g Version 7 - Micro
Contents
1. Figure 22 Convert Utility Dialog Box e Input File Path Name This is the name of the DDT or compatible binary absolute gravity data file g Convert supports most DDT files but may not support some versions If you have trouble converting files please contact MGS immediately e Freefall Project Name This is the base name to be used with the g project file e Output Project Directory This is the location at which all g converted files FG5 and gsf will reside Additional Utilities gProjectMerge gProjectMerge is a program that lets users combine multiple projects into one single project file This is useful in the case when data acquisition is interrupted and a single project is desired Note that gProjectMerge assumes that all acquisition parameters are identical i e perhaps a run was stopped after a few sets and a new project was created and begun immediately gProjectMerge is not intended to combine projects with different parameters if doing so it is at your own risk Figure 23 shows the gProjectMerge interface 44 N g7 Absolute Gravity Data Acquisition and Processing Software Dutput Directory Final Project Name Untitled Merge Merge Files Add File Remove Fie Figure 23 Project Merge Dialog Box e Output Directory This is the location where the merged project will reside e Final Project Name This is the2. 09 Check Blue 1 09 ja Set Break Point Clear Break Point Figure 11 Right Mouse Button State View Control Window Optionally if the left mouse button is single clicked over the filename the set is highlighted To highlight multiple sets highlight one set then use the lt SHIFT gt key and lt T gt or lt gt arrow keys accordingly The right mouse button will bring up the floating menu shown in Figure 4 The following options are available e Check Selected Checks all highlighted sets e UnCheck Selected Unchecks all highlighted sets e Check Checks all sets e Check Red Checks all odd numbered sets for use in ML 1 Red Blue Lock Analysis e Check Blue Checks all even numbered sets for use in ML 1 Red Blue Lock Analysis 26 N e Set Break Point Places a Break Point marker by the selected set g will process up to the break point and pause e Clear Break Point Clears the breakpoint g7 Absolute Gravity Data Acquisition and Processing Software When reprocessing data for the first time after collecting data and reopening a project it is best to process all sets in the project then go back and delete unwanted sets The Process Quick Update option from the main menu can be used to quickly recalculate the mean project gravity value and update the set views if no parameters are changed If any processing parameters are
3. 206 130 3 Acquisition 12 100 60 10 Project Drop 00 08 26 079647283 36 2741 0 96 1 05 46 41 01002 Gravity 979647292 65 97 Absolute Gravity Data Acquisition and Processing Software Tide 27 58 Load 0 00 Polar 6 66 Baro 1 20 Transfer 91 51 RefXo 0 01 Set Scatter 2 14 Uncertainty 2 11 Temp 0 997 tony 000 presa 846 65 5197 Spring ay 0 01 Laser 3 0 76 Seis 27 0 00 Load Polar Set 00 16 44 979647290 83 227 waj 1 99 Baro Tide 22 40 Load 0 00 Polar 6 66 Baro E Transfer 91st RefXo 0 01 Figure 14 State Window n As previously mentioned the State Window is always displayed and contains the most information of any of the twelve views In Figure 14 basic project setup information 15 shown in the top window including the position 40 02885 105 04603 1528 nominal pressure 842 65 gradient 3 02 the instrument type and serial number FG5 206 and the acquisition parameters 12 sets 100 drop set 60 minute set intervals 10 second drop intervals In order to display information to the user and keep the view uncluttered many of the boxes are not labeled However by hovering the mouse cursor over each box a tool tip including units will appear with a description of the value The second box Drop contains information pertaining to the current drop being
4. consistent with earlier sets See Figure 10 for an example 23 N i3 SSE 97 Absolute Gravity Data Acquisition and Processing Software Figure 10 Current Set Value Update A10 example data The first 5 sets are complete 100 drops each and the 6th set is only on drop 3 The mean value of the 6th will approach the established mean and the error bars will decrease as more drops are acquired Additional Window Displays In addition to the default displays Tree Control State Drops Sets and Fit Residuals g also supplies a variety of views to convey information about processing or data acquisition status A description of each view not previously described follows e Set Histogram Displays a histogram of the processed sets In general users should expect to see normally distributed data e Set Sensors Displays up to six separate charts Charts 1 5 show the default channels for a Micro g Patch Panel Temperature Super Spring Ion Pump Laser and Barometer The sixth chart 15 reserved for channels 6 7 and 8 and stacks all three channels onto one graph if enabled e Set Corrections Displays six separate charts one for each type of correction applied to the calculated gravity value Tide Ocean Loading Polar Motion Barometric Datum Transfer and Reference Xo Units are in Gals e Set Fit Sensitivity Displays the set standard deviations e Drop Histogram Displays a histogram of the processed drops
5. processed In the case of Figure 14 the drop is 100 The time of the drop is displayed 01 24 56 the corrected absolute gravity value of the last drop 979647287 69 the standard deviation of the drop 26 39 the RMS of the drop fit nm 0 93 the drop number 100 whether or not the drop was accepted or rejected and the peak lock aE implies accepted E lock The next six boxes show the corrections in uGal for tide 25 00 ocean loading 0 0 polar motion 6 66 barometric 1 80 datum transfer 91 51 and reference Xo 0 01 The final six boxes show the current value of the sensor channels for ONLY the first six channels values are listed in Volts and correspond to the standard patch panel configuration on all Micro g instruments 30 N The third box Set contains information pertaining to the current set being processed In the case of Figure 14 it is Set 2 average time of the accepted drops used to calculate the set mean is displayed 01 16 33 the average corrected gravity value 979647288 94 the uncertainty of the set in uGal 2 33 the drop to drop scatter in uGal 9 19 the set number 2 and the number of drops accepted 97 The next six boxes display the average value of the corrections applied in uGal tide 18 ocean loading 0 00 polar motion 6 66 barometric 1 71 datum transfer 91 51 and reference Xo 0 01 97 Absolute Gravity Data Acquisition and Processing Software The final bo
6. voltage on the Patch Panel Laser input channel g uses the measured voltage on Channel 3 to determine which peak DEFG or GHI was valid during the drop If for some reason the voltage in Channel 3 is invalid the user can still deselect Automatic Peak Detection and manually enter the wavelength from the pull down menu o Modulation Frequency includes the modulation frequency entered in the System Laser Setup page in the equation of motion This option should always be selected when using a WEO 100 laser e WEO 200 o By selecting Lock Detection and connecting the Laser Lock signal from the back of the WEO 100 controller or the WEO 200 to CH 7 of the SIM or older Patch Panel units the software will ignore drops that occur while the laser is unlocked The software will then try another drop immediately until the laser is locked The software will then process drops it until it catches up with the desired drop interval e ML I o For ML 1 or AL 1 lasers the user can select the red or blue wavelength or select Alternate In Alternate mode the software will send an impulse signal through the digital output of the patch panel and switch between the two modes between each set Blue lock sets will be displayed in blue on the Sets view while Red lock sets will be displayed in Red Note that in normal situations it is highly recommended to use Alternate Mode The software automatically takes an average of the red sets an average
