lynx ssv overview

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Lynx SSV Overview 1 of 21 Overview of Seismic Section Vectorising with LEASSV The LEASSV software package contains a complete set of programs for conversion of seismic section raster images to output SEG-Y data. This document describes the most basic procedures involved in using LEASSV to produce SEG-Y data from scanned images and is used in combination with the documentation for each individual application. Getting started 1. Preparation , scanning and raster editing (scanner and imaging software) 2. Vectorising (SSV) 3. Trace Processing (TRACEPREP) 4. Trace Editing (TRACEFIX) 5. Output as SEG-Y (TRACEPREP) 6. Getting Started On your PC's desktop, click the Lynx Icon . This starts Launcher which shows a list of Lynx applications available on your PC. For more detailed information about installation, setup and system utilities, see Lynx Exploration Archivist Setup You will mainly be using the following applications: SSV - Seismic Section Vectorising TRACEPREP - Seismic Trace Processing TRACEFIX - Seismic Trace File Fix-up First, create a working folder for your project files. This can be anywhere on the network or local PC, but

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Overview of Seismic Section Vectorising with LEASSVThe LEASSV software package contains a complete set of programs for conversion of seismic section rasterimages to output SEG-Y data. This document describes the most basic procedures involved in usingLEASSV to produce SEG-Y data from scanned images and is used in combination with the documentationfor each individual application.

Getting started1.Preparation, scanning and raster editing (scanner and imaging software)2.Vectorising (SSV)3.Trace Processing (TRACEPREP)4.Trace Editing (TRACEFIX)5.Output as SEG-Y (TRACEPREP)6.

Getting Started

On your PC's desktop, click the Lynx Icon

.

This starts Launcher which shows a list of Lynx applications available on your PC. For more detailedinformation about installation, setup and system utilities, see Lynx Exploration Archivist Setup

You will mainly be using the following applications:

SSV - Seismic Section VectorisingTRACEPREP - Seismic Trace ProcessingTRACEFIX - Seismic Trace File Fix-up

First, create a working folder for your project files. This can be anywhere on the network or local PC, but

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you must have full read/write access rights to it. The working folder is the folder which first appears whenFile-Open is selected in a Lynx application. Click the File-Favourite Folders menu item in Launcher to set the working folder. The sample files installed with this overview are by default in subfolders ofC:\LynxData\SSV_Examples, and the example used in this overview is in the VAI folder, so you could set this as your working folder to follow along.

Scanning the Section

Preparation For each section, write down the following information, or make sure that it is clearly visible on the section:

Line Name1.Start time in milliseconds2.End time in milliseconds3.Number of traces to vectorise4.Shotpoint of the first trace to vectorise5.Shotpoint increment, ie number of shotpoints per trace6.

On the section, check for a well defined time origin. If the tiime zero (or datum) line is poorly marked, draw apencil line over it with a ruler before scanning. Interpretation marks should be erased where possible using apencil eraser, or “whited out” with a suitable marker eg white crayon, white ink or correction fluid. Ifinterpretation cannot be removed prior to scanning, raster editing will have to be done using availablesoftware, eg PhotoShop.

Before scanning, you should bear in mind the vectorising algorithm that will be used in SSV - someexperimentation may be necessary to find the most effective combination of scanning and vectorisingparameters.

Choosing a vectorising method (algorithm) SSV program has several vectorising methods, or algorithms, to suit the various seismic display types andqualities found in the archives of the oil exploration indusstry. The choice of vectorising algorithm will alsodepend on the image quality of the seismic sections you have to work with, eg paper or film sections,microfiches, screen dumps, photographs or raster files and on the sort of results that you hope to achieve.For most seismic data scanned as a bi-level (black and white) raster, the VAI (Variable Area Integration) algorithm provides a decent output with the minimum of parameter setup.

Check the printed quality of the seismic data - if the troughs are very dark, or the peaks merge together,editing to clarify events can be beneficial. Note for very poor quality data it might be easier to scan to agreyscale Tiff format and vectorise using the VDR (Variable Density Reconstruction) algorithm.

Orientation The scanned orientation is not critical, but it is normal to put the section’s left-hand edge into the scannerfirst - this corresponds to the default orientation 2 in SSV.

