Moving platform data reduction (C10)
Contents
1. Continue searching and splitting for all 6 start and end fiducial pairs When done you should have 13 groups in your dataset Press Cancel to close the Edit Find box Now that our dataset consists of mutiple groups we need to allocate each group a unique Seq line number With the Spreadsheet editor still open choose the Edit Replace function Click the Load Formula button and load Seq frm Click OK This formula overwrites the value of Seq and assigns a sequential number to each group in the dataset Now launch the Flight Path editor Load the marine_grav DIR dataset Zoom in on the survey area as you did before Choose Line Display Single Line in Red Highlight the first line number and click OK That line will display in red By choosing each line number in turn you can identify the line numbers of the three N S and E W lines of interest You should find that they correspond to lines 2 4 6 8 10 12 of our dataset We want to keep these lines and delete the rest 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 7 Library Help Top Library Help Top 4 Back gt Close the Flight Path editor Using the Spreadsheet editor navigate to Seq 1 Choose the Edit Delete Current Group function You may find it necessary to toggle to the next or previous group to force a screen refresh Navigate to the next Seq you wish to delete Seq 3 and repeat the deletion Con2. 4 Vcc 63 70 real 4 AL 72 79 real 4 AX 81 88 real 4 VE 90 97 real 4 AX2 99 106 real 4 Xacc2 108 115 real 4 Lacc2 117 124 real 4 Xacc 126 133 real 4 Lacc 135 142 real 4 Eotvos 144 151 real 4 longitude 153 165 real 8 PROJ GEODETIC WGS84 IsxX latitude 167 179 real 8 PROJ GEODETIC WGS84 IsyY velocity 181 187 real 4 heading 189 196 real 4 GROUP BY Seq You can run the INTREPID Import tool either interactively or in batch If you wish to run it in batch the task specification job file import_dat job is set up to perform the operation To run the task launch a command window and type the command fmanager exe batch import_dat job INTREPID imports the data and creates a Line dataset called marine_grav DIR This is our primary dataset Note that because we are creating a Line dataset we need to define a line or sequence number The format of the raw data does not include an explicit line number so we need to create one The Seq field in the DDF file is defined for this purpose It does not matter what value it is assigned on import so long as it exists We will be changing it later 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 4 Library Help Top Library Help Top 4 Back gt For the file S 133 ENV use ASCII Columns input format with the following data definition file DDF In our worked example this DDF is called import_env ddf TYPE LIN
3. Tension Beam Vcc AL AX VE AX2 Xacc2 Lacc2 Note at this point there is no Cross Coupling field in the dataset Tab to Levelling and allocate alias names for DateCode and TimeOfDay DateCode is aliased to YYYMMDD and TimeOfDay is aliased to timeofday You must also allocate an alias name for ObsGravity Currently this must be done manually Open the marine_grav isi file in a text editor and insert the line Alias ObsGravity in the Begin End syntax block for the field Gravity If you wish to allocate the alias names by using the batch language refer to the task specification job file alias job Reconstruct the cross coupling error field The cross coupling error field CC_reconstruct can be calculated from 5 of the monitors and the monitor gain factors using the following equation CCreconstruct Coen VCC Cye VE Cal AL AX Cax2 AXZ It uses the Marine Aquisition aliases to identify the monitor fields VCC VE etc These should be set to the unfiltered monitor fields as you did in Step 5 The monitor gain factors are stored in the gravimeter cfg file This process must be run in batch The task specification job file CC_reconstruct job is set up to perform the operation Once the job file has been run and the CC_reconstruct field has been created you must use the Project Manager to set the CrossCoupling alias to CC_reconstruct Note Under some circumstances you may get the following error