7. IMPORTANT Due to how the software protection in g works if at any time the user adds or removes hardware from the computer in which g is installed they must obtain a new password file by following the above steps N Real time Data Acquisition g7 Absolute Gravity Data Acquisition and Processing Software g allows both real time data acquisition and post mission processing To begin a data acquisition project choose Project New from the main g menu The four default screens will appear but there will be no information in the Set Tree view By default g is set to run an FG5 instrument at the Micro g LaCoste facility To set the software up for data acquisition and processing at your location you must modify some or all of the parameters under Process Setup Information This menu is concerned with where the instrument is located e Site Name free form text Site Code free form text Latitude decimal degrees DD Longitude DD Elevation meters above sea level Nominal Pressure mBar this is the long term mean pressure value at the site which is in generally not the current pressure value e Vertical Gravity Gradient uGal cm normally always negative If unknown the standard free air value is 3 09 uGal cm e Transfer Height cm This is the height that the gravity value is reported at Typical values are 0 100 130cm The gradient value is used to transfer the gravity value calculated at the top of the dro
8. Rubidium Frequency 10000000 00000 13 63239142704 mm 0 90 v Modulation Frequency 8333 420 Processing Results 01 10 02 Time Offset D h m s 0 0 0 0 Gravity 979647292 54 1 Set Scatter 1 11 pcal i 0 32 peal Total Uncertainty 2 05 pal Number of Sets Collected 12 Number of Sets Processed Set 25 Processed 4 Number of Sets NOT Set NOT Processed Number of Drops Se Total Drops Accepted Total Drops Rejected Total Fringes Acquired Fringe Start 0 Processed Fringes GuideCard Multiplex CuideCard Scale Factor Acquisition Settings Set Interval 60 min HI T 2 64 1 Transfer Height 91 51 yen Reference Xo 0 01 pca e Sigma Reject 3 00 Earth Tide Factor 0 001 Average Earth Tide Uncertainty Ocean Load Factor 0 10 System Setup 1 1 Gradient 0 91 icai C 0 03 pGal cm Comments test run lt Figure 15 project txt Output Summary File Set Summary File The set summary file contained in goutputl set txt contains set by set information including Set Number Time Day of Year Year Gravity Set Standard Deviation Set measurement precision Set uncertainty tide correction barometric correction polar motion correction datum transfer correction reference Xo correction temperature 32 N pressure auxiliary channels and number of drops accepted and number of drops rejected The file is tab delineated and is easily imported into most spreads
9. interval in seconds Recommended rates are system dependent Please consult the system manual e Set Interval Used to select the interval in minutes at which to start new sets The drop down menu contains some commonly used intervals e Pulse Delay This is the amount of time in seconds between the drop and the time the object is lifted Systems with digital controllers need much less time to lift than do systems with analog controllers An approximate value is set automatically by g 97 Absolute Gravity Data Acquisition and Processing Software Red Blue Sequencing Red Blue sequencing allows users with L Series lasers to acquire data with both laser frequencies in a short time interval and still spread the entire project over a longer time interval For example data can be acquired with the red mode and then a few minutes later with the blue mode Then after an hour the whole red blue sequence can begin again e Enable Enables red blue sequencing e Red Blue Interval Time interval between the start of a red set and the start of the next blue set typically a few minutes e Sequence Interval Time interval between the start of two red sets An example of Red Blue Sequencing is shown below Sar Figure 2 Example of Red Blue Sequencing Acquisition Mode 12 N g7 Absolute Gravity Data Acquisition and Processing Software Control The following information may be set from the Control Page r Cor
10. location of the GuideTech configuration file the base address of the card the Input Multiplexor and Scale Factor an number of fringes to acquire Recommended parameters for an FG5 A10 or FGL are o FPG File c Program Files Guide GT650 FPGA gt65x2 fpg N Oo 97 Absolute Gravity Data Acquisition and Processing Software Address 0 Input Multiplexor 4 Pre Scale 250 100 No Fringes Acquired 700 e Currently g supports the IOTech 200 ISA or 2000 PCI series A2D boards and the National Instruments PCI 6013 A2D board The SETUP button allows the user to set the acquisition parameters for each channel For the standard Micro g configuration these parameters should be for Channel s respectively O00 Advanced Temperature 0 UniPolar 1 25V 0 100 Super Spring 1 BiPolar 1 25V 0 1 Ion Pump 2 BiPolar 5V 0 1 Laser Voltage 3 BiPolar 5V 0 1 Barometer 4 UniPolar 10V 0 1 Serial Barometer 0 68 947 Analog 537 5 125 User Sensor 5 BiPolar 5V 0 1 User Sensor 6 BiPolar 5V 0 1 User Sensor or Seismometer 7 BiPolar 0 3125V 0 1 The Advanced button should only be used by knowledgeable users Options settable under the Advanced menu include e Factory Height Instrument Specific and Set ONLY by Micro g LaCoste This is the sum of all the internal hardware heights Please refer to your instrument materials for a precise v
11. name which the merged project will be saved as e Merge Files These are the files that will be merged together to create the merged project e Add File Button This button is for adding more files to the Merge Files list e Remove File Button This button is for removing files from the Merge Files list This button will remove the selected item If no items are selected it will remove the first item e Merge Button This button is used to start merging the file 3 Additional Utilities gProjectCopy gProjectCopy is a program that lets users easily change the name of their projects This is useful if the user entered the wrong name for a project and needs to change it later Figure 24 shows gProjectCopy 45 97 Absolute Gravity Data Acquisition and Processing Software 2 Uned Input Fis ff Coy New Project Bl Figure 24 Project Copy Dialog Box Input File This is the file which the user wants to copy New Project This is the name of the output project name Copy Button This button starts the copying process 46 N License Information Licensed users of g are entitled to three install platforms with the Main License Additional installations including support are purchased one seat at a time directly from Micro g If your institution or company requires g to run on more than three platforms please contact MGL directly or visit our website
12. www microglacoste com for more information g7 Absolute Gravity Data Acquisition and Processing Software Support Questions concerning the operation of g software and any problems using g should be directed to info microglacoste com You can expect to receive an email or phone call within forty eight hours of your inquiry Maintenance Periodically MGS will post an upgrade patch for g on the website These patches will be posted without notification so please check back every few weeks to get the latest patch if applicable 47
13. For example the Oceanload files for site TMGO are named Oceanload TMGO This helps avoid the situation in which the ocean load files for a different location are accidentally used in the calculation resulting in the wrong gravity value g will use the information from the Information page to get all the data that it needs to create the OceanLoading files The values it uses are Name Site name for the g project file Latitude Latitude of the site Longitude Longitude of the site Elevation Mean Sea Level elevation for the site 36 N The ocean tide files are supplied to Micro g by Dr Olivier Francis http www ecgs lu g7 Absolute Gravity Data Acquisition and Processing Software Advanced Users Setup allows the selection of three common ocean tide model for each term e Schwiderski e FES2004 e CSR3 0 Users unfamiliar with these wave file models should accept the default values Note that the FES2004 model is considered state of the art but due to the high resolution of the model it can take a few minutes to calculate the ocean load For quick setup purposes the default model is still that of Schwiderski g allows users to use already existing OceanLoad files or it can dynamically create the necessary files that the user specifies on the fly To use existing files enable OceanLoad by clicking the check box in the Setup option and then search for the specified olf and dff files Or to
