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Line correction and tie levelling (T30)

1. Not withstanding this dilemma there are simple trasnform that can successfully be undertaken using gravity gradient component measures that are non conventional this part of the tool is strictly alpha only as there are still no fiully operational Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 54 Library Help Top lt 4 Back gt examples of commercial grade systems in operation as yet f o e Choose Single Gradient Corrections Input Altitude Correct Vertical Gradient Profiles Altitude Correct VKa C Altitude Correct VKc All need required height above ground Output Gz C Gzzz C VKe Average Flying Height 0 000000 Average Latitude OK Cancel The options deal with converting a Rio style instruments signal to other more conventional signal types Tensor Corrections Library Help Top New to V4 5 is the tensor corrections selections While many of the previous algorithms already work on the generalised notion of a geophysical signal some tensor specific algorithms are also required that do not work on scalar signals Some of these are light weight as in the Earth effect for the Full tensor Gravity Gradiometry signal and some make heavy use of local approximation theory based upon 3rd order truncated Fourier series equation fitting f E Choose Required Tensor Corrections CoordSys ENU Some require an
2. 4 Back gt Stage 3 Levelling the individual acquisition lines After we have levelled the flights there may still be some residual errors that are line specific e g heading errors See Heading corrections for errors due to aircraft direction for a description of these errors INTREPID calculates least squares fit curves for the misclosures along each line and uses then as sources for the corrections to their respective acquisition line Signal values For a diagram of this operation refer to the diagram of step 2 in the tie line levelling stage above The acquisition line correction is similar except that you are calculating the curve along the acquisition line instead of the tie line This step is sometimes described as Drifting the acquisition lines individually to the tie lines Stage 4 Levelling the individual tie lines again After we have levelled the individual acquisition lines there may be some remaining residual errors in the tie line Signal values If you perform this step INTREPID calculates least squares fit curves for the misclosures along each tie line and uses then as sources for the corrections to their respective tie line Signal values For a diagram of this operation refer to the diagram of step 2 in the tie line levelling stage above This step is sometimes described as Drifting the tie lines individually to the acquisition lines Additional information about polynomial levelling INTREPID can w
3. We generalise all statistics for fields in the same way We have rewritten all operations such as interpolation and filtering support the new data types Tie Line Levelling Pro includes a new section especially for tensor data This is particularly useful for gravity tensors You can add or remove Earth effects We have generalised the Heading correction to take advantage of the fact that for most surveys there are 4 cardinal directions employed during surveying the survey team gathers group statistics for these 4 directions and we use such data as the various systematic tensor and vector differences as the basis for the Heading correction This avoids the difficult task for the user of having to estimate these heading errors before being able to apply the correction There is also a new Altitude correction This uses a locally fitted truncated Fourier series to the potential With this series on an observation by observation basis we make the altitude adjustment to a drape surface The Loop levelling algorithm is a least squares minimum residual method We also rewrote this to so that it works on Tensor data The Frobenius norm of the cross over difference has proven a driving measure to minimize residuals As well as Tensor the other common case for airborne geophysics is the observed scalar field together with measured gradients Tie Line Levelling Pro uses a single pass method to level the complete signal Tie Line Levelling Pro can p
4. At each crossover point there may be a misclosure or difference between the Signal values on the acquisition and tie lines INTREPID examines the misclosure of a target crossover and that of its four neighbours along the lines For example in the above diagram crossover A has neighbouring crossovers with misclosures M M4 INTREPID makes a first estimate of the correct value for each crossover as the mean of its two Signal values It then adjusts the proposed correction of the target crossover using the current estimates for the neighbouring crossovers and their average original misclosure After calculating a new current estimate for the target crossover INTREPID then makes the next crossover the target crossover This would be crossover B in the diagram above and crossover A becomes one of its neighbouring crossovers and performs the same adjustment for it INTREPID continues until all it has adjusted all crossovers INTREPID then repeats the process on all crossovers in reverse order This two way pass makes up one loop closure iteration INTREPID performs a number of iterations and notes the changes to the crossover estimates Repeated iterations will reduce and distribute the overall misclosure for the dataset INTREPID terminates the iterations after it has performed a specified number or when the average change for crossovers falls below a specified level This algorithm can be simply improved to also follow the same st
5. To load an existing crossovers dataset use Load Crossovers from the file menu INTREPID displays the crossover data graphically See Calculating crossovers and Creating and Using Crossovers Datasets for detailed instructions 7 Disable crossovers you wish exclude from the levelling process if any See Excluding crossovers from the levelling calculation for instructions 1 This summary assumes that you are performing an entire typical levelling process in one session You can save intermediate data and continue work in a different session or repeat stages of the process as required You can vary many of the steps described here See the following sections of the manual for more detail Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 5 Library Help Top 8 10 11 12 13 14 Library Help Top 4 Back gt Specify the corrections you require Use the options in the Corrections menu entering any parameters required in the dialog boxes that INTREPID displays See INTREPID Levelling corrections and the sections following it for detailed instructions Some corrections require preliminary operations before you select their option from the Corrections menu If you are performing Diurnal corrections you must load the base station dataset before specifying the correction See Diurnal corrections for instructions If you are using Polynom
6. Earth s core magnetic field The zero settings of older magnetometers vary exponentially with time this is called magnetometer drift Measurements will be affected by the ground clearance of the survey craft Luyendyk 1997 gives a comprehensive description of the sources of error in aeromagnetic surveys and the corrections that can be applied The Levelling tool will assist you to correct these errors It measures and represents graphically the discrepancies between your acquisition lines and tie lines It then corrects your data using the geomagnetic reference data and by comparing it with tie line and base station data Levelling Pro Library Help Top The Pro version of the Tie Line Levelling tool uses sophisticated tensor and gradient methods for altitude and heading correction and for loop levelling It uses the same task description job language as the standard version At v5 0 this is depricated by a new GOOGLE protobuf syntax that describes all this tool s processes in a unique and fully transparent language which INTREPID is publishing along with new example instances of the task control language duplicating all the previously published examples The V5 0 strategy is to support both old and new syntax to allow you to transition and verify that all works as required This means that the algorithmic compatibility for all existing scalar geophysics measurements is also extended to include support for new tensor
7. INTREPID can create a crossovers dataset which consists of all the crossover points in the original line dataset including the unadjusted and adjusted values for a specified data field The crossovers dataset mimics the original dataset in that it is a line dataset covering the same region with the same number and location of lines It differs in that it contains only data points which occur at the crossover points Crossover datasets act as a check point allowing you to investigate and reflect on your current task using them instead of always having to re establish them from the original data INTREPID does not save any Levelling parameters you have specified When you load a crossover dataset to continue working with it you need to respecify the corrections You can perform trial gridding on crossovers datasets and examine them using INTREPID tools such as the Spreadsheet Editor Profile Editor and visualisation tools 1 4 The grid may provide an aid to interpreting the crossovers dataset even though it may not resemble a conventional grid Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 56 Library Help Top lt 4 Back gt Saving and loading crossovers datasets gt gt To save the crossovers Calculate the crossovers then choose Save Crossovers from the File menu INTREPID displays the Save Crossovers dialog box Specify the name of the cr
8. If you retrieve a crossover based proposed correction it becomes the current proposed correction for its correction type If you do not retrieve a crossover based proposed correction the corresponding correction type will have no current proposed correction Immediate proposed corrections are for information only in the crossovers dataset and have no effect on any immediate correction operation in this tool See Creating and Using Crossovers Datasets for further information about crossovers datasets When you choose Apply Corrections INTREPID uses the current proposed correction for each crossover based correction type 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 25 Library Help Top lt 4 Back gt Clearing beta misclosures The beta misclosure is a running total of the current proposed corrections INTREPID does not use it in the correction process You can clear 1 e set back to equal the original misclosure beta misclosures from the dataset if you wish If you clear the beta misclosures you will no longer have a running tally of the corrections made in the current session Clearing the beta misclosures has no effect on any proposed corrections or immediate correction specifications gt gt To clear the beta misclosures Choose Clear betas from the Crossovers menu J Intrepid ProLevelling Tool File Corrections Display Tie Management CrossOver Manag
9. Markers Red ve as a t K t t E Colour Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 60 Library Help Top lt 4 Back gt Crossover and line display options You can view a wide variety of crossover data graphically in the dataset display area INTREPID represents the values as markers or using colours for different ranges See Display style markers vs colours for details gt gt To choose a display option Choose the data for display using the Display menu or its cascades I J Intrepid ProLevelling Tool Acq Lines Acq Gradient Acq Flights Acq Corrections gt Tie Lines Tie Gradients Tie Flights Tie Corrections gt Gradient Diffs 5997 5 4 Misclosure Betas Crossovers Elevation Mis 5995 0 Clear Viewer BEER Hebe tet tt EE z He Hee ttt tt tt ttt a o era E Ey pid rteeting Tol irvepd Poteveting T N nvcpd Potvin T File Corrections Tie Management CrossOver Management Ma File Corrections Display Tie Management CrossOver Management Magn Acq Lines Misclosures Acq Lines Misclosures Acq Gradient t t Acq Gradient H kd 6000 0 Acq Flights H Hi Hi 6000 0 Acq Flights kaj E E Acq Corrections gt T Acq Corrections gt Heading z Tie Lines t Tie Lines XYmove ak Tie Gradients af Tie Gradients Diurnal es Tie Flights f Tie Flights GR
10. One Flight for Tie option from the Tie Line menu All Flights for Tie If you choose this INTREPID displays the profile for the whole tie line One Flight for Tie If you choose this INTREPID displays the profile for crossovers whose acquisition line belongs to one selected flight 3 Choose the display option you require from the Display Tie Graph cascade in the Tie Line menu E Intrepid ProLevelling Tool File Corrections Display Tie Management CrossOver Management Magnetism BaseStatior Create List Show List Complete List 6000 0 Delete List Load List Save List All flights for Tie One flight for Tie Display tie graph gt 5997 5 wn i 5995 0 Tie line value wt Misclosure Elevation Misclosure Poly Correction Betas fea E The profiles will show the values specified for each crossover Readings The original Signal value of the tie line Acquisition line gradients The gradient of the acquisition line Signal values Tie line gradients The gradient of the tie line Signal values Tie line gradient weights The Polynomial levelling weights for the tie line gradients See Crossover weighting methods Tie line value weights The Polynomial levelling weights calculated as VSignal values See Crossover weighting methods Misclosures the difference between acquisition and tie line Signal values Polynomial Corrections The c
11. Original crossover point on other line direction perpendicular to page surface in this diagram A New crossover point on higher gradient line with zero misclosure Using the Level XY correction Library Help Top The Level XY correction alters the X Y and Signal values of the data gt gt To use the Level XY corrections 1 Ifyou have not already done so e Perform Parallax Diurnal and GRF corrections as required then commence a new Levelling session Reconstruct the flights Calculate the crossovers for the dataset 2 Choose Level XY from the Corrections menu INTREPID displays the Level XY radius of influence dialog box Enter radius of influence Enter radius of influence 5 0 _Ok Cancel 3 The radius of influence is the radius in metres within which INTREPID may extrapolate along the gradients searching for points of zero misclosure Enter the required radius of influence in the text box 1 You may perform Diurnal and GRF corrections simultaneously with the Level XY correction if you do not need to examine their results before proceeding 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 38 Library Help Top lt 4 Back gt 4 Choose OK INTREPID will calculate proposed corrections for all enabled crossovers It can display the proposed corrections as line vectors in the dataset display area See Crossover and li
12. The best direction and method of extrapolation is to change X Y and Signal values in a direction along a straight line with the following characteristics It passes through the higher gradient crossover point e It has a gradient equal to the crossover gradient The direction makes the higher gradient crossover Signal value approach the 1 This may be any measure of sensor height See Using different height measures for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 36 Library Help Top lt 4 Back gt corresponding crossover Signal value in the other line Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 37 Library Help Top lt 4 Back gt 5 Within a radius that you have set as a limit you may find a point on this extrapolation line where the Signal value is equal to the other crossover Signal value zero misclosure Adopt this new point as the correct crossover point This involves changing the X Y and Signal values of the crossover XY Level Correction Process Gradient line at crossover A JN A e B i I 1 i I 1 i I i i V V N Higher gradient line profile gt Radius of influence i gt Higher gradient line direction A Original crossover point on higher gradient line B
13. compute a fixed elevation GRF using the nominal sensor height click Cancel 5 Choose OK INTREPID will note the corrections and apply them next time you choose Trial Corrections or Apply Corrections 1 op cit p 33 2 This may be any measure of sensor height See Using different height measures for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 35 Library Help Top lt 4 Back gt GRF Parameters Survey date and height AGRF IGRF See The geomagnetic reference field in INTREPID R15 for an explanation of these parameters i GRF computation interval Since the GRF field varies very slowly within surveys a single correction applied to a number of points within one line segment may be accurate enough instead of calculating the GRF for all points The GRF computational interval is the length of the line segment for which a single GRF correction value will suffice The computation interval need not be small INTREPID calculates the GRF correction for the centre point of each interval It then interpolates individual corrections for each data point between the centre points The default of every 100 m is reasonable We recommend that this interval be not more than 1 3 of the line length Of course if measuring magnetic tensor data a GRF correction is not likely to be needed as a gradient measure does not contain any Common Mode signal or another way