4. this example it is called reconstruct rpt The following diagram shows an example of the filtered contractor gravity versus the reconstructed lagged gravity The dataset used in this diagram is not the same as your test data Intrepid Profile Editor 3 6 release cut 114 5 x File Edit Layout Window Help f REQONS NRUCT_LOW 7490 8 Edit Profile vel Search Profile Line 50 7470 8 Zoom X 1 0 7460 8 Mouse Mode Move Points C Select Points C Query Points C Zoom p 72208 i paneo aopA peed i poeno l 9 Filter the reconstructed observed gravity signal The reconstructed observed gravity contains a lot of high frequency noise It is necessary to remove this noise by using the same filter that was used on the monitor data This is done before the crosscorrelation process so that the monitors and the reconstructed observed gravity will have a similar frequency content The filtering can be done either interactively or in batch The task specification job file filter_reconstruct job is set up to perform the operation 10 Calibrate correct for Eotvos Earth tide platform motion and drift The Stabilized Platform Correction performs several processes as follows Calibration and Conversion INTREPID converts the raw gravity reading as measured in counter units to relative mGal using a lookup table and interpolating between ranges Library Help Top 2012 Intrepid Geophysics 4 B
5. Accelerometer 2 Beam Velocity AX2 0 0000 Cross Accelerometer 2 XACC2 0 0000 Long Accelerometer 2 LACC2 0 0000 Stabilized platform corrections report He e He Fe He He ke He He He He ke He ke He e KKK He ke He ke ke He ke ke ke ke ke k k k k k k k k k k k k k k k k k k k k k k Intrepid Gravity v3 5 release cut 112 Start processing 16 5 2001 18 52 1 He e He Fe He He e He e He He ke He ke He e ke He ke ke ke He ke ke ke ke ke ke ke ke k k k k k k k k k k k k k k k k k k k kk k Calculating stabilized corrections for L amp R S meters For survey database DB grav Observed gravity field Converted gravity field Long Accelerometer Beam Position VCC Long Accelerometer Beam Velocity AL Cross Accelerometer Beam Velocity AX Square of the Beam Velocity VE Cross Accelerometer 2 Beam Velocity AX2 Cross Accelerometer 2 XACC2 Long Accelerometer 2 LACC2 DB grav Gravity DB grav CorrectedGravity DB grav Vec_filt DB grav AL_filt DB grav AX_filt DB grav VE_filt DB grav AX2_filt DB grav Xacc2_filt DB grav Lacc2_filt Easting Latitude DB grav Northing Northing Longitude DB grav Easting Velocity DB grav vel Bearing Heading North 0 DB grav Azimuth DateCode YYMMDD DB grav YYMMDD TimeOfDay decimal local hours DB grav timeofday Input datum Gravity units SN71 Milligals LCR_S LCS Meter S32 Adjustment to Manufacturers Scale
6. E char 1 4 character 10 Seq 6 6 integer 4 Year 6 9 integer 4 Month 11 12 integer 4 Day 14 15 integer 4 HH 17 18 integer 4 MM 20 21 integer 4 SS 23 27 real 4 Jday 29 31 integer 4 meter_id 33 42 character 10 meter_pressure 44 51 real 4 meter_temp 53 60 real 4 ambient_temp 62 69 real 4 k_ factor 71 81 real 4 Vcec_coeff 83 90 real 4 AL_coeff 92 99 real 4 AX coeff 101 108 real 4 VE_coeff 110 117 real 4 AX2_ coeff 119 126 real 4 serial_filt_length 128 131 real 4 QC_filter_length 133 136 real 4 GROUP BY Seq You can run the INTREPID Import tool either interactively or in batch If you wish to run it in batch the task specification job file import_env Job is set up to perform the operation To run the task assuming that the task specification file is called import_env job use the command fmanager exe batch import_env job INTREPID will import the data and create a Line dataset called marine_env DIR Note that because we are creating a Line dataset we need to define a line or sequence number Similar comments apply to the Seq field as before Define a fiducial field in our primary dataset Allocate some standard INTREPID alias names Then use the INTREPID editors to identify and define the NS EW lines of interest and delete non essential data such as transit lines To use the INTREPID editors to manipulate our data it is necessary to define a fiducial field essentially a sequential counter in our dataset Acqu
7. Factor 1 000000 Manufacturers settings Long Accelerometer Beam Position VCC 0 2350 Long Accelerometer Beam Velocity AL 0 2910 Cross Accelerometer Beam Velocity AX 0 2500 Square of the Beam Velocity VE 0 0066 Cross Accelerometer 2 Beam Velocity AX2 0 0000 Cross Accelerometer 2 XACC2 0 0000 Long Accelerometer 2 LACC2 0 0000 using the above given factors for each monitor to correct motion Performing an Earth Tide Correction step UTC offset Group 0 Number of raw obs 39225 Library Help Top 1 000 hr 2012 Intrepid Geophysics 4 Back gt
