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Spectral domain grid filters tool (GridFFT) (T40)

1. The filter applied The output dataset Spatial View Spectral Image View Radial Power Spectrum Input Spectrum Filter Response Filtered Spectrum Amplitude Phase Amplitude Phase Amplitude Phase Spatial View Spectral Image View Radial Power Spectrum Input Spectrum Filter Response Filtered Spectrum Amplitude Phase Amplitude Phase Amplitude Phase Radial Power Spectrum tab This tab show the radially averaged power spectrum graphs of the input dataset blue and the output dataset red See Power spectrum graphs in INTREPID 7 spectral domain operations reference R14 for more information about these graphs Spatial View Spectral Map Vie 10 a Shows the radial power spectra before and after filtering 8 o sE a a 6 anon age anooongg a 4 SEIMEI sence aa 3 Aee A fo 9999990999 So 5oc 0000 9000 000 09 ooto 0 2 Wavenumber in cy km 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 8 Library Help Top lt 4 Back gt Specifying Input and Output Filtered Datasets Parent topic In this section Spectral An R x domain grid e Specifying input and output filtered datasets overview filters tool I t erid dataset Grid FFT nput grid datase T40 Expanded and filled input grid dataset Expanded input grid after edge damping Saving FFT of input grid dataset Output grid da
2. Here is an example Begin End block Reduction2D Begin FromInclination 7 709789858562574 FromDeclination 20 067014031276116 ToInclination 90 0 ToDeclination 0 AmplitudeLimit 20 0 LowLatitude No Variable No TaylorExpansionOrder 1 UseDirCos No HalfWidth 20 0 RolloffDeg 0 5 Reduction2D End Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Spectral domain grid filters tool GridFFT T40 IGRF Calculator gt gt To use the IGRF Calculator 1 In Reduction Properties click IGRF INTREPID displays the IGRF Calculator Pr IGRF International Geomagnetic Reference Field Calculator Parameters Day 26 v Month November X Year 2012 X Epoch IGRF2010 Altitude Latitude Longitude Resultant Field Magnetic Field Dedination Indination 7 71 25181 22nT 20 07 29 4 Back gt 2 Set Day Month Year IGRF Epoch Altitude Latitude and Longitude of the input data see table below describing the parameters 3 Note the calculated Field Strength Declination and Inclination values 4 Click OK INTREPID inserts the new calculated values into the To Declination and To Inclination text boxes IGRF Calculator parameters Parameter Unit Description Default Day Day Date of survey Today s Date Month Month Date of survey Year Year Date of survey IGRF Epoc
3. Input Band No 1 Grid File distance units metres 7 CAlntrepiditutorials corr_grid_FFT i 2 Tick the Save FFT of Input Grid checkbox 3 The default filename for the FFT grid is input grid name with _FFT appended If you want a different name specify it using FFT of Input Grid text box FFT of Input Grid browse button Saving FFT of input grid dataset task files To keep the spectral domain transformed grid use the F tGridName keyword and assign a filename for the grid Example FftGridName dargo_fft If you leave out this statement GridFFT deletes the spectral domain input grid during the post filtering file clean up 2012 Intrepid Geophysics 4 Back gt Library Help Top INTREPID User Manual Spectral domain grid filters tool GridFFT T40 13 Library Help Top 4 Back gt Output grid dataset Parent topic Specifying Input and Output Filtered Datasets Interactive Task files Library Help Top GridFFT can directly create filtered output datasets in the following formats e INTREPID grid datasets GRID ERMapper grid files ers Geosoft grid files grd The file extension you use GRID ers or grd determines the format of the output grid The default output grid precision IEEE4ByteReal If you want a different precision you need to specify it Output grid dataset interactive Specify the output grid dataset for the filtered g
4. See Frequency or wavelength units For projected grids you can enter distances in single or x 1000 multiple units See Distance unit multiples x 1 and x 1000 e For geodetic grids you can enter distances in metres or degrees Each time you enter a value INTREPID checks that it is between the Fundamental and Nyquist value for the dataset See Fundamental and Nyquist Frequencies of the Input Grid The following diagram shows the possible views of the Low Pass properties e Low Pass Properties Wavelength input Cutoff 3125 m deg Cm Rolloff J 1612 90322581 m Cutoff oom deg Rolloff o0 deg xX Reset default rolloff Reset default rolloff Low Pass Properties Low Pass Properties Frequency input C cyfdeg cy m Cutoff 0 01 cy m 22 19464286 cy deg Cutoff Rolloff 0 0001 cyim Rollott EZ cy deg EA Reset default rolloff Reset default rolloff Projected grid Geodetic grid has choice of input in metres or degrees If your input grid is geodetic GridFFT displays option buttons for you to choose metres or degrees Specify the unit you require then use that unit to enter the parameter values If you specify a value then select the other option button INTREPID automatically converts and displays the value in the new unit using Robin s formula This conversion between metres and degrees is an approximation INTREPID bases it on the mid latitude of the grid Library Help Top 2012 Intrepid
5. Data display area Apply button The following table describes the screen elements Element Purpose Title bar Shows the name of the tool and the input grid dataset Menu bar Enables you to specify input datasets output datesets job files and to view on line help Toolbar Buttons for specifying input and output datasets as well as units and multiples for the filter parameters Fundamental and Nyquist Fundamental and Nyquist frequencies for the input dataset This frequencies or wavelengths also shows the units and multiples you have selected and whether you have selected frequency or wavelength mode Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top Spectral domain grid filters tool GridFFT T40 6 4 Back gt Element Purpose Available filters list A list of filters available You can select filters from this list Filtering process list Sequence of steps in the filtering process When you click an item in the list INTREPID displays the step s properties in the Process step properties area Add amp Remove buttons Use these buttons to add and remove filters from the Filtering process list Process step properties Properties of the currently selected Filtering process step Apply button Click this button to run the filtering process Data display tabs Use these to select the data d
6. FFT Filters Filtering Process Low Pass Input Grid Dataset High Pass Pre FFT Grid Conditioning Band Pass EA Horizontal Derivative Post FFT Grid Restoration Vertical Derivative Output Grid Dataset Continuation Analytic Signal j Total Horizontal Derivative 2 Inthe Filtering Process list select the Filter INTREPID displays the Properties for the filter Filtering Process Continuation Properties Input Grid Dataset Direction Upward x Pre FFT Grid Conditioning Filter 1 Reduction Distance 100 m Filter 2 Continuation Post FFT Grid Restoration W Output Grid Dataset l Use Damping Damping Frequency 5 cyi m 3 Specify the parameters for the filter There is no OK button When finished continue to the next operation Specifying a combinable filter task files Parent topic GridFFT filters overview Task files The CompositeFilter Begin End block contains one or more filter definition Begin End blocks You can only have one CompositeFilter Begin End block in a task file If there are no filters in the CompositeFilter Begin End block you can leave it out The order of filters within the CompositeFilter block is generally unimportant GridFFT combines the filters in a set order and then applies them to the spectral domain transformed data Downward continuation has an exception to this rule about order of filters See Continuation filter Gr
7. File 4 Use the Save Edge Rolled Off Grid File text box or browse button to specify the name of the expanded and edge rolled off input grid dataset Expanded input grid after edge damping task files To keep a copy of the grid after the edge roll off process use the WindowedGridName keyword and assign a filename for the grid Example WindowedGridName dargo_wind If you leave out this statement GridFFT deletes the grid during the post filtering file clean up 2012 Intrepid Geophysics 4 Back gt Library Help Top INTREPID User Manual Spectral domain grid filters tool GridFFT T40 12 Library Help Top 4 Back gt Saving FFT of input grid dataset Parent topic Specifying Input and Output Filtered Datasets Interactive Task files GridFFT saves the spectral domain transformed grid in a grid datsaset to use as input for the filtering operation After use GridF FT normally deletes this grid It is sometimes useful to keep this grid See Saving pre FFT and FFT grid processing products for later reference in INTREPID spectral domain operations reference R14 for details Saving FFT of input grid dataset interactive gt gt To enable saving the FFT of the input grid and specify a filename 1 Display the Input Grid Dataset Properties area click Input Grid Dataset in the Filtering Process list Input Grid Dataset Input Grid CAlntrepiditutorialsicorr_grid PD ers on