14. correction parameters you have specified for the four directions If you do not know how to estimate the Heading errors in this context INTREPID The Heading correction alters the Signal values of the data INTREPID gt gt To specify the Heading correction 1 Choose Headings from the Corrections menu INTREPID displays the Headings corrections dialog box Enter Bearings Correction factors from North deg nT deg nT deg nT deg nT note a minimum of 4 and u eee Enter Bearings Correction factors from North deg nT deg nT deg nT deg nT note a minimum of 4 and up to 10 pairs 0 0 0 0 90 0 0 0 180 0 0 0 270 0 0 0 Estimate 4 flight direction heading errors Ok Cancel 2 Enter four directions and the adjustment for each direction using the format d a d a d a d awhere dis the direction in degrees from North a is the adjustment in nanoTeslas nT For example 0 0 2 0 90 0 3 0 180 0 0 0 270 2 0 3 Choose OK INTREPID will note the corrections and apply them when you choose Apply Corrections Gradient Extensions As it is difficult to see how you can specify a tensor heading correction in a simple manner along the lines of a pop up dialog box INTREPID instead relies on the automatic estimation from statistics approach for a Heading correction for a tensor vector signal It is proposed that a Heading correction is in fact a compromised concept and a Full Rotational levelling correction is the
15. elevation field Remove Gravity Earth Effect C Add Gravity Earth Effect C Remove Average Line Tensor Heading correction in 4 main line directions C Remove Average Flight Tensor Flight bias corrections Reconstruct flights first Estimate Tensor Error Norms C Estimate Vertical Component from FTG Report each line separately C Altitude Correct Tensor Profiles Potential Needs Required drape elevation Average Flying Height 0 000000 Average Latitude 0 000000 Required samples for estimating potential ju A truncated piecewise 3D Fourier series is used OK Cancel All the methods in this section are profile based The first two options are FTG specific with a simple model for the Earth gravity tensor effect at the surface based around the Free Air correction gradient of 3048 Eotvos As most survey data does not have this portion of the signal present as it is not really being measured this is academic The option to remove a calculated Heading tensor error in each of the 4 cardinal flying directions for a standard survey is given next If you try this examine the 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 55 Library Help Top lt 4 Back gt levelling report to make sense of the statictical reporting followed by application of average difference tensors The next option is similar but is flight based statistically Estimat
16. not assigned aliases or if some aliases are missing INTREPID will also prompt you to specify the fields missing See the list above 1 If your Fiducial field is missing you can create a fake fiducial field for the data using the Spreadsheet tool Create a new field called FID and generate a unique fiducial number for each point in the dataset See Frequently asked questions in Spreadsheet Editor T15 2012 Intrepid Geophysics 4 Back gt Library Help Top INTREPID User Manual Line correction and tie levelling T30 10 Library Help Top 4 Back gt Specify Output Because some of the corrections involve changes to the location data you will need to save new sets of X and Y values as well as Signal values You can save output corrected values to the output X Y and Signal fields or output the corrections themselves To output corrections turn on Output Changes Only in the Levelling window To output corrected values ensure that the check box is turned off Choose Specify Output from the File menu INTREPID displays Save dialog boxes for X Y and Signal in turn For each specify the name of the new file or the old one if you wish to overwrite it Load Crossovers If you have previously saved a crossovers dataset for the current levelling task use this to load the crossovers dataset into the Levelling tool See Creating and Using Crossovers Datasets for details Save Crossovers After you have calcu
17. proper way to think of this class of systematic 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 27 Library Help Top 4 Back gt error Parallax corrections cable length Acquisition instruments are usually in a different position to the navigation instrument Parallax corrections involve a slight adjustment to the location of the data to allow for this positional effect INTREPID will adjust all points to have a different location It bases the new location on e The reported geographic location X and Y The direction of travel The separation of the instruments The Parallax correction alters the X and Y values of the data gt gt To specify Parallax corrections 1 Choose Parallax from the Corrections menu INTREPID displays the Parallax corrections dialog box Choose Correction Method Choose Correction Method Cable Length Correction m 20 000000 Ok Cancel 2 Enter the separation in metres into the Cable length text box 3 Choose OK INTREPID will note the corrections and apply them when you choose Apply Corrections Diurnal corrections The background radiation or magnetism may fluctuate during surveys These are called diurnal fluctuations because they vary over a 24 hour period with some regularity Some are attributable to sun spots These fluctuations can occur during the course of a flight and so can conf
18. should set the Fiducial factor to 1 Reconstructing the flights gt gt To reconstruct the flights 1 Ensure that you have assigned the time field to the Fiducial alias if required commenced the Levelling session and specified the input Signal field to be levelled 2 Choose Date Time Fiducial or Julian Day Time Fiducial from the Reconstruct Flights cascade in the File menu INTREPID will prompt you to specify the date or the Julian day field depending on the option you chose from the Reconstruct Flights cascade 3 Specify the flight date field 4 INTREPID will prompt you for the flight start time field If you assigned the time field to the Fiducial alias do not specify the same field as the start time field here If a flight start time field exists specify it here other wise choose Cancel 5 Ifyou specified Date Time Fiducial INTREPID displays the Fid Factor and Date Format dialog box If you specified Julian Day Time Fiducial INTREPID displays the Fid Factor dialog box Enter FID Factor sec FID amp date s Enter FID Factor sec FID Enter FID Factor sec FID amp date style Enter FID Factor sec FID YearMonthDay Ok Cancel C DayMonthYear Ok Cancel Enter the fiducial factor This would normally be 1 if you assigned the time field to the Fiducial alias 6 Specify the date format if required 7 Choose OK INTREPID will reconstruct the flights Library Help Top 2012 In
19. tie line and the tie line order Loop closure levelling The loop closure method repeatedly adjusts the Signal values in the acquisition lines to minimise overall misclosure for the dataset and distribute the residual errors This method is simple and fast to use but results may be unstable in high gradient areas gt gt To specify loop closure correction 1 Ifyou have not already done so and it is appropriate Perform Parallax Diurnal and GRF corrections as required then commence a new Levelling session Reconstruct the flights e Calculate the crossovers for the dataset 2 Choose Loop closure from the Corrections menu INTREPID will calculate proposed corrections for all enabled crossovers It can display the proposed corrections as colours or red black crosses in the dataset display area See Display style markers vs colours and Crossover and line display options for instructions 1 1 Luyendyk A P J op cit p 36 2 2 You may perform Diurnal and GRF corrections simultaneously with the Loop closure levelling if you do not need to examine their results before proceeding Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 52 Library Help Top lt 4 Back gt The loop closure process The loop closure process is described in detail by Green 1983 ws A set of acquisition and tie line form a grid as shown in the diagram above
20. tie lines individually to the acquisition lines Stage 1 Levelling the tie lines 1 We select the principal tie line It should have the following characteristics It should be one that was flown during a period of quiet diurnal activity Be located over a region of low magnetic relief and Be located approximately at the centre of the survey region 2 INTREPID creates a polynomial function f fid along a flight The function s curve is a least squares fit of the misclosures on the principal tie line We assume that the principal tie line contains no levelling errors so this curve represents acquisition line only errors 1 Luyendyk A P J op cit p 35 Bullets added 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 41 Library Help Top Library Help Top 4 Back gt 3 INTREPID examines the second tie line s misclosures and records their offsets from the curve created in step 2 Since the curve represents acquisition line only error these offsets must be errors in the tie line Signal values for the second tie line Levelling of tie line data Step 1 First estimate of the acquisition line only error curve x E E x x S g 2 i x 2 x am a gt v n Time along flight Misclosures on principal tie line The curve is calculated by least squares fit to misclosures on the principal t
21. vector measures for all the supported levelling methods You can easily assess it relative to the existing 1 Luyendyk A P J 1997 Processing of airborne magnetic data AGSO Journal of Australian Geology and Geophysics 17 2 31 38 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 2 Library Help Top 4 Back gt production tool We retained the GUI of the old tool but made engine room improvements one by one We completely rewrote and restructured the engine room to use INTREPID s powerful data objects Tie Levelling Pro can process any of the new vector tensor quaternion style data fields in a database However probably the best way to check on available functional status of any of the levelling methods is to directly examine the intrepid tasks proto file at V5 0 to confirm what you would like to do is supported The complete re write and generalization of the engine room is not a simple or linear process It has already taken a lot of time and effort to get things to fall into place Our new levelling support library integrates the previous independent codes for airborne and the special methods we developed to serve the marine levelling tools Marine levelling cross overs include an estimate of the strike and dip of the measured field at the cross over point This is useful for 3D GeoModeller when we have seismic picks for different horizons
22. vertical line through the square You can perform the same set of operations during the tie line levelling stage as during the flight levelling process See step 8 above for a list of possible operations substituting tie line for flight INTREPID displays the Repeat Iteration dialog box Please Choose PN i Do you want to run another iteration Yes No INTREPID can repeat the whole Polynomial correction process using the current set of corrected crossovers creating a more levelled result If you require this choose Yes otherwise No If you choose Yes INTREPID will go back to step 7 Repeat steps 7 11 as often as you require INTREPID will calculate proposed corrections for all enabled crossovers It can display the proposed corrections as colours or red black crosses in the dataset display area See Display style markers vs colours and Crossover and line display options for instructions INTREPID can also display a profile of proposed polynomial levelling corrections along any tie line See Displaying profiles along individual tie lines for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 49 Library Help Top lt 4 Back gt Crossover weighting methods The stability of crossover data can vary All data is subject to noise which causes rapid fluctuations in the Signal values High frequency Signal data is an indicator of noise You can assign
23. view profile graphs in separate windows of Diurnal data for a flight or a day See Flight Cruise or Day profile graphs for details Tie line data See Displaying profiles along individual tie lines for details During the polynomial levelling process INTREPID displays profile graphs of the polynomial curves with the errors to be adjusted marked as points in the profile See Polynomial levelling for details e You can save a crossovers dataset and view it in an INTREPID visualisation tool or the Spreadsheet tool See Creating and Using Crossovers Datasets for details Panning and Zooming the display You can enlarge and reduce the display zoom in and out and view different parts of it pan gt gt To zoom in and out enlarge reduce Zoom In Zoom Out To zoom in enlarge the display choose Zoom In at the right edge of the Levelling window Each time you choose this button INTREPID will enlarge the display by one step To zoom out reduce the display choose Zoom Out at the right edge of the Levelling window Each time you choose this button INTREPID will reduce the display by one step Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual 12 Line correction and tie levelling T30 Library Help Top lt 4 Back gt gt gt To pan the display view different parts The Pan zoom indicator near the bottom right corner of the Levelling window consists of a small squa
24. weights to crossover data when calculating the polynomial so that less stable data has less influence on the polynomial calculation F TAE Select weighting method ea 1 Gradient of Signal 1 Square root of Signal All weights 1 Ok Cancel When you commence the polynomial levelling process See Step 2 in Section Using the Polynomial levelling process INTREPID prompts you to specify the weighting method using the Select Weighting Method dialog box In assigning weights INTREPID examines the Signal value of the line that it is correcting i e the tie line for stages 1 and 4 and the acquisition line for stages 2 and 3 in Section Using the Polynomial levelling process INTREPID has three weighting method options Gradient of Signal If you select this option INTREPID will assign a lower weight to crossovers with high gradient Signal values before calculating the polynomial High gradient crossovers will contribute less than crossovers with a low gradient Use this method with magnetic data For magnetic data the gradient of Signal corresponds to the stability of the data 1 0 1 adient ef x gradient weight Square root of Signal If you select this option INTREPID will assign weights to crossovers according to the square root of the Signal value High Signal value crossovers will contribute less than crossovers with a low Signal value Use this method with radiometric data For radiometric data the
25. 6 394842 13 395167 22 395492 28 scaled FID OK Choose OK when you have finished viewing the graph Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 34 Library Help Top 4 Back gt GRF Subtracting the Earth s core magnetic field Library Help Top If you are levelling magnetic data you will need to subtract the intensity of the Earth s core magnetic field using a Geomagnetic Reference Field GRF resource See The geomagnetic reference field in INTREPID R15 for an explanation of GRF The correction will remove the influence of the Earth s core magnetic field Luyendyk 1997 gives a detailed explanation of the GRF correction Intrepid can calculate the GRF either by using a fixed survey date or a variable date For a fixed date GRF typically the survey date will be the mean survey date For a variable date GRF you must specify a date field in the Reconstruct flights Date time Fids phase if you wish Intrepid to use it In this case the date field will override the survey date defined in the GUI Intrepid can calculate the GRF using either a fixed elevation or a variable elevation For a fixed elevation GRF typically the nominal fixed height will be the mean height of the sensor above sea level For a variable elevation GRF you must nominate a field that provides Intrepid with height data above the spheroid eg GPS heigh
26. 80 42510 435 New Flight 2 Lines 2942 2992 2931 2921 7111 2982 3032 Type Line Line Line Line Tie Line Line Rows 21 27 20 19 33 26 32 ees Start Fids 309612329380336802352908497346507152507376 End Fids311732335183351821365604499188509146508820 Julians2448166 2448166 2448166 2448166 2448166 2448166 2448166 Relative Julians0 35830 38120 38980 40850 57560 5870 5872 Total Numberof Flights 2 If you do not specify a date field INTREPID omits the Julian date time rows of the table Calculating crossovers INTREPID can extract a sample from your dataset containing all of the data points where acquisition and tie lines cross crossovers You can use this sample to prepare and test corrections before applying them to the whole dataset If there are no crossovers several of the levelling methods cannot be used The sample is called the crossovers The advantages of using the crossovers in this way are as follows The set of crossovers is the focus for several of the Levelling tool corrections Line datasets can be large and slow to process If you are testing possible corrections it will save time to use a sample of the data for testing You can save the crossover values as a small sample dataset for easy examination using other tools How INTREPID calculates the crossovers Crossover points and values INTREPID calculates the crossover values in the following way When viewed from above the points at which tie lin