8. Gravity Processing The Corrected gravity field generated by this process has the following done to it 1 For each record where the navigation data is not nulled a cross correlation correction is computed using the filtered monitors and the gain factors The gravity screw reading is converted to an adjusted reading via the manufacturers lookup table The E tv s correction is computed The Earth Tide correction is computed The Absolute value at the Still or dock locations was added to all meter readings after subtracting the still value for the meter All of these corrections are added and form the basis of the output References Valliant Herbert 1986 The La Coste amp Romberg Air Sea Gravity Meter An Overview CRC Handbook of Geophysical Exploration at Sea 2nd Edition Chapter 7 LaCoste Lucien J B 1978 Cross correlation Method for Evaluating and Correcting Shipboard Gravity Data Geophysics Vol 38 No 4 pp 701 709 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Sample file listings List of aliases Library Help Top Alias Begin Fiducial Time_sec LineNumber Line X Y Easting Northing LineType Linetype TimeOfDay Time DateCode date Velocity vel Bearing Azimuth ObsGravity GRAVITY BEAM cc Vcc AL AX VE AX2 XACC2 LACC2 Beam CC_reconstruct Vec_filt AL filt AX fil
9. INTREPID User Manual Moving platform data reduction C10 1 Tibrary Help Top Back Moving platform data reduction C10 Top Introduction Typically gravity surveys are conducted as part of a seismic acquisition program In this chapter we will process some marine gravity data which has been collected onboard a ship using a LaCoste and Romberg S meter The LaCoste and Romberg Air Sea gravity meter Model S is essentially an electro mechanical device with the following modifications from the original land based meter the damping is much higher and the unit is on a stabilized platform with auto feedback to keep the meter spring tension tending to zero Monitors of acceleration and velocity of the motion of the stabilized platform are recorded along with a logged filtered observed gravity a spring tension and cross coupling The processing of marine or aircraft gravity data from the LaCoste and Romberg S meter follows the process derived from papers published by LaCoste 1973 and Valliant 1986 The main objective in the process is to use the monitor data to correct for the motion of the meter Factory calibration of the S meter gives the normal screw gravity look up table In addition there are 7 monitor gain coefficients used to compute zero correlation between the observed gravity and the monitors Location of sample data for Cookbooks Where install_path is the path of your INTREPID installation the project directory for th
10. The survey data becomes unreliable when the ship changes direction 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 6 Library Help Top Library Help Top lt 4 Back gt When you have completed this part of the exercise close the Flight Path editor Intrepid Flight Path Editor 3 7 release cut 278 oj x File Edit Line Display Point Display Grid Display Window Help marine_gray DIR rid Point Xx 120 5065 Y 35 8325 Line 2 FID1 8465 FID2 Dist m 0 0001 414 Value 1 20 506534 Km 0 252893 Zoom In E zoom Out Stop Redraw Mouse Mode C Zoom Query C Select Ends C Select Segmnt Next launch the Spreadsheet editor and load the marine_grav DIR dataset You may want to use the Re order columns function to rearrange the field ordering in the editor Using the Edit Find function search for the start fid of the first line segment In the Search For box type Time_sec 8465 and click the Forward button You can leave the Edit Find box open Under Edit choose Split Group At Current Row This operation will create a new group line segment in the dataset Next search for the end fid of the first line segment which is Time_sec 10521 In the Search For box type Time_sec 10521 and click the Forward button Under Edit choose Split Group At Current Row This operation will create a new group line segment in the dataset
11. ack gt INTREPID User Manual Moving platform data reduction C10 12 Library Help Top Library Help Top 4 Back gt Earth Tide correction The Longman Earth Tide model approximately describes the Sun and Moon tidal forces at any point and time on Earth Itis not numerically a large error correction typically 0 1 mGal applies E tv s correction The largest source of error is caused by the E tv s effect This correction compensates for the velocity of the gravimeter across the rotating Earth and it can typically be 15 mGal INTREPID uses the calculated ship or aircraft velocity and bearing to make this correction Cross correlation analysis and correction There should be no crosscorrelation between variations in observed gravity and variations in any of the monitors If crosscorrelation exists then the observed gravity signal is being affected by platform motion Correction for platform motion is achieved by subtracting fractions of the monitor data from the observed gravity to make a zero correlation Each monitor has a gain factor which determines what fraction of the monitor is subtracted There are two options for deriving the monitor gain factors STABILIZED_PLATFORM_CORRECTION This option uses the factory set gain factors for each monitor These are stored in the gravimeter cfg file STABILIZED_PLATFORM_CALIBRATE_CORRECT This option computes the gain factors by calculating how the observed grav
