Depth estimation with the matched filter (C03)
Contents
1. deep regional slope H Separate each pair of numbers using a space In our example you will enter 10 9 1 17 0 84 11 6 Filter Coefficients b h near surface and B H regional Filter Coefficients b h near surface and B H regional 10 9 1 17 0 84 11 6 Ok Cancel 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Depth estimation with the matched filter C03 6 Library Help Top Examine the resulting power spectrum graph Library Help Top lt 4 Back gt 12 Choose Apply INTREPID will apply the filter and save the output dataset and display the Filtering process successfully completed message when it has finished The main window will contain a colour display of the filter response and results Intrepid Grid Filter tool 3 2a9 PI File Gradients Reductions Continuations Complex Standard Directional Mag Field Window Help Input spectrum Filter response Filtered spectrum Status R eduction done Selected filter s MATC Apply Clear Filter Sto 13 Display the power spectrum graph Choose Radial Power Spectrum from the Window menu Intrepid Grid Filter tool 3 2a9 File Gradients Reductions Continuations Complex Standard Directional Mag Field Window Help Original data Filtered data Zoomin Natural Log radially averaged spectrum s wn cy km Blue represents input spectrum Zoom out 2012 Intrepid Geophysics 42. Back gt INTREPID User Manual Depth estimation with the matched filter C03 7 Library Help Top lt 4 Back gt View the Display the results using the Flight Path Editor or the UNIX visualisation tool filtered grid The illustration below shows the original mlevel_grid and the solution dataset we have provided called match_grid Intrepid Flight Path Editor 3 2a9 mel Intrepid Flight Path Editor Y3 2a9 File Edit Line Display Point Display Grid Display Window Help mlevel_grid Type Image Xx Zoom Iin Zoom In Zoom Out Zoom Out Stop Redraw Stop Redraw Mouse Mode Mouse Mode C Zoom C Zoom C Query C Query C Select Ends C Select Ends C Select Segmnt C Select Segmnt Original grid Matched filter results showing basement Tips and further exploration You must mark the straight line segment using a straight section of the curve not a tangent To obtain the shallow component of the dataset subtract the results of the matched filter from the original data You can do this using the Spreadsheet Editor Load both grid datasets into the Spreadsheet Editor where they will occupy adjacent columns Create a new column with the difference between the grids as the initial value 1 e mlevel_grid match_grid INTREPID will save the new column as a separate grid dataset To apply the matched filter using the depth slicing approach with the data used in the worked example use parameters1 0 0 84 11 6 We have pro
3. the same transfer function as the separation technique but assumes that the near surface component is characterised by a horizontal line segment Log Power Depth Slicing Power Spectrum Wavenumber The near surface parameters b intercept and h slope are therefore 1 and 0 respectively The formula for the regional component is therefore simplified to regional component spectrum This 1s similar to an upward continuation which is expressed as On calculating the regional component D1 subtract it from the original spectrum to give the sources from the surface to the top of the regional sources product S1 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Depth estimation with the matched filter C03 3 Library Help Top 4 Back gt You can repeat the process on product S1 to produce a deep component D2 subtract the D2 from S1 to give a shallower set of solutions product S2 You can repeat the process a number of times The products D1 D2 represent depth slices and the products S1 S82 represent the residual shallower sources in each case Reference Manual sections See Querying the power spectrum graph OldGridFFT in Old spectral domain grid filters OldGridFFT T38 for instructions on obtaining the Spector Grant filter depth estimate intercept and slope for a straight line segment in a grid s power spectrum See Matched filter reference in INTREPID sp
4. INTREPID User Manual Depth estimation with the matched filter C03 1 Library Help Top 4 Back gt Depth estimation with the matched filter C03 Top This chapter describes two approaches to depth estimation that use the matched filter HEH e Separation filtering as described by Cowan and Cowan 1993 Depth slicing as described by Norman 1993 Spector and Grant 1970 provide a foundation for these techniques This method uses the power spectrum graph of a magnetics grid in the spectral domain Magnetic sources at similar depths show straight line segments in this graph Location of sample data for Cookbooks Where install_path is the path of your INTREPID installation the project directory for the Cookbooks sample data is install_path sample_data cookbooks For example if INTREPID is installed in C Program Files Intrepid Intrepid4 5 then you can find the sample data at C Program Files Intrepid Intrepid4 5 sample_ data cookbooks For information about installing or reinstalling the sample data see Sample data for the INTREPID Cookbooks in Using INTREPID Cookbooks R19 For a description of INTREPID datasets see Introduction to the INTREPID database G20 For more detail see INTREPID database file and data structures R05 Separation filter theory This method assumes that you can summarise the power spectrum in terms of two straight line segments characterising the regional and shallow sources The slop