27. AGRF XDELTAYDELTA XYDELTA POLYDELTA LOOPDELTA N B TGRAD is implied with LGRAD e g LGRAD gt 10 LGRAD lt 10 this means you want to turn off all cross overs with higher gradients Operators are C like ie lt gt amp amp etc If ABS LGRAD gt 100 OK Cancel 2 Enter the logical expression into the text box then choose OK INTREPID will disable the crossovers for which the condition is true Enabling all crossovers gt gt To enable all crossovers Choose Re enable All from the Crossover menu INTREPID will enable all crossovers INTREPID Levelling corrections There are two types of Levelling correction crossover based and immediate INTREPID records proposed corrections for both types but only uses them with crossover based corrections INTREPID keeps a running total of the corrections you specify as beta misclosures The following sections contains an explanation of these terms Proposed corrections and the beta misclosure A correction calculated for a crossover is a proposed correction INTREPID records proposed corrections for each correction method It keeps a running total of proposed corrections in the beta misclosure A beta misclosure is constructed as a proposed alternative misclosure for the crossover Therefore a blank beta misclosure is equal in value to the original misclosure for the crossover Library Help Top 2012 Intrepid Geophysics 4 Ba
28. Back gt INTREPID User Manual Line correction and tie levelling T30 30 Library Help Top lt 4 Back gt Flight Fiducial Synchronisation If you choose Flight Fiducial Synchronisation INTREPID will prompt you to specify the flight number fiducial and Signal fields of the base station dataset See Specifying input and output files for general instructions about specifying files 3 Ifyou specified Date Time Fiducial Synchronisation INTREPID displays the Fid Factor and Date Format dialog box If you specified Julian Day Time Fiducial Synchronisation INTREPID displays the Fid Factor dialog box Enter FID Factor sec FID amp date style ja Enter FID Factor sec FID E YearMonthDay Enter FID Factor sec FID amp date s Enter FID Factor sec FID Ok Cancel C DayMonthYear Ok Cancel Enter the fiducial factor This would normally be 1 if you assigned the time field to the Fiducial alias 4 Specify the date format if required then choose OK 5 INTREPID displays the Signal field Pre Process dialog box r a Signal Pre Processing None C Convolve C Naudy despiker C Median Convolve Naudy Median Alias Filter Window Size data points 3 Naudy Filter Tolerance 0 100000 Use Corrected Data C Use Rejected Data OK Cancel Select the process you require from the Pre Process options The default process is None Diurnal variat
29. Choose one of the options from the Base station menu Po Intrepid ProLevelling Tool File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Style Help Show BaseStation Acq List Diurnal by Flight Cruise 6000 0 Diurnal by Day Diurnal by SimpleFid a ae Show Full Survey FlightList TATRA rrous1 2 Ifyou choose Display Flight Cruise or Display Day INTREPID will prompt you to enter the date or select the flight number or julian day Specify the data required vtec HH HHHrtt t teH t H HHH HHHH t t HHH ttt tt 3 INTREPID displays the information you require 4 When you have finished viewing the information choose OK Base station or Full Survey Flight list If you choose Show Base Station Acquisition List INTREPID displays a message box showing all of the flights or Julian days depending on the synchronisation method for which data exists in the base station dataset Choose OK when you have finished viewing the list level Basestation Flights 111111111111111112222222222222222222 List of flights with data in the base station dataset level Basestation Julians 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 List of Julian days with data in the base station dataset The numbers are repeated in these message boxes because INTREPID is listing the flight or Julian day for each group corresponding to a traverse line in the dataset If you c
30. F be Tie Corrections gt Heading Tie Corrections gt Loop 6997 5 4 z Eje E a DAE A z f Gradient Diffs XYmove t Gradient Diffs Polynomial f V Misclosure Sna f V Misclosure a TE Betas SRE Betas t A Crossovers Loop Crossovers a 4 Elevation Mis Polynomial Elevation Mis t ea 5995 j gt 5995 0 i Clear Viewer e Clear Viewer F 2 F es Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top Line correction and tie levelling T30 The following table lists the available display options 61 4 Back gt Data displayed Representation Menu option Crossover points black points Crossovers Misclosures colours or red and black symbols Misclosure Beta misclosures Betas Acquisition line or tie line paths lines Acq Lines Tie Lines Acquisition line or tie line crossover gradients colours or red and black symbols Acq Gradients Tie Gradients Acquisition line or tie line flight coloured lines one colour for each flight Acq Flights paths Tie Flights Difference between acquisition and colours or red and black symbols Gradient Diffs tie line gradients Size of Signal value corrections to acquisition line and tie line data Acq Corrections gt Tie Corrections gt Heading corrections colours or red and black symbols Heading Level XY corrections squares with line vector
31. INTREPID User Manual Line correction and tie levelling T30 1 Library Help Top 4 Back gt Line correction and tie levelling T30 Top Measurements taken during traverses are subject to errors or undesirable data from a number of sources These include Interaction between the direction of the Earth s magnetic field and that of the aircraft may be affecting the measurements The aircraft position is measured using an instrument inside the aircraft but some data e g magnetic may be taken from a sensor at the end of a cable some distance from it The measurements may therefore be incorrectly located This is called systematic parallax error Variable aircraft speed may create an additional variable parallax error due to the navigation instrument and acquisition instruments having a variable time difference in passing over points in the survey area There may be inaccuracies in recording the survey craft s location and or height when a measurement is taken There will be a certain error in recording the aircraft attitude and even if the instruments are on a stabilized platform Roll Pitch and Yaw estimated values will have an error and for gradiomtery this error will leak into the signed tensor components The readings are all taken at different times If the background magnetism or radiation is changing during this time these changes will confound the measurements Magnetic measurements will include the
32. OK OK OK OK OK Total number of Crossovers Crossovers datasets 63 Line correction and tie levelling T30 20 lt 4 Back gt You can save the crossovers for examination or further testing in a later levelling session See Creating and Using Crossovers Datasets for full instructions Examining individual crossovers Library Help Top Current Crossover Acq Line 140611 0 Acq Line Fid 257894 9 Flight Cruise 5 Acq Line value 59345 40 Acq Line grad 0 07 Tie Line 176031 0 Tie Line Fid 155050 70 Tie Flight No 30 Tie Line value 59355 23 Tie gradient 0 07 Misclosure 9 83 l Beta value 93 83 Long E ast 476 67 Lat North 5991 19 Elevation 514 95 V Use xover Acq Lines 69 Tie Lines 8 No Flights No Xovers 487 Diff Sum M Output Changes Only At the right of the Levelling window is the individual crossover display area You can use the display areas and text boxes to View values for individual crossovers e Enable or disable individual crossovers gt gt To view data for an individual crossover Select the crossover you wish to view by clicking it in the dataset display area 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 21 Library Help Top Library Help Top 4 Back gt Data displayed for each crossover INTREPID displays the following information about the current crossover For the
33. a list Choose Next Previous or Go To Recalculate the curve and corrections for the current flight and all flights that follow it in the flight reconstruction order then commence the next levelling stage Choose OK Turn individual crossovers off or on See Excluding crossovers from the levelling calculation for instructions Levelling the acquisition lines assuming that the tie lines are correct 9 Ifthe Level Acquisition Lines Assuming that the Tie Lines are Correct check box in the Select Defaults for Polynomial dialog box was off go to the next step INTREPID will calculate the polynomial for the first acquisition line s using the misclosures corrected by the tie line and or flight levelling process es if performed Steps 7 and or 8 Under the assumptions of polynomial levelling this curve represents acquisition line error only INTREPID displays the curve with the crossover misclosure values corrected so far of the first acquisition line The offsets of the misclosures from this curve represent acquisition line errors in the flight which INTREPID proposes to correct creating new acquisition line Signal values The graph is similar to that shown in steps 7 and 8 and shows the crossovers as small squares the polynomial as a single line curve and the weight assigned to the crossover as a vertical line through the square You can perform the same set of operations during the acquisition line levelling stage as durin
34. and know the correction parameters you require you can perform most of them in the same session You must perform the Parallax correction separately We recommend the following levelling sessions 1 Perform Parallax corrections 2 Perform all other corrections Components of the Levelling window The menu bar has pulldown menus that enable you to operate the Levelling application The dataset display area occupies most of the window This area shows the data you are processing and has Latitude and Longitude as its axes The individual crossover display area enables you to e View values for individual crossovers e Disable and enable individual crossovers The Pan zoom indicator and Zoom buttons enable you enlarge and reduce zoom the display and select different parts of it for viewing pan The status line at the bottom left of the Levelling window shows information about the current files and activity The calculations command buttons enable you to find the crossovers and apply the corrections to the data Specifying input and output files To perform Levelling you will need to specify the Signal field of the line dataset to be levelled as well as the location fields the fiducial field and the flight number field If you are reconstructing the flights using flight dates and times you must also specify a flight date field and optionally a time field The levelling process will produce corrected data or corrections in the form o
35. ataset Aliases from the File menu See Vector dataset field aliases in INTREPID database file and data structures R05 for further instructions File operations not listed in the File menu Library Help Top When you reconstruct the flights INTREPID automatically saves a flight reconstruction report See The flight report file for details e When you calculate the crossovers INTREPID automatically saves a crossovers report See The crossover report file for details e You can save and load tie line lists which define the principal and subsequent tie lines for polynomial levelling See Choosing the principal tie line and the tie line order for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 11 Library Help Top lt 4 Back gt Data display with the Levelling tool The Levelling tool provides a wide variety of options for displaying your data so that you can examine it You can view numerical information about individual crossover points in the Individual crossover Display Area See Examining individual crossovers for details You can view a variety of crossover point information graphically in the Dataset Display Area See Display style markers vs colours and Crossover and line display options for details You can enlarge reduce and view different parts of the data in the Dataset Display Area See Panning and Zooming the display You can
36. ating them See Creating and Using Crossovers Datasets for instructions The crossover report file INTREPID writes a crossover report to the rpt file crossover rpt in the dataset directory This is an ASCII file which you can print or read edit with any text editor It consists of a matrix with one acquisition line per row and one tie line per column Each cell in the matrix therefore represents a potential intersection point INTREPID represents the potential intersection points as follows Type of intersection Notation Crossover data calculated OK Crossover not found but minimum bounding rectangles of tie line number followed by R acquisition and tie lines overlap e g one line may stop short of the other but its end still lie close to the other line Crossover not found and minimum bounding rectangles of tie line number acquisition and tie lines do not overlap Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Here is an example of a crossover report file CROSSOVER REPORT for raw_mag CROSSOVER GRID CONTAINS 33 LINES AND 3 TIES CROSSOVER REPORT CROSSOVERS NOT FOUND INDICATED BY TIE NUMBER OTHERS BY OK LINE 2731 2742 2751 2761 2771 2781 3001 3012 3013 3021 3032 STATUS OF TIES OK OK OK OK OK OK OK 7111 OK OK 7111 OK OK OK OK 7121 7121 7121 7121 7121 7121 7121 7122 7122 7122 7122R OK OK
37. cedure If you grid the data you may be able to see levelling busts in the grid If these are alternate highs and lows corresponding to traverse lines try the Heading correction You can estimate the corrections required by examining Signal values at different places in the grid using the Visualisation tool see Querying points in Visualisation T26 Alternatively you can calculate mean Signal values for each group traverse line using the Spreadsheet If these means are alternately high and low you can calculate the value for the Heading correction from their difference Levelling suggestions case 2 A full original located data set is available including all time variables Suggested corrections All Levelling options are available Suggested procedure 1 If base station data is available perform the Diurnal correction 2 Make the GRF correction 3 Apply the corrections and save the new Signal values 4 Try to improve the coherency of the features in the data by experimenting with parallax corrections Use positive and negative corrections 5 Starting with the Diurnal and GRF corrected data calculate crossovers again and look at the misclosures You can obtain more information about its current state by creating a trial grid based on either the full dataset or the reduced crossover dataset 6 Perform a Polynomial correction Levelling suggestions case 3 Library Help Top A full tensor gravity gradie
38. cify Basestation Flight Fiducial Synchronisation Save Options Julian Day Time Synchronisation Simple Fid Synchronisation Wizard for Easy Levelling Edit Database Aliases Reconstruct flights gt Quit oe Ti ae n as ors a z 4 ai a HH HH t 1 Ifyou have not already done so reconstruct the flights See Chronological order reconstructing the flights for full instructions 2 Choose one of the options from the Specify Basestation cascade in the File menu See Base station Survey data synchronisation methods for an explanation of the Flight date time and Julian day time options Date Time Fiducial Synchronisation If you choose Date Time Fiducial INTREPID will prompt you to specify the Date start time fiducial and Signal fields of the base station dataset If the base station dataset has a time field with a time for each data point and you will be specifying this as the fiducial field do not specify the same field as the start time field Julian Day Time Fiducial Synchronisation If you choose Julian Day Time Fiducial INTREPID will prompt you to specify the Julian day start time fiducial and Signal fields of the base station dataset If the base station dataset has a time field with a time for each data point and you will be specifying this as the fiducial field do not specify the same field as the start time field 2012 Intrepid Geophysics 4
39. ck gt INTREPID User Manual Line correction and tie levelling T30 24 Library Help Top lt 4 Back gt Correction types Immediate corrections Immediate corrections involve applying a correction directly to all data These correction do not require crossovers The immediate corrections are Heading e Parallax e Diurnal gt GRF When you specify an immediate correction INTREPID calculates and records the correction for each crossover and adds the correction to the beta misclosure for the crossover The proposed corrections are for your information only INTREPID does not use them when applying the corrections Crossover based corrections Crossover based corrections involve first calculating corrections for the crossovers then interpolating them between the crossovers for the rest of the dataset The crossover based corrections are Level XY e Polynomial levelling Loop closure Single gradient alpha only mainly for Rio Tensor corrections When you specify a crossover based correction INTREPID calculates and records a proposed correction for each crossover and adds the proposed correction to the beta misclosures for the crossovers Proposed corrections and crossovers datasets Library Help Top Crossovers datasets contain sets of proposed corrections When you load a crossovers dataset INTREPID will prompt you to specify which if any of its proposed corrections to retrieve