8. Taylor series approximation for the gradient of the inclination and declination In this case the IGRF field is used and inclination and declination values cannot be entered manually The user can choose the order of the Taylor series expansion 1 2 3 The higher the order the more accurate the calculation For geomagnetic surveys near the equator at low magnetic field inclinations lt abs 20 the RTP tends to become numerically unstable particularly in the presence of noise The problem usually presents as declination parallel striping in the transformed grid Experience has found that this instability can be partially compensated for by using a pseudo field inclination ie 20 when computing the amplitude component of the RTP transform while still preserving the phase The user can choose the inclination limit at which the transform stabilises The reduction filter also provides an option to apply a directional cosine roll off to reduce the declination parallel striping in the output This is considered a last resort solution and is untenable if there are real magnetic features with trends close to the IGRF declination direction The directional cosine filter is always applied in the declination direction but the user can choose the Rolloff Degree and the Azimuthal Half Width Directional cosine filter parameters so as to restrict the filter to a narrow corridor in the declination direction Task files Reduction filter task files
9. grid dataset Expanded and filled input grid dataset iask files To keep the expanded and filled grid use the ExpandedGridName keyword and assign a filename for the grid Example ExpandedGridName dargo_exp If you leave out this statement GridFFT deletes the grid during the post filtering file clean up 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 11 Library Help Top 4 Back gt Expanded input grid after edge damping Parent topic Specifying Input and Output Filtered Datasets Interactive Task files During the pre FFT processing GrifFFT saves a copy of the input grid after it has coompleted the edge roll off process After use GridFFT normally deletes this grid It is sometimes useful to keep this grid See Saving pre FFT and FFT grid processing products for later reference in INTREPID spectral domain operations reference R14 for details Expanded input grid after edge damping interactive gt gt To specify saving the expanded and edge rolled off input grid dataset 1 Click Pre FFT Grid Conditioning in the Filtering Process list INTREPID displays the Pre FFT Grid Conditioning properties 2 Click Advanced INTREPID displays the Advanced Pre FFT Grid Conditioning dialog box s Advanced Pre FFT Grid Conditioning Opti x M Save Expanded Grid File Cult imag_SouthDykesEN_EXP 3 Tick Save Edge Rolled Off Grid
10. in INTREPID datasets in INTREPID database file and data structures R05 for a list of data types available and their notation Example OutputPrecision Signed32BitInteger If you leave out this statement GridFFT creates the output dataset with the data type IEEE4ByteReal 4 byte real 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 14 Library Help Top lt 4 Back gt Load options Parent topic If you wish to use an existing task specification file to specify the GridFFT process Specifying use Load Options from the File menu INTREPID uses the file to set all of the oo parameters See Task specification job files in GridFFT for more information Filtered Datasets Save options Parent topic If you wish to save the current GridFFT file specifications and parameter settings as Specifying a task specification file use Save Options from the File menu to specify the filename ea and save the file See Task specification job files in GridF FT Filtered Datasets Frequency wavelength and distance unit multiples Parent topic In this section Spectral domain grid Frequency wavelength and distance unit multiples overview filters tool F i GridFFT requency or wavelength units T40 e Distance unit multiples x 1 and x 1000 Frequency wavelength and distance unit multiples overview Parent topic GridFFT accepts parameters
11. is required YES YES Automatic rolloff at 0 5 x Cutoff value LowPass2D End HighPass2D Begin High pass filter definition Cutoff 0 001 Cutoff frequency for high pass filter cyc m oblig or cyc Rolloff lt number gt Frequency for start of rolloff cyc m oblig If this statement is present it sets AutoRolloff or cyc NO AutoRolloff lt YES NO gt NO Rolloff statement is required YES YES Automatic rolloff at 0 5 x Cutoff value HighPass2D End BandPass2D Begin Band pass filter definition Low lt number gt Cutoff frequency for low pass filter cyc m oblig or cyc High lt number gt Cutoff frequency for high pass filter cyc m oblig or cyc LowRolloff lt number gt Frequency for start of low end rolloff cyc m oblig If this statement is present it sets AutoRolloff or cyc NO HighRolloff lt number gt Frequency for start of high end rolloff cyc m oblig If this statement is present it sets AUtoRolloff or cyc NO Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 46 Library Help Top lt 4 Back gt Statement Description Unit Default AutoRolloff lt YES NO gt NO LowRolloff andHighRolloff YES statements are required YES Automatic rolloff at 0 5 x Low and 0 5 x High values respectively BandPass2D End Reduction2D Begin Reduction filter definition FromInclination lt number gt I
12. spatial grid using a polynomial of degree n 0 1 is aconstant 1 is a slope 2 is curved FillType lt ARTHUR MEM gt Fill type for dummy data in new cells of expanded grid ARTHUR RolloffType lt COSINE Roll off type for the edge of the expanded grid Use COSINE gic RolloffType OR WindowType not both Set RolloffType to NONE if you use WindowType WindowType Roll off method applied across the whole of the grid Use NONE Here ANNIKI RolloffType OR WindowType not both Set BLACKMAN TRIANGLE NONE gt WindowType to NONE if you use RolloffType Post FFT process ReApplyTrendAfterReverseF ft Restore the trend that was removed in pre FFT grid NO lt YES NO gt conditioning ApplyMaskAfterReverseFft Use the input grid to restore all nulls in the filtered output NO lt YES NO gt orid ImagePresentation Begin GridFFT uses these statements in ArcView but ignores aa them here ImagePresentation End Filter definitions CompositeFilter Begin Composite filter definition Do not use with CalculateHorizonat1Derivative or CalculateAnalyticSignal Begin Filter definition within composite filter see see Filter definitions below End More filter definitions if required CompositeFilter End Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 45 Library Help Top lt 4 Back gt Statement Description
13. the filters interactive only Exit from GridFFT interactive only Help interactive only Task specification job files in Grid FFT 1 We also support the previous tool Old GridFFT See Old spectral domain grid filters OldGridFFT T38 for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 2 Library Help Top lt 4 Back gt How to use this chapter Parent topic In this section Spectral domain grid e Chapter overview filters tool Finding out more about spectral domain operations GridFFT T40 The GridFFT Wizard Chapter overview Parent topic This chapter describes the operation of the GridFFT tool You can use the GridFFT Howtousethis _ oth interactively and in INTREPID batch processing mode using INTREPID task chapter spe i specification job files Where needed in this chapter there are separate Interactive and Task files sections Some sections are marked Interactive only or Task files only You can find out how to use the tool and also get background information as follows For instructions on using the tool interactively see Using the GridFFT tool interactive only For details about task specification job files see Task specification job files in GridFFT For instructions on using the tool in batch mode see Using task specification files For relevant information in other chapters s
14. the grid data and on settings in Grid FFT Range Acceptable range for parameter value Default Task files only INTREPID assigns this value if you leave out the statement In interactive mode GridFFT shows the default value on the screen Combinable filters Parent topic This section describes the combinable filters available in GridFFT Spectral f domain grid In this section oa Vertical derivative filter GridFFT T40 Horizontal derivative filter GridFFT Reduction filter GridF FT Continuation filter GridFFT Entering parameters for pass filters interactive only Low pass filter GridFFT High pass filter GridFFT Band pass filter GridFFT Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 25 Library Help Top 4 Back gt Vertical derivative filter GridFFT Parent topic This is a generalised vertical derivative filter It calculates a vertical derivative with aa the degree that you specify For example degree 1 is the first vertical derivative You MPERA can specify a fractional degree for the derivative See Single derivative filters in INTREPID spectral domain operations reference R14 and specifically Vertical derivative filter including fractional vertical derivative reference in INTREPID spectral domain operations reference R14 for d
15. 5 Library Help Top lt 4 Back gt These settings affect the following parameters and displays Fundamental and Nyquist see Fundamental and Nyquist Frequencies of the Input Grid e Pass filter parameters see Entering parameters for pass filters interactive only Continuation filter parameters see Continuation filter GridFFT The following table summarises the results of distance unit multiple and mode selections for projected and geodetic grids Projection selected multiple and distance unit Projected x 1 Projected x 1000 Geodetic m ft du m ft du E Spatial m ft du km kft kdu 3 ft Id Ik kft kd Spectral frequency EA ere E EAER p SACE lec Esa o A amp Spectral wavelength X ue ft du km kft kdu Frequency or wavelength units Parent topic Specifying Input and Output Filtered Datasets Library Help Top You can specify and view spectral domain values as frequencies or wavelength Use the Frequency and Wavelength buttons on the Toolbar to select the system you require See Frequency wavelength and distance unit multiples for more information about units display and input EA i gt gt To use frequency values in the spectral domain Click the Frequency g button gt gt To use wavelength values in the spectral domain Click the Wavelength x button 2012 Intrepid Geophysics lt 4 Back
16. Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 34 Library Help Top 4 Back gt Low pass filter GridFFT Parent topic The low pass filter removes data with frequency above a level that you specify You P S can specify the sharpness of rolloff or allow GridFFT to automatically apply rolloff i See Low pass filter reference in INTREPID spectral domain operations reference R14 for further details You can apply this filter to a full tensor grid Low pass filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Cutoff frequency OR IT Cutoff cyc m or cyc Cutoff wavelength OR more Size of rolloff zone 2 IT Rolloff cyc m or cyc OR m or Automatic rolloff zone size T AutoRolloff YES NO YES Auto calculate rolloff zone 4 I lUse the distance unit of your dataset m shown here as an example In interactive mode you can specify wavelength and the x 1000 multiples such as km In task files you can only specify frequency in single units such as m or ft 2 In task files if present sets AutoRolloff to NO 3 Task files only If YES sets Size of rolloff region to 0 5 x Cutoff frequency If NO Rolloff statement is required 4 Interactive only Automatically calculates a suitable rolloff region based on the dataset Interactive Low pass filter interactiv
17. Help Top Band pass filter GridFFT The band pass filter has two cutoff frequencies and removes data with frequency Parent topic Spectral domain grid filters tool GridFFT T40 37 lt 4 Back gt Combinable outside the range defined by the two cutoffs You can specify the sharpness of rolloff paren or allow GridFFT to automatically apply rolloff at the two cutoff frequencies See Band pass filter reference in INTREPID spectral domain operations reference R14 for further details You can apply this filter to a full tensor grid Band pass filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Low cutoff frequency OR IT Low cyc m or cyc Low cutoff wavelength OR mor High cutoff frequency OR IT High cyc m or cyc High cutoff wavelength OR mor Size of rolloff zone low 2 IT LowRolloff cyc m or cyc OR mor Size of rolloff zone high IT HighRolloff cyc m or cyc OR mor Automatic rolloff zone size T AutoRolloff YES NO YES Auto calculate rolloff zone 4 I 1 Use the distance unit of your dataset m shown here as an example In interactive mode you can specify wavelength and the x 1000 multiples such as km In task files you can only specify frequency in single units such as m or ft 2 In task files if either rolloff statement is present sets AutoRo
18. INTREPID User Manual Spectral domain grid filters tool GridFFT T40 1 Library Help Top 4 Back gt Spectral domain grid filters tool GridFFT T40 ae This chapter refers to the current Spectral Domain Grid Filters tool GridFFT You can use the INTREPID GridFFT to enhance a grid dataset by Enhancing features so that you can analyse them to better effect Correcting the measured position of features Removing irrelevant features patterns or noise in the grid Transform the signal using the principles of physics The INTREPID GridFFT process has three basic steps 1 Prepare and transform your grid dataset from the spatial domain to the spectral domain using a Fast Fourier Transform FFT Apply a range of geophysical directional noise removal and wavenumber dependent filters It can apply filters singly or combine as many as you wish Transform your grid dataset back to the spatial domain using a Reverse Fast Fourier Transform ReverseFFT In this chapter Library Help Top How to use this chapter Using the GridFFT tool interactive only The GridFFT window Specifying Input and Output Filtered Datasets Frequency wavelength and distance unit multiples Fundamental and Nyquist Frequencies of the Input Grid Pre FFT Grid Conditioning Post filter transformation options GridFFT filters overview Combinable filters Compound derivative filters Tensor compatible filters FTG and FALCON Apply
19. If the input data is in the spatial domain not already FFT transformed Ifyou want to save a copy of the FFT transformed grid for future use to save processing time specify this and the dataset name for this grid See Saving FFT of input grid dataset below for detailed instructions Use Pre FFT Grid Conditioning properties to specify the parameters for the transformation See Pre FFT Grid Conditioning for detailed instructions Select the filters to be used in the process from the Available filters list For each filter set its parameters See GridFFT filters overview and INTREPID spectral domain operations reference R14 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 4 Library Help Top lt 4 Back gt 6 Use Post FFT Grid Restoration properties to set parameters for the post filter reverse FFT transformation See Post filter transformation options below for detailed instructions 7 Specify the output grid dataset for the results of the filtering Use one of the methods in Specifying Input and Output Filtered Datasets 8 Choose Apply INTREPID performs the filter process saves the output dataset and displays the results graphically in the Data display tabs a Intrepid Grid Filter C Intrepid tutorials mlevel_grid PD ers E 5 x File Help aaa Nyquist 0 16 km SRE LX ik Fundamental 12 0 km Available FFT F
20. Open Input Grid Dataset from the File menu Input Grid Dataset toolbar button Input Grid text box in the Input Grid Dataset Properties area type in the filename and path Input Grid Dataset browse button in the Input Grid Dataset Properties area gt gt To specify the input grid dataset 1 Click Input Grid Dataset in the Filtering Process list INTREPID displays the Input Grid Dataset properties Input Grid Dataset Input Grid CAlntrepiditutorialsicorr_grid PD ers l Input Band No 1 Grid File distance units Metres x l 2 Specify the input grid dataset filename using one of the methods described above 3 Specify the input grid band number for filtering using the Input Band No spin box 4 Specify the distance units for unit labels in the display See Grid file distance units If you load a tensor grid GridFFT configures itself to show the available filters Input grid dataset task files In the task file use the InputGridName keyword with the path and name of the input grid header or marker file For example InputGridName C dfa_jobs input_grids dargo3061l ers There is no default value for InputGridName You must include this statement Use the Band keyword to specify the band to be filtered For example Band 3 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 10 Library Help Top lt 4 Back gt Gri
21. Output check box Task files Reproducing the trend task files You can specify whether to reproduce the trend using the ReApplyTrendAfterReverseFft keyword Assign the value YES or NO or 1 for yes 0 for no Example ReApplyTrendAfterReverseFft YES If you leave out this statement GridFFT does not reapply the trend Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 22 Library Help Top lt 4 Back gt Regenerating the data gaps Parent topic GridFFT can restore null values to cells that had this value before FFT See Post filter Regenerating the data gaps in INTREPID spectral domain operations reference hn Soa R14 for an explanation This only refers to cells within the grid INTREPID always removed the expanded edges of the grid during the post FFT process Interactive Regenerating the data gaps interactive If you want to restore nulls that existed in the grid before the Pre FFT process tick the Apply Mask on Output check box Task files Regenerating the data gaps iask files You can specify whether to restore the null values using the ApplyMaskAfterReverseFft keyword Assign the value YES or NO or 1 for yes 0 for no Example ApplyMaskAfterReverseFft YES If you leave out this statement GridFFT does not restore the null values GridFFT filters overview Parent topic GridFFT provides Spectral z doma
22. Process list INTREPID displays the The Post FFT Grid Restoration properties Filtering Process Post FFT Grid Restoration Input Grid Dataset I ReApply Trend on output Pre FFT Grid Conditioning Filter 1 Vertical Derivative I Apply Mask on output Post FFT Grid Restoration Output Grid Dataset 2 There are no options to select for the reverse FFT process See Reverse FFT and removing the expanded edge 3 Ifyou want to reapply the trend that you removed before the FFT tick the Reapply Trend on Output check box See Reproducing the trend 4 Ifyou want to restore nulls that existed in the grid before the Pre FFT process tick the Apply Mask on Output check box This refers to nulls within the grid not in the expanded edge See Regenerating the data gaps Reverse FFT and removing the expanded edge Parent topic GridFFT always applies reverse FFT and removes the expanded edge of the dataset Post filter after reverse FFT See Reducing the dataset in INTREPID spectral domain transformation operations reference R14 for details options Reproducing the trend Parent topic GridFFT can reapply the trend that it removed when preparing for FFT See Post filter Reproducing the trend in INTREPID spectral domain operations reference R14 for transformation an explanation options Interactive Reproducing the trend interactive If you want to reapply the trend that you removed before the FFT tick the Reapply Trend on
23. REPID spectral domain Compound operations reference R14 for details about this filter You cannot use it with the derivative Analytics 1 filt filters nalytic signal filter Interactive Total horizontal derivative filter interactive Specify the filter as shown in Specifying a filter interactive Note that there are no parameters for this filter Task files Total horizontal derivative filter task files The statement for this filter goes outside the CompositeFilter Begin End block To calculate the total horizontal derivative use the CalculateHorizontalDerivative keyord and assign the value YES or 1 Example total horizontal derivative statement CalculateHorizontalDerivative YES If you leave out this statement GridFFT will not calculate the total horizontal derivative Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 39 Library Help Top lt 4 Back gt Analytic signal filter GridFFT Parent topic See Analytic signal filter reference in INTREPID spectral domain operations Compound reference R14 for details for details about this filter You cannot use it with the derivative s filters Total horizontal derivative filter Interactive Analytic signal filter interactive Specify the filter as shown in Specifying a filter interactive Note that there are no parameters for this filter Task files Analytic si
