GEPH316 Field Data: Automatic Gain Correction

GEPH316 Seismic Data Processing

Field Data Workshop 2000

20 AGC Correction


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AGC correction of final section

Investigate the seismic unix Automatic Gain Correction AGC command sugain to see how it operates.

sugain

For comparison, redisplay the final stacked line as the xmovie plot.

suxmovie < line.stack title='Final stacked line' windowtitle='Final stacked line' label1='Time (s)' label2='Trace = CDP position - 6 (m)' &

Prof Jon Claerbout has designed a standard AGC function, which we can test on our data.

sugain < line.stack > line.gain jon=1
suxmovie < line.gain title='AGC line with jon=1' windowtitle='AGC line with jon=1' label1='Time (s)' label2="Trace = CDP position - 6 (m)" &

Compare the plots before and after the AGC is applied.
It appears that the AGC enhances the tail end of our seismic section to see later seismic events, but perhaps it is a little too strong.
The following AGC may be applied. It uses an automatic gain amplification with a time window of 0.05s, which makes each 0.05s section of each trace have the same maximum amplitude.

sugain < line.stack > line.gain agc=1 wagc=0.05
suxmovie < line.gain title='AGC line with agc=1 wagc=0.05' windowtitle='AGC line with agc=1 wagc=0.05' label1='Time (s)' label2="Trace = CDP position - 6 (m)" &

Compare the plots before and after the AGC is applied.
It appears that the AGC enhances the tail end of our seismic section to see later seismic events, with a better balance than the Jon Claerbout gain.
You can plot the data in wiggle trace format using the following command.

suxwigb < line.gain title='AGC line with agc=1 wagc=0.05' windowtitle='AGC line with agc=1 wagc=0.05' label1='Time (s)' label2="Trace = CDP position - 6 (m)" &

You can produce printed copies of this line in wiggle and movie format using:

supswigp < line.gain title='AGC line with agc=1 wagc=0.05' windowtitle='AGC line with agc=1 wagc=0.05' label1='Time (s)' label2="Trace = CDP position - 6 (m)"  | lp -d mono
supsmovie < line.gain title='AGC line with agc=1 wagc=0.05' windowtitle='AGC line with agc=1 wagc=0.05' label1='Time (s)' label2="Trace = CDP position - 6 (m)"  | lp -d mono

Remove the unwanted graphical windows and files.

zap xmovie
zap xwigb
ls


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