40. ction of the day You can see this data in the flight report file See The flight report file The flight report file INTREPID produces a flight report file flight rpt in the dataset directory You can examine this file in detail to confirm that the flight reconstruction was correct The flight report is an ASCII file which you can print or read edit with any text editor It consists of a set of tables one for each flight Tables have one column for each traverse line and six rows of data Line Number Line Type original position of the line in the dataset Rows starting Fiducial number Julian day Relative Julian time since the start of the flight Relative Julian time is a number representing the time since the start of the flight Its fractional part represents a fraction of 24 hours For example if the flight commenced a midnight 0 3 represents 7 12 am 0 3 x 24 7 2 7h 12 min Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 16 Library Help Top lt 4 Back gt Here is part of a sample flight report file FLIGHTREPORT for raw_mag New Flight 1 Lines 2862 2771 2851 2842 2742 2811 Type Line Line Line Line Line Line Rows 13 4 12 11 1 8 aaa Start Fids 255680273594284398304852367252375802 End Fids257464275376286200306458368900377556 Julians2448166 2448166 2448166 2448166 2448166 2448166 Relative Julians0 29590 31670 32920 352
41. current acquisition line e Acquisition Line number e Acquisition Line Flight cruise number e Acquisition Line Crossover fiducial e Acquisition Line Crossover value e Acquisition Line Crossover gradient For the current tie line Tie Line number Tie Line Flight cruise number Tie Line Crossover fiducial Tie Line Crossover value Tie Line Crossover gradient For the current crossover e Milisclosure Beta misclosure See Proposed corrections and the beta misclosure for a definition Longitude East e Latitude North Use crossover check box On if crossover enabled for levelling Offif crossover disabled for levelling For the whole dataset Number of acquisition lines Number of tie lines Number of flights Number of crossovers e Cumulative length of all traverses Output Changes Only This check box controls whether the output X Y and Signal fields contain corrected values or the values of the corrections It is not part of the individual crossover display See Applying the corrections to the whole dataset for further details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 22 Library Help Top 4 Back gt Excluding crossovers from the levelling calculation Library Help Top For crossover based corrections Level XY Polynomial and Loop Closure you may wish to exclude some crossovers from the process You can do this using a condi
42. d XY correction to Y field of the line Signal The interpolated signal at the cross over position Possible operations with reloaded crossovers datasets Library Help Top You can use reloaded crossovers datasets for enabling and disabling crossovers and for viewing crossovers data and as a source of crossover based corrections to apply to the dataset to be levelled 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 59 Library Help Top lt 4 Back gt If you load an existing crossovers dataset during a Levelling session you can Specify which sets of crossover based proposed corrections from the crossovers dataset INTREPID should retrieve and treat as current proposed corrections See Proposed corrections and crossovers datasets for details Examine crossover data in the Individual Crossover Display Area See Examining individual crossovers for details Enable and disable crossovers See Excluding crossovers from the levelling calculation for instructions Examine the crossover data using options from the Display menu See Display style markers vs colours and Crossover and line display options for instructions Respecify corrections as required See INTREPID Levelling corrections Save a new copy of the crossovers dataset if required See Saving and loading crossovers datasets for instructions Viewing the crossovers dataset as a
43. ducial 0 is midnight at the start of the flight date Date record and formats The date must be recorded in integer 4 byte field of the survey dataset INTREPID will only examine the first date for each line so we recommend that the date field be a group by field The date can be expressed as Julian date A positive integer representing the number of days since the beginning of a datum year A day you regard as a start date for your surveys In practice as long as your data is internally consistent the value of the start date does not matter If you are using other software with your data for example importing it into a general purpose spreadsheet such as Microsoft Excel you may wish to use a start date consistent with the general purpose software you intend to use In Microsoft Excel a date whose integer part is 1 represents 1 January 1900 yymmdd format A positive integer which will represent a date in yymmdd format when it is expressed in base 10 using 6 digits For example the number 970223 represents the date 23 February 1997 ddmmyy format A positive integer which will represent a date in ddmmyy format when it is expressed in base 10 using 6 digits For example the number 050293 represents the date 5 February 1993 Time record and format If your dataset includes a time field containing a time for each reading you can use the time field for reconstructing the flights In this case you must assign the time field to
44. e and longitude gt gt To use the GRF calculator 1 Choose AGRF or IGRF from the Mag Field menu lt OOOO File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Lines IGRF Manual INTREPID displays the GRF calculator dialog box a height m lat deg lon deg date dd mm yy Ad Enter 6 fields blank seperated height m lat deg lon deg date dd mm yyyy 100 0 0 000 0 000 01 1 2000 Ok Cancel 2 Enterin the parameters text box separated by spaces e Height of location in metres Latitude of location in degrees Longitude of location in degrees Date for the calculation in the format dd mm yy 3 Choose OK INTREPID displays the value in the GRF value dialog box a Field 31406 2 nT inclination 28 2 deg declination 7 3 deg Intl GeoMagnetic Reference Field magnitude inclination and declination See The geomagnetic reference field in INTREPID R15 for an explanation of these parameters Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 65 Library Help Top 4 Back gt Suggested levelling procedures for different cases Levelling suggestions case 1 An old survey badly levelled without any time based information such as Flight Date Time or Fiducial record Suggested corrections Parallax GRF Heading LevelXY Loop Suggested pro
45. eight the contribution of crossover point Signal values in calculating the polynomial for the curve according to their estimated stability See Crossover weighting methods for details of the weighting methods available INTREPID uses a piecewise low order polynomial for the curve in the process Using the Polynomial levelling process Library Help Top gt gt To use Polynomial levelling 1 Ifyou have not already done so e Perform Parallax Diurnal and GRF corrections as required then commence a new Levelling session Reconstruct the flights Calculate the crossovers for the dataset e Create a lie line list See Chronological order reconstructing the flights for full instructions 1 You may perform Diurnal and GRF corrections simultaneously with the Polynomial levelling if you do not need to examine their results before proceeding 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 44 Library Help Top lt 4 Back gt 2 Choose Polynomial from the corrections menu INTREPID displays the Select Weighting Method dialog box Generally for TMI you should pick an inverse of the gradient of the Signal The rationale is that in high gradient regions the error is likely to be exaggerated For radiometrics signals the usual advice is to suggest the inverse of the square root of the signal as the weighting If you do not want any bias just choose all wei
46. elp Top The Levelling tool can perform a number of levelling functions in the same session It will be appropriate in some circumstances for you to complete your levelling operations over several Levelling sessions We recommend that after performing a correction on a dataset you exit from Levelling and launch it again for the next task The following regimes are a pair of extremes Generally speaking apart from the Parallax correction which you should always perform first you can combine corrections or perform them separately as required New datasets If you are processing fresh data you will most likely wish to grid the results of each step and examine them before proceeding to the next We recommend the following Levelling sessions for an unfamiliar dataset Repeat each step until the results are the best possible Note the parameters that you used to produce this result 1 Perform Diurnal and GRF corrections then grid and examine the results These corrections may be performed together 2 Perform Parallax corrections then grid and examine the results 3 Perform Heading or Level XY or Polynomial or Loop Closure corrections as required then grid and examine the results 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 7 Library Help Top lt 4 Back gt Datasets for which you have established required correction parameters If you are reprocessing a dataset
47. ement Magnetism BaseStation 6000 ot tttt of fe tite Levelling corrections brief descriptions INTREPID provides seven types of levelling correction for your data You can see a list of them in the Corrections menu E Intrepid ProLevelling Tool File Display Tie Management CrossOver Mar Heading Parallax 60l Diurnal GRF Level XY Polynomial levelling Loop Closure 59 Single Gradient corrections alpha only Tensor Corrections Ei 4 Headings corrections Immediate Corrects errors due to aircraft or ship direction Parallax corrections Immediate Corrects errors in location of readings arising from the horizontal distance separating the acquisition instrument and the navigation instrument Diurnal corrections Immediate Corrects for diurnal variation in the background signal that occur over time and confound the readings INTREPID compares the flight data with data collected at a base station during the same time interval GRF corrections Immediate Subtracts the intensity of the Earth s core magnetic field Level XY corrections Crossover based Infers the correct location of a crossover point by extrapolating a line at the crossover point and seeking a point of intersection Polynomial levelling Crossover based Levels the dataset by fitting the data to a curve along the tie lines then along the flights and finally along each acquisition line Librar
48. eps but genralised to vectors and tensors provided the appropriate swums divisions and rotational algebra are carefully created and tested This is what INTREPID have implimented 1 8 Green A A A comparison of adjustment procedures for leveling aeromagnetic survey data Geophysics 48 6 June 1983 745 753 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 53 Library Help Top lt 4 Back gt Loop closure parameters The loop closure process uses two parameters If you wish to change them you must use a task specification job or task file for the Levelling process and edit the file according to your requirements You can use the file in interactive or batch mode Max_Iterations controls the maximum number of loop closure iterations performed The default value is 500 Max_Change When the average change to the crossovers in an iteration falls below the value of this parameter the process will stop The default value is 0 01 See Displaying options and using task specification files for more information Process reports for the loop closure method You can inspect a report of the progress of the loop closure process and the original and final average misclosure Under Unix this appears in the background window Under Windows it can be written to an WINXX username log report file See Diagnostic reporting options in Configuring and usi
49. er 7 Use xover j Acq Lines 69 l Acq Lines 69 Tie Lines 8 Tie Lines 8 i No Flights 5 No Flights 5 5992 5 No Xavers 487 i 5992 5 No Xovers 487 ji Diff Sum j Diff Sum li ks Output Changes Ony Output Changes Only j i Find Crossovers I Find Crossovers Apply Corrections I Apply Corrections i 5990 0 CrossOver Corrections 5990 0 CrossOver Corrections 20 amr CELIA Fe o 405 0 Ar e RGA 485 0 487 5 475 as ao As Aes 487 5 tatus Line Save As Zoom In possas Save As Zoomin Sig rawmag PD Zoom Out Eaa roemog PD Zoom Out ine Type linetype 1 Gr light flight light flight Query C Query Zoom Rectangle C Zoom Reuangis Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 62 Library Help Top lt 4 Back gt Displaying profiles along individual tie lines You can display crossover data using profile graphs along individual tie lines INTREPID uses a separate window to display the values as a profile graph with fiducials on the horizontal axis You can display data from the crossover points of a single flight or all flights gt gt To display data as a profile graph along a tie line 1 Ensure that the flights are reconstructed See Chronological order reconstructing the flights for full instructions 2 Choose the All Flights for Tie or
50. erform this using both the heading and loop levelling methods We are still developing the generalised Polynomial levelling method So far it continues to work for scalars and there is primary testing to show it working on tensors as well Using the Levelling tool Library Help Top You can set up the Levelling process in the following ways e Use the Levelling tool wizard e Use the menu options and controls in the Levelling tool window 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 3 Library Help Top 4 Back gt gt gt To use the Levelling wizard 1 From the File menu select Wizard for Easy Levelling 2 Follow the wizard steps referring to corresponding sections in this chapter as required Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 4 Library Help Top lt 4 Back gt gt gt To use the Levelling tool 1 Ifrequired ensure that correctly configured aliases exist for the dataset you are levelling In particular if you are reconstructing the flights using a time field which has the time for each data point assign the time field to the Fiducial alias See Specifying input and output files for details 2 Choose Tie_Line_Levelling from the Levelling menu in the Project Manager or use the command newlevel exe INTREPID displays the Levelling window E in
51. es so you can compare and contrast the changes forced by the adoption of the GOOGLE parser messaging technology it is very close fit and the benefits far outweigh the downside of making this change 4 you get access to the full data processing model for all of Intrepid and Geomodeller via the proto files we now distribute at V5 0 5 The GOOGLE parsers are very good at reporting syntax errors in the language down to line and column 6 INTREPID can move to a client server super computer cloud computing architecture with a completely independently designed and supported messaging language as the glue This is after all one of the technologies upon which GOOGLE runs its business gt gt To use a task specification file for a batch mode Levelling task Type the command newlevel exe with the switch batch followed by the name and path if necessary of the task specification file Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 70 Library Help Top lt 4 Back gt For example if you had a task specification file called surv329 job in the current directory you would use the command newlevel exe batch surv329 job Note The current version of INTREPID cannot load task specification files for interactive use You can load previously specified operations to some extent using crossovers datasets but these operate differently from task specification f
52. es and acquisition lines intersect are called crossover points INTREPID infers the crossover values in the tie line and the acquisition line at this point by finding an average of the points on either side of the crossover point INTREPID weights the contributions of the points to the average according to the distance of the points from the crossover point The misclosure at a crossover point is the original difference between the acquisition line crossover value and the tie line Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 17 Library Help Top lt 4 Back gt crossover value The BETA at a crossover point is the current difference between the acquisition line value and the tie line value These concepts also apply to tensor vector readings Crossover gradients INTREPID calculates the crossover gradient with respect to fiducial data in a line at the crossover points It uses the Signal data values on either side of the crossover points to calculate ASignal INTREPID calculates the crossover gradients with respect to the fiducials for convenience Since the aircraft is likely to be travelling at a constant speed these gradients are also an accurate estimate of the gradients with respect to distance and INTREPID uses them as such If the gradient at the crossover is high you may need to pay special attention to it during some corrections To en
53. f a corrected Signal field and or corrected X and Y fields You will need to specify names for these fields You may also need to specify a base station dataset for diurnal data You can save the crossover point data for examining using other INTREPID tools then load it for use during a subsequent levelling session Most file operations are listed in the File menu Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Library Help Top LE Intrepid ProLevelling Tool Corrections Display Tie Manager Specify Input Specify Output Specify Report Load cross overs Save cross overs Specify Basestation Save Options Wizard for Easy Levelling Edit Database Aliases Reconstruct flights Quit 2012 Intrepid Geophysics Line correction and tie levelling T30 8 4 Back gt lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 9 Library Help Top 4 Back gt In each case INTREPID displays an Open or Save As dialog box Use the directory and file selector to locate the file you require See Specifying input and output files in Introduction to INTREPID R02 for information about specifying files INTREPID can obtain information from the dataset aliases It can use the following aliases to identify appropriate field files Alias Field X X coordinate location Y Y coo