24. Unit Default CalculateHorizontalDerivative Total horizontal derivative NO lt YES NO gt Do not use with CompositeFilter or CalculateAnalyticSignal CalculateAnalyticSignal Analytic signal NO lt YES NO gt Do not use with CompositeFilter CalculateHorizonatlDerivative Parameters End Process End Filter definitions within CompositeFilter block HorizontalDerivative2D Begin Generalised horizontal derivative definition Azimuth lt number gt Direction for horizontal derivative S 0 0 grid Y 90 grid X Degree lt number gt The degree of the derivative 1 first derivative 1 HorizontalDerivative2D End VerticalDerivative2D Begin Vertical derivative definition Degree 1 The degree of the derivative 1 first derivative 1 VerticalDerivative2D End Continuation2D Begin Continuation filter definition Distance lt number gt Continuation distance mor oblig UseDamping lt YES NO gt Apply roll off to higher frequencies NO downward continuation only DampingDegree lt 0 15 gt Degree of damping roll off 10 DampingFrequency lt number gt Median frequency for damping rolloff cyc m cale or cyc Continuation2D End LowPass2D Begin Low pass filter definition Cutoff lt number gt Cutoff frequency for low pass filter cyc m oblig or cyc Rolloff lt number gt Frequency for start of rolloff cyc m oblig If this statement is present it sets AutoRolloff or cyc NO AutoRolloff lt YES NO gt NO Rolloff statement
25. ample RolloffType LINEAR WindowType NONE If you leave out this statement and specify a window rolloff method GridFFT uses the window rolloff method If you leave out this statement and don t specify a window rolloff method GridF FT uses a cosine edge rolloff method Whole window roll off See Damping of dataset edges before spectral transform in INTREPID spectral domain operations reference R14 for an explanation of this method and its options Whole window roll off interactive gt gt To specify Whole Window rolloff 1 Select the option button for the method you require 2 Select the filter you require from the Whole Window drop down list 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 20 Library Help Top lt 4 Back gt Task files Whole window roll off iask files To specify a the whole window roll off method use the WindowType keyword and assign a value to it GrifFFT provides five window roll off methods as shown in the following table If you specify a whole window rolloff method you normally do not specify an expanded edge roll off Rolloff Type method as well See Expanded edge roll off above Window roll off method WindowType value Required RolloffType value Linear COSINE_BELL NONE Cosine HANNING NONE Hamming HAMMING NONE Blackman BLACKMAN NONE Bartlett or Triangular TRIANGLE NONE No roll off NONE as
26. and displays data in a variety of modes and units o depending on the dataset and the options you select You can select from the the ig following sets of options Filtered Distance units seeGrid file distance units in Input grid dataset Datasets With a projected grid you can work in metres feet or distance units GridF FT labels its display with the unit you select GridFFT always uses degrees with geodetic grids e Distance multiples see Distance unit multiples x 1 and x 1000 e Using the x 1 or x 1000 multiple button with a projected grid you can specify parameters in your selected distance unit singly or in multiples of 1000 For example you can specify metres as the distance unit but use the x 1000 multiple In this case GridFFT accepts parameters and displays data in kilometres Note It does not change the unit of the output data this is still in metres Frequency and wavelength modes see Frequency or wavelength units Using the Frequency Eal and Wavelength X buttons in the spectral domain you can specify parameters and view results using frequencies or wavelengths When you switch between multiples and modes GridFFT automatically converts all parameter settings If you switch distance units GridFFT changes labels but this does not affect values or calculations Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 1
27. ctions 4 Back gt eaae PEEN A complete task specification file outline with all possible statements and blocks job files in including eld File specifications e Pre FFT process parameters e Post FFT process parameters The CompositeFilter Begin End block Compound derivative filters The possible filter description blocks for the CompositeFilter Begin End block Statement Description Unit Default GridFFT task specification job file Process Begin Task definition Name gfilt Specifies GridFFT as the application for this task Parameters Begin Start of parameters block File specifications InputGridName lt path gt The input grid with relative or absolute path if necessary oblig Can be a spatial or an FFT grid Band lt ord gt Band of grid to be filtered 1 FilteredGridName lt path gt The filtered output grid with relative or absolute path if cale necessary OutputPrecision lt datatype gt Precision of data in filtered output grid IEEE4byteReal FftGridName lt path gt FFT of the input grid for use in future tasks not saved ExpandedGridName lt path gt Expanded and filled intermediate grid INTREPID not saved normally deletes it Save it if required for debug check WindowedGridName lt path gt Expanded grid with rolloff applied to edges INTREPID not saved normally deletes it Save it if required for debug check Pre FFT process DetrendDegree lt 0 1 2 gt De trend the
28. d file distance units This drop down list in the Input Dataset Properties specifies unit labels for the display It does not affect any data or the value of any data display For projected grids the default unit is metres GridFFT labels distances as m and frequencies as cycles m You can also choose feet and distance units For geodetic grids the only distance unit available is degrees GridFFT labels distances as and frequencies as cycles Expanded and filled input grid dataset Parent topic Specifying Input and Output Filtered Datasets Interactive Task files Library Help Top During the pre FFT processing GrifFFT saves a copy of the input grid after it has detrended expanded and filled the new cells After use GridFFT normally deletes this grid Itis sometimes useful to keep this grid See Saving pre FFT and FFT grid processing products for later reference in INTREPID spectral domain operations reference R14 for details Expanded and filled input grid dataset interactive gt gt To specify saving the expanded and filled input grid dataset 1 Click Pre FFT Grid Conditioning in the Filtering Process list INTREPID displays the Pre FFT Grid Conditioning properties 2 Click Advanced INTREPID displays the Advanced Pre FFT Grid Conditioning dialog box 3 Tick Save Expanded Grid File 4 Use the Save Expanded Grid File text box or browse button to specify the name of the expanded input
29. e Library Help Top Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Depending on your tool settings and the grid the properties area has different labels and options See Entering parameters for pass filters interactive only for details Low Pass Properties Cutoff 0 01 cy m Rolloff 0 0001 cym Reset default rolloff 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 35 Library Help Top Task files 4 Back gt Low pass filter task files Here is an example Begin End block LowPass2D Begin Cutoff 0 001 Rolloff 0 0001 AutoRolloff 0 or 1 LowPass2D End High pass filter GridFFT Parent topic The high pass filter removes data with frequency below a level that you specify You Combinable can specify the sharpness of rolloff or allow GridFFT to automatically apply rolloff nes See High pass filter reference in INTREPID spectral domain operations reference R14 for further details You can apply this filter to a full tensor grid High pass filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Cutoff frequency OR IT Cutoff cyc m or cyc Cutoff wavelength OR mor Size of rolloff zone 2 IT Rolloff cyc m or cyc OR mor Automatic rolloff zone size T AutoRoll
30. ee Finding out more about spectral domain operations and The GridFFT Wizard Finding out more about spectral domain operations Parent topic This chapter briefly describes the GridFFT tool s operations How to use this chapter INTREPID has a number of tools that perform spectral domain operations and use spectral domain filters We have created a common reference chapter which has detailed explanation of INTREPID spectral domain operations It includes an explanation of pre processing and post processing as well as details of the available filters NOTE this tool now supports Full Tensor Gradient FTG and FALCON Partial Tensor Gradient grid operations Curvature Gradients This takes the form of some Low Band amp High pass operations and Tensor Integration A Full Tensor Complex grid is created to support the FFT operations in this case See INTREPID spectral domain operations reference R14 for full details The GridFFT Wizard Parent topic The GridFFT Wizard uses your answers to a set of questions to automatically Howtousethis generate a GridFFT task file After generating the file the GridF FT Wizard executes chapter eas it in batch processing mode See Spectral domain grid filters GridFFT wizard T39 for further information Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Using the GridFFT tool interactive only Parent topic Spectral domai
