SUMIGPREFD - The 2-D prestack common-shot 45-90 degree finite-difference migration.

Usage:
sumigprefd <indata >outfile [parameters]

Required Parameters:

nxo= number of total horizontal output samples
nxshot= number of shot gathers to be migrated
nz= number of depth sapmles
dx= horizontal sampling interval
dz= depth sampling interval
vfile= velocity profile, it must be binary format.
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.

Optional Parameters:

dip=79 the maximum dip to migrate, it can be 45,65,79,80,87,89,90",
The computation cost is 45=65=79<80<87<89<90

Fmax=25 the peak frequency of Ricker wavelet used as source wavelet

f1=5,f2=10,f3=40,f4=50 frequencies to build a Hamming window

lpad=9999,rpad=9999 number of zero traces padded on both
sides of depth section to determine the migration aperature, the default",
values are using the full aperature.


Credits: CWP, Baoniu Han, bhan@dix.mines.edu, April 19th, 1998


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