14. Mic oe ACOSTE WWW MICROGLACOSTE COM 07 User s Manual MARCH 2007 N g7 Absolute Gravity Data Acquisition and Processing Software Table of Contents Introduction 4 System Requirements 4 Installing and Starting g for the First Time 7 Real time Data Acquisition 8 Information 8 System 9 Instrument 9 Seismometer Prototype FGL Only 9 Computer Interface Cards 9 Acquisition Id Sampling 11 Time 11 Rates 12 Red Blue Sequencing 12 Control 13 Corrections 13 Laser 15 Seismometer 15 Tidal Correction 16 Drop Fit 16 Fit Sensitivity 16 Uncertainty 17 Setup 17 e Modeling 18 e System 19 e Environmental 19 e Set up 19 Comments 19 Beginning Acquisition or Reprocessing 20 Start Processing 20 The State Window 20 Drops 22 Fit Residuals 22 Sets 23 N g7 Absolute Gravity Data Acquisition and Processing Software Additional Window Displays Specific Post Processing Features The Set View Control Window Reviewing Processing Parameters Output File Status Processing Status Processing Finished Reviewing Processing Results Project Summary File Set Summary File Tide Correction Models Berger ETGTAB Potential Filename Tidal Parameters Filename OceanLoad Oceanloading Format Figure 18 Example Ocean Load File Format g Binary Data Fil
15. System FG5 206 1203 Acquisition 12 100 10 Drop Project 00 08 26 979647283 36 27 41 0 96 1 x 05 46 41 01002 o Tide 27 58 Load 0 00 Polar 6 66 Baro 120 Transfer 91 51 RefXo 0 01 Gravity 979647292 65 Set Scatter 2 14 Uncertainty 241 Temp c 0 9 2 000 pres 4 846 65 Tide 5197 Spring ay 0 01 Laser 3 0 76 Seis Z 7 0 00 Load Set Eon 00 16 44 979647290 83 2 27 10 24 BEJ Tide 22 40 Load 0 00 6 66 Baro 1 27 Transfer 91 51 RefXo 0 01 Figure 7 State Window m e Setup Basic setup and station information is displayed here including Latitude Longitude Elevation Standard Pressure Gradient System Type System Serial Number Number of Sets Acquired or to Acquire for Realtime Number of Drops per sets Time interval in minutes between sets and time interval in seconds between drops e Drop Information about each individual drop including time absolute gravity standard deviation RMS number accepted a or rejected r and Laser Lock code tide correction ocean loading correction polar motion correction barometric correction transfer height correction reference Xo correction temperature C super spring position V Ion pump monitor V laser output V barometric pressure mBar and average seismometer reading V e Set A group of drops is referred to as
16. The default value is 3 which means that in a set any drop that is more than 3 from the mean is rejected Note that this function is purely statistical there 1s no hardware information used to reject drops e Setup On the lower left hand corner of the Uncertainty Setup page is a drop down dialog box and an Apply button To set the MGS recommend guideline values for a specified instrument choose the appropriate instrument in the dialog list and press the Apply button g now calculates the total uncertainty for each set and for the final project gravity value The total uncertainty is given by _ fg 2 Pa where is the statistical uncertainty given by the set scatter standard stat deviation divided by the square root of the number of sets Oa lAN stat set set and 6 is the total systematic uncertainty which is described below The Statistics Setup button leads to the menu shown in Figure 5 The statistical uncertainty estimate is based on the estimated uncertainties for many different components of the measurement Components are grouped into four separate 17 97 Absolute Gravity Data Acquisition and Processing Software areas Modeling System Environmental and Set up Default values are determined from previous publications and from in house experience Uncertainties Modeling Environmental Earth Tides Factor 0 001 oe Tide Swell ual 0 tor ater aha Wa
17. a set Information about each individual set including mean time of the accepted drops in the set mean absolute gravity total uncertainty drop to drop scatter set number number of accepted drops percentage of accepted drops mean tide correction mean ocean loading correction mean polar motion correction mean barometric correction mean datum transfer correction and mean reference Xo correction e Project The group of all the sets constitutes a project Summary information about the project including mean time of sets processed set to set scatter total uncertainty mean tide correction mean ocean loading correction mean polar N motion correction mean barometric correction mean datum transfer correction and mean reference Xo corrections g7 Absolute Gravity Data Acquisition and Processing Software Drops The Drops view displays individual drops minus the mean value of the set Accepted drops i e those that are within the user selected statistical range are plotted in green while rejected drops are plotted in red The top of the view informs the user of the current set number the current drop number the current drop to drop scatter of the set as well as the number of drops accepted and the number of drops rejected Fit Residuals The Fit Residuals View displays the residual signal the difference between the actual fringe time and the least squares fit estimate of the position at that time With system res
18. al time plot capabilities and statistical analyses allowing the user a clear understanding of the gravity data The manual below starts with real time set up of the software This includes site and instrument specific parameters in addition to control of the corrections It then continues with post processing considerations Finally it ends with a more detailed description of the tidal routines and advanced software functions N Installing and Starting g for the First Time g7 Absolute Gravity Data Acquisition and Processing Software You will either have received a Compact Disc media with at least the folowing f means file and means directory or you will have downloaded the g Setup file from http www microglacoste com e Completely uninstall all previous versions of g e Double click Setup exe Follow the instructions It is highly recommended that you accept ALL default installation paths e When starting g for the first time it will prompt you to create a small binary file SysChk bin that is unique to your computer e Email SysChk bin to Aaron Schiel at mking microglacoste com and wait for him to send you gPWinfo bin This usually takes less than twelve hours during normal the business week Note that the files are unique for each computer so please send one file at a time e Upon receipt of gPWInfo bin run g again and follow the program s instructions to install the password file You are now ready to run g
19. alue e Clock Frequency Nominally 10 MHz but is calibrated by Micro g LaCoste or a standards laboratory Again the precise value is unique to your instrument e Hardware TTL Prescale Factor Determined by Micro g LaCoste Typically this value is 1 for FG5 and FGL and 4 for A10 Please refer to your instrument materials for the correct value Serial Barometer use the offset and multiplier inside the A2D card set for scaling 10 N Acquisition The Acquisition set up page is shown below g7 Absolute Gravity Data Acquisition and Processing Software Information System Acauistion Control Comments Sampling Time Sets 12 2 Mon Feb 12 2007 16 43 34 H7 Red Blue Sequencing Enable Sequence Interval min 22 z Red Blue Interval min Figure 1 Process Setup Acquisition Dialog Box Sampling e Sets Select the number of Sets to acquire during the project e Drop Set Select the number of drops in each set during acquisition Time e Start Immediately Instructs the software to begin data acquisition immediately following Process Go or F5 e Start at Specified Time Instructs the software to begin data acquisition at the time indicated Note Time on the PC Clock must be set to Coordinated Universal Time GMT with daylight savings disabled not local time 11 N Rates e Drop Interval Used to select the drop rate
20. arate sections For more advanced information you can contact Olivier Francis at Olivier ecgs lu 34 97 Absolute Gravity Data Acquisition and Processing Software er iat r Potential Filename C Program Files Micro g Solutions Inc ETCPOT DAT or equivalent m Ocean Load Files Delta Factor Filename Model C Observed C gData OceanLoad MGL dif s ETGTAB INI dff or equivalent Ocean Loading Filename On Off C gData OceanLoad MGL olf M Run Ocean Load Default Setup OK Cancel Figure 16 ETGTAB Setup Dialog Box Potential Filename The first section allows the user to enter the Tidal Generating Potential File For most users this file is called ETCPOT dat and is located in the gWavefiles directory The default file contains Tamura s potential Tidal Parameters Filename This file can be supplied by the user or generated on the fly as discussed earlier The format of the file is shown in Figure 17 The default setup for g enabled by checking the Default box is for a dff file generated by the Oceanload Model This setup does NOT contain any ocean loading component If the user has a compatible model or observed tidal parameters for the gravity station the Default button may be unchecked and if applicable the Observed radio button checked Phase Kappa is set to Zero 97 Absolute Gravity Data Acquisiti