31. endDegree 1 If you leave out this statement GridFFT detrends the grid with degree 0 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 18 Library Help Top lt 4 Back gt Fill method Parent topic After expanding the grid GridFFT assigns values to the new cells in the grid using an Frequency extrapolation process You can choose one of two available methods See Estimating waveleng h values for data gap cells in INTREPID spectral domain operations reference R14 and distance unit multiples for details Interactive Fill method interactive Select Arthur or MEM Maximum Entropy from the Fill Method drop down list Task files Fill method task files To select a fill method use the FillType keyword The following methods are available Fill method Value to assign Linear interpolation Arthur ARTHUR Maximum entropy MEM Source fill SOURCE_GRID Example FillType ARTHUR If you leave out this statement GridFFT uses the linear interpolation Arthur method Edge damping rolloff options Parent topic For best results from the FFT the edges of the grid must be set to zero but without Frequency sudden changes from the data within the grid The grid data needs to roll off to zero ile aioe at the edge See Damping of dataset edges before spectral transform in INTREPID unit multiples spectral domain operations reference R14 for detail
32. etails Vertical derivative filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Order of differentiation IT Degree 1 3 1 Interactive Vertical derivative filter interactive Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Vertical Derivative Properties Derivative degree 1 z Task files Vertical derivative filter task files Library Help Top Here is an example Begin End block VerticalDerivative2D Begin Degree 1 VerticalDerivative2D End 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 26 Library Help Top 4 Back gt Horizontal derivative filter GridFFT Parent topic This is a generalised horizontal derivative filter It calculates a horizontal gradient Combinable in any specified azimuth direction See Single derivative filters in INTREPID i spectral domain operations reference R14 and specifically Generalised horizontal derivative filter reference in INTREPID spectral domain operations reference R14 for details Horizontal derivative filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Direction IT Azimuth 9 0 360 0 Order of differentiation IT Degree 1 3 1 Interactive Horizo
33. files Parent topic Task specification job files in GridFFT Library Help Top You can store sets of file specifications and parameter settings for GridFFT in task specification job files gt gt To create a task specification file with the GridFFT 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 gt gt To use a task specification file in an interactive GridFFT session Load the task specification job file File menu Load Options modify any settings as required then choose Apply gt gt To use a task specification file for a batch mode GridFFT task Type the command gfilt exe with the switch batch followed by the name and path if necessary of the task specification file For example if you had a task specification file called surv329 job in the current directory you would use the command gfilt exe batch surv329 job 2012 Intrepid Geophysics 4 Back gt
34. gnal filter task files To calculate the analytic signal use the CalculateAnalyticSignal keyord and assign the value YES or 1 Example analytic signal statement CalculateAnalyticSignal YES If you leave out this statement GridFFT will not calculate the analytic signal Tensor compatible filters FTG and FALCON Parent topic Continuation filter GridFFT Spectral domain grid Continued tensor grids can suffer from the Gibbs effect and phase busts may filters tool degrade results A fix for this problem is currently being investigated cat Low pass filter GridFFT High pass filter GridFFT Band pass filter GridFFT Butterworth filter reference Directional cosine filter reference Full Tensor Integration Query FTG or other full tensor grids e FALCON Partial Tensor Transform Query Butterworth filter for tensors Apply the filters interactive only Parent topic Spectral domain grid filters tool GridFFT T40 Interactive After you have specified the filtering task click the Apply button During execution a speed bar shows task progress When the process is complete INTREPID creates thumbnail images in the data display tabs You can change the task settings and click Apply as many times as you like Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 40 Library Help Top 4 Back gt Exit fro
35. gree 0 15 10 Library Help Top 1 In task files Positive upward continuation Negative downward continuation Interactive See Continuation filter interactive 2 Downward continuation only If you do not specify Median frequency of rolloff INTREPID calculates a suitable value This is based on the rate at which the continuation is increasing high frequencies See also Suggested values for Degree of Rolloff 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 31 Library Help Top lt 4 Back gt Interactive Continuation filter interactive Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Continuation Properties Continuation Properties Direction Downward Distance 100 0 m Direction Downward Distance 100 0 m J7 Use Damping JZ Use Damping 0 0009 deg Sharpness fo Sharpness fso C Automatic j Automatic Specify damping cuttoff Cutoff 0 016 cydes m Cutoff 0 016 cydes Reset Defaults Reset Defaults Projected grid Geodetic grid has choice of input in metres or degrees If your input grid is geodetic GridFFT displays both a metres and degrees text box for you to specify the Level of continuation Whatever you enter in one of the text boxes INTREPID automatically converts and displays the equivalent in the other text box using Robi
36. gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 16 Library Help Top 4 Back gt Distance unit multiples x1 and x 1000 Parent topic Specifying Input and Output Filtered Datasets You can specify and view distance units as single units m ft distance units dU or x 1000 multiples km kft kdU Use the x 1 and x 1000 buttons on the Toolbar to select the multiple you require See Frequency wavelength and distance unit multiples for more information about units display and input a jme These buttons are disabled when your input grid is geodetic gt gt To use single distance units Click x 1 to use single distance units m ft dU gt gt To use x 1000 distance units Click x 1000 to use x 1000 multiple distance units km kft kdU Fundamental and Nyquist Frequencies of the Input Grid Parent topic Spectral domain grid filters tool GridFFT T40 GridFFT automatically displays the fundamental and Nyquist frequencies of the input grid dataset at the right end of the Toolbar Nyquist 0 16 km Fundamental 12 0 km It displays the values using the units and multiple you have selected See for Frequency wavelength and distance unit multiples for instructions For information about the fundamental and Nyquist frequencies see The spatial and spectral domains in INTREPID spectral domain operations reference R14 Pre FFT Grid Conditioning Parent top
37. h IGRF Epoch ie IGRF2010 IGRF Model update Most recent epoch year every 5 years a list of current amp older models for the chosen http www ngdc noaa gov IAGA vmod igrf_old_models html survey date Altitude km Specify the altitude of the survey 0 Latitude Specify the latitude and longitude of the input data Midpoint of grid Longitude for the IGRF calculation Field Strength nT Output field strength from the IGRF model Declination Output declination and inclination from the IGRF ae model Inclination Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top Continuation filter GridFFT The continuation filter can calculate an upward or a downward continuation The Parent topic Spectral domain grid filters tool GridFFT T40 30 lt 4 Back gt Combinable filter includes optional damping for controlling the stability of downward ners continuation See Continuation filters reference in INTREPID spectral domain operations reference R14 for further details Continuation filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Direction I Upward or Downward Level of Continuation IT Distance m or Use Damping 2 IT UseDamping YES NO NO Median Frequency of IT DampingFrequency cyc m or auto Rolloff cyc Degree of Rolloff T DampingDe
38. ic Spectral domain grid filters tool GridFFT T40 Library Help Top You can specify how GridFFT prepares the input grid for FFT This section briefly describes the steps in the process and the parameters For detailed discussion see Preparation of data for spectral transform in INTREPID spectral domain operations reference R14 In this section Pre FFT Grid Conditioning Overview Interactive e Expanding the grid e Detrending Fill method Edge damping rolloff options 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Spectral domain grid filters tool GridFFT T40 17 lt 4 Back gt Pre FFT Grid Conditioning Overview Interactive Parent topic Frequency wavelength and distance unit multiples Interactive gt gt To specify Pre FFT Grid Conditioning 1 Click Pre FFT Grid Conditioning in the Filtering Process list INTREPID displays the The Pre FFT Grid Conditioning properties p Filtering Process Pre FFT Grid Conditioning oput Gria Dataset Degree of Trend Removal 1 5 Pre FFT Grid Conditioning Filter 1 Reduction Fill Method ARTHUR E Grid Edge Rolloff C Whole Window 7 Post FFT Grid Restoration Output Grid Dataset ExpandedEdge ee sa lSmm Advanced 2 There are no options to select for expanding the grid See Expanding the grid 3 Specify the Degree of trend removal using the corresponding sp
