Geol 492/692 - Reading SEG-Y Data

Reading SEG-Y Data

Viewmat starts up with a default blank data set. Locate the menu bar at the top and select Read Binary File... from the File menu. A dialog box comes up asking you to navigate to the folder with your SEG-Y seismic data file. Select the ``dixie-refr.sgy'' file and click OK.
Another dialog pops up asking for a description of the data file. Leave Binary File Type set to SEG-Y. If you want to read in just a few records of a large multi-record file, you would enter the first and last field record numbers (field file IDs or FFIDs) into the fields below.
- For the ``dixie-refr.sgy'' file you have to put some default values into the field record number fields, or Viewmat will put all the records side-by-side in one plane. Enter ``0'' and ``1000'' into the fields. With that, Viewmat will load all five records in the file as separate planes in a data volume.
  You may experience difficulties on older or smaller PCs if you try to load larger files, with more than 20 megabytes worth of records. (See the note in the Display instructions on increasing the memory available to Viewmat.)
- Although the SEG-Y format does not officially support having records of different length together in one file, you may encounter them later. Enter the field record number of the first record that has the length you want, and Viewmat will pick out of the file all the records that are similar.
- Some SEG-Y files written to disk from a tape, or from certain organizations, will not begin with the required 3600-byte tape reel header block. If you know this to be the case, uncheck that item in the dialog. The ``dixie-refr.sgy'' file does not have the reel header, so uncheck the box.
- Although the standard binary format for SEG-Y trace data is 4-byte IBM Float, some conversion programs will write different formats. If you know the format and it is not IBM Float, select it under Trace Data Type. For our ``dixie-refr.sgy'' file, select IEEE/Java Float.
When you have finished setting your SEG-Y options, click the Read Binary File button.
- If you get an error message about the file not being in SEG-Y format, select Open Binary File from the plot window's File menu, and try changing your field record number selections, or the reel header checkbox.
- If the data plot does not look like seismic waves, or appears badly clipped, try changing the selected Trace Data Type.
After a moment a new data display window will pop up with an image of the first record. You may only see the near-source traces, since the plot is of raw data without any amplitude balancing. You can close the old window of the zero data plot and proceed to the next section to effectively display your records.