21. are included in the figure but are not normally part of the output file The output data is divided into related sections File creation and Header Information Station Information Instrument Data Processing Results Gravity Corrections Uncertainties and Comments Depending on the options selected Laser Tide Model Ocean Loading sections may include additional information 31 97 Absolute Gravity Data Acquisition and Processing Software Els UJ jan 02a projectx Notepad File Edit Format View Help Micro g Solutions Processing Report File Created 02 13 07 03 26 08 Project Erie 09 jan 02 g Acquisition Version 1 121700 Processing Version 7 070208 Institution Operator Kip Station Data Name Micro g Solutions Inc Site Cod 1 Pressure 842 65 mgar Barometric Admittance Factor 0 30 Polar Motion Coord 0 1829 0 3169 Earth Tide Selected Potential Filename egram Files Micro g Solutions Inc gwavefiles ETCPOT dat Delta Factor Filename C gData OceanLoad Micro g Solutions Inc dff Delta Factors Amplitude Phase Term 1 000000 Dc o BRE SS Hs oum 00009009905 ERBBBEERBRE oo Oo 00 EI Ocean Load ON Filename C gData OceanLoad Micro g Solutions Inc olf M2 5 x2 91 ssa 0 513 0 263 1 252 0 754 0 044 0 382 0 065 0 150 0 020 0 008 0 104 108 7 13 6 56 3 70 0 166 8 57 3 353 3 79 9 44 1 123 7 89 9 Factory Height 116 30
22. ase refer to the Instrument operators manual for more information In general it is never necessary to change the laser wavelength Finally the Modulation Frequency is unique to each WEO 100 laser This must be entered accurately to x xxx xxx decimal places o WEO 200 Wavelength and Serial Number In general it is never necessary to change the laser wavelength o ML 1 Blue and Red Lock wavelength and Warm up Mode Refer to the information provided with your instrument for the wavelength values These values are unique to each ML 1 laser and must be entered accurately to xxx xxx xxx decimal places Do not change these values unless told to do so this will directly affect the calculated gravity value Warm up mode should typically be about 60 seconds this refers to the amount of time before data acquisition that the laser enters lock mode Enter the serial number for note keeping purposes Seismometer Prototype FGL Only Seismometer Type Users may select from a variety of seismometer options supported by Micro g Sampling Frequency Users may enter the sampling frequency Recommend is 10xCutoff Sampling Time Users may enter the amount of time to sample Recommended is 200ms for small dropping chambers Computer Interface Cards Fringe Card Currently Micro g supports only the GuideTech ISA or PCI GT650 series time interval analyzer in real time acquisition The Setup button allows the user to change the default
23. changed g automatically recalculates gravity for the entire data set Reviewing Processing Parameters Processing parameters may be reviewed and or modified in the Process Setup screen shown in Figure 12 the user may also press the F3 key to vie the Setup screen Listed below are the Setup parameters that may be altered before reprocessing old data Information System Acquisition Control Comments r Site p Setup Lookup 1 Name Micro g Solutions Inc Setup Height cm 14 Code MGSNU Polar X arc sec 0 1829 eg Longitude dd E 105 04603 Convert Bevation m 1528 Nominal Pressure mBar 842 65 Set Gradient uGal cm 3 02 Bao Fact G mBay 03 Figure 12 Process Setup Dialog Box e Information This menu is concerned with where the instrument is located The user can enter Site Name Site Code Latitude Longitude Elevation Nominal Pressure Gravity Gradient Transfer Height Measured Setup Height Barometric Factor Polar motion values 27 N e System This menu allows the user to enter Instrument Type Model Serial Number Interferometer Type Laser Type and wavelengths if applicable Seismometer data collection enabled if applicable FGL Series instruments only Analog to Digital data acquisition card and setup Serial Barometer setup The Advanced parameters may also be changed e Acquisition These parame
24. dynamically create the files enable OceanLoading and then pick an base name for the OceanLoad files Then when g is run for the first time it will ask to create the specified files Oceanloading Format As discussed above depending on the information modeled versus observed contained in the tidal parameters file an Ocean Loading file may or may not be entered The format of the Ocean Loading file is shown in Figure 18 Users may generate this file using the OceanLoad tool as explained above or from their own data source BD Oceanload Golf Notepad File Edit Format View Help OceanLoad MGL Component Amplitude 0998e 009 6316e 009 2536e 008 5513e 009 3893e 010 8248e 009 4800e 010 5014e 009 9891e 010 4001e 011 124 612 1 0427e 009 8 988e 001 5 e 2s LA Me CE a 4 3 6 1 s 2H Figure 18 Example Ocean Load File Format 37 N g Binary Data Files Structure g maintains a binary project file that contains all the station system acquisition control and comments information used when occupying a absolute gravity station as well as a list of all names of the set files Project files have the project name as the prefix and end in a fg5 extension For example the gSampleData directory contains a project called Erie 09 jan 02a fg5 g7 Absolute Gravity Data Acquisition and Processing Software Raw observation data for each set is stored in a binary gravity set file with a gsf exte
25. ed drop of Set 2 28 97 Absolute Gravity Data Acquisition and Processing Software Eri2 UJ jan VELIAJ Broject Edit view Process Options Output Window sew m m w e zd xd Erie 09 jan 023001 gsf sees RS Aspen i 39 a Project esse amr 7 0 231 mec 0 se Ere C9 jan 0280120 SOM ETHER 17 EEI E E GE 8 88 E 2 92 SRNL fs TRE as ae Baro im Rexo Figure 13 Processing Status after completion of Set 2 The Sets window in the upper left hand corner of shows the two previously processed sets and their Uncertainty error bars The two sets are plotted with the mean subtracted The mean value is written above the graph The Fit Residuals window in the upper right hand corner of Figure 13 shows the average residual signal for Set 2 in blue and the single drop residual signal for Drop 100 Set 2 in green The Drops window in the lower right hand corner shows all the gravity values for Set 2 with the mean subtracted while the State window in the lower left hand corner shows text information for Drop 100 Set 2 Set 2 and the cumulative average for the entire project Figure 14 is another look at the State Window also shown above 29 N Setup Position 40 02885 105 04603 1528 842 65 3 02 100 System FG
26. es Structure Additional Menu Options Project New Open Close Save Save as Project Save as Template Edit Reset Time Offset Process Rate Set Break Point Go Step Break Stop 24 26 26 27 28 28 31 22 31 32 34 34 34 35 39 36 37 37 38 39 39 39 39 39 39 39 39 40 40 40 40 40 41 41 41 41 41 N 97 Absolute Gravity Data Acquisition and Processing Software Quick Update View Channels Options Output Additional Utilities Convert Additional Utilities gProjectMerge Additional Utilities gProjectCopy License Information Support Maintenance 41 41 42 43 44 44 45 47 47 47 N Introduction g7 Absolute Gravity Data Acquisition and Processing Software This manual explains the operation of the Micro g LaCoste Absolute Gravity Data Acquisition and Processing Software The software operates in the Windows environment g can be used with all MGL absolute gravimeters including the FG 5 A 10 FG L gravimeters and is capable of processing archived data collected with most Olivia versions after being converted to the g format using the included Convert application The software package provides sophisticated data collection processing and analysis capabilities including standard environmental gravity c
