SUKDMIG2D - Kirchhoff Depth Migration of 2D poststack/prestack data	    sukdmig2d  infile=  outfile=  ttfile=   [parameters] 		 Required parameters:							 infile=stdin		file for input seismic traces			 outfile=stdout	file for common offset migration output  	 ttfile=		file for input traveltime tables		 ...  The following 9 parameters describe traveltime tables:		 fzt= 			first depth sample in traveltime table		 nzt= 			number of depth samples in traveltime table	 dzt=			depth interval in traveltime table		 fxt=			first lateral sample in traveltime table	 nxt=			number of lateral samples in traveltime table	 dxt=			lateral interval in traveltime table		 fs= 			x-coordinate of first source			 ns= 			number of sources				 ds= 			x-coordinate increment of sources		 Optional Parameters:							 dt= or from header (dt) 	time sampling interval of input data	 ft= or from header (ft) 	first time sample of input data		 dxm= or from header (d2) 	sampling interval of midpoints 		 fzo=fzt		    z-coordinate of first point in output trace	 dzo=0.2*dzt		vertical spacing of output trace 		 nzo=5*(nzt-1)+1 	number of points in output trace		",	 fxo=fxt		    x-coordinate of first output trace 		 dxo=0.5*dxt		horizontal spacing of output trace 		 nxo=2*(nxt-1)+1  	number of output traces 			",	 off0=0		   	first offest in output 			 doff=99999		offset increment in output 			 noff=1	 	number of offsets in output 			",	 absoff=0      flag for using absolute offsets of input traces		               =0 means use offset=gx-sx                		               =1 means use abs(gx-sx)                  		 limoff=0      flag for only using input traces that fall within the range               of defined output offset bins (off0,doff,noff) 		               =0 means use all input traces                 		               =1 means limit traces used by offset           		 fmax=0.25/dt		frequency-highcut for input traces		 offmax=99999		maximum absolute offset allowed in migration 	 aperx=nxt*dxt/2  	migration lateral aperature 			 angmax=60		migration angle aperature from vertical 	 v0=1500(m/s)		reference velocity value at surface		",	 dvz=0.0  		reference velocity vertical gradient		 ls=1			flag for line source				 jpfile=stderr		job print file name 				 mtr=100  		print verbal information at every mtr traces	 ntr=100000		maximum number of input traces to be migrated	 npv=0			flag of computing quantities for velocity analysis rscale=1000.0 	scaling for roundoff error suppression		   ...if npv>0 specify the following three files:			 tvfile=tvfile		input file of traveltime variation tables				tv[ns][nxt][nzt]				 csfile=csfile		input file of cosine tables cs[ns][nxt][nzt]	 outfile1=outfile1	file containning additional migration output   				with extra amplitude				 Notes:								 1. Traveltime tables were generated by program rayt2d (or other ones)	    on relatively coarse grids, with dimension ns*nxt*nzt. In the	    migration process, traveltimes are interpolated into shot/gephone 	    positions and output grids.					 2. Input seismic traces must be SU format and can be any type of 	    gathers (common shot, common offset, common CDP, and so on).	",  3. Migrated traces are output in CDP gathers if velocity analysis	    is required, with dimension nxo*noff*nzo.  			",  4. If the offset value of an input trace is not in the offset array 	    of output, the nearest one in the array is chosen. 		 5. Memory requirement for this program is about			    	[ns*nxt*nzt+noff*nxo*nzo+4*nr*nzt+5*nxt*nzt+npa*(2*ns*nxt*nzt   	+noff*nxo*nzo+4*nxt*nzt)]*4 bytes				    where nr = 1+min(nxt*dxt,0.5*offmax+aperx)/dxo. 			 6. Amplitudes are computed using the reference velocity profile, v(z),    specified by the parameters v0= and dvz=.				 7. Input traces must specify source and receiver positions via the header    fields tr.sx and tr.gx. Offset is computed automatically.		 8. if limoff=0, input traces from outside the range defined by off0, doff,     noff, will get migrated into the extremal offset bins/planes.  E.g. if     absoff=0 and limoff=0, all traces with gx<sx will get migrated into the     off0 bin. Author:  Zhenyue Liu, 03/01/95,  Colorado School of Mines  Modifcations:    Gary Billings, Talisman Energy, Sept 2005:  added absoff, limoff. Trace header fields accessed: ns, dt, delrt, d2 Trace header fields modified: sx, gx