Resolution As a guide it is useful to maintain a minimum of about 8 pixels per trace spacing. For example, data with>1mm trace spacing use 200dpi (8px/mm), 0.7 to 1mm trace spacing use 300dpi (12px/mm) and for data<0.7mm use 400dpi (16px/mm). There is little to be gained by going above 20 pixels per trace spacing. TheVDR algorithm can be used with a much lower resolution of 2 pixels per trace spacing, which will help toavoid large file sizes.

Skew The section should be scanned as squarely as possible, but if necessary straighten the scanned imageusing available options with the scanner software. Skew will be tolerated in SSV, but calibration is easier ona straight section.

Setting the Scanning ThresholdWhen scanning to a bi-level (black and white) image format , you must determine a suitable threshold for thedata. This is usually done interactively with the scanner software as part of the image preview. It depends onthe algorithm you intend to use for vectorising. For VA, VAI and VAD algorithms, make the scan fairly light -the ‘wiggles’ in the trace troughs (negative part of the waveform) can almost disappear, but the black peaksshould remain solid. On good quality data when the VAWG algorithm will be used the section should bescanned darker with the troughs as clear as possible, but without too much ‘bleeding’ where the traces cross

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timing lines etc.

Format SSV supports over sixty raster image file formats. Vectorising algorithms VA, VAD, VAI and VAWG require abi-level (black and white) image, having one bit per pixel. If available, TIFF Group 4 format provides a highdegree of compression, without loss of image quality. On older scanners, RLC (CAD Overlay) format can beused. . The VDR algorithm requires a "grey level" image, ideally with 8 bits per pixel, e.g. uncompressedTIFF, LXW TIFF, GIFF or JPEG. Note that colour raster images are not supported, and can createunexpected results. Colour images should be converted to greyscale before running SSV.

Size mattersRaster images in SSV are limited to 32,000 x 32,000 pixels and, more importantly, by the free RAM on yourPC. As a rule of thumb, images up to about two thirds the PC's available RAM can be loaded. For example,if your PC has 128MBytes of RAM, you can load images up to about 96MBytes. Note that this will depend onwhich variant of Windows you are using and on the other programs that you are running.

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The Seismic Scan Vectorising (SSV) Program

Using SSV, a scanned raster image of a seismic section can be converted to a format suitable for furtherprocessing or output to SEG-Y

SSV will use three files:

Input Raster File - for standard vectorising this will be a bi-level raster image. Most common formatsare TIFF Group 4 (compressed) and RLC (Cad Overlay)

1.

The Parameter File - with extension .SV4 contains calibration data and parameters which control thevectorising process

2.

The Trace File - with extension .TR0 - this contains the output seismic traces in a Lynx format. You willneed to apply further processing to this data before outputting it to SEG-Y.

3.

Running SSV

Select SSV from the Launcher window.

Selecting a raster file

Go to File-Open, or press and select the raster image for vectorising:

The image should appear in the normal orientation for a a seismic section. If it doesn't, the orientationneeds to be changed. You can of course do this by re-scanning the section, or using your scanner'ssoftware to re-orient the image. Alternatively, you can use SSV's orientation parameter, which is accessedfrom the Setup-Params menu on the Input Scanned Image page. There are 8 possible orientations, numbered from 0 to 7, representing combinations of horizontal mirror, vertical mirror and 90-degreerotation,.which transform the orientation of the input file so that it appears "the right way round" in SSV.

set a new orientation on the Input Scanned Image parameter page 1.re-open SSV (File-Open menu)2.if the orientation still isn't correct - go back to 1.3.

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Setting the Parameters

Select the current parameters from the Setup-Params menu, or by pressing . This invokes the standardLynx parameter editor. Parameters are grouped into pages, and you can move between pages using thePage-Back and Page-Forward menus. The first page enables various options to be set, which in turndetermine the other pages appearing in the setup.

These Vectorising Options can be used for the majority ofsections

Most sections can be vectorised quite effectively using the VAIalgorithm, which uses the trace peak information and interpolates a negative trough. This is a robust algorithm which toleratespoorer image quality (ie less clearly defined peaks than the VA or VAWG algorithms along with missing or washed out troughs). It isa good compromise between speed and accuracy - algorithmssuch as VAWG can only be used on good quality images andrequire more careful attention to calibration and parameter setup.