54. f the line group by field LNUM Line number group by field TYPE Line type group by field TIEFLIGHT Flight number of other line at the crossover point TNUM Other line number at the crossover point LFID Fiducial value on the line at the crossover point It will usually be fractional because crossover point will most likely be between two original data points TFID Fiducial value on the other line at the crossover point It will usually be fractional because the crossover point will most likely be between two original data points X X location of crossover point Y Y location of crossover point Signal Original Signal value on the line at the crossover point LGRAD Gradient of the Signal profile on the line at the crossover point or near it if you used the search radius See Crossover gradients for further details about crossover gradients FLAG Flag indicating whether the crossover is enabled MISCLOSURE Original misclosure BETA Sum of all proposed corrections expressed as a revised misclosure INTREPID only calculates this if you specify XY polynomial or loop closure correction DIURNAL Proposed Diurnal correction HEADING Proposed Heading correction IORAGRF Proposed Earth s core magnetic field correction LOOPDELTA Proposed Loop Closure correction POLYDELTA Proposed Polynomial correction XYDELTA Proposed XY correction to Signal field of the line XDELTA Proposed XY correction to X field of the line YDELTA Propose
55. from the Tie Line menu EE Intrepid ProLevelling Tool File Corrections Display CrossOver Mana Create List Show List Complete List Delete List Load List Save List All flights for Tie 5997 One flight for Tie a H Display tie graph gt Hp ebb tt th tbid HEHE HHH HH 4 4 2 Click once any point or crossover of the most level tie line in the dataset display area INTREPID will record it as the first tie line for calculation 3 Click once any subsequent tie lines you wish to individually select INTREPID will record them 4 Choose Complete List from the Tie Line menu INTREPID will create the rest of the list automatically Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 39 Library Help Top lt 4 Back gt 5 Display the list to check that it has been constructed properly choose Show List from the Tie Line menu INTREPID displays the list in a message box This example is from Albury ee ee List of Ties 174071 000000 174041 000000 174091 000000 176031 000000 176051 000000 176041 000000 174081 000000 174061 000000 eee 6 Choose OK when you have finished viewing the list 7 Save the tie line list for subsequent leveling sessions with this dataset if required gt gt To clear the tie line list Choose Delete List from the Tie Line menu Tie line list files You ca
56. g the Earth s core magnetic field and Flight reconstruction involves choosing one of the options from the Reconstruct Flights cascade in the File menu EI intrepid Protecting Too i Greets Display Tie Management CrossOver Management Specify Input Specify Output Specify Report Load cross overs Save cross overs Specify Basestation gt Save Options Wizard for Easy Levelling Edit Database Aliases Reconstruct flights gt Quit Date time Fids Julian day Fids Fiducials only The procedures for flight reconstruction differ slightly depending on the option you choose as described in the following sections 2012 Intrepid Geophysics Library Help Top 4 Back gt INTREPID User Manual Line correction and tie levelling T30 13 Library Help Top 4 Back gt Flight reconstruction using flight date and time If your survey data includes the date of each flight you can reconstruct the flight on a time basis If your survey has a TimeOfDay alias field with the time of each reading INTREPID can use this for reconstructing the flights If the survey has a TimeOfDay alias field which gives only the starting time of each flight INTREPID can use it in conjunction with the Fiducial alias field to determine the time for each reading If the survey has no TimeOfDay alias field INTREPID will calculate the time of each reading from the Fiducial alias field It assumes that fi
57. g the flight levelling process See step 8 above for a list of possible operations substituting acquisition line for flight 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 48 Library Help Top 4 Back gt Levelling the tie lines assuming that the acquisition lines are correct 10 11 12 13 Library Help Top If the Level Tie Lines Assuming that the Acquisition Lines are Correct check box in the Select Defaults for Polynomial dialog box was off go to the next step INTREPID will calculate the polynomial for the first tie line using the misclosures corrected by the tie line and or flight and or acquisition line levelling process es if performed Steps 7 and or 8 and or 9 To be performing this step you will normally have performed steps 8 and or 9 If this is the case then under the assumptions of polynomial levelling this curve represents any residual tie line error after the acquisition line levelling process INTREPID displays the curve with the crossover misclosure values corrected so far of the first tie line The offsets of the misclosures from this curve represent tie line errors in the flight which INTREPID proposes to correct creating new tie line Signal values The graph is similar to that shown in steps 7 and 8 and shows the crossovers as small squares the polynomial as a single line curve and the weight assigned to the crossover as a
58. ghts set to 1 Sect nihin ci a 7 1 Gradient of Signal 1 Square root of Signal All weights 1 3 Select click the weighting method you wish to use then choose OK See Crossover weighting methods for details about weighting methods 4 INTREPID displays the Select Defaults for Polynomial dialog box E Se E Enter smoothing length default order of correction functions and width of piecewise window 5150 V Level tie lines to principal tie line Level acquisition lines assuming that the tie lines are corre M Level tie lines assuming that acquisition lines are correct M Use Distance Weighting Ok Cancel 5 Enter the initial smoothing length default order of correction functions and the width of the piecewise window See Polynomial levelling for details 6 Turn on check boxes corresponding to the polynomial levelling stages you wish to perform See Selecting polynomial levelling process stages for details A new distance weighting option has been introduced largely for marine levelling situations where the sampling intervals can be very different You do not want equal weight given to a signal measured at a far distance to the current cross over compared to a much more local reading This is unlikely to be needed for standard airborne surveying Choose OK Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie leve
59. hoose Show Full Survey Flight List INTREPID displays the list in a message box Choose OK when you have finished viewing the list level x Full Survey Flights 12 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 33 Library Help Top lt 4 Back gt Flight Cruise or Day profile graphs If you choose Display Flight Cruise INTREPID displays the Select Flights dialog box containing a list of the flights for which the base station dataset contains data Select click the flight for the profile display then choose OK If you choose Display Day and you are using Julian day time synchronisation INTREPID displays the Select Julians dialog box containing a list of the days for which the base station dataset contains data Select click the flight for the profile display then choose OK If you are using Flight Fiducial synchronisation and choose Display Day INTREPID displays the Enter date dialog box Enter the date for the profile in yymmdd format e g 970221 for 21 February 1997 then choose OK Select Flight to be Select Julian to b Ok Cancel NNNNNN N ae eee ee _ 0k Cancel INTREPID displays the flight or all flights for the day in a graph with Fiducial record on the horizontal axis Intrepid Levelling Tool V3 2beta9 1979 49 Base Station Readings Flight 1 1977 73 1975 97 1974 21 JS 1972 45 1970 68 394192 00 394517 0
60. hosen the Naudy filter specify The filter wavelength in data points using the Window Size data points text box The filter tolerance in Signal units using the Tolerance text box 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 18 Library Help Top lt 4 Back gt See Naudy filter in INTREPID spatial and time domain filters and transformations R13 for further information Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 19 Library Help Top lt 4 Back gt 3 Choose OK INTREPID displays the Search Radius for Gradient dialog box P wl Search radius for Gradient Ignore C Use Accuracy in metres 10 0 OK Cancel 4 Ifyou require INTREPID to search the neighbourhood of each crossover point for the highest gradient to record as the crossover gradient select Use and specify the radius in metres around the crossover point for selection of the maximum gradient If you wish INTREPID to always record the gradient precisely at the crossover point as the crossover gradient select Ignore See Crossover gradients for further explanation 5 Choose OK INTREPID will calculate and display the crossovers and write the crossover report file You can save the crossovers if you wish to use them in a later session without recalcul
61. ial levelling you will need to select the principal tie line and specify the levelling order for the other tie lines See Polynomial levelling for instructions Viewing the data You can Choose between Markers and Colours for your data display using the options in the Style menu See Display style markers vs colours for detailed instructions Use the Zoom In Zoom Out buttons and the Pan zoom location indicator to adjust the magnification and position of the display See Panning and Zooming the display for detailed instructions View crossover data graphically in the dataset display area Use the options in the Display menu to choose the display you require See Crossover and line display options for detailed instructions View a profile graph along a single tie line See Displaying profiles along individual tie lines for detailed instructions View a profile graph of base station data for a flight or day See Flight Cruise or Day profile graphs for details View values for individual crossovers See Examining individual crossovers for instructions Saving crossovers You can save the current crossovers and proposed corrections at any stage after obtaining the crossover data for the session See Proposed corrections and crossovers datasets and Creating and Using Crossovers Datasets for instructions When you are satisfied that the corrections are as you require and if you wish to carry out the corrections choose Apply Correc
62. ie line points marked Misclosures on second tie line Since the principal tie line Z values are assumed to have no error the curve represents the errors due to acquisition line Z values only The deviation of the second tie line misclosures from this curve must be due to errors in the second tie line Z values We can record these errors and use them to correct the second tie line Z values Errors due to tie line Z value offsets from acquisition line only error curve una erat enews 2 INTREPID repeats step 2 and 3 for all flights with acquisition lines crossing the principal tie line In this way it collects a complete set of corrections for the second tie line INTREPID corrects the second tie line Signal values for the errors determined in step 3 It does this by calculating a least squares fit curve for the errors along the tie line It then uses values on the curve as sources for the tie line Signal values corrections Levelling of tie line data Step 2 Correction curve for tie line Z values gt Size of misclosure Z units Time along tie line Error due to tie line Z value size of offset from acquisition line only error curve The curve is calculated by least squares fit to the tie line errors and represents the errors due to tie line Z values on this tie line It is the source of correction for levelling the tie line 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Hel
63. iles See Creating and Using Crossovers Datasets for information about crossovers datasets Task specification file examples Examples of Levelling task specification files appear below Example 1 All corrections except polynomial levelling PARMS syntax Process Begin Name newlevel InputZ disk1 surveys ebagoola_S raw_mag InputX disk1 surveys ebagoola_S x InputY disk1 surveys ebagoola_S y inputFid disk1 surveys ebagoola_S fid TYPEName disk1 surveys ebagoola_S linetype inputLine disk1 surveys ebagoola_S line inputFlights disk1 surveys ebagoola_S Flight DiurnalFlight disk1 surveys basel1 Flight DiurnalFid disk1 surveys basel fid DiurnalReading disk1 surveys basel diur_mag OutputZ disk1 surveys ebagoola_S z_lev OutputX disk1 surveys ebagoola_S x_lev OutputY disk1 surveys ebagoola_S y_lev OutputXover disk1 surveys eba_xover Parameters Begin Save_Changes_Only No Gradient_Radius 10 0 SurveyStyle Begin FID_Factor 0 1 Use_XY_Accuracy No if not reconstructing flights use the following line Reconstruct_Flights_by Date No Reconstruct_Flight_Method Date_Fid Date_Style YYMMDD Diurnal_Style FLIGHT_DATE_TIME SurveyStyle End Zfilter None HeadingCorrection Begin Bearing_Corrections 0 0 0 10 90 0 0 10 180 0 0 02 270 0 0 05 Headings 0 0 0 10 90 0 0 10 180 0 0 02 270 0 0 05 Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual L
64. ine correction and tie levelling T30 71 Library Help Top lt 4 Back gt HeadingCorrection End ParallaxCorrection Begin Cable_Length 100 0 ParallaxCorrection End DiurnalCorrection Begin Time_Lag 0 1 DiurnalCorrection End GrfCorrection Begin Sensor_Elevation 50 0 UseClearance No Year 96 Month 08 Day 25 GrfType Igrf Recalculation_Interval 60 0 GrfCorrection End LevelXYCorrection Begin Radius 5 0 LevelXYCorrection End LoopCorrection Begin Max_Change 0 01 Max_Iterations 500 LoopCorrection End Parameters EndProcess End Notes In loop closure levelling you can modify the Max_Change and Max_Iterations parameters by changing the value in the corresponding line See Loop closure parameters for details Example 2 Polynomial levelling Julian flight date and time PARMS syntax Process Begin Name newlevel outputXover disk1 survey eba eba_xol_btch InputZ disk1 survey eba eba_mag dtm InputX disk1 survey eba eba_mag X3 InputY disk1 survey eba eba_mag Y3 inputFid disk1 survey eba eba_mag fid TYPEName disk1 survey eba eba_mag linetype inputLine disk1 survey eba eba_mag line inputFlights disk1 survey eba eba_mag flight OutputZ disk1 survey eba eba_mag poly_dtm2 Parameters Begin Save_Changes_Only No Gradient_Radius 10 0 SurveyStyle Begin FID_Factor 0 8 Use_XY_Accuracy No Reconstruct_Flight_Method Julian_Fid Date_Style YYMMDD Diurnal_Style JULIAN_TIME Sur
65. ing T30 47 Library Help Top Library Help Top 4 Back gt The horizontal axis of the graph represents time in seconds or fiducial numbers from the beginning of the flight depending on the basis of the flight reconstruction The vertical axis represents the misclosure difference between acquisition and tie line values in Signal units The graph shows the crossovers as small squares the polynomial as a single line curve and the weight assigned to the crossover as a vertical line through the square You can Without changing the parameters view the results for the next or previous flight in flight reconstruction order or a flight you choose from a list Choose Next Previous or Go To Specify automatic or manual Y axis scaling for the graph Turn the Y Auto Scale check box on or off If you turn Auto Scale off specify the scale in Signal units cm in the Scale text box Change the Polynomial Order Piecewise Window or Smoothing Length parameters for the next curve calculation See Polynomial levelling parameters for details about the purposes of these parameters Recalculate the curve for the current flight using the currently displayed parameters and display the results Choose Apply Ifyou have changed the parameters recalculate the curve for the current flight then recalculate and view the results for the next or previous flight in flight reconstruction order or a flight you choose from
66. ing the Frobinus error Norm is a QC option An 11 point window is passed down each profile with the signal at the middle point in the filter subtracted from the estimated signal using 5 points either side The Norm of the difference tensor is then saved to the output channel as a primary indicator of the background noise in the measured signal Using somewhat similar techniques instead of estimating the middle point s tensor signal it is equally easy to integrate the tensor and estimate the vertical component which for gravity is quite interesting Remember this is high passed and cannot have much longer wavelength present Perhaps the most challenging levelling method is to drape continue the measured tensors from an observed flying height to another surface height This is required for joining surveys together and various other purposes The algorithmic challenge here is to constrain the cross gradient terms locally as data on adjoining lines must be referneced to accomplish this feat With V5 0 we now use a spatial indexing technique to sort all the observed data for a survey into a local neighbourhood context this then makes it easy to find observed tensors values locally in all directions not just along profiles os we then can successfully do the required continuations without having numeric instabilities Use more samples and you will get a smoother result that is less high passed Creating and Using Crossovers Datasets