12. dd factory calibration information to the file gravimeter cfg The gravimeter cfg file is stored in the INTREPID config directory The S meter entry also allows for the extra calibration factors in the usual INTREPID block structure language syntax Normally when starting a job you would add a new entry to this file identifying the meter which was used to acquire the data In this worked example the S133 meter was used to acquire the data and we have already added an entry into the gravimeter cfg file for this meter The gain factors have been taken from the marine_env DIR dataset The entry for the S133 meter appears as follows GRAVIMETER 133 Parameters Begin qingdao test data Sept 2003 Calibration_Factor 0 9978 BEAM_SCALE_FACTOR 0 096360 VCC_MON 0 525 AL_MON 0 04580 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 8 Library Help Top Library Help Top lt 4 Back gt AX_MON 0 05 VE 1 064 AX2 0 33 XACC2 0 0 LACC2 0 0 Parameters End Allocation of standard field names and aliases Aliases can be declared either interactively or by using the batch language To declare them interactively use the Project Manager to highlight the dataset Tab to Fields then click under the Alias column and select the More option The Configure Aliases dialog box will appear Tab to Marine and use the pull down menus to allocate alias names for Spring
13. e Cookbooks sample data is install_path sample_data cookbooks For example if INTREPID is installed in C Program Files Intrepid Intrepid4 5 then you can find the sample data at C Program Files Intrepid Intrepid4 5 sample_data cookbooks For information about installing or reinstalling the sample data see Sample data for the INTREPID Cookbooks in Using INTREPID Cookbooks R19 For a description of INTREPID datasets see Introduction to the INTREPID database G20 For more detail see INTREPID database file and data structures R05 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 2 Library Help Top 4 Back gt Moving platform data reduction worked example Overview Import the raw data into INTREPID line datasets using the Import tool Use editors to identify and define NS EW lines of interest Create ancillary fields timeofday YYYYMMDD Add factory calibration information to the file gravimeter cfg Allocate standard field names and INTREPID alias names Reconstruct the cross coupling field from the monitor data Filter the monitor data to remove noise ON Oa fF wWOD Reconstruct the observed gravity signal from raw components 9 Filter the reconstructed observed gravity signal to remove noise 10 Calibrate correct for Eotvos Earth tide platform motion and drift 11 Use the profile editor to view reconstructed observed
14. ect monitors A report of the RMS of the before and after observed gravity curvatures is made together with the ratio Still Readings Datum Drift Correction The in port still readings are of use for two purposes A report for drift correction e A tie in to the Fundamental Network Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Example gravity processing reports Moving platform data reduction C10 16 4 Back gt Reconstruction of observed gravity report kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk Intrepid Gravity v3 5 release cut 112 Start processing 23 5 2001 10 8 37 He e He Fe He He ke He e He He ke He ke He e ke He ke He ke He ke ke ke ke ke ke ke ke k k k k k k k k k k k k k k k k k k k kk k Reconstructing Observed Gravity for a stabilized L amp R S meters For survey database DB grav Contractor supplied Observed gravity Reconstructed gravity field Spring Tension Beam Position Cross Coupling Gain Factor for Beam Slope DB grav GRAVITY DB grav reconstruct DB grav Spr_ten DB grav Beam_filt DB grav CC_filt 1 6001 LCR_S LCS Meter S32 Adjustment to Manufacturers Scale Factor 1 000000 Manufacturers settings Long Accelerometer Beam Position VCC 0 2350 Long Accelerometer Beam Velocity AL 0 2910 Cross Accelerometer Beam Velocity AX 0 2500 Square of the Beam Velocity VE 0 0066 Cross