39. idFFT below Only use a particular filter definition Begin End block once in a CompositeFilter Begin End block If you repeat a particular filter GridFFT ignores the second occurrence If you need to apply a filter twice use two separate GridFFT tasks Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 24 Library Help Top lt 4 Back gt Specifying a compound derivative filter task files Parent topic GridFFT filters overview Task files You can only use one of the compound derivative filters at a time To specify one include its statement set to YES in the Parameters Begin End block outside the CompositeFilter Begin End block Example CalculateHorizontalDerivative YES Filter parameter tables Parent topic The parameters tables in this manual show the parameters for each filter They GridFFT filters include parameters for both interactive mode and task files These usually pn correspond and footnotes explain any differences The following table explains the parts of the parameters table Heading Purpose Parameter The INTREPID term for the parameter This appears in the properties area in the interactive tool Mode I Interactive T Task files Keyword Task files only Keyword for specifying the parameter in a task file Unit Unit of the parameter value for example metres This may depend on
40. ilters CompositeFilter Begin Composite filter definition ee Filter parameter blocks CompositeFilter End End Parameters End End Process End End Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 43 Library Help Top lt 4 Back gt Sample GridFFT task specification job file Parent topic Here is an example of a GridFFT task Task specification Gob files in Process Begin Comments Intrepid Audit Stamp v3 5 Cut 110 11 5 2001 Parameters Begin InputGridName C dargo3061 ers Band 0 FilteredGridName C dargo_HorDerivN ers OutputPrecision IEEE4ByteReal FftGridName dargo_fft ExpandedGridName dargo_exp WindowedGridName dargo_wind DetrendDegree YES FillType ARTHUR RolloffType COSINE WindowType NONE ReApplyTrendAfterReverseFft NO ApplyMaskAfterReverseFft YES ImagePresentation Begin DataTransformType none HistogramStretchType none Palette none ImagePresentation End CompositeFilter Begin HorizontalDerivative2D Begin Azimuth 0 0 Degree 1 0 HorizontalDerivative2D End CompositeFilter End Parameters End Process End Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top Syntax table Parent topic Spectral domain grid filters tool GridFFT T40 44 This table contains the following se
41. ilters Filtering Process Input Grid Dataset Low Pass put Grid Dataset Input Grid High Pass Pre FFT Grid Conditioning ICAlntrepiditutorials mlevel_grid PD ers 5 Horizontal Derivative Filter 1 Vertical Derivative input Band No a Reduction Post FFT Grid Restoration Continuation Output Grid Dataset Grid File distance units Metres bs Analytic Signal wee 5 Total Horizontal Derivative Save FFT of Input Grid Band Pass av Spatial View Spectral Map View Radial Power Spectrum Before After 9 Examine the graphical display of the filter process and results in the Data display tabs See Data display tabs below for information 10 If you wish to record the specifications for this process in a job file so that you can perform a similar task later use Save Options from the File menu See Specifying Input and Output Filtered Datasets below for detailed instructions 11 If you wish to repeat the process repeat steps 2 10 varying the parameters and data files as required 12 To exit from GridFFT choose Quit from the File menu After using GridFFT you can carry out a more detailed inspection of the filtered grid using an INTREPID visualisation tool See Visualisation T26 You can choose options from the Help menu See Help interactive only below You can execute GridFFT as a batch task using a task specification job file that you have previously prepared See Using task specification fi
42. in box See Detrending 4 Specify the Fill method using the corresponding drop down list See Fill method 5 Select the edge damping method Whole window or Expanded edge using the Grid edge rolloff option buttons For the method you choose select the filter type from its drop down list See Edge damping rolloff options 6 If you want to save the expanded and filled or expanded and rolled off version of the input grid use the Advanced button See Expanded and filled input grid dataset and Expanded input grid after edge damping Expanding the grid Parent topic Frequency wavelength and distance unit multiples Detrending Parent topic Frequency wavelength and distance unit multiples Interactive Task files Library Help Top GridFFT always expands the grid to dimensions suitable for FFT There are no parameters attached to this process See Expanding the data area in INTREPID spectral domain operations reference R14 for an explanation of this stage GridFFT always detrends the grid See Detrending data values in INTREPID spectral domain operations reference R14 for information The value you select or assign to the keyword corresponds to the degrees in this reference topic Detrending degree interactive Select the degree required from the Degree of Trend Removal drop down list Detrending degree task files You can specify the degree of the detrending using the DetrendDegree keyword Example Detr
43. in grid Filters that you can combine with other filters in the same task filters tool Continuation downward and upward GridFFT T40 e High pass low pass and band pass Vertical derivative Horizontal derivative e Reduction to inclination and declination including pole and equator In task files these filters are within the CompositeFilter Begin End block Compound derivative filters You can only apply one of these in any GridFFT operation Total horizontal derivative Analytic Signal In task files these use single statements in the Parameters Begin End block outside the CompositeFilter Begin End block In interactive mode if you load a tensor grid GridFFT configures itself to show the available filters In this section Specifying a filter interactive Specifying a combinable filter task files Specifying a compound derivative filter task files e Filter parameter tables Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 23 Library Help Top lt 4 Back gt Specifying a filter interactive Parent topic GridFFT filters overview Interactive gt gt To specify a filter 1 Select a filter from the list of Available FFT Filters and use the gt button to add the selected filter to the Filtering Process You may add further filters to create a composite filter Available
44. isplay you require See Data display tabs Data display area Panel size adjustment Graphic display of data from the filtering process Use this to change the relative size of the data display area and the lists and properties area Changing the display panel size Parent topic Use the panel size control to change the relative size of the data display area and the Howtousethis task control area chapter gt gt To adjust the size of the data display and task specification areas Drag the panel size control up or down OR Click the up and down arrow icons j to make the data display or task specifcation area occupy the whole wondow Click the icons again to restore the display so that both areas are visible Data display tabs Parent topic After you have applied a filter you can view the results graphically using the data How to use this display tabs chapter Spatial view tab This tab shows the input and output grid in pseudocolour in the spatial domain The display shows the input grid and the final result Spatial View Spectral Image View Radial Power Spectrum Before Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 lt 4 Back gt Library Help Top Library Help Top Spectral Map View tab This tab shows graphically the spectral amplitude and phase maps of e The input dataset
45. le should be set to that of your survey to minimise any horizontal offsets in the East West direction 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 27 Library Help Top lt 4 Back gt that may be caused during the calculation of this correction Reduction filter parameters See Filter parameter tables for an explanation of parameters tables Parameter Mode Keyword Unit Range Default Inclination for input dat IT FromInclination 0 90 1 Declination for input data IT FromDeclination 0 360 1 Date of input data 2 F Date task file and dd mm yyyy today s IGRF block date Elevation of input data T Elevation m 0 0 Target inclination 4 IT ToInclination z 0 90 90 Target declination 4 IT ToDeclination 0 360 0 Taylor Expansion Order IT TaylorExpansionOrder 1 3 1 Inclination limit IT AmplitudeLimit 0 90 20 1 INTREPID calculates default values from middling latitude and longitude using the IGRF model In task files it calculates the default values if you leave the statements out 2 Task files only If you specify a date and elevation INTREPID uses them with the IGRF model for better 1 values 3 Interactive only INTREPID calculates and displays default input values from middling latitude and longitude using the IGRF model Click IGRF to adjust these using the IGRF calculator 4 I
46. les below for details Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 5 Library Help Top 4 Back gt The GridFFT window Parent topic In this section Spectral a Elements of the GridFFT window filters tool 3 Grid FFT Changing the display panel size T40 e Data display tabs Elements of the GridFFT window Parent topic Here is a diagram of the GridFFT window How to use this chapter Fundamental and Nyquist frequencies or wavelengths Title bar Oe Process step properties ak Intrepid Grid Filter C Intrepid tutorials mlevel_grid PD ers 0 x Menu bar Fie Help H a x x1 x1000 Toolbar pe Available FFT Filters Filtering Process Low Pass Input Grid Dataset Nyquist 0 16 km Fundamental 12 0 km Input Grid Datass Input Grid High Pass Pre FFT Grid Conditioning C lntrepiditutorialstmlevel_grid PD ers Ri Horizontal Derivative Filter 1 Vertical Derivative i i Available filters list Reduction Post FFT Grid Restoration Mtisene so U Output Grid Dataset Grid File distance units Metres Continuation I Save FFT of Input Grid Derivative Band Pass z e Add amp Remove buttons Filtering process list Panel size adjustment av Spatial view Spectral Map View Radial Power Spectrum Data display tabs etre After