67. ions are predominately large wavelength phenomena with respect to time and often base station data contain noisy spikes We therefore recommend subtle pre filtering of the diurnal magnetic data using either the Convolve Fuller or Naudy filters If you have selected Convolve Fuller specify the size of the convolution window in data points using the Window Size data points text box See Fuller filter in INTREPID spatial and time domain filters and transformations R13 for further information Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 31 Library Help Top 4 Back gt If you have chosen the Naudy filter specify The filter wavelength in data points using the Window Size data points text box The filter tolerance in Signal units using the Tolerance text box See Naudy filter in INTREPID spatial and time domain filters and transformations R13 for further information INTREPID displays the Enter Time Lag dialog box Enter Time Lag Enter Time Lag o Ok Cancer Enter the time lag in seconds and choose OK See Time lag for an explanation Examine the base station data if required You can do this at any time after loading base station data See Examining base station data for instructions INTREPID will note the base station Signal field that you specified as corrections and apply them when you choose Apply Co
68. lated the crossover data use this to save a crossovers dataset See Creating and Using Crossovers Datasets for details Specify Basestation If you are performing diurnal corrections use this to specify the base station dataset See Diurnal corrections for instructions Save Options If you wish to save the current Levelling file specifications and parameter settings as an task specification file use this option to specify the filename and save the file You can only use Levelling task specification files in batch mode See Displaying options and using task specification files for more information Note The current version of INTREPID cannot load task specification files for interactive use You can load previously specified operations to some extent using crossovers datasets but these operate differently from task specification files See Creating and Using Crossovers Datasets for information about crossovers datasets Reconstruct Flights When you reconstruct the flights using a flight date and possibly a flight time field you need to specify the fields containing the flight dates and optionally the flight times See Chronological order reconstructing the flights for instructions Editing aliases You can edit the aliases for any dataset This process is independent of any currently loaded dataset so you can use it before or after specifying the Signal field to be levelled gt gt To edit the aliases for a dataset Choose Edit D
69. lling T30 45 Library Help Top Library Help Top 4 Back gt Levelling the tie lines assuming that the principal tie line is correct 7 Ifthe Level Tie Lines to Principal Tie Line check box in the Select Defaults for Polynomial dialog box was off go to the next step INTREPID displays a panel for the first selected stage of levelling tie lines with the parameters you defined in steps 5 and 6 Choose Apply to calculate the first polynomial INTREPID displays the curve with the crossover misclosure values of the second tie line The offsets of the misclosures from this curve represent tie line errors which INTREPID proposes to correct creating new tie line Signal values TIE LINES Choose poly parameters V Y AutoScale 3 9 lunitsfem Polynomial Orde 1 Piecewise WindowS0 Smoothing Length 5 APPLY CANCEL The horizontal axis of the graph represents time in seconds or fiducial numbers from the beginning of the line depending on the basis of the flight reconstruction The vertical axis represents the misclosure difference between acquisition and tie line values in Signal units The graph shows the crossover errors as small squares the polynomial as a single line curve and the weight assigned to the crossover as a vertical line through the square The longer the vertical line the bigger the gradient value and so the smaller the weight applying to this mis closure You can Withou
70. ly error curve x INTREPID repeats step 6 and 7 for all flights with acquisition lines crossing the principal tie line In this way it collects a complete set of corrections for the third tie line 7 INTREPID corrects the third tie line Signal values for the errors determined in step 7 It does this in the same way as it did with the second tie line in step 5 8 INTREPID repeats steps 6 9 including the corrected third tie line in the calculation of the acquisition line only error curve and calculating corrections for the 4th tie line It continues in this way until it has corrected all of the tie lines Stage 2 Levelling the flights Having levelled the tie lines we may now assume that the remaining misclosures are due to acquisition line errors INTREPID calculates a least squares fit curve for the misclosures along the flight and uses it as a source for the corrections to the acquisition line Signal values in the flight For a diagram of this operation refer to the diagram of step 2 in the tie line levelling stage above The flight correction is similar except that you are calculating the curve along the flight instead of the tie line This step is sometimes described as Drifting the acquisition lines by flight to the tie lines If your dataset has no flight number field you must omit this step 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 43 Library Help Top
71. meters do not have significant changes in accuracy with time but the readings are subject to other sources of error such as diurnal variations Radiometric data are also subject to various errors such as the changing of energy windows boundaries with temperature Whatever the source of errors we refer to them as instrument drift or simply drift And assume that they can be approximated as a function of time by a piecewise polynomial the so called drift curves Whatever the source of drift provided that the basic polynomial approximation assumption holds the polynomial levelling method is an effective technique for cross referencing acquisition and tie line data and systematically apportioning the misclosure between the acquisition and tie lines Steps in polynomial levelling Polynomial levelling has up to four stages 1 Level the tie lines assuming that the principal tie line has no errors 2 Correct each flight assuming that the tie lines are correct This step is sometimes described as Drifting the acquisition lines by flight to the tie lines 3 Correct the individual acquisition lines assuming that the tie lines are correct This step is sometimes described as Drifting the acquisition lines individually to the tie lines 4 Correct the individual tie lines again assuming that the acquisition lines are correct This is an optional step intended to remove any last residual errors This step is sometimes described as Drifting the
72. n store tie line lists as text files for use in batch mode tasks or later sessions If you will be executing a task in batch mode using a tie line list you must create a tie line list file Here is an example of tie line list file which could have the name eba_tie parm TieList Begin List 7122 7111 7121 TieList End gt gt To save the current tie line list Choose Save List from the Tie Line menu INTREPID displays the Save List dialog box Locate the directory for the list file if necessary Specify the name for the list file INTREPID will automatically add the extension parm and choose Open gt gt To load an existing tie line list If the tie line list you require already exists as a tie line list parm file choose Load List from the Tie Line menu INTREPID displays the Load List dialog box Locate the directory for the list file if necessary Select click the file required and choose Open Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 40 Library Help Top 4 Back gt The Polynomial drift estimation levelling method Library Help Top Drift curves The polynomial levelling method involves the calculation of least squares fit along flights tie lines and acquisition lines These curves plot misclosure differences between Signal values in tie lines and acquisition lines against time Modern magneto
73. nd time data then you can use this data to synchronise the datasets Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 29 Library Help Top lt 4 Back gt Time matching options As long as the results match properly i e INTREPID can calculate matching internal Julian time fields from them the two datasets involved can have any of the following A start time field and time calculated from fiducial numbers Fiducial alias and a fiducial factor FiducialFactor alias No start time field and time calculated from fiducial numbers Fiducial alias and a fiducial factor FiducialF actor alias assuming fiducial 0 represents midnight at the start of the survey day No start time field and a time field nominated as the fiducial field Fiducial alias Flight Fiducial synchronisation If you reconstructed the flights using flight and fiducial numbers and the base station dataset has matching flight and fiducial numbers you can use them to synchronise the datasets Specifying Diurnal corrections Library Help Top gt gt To specify Diurnal corrections Intrepid ProLevelling Tool Corrections Display Tie Management CrossOver Management Magnetism Base Specify Input i 3 Specify Output T ws H P ae H Specify Report F E H Load cross overs ua E e Save cross overs Spe
74. ndow Displaying options and using task specification files Displaying options You can view a list of the files and parameters options you have set for the current Levelling session by saving a task specification file see next section then viewing it in a text editor You can view graphically the effects of options that you have set in the Levelling window See Display style markers vs colours and Crossover and line display options for instructions Examining the crossovers dataset is another way of obtaining information about your specifications in a Levelling session See Creating and Using Crossovers Datasets for details Using task specification files gt gt To create a task specification file with the Levelling tool 1 Specify all files and parameters 2 If possible execute the task choose Apply to ensure that it will work 3 Choose Save Options from the File menu Specify a task specification file INTREPID will add the extension job INTREPID will create the file with the settings current at the time of the Save Options operation For full instructions on creating and editing task specification files see INTREPID task specification job files R06 V5 0 Intrepid also re leases GOOGLE protobuf syntax for this tool thereby deprecating this older PARMS syntax In the examples directory distributed with the software are directories jobs levelling and tasks levelling Identical processes are given there with both syntax
75. ne depend on the corrections for the previous tie line INTREPID however does not automatically recalculate all of the corrections for tie lines later in the list if you change the parameters for one of the tie lines When INTREPID calculates the polynomial and corrections for a tie line it always uses the set of existing corrections for earlier tie lines at the time it is performing the calculation Levelling the flights assuming that the tie lines are correct 8 Ifthe Level Flights Assuming that the Tie Lines are Correct check box in the Select Defaults for Polynomial dialog box was off go to the next step INTREPID displays a panel for the next selected stage of levelling flights Choose Apply to calculate the polynomial for the first flight using the misclosures corrected by the tie line levelling process if performed Step 7 Under the assumptions of polynomial levelling this curve represents acquisition line error only INTREPID displays the curve with the crossover misclosure values corrected so far of the first flight The offsets of the misclosures from this curve represent acquisition line errors in the flight which INTREPID proposes to correct creating new acquisition line Signal values V Y AutoScale units cm Polynomial Order Piecewise Window0 Smoothing Length OK APPLY CANCEL 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levell
76. ne display options for instructions Polynomial levelling You can use the Polynomial correction technique to eliminate the effects of instrument drift and gross levelling errors The technique involves fitting a polynomial curve through the misclosures along the tie lines then along the flights and finally along each acquisition line This method uses as a starting point the tie line that you consider to be the most level 1 e with the smallest average misclosure and the smallest variation in misclosures INTREPID uses this tie line the principal tie line to detect errors in other tie lines and in acquisition lines The Polynomial levelling correction alters the Signal values of the data Choosing the principal tie line and the tie line order To prepare for the polynomial corrections you must choose the principal tie line then determine the order in which the rest of the tie lines will be processed You can choose one or more further tie lines after the first that you consider to be reasonably level INTREPID will use them after the initial tie line INTREPID will then automatically select the rest of the tie lines in sequence To assist you to select the most level tie line INTREPID can display data for crossovers along a tie line in a variety of ways See Crossover and line display options and Displaying profiles along individual tie lines for instructions gt gt To create the tie line calculation list 1 Choose Create List
77. ng INTREPID R04 for more information about background window or ntout file reports Single Gradient Corrections Gedex and Rio have invested significantly in single gravity gradient measuring systems in the hope that this strategy will deliver a superior signal for detecting ore bodies compared to a full tensor gradient system One channel measured with a 1 Eotvos noise envelope maybe more easily achieved than 6 channels with 2E The hope has also been that Fourier theory can be used to recover what has not been measured in terms of the other tensor gradient components This is easy enough to propose but of course Mother Nature has her own ways and you tend to get nothing for nothing in this type of context The spatial indexing technique described in the next section probably gives you the best chance at something which yields stabilised estimates of non measured components while still residing in the profile world Otherwise you have to level and grid your signal before you have any chance and with those steps you immediately lose 80 of the signal content along the profiles and so the high frequency resolving power you have hoped for is immediately compromised Transverse gradients are very important when defining sources off line Any anomaly bull s eyes will also remain under the profile and not off line This is not an issue with FTG data All teachers of geophysics and would be inverstors in geophysical survey instruments take note
78. nt survey is newly acquired and you wish to get a sense of the turbulence encounted as the survey was flown Suggested query 1 Use the tensor correction calculate the Frobinius Norm field 2 Apply the correction and save the new QC signal field 3 Examine this field in the flight path plot tool 1 5 Levelling busts patterns in the grid that look as if they are associated with discrepancies in flight data 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 66 Library Help Top 4 Back gt 4 Alternatively grid the new field and examine the flight lines for noise levels Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top Applying the corrections to the whole dataset Line correction and tie levelling T30 67 lt 4 Back gt After you have specified your corrections for the dataset to be levelled you can apply the corrections to all data points gt gt To apply the corrections to all data points 1 Specify whether to save new corrected X Y and Signal values or values of corrections in the output field using the Output Changes Only check box below the individual crossover display area turn off for corrected values You are most unlikely to see the following pop up as you would need to be simultaneously having BETA change sets for each of the listed correction types The usual situation is to a
79. of saying it the GRF is differenced out of the signal Level XY corrections inferring the correct location Two readings on the same location with diurnal and parallax corrections applied should be the same If there is a non zero misclosure for a crossover point it could be the result of an error in the measurement of location Now that we use GPS navigation the degree and frequency of this error is vastly reduced Non zero misclosures are more likely due to problems with acquisition height In the Level XY correction process INTREPID searches for the true location of the crossover point by trying to find a position nearby where extrapolated crossover values are the same for the tie line and the acquisition line To search for this point INTREPID uses the gradients that it calculated for the tie line and the acquisition line at the crossover point INTREPID adjusts the line with the highest crossover gradient the higher gradient line As this is a positional adjustment there is nothing special required for tensors Theory of the Level XY correction Library Help Top 1 The readings near the crossover on the higher gradient line may have been attributed to the wrong location due to navigational errors 2 The location of readings near the crossover on the other line may be more accurate 3 By a process of extrapolation you can estimate values at other locations near the measured crossover point in the higher gradient line 4
