure or polynomial approximation Which method gives better results loop closure or polynomial approximation In practice loop closure levelling does not work as well as polynomial levelling in areas of high magnetic gradient However if the range of misclosures values is low across the dataset it is an effective method For this reason it also work well on other types of data such as DEM and radiometric data which tend to have a lower range of misclosures Which method gives the user more control over the levelling process If you have time repeat the polynomial levelling using a higher polynomial order Does a higher order necessarily improve
16. or all the traverse lines This operation is also very quick Observe how the traverse lines have fewer intersection points than the tielines which in turn have fewer intersection points that a typical flights worth of data TRAVERSES Choose poly parameters push Next lv Y AutoScale 1 7 unitsfem Polynomial Orden Piecewise Window Smoothing Length 3 The Please Choose chooser appears INTREPID gives you the option of applying another round of tie line flight traverse line levelling using the adjusted misclosure errors In practice we find that nearly all of the error adjustments are made in the first polynomial fitting iteration Choose No 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 11 Library Help Top lt 4 Back gt 11 Apply the levelling adjustments to the data and create the output field Choose Apply Corrections The button is located at the bottom of the Levelling tool window The Apply Save dialog box appears Under Choose Corrections to Apply check the Level POLY box Now choose Apply Apply Save Choose Corrections to Appl W LevelPOLY Save As magdigrt Quick review At this stage INTREPID has only calculated the adjusted values at each crossover point These corrections are now interpolated along each line by a local
17. rossover points These are the points at which the traverse lines and tie lines intersect Choose Filles P As Signal Pre Processing None C Convolve C Naudy despiker Median Search radius for Gradient Ignore Use Accuracy in metres 10 0 Convolve Naudy Median Alias Filter OK Cancel Window Size data points Naudy Filter Tolerance 9 100000 Use Corrected Data C Use Rejected Data OK Cancel 6 Display crossover point information From the Display menu select Misclosure INTREPID colours the crossover points according to the sign of the misclosure errors Remember that the Misclosure is the difference between the tie traverse data value for the selected crossover If the traverse line data value is higher than the tie line data value the crossover point is coloured red If the tie line data value is higher it is coloured black 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 7 Library Help Top 4 Back gt Select one of the coloured crossover points and observe the contents of the Current Crossover report on the right hand side of the Levelling tool window The report provides information about that particular crossover point a gt A Fie Cowerors Oepley b Tat Menagement Cover Management MMagneam Beveitemom Sake Heip f jei i i he He See es Sa 53 E E SA tHe 44 Note If at any s
18. ry Help Top 2012 Intrepid Geophysics q Back gt INTREPID User Manual Library Help Top Library Help Top 3 Specify the output field name Levelling tie line levelling G13 5 4 Back gt From the File menu choose Specify Output If a Save Dataset dialog box appears select albury DIR The Save Levelled Signal dialog box appears Click in the Enter New Field Name text box and delete any text that 1s in it possibly Zout Now type magdpoly for the new field name Choose OK mi Intrepid Prolevelling Tool Corrections Specify Input Specty Output Display Tie Manage Specify Report Load cross owers Save cross owers Specity Basestation e Wizard for Easy Levelling Edit Database Aliases Reconstruct flights Curt 4 Reconstruct the flights Save Levelled Signal Enter New Field Name magdpoly Existing Fields Ok Cancel The process of reconstructing the flights sorts the data into chronological order This is a necessary step 1f the Levelling tool is to do any time based processing The sort is only applied temporarily and it does not affect your dataset Quick review INTREPID tie line levelling involves fitting a polynomial curve to the intersection errors along a flight traverse or tie as a function of time These polynomials also called drift curves are then subtracted from the data reducing the intersection errors For the method to work properly the da