27. for the currently processed set In general users should expect to see normally distributed data e Drop Sensors Displays up to six separate charts for the currently processed set Charts 1 5 show the default channels for a Micro g Patch Panel Temperature 24 N Super Spring Ion Pump Laser and Barometer The sixth chart is reserved for channels 6 7 and 8 and stacks all three channels onto one graph if enabled e Drop Corrections Displays six separate charts one for each type of correction applied to the calculated gravity value for the current set Tide Ocean Loading Polar Motion Barometric Datum Transfer and Reference Xo Units are in ii Gals e Drop Parabola Displays the trajectory of the object with time on the X axis and distance on the Y axis This graph is useful to view dropping chamber and fringe data acquisition performance e Drop Seismometer This view is applicable for LS meters only and has two components If seismometer data is used directly in the solution the graph shows the compensated versus uncompensated residuals nm If the seismometer data 1s NOT used in the solution the graph shows the seismometer velocity mV e Drop Residual PSD This view shows an autoscaled PSD of the residual signal ONLY IF Frequency Response is enabled e Drop Fit Sensitivity Top and Bottom Displays the change in the calculated gravity value as different portions of the drop fit are selected Values are disp
28. heet programs 97 Absolute Gravity Data Acquisition and Processing Software 33 N Tide Correction Models g7 Absolute Gravity Data Acquisition and Processing Software g software accommodates two Tide Correction methods ETGTAB and Berger Within each it is possible to incorporate an Ocean Loading model Most users should use the modern ETGTAB routine but the Berger model is provided for completeness The amplitude and the phase of the gravity loading are computed using the Farrell s method The Green s functions for the PREM model are used and a correction for the mass conservation is included The users may choose different ocean tides models Details of the choices and options are discussed below Berger In the Berger correction the tidal parameters are set using a constant delta factor of 1 1554 and a phase Kappa of zero This delta factor cannot be modified except for the DC term Honkasalo correction The tidal potential is also set once for all The gravity body tide is computed and applied to the observations each drop The program used for this computation was originally written by Jon Berger November 1969 and was modified by J C Harrison Judah Levine and Karen Young University of Colorado Duncan Agnew University of California San Diego IGPP and Glenn Sasagawa NOAA ETGTAB If ETGTAB is selected from the drop down list box the Setup button leads to the menu shown in Figure 16 The Setup dialog has three sep
29. ialog Box Process Rate This option sets the rate at which drops are processed in Post Mission mode only On some machines with slower graphics it may be necessary to set the rate to 50ms or N greater in order to avoid synchronization problems occurring between mathematical processing and graphical display g7 Absolute Gravity Data Acquisition and Processing Software Set Break Point This option allows the manual setting of a break point in Post Mission mode only In general it is much easier to set a break point from the tree menu Go This option starts the processing in both Post Mission and Real Time Step This option allows users to view process drops step by step in Post Mission mode only Break This option allows user to Pause processing and should only be used in Post Mission mode Stop This option stops all processing in Post Mission processing or Real time data acquisition Quick Update This option is enabled after all sets have been processed If a users wishes to discard Sets to be included in the final determination of the absolute value of gravity after the sets are deselected on the tree Quick Update will update the project number according to the last setup of processing parameters If any processing parameters change Quick Update automatically reprocess all selected sets View Channels This option allows users to view data channels before and after processing This is useful since users s
30. ity data for all of the sets raw fringe times for every drop and the associated analog sensor data g7 Absolute Gravity Data Acquisition and Processing Software Import To import ASCI I data it must be in the format identical to that created by the Export function you must first create a New Project Then select Import and you will be prompted to enter the lt project name gt fg5 txt file name Note that there must be a corresponding lt project name gt gsf txt file with the fringe data again in the correct format which g will open automatically The ASCII data are then converted to the standard g format for processing Edit Reset This option allows users to reset all or some of the project file parameters to the values at the time of original data acquisition Time Offset This option allows application of a time shift in the event that the computer time was not set to the correct time To calculate the offset change the True Start Time to the correct time the time that should have been and then press Calculate Check the time offset as listed in the grayed edit box If the time offset is correct check the Apply Time Offset option to make the time offset effective during processing inis Ofisse Original Start Time 2002 Jan 24 16 29 30 True Start Time 2002 Jan 24 16 29 30 E Time Offset D h m s 0 00 00 00 Apply Time Offset DK Cancel Calculate aa Figure 19 Project Time Offset D
31. layed relative to the value determined at the nominal fit selected in Setup Control 97 Absolute Gravity Data Acquisition and Processing Software Note Viewing many displays can significantly slow down data processing and this can in turn result in potential memory violations If your system does NOT have a high end graphics card gt 32mb on board memory minimize the number of open views 25 N Specific Post Processing Features g7 Absolute Gravity Data Acquisition and Processing Software The Set View Control Window When opening an old project where data has already been acquired g automatically displays the Set View Control Window at start up This window is used to select which sets are to be processed and to set a break point in the processing if necessary The figure below shows a detailed view of the Set View Control Window The check boxes to the left of the Set Filename indicate whether or not the set is included in the processing Sets may be checked or unchecked by placing the mouse cursor directly over the box and clicking the left mouse button wj Erie 09 jan 02a001 gsf 09 jan 023002 gsf 09 jan 022003 gsf Erie 09 jan 028004 asf 09 jan 02a005 gsf tee E T Me Gie 09i Check Selected 1 09ja 41 Eie 09 M i 09 Check all 09 Check Red
32. notification can be set for never after every completed set after every other completed set or only at the end of a completed project 42 N g7 Absolute Gravity Data Acquisition and Processing Software Email m E mail Server misewecom 000000000 From FGS araviymetercom To H g ES j EM Subject Gravity Data Body Included Data In Body Project Gravity Set Gravity IV Uncertainty Set Scatter Drop Scatter IV Number of Sets Never v Suppress Error Messages Cancel Figure 21 Email notification setup window Project File Set File Attached Files Sent Output There are three options under Output Text Raw Dump and Graphics By default g outputs a text file for Project Summary and Set by Set Summary If users wish to have additional information output to file Drops Graphics jpg image of the displayed view or Raw Data these options must be selected before processing the data Note The view must be opened for g to save the graphical images 43 N Additional Utilities Convert Convert is the utility used for converting files obtained with Olivia DOS software into the new g format Figure 22 shows the Convert menu g7 Absolute Gravity Data Acquisition and Processing Software Input File Path Name Freefall Project Name Dutput Project Directory 5 i ni var H ia