80. on along each line of the dataset containing the crossovers Since each crossover point occurs at the intersection of two lines there are two records of each crossover one from the acquisition line and one from the tie line In each record there is information about both lines Each group in the crossovers dataset contains a line labelled LNUM which intersects with one or more other lines labelled TNUM Therefore a histogram of the misclosures in the crossovers dataset will appear symmetrical around zero since each misclosure occurs twice in the dataset one having a positive value the other having a negative value The BETA misclosure is the proposed new misclosure after levelling corrections have been applied The initial value for BETA is the same as the misclosure value It gets progressively altered as each levelling attempt is applied Normally a single levelling pass is done but it is possible to do repeated levelling In this case INTREPID stores all Signal value corrections as changes to the misclosure and BETA represents the final misclosure value after all levelling attempts have been applied Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Line correction and tie levelling T30 58 4 Back gt For each crossover point the dataset has the following fields Field Description FLIGHT Flight number o
81. ossover dataset and choose Save See Specifying input and output files for general information about loading and saving data Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 57 Library Help Top lt 4 Back gt gt gt To open a crossovers dataset 1 Choose Open Crossovers from the File menu INTREPID displays the Open Crossovers dialog box 2 Specify the dataset See Specifying input and output files for general information about loading and saving data INTREPID will prompt you to specify which sets of proposed corrections from the crossovers dataset to retrieve and treat as current proposed corrections Choose Corrections to Apply F Heading T Parallax TC Gr T Diurnal F Levelxy F LevelPOLY F LevelLoop Apply Cancel This dialog box contains a check box for each set of proposed corrections contained in the crossovers dataset 3 Turn on the check boxes for the corrections you wish to load as the current proposed corrections then choose Apply OK INTREPID will load the crossovers dataset INTREPID will adopt the selected crossover based proposed corrections lt Immediate proposed corrections are for information only in the crossovers dataset and have no effect on any immediate correction operation in this tool Crossovers dataset description The crossovers dataset is a line dataset containing crossover informati
82. ound your data To correct for this you can take readings from a nearby stationary base station during the flight synchronised by the fiducial clock These readings will show only the diurnal fluctuations If you subtract the base station readings from the flight data you will remove the background errors The Diurnal correction alters the Signal values of the data It requires a separate line dataset containing the base station data Base station Survey data synchronisation methods Library Help Top Before applying diurnal corrections INTREPID must be able to synchronise the dataset to be levelled with the base station dataset matching the survey data with the correct base station data INTREPID provides synchronisation methods corresponding to your flight reconstruction method Date Time Julian Day Time and Flight Fiducial 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 28 Library Help Top lt 4 Back gt matching See Chronological order reconstructing the flights for details of this process Date time synchronisation If you reconstructed the flights using Date and time data and the base station dataset has matching Date and time data then you can use this data to synchronise the datasets Julian day time synchronisation If you reconstructed the flights using Julian day and time data and the base station dataset has matching Julian day a
83. p Top Library Help Top Line correction and tie levelling T30 42 4 Back gt 5 INTREPID uses the principal tie line Signal values and the corrected second tie line Signal values to calculate a new curve along a flight This is based on more data and is therefore a better estimate of the acquisition line only errors for the flight 6 INTREPID examines the third tie line s misclosures records their offset from the curve created in step 6 Since the curve represents acquisition line only error these offsets must be errors in the tie line Signal values for the third tie line Levelling of tie line data Step 3 Second estimate of the acquisition line only error curve x gt Size of misclosure Z units Time along flight The curve is calculated by least squares fit to misclosures on the principal tie line and corrected misclosures on the second tie line points marked O Since the principal and second tie line Z values are both now assumed to have no error the curve represents the errors due to acquisition line Z values only The deviation of the third tie line misclosures from this curve must be due to errors in the third tie line Z values We can record these errors and use them to correct the third tie line Z values Misclosures on principal tie line Corrected misclosures on second tie line Misclosures on third tie line Errors due to tie line Z values offsets from acquisition line on
84. point dataset You can view the crossovers as either a line or point dataset in INTREPID tools if desired If you wish to view crossovers as a point dataset you must first prepare it gt gt To prepare and view a crossovers dataset as a point dataset 1 Create a file with the extension PNT in the crossovers dataset directory INTREPID will not look inside this file so it may have any content 2 Open the crossovers dataset as a point dataset in the tool you wish to use If you are using the Flight Path Editor choose Cancel when INTREPID prompts you for the Signal fields for point colour and size INTREPID displays the dataset as a point dataset Display style markers vs colours You can display data for crossover points using crossover markers or crossover colours Crossover markers are cross symbols They are black if they represent a i negative quantity and red if they represent a positive quantity Their size t directly corresponds to the magnitude of the quantity they represent a Crossover colours are coloured dots Their colour corresponds to a value according to a table of value ranges and colours within the Levelling program gt gt To select crossover markers or colours Choose Markers or Colours from the options in the Style menu PZ Intrepid ProLeveling Tool p So a File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Help Original Misclosures V
85. rdinate location Line Type Line type Line Number Line number Fiducial Fiducial count Flightnumber Flight number Clearance Sensor height a This alias normally refers to the distance from the sensor to the ground In Levelling the field is only used for the GRF correction and may therefore be any sensor height measure See The geomagnetic reference field in INTREPID R15 for details If your survey has a time field containing the time for each data point and you wish to reconstructing flights using this field you must assign the time field to the Fiducial alias See Chronological order reconstructing the flights for details of this process If there is no flight number field in the dataset you can still perform all levelling corrections except for Levelling the flights assuming that the tie lines are correct in Polynomial levelling You should omit this process if you are performing the Polynomial levelling correction See The Polynomial drift estimation levelling method and Selecting polynomial levelling process stages for instructions See Vector dataset field aliases in INTREPID database file and data structures R05 for more information about aliases File menu options Specify Input Choose Specify Input from the File menu INTREPID displays the Load Signal dialog box Locate the correct dataset directory if necessary Specify the name of the Signal values field to be levelled and choose Open If you have
86. re within a larger square The large square represents the whole display and the small square the part visible on the screen When you drag the small square to a different part of the large square INTREPID shows the corresponding part of the display If you have zoomed out to view the whole display the small square may occupy the whole of the large square and may therefore not be visible Chronological order reconstructing the flights You must reconstruct the flights if you wish to perform any of the following operations Make diurnal or GRF corrections for changes in the background signal See Diurnal corrections and GRF Subtracting the Earth s core magnetic field e Make crossover based corrections See Level XY corrections inferring the correct location Polynomial levelling and Loop closure levelling View graphs of data along individual flights See Displaying profiles along individual tie lines Reconstructing the flights will internally sort the data into chronological order If INTREPID only has available the flight numbers and fiducials it will simply sort the data in order of flights then the traverse lines of each flight in order of first fiducial value If you supply a flight date field and optionally a time field INTREPID will be able to sort the data using these fields You must supply flight date and time if you wish to apply GRF and or diurnal corrections with maximum accuracy See GRF Subtractin
87. rrections Since base station data typically has only one data point for about 100 data points in the survey dataset INTREPID will interpolate the corrections for the data points that do not have corresponding data points in the base station dataset Time lag Some diurnal fluctuations occur quite rapidly and may be due to sunspot activity This may be vary with the angle of the sun If the base station is some distance from the survey area the angle of the sun at a certain time during the survey will occur at a slightly different time at the base station due to the Earth s rotation You can specify the time difference in seconds between the base station and the central point of the survey area Specify the difference in seconds using a positive number if the base station is East of the survey area and a negative number if it is West Examining base station data You can view the following base station data Library Help Top A list of flights or julian days for which data exists in the base station dataset A list of all flight numbers in the dataset being levelled A profile graph of the base station Signal field for a given flight A profile graph of the base station Signal field for a given date or julian day 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 32 Library Help Top Library Help Top 4 Back gt gt gt To examine base station data 1
88. s XYmove Diurnal corrections colours or red and black symbols Diurnal GRF corrections GRF Loop closure levelling corrections Loop Polynomial levelling corrections Polynomial The following illustrations show displays from the Display menu options eas E Intrepid Proteveling Tool _ EZ Intrepid ProLevelling Tool po GI eiei m ie table eed ist tie nt ate Anan File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Style Help eines Coron Crossover Tiss w w Current Crossover Aoa iins 140351 0 6000 0 6000 0 AcqLineFid 467916 82 FlighCruise 25 Acq Line value 59315 56 Acq Line grad 0 04 Acq Line grad 0 04 Tie Line 174071 0 Tie Line 174071 0 Tie Line Fid 96605 99 Tie LineFid 96605 39 Tie FlightNo 29 Tie FlightNo 29 5997 5 Tie Linevalue 59317 67 5997 5 Tie Line value 59317 67 Tie gradient 0 06 Tie gradient 0 06 is 2 11 i E Misclosure l Misclosure 211 Betavalue 21 Betavalue 211 Long East 480 57 i Long East 480 57 LatNorth 5996 37 5996 37 5995 0 No 5995 0 Lat North Elevation 472 85 I Elevation 472 85 7 Use xov
89. sk you to confirm you want to commit to the change set from the single levelling method you have been using Choose Corrections to Apply M Heading l Parallax l Gr l Diurnal M Levelxy M LevelPOLY M LevelLoop Apply Cancel 2 Choose Apply Corrections near the bottom right corner of the Levelling window INTREPID displays the Choose Corrections to Apply dialog box This dialog box contains a check box for each correction that you have specified in this session or that was present in the last crossovers dataset that you loaded 3 Turn on the check boxes for the corrections you wish to apply then choose Apply INTREPID will apply the corrections to the whole dataset 4 Ifyou wish to apply other already specified corrections go to step 1 Help You can use the Help menu to display help text on the topics shown in the menu illustration below Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 68 Library Help Top lt 4 Back gt Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 69 Library Help Top lt 4 Back gt Exit from the Levelling tool gt gt To exit from the Levelling tool 1 Check that you have saved any crossover or corrected data files that you wish to keep 2 Choose Quit from the File menu INTREPID will close the Levelling wi
90. square root of the Signal value corresponds to the standard deviation and indicates the stability of the data weight Z All Weights 1 If you select this option INTREPID assigns weight 1 to all crossover values Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 50 Library Help Top 4 Back gt Polynomial levelling parameters When you commence a polynomial levelling process See Step 4 5 in Section Using the Polynomial levelling process and for each line or flight at each stage of the process See Steps 7 8 9 10 you can specify the order of the polynomial function the width of the piecewise window and the smoothing length Polynomial order Default Order of Correction Functions This parameter determines the order of the piecewise polynomial The default order is 3 Piecewise window size This parameter determines the number of adjacent crossovers to use in computing the piecewise polynomial for a section of a line The default value is 50 Smoothing length The polynomial fit may be poor at the ends of a line or flight so INTREPID applies a smoothing filter in this region This parameter determines the number of crossovers at the end of the line or flight to which INTREPID apples the smoothing filter The default value is 5 Selecting polynomial levelling process stages Library Help Top You can specify the polynomial levelling s
91. sure convergence NumberSamples_EstimatePotential 21 the bigger the window the smoother the result Library Help Top 2012 Intrepid Geophysics lt 4 Back gt
92. sure that it locates a high gradient if it exists at a crossover INTREPID can search for the highest gradient in the region of the crossover and record that as the gradient at the crossover See step 3 in Section Calculating the crossovers for instructions Crossover report INTREPID writes a crossover report to a file in the dataset directory See The crossover report file for more details Calculating the crossovers Library Help Top gt gt To calculate the crossovers 1 Choose Find Crossovers at the bottom right of the Levelling window INTREPID will specify the Signal Field Pre Process dialog box This adapts for scalar tensor signals F E F oeme E T a APPLY Vector Tensor signal FILTER C Convolve None C Naudy despiker C LaCosteRC C Median LaCosteCurvature Convolve Naudy Median Alias Filter C Local Mean Window Size data points Naudy Filter Tolerance 100000 Use Corrected Data C Use Rejected Data OK Cancel M Marine acquisition data Sample Interval seconds _ 1 00 OK Cancel 2 Select the process you require from the Signal Field Pre Process options The default process is None If you have selected Convolve Fuller specify the size of the convolution window in data points using the Window Size data points text box See Fuller filter in INTREPID spatial and time domain filters and transformations R13 for further information If you have c
93. t In this case the height field will override the fixed height defined in the GUI The GRF correction alters the Signal values of the data The GRF field itself can be saved by clicking the Output Changes Only box on the right hand side of the tool In this case the specified output field will contain the calculated GRF gt gt To specify the GRF correction 1 Choose GRF from the Corrections menu INTREPID displays the GRF Corrections dialog box if Enter nominal fixed height m survey date dd mm yyyy GRF computatior n interval m am Enter nominal fixed height m survey date dd mm yyyy GRF computation interval m 0 0 01 1 2000 100 0 C IGRF C AGRF Available GRF epochs from 1945 to 2010 After this dialog you will be prompted fora DataBase Field Height_Above_Spheroid SEA Level This overrides nominal sensor ht Also the fixed date can be overridden by the date field that is prompted for in Reconstruct Flights Ok Cancel d 2 Enter the mean sensor height ASL in metres survey date in the format dd mm yyyy and the GRF computation interval in metres in the parameters text box 3 Choose IGRF International or AGRF Australian using the IGRF AGRF option buttons 4 Choose OK Intrepid will display a chooser requesting a field containing height above spheroid data If you wish to compute a variable elevation GRF select the field and click OK If you wish to
