SUMIGSPLIT - Split-step depth migration for zero-offset data. sumigsplit outfile vfile= [optional parameters] Required Parameters: nz= number of depth sapmles dz= depth sampling interval vfile= name of file containing velocities Optional Parameters: dt=from header(dt) or .004 time sampling interval dx=from header(d2) or 1.0 midpoint sampling interval ft=0.0 first time sample fz= first depth sample 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 input velocity file \'vfile\' consists of C-style binary floats. The structure of this file is vfile[iz][ix]. Note that this means that the x-direction is the fastest direction instead of z-direction! Such a structure is more convenient for the downward continuation type migration algorithm than using z as fastest dimension as in other SU programs. Because most of the tools in the SU package (such as unif2, unisam2, and makevel) produce output with the structure vfile[ix][iz], you will need to transpose the velocity files created by these programs. You may use the SU program \'transp\' in SU to transpose such files into the required vfile[iz][ix] structure. Credits: CWP Baoniu Han, July 21th, 1997 Reference: Stoffa, P. L. and Fokkema, J. T. and Freire, R. M. and Kessinger, W. P., 1990, Split-step Fourier migration, Geophysics, 55, 410-421. Trace header fields accessed: ns, dt, delrt, d2 Trace header fields modified: ns, dt, delrt