33. nsion All raw data including time of drop fringe times and auxiliary sensor s data is stored in this file The files must be accompanied by the corresponding project file in order to be processed by the g software Set files are named sequentially based on the project file name the number of the set and the gsf extension For example in the gsampleData where the project name is Erie 09 jan 02a fg5 the raw data file for the 5 set is named Erie 09 02a005 gsf The raw data file for the 12 set is named Erie 09 02a012 gsf Note When transferring sharing or archiving g data it is necessary to include the Project file fg5 and ALL the set gsf files together The other files txt and project graphs can be recreated by the software and it is technically not necessary to archive those For g Versions 6 at later it is now possible to Import and Export all the project parameters and raw data in ASCII format Please see the Section on Additional Menu Options for more information 38 N Additional Menu Options g7 Absolute Gravity Data Acquisition and Processing Software Project New This option creates a new project file from scratch All parameters are default and users must change the options according to their setup location instrument and system data acquisition parameters and control parameters This includes the System Factory Height Rubidium Clock Frequency ML 1 Laser Wavelengths for A10 and FGL in
34. of the blue sets and then the resultant average of these values It is the average of the blue and red wavelengths that is stable over long time periods many months Seismometer This enables the compensation of the seismometer data when used on the FGL Prototype instruments N Tidal Correction Please see the section Tidal Corrections below for a detailed discussion of the earth tide and ocean loading corrections Please note that in general it is necessary to run the Ocean Load program once for each new location occupied by the gravity meter g7 Absolute Gravity Data Acquisition and Processing Software Drop Fit This allows a subset of the collected fringes to be processed to avoid fitting during the sensitive release and catch phases of the drop Default parameters for an FG5 A10 FGL are e Start Time 35 20 ms e Stop Time 200 135 ms Fit Sensitivity The calculated gravity value is determined using the fringes selected in Drop Fit Ideally this value is not heavily dependent on the choice of these fringe values The Fit Sensitivity plots in the View menu allow the user to determine the change in the calculated gravity value as different portions of the drop fit are processed By default a few milliseconds around the start time and stop time are plotted Typically the gravity value should be constant within a few uGals Given the nominal fit times above the sensitivity settings for an FG5 A10 FGL
35. om the Process menu 2 Press the Go button gt 3 Press F5 In real time mode the drops will occur as prescribed in Setup Acquisition In Post Processing mode the drops will be processed as prescribed in Process Rate Note that if a minor problem is detected in the Setup as acquisition begins it is possible to Pause the data collection and then resume As the project progresses the Set data filenames are displayed in the left set view control window Notice that for this example each set is named sequentially in this example 001 through 012 with the project name used as the prefix and gsf as the suffix By default g opens four Views of the data at start up Each view can be enabled by the tab control at the lower part of the window The default windows are o ia RR ER ER ERA u i E i E zi zi 2 i zi z E om Figure 6 Open project file The State Window The main window g uses to convey information to the user is the State Window The State Window contains four separate sections note that the meaning of each box value 20 can be determined by hovering the mouse cursor over the box until the tool tip appears 97 Absolute Gravity Data Acquisition and Processing Software r Setup Do 40 02885 105 04603 1528 842 65 3o 1
36. ometimes would like to know what data is coming in from channels with out having to process any of the data 41 97 Absolute Gravity Data Acquisition and Processing Software Ghannel Visi Figure 20 View Channels Live Update Window Options Graphics This option allows users to manually set all scales in the graphs Graphical scales are saved to the project file The user can also enable or disable Data Review mode Data review when enabled allows users to click on a particular drop or set in the tree view and view the last data that was stored For Data Review mode to work properly this option must be enabled before processing the data Email For system controllers with an internet connection g can be set up to send periodic emails with real time processing results Note that by default email notification is off Figure 21 shows the Email Notification Dialog Box The User must enter an email server a valid identity for that server and a valid recipient Note that any errors encountered are suppressed to avoid interference with data acquisition If enabled the default information provided is e Current total project gravity value Current set scatter Gravity value of the last completed set Drop scatter of the last completed set Total project uncertainty The number of the last completed set A copy of the latest version of the project txt file A copy of the latest version of the set txt file The
37. on and Processing Software View Help 0 000000 002428 721500 921941 989049 999853 719381 923766 991787 003032 753244 791964 002427 249951 000000 160000 154250 154240 149150 134890 161720 161720 161720 161720 07338 03900 Te Se ee m em bod ae od 0999699999909 i 1 i 2 2 3 937897 Figure 17 Example Delta Factor File Format NOTE An Observed Gravimetric Delta and Kappa Factors File contain the Ocean Loading component and therefore the Oceanloading Filename option is disabled automatically OceanLoad Previous versions of g came with a separate tool for calculating OceanLoading but it is now built into the program Two files are created by the OceanLoad tool e Delta Factor File Oceanload dff This ASCII text file contains the listing of start frequency end frequency the Delta factor amplitude and phase in degrees in a format compatible with ETGTAB This file can ONLY be used with the ETGTAB option e Ocean Loading File Oceanload olf This ASCII text file contains the ocean load parameters Wave Amplitude and Local Phase listing The file has an olf extension by default and can be used with Berger OR ETGTAB options It is recommended that the base name Oceanload be modified to something unique for the current instrument location of g6 the site name is automatically appended to the basename of Oceanload
38. orrections necessary for uGal gravity measurements The software allows the user to customize the data acquisition program for each site including geodetic coordinates delayed start up set and drop rate and other detailed site information g requires a binary security file that is unique to each individual system to operate g users familiar with previous version of g Olivia or absolute gravity data acquisition will find the software easy to use and operate Those new to absolute gravity measurement should read this operation manual carefully before operating any MGS absolute gravimeter or post processing any absolute gravity data System Requirements g relies on both text and graphical output to assist users in quickly evaluating instrument performance and results g runs best with the following minimal standards Operating System Windows 98 2000 NT XP Vista Free Hard Drive Space 1 GB or greater RAM 512 MB or greater Processor Intel P3 or greater Processing Speed 1 GHz or greater N How g Processes Gravity Data g7 Absolute Gravity Data Acquisition and Processing Software This manual assumes the user is familiar with the operation of a Micro g LaCoste freefall gravimeter An object is dropped in a vacuum and a laser interferometer is used to accurately track the freefall The precise timing of optical fringes which provide distance information allows the acceleration of gravity g to be determined The g softwa
39. p different for each instrument to the requested transfer height e Measured Setup Height cm This changes from setup to setup e Barometric Factor uGal mBar Typically 0 3 uGal mBar e Polar motion X and Y components arcsec These need to be updated approximately once per week Current values are always available at http microglacoste com Note in previous versions of the g Software the Setup Height was referred to as the Reference Height and the Transfer Height was referred to as the Datum Height The name changes were done only for the purposes of clarity Convert Button use this feature to convert Degree Minutes Second DMS coordinates or Universal Transverse Mercator UTM coordinates to decimal degrees DD N System System The following parameters may be set from the System Page g7 Absolute Gravity Data Acquisition and Processing Software Instrument Instrument Type Select FG5 A10 or FGL Certain options are enabled or disabled according to the instrument selection S N Enter the serial number for note keeping purposes Laser Type Select the laser type and parameters associated with the laser o 100 Laser Voltage Wavelengths and Serial Number Enter the 1 voltages for each peak DEFG it is not necessary to enter values for HIJ if the measurement begins with peak D E F or G selected The software will use this voltage to determine the laser peak in use Ple