Input Scanned Image

This page sets information which will be stored in the trace file header. Resolution will in most cases beread from the input raster file, but can be reset if this information is incorrect or wrongly set. Trace spacingand time scale are nominal and relative to the input resolution. The actual trace spacing and time scale willbe set according to the calibration.

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Output Trace Parameters

This page should be correctly set up BEFORE you do thecalibration.

The start and end time, and trace number information entered onthis page will be used for calculating the limits of the calibrationgrid.Shotpoint information will be stored in the trace file header. Selecting a sample interval of 4.0msec is usually sufficient. However, for data with frequencies of 70Hz and above it is betterto select a 2.0msec interval.Trace file type should be set to LYNX - although you canvectorise directly to SEG-Y format, timing and clibration information will not be preserved in the trace headers, which willcause problems if you have to stop and re-vectorise the file. One byte sample format is normally adequate for vectorised data.

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Variable Area Integration

Typical VAI parameters are as above. See SSV program documentation for more detail. The Max Slope parameter isprobably the most critical and determines the maximumpermissible trace slope estimated from the data. If you get largeswings in the amplitude of a given event, from trace to trace, thenreduce this parameter.

Peak repair can be used when the trace peaks are washed out, i.e. contain white pixels.The parameter should be set to a valuejust slightly greater than the missing gap in milliseconds.

Peak splitting will separate large peaks into a doublet and can beused to separate peaks which are very close together on the original and appear to be merged i.e. have no intervening trough.This may happen when the orginal section is too dark or of poorresolution.

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Timing Line Search

SSV searches for and suppresses timing lines, by searching forblack horizontal lines at the expected position of each timing line. The resulting "gaps" in the trace are interpolated from the nearestvalid trace data on either side of the gap.

Alternative, but generally less effective, ways of attacking timinglines are

by setting the minimum segment length in the Output TraceInterpolation page to greater than the timing line thickness. This won't work very well if the timing lines are thick, closelyspaced or have varying thicknesses.

1.

by filtering them out after vectorising, using a onedimensional bandpass or notch (band reject) filter. A high cut filter will help if the timing lines are very thin and a notchfilter sometimes helps with 10msec timing lines. Bothmethods tend to damage the seismic data as well

2.

by filtering them out after vectorising, using a 2-d dip filter,such as XTFILT. In this case, the filter is set to reject horizontal dips, but accept all other dips. This has theproblem that horizontal data will also be indiscriminatelysuppressed.

3.

The default parameters are useful as a starting point, but the parameters must be "fine tuned" to suit thedata. Adjust the timing line interval as necessary. For poor quality, badly defined timing lines increase theSearch Window and Width to Search values and decrease the Line Density percentage The Min and MaxLine thickness parameters determine the limits for the thickness of a line that can be recognised as a timingline.

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Calibration

When the parameters are set up, proceed to Calibration, by selecting the Setup-Calibrate menu. This willbring up the calibration toolbar:

Calibration sets up the relationship between points on the raster image, as measured in pixels and thecorresponding points in the rectangular trace and time coordinate system. The raster image produced by thescanner will be distorted for various reasons eg

paper stretchcreases in the paperpaper not squarely inserted in the scanneroptical distortion due to copyingbad joins or splices in the originalslippage through the scanner rollers

SSV establishes a network of triangles, using the calibration points that you enter. Within each triangle, thecorner points establish a linear transformation between pixel- and trace/time- coordinate systems. Thenumber of calibration points will depend on how much distortion there is in the image and the degree ofaccuracy that you require. Four calibration points are required as a minimum. Proceed as follows:

Click on calibration corner point 1 , position the mouse cursor at theorigin of the first trace to bevectorised, and click the mouse. If you place the cross in the wrong place, just click again to reposition it.

Click on calibration corner point 2 , and position the cursor at the end time of the last trace to bevectorised.

In the same way set calibration corner point 3 as the start time of the last trace to be vectorized, and point

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4 as the end time on the first trace to be vectorized

Finally click on the button again, to enable the other buttons on the tool bar

Adjusting the calibration

To see the how well the image is calibrated, click , which switches on a green grid overlay. The grid linescorrespond to regularly spaced trace and time lines, which should more or less exactly overlay thecorresponding traces and time lines.If the accuracy is not good enough, then you need to insert morecalibration points. The default grid is set for twenty traces at 100 millisecond intervals. (This can be adjustedby going into the Params-Config menu and editing the “Time Cal Grid” and “Trace Cal Grid” values).