15. gravity signal Preliminary notes Library Help Top The example data can be found in install_path sample_data cookbooks moving_platform The data we shall use for this example comprises three N S lines crossing three E W lines for nine intersections The data is in LaCoste and Romberg Air Sea System II format Air Sea System II produces two types of data files with file extensions DAT and ENV The data file has 21 comma separated records recorded once per second The environment file contains information about system conditions during data acquisition and includes the k factor and gain coefficients for the monitors It is recorded once every 10 seconds The data files are in the Rawdata directory and called S 133 DAT and S 133 ENV 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Moving platform data reduction C10 3 Library Help Top Steps to follow 1 Library Help Top 4 Back gt Import the ASCII files S 133 DAT and S 133 ENV into INTREPID line datasets For the file S 133 DAT use ASCII Columns input format with the following data definition file DDF In our worked example this DDF is called import_dat ddf TYPE LINE char 1 4 character 10 Seq 6 6 integer 4 Year 6 9 integer 4 Month 11 12 integer 4 Day 14 15 integer 4 HH 17 18 integer 4 MM 20 21 integer 4 SS 23 27 real 4 Jday 29 31 integer 4 Gravity 33 40 real 4 Spr_ten 42 49 real 4 Beam 51 61 real
16. he raw data contains some corrupted records which is affecting the latitude and longitude ranges Use the zoom function to examine the eastern end of the line If you zoom right in you will see the three N S lines criss crossing the three E W lines They are the lines we want to process Presently they exist as a single long line We need to split the single line into separate lines The other lines are transit lines which we want to delete from our dataset This process of preparing the data for processing may seem tedious but it is a necessary part of the data processing operation If you do not wish or do not have time to perform the editing and splitting of the dataset lines you can skip this section and proceed to Step 3 An edited and prepared dataset is included for you in the example data marine_grav_prepared DIR Dataset editing is best accomplished using a combination of INTREPID editors With the Flight Path editor open use the query function to report the start and end fiducial for each of the three N S and three E W line segments we want to process Starting at the western end of the northern most E W line the query function should report a start fid value of approximately 8465 and an end fid value of approximately 10521 Write these fids down as you go You should end up with six sets of start and end fids which define the start and end points of our six lines of interest Do not clip the lines too close to where the ship turns
17. in batch to perform this style of RC filtering You can experiment with different filters if you have time We have found that the RC style of filtering works best on very noisy monitor data Filter Processing This filtering is done using the line filter tool Note the data is collected on a one second basis so set Fid factor to 1 0 A job file to pass all monitors through whichever variation on filtering is required is used to automate this process The monitors filtered are VCC AL AX VE AX2 XACC2 LACC2 Each of these monitors is acquired at 25 Hz in real time in the ZLS system and logged at 1 second intervals The task specification job file ilter_monitors Job is set up to perform the filtering At this stage it is important to check the data visually to ensure that the filtering process is performing as expected From the INTREPID editors menu launch the Profile editor Load two or three of the unfiltered and filtered fields and visually check the results of the filtering The following is a snap shot of data demonstrating this The most important monitors are Beam CC Vcc AL VE and AX The other monitors play less part in the correction for a well adjusted meter Intrepid Profile Editor 3 7 release cut 280 loj xj File Edit Layout Window Help Edit Profile CC_reconstruct Search Profile 7 Zoom X 1 0 CC_FILT oat A i 4 ie X rm i Mouse Mode C Move Points vee C Select Points ji i C Que
