SUMIGPREPSPI --- The 2-D PREstack commom-shot Phase-Shift-Plus 	
			interpolation MIGration.			

   sumigprepspi <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.		

 Optional Parameters:						   	
 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.		
  
 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, bhan@dix.mines.edu, April 19th, 1998


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