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                    PROCESS LOGSTX, where X = { 1, 2 }

Document Date: 31 October 1991

PROCESS LOGSTX applies a log function to "stretch" each trace in time.
The most common use of process LOGSTX is prior to, and subsequent to, 
PROCESS DMO, exact log Dip Move OUT.  Log stretching allows DMO to work
in F-K space while preserving the DMO ellipse.

Prior to dip move out in quasi-FK space [Fourier Transform of log
stretched trace does not give F, but a log frequency (OMEGA) -see Liner,
Geophysics May 1990] use log stretch type 1(stretch), after DMO use log
stretch type 2 (compress).

To preserve dips in OMEGA-K space the data which is resampled via a
cubic spline must be resampled at an adequate rate to prevent temporal
and spatial aliasing of frequency content and seismic dips, respectively.

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TYPE   - The type of log stretch to be applied 1 or 2.
       = 1, "Stretch", tau = ln(t/tc) where tau is the new log time, t
         is time of trace, and tc is the cutoff time which prevents the
         log of zero to be taken.
       = 2, "Compress" = 2, t = tc*exp(tau) where the variables (t,tc
         and tau) are defined as above.
         Preset = 1 "compress"

TSAMP1 - The new sample rate (*1000) for the log stretched trace.  May
         be different than time sample rate.   Used in Process LOGST1
         Preset = 0.004  (250 samples/sec)

TSAMP2 - The new sample rate (*1000) subsequent to log compression.  May
         be different than initial sampling or log sampling.  Used in
         process LOGST2.
         Preset = 0.004  (250 samples/sec)

TCUT   - Time cut for log stretch/destretch.  Must be same for processes
         LOGST1 and LOGST2.  Times prior to TCUT will be nulled.
         Preset = 0.1 seconds

SLTIME - Start time of trace subsequent to DMO and "unstretch".
         Preset = 0.0

ELTIME - End time of trace subsequent to DMO and "unstretch".
         Preset = 6.0

LOGHZ  - Highest frequency (prestretch) used.

Copyright (C) 1991 The Regents of the University of California
ALL RIGHTS RESERVED.  Written By Graham Kent, September 1991
Go to the list of seismic processes.      Go to SIOSEIS introduction.