94. t changing the parameters view the results for the next or previous tie line or a tie line you choose from a list Choose Next Previous or Go To Specify automatic or manual Y axis scaling for the graph Turn the Y Auto Scale check box on or off If you turn Auto Scale off specify the scale in Signal units cm in the Scale text box Change the Polynomial Order Piecewise Window or Smoothing Length parameters for the next curve calculation See Polynomial levelling parameters for details about the purposes of these parameters 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 46 Library Help Top Library Help Top 4 Back gt Recalculate the curve for the current tie line using the currently displayed parameters and display the results Choose Apply INTREPID only recalculates results for the current tie line at this time If you have changed the parameters recalculate the curve for the current tie line then recalculate and view the results for the next or previous tie line or a tie line you choose from a list Choose Next Previous or Go To INTREPID only recalculates results for tie lines whose graphs you view Recalculate the curve and corrections for the current tie line and all tie lines that follow it in the list then commence the next levelling stage Choose OK Note According to the tie line levelling method the corrections for each tie li
95. tages for INTREPID to perform Each stage can be performed independently If you omit an earlier stage you are assuming that it is not necessary When you commence polynomial levelling See Step 4 6 in SectionUsing the Polynomial levelling process INTREPID prompts you to select the levelling stages to perform using the Select Defaults for Polynomial dialog box Enter smoothing length default order of correction functions and width of piecewise window 5150 V Level tie lines to principal tie line iV i V Level acquisition lines assuming that the tie lines are corret F Level tie lines assuming that acquisition lines are correct F Use Distance Weighting Ok Cancel L Level Tie Lines to Principal Tie Line Turn this check box on if you wish to level the tie lines assuming one tie line is correct See Stage 1 Levelling the tie lines and Step 7 in Using the Polynomial levelling process for details Level Flights Assuming that the Tie Lines are Correct Turn this check box on if you wish to level the flights assuming that the tie lines are correct If your dataset has no flight number field you must turn off the check box for this step See Stage 2 Levelling the flights and Step 8 in Using the Polynomial levelling process for details Level Acquisition Lines Assuming that the Tie Lines are Correct Turn this check box on if you wish to level the acquisition lines assuming
96. that the tie lines and flights are correct See Stage 3 Levelling the individual acquisition lines and Step 9 in Using the Polynomial levelling process for details Level Tie Lines Assuming that the Acquisition Lines are Correct Turn this check box on if you wish to level the tie lines assuming that the acquisition lines are correct See Stage 4 Levelling the individual tie lines again and Step 9 in Using the Polynomial levelling process for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 51 Library Help Top lt 4 Back gt Improving the polynomial fit at line and flight ends At the ends of lines or flights the fit of the polynomial may be poor because there is no constraint on the polynomial beyond the limits of the data and they may diverge from the expected result To help remedy this INTREPID applies a smoothing filter at the ends of the lines or flights You can determine the number of crossovers to be filtered using the Smoothing Length parameter See Polynomial levelling parameters If the ends of the tie lines whip out of control in this way try the following in order of preference 1 Change the piecewise window size See Polynomial levelling parameters 2 Reduce the polynomial order if it is greater than 4 See Polynomial levelling parameters and 3 Vary the tie line order for the tie line levelling process See Choosing the principal
97. the Fiducial alias before commencing the Levelling session See Specifying input and output files for details If your dataset includes a time field that specifies the start time for each flight or each line you can use it and the Fiducial field to calculate the time for each reading In this case it would be appropriate for the time field to be a group by field We can call it a start time field If your dataset has no time field then INTREPID assumes that fiducial 0 is midnight sat the start of the flight date The time must be expressed in number of seconds since midnight at the beginning of the flight date For example 6 30 am will be 23400 60 x 60 x 62 2012 Intrepid Geophysics 4 Back gt Library Help Top INTREPID User Manual Line correction and tie levelling T30 14 Library Help Top lt 4 Back gt Using Fiducial numbers to calculate time INTREPID will calculate and record internally a time for each data point For each data point it converts the fiducial count into seconds using the Fiducial factor then adds the value of the start time field if specified to give the time for the data point since midnight at the start of the flight date Fiducial factor This parameter is the sampling interval of the dataset being levelled For example a fiducial factor of 0 1 indicates 10 fiducial counts per second If you have specified a time field expressed in seconds by assigning it to the Fiducial alias you
98. tion logical expression or by turning crossovers on and off individually Crossovers that are turned on to be included in the corrections are enabled Crossovers that are turned off not to be included in the corrections are disabled The Use Xover check box indicates whether the current crossover is enabled for the levelling process If it is on the crossover is enabled If it is off the crossover is disabled INTREPID still displays excluded crossovers in the dataset display area Disabling and enabling individual crossovers gt gt To disable a crossover 1 Select the crossover you wish to view by clicking it in the dataset display area with the left mouse button 2 Turn off the Use Xover check box gt gt To enable a crossover 1 Select the crossover you wish to view by clicking it in the dataset display area with the left mouse button 2 Turn on the Use Xover check box Disabling crossovers using a condition You can disable crossovers using a condition in the form of a logical expression The expression must use standard INTREPID expressions notation and can involve any crossovers dataset field name See Creating and Using Crossovers Datasets for further details about crossovers datasets You must save a crossovers dataset in order to use the condition expression In the Disable Crossover Points dialog box see below INTREPID lists the names of the crossovers dataset fields Notes The crossovers for which the e
99. tions mauritania_ftg_subset_Intrepid DIR GS_Fiducial TYPEName D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR GS_LType inputLine D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR GS_Line inputFlights D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR GS_Flight InputHeightAboveSpheroid D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR Altitude InputRequiredHeightAboveSpheroid D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR Drape OutputZ D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR Zout ReportFile prolevelling rpt runType Tensor_Level select the main run type Save_Changes_Only false Gradient_Radius 10 0 not needed FID_Factor 0 1 Use_XY_Accuracy false not needed Date_Style DECIMAL_YEAR not needed Diurnal_Style FLIGHT_DATE_TIME not needed Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 73 Library Help Top lt 4 Back gt TensorCorrection parameters FlightBiases false used for a tensor heading correction Tensor_Adjustment Profile_Adjust_Altitude Tensor_Forcing TENSORnote_Norm used for loop levelling a tensor signal how to mea
100. tions near the bottom right corner of the Levelling window INTREPID will apply the corrections to the whole set of data See Applying the corrections to the whole dataset for instructions and options If you wish to record the specifications for this process in a job file in order to perform a similar Levelling task in batch mode use Save Options from the File menu See Specifying input and output files for detailed instructions If you have corrections to make to another dataset repeat steps 3 12 for the another dataset Exit from Levelling by choosing Quit from the File menu 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Line correction and tie levelling T30 6 4 Back gt You can view Help information by choosing options from the Help menu See Help You can execute Levelling in batch mode using a task specification job file that you have previously prepared See Displaying options and using task specification files for details Preliminary processes The following table lists the corrections available in this tool and the preliminary processes required before you can perform them Reconstruct Specify base Calculate Specify tie flights station data crossovers line list Parallax Heading Diurnal yes yes GRF yes Level XY yes yes Polynomial yes yes yes Loop closure yes yes Suggested Levelling regimes Library H
101. trepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 15 Library Help Top lt 4 Back gt Flight reconstruction where flight date and time are not available If you do not have dates and times available for the dataset being levelled you can reconstruct the flights using flight number and fiducial numbers only In this case INTREPID simply sorts the data into order of flight number then fiducial order within each flight gt gt To chronologically sort the data using fiducials only Choose Flight Fiducial from Reconstruct flights cascade in the File menu If there is no field specified for the Flightnumber alias INTREPID will prompt you for the Flight number field If there is no flight number data in the dataset you can use the line number instead Without flight numbers you can still perform all levelling corrections except for Levelling the flights assuming that the tie lines are correct in Polynomial levelling You should omit this process if you are performing the Polynomial levelling correction See The Polynomial drift estimation levelling method and Selecting polynomial levelling process stages for instructions INTREPID will reconstruct the flights Internal calculated date and time INTREPID calculates a date for each line and a time for each data point It expresses these values in Julian format with date as a whole number and time as a number between 0 and 1 a fra
102. trepid Proteveliing Tool ID LUZ 60 Je es File Corrections Display Tie Management CrossOver Management Magnetism BaseStation Style Help Acq Line Acq Line Fid FlighlCruise Acq Line value Acq Line grad Tie Line Tie Line Fid ie Fli o Tie Line value Tie gradient Misclosure CrossOver Corrections 250 000 x s500 0 750 0 atus Line Save As Zoomin Zoom Out C Query C Zoom Rectangle 3 Specify the Signal field of the line dataset whose values you wish to level Use Specify Input from the File menu See Specifying input and output files for detailed instructions 4 Specify field names for your corrected data or corrections using Specify Output from the File menu INTREPID displays Save dialog boxes for X Y and Signal in turn See Specifying input and output files for detailed instructions 5 Ifrequired sort the data into chronological order INTREPID sorts its working copy of the data not the dataset itself Choose Reconstruct Flights from the File menu and select either Date time Julian Day or Fiducials as a basis for the sorting See Chronological order reconstructing the flights for detailed instructions 6 If required obtain the Crossover data the data points where there is both an acquisition line and a tie line reading for the same location To calculate the crossovers use Find Crossovers at the bottom right of the Levelling window
103. urrent Polynomial proposed correction Betas Beta Misclosures The current running total of proposed corrections expressed as a modified misclosure See Proposed corrections and the beta misclosure for a definition Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 63 Library Help Top lt 4 Back gt 4 INTREPID displays the Select Tie to be Displayed dialog Select Tie to be display box 174041 00 Select click the number of the tie line you wish to examine then choose OK 5 Ifyou selected the One Flight for Tie option in step 2 above INTREPID displays the Select Flight dialog box Select click the number of the flight you wish to examine then choose OK INTREPID displays the tie line profile in a separate window READING Tie 174061 000000 59406 79 Mag Intensity 378 15 iv 4349 51 9320 86 59292 22 83484 52 85412 57 87340 63 89268 69 scaled FID 6 When you have finished viewing the display choose OK INTREPID will close the Display Along Individual Tie Lines window Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 64 Library Help Top lt 4 Back gt The Geomagnetic Reference Field calculator You can use this calculator to obtain a Geomagnetic Reference Field GRF value for any location expressed in latitud
104. veyStyle End PolynominalCorrection Begin Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Line correction and tie levelling T30 72 Library Help Top lt 4 Back gt Level_to_Principal_Tie Yes Tie_line Begin Poly Order 3 Piecewise_Window 80 Smoothing_Length 15 Tie line End Drift_Flights_onto_Ties Yes Flight Begin Poly Order 2 Piecewise _ Window Smoothing_Length Flight End Drift_Traverses_onto_Ties Yes Traverse Begin Poly Order 0 Piecewise Window Smoothing_Length Traverse End Drift_Ties_onto_Traverses No Tie_Traverse Begin Poly Order 3 Piecewise_Window 50 Smoothing_Length Tie Traverse End Poly Iterations 1 PolyTieListFile disk1 survey eba tiel parm PolynominalCorrection End Parameters End Process End Ist 1 o ll au o l o Tensor Altitude drape correction Example Protobuf syntax Example task file V5 0 protbuf syntax levelling Usage fmanager batch tensor_drape_correction task Show an altitude correction for the FTG processing IntrepidTask Levelling InputZ D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR Tensor_FAlev InputX D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR x InputY D test_data FullTests tensor drape_corrections mauritania_ftg_subset_Intrepid DIR Y inputFid D test_data FullTests tensor drape_correc
105. xpression is true will be disabled Ifyou use the crossover gradient in the expression use the field LGRAD e g ABS LGRAD gt 10 There are records for each line in the dataset so in fact each crossover is represented twice in the crossovers dataset once from the viewpoint of the acquisition line and once from the viewpoint of the tie line The condition will therefore be applied twice for each crossover If you specifically wish to apply the condition to acquisition lines or tie lines only include a reference to line type in the expression e g amp amp LTYPE 2 will exclude all lines except acquisition lines See INTREPID expressions and functions R12 for full information about expressions 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 23 Library Help Top lt 4 Back gt gt gt To disable crossovers using a condition 1 Choose Disable from the Crossover menu fed Intrepid ProLevelling Tool File Corrections Display Tie Management CrossOver Management Magnetism BaseStation ZE INTREPID displays the Disable Crossover Points dialog box containing a list of the crossovers datasets fields and a text box for the logical expression Disable cross over points Re enable all Clear betas t t Ht t ttt Available cross over fields xY_Z MISCLOSURE BETA LGRAD TYPE LNUM FLIGHT _LFID TNUM TIEFLIGHT TFID HEADING DIURNAL IOR
106. y Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Line correction and tie levelling T30 26 Library Help Top 4 Back gt Loop closure corrections Crossover based Finds an optimum correction for each crossover using an iterative procedure Single Gradient corrections alpha only and also Cross over based Finds 3D Truncated Fourier series methods to attempt to recover the tensor from one of its parts The VKc is Tzz Tyy Tensor corrections Crossover based Leads into a new space for a arnge of innovative tensor only methodes to assist in levelling this data signal type Heading corrections for errors due to aircraft direction Library Help Top Due to a combination of the Earth s magnetic field and the permanent magnetisation of the sensing craft measurements may slightly differ depending on the direction of travel Compensation for scalar measurments have been turned into a black box process over the years This does not work for highjer order gradient measures and a whole new invention of techniques is required to correct for Roll Pitch and Yaw errors in the coming years Traditionally for a TMI scalar signal after aircraft compensation you can specify correction adjustments for four directions and add an adjustment to each data point according to the line direction INTREPID calculates the correction for each direction using a smooth curve from 0 360 passing through the

Line correction and tie levelling (T30)

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