18. isition time makes a suitable fiducial quantity however our dataset contains the time as HH MM SS which is not in a suitable format for us to use Therefore we will use the Spreadsheet editor to convert HH MM SS to time in seconds after midnight You can perform this operation either interactively or in batch If you wish to run it in batch the task specification job file convert_time Job is set up to perform the operation 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 5 Library Help Top Library Help Top lt 4 Back gt To run the task use the command fmanager exe batch convert_time job INTREPID will perform the task and create a new field called Time_sec This will be our fiducial field Having created a fiducial field we now need to define it as the Fiducial Alias so that INTREPID knows about it see example in List of aliases Launch the INTREPID Project Manager and navigate to your working directory Highlight the dataset marine_grav DIR and click on the Fields tab Set the Time_Sec field to Alias Fiducial Since it is a line dataset we also need to define a Line Alias so set the Seq field to Alias LineNumber Now we have defined appropriate fields as Aliases we can display our dataset in the Flight Path Editor Launch the Flight Path Editor and load the marine_grav DIR dataset It should appear as a single long line The reason for this is that t
19. ity correlates with all or some of the monitors INTREPID uses the curvature product cross correlation approach accumulating a matrix of all observations for straight line segments and solving them for a best fit Using the report which the process creates you can check for zero correlation line by line or for the total survey and recalculate line by line or total survey gain factors Meter drift absolute tie in The data can be corrected for meter drift by taking repeated Still readings during the course of the survey A Still value taken at the dock or airfield is used to tie in the relative gravity data to an absolute value The Stabilized Platform Correction process must be run in batch The task specification job file platform_correction job is set up to perform the operation It requires a meter number input dataset and observed gravity that can either be the contractor supplied or the reconstructed gravity The process writes out a report file which you should examine after running the process In this example it is called reconstruct rpt Peculiar to the marine gravity practice is the use of a linear curvature function to assess the derivatives of observed acceleration components and gravity This is used For the purpose of minimizing the cross correlation between ship movement and gravity As a spike detector in those parts of the survey that may be associated with ship turning or such like To assess overall im
20. message in the log file after running the batch file ERROR The input cross coupling data base field has not been defined If you get this error message then do the following Create a new field CC_reconstruct in the marine_grav DIR Alias it to CROSS_COUPLING Then rerun fmanager exe batch CC_reconstruct job Filter the monitor data to remove noise and reset INTREPID aliases to the filtered monitors 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Library Help Top Moving platform data reduction C10 9 lt 4 Back gt All monitors are to be low pass filtered The monitors are extremely noisy and this is a vital step The aim is to isolate those frequencies in the monitor data that is associated with wave action so the LowPass is designed to filter out spurious high frequency noise The contractor used 10 minute RC filtering as a Quality Control measure during data acquistion and so introduced a lag of 300 seconds into the Observed Gravity record 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Moving platform data reduction C10 10 Library Help Top Library Help Top 4 Back gt RC Filtering LaCoste recommends 3 passes of 27 sec and 2 passes of 150 sec using RC resistance capacitance type filters A Compound filter has been set up in the INTREPID filter library that can be used by the line filter tool either interactively or
21. provement in gravity estimation as measured by the ratio of RMS of before and after signal 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 13 Library Help Top 4 Back gt The report file contains a summary of curvature for the input and output fields It also quotes improvement in ratio of curvature as ratio of RMS of output over input on a line by line basis and also a total survey basis The report should be examined carefully The aim is to get the ratio as low as possible indicating that the processing has resulted in a smoother gravity signal even though it has had no more filtering An improvement ratio of 0 9 is typical for this dataset Hint Unless a large amount of data taken with many different headings are analysed it is not safe to use more than two or three monitors in the crosscorrelation because the monitors are not entirely independent The report also contains a summary of the cross correlation calculation in the form of a matrix of cross correlation coefficients for all monitors and observed gravity The first row gives the correlation coefficient for each monitor correlated with observed gravity A correlation coefficient of unity indicates perfect correlation and zero indicates no correlation A negative value indicates the signals are out of phase 11 Use the profile editor to view the reconstructed observed gravity signal Generated Outputs from