40. ponse disabled Figure 8 the green signal is the residual vector from the current drop while the blue signal represents the average residual of the accepted drops If the instrument is working properly the blue signal should ALWAYS be smaller in amplitude than the green signal Ifa drop is rejected it s residual signal is plotted in red If system response is enabled Figure 9 see System Response discussion below the orange signal is the compensated residual vector from the current drop the green signal is the uncompensated residual vector from the current drop and the purple signal represents the compensated average residual of the accepted drops Residuals Bee m Figure 8 Drop Residuals System Response Disabled 22 97 Absolute Gravity Data Acquisition and Processing Software s N A A it Figure 9 Drop Residuals System Response Enabled Sets The Sets view displays individual set gravity values minus the mean value of the project Each set is plotted with an error bar that indicates the range of the uncertainty for the individual set based on the drop scatter The top of the view informs the user of the current cumulative mean for the project the set to set scatter and the total uncertainty of the project mean For g Versions 6 and later the current set value will be updated with each drop this is true after the first set is complete This allows quick verification that the mean value is
41. re communicates with the Time Interval Analyzer TIA card in the computer to record the precise time of the zero crossing of the optical fringes Plotting the distance as a function of time results in the expected parabolic curve The precise formula is 1 0 ey 1 Bol Pu ten tU ol 5 73 C The complications arise due to the fact that the gravity gradient can not be neglected and that the path length of one of the interferometer arms is decreasing this latter effect is sometimes referred to as the speed of light correction The g software uses a least squares fit to calculate the best fit of the xi ti data to the above equation The free parameter of interest is g the acceleration X Xy t vef t t 1 This determines the best estimate of the absolute value of g at the beginning of the drop However to be a truly useful value a series of corrections are usually performed e Transfer Height Correction This transfers the gravity value from the height of the top of the drop which can change from setup to setup and from instrument to instrument to a more convenient value e Barometric Pressure Correction As the local air pressure changes so will the measured gravity value due to direct attraction comparing the current pressure with the standard local value the gravity value can be corrected to better estimate the value on a normal day e Earth Tide and Ocean Load Corrections As the earth changes
42. rections r Laser IV Barometric Pressure Lock Detection IV Polar Motion IV Auto Peak Detection Reference Xo Peaks wEo100G IV Transfer Height WEO Wavelength Modulation L pu Tidal Correction Uncertainty Ceea d Lap Apply Setup Compensated Setup Drop Rt Ft Sensitivity Start Time ms 44 01 Stop Time ms 201 56 ne 541 Start Fringe 30 TotalFringes 600 Stop ms 44 74 Update Fringe Windows Apply Figure 3 Process Setup Control Dialog Box Corrections e Barometric Pressure applies barometric pressure correction The observed gravity 1s normalized to a nominal pressure at each site by applying a correction based on the observed atmospheric pressure during the observations This pressure correction is applied at each drop The formula used to compute the pressure correction is C p A P o P n 13 N Where A The barometric admittance factor uGal mBar specified in the Information Setup This value is usually between 0 30 and 0 42 The recommended value per IAG 1983 is 0 30 C p Barometric Pressure Correction in Gal P o Observed barometric pressure P n Nominal barometric pressure in accordance with DIN Standard 5450 e Polar Motion applies polar motion correction This correction compensates for changes in centrifugal acceleration due to variation of the distance of the earth s rotation a
43. s datum transfer correction The gravity value is actually determined at the top of the drop inside the instrument dropping chamber This height can vary from instrument to instrument and is in general a not so useful location However the observed gravity for each drop can be transferred to a user specified height labeled transfer entered on the site information page Typical gravity transfer heights are 0 cm 100 cm or 130 cm often used for FG5s The transfer is calculated by adjusting the gravity value using the difference between the measured s height plus factory height and the transfer height and multiplying the difference by the site gravity gradient For more information see Niebauer et al A New Generation of Absolute Gravimeter Metrologia 1995 N Note that in earlier version of the g Software this was known as the Datum Height 97 Absolute Gravity Data Acquisition and Processing Software Laser WEO 100 o By selecting Lock Detection and connecting the Laser Lock signal from the back of the WEO 100 controller or the WEO 200 to CH 7 of the SIM or older Patch Panel units the software will ignore drops that occur while the laser is unlocked The software will then try another drop immediately until the laser is locked The software will then process drops it until it catches up with the desired drop interval o Automatic Peak Detection determines the locked peak by checking the input
44. shape due to solar and lunar attraction and as the mass of the oceans deform the earth s crust the local value of g will change by 100s of Gals Through empirically derived formulas these effects can be minimized to estimate the expected average value of g for any given time at the current location e Polar Motion Correction As the earth wobbles on its axis the local centripetal acceleration will change the local value of g By entering parameters related to the earth s current orientation this effect can be corrected N In addition to these environmental considerations there are also instrument details that need to be accounted for e Reference X Correction The mechanics of the dropping system are such that it cannot return exactly to the same height each time However xo is one of the free parameters in the equation of motion Using this value to normalize all of the drops to same height is technically necessary Note however that this correction is usually on the order of 0 01 Gal insignificant e The wavelength of the laser may change over the course of time or may hop to a new value mid measurement The software needs to be able to account for this 97 Absolute Gravity Data Acquisition and Processing Software The g software is a complete package designed to work with Micro g LaCoste absolute gravimeters to acquire and process gravity data In addition to the above calculations and corrections the software provides re
45. should be approximately e Top Start 25 15 ms e Top Stop 45 25 ms e Bottom Start 195 130 ms e Bottom Stop 205 140 ms System Response System response is an advanced fitting routine that fits multiple numbers of damped sinusoids to the standard equation of motion Note that in most applications it is not necessary to use system response It is designed for field applications in which the measurement surface is hollow or otherwise unstable In laboratory or stable pier type situations it will not be necessary to use System Response Because System Response can mask a problem with the site by flattening out a residual signal that would otherwise indicate a problem it is recommended to only use System Response in post processing mode 16 N g7 Absolute Gravity Data Acquisition and Processing Software Frequency Response Setup Max Number of Terms 3 Significance Threshold 0 7 Minimum Frequency Hz 15 cea Figure 4 System Response Setup Dialog Box To apply System Response check the box and press the Setup button The menu shown in Figure 9 to the right will appear It is recommended to accept the default values of 3 terms 20 significance threshold and 15 Hz When System Response is enabled it is possible to view the Power Spectral Density of the Residual Signal Uncertainty Drop rejection significance determines which drops are automatically rejected by the software
