Displaying Seismic Records in JRG

To easily pick first arrivals, you will probably want to change how Viewmat initially shows your data. First, though, if you have loaded a multi-record file, press the Animate button. The first record of a survey is often the worst!
You may notice that your records are longer than they need to be for first-arrival picking. The ``dixie-refr.sgy'' file has just one second of data, so you will not need to change the time length. If you did want to change the length, from the Methods menu, and its On Each Vector sub-menu, you would select cutTime.
The cutTime dialog shows you the starting time of the traces, and their length in seconds. For many surveys you can probably enter a new Trace Length of a quarter of the old, or less, and press the cutTime button.
- If you get an Out of Memory error in the DOS window running Viewmat, you have to close it down by selecting Exit Java from the File menu. Then start it up again, reading fewer records from your file. Or try running with more memory dedicated to Viewmat, with a command like jre -mx64000000 Viewmat typed into a DOS window (that will give 64 Mb to Viewmat; don't give a size larger than 3/4 of your PC's installed RAM).
If you have not cut away too much time, you can close the old plot by selecting Close Window from the old plot's File menu, to save memory.
Apply trace balancing by selecting tegain from the On Each Vector sub-menu of the Methods menu on the new display. Press the tegain button in the tegain dialog.
tegain changes the overall amplitude of the data, so it may appear gray or clipped. From the Edit menu, select Clip at 3*RMS for a better display. Press the Animate button to see all the records of a multi-record file.
You may want to change the aspect ratio of the display, or try a color image:
- Select Plot Parameters from the Edit menu.
- A Properties dialog appears that will allow you to change virtually all of the display options.
- You might edit the Title text to be more than the file path.
- After using cutTime, you might want to double the vertical exaggeration, or more.
- For a color image, try setting the Color Table for Image to Seismic Red-White-Blue, a popular representation for reflection data. Time picks plot in black and may show up better on a color image. The default gray plot is called Seismic Variable Density.
- If you have a survey with constant trace spacing and no gap, you can set the Vectors: Zero, Delta, and Units fields for the plot. This is not possible for the ``dixie-refr.sgy'' file. For example, with 48 reflection traces starting with a minimum offset of 50 feet at channel index 0, and 10 feet geophone group spacing, set Vectors: Zero to 50, Delta to 10, and Units to ``Offset, feet''.
- If you have multiple records, and they were in order in the SEG-Y file, you can set the Planes: Zero, Delta, and Units fields for the plot. For example, with 23 records starting at record 1025, set Planes: Zero to 1025, Delta to 1, and Units to ``Field Record Number''. This is also not possible with our ``dixie-refr.sgy'' file.
- Click the Apply Changes button in the dialog.
- Go back to the display window and try Animate to check all the records.
- You can make more changes in the Properties window, and click Apply Changes again.
- After you have made a number of changes, save your parameters by selecting Save Parameter File from the File menu of the Properties window. You may have to navigate back to your data directory in the Save Viewmat Parameter File dialog that appears. Be sure to give the parameter file a name that will not over-write your data file! The next time you open this data file, just select Apply Parameter File from the display window's Edit menu, and your custom plot configuration will be restored.
To enlarge the data display, select 200% or 500% from the Zoom Image To: sub-menu of the View menu.