22. ry Points i C Zoom i 4 gt Navigate By Line C Fid in line lt lt Previous lt lt Goto gt gt Next gt gt Having done the filtering you now need to re define the INTREPID Marine Acquisition aliases to point to the filtered fields Aliases can be defined either interactively or by using the batch language as you did previously The INTREPID aliases should now point to the following fields Vec_filt AL filt AX_filt VE_filt AX2_filt Xacc2_filt Lacce2_filt 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Moving platform data reduction C10 11 Library Help Top lt 4 Back gt 8 Reconstruct the Observed Gravity signal The contractor supplied observed gravity field is heavily filtered Typically they may use a 10 minute filter The observed gravity can be reconstructed and less heavily filtered to increase the signal content This is done from the raw components of the measurement namely Spring Tension Beam velocity and Cross Coupling correction Reconstruct G Spring k Beam CrossCoupling The factor k is the gain factor to calibrate the beam slope to mGal and is provided in the calibration table For 133 this is 0 096360 Units are Still meter units This process must be run in batch The task specification job file gravity _reconstruct job is set up to perform the operation The process writes out a report file which you should examine after running the process In
23. t VE_filt AX2 filt Xacc2_ filt Lacc2_ filt VCCPHASE VCCPHASE AXPHASE AXPHASE ALPHASE ALPHASE Alias End 2012 Intrepid Geophysics Moving platform data reduction C10 14 4 Back gt 4 Back gt INTREPID User Manual Moving platform data reduction C10 15 Library Help Top lt 4 Back gt Detailed explanation of other inputs and options Lag factor The data may lag as it is filtered in the hardware Thus a Lag factor in reading units for a reading every second is required and for a 10 minute averaging scheme a reading is logged 5 minutes behind or 300 seconds In the Marine Begin End block set GravityLAG 300 E tv s Make the E tv s correction In the Marine Begin End block set IgnoreEotvos No A velocity and latitude are required for this The velocity alias must be set A user friendly code option to convert from UTM to latitude obviates any special action for the latitude Do Earth Tide Correction In the Levelling Begin End block set SkipEarthTideCorrection YES NO Offset of Time Zone from UTC in hours In the Marine Begin End block set UTC_Offset 1 Other required time fields for this are TimeOfDay in decimal hours set via the alias And also DateCode in YYMMDD format also set by alias Do the Cross Correlation correction In the Marine Begin End block set IgnoreDecorrelation No Also make sure the alias fields are pointing to the corr
24. tinue deleting the non essential lines until the dataset contains only the six lines we are interested in When you have done this re sequence the lines using Edit Replace Load Formula Seq frm Exit from the Spreadsheet editor Launch the Flight Path editor and load the marine_grav DIR dataset Check that you have three E W and three N S lines in the dataset Use the INTREPID editors to create some additonal fields timeofday YYYYMMDD which are required for the processing of the data Note If you skipped the editing section of the tutorial you will need to rename the supplied dataset marine_grav_prepared DIR to marine_grav DIR in order that the supplied batch job files work correctly Use the Project Manager to rename the dataset In addition to the fields already in the dataset INTREPID requires some extra fields to be created We need to create a timeofday field which is time in decimal hours and also a YYYYMMDD field which can be easily created since we already have the Year Month and Day in our dataset You can perform these operations either interactively or in batch If you wish to run them in batch the task specification job files timeofday job and YYYYMMDD job are set up to perform the operations To run the tasks use similar commands as before eg fmanager exe batch timeofday job fmanager exe batch YYYYMMDD job INTREPID will perform the tasks and create new fields as specified by the task files A
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