46. struments as determined by Micro g LaCoste and the Laser Modulation frequency as determined by Winters Electro Optics WEO Open This option opens an existing FGS file Close This option close the current FGS file Save This option saves the current FG5 file Save as Project This option allows you to save a copy of the current FG5 file to disk marking the file as real time as opposed to Post Mission The current 5 file is closed and the copy is opened Save as Template This option allows users to write a copy of the current project file to disk marking the file as a GTF These files are usually not edited and the user cannot acquire data with a GTF file GTF files are meant to be used for creating new FGS files or other GTF files Export g employs it s own binary format when storing both the header fg5 and set gravity data gsf For archiving and certain analysis purposes g also allows the exporting and importing of ASCII data Real time processing is still carried out using the g format but in replay mode and ASCII version of the data can be created by pressing Export This creates two files that are editable with any plain text editor e lt project name gt fgS txt this file contains all of the project Setup information Information System Acquisition Control and Comments as well as any processing information 39 N e lt project name gt gsf txt this file contains all of raw grav
47. struments and observations taken from these types of instruments should be weighted much more than those taken from an FgL Recommended values for modeling uncertainties are g7 Absolute Gravity Data Acquisition and Processing Software Laser 0 05 uGal WEO 0 1 uGal ML 1 Clock 0 5 uGal Rubidium Oscillator System Model 1 1 uGal FG5 10 wGal A10 5 wGal A5 10 wGal FGL e Environmental Environmental errors are highly site dependent and should be modified by only experienced users Recommended values for all environmental uncertainties are 0 0uGal zero unless a user is very knowledgeable about the site in question e Set up Set up uncertainties are depending on both the instrument AND the operator For example and experienced operator can set up an FG5 with a system error of 1 0uGal An experienced relative meter operator can measure a gradient to 0 03uGal cm Set up errors change according to the instrument and may be increased with respect to the operator e Gradient 0 03 uGal cm For experienced relative meter operators Comments Users may enter up to 100 lines of field or processing notes in this section To enter a new line press Ctrl Enter 19 N Beginning Acquisition or Reprocessing g7 Absolute Gravity Data Acquisition and Processing Software Start Processing Once g is setup according to user set parameters it is ready to begin processing the data Processing can be started three ways 1 Select Go fr
48. ter Table 0 Barometric Unmodeled 0 Polar Motion 0 05 r System Set up Laser 0 01 System 1 EN E Grad Uncert u 3al cm 0 03 System Model ual 1 Gradient BE Uncertainty due to gradient depends on vertical transfer System Model FG5 Em Total quadrature Systematic Uncertainty 2 02 Update toes Figure 5 Systematic Uncertainty Setup Dialog Box e Modeling Modeling uncertainties usually do not vary from station to station or among different instrument serial numbers or models Recommended values for modeling uncertainties are Barometric 1 0u Gal Polar Motion 0 05 Gal The errors for the earth tide and ocean load calculations are estimated as fractions of the size of the actual correction determined at the time of the measurement and are nominally Earth Tide 0 001 x Correction Ocean Load 0 1 x Correction For example if at a given time the earth tide correction is 50 ui Gal then the uncertainty on the correction is 0 05 uGal The default values are guidelines only For details including position and seasonal variation see Niebauer et al A new generation of absolute gravimeters Metrologia 1995 18 N e System System uncertainties vary depending on what elements are contained in the absolute gravimeter system 5 are the most accurate and precise MGS in
49. ters may not be changed in post processing e Control parameters may be changed with the exception of the laser lock WEO or alternate ML1 functions e Comments 97 Absolute Gravity Data Acquisition and Processing Software Output File Status After starting to reprocess data g will prompt the user whether or not to overwrite the current existing Project and Set summary files g creates two output ASCII text files by default the Project Summary and Set Summary File By default the files are named lt project name gt project txt and project name gt set txt In some cases users will want to change the names of the output files to preserve prior processing results For details of the ASCII output file structure and contents see Appendix 2 ASCII Output Files Let s select No and enter our own default base name goutputl By default then g will create two ASCII text files goutputl project txt and goutputl set txt After pressing the button g will begin processing the data Selecting Yes would simply overwrite the lt project name gt project txt and project name gt set txt files Processing Status With the default windows displayed State Drops Sets and Fit Residuals the user is able to quickly evaluate the status of data processing In the figures below we have set a break point at Set 3 to pause the processing The screen in Figure 13 is captured immediately following the last process
50. x Project contains information pertaining to the current state of the project through the last processed set In this case Set 2 The average time of the sets is shown 00 46 41 the day of the year and last two digits of the current year 01002 implies the tenth day of the year 2002 the number of sets processed 2 the average corrected gravity 979647289 79 the set to set scatter in wGal 0 94 the set uncertainty in Gal 2 13 and the average applied corrections in uGal Processing Finished Processing is complete when the two beeps sound from the computer s speaker NOTE the beeps do not sound from an installed sound card but ONLY the computer s local speaker and when the bottom message window indicates Finished For our example the final gravity value is 979647292 67uGal with a set scatter of 2 26uGal and a total uncertainty of 2 24uGal Reviewing Processing Results Remember when we changed the output name to goutputl If we use Windows Explorer to navigate to the gSampleData directory we will see two new files goutput l project txt and goutputl set txt These files are ASCII text and can be opened with any text editor Project Summary File The project summary file is designed to be a snapshot of the acquisition and data processing It is intended to serve as the primary resource for archiving absolute gravity data The project summary file is reproduced below in Figure 15 Explanations of each line
51. xis from the gravity station This correction is normally re computed using pole positions that are determined nearest to the observation time for each station The formula specified in the IAGBN Absolute Observations Data Processing Standards 1992 is used The formula reads 1 164x10 25 4 ysin A 97 Absolute Gravity Data Acquisition and Processing Software where dg polar motion correction in 5 earth s angular rotational velocity rad s a semi major axis of the reference ellipsoid m geodetic latitude rad geodetic longitude rad x y polar coordinates in the IERS system rad Mean pole positions are determined at daily intervals and issued daily by the IERS Bulletin The Bulletin A containing the polar motion coordinates in final and predicted format is available at no cost on the web at http maia usno navy mil bulletin a html In addition the Micro g LaCoste website http www microglacoste com has daily updates of the polar motion as well e Reference Xo applies reference Xo correction In the equation of motion2 as used in g gravity is determined at to not at xo In order to calculate the gravity at the reference position the distance to the start position xo is multiplied by the site gravity gradient and used to correct the final calculated gravity value This correction is generally very small lt 0 05uGal e Transfer Height applie
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