Inserting extra calibration points

After setting the four corner points the grid can be adjusted using the “Snap to Grid” tool . As you move themouse around over the image, the nearest grid node to the cursor is illuminated and trace and time valuesare shown when this option is toggled “on”. In this mode, new calibration points can be made by clicking ona grid node to select it, then clicking again where you want the node to be repositioned.

If a point is set incorrectly it can be deleted using the delete button . This will delete the current calibration point, indicated at the top of the calibration tool bar. To select a calibration point, click and then click thecursor near the desired point.

When you are satisfied with the calibration, save and exit by pressing the red tick button. To cancel andrevert to the parameters currently stored in the parameter file, press .

Vectorising

After parameter setup and calibration, you are ready to vectorize, by pressing the button. As each trace isvectorised, an output trace is written and a red trace overlay display appears over the raster image. You can

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stop vectorising at any time by pressing .

Other useful things to know about SSV

To find out more about vectorising options and features, read the SSV help file (SSV.htm)1.Use the File-Set Default menu to create a parameter file "template", named default.SV4, which will be used for default parameters whenever you select a new raster file in the same folder.

2.

If you change the number of traces to be vectorised in the Output Trace Parameters page, you must re-do the calibration.

3.

If you have to change the start or stop time of the output traces, when you have already produced anoutput trace file, you must reset the trace file using File-Reset Traces.

4.

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Trace Processing

Following vectorising, the "raw" trace information will be in a trace file with the same name as the inputraster, but with file extension .TR0. You can view this file directly, using SEISVIEW, TRACEPREP or TRACEFIX. It probably won't look very pretty. You need to do further processing and editing, with a view tomaking the vectorised data look as much like the original as possible. The data can also in some cases evenbe enhanced, by comparison with the original, with processes such as deconvolution and migration, but thisis outside the scope of this section.

The image above shows a TR0 file in the TRACEPREP viewer.

There some obvious intial problems, which can be corrected by a little seismic processing:

The traces are biased, ie the sample average is non-zero. For various reasons, raw vectorised tracesare usually positively biased - this condition can most easily be removed by applying a low cut filter.

1.

The traces are noisy. Vectorising can introduce various types of noise, most commonly high frequencyquantising noise, due to the discrete nature of the raster image and impulsive noise due to"mis-picking" of peaks or troughs. By restricting the bandwidth to that of the original section, this noisecan be substantially reduced. The safest filter to apply at this point will be a time variant or fixedbandpass filter, having approximately the same characteristics as the final filter used for the orignalprocessing. Sometimes, a light mix will help to reduce the effects of mis-picking.

2.

The character of the traces may differ from the original. This can also occur due to the outputbandwidth of vectorising differeng from that of the original data - the same filter as applied in 2) willhelp..

3.

The traces vary in amplitude. All vectorising algorithms are, to some extent, sensitive to variations onthe intensity of the original image and the scanning threshold. An RMS trace balance can be used tonormalise the amplitudes.

4.

The traces need muting - there is noise in the lead-in zone, where the trace amplitude would havebeen zero on the original. To correct this problem, you need to re-pick the water bottom and lead inand apply this as a mute. The mute times can be picked either in SSV and output as a mute file, or inTRACEFIX (see below), where there are several options for saving the mutes times either as aseparate file, or in the trace headers.

5.

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TRACEPREP is used to apply the necessary processing, in a sequence as below. Click on TRACEPREP inLauncher.

The minimum processing applied to vectorised data is usually a bandpass filter and RMS balance. Thiswould equate to the following processing sequence in TRACEPREP:

INFILE - select your input TR0 fileBPFILT - apply a filterRMS - balance the tracesOUTFILE - creates a new TR file (eg TR1)

The following example demonstrates a slightly more complex processing sequence: select INFILE, MIX,BPFILT, RMS, VIEWER and OUTPUT processes.........