5. e of a line segment indicates the depth of the sources that it characterises The intercept with the vertical axis is an indication of the intensity of the source at that depth Log Power Separation Filter Power Spectrum Wavenumber Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Depth estimation with the matched filter C03 2 Library Help Top lt 4 Back gt Where B is the Y intercept of the line segment representing the regional sources b 1s the Y intercept of the line segment representing the shallow sources H is the slope of the line segment representing the regional sources h is the slope of the line segment representing the shallow sources A1 r is the regional component of the spectrumA2 r is the shallow component of the spectrum You can represent the complex spectrum as E r Al r A2 r Regional component transfer function Therefore Regional component complex spectrum transfer function complex spectrum Thus by applying the transfer function to the complex spectrum you can obtain the regional component The matched filter performs this operation To obtain the shallow component subtract the calculated regional component from the complex spectrum The input parameters for the matched filter are b h B H as calculated from the power spectrum graph Depth slicing theory Library Help Top The depth slicing approach Norman 1993 uses
6. ectral domain operations reference R14 for general information about the matched filter in INTREPID See Matched Filter OldGridFFT in Old spectral domain grid filters OldGridFFT T38 for instructions on using this filter with grids Matched filter worked example Overview Start S D Grid Filters Specify input and output datasets Library Help Top This worked example demonstrates the use of the separation filtering approach for extracting the regional component of a survey You will use the Spectral Domain Grid Filter tool You will use the power spectrum graph of a grid dataset to calculate intercept and slope for two line segments representing the regional and shallow sources You will then apply a matched filter with these parameters to the grid dataset and examine the results 1 Inthe INTREPID Project Manager locate the Cookbook interpretation data directory e g d intrepid sample_data cookbooks interp min 2 Start the Spectral Domain Grid filters tool FFT_Filter from the Filtering menu 3 Specify mlevel_grid as the Input Dataset Specify an Output Dataset You must output to the grid match_grid1 if INTREPID is running in demonstration mode We provide an identical solution dataset for you to compare called match grid Accept the default forward and reverse FFT options as displayed in the corresponding dialog boxes 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Depth estimation wit
7. h the matched filter C03 4 Library Help Top lt 4 Back gt Calculate the 4 Choose Apply INTREPID will apply the FFT and generate the power spectrum power l for the dataset displaying a Filtering process successfully completed message spectrum View when it has finished the graph 5 Display the power spectrum graph Choose Radial Power Spectrum from the Window menu a Intrepid Grid Filter tool 3 2 Ioj Xx File Gradients Reductions Continuations Complex Standard Directional Mag Field Window Help Zoom in Natural Log radially averaged spectrum vs wn cy km Blue represents input spectrum Zoom out Tip The horizontal axis represents frequency of the data in cycles km The vertical axis is the natural logarithm of the energy at that frequency averaged for all directions in the dataset Query the 6 Query the graph for the deep regional sources Spector Grant depth estimate graph for deep Locate a straight line segment in the low frequency deep source range and click regional each end of it Note The straight line must be a segment of the curve not a SOUrCeS tangent to it INTREPID displays the segment using a white line and report the Y intercept the slope and Spector Grant depth estimate for the segment In our example Y intercept B 0 84 Slope H 11 16 km cycle Spector Grant depth estimate 888 m Information x N b intercept 0 84 and h slope 11 16 km cy Specto
8. r Grant depth estimate 888 m 7 Note the results of the query Choose OK in the message box and click the display once only instructing INTREPID to clear the line segment It will disappear when you click the first of the next pair of points Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Depth estimation with the matched filter C03 5 Library Help Top Query the graph for shallow sources Specify the Matched filter then apply it Library Help Top 8 9 10 11 4 Back gt Repeat the process with a line segment in the medium frequency shallow source range This will give you a Spector Grant estimate of the shallow sources In our example Y intercept b 10 9 Slope h 1 17 km cycle Spector Grant depth estimate 93 m Information x AN b intercept 10 90 and h slope 1 17 km cy Spector Grant depth estimate 93 m Note the results of the query Choose OK in the message box and click the display once only instructing INTREPID to clear the line segment Display the Spectral Domain Grid Filters main window Choose Main FFT from the Window menu Choose Matched from the Standard menu INTREPID displays the Matched Filter Coefficients dialog box Enter the slopes and intercepts that you obtained by querying the graph Enter them in the following order shallow intercept b shallow slope h deep regional intercept B
9. vided a task specification job file match_filt job for the matched filter task You can edit it and use it as required to experiment with the match filter JOB Limitations of the matched filter Magnetic source at any depth can be associated with a range of frequencies Shallow sources can have some low frequency components and there can be some high frequency components associated with deeper sources Thus the matched filter only serves to give an indication of the sources at each level rather than conclusive information Library Help Top 2012 Intrepid Geophysics 4 Back gt
Download Pdf Manuals
Related Search