47. llof f to NO 3 Task files only If YES sets Size of rolloff region to 0 5 x Cutoff frequency If NO Rolloff statement is required 4 Interactive only Automatically calculates a suitable rolloff region based on the dataset Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 38 Library Help Top lt 4 Back gt Interactive Band pass filter interactive Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Depending on your tool settings and the grid the propoerties area has different labels and options See Entering parameters for pass filters interactive only for details Band Pass Properties Low Cutoff 0 01 cyim High Cutoff 00s cy m Low Rolloff fo 0001 cy m High Rollotf 0 0001 cym Reset default rolloff Task files Band pass filter task files Here is an example Begin End block BandPass2D Begin Low 0 0010 High 0 00276 LowRolloff 1 0E 4 HighRolloff 1 0E 4 AutoRolloff NO BandPass2D End Compound derivative filters Parent topic This section describes the compound derivative filters Spectral domain grid In this section aoa Total horizontal derivative filter GridFFT T40 e Analytic signal filter GridFFT Total horizontal derivative filter GridFFT Parent topic See Total horizontal derivative filter reference in INT
48. m GridFFT interactive only Parent topic Spectral domain grid filters tool GridFFT T40 Interactive To exit from GridFFT select Exit from the File menu Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 41 Library Help Top lt 4 Back gt Help interactive only Parent topic Spectral domain grid filters tool GridFFT T40 Interactive You can use the Help menu to display help text on the topics shown in the menu illustration below Note the Help system is available only from the CD installation not the web install version This is done to keep the web version small for downloading File Low Pass Contents High Pass PAN caa Band Pass LowPaSSs Reduction High Pass Continuation Vertical Derivative Horizontal Derivative Band Pass Horizontal Derivative Vertical Derivative Reduction Analytic Signal Continuation Pre FFT Grid Conditioning Analytic Signal Post FFT Grid Restoration Total Horizontal Der Input Grid Output Grid Dataset Task specification job files in GridFFT Parent topic Spectral domain grid filters tool GridFFT T40 Task files This section gives an overview example and describes the syntax of GridFFT task specification files A GridFFT task specification job file specifies Input and output grid filenames Pre filtering and post filtering req
49. n s formula This conversion between metres and degrees is an approximation INTREPID bases it on the mid latitude of the grid Task files Continuation filter task files Note The sign of the Level of continuation parameter Distance determines the direction If it is positive the continuation is upward if negative the continuation is downward Here is an example Begin End block Continuation2D Begin Distance 100 0 ve upward ve downward UseDamping Yes DampingDegree 5 0 DampingFrequency 0 016 cycles m wavelength in metres 62 5 Continuation2D End Units for Level of Continuation Specify the Level of continuation using the same distance units as the spatial version of the grid For example if the grid is in metres then specify Level of continuation in metres For geodetic grids specify it in degrees Interactive only Remember that you can set GridFFT to display the correct units for the grid See Frequency wavelength and distance unit multiples for details This may help avoid confusion Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Library Help Top Spectral domain grid filters tool GridFFT T40 32 Level of Continuation examples 4 Back gt Enter the relative distance for continuation the distance by which you want to change the effective height For example you may have a survey flown at 90 m mean terrai
50. n clearance and recorded in metres If you want to change its effective height to 60 m specify a downward continuation of 30 Specify the continuation in the same units as the grid If you fail to do this you will get incorrect results The following examples describe grids with the same cell size but measured in different units If we specify a downward continuation of 30 e For a projected grid in metres with 100 m cell size the continuation distance will be 30 m For a projected grid in feet with 300 ft cell size the continuation distance would be 30 ft or 9 4 m e For a geodetic grid with 0 001 cell size the continuation distance would be 30 or 3000 km Suggested values for Degree of Rolloff Degree Effect 2 Gradual 5 10 Moderately sharp 10 Recommended and default degree 30 Sharp 50 or more Tending to a square cutoff 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 33 Library Help Top lt 4 Back gt Entering parameters for pass filters interactive only Parent topic Combinable filters Interactive You have a number of choices for entering spectral domain parameters the pass filters These include frequency wavelength and distance unit multiples see Frequency wavelength and distance unit multiples and alternatives for geodetic grids You can enter parameters as frequency or wavelength
51. n grid filters tool Spectral domain grid filters tool GridFFT T40 3 lt 4 Back gt GridFFT T40 Interactive gt gt To use GridFFT with the INTREPID graphic user interface 1 Choose GridFFT from the Filter menu of the Project Manager or use the command gfilt exe INTREPID displays the GridFFT window Intrepid Grid Filter E output pello_kth_suhde ers BAX File Help z3 FE FRF Eo Nyquist 0 01 cy m H 1 A x1 1000 Fundamental 0 0000135 cy m Available FFT Filters Filtering Process Low Pass Properties High Pass a Input Grid Dataset A Band Pass Pre FFT Grid Conditioning Cutoff 0 005 cy m Horizontal Derivative Filter 1 Low Pass Vertical Derivative Post FFT Grid Restoration Rolloff 0 001 cy m Reduction Output Grid Dataset Continuation Analytic Signal Total Horizontal Derivative Directional Cosine Hilbert Transform Pseudo Gravity Matched Filter Butterworth bA hal av Spatial View Spectral Image View Radial Power Spectrum Before 2 If you have a task specification file load it using Load Options from the File menu See Specifying Input and Output Filtered Datasets below for detailed instructions If all of the specifications are correct in this file go to step 8 If you wish to modify any settings carry out the following steps as required Specify the input grid dataset to be filtered Use one of the methods in Specifying Input and Output Filtered Datasets
52. n interactive mode you can also select the Reduction to Pole Reduction to Equator Variable RTP and Low Latitude options These have preset inclination and declination values Interactive Reduction filter interactive Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Reduction Filter Properties Indination Declination 20 07 Specified Indination 90 00 Dedination 00 e Equator RTE Pole RTP Average RTP Variable RTP Taylor Expansion Order 1 Low Indination Indination Limit 20 0 F Add Dir Cos Rolloff Degree 0 5 Azimuthal Half Width 20 By default INTREPID calculates the IGRF inclination and declination at the input data centroid at 0 altitude using today s date and the latest epoch To change this do Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 28 Library Help Top 4 Back gt one of the following Enter your own values for Inclination and Declination Use the IGRF Calculator See IGRF Calculator Choose type of Reduction Equator or Pole For RTPole the normal option is the average correction for the middle of your grid For large grids 100km extents the approximation of using the inclination and declination at the grid centroid becomes inaccurate In this case choose the Variable RTP option and the RTP calculation will be made using a
53. nclination of source data INTREPID calcluates default R calc from middling latitude and longitude using IGRF model FromDeclination lt number gt Declination of source data INTREPID calcluates default 2 cale from middling latitude and longitude using IGRF model Date Date of source data in format DD MM YYYY Epoch 2000 Elevation Elevation of source data m 0 ToInclination lt number gt Inclination of output data i 90 pole ToDeclination 0 Declination of output data j 0 AmplitudeLimit 20 0 Latitude for amplitude limiting S 20 LowLatitude lt YES NO gt Turn on off directional cosine filter Reduction2D End If AutoRolloff NO then this statement is required and you must assign a value Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 47 Library Help Top 4 Back gt GridFFT Wizard statements for third party products Parent topic Task specification job files in GridFFT The GridFFT Wizard is mainly for use with third party products It automatically inserts statements that allow the third party products to use GridFFT The statements may include the following ImagePresentation Begin ImagePresentation End If you are editing a task file that the GridFFT Wizard has produced ignore these statements See Spectral domain grid filters GridFFT wizard T39 for further information about them Using task specification