Then set up each of the processes in turn, along the lines suggested below

INFILE process reads traces from the raw trace file (TR0) generated by SSV

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MIX is used in this case to apply a 3-trace mix - this will be quite strong enough with an outside weight of0.25. If a stronger mix is used, the output data may be too "smeared".

BPFILT is used to apply a simple band pass filter. To match the filter more accurately to the data, useTVFILT instead.

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This RMS process will normalise the trace amplitudes to a constant root mean square value of 10. If the dataare to be output to SEG-Y fixed point format, you should use an RMS of about 2500.

The VIEWER process can be added to the process list to display the output of the previous process. ThisVIEWER process is set up for VA/Wiggle display and a fairly large display scale so that the quality of theresults can easily be monitored

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Finally, OUTPUT the data to a new trace file - the default file name will be the same as the input file, with thenext available TR number extension, eg TR1

Finally press to run the processing sequence and see the processed data.

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The input traces will be processed, and output to a new trace file, and will also be displayed in a windowsimilar to the one above.

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Trace Editing

After processing, some problems may still remain:

The section needs to be re-muted (observe the noise and residual timing lines in the section above)1.The shotpoint numbers may be incorrect - the original may have irregular, missing or discontinuousshotpoints

2.

There may be obviously bad traces, where there were defects in the original image, such as splices,creases, dark or light patches

3.

Despite your best efforts at calibration, there may be timing errors in places4.

These and other related problems can be corrected using TRACEFIX, which you can open from Launcher. Use the File-Open menu and select the file created by TRACEPREP (usually a TR1 file).

TRACEFIX allows you to edit the file header of the trace file (eg to change the line name, first shotpoint and shotpoint increment or edit the C-Cards). It also allows you to print QC plots to any Windows printer(you can set the scale and style of the plot using the Options - Set Display Parameters menu option). You can also zero or regenerate traces (to deal with bad splices on the original scanned section), or mergetrace files together.

However, the major task you will use TRACEFIX for is to mute the seismic data. There is usually a smallamount of noise introduced into the data by the vectorising process which is especially apparent in thelead-in.zone.

Select the Traces-Select Mute Horizon menu option, and select 'Mute Stop Times' from the dialoguedisplayed.

Now use the mouse to pick the along the seismic traces to select the area to mute, starting at trace 1 on theleft-hand side:

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The screenshot above was during the process of mute picking. You can see that the mute has been pickedup to about trace 160/shotpoint 1050. Remember that you can zoom, scroll, and change the display style (egto VA/Wiggle) while you are muting. You can also right-click in the TRACEFIX view window to access acontext menu giving you additional options including 'Insert Point at Cursor' and 'Delete Point at Cursor'.When you have finished defining your mute, click the Traces-Horizons On/Off menu, and select 'Yes' to save your mute.

Next click the Traces-Apply Mutes to Traces menu, and click OK in the dialogue, to apply the mute and copy the mute stop time to the header of each trace.

You should now see something like this:

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When you exit TRACEFIX, you will be prompted to save your changes to a new trace file with the nextavailable TR number (eg TR2), and also to save the mute to a Trace Auxiliary (TAX) file. This TAX file, orthe mute values in the trace headers, can be re-used if you wish to re-mute a different version of this seismicline, eg after migration, in TRACEPREP.

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Output to SEG-Y

Most applications using SEG-Y format these days work directly from disk files, so that it is rarely necessaryto output to tape.

SEG-Y Output to diskUsing TRACEPREP, create a processing sequence with INFILE and SEGYOUT. You can select whether tooutput to 4-byte (32-bit) or 2-byte (16-bit), and Standard, Lynx or Revision1 SEG-Y. The Lynx variant ofSEG-Y retains extra header information which Lynx applications can use when the file is loaded. See theSEGYOUT help file for more details of the options available.

SEG-Y Output to tapeTo copy SEG-Y files onto tape, you can use the TAPEFILE utility in the Launcher. This is a general-purposeutility for copying data to and from tape devices, and has options to deal explicitly with the variable-lengthblocking required for SEG-Y format tapes.

Thank you for reading this overview, we hope it has got you off to a good start with the software. To find outmore you can read the help files located in your LYNXSYS\DOCS folder, accessible from the Launcher'sHelp menu, or email us at [email protected] with any queries.

Copyright © Lynx Information Systems Ltd 2006