README for residual refraction statics demo by Chris Robinson

This directory illustrates the conventional application of statics:
residual refraction statics applied before stack, and average
statics applied after stack.  If you are new to SU, start by 
reading "The SU User's Manual" and the README in $CWPROOT/src/demos.

To run the demo:

cd ./MakeData               go to directory to create data

run the shell script

    Xcshot                    displays model and creates datafile

Then cd ..                     return to main directory

Run the following shell scripts to complete the demo:
Residual                  computes residual and average statics,
                          and applies residual statics to prestack
                          data
NMO                       nmo corrects and stacks data, followed by
                          poststack application of average statics
Xdisplay                  displays results with Xwindows
  or
PSdisplay                 saves results as postscript files


Notes:  The conventional application of refraction statics divides
the procedure into two parts:  application of residual refraction 
statics before stack, and the application of average refraction statics
after stack.  This splitting allows one to avoid the problem of stacking
velocity biasing endemic to statics application.  To do this, sustaticrrs.c
uses an input velocity file to compute residual and average refraction
statics and apply residual statics with the options hdrs=3 and hdrs=4.
The residuals values are stored in the "gstat" header field, and the 
average value is stored in the "tstat" header field.  After stack,
option hdrs=5 is used to access the "tstat" header field and apply
the average static.  A horizontal reference datum is usually chosen to 
be above the highest topographic point in the survey area.  The
velocity with which data are static shifted to this datum is the 
replacement velocity, V_r.