54. ntal derivative filter interactive Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Horizontal Derivative Properties Direction 0 0 Derivative degree 1 0 Task files Horizontal derivative filter task files Here is an example Begin End block HorizontalDerivative2D Begin Azimuth 0 0 Degree 1 0 HorizontalDerivative2D End Reduction filter GridFFT Parent topic Combinable filters Library Help Top The Reduction filter is a generalised reduction filter that can perform reduction to any orientation of the Earth s magnetic field The most common reductions are to the Pole and to the Equator You need to specify the target magnetic field orientation you can input this manually or allow GridFFT to calculate it for you If you are reducing to a low latitude you can specify the IGRF field inclination limit for the amplitude calculation There is also a special low latitude switch which uses a directional filter to suppress declination parallel striping See Reduction filters reference in INTREPID spectral domain operations reference R14 for further details GridFFT uses the International Geomagnetic Reference Field IGRF model to calculate the Earth s magnetic field for the mean position of the input grid See The geomagnetic reference field in INTREPID R15 for information about the IGRF For Reduction to the Equator we recommend that the Declination ang
55. off YES NO YES Auto calculate rolloff zone 4 I Library Help Top 1 Use the distance unit of your dataset m shown here as an example In interactive mode you can specify wavelength and the x 1000 multiples such as km In task files you can only specify frequency in single units such as m or ft 2 In task files if present sets AutoRolloff to NO 3 Task files only If YES sets Size of rolloff region to 0 5 x Cutoff frequency If NO Rolloff statement is required 4 Interactive only Automatically calculates a suitable rolloff region based on the dataset 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Interactive Task files Library Help Top High pass filter interactive Spectral domain grid filters tool GridFFT T40 36 4 Back gt Specify the filter as shown in Specifying a filter interactive The properties area is illustrated here Depending on your tool settings and the grid the propoerties area has different labels and options See Entering parameters for pass filters interactive only rHigh Pass Properties Cutoff 0 01 cyim Rolloff 0 0001 cyim Reset default rolloff High pass filter task files Here is an example Begin End block HighPass2D Begin Cutoff 0 001 Rolloff 1 0E 4 AutoRolloff NO HighPass2D End 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library
56. required Example RolloffType NONE WindowType BLACKMAN If you leave out the WindowType statement GridFFT uses an expanded edge rolloff method If you leave out this statement and don t specify an expanded edge rolloff method GridFFT uses a cosine expanded edge rolloff method Post filter transformation options Parent topic Spectral domain grid filters tool GridFFT T40 Library Help Top After applying the filters GridFFT restores the filtered grid to correspond with the input grid The post filter transformation operations are as follows Apply reverse FFT to return the grid to the spatial domain Remove the expanded edge of the grid Reapply the trend optional Restore null to cells that were originally null optional See Post filter transformation in INTREPID spectral domain operations reference R14 for details In this section Post FFT transformation options overview Interactive Reverse FFT and removing the expanded edge e Reproducing the trend e Regenerating the data gaps 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 21 Library Help Top lt 4 Back gt Post FFT transformation options overview Interactive Parent topic Post filter transformation options Interactive gt gt To specify Post FFT transformation options 1 Click Post FFT Grid Restoration in the Filtering
57. rid data using one of the following Specify Output Grid Dataset from the File menu Output Grid Dataset toolbar button e Output Grid text box in the Output Grid Dataset Properties area Output Grid Dataset browse button in the Output Grid Dataset Properties gt gt To specify output grid dataset and its properties 1 Click Output Grid Dataset in the Filtering Process list INTREPID displays the Output Grid Dataset Properties area Output Grid Dataset Filtered Grid File CAlntrepiditutorials mlevel_grid_FILT on Data Format IEEE 4ByteReal 7 2 Specify the output grid dataset filename using one of the methods described above If you do not specify an output grid dataset GridF FT generates an output dataset name based on the input grid name 3 Use the Data Format drop down list to specify the precision you require See Data Types in INTREPID datasets in INTREPID database file and data structures R05 for the available numeric data types Output grid dataset task files Use the FilteredGridName keyword with the path and name of the output grid header or marker file For example FilteredGridName C dfa_jobs gfilt_test dargo_HorDerivN GRID If you leave out this statement GridFFT generates an output dataset name based on InputGridName and filters applied You can specify the data type of the output grid Use the OutputPrecision keyword with the precision you require See Data Types
58. s of this process GridFFT has two main roll off methods each of which has a number of filters It is normal to only use one of the methods Method Description Filters available Expanded edge Rolloff operation only on the edges of the Cosine roll off grid Linear Whole window Rolloff operation across the whole grid Cosine bell roll off Hanning Hamming Blackman Triangle Expanded edge roll off See Expanded edge rolloff in INTREPID spectral domain operations reference R14 for an explanation of this method and its options Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 19 Library Help Top Interactive Task files Interactive Library Help Top 4 Back p gt Expanded edge roll off interactive gt gt To specify Expanded Edge rolloff 1 Select the option button for the method you require 2 Select the filter you require from the Expanded Edge drop down list Expanded edge roll off task files To specify an expanded edge roll off filter use the RolloffType keyword and assign a value to it If you specify a rolloff method you normally do not specify a window roll off WindowType method as well See Whole window roll off below Roll off method RolloffType value Required WindowType value Linear LINEAR NONE Cosine COSINE NONE No roll off NONE as required Ex
59. taset e Load options Save options Specifying input and output filtered datasets overview Parent topic The GridFFT process involves an input grid dataset an output grid dataset and a Specifying number of intermediate datasets Input and Output When using GridFFT specify the following Filtered Datasets Input grid dataset and band number if not band 0 Optional Detrended expanded and filled input dataset Optional Rolled off input dataset Optional FFT tranformed input dataset e Output dataset and precision if not IEEE4ByteReal Filenames can have paths attached Paths can be relative or absolute The following diagram show the ways of specifying input and output datasets in interactive mode Help l Filtering Process Knit Dataset Input dataset Open Input Dataset Input Grid Dataset i Specify Output Dataset Pre FFT Grid Conditioning c ntrepicttutorialstmlevel_grid PD ers properties y ead Options Filter 1 Vertical Derivative Input Band No i H Post FFT Grid Restoration j Save Options Output Grid Dataset Grid File distance units Metres 7 Exit V Save FFT of Input Grid File menu CAlntrepicitutorialstmlevel_grid_FFT i H Filtering Process A Output Grid Dataset Input and output Input Grid Dataset Filtered Grid File T Output dataset Pre FFT Grid Conditioning exntrepicttutorialstmievel_grid FT properties dataset toolbar Filter 1 Vertical Derivative Data Format bu
60. ttons Post FFT Grid Restoration EEE4BteRe O YS Output Grid Dataset If you choose a toolbar button menu option or browse button 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 You can also type the path and filename of the dataset in the text boxes in the Properties area Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 9 Library Help Top 4 Back gt Input grid dataset Parent topic Specifying Input and Output Filtered Datasets Interactive Task files Library Help Top GridFFT can directly input and process the following grid dataset types INTREPID ERMapper grid files ers Geosoft grid files grd You can specify already FFT transformed datasets as input GridFFT automatically detects that they are transformed and skips the pre processing steps You can specify an INTREPID grid dataset as if it is an ERMapper grid file Specify the ers file The default band for filtering is 1 If you are filtering a single band grid or want to filter the first band of a multiband grid you don t have to specify the grid band Input grid dataset interactive You can specify the input grid dataset interactively using
61. uirements The required filters and filter parameters In this section Finding out more about task files and batch processing mode e Main block structure of a GridFFT task file Sample GridFFT task specification job file Syntax table GridFFT Wizard statements for third party products Using task specification files Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Spectral domain grid filters tool GridFFT T40 42 Library Help Top lt 4 Back gt Finding out more about task files and batch processing mode Parent topic Use the following references Task specification job files in GridFFT Introduction to INTREPID auxiliary files INTREPID Auxiliary files in INTREPID database such as task files file and data structures R05 Structure syntax and use of INTREPID task INTREPID task specification job files R06 files Running INTREPID in batch processing How to start INTREPID Overview in Introduction mode to INTREPID R02 Main block structure of a GridFFT task file Parent topic The following table shows the main block structure of a GridFFT task file See Task Syntax table for more details specification job files in se GridFFT Block definition Contents Process Begin Task file outer block rei Tool name and date stamp Parameters Begin Parameters block Filenames Pre and post FFT parameters ee Parameters for non composite f

Spectral domain grid filters tool (GridFFT) (T40)

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