University of Bergen
Institute of Solid Earth Physics
Allé gt. 41, N-5007 Bergen, NORWAY
Tel: (+47) 5558 3420 Fax: (+47) 5558 9669
http://www2.ifjf.uib.no/

Document status: DRAFT
Last update June 12, 2001 by OM
Arctic Ocean 2001 Geophysical Surveys
Processing of data from Geometrics ES-2401

Processing uses Seismic Unix (SU), The Center for Wave Phenomena, Colorado School of Mines.

This web page is based on Field Analyzer documentation (by A. Sjursen).

1 Getting field data (SEG-2) into the system

The Geometrics ES2401 recording instrument produces data files in the SEG2 format. Each file contains data from a single shot. Files are normally given names according to the shot number, e.g. 001.1, 002.1, 003.1, ....

If the files are already on the computer with the SU software, you are lucky. Just do these steps:

  1. Make your own directory (e.g.   mkdir   /data/SVAL98/arne)
  2. Copy the wanted files to this directory (e.g.   cp   /data/DEMO/001.1   /data/SVAL98/arne)
  3. Repeat step 2 for all the files you need

If your data is on diskettes, you can do one of the following:

You have got access to the floppy drive on the computer with the SU software
  1. Make your own directory (e.g.   mkdir   /data/sval98/arne )
  2. Move to this directory (e.g.   cd   /data/SVAL98/arne )
  3. Copy the wanted files from the diskette (e.g.   mcopy   a: )
  4. Repeat step 3 for all your diskettes

You have got access to a PC on the network

  1. Make your own directory on the SU system (e.g.   mkdir   /data/SVAL98/arne )
  2. Copy all the files on the diskettes to your PC
  3. Transfer the files from your PC to your directory on the SU system using ftp

2. Data conversion

  1. Move to your working directory (e.g.   cd   /data/SVAL98/arne )
  2. Copy the seg* files from the /data directory (   cp   /data/seg*   . )
  3. If you want to convert the file 001.1 to SEG-Y, do the command   ./seg2segy   001.1   1
  4. If you want to convert the files 011.1 to 020.1 into a single SEG-Y file, do the command   ./seg2segy   011.1   10

The syntax for the seg2segy program is
seg2segy   FirstFile   NumberOfFiles
The name of the SEG-Y file is the same as the FirstFile, but with the extention sgy.

Note:

  • For further processing, you should run the process described below.
  • It may be necessary to recompile the source code for the seg2segy program. Go to the directory where the program is normally placed, /$CWPROOT/src/ThirdParty/seg2segy/. Enter the command make seg2segy. Then make a symlink to the new executable in /$CWPROOT/bin by typing ln -s /$CWPROOT/src/ThirdParty/seg2segy/seg2segy (assuming you are in /$CWPROOT/bin). $CWPROOT is a variable normally set in /etc/profile. Type echo $CWPROOT to see its current value.

3. Viewing the data

To look at the data in the file 001.sgy, run this the processing job
segyread tape=001.sgy endian=0 | segyclean | suxwigb

You should now get somthing like this:

To terminate the job press q in the plot window, or control-C in the command window.

The job consists of three programs chained together:

  1. segyread tape=001.sgy endian=0 - Read in the data from the given source (001.sgy), specify little-endian byte ordering.
  2. segyclean - Clean up header values so SU don't get confused
  3. suxwigb - Plot the data

Note:
To zoom in on a part of the plot, you can hold down the left mouse button and drag out a rectangle you want a closer look at. To undo the zoom, just click on the left button.

4. Scaling the data

We will here describe two types of scaling.

Scaling the plot

This is done with options to the suxwigb program, e.g. perc=95.
To test this run the following job:
segyread tape=001.sgy | segyclean | suxwigb perc=95

You should get somthing like this:

Scaling the data

To automatically scale the data according to the amplitude of the data, you can use the program   sugain.
To test this run the following job:
segyread tape=001.sgy | segyclean | sugain agc=1 | suxwigb perc=95

The output should be similar to this:


Note:
If you are going to use the data for further processing, they should not be scaled at this stage.

5. Using just some of the data

To use just a subset of the data you can use the program   suwind.
To test this run the following job:
segyread tape=011.sgy | segyclean | suwind key=tracf min=10 max=10 | sugain agc=1 | suxwigb perc=95

The output should be similar to this:

The job selects the trace (channel) 10 from all shots and throws away the rest.

To see the whole dataset you can run
segyread tape=011.sgy | segyclean | sugain agc=1 | suxwigb perc=95

The output should be similar to this:


Note: Due to the limited resolution on the screen, the image above is not very clear. Run the example to get a better view.

6. Output for further processing or storage (SEG-Y)

To generate a SEG-Y output file from a job, you can use the program segywrite.
To test this run the following job:
segyread tape=001.sgy | segyclean | segywrite tape=result.sgy endian=0

This job will generate the SEG-Y file   result.sgy.
The option endian=0 should be used on PCs. On other computers you may have to use the value endian=1

To generate a SEG-Y tape instead of a disk file, use the option tape=/dev/st0 (st0 is the name of the tape drive).

7. Reading SEG-Y data back in

If you want to read again a SEG-Y file you have generated before, you can run something like this.
segyread tape=result.sgy endian=0 | segyclean | sugain agc=1 | suxwigb perc=95

 

University of Bergen
Institute of Solid Earth Physics
Allé gt. 41, N-5007 Bergen, NORWAY
Tel: (+47) 5558 3420 Fax: (+47) 5558 9669
Email: Yngve.Kristoffersen@ifjf.uib.no