19. splining procedure and applied to create an output field When completed an information box appears telling you that the process is finished INTREPID produces a report file called levelling rpt Choose OK on the information box You have now completed the tie line levelling correction At this point you should have a new tie line corrected field in your dataset called magdpoly 12 Exit from the tool To exit from the Levelling tool choose Quit from the File menu The Please Choose chooser appears INTREPID gives you the option of saving the crossover points to an INTREPID point dataset Choose No Do you really want to quit choose Yes The levelling rpt file opens in Notepad You can examine this report file if you wish and exit from 1t when you are finished It constains a complete summary of all the steps you have taken 1 Flight reconstruction showing a coherent temporal view of how the data was collected 2 Crossover network report 3 Before and after statistics for the signal field that is being levelled Tie line levelling using loop closure The loop closure method is much simpler to run than the method of polynomial approximations The process itself requires no parameters This was the first of the more traditional levelling methods upgraded to support tensors and vectors Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling tie line levelling G13 12 Library Help
20. ta must be ordered correctly in time To reconstruct the flights from File select Reconstruct Flights and then Date time Fids The Load Date chooser appears Select date from the list of fields and choose OK The Optional Time chooser appears Select time from the list of fields and choose OK The FID Factor and date style dialog box appears The FID factor is the number of seconds per fiducial Leave it as 0 1 default The date style for this dataset is YYMonthDay Select it in the date style list If you wish you may verify this yourself by using the Project Manager to obtain statistics for the date field J E i y 7 Optional Tne sce mi igh Intrepid ProLevelling Tool py Enter FID Factor sec FID amp date style a ee Corrections Display Tie Management CrossOver Management Specify Input Specify Output Specify Report Load cross overs Save cross overs Specify Basestation gt Save Options Wizard for Easy Levelling Edit Database Aliases Reconstruct flights b Quit 5995 0 S Date time Fids Julian day Fids Fiducials only 2012 Intrepid Geophysics Enter FID Factor sec FID amp date style C YYYYMonthDay C YYYY decimal GS_Date default C DayMonthYear yda4ngadh C JulianDay Ygde4ngath Ok Cancel 4 Back gt INTREPID User Manual Levelling tie line levelling G13 6 Library Help
21. tage of the tutorial the Levelling tool window gets overwritten by other windows you can easily recover the display by choosing Zoom in then Zoom out Refresh problems can also be fixed by covering then uncovering the tool window with a File Explorer window 7 Select the Principal tie line and create a tie list Quick review INTREPID processes the tie lines 1n a certain order which must be established by the user to get the best results The Principal tie line 1s chosen first It is the absolute reference for the levelling and is assumed to have zero drift The Principal tie line should be what you consider to be the best levelled tie line The next 2 or 3 tie lines in the list should be as far away as practicable from the Principal tie line From the Tie Line menu select Create List Select the middle tie line Keep selecting it until it registers The Current Crossover report displays information about the crossover point you have selected From the Tie Line menu select Show List An information box appears showing you the Principal tie line you have chosen If you selected the middle tie line the box shows line 174071 Intrepid ProLevelling Tool p g 1 Information File Corrections Display Tie Management CrossOver Manageme File Corrections Display Tie Management CrossOver Management Magnetism BaseStatic i Create List H to i T Showlit g000 0 6000 0 ad Complete List
22. the result not necessarily Key points for this guided tour In this guided tour you have e Used the Levelling Tool to tie line level the data using polynomial approximations e Used the Levelling Tool to tie line level the data using loop closure Frequently Asked Questions Q Can I remove bad crossover points from the levelling process A Yes individual crossover points can be turned on or off Q Can I remove all crossover points which have a misclosure greater than 10 from the levelling process A Yes the Level tool support a logical expression language which allows this Q Why would I want to save the crossovers to an INTREPID dataset A You can re use the crossovers which saves having to calculate them again For a very large dataset this saves computing time It is also a useful quality control measure about the survey itself Q Can I do levelling of integrated signal and its gradients A The Pro version of the tool uses the Observed Field datatype This enables you to group the signal and its three gradients and to loop level all parts simultaneously Q Can I level full tensor curvature gradients A Yes the Pro version supports heading loop and altitude corrections for full tensor gradient data The big difference for heading errors is that really the error is poorly charaterised as just this when Roll Pitch and Yaw are all implicated and tensors are very unforgiving when it comes to rotationa
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