SUMIGPSPI - Gazdag's phase-shift plus interpolation migration for zero-offset data, which can handle the lateral velocity variation.

sumigpspi <infile >outfile vfile= [optional parameters]

Required Parameters:
nz= number of depth sapmles
dz= depth sampling interval
vfile= name of file containing velocities
(Please see Notes below concerning the format of vfile)

Optional Parameters:
dt=from header(dt) or .004 time sampling interval
dx=from header(d2) or 1.0 midpoint sampling interval

tmpdir= if non-empty, use the value as a directory path
prefix for storing temporary files; else if the
the CWP_TMPDIR environment variable is set use
its value for the path; else use tmpfile()

Notes:
The structure of such a file is vfile[iz][ix], the x-direction is the
fastest direction instead of z-direction, such a structure is quite
convenient for the downward continuation type migration algorithm.
Since most of the velocity file is in vfile[ix][iz] structure, you can
use 'transp' in SU to transpose them into vfile[iz][ix] structure.



Credits: CWP, Baoniu Han, April 20th, 1998

Trace header fields accessed: ns, dt, delrt, d2
Trace header fields modified: ns, dt, delrt