SUSTATICRRS - Elevation STATIC corrections, apply corrections from	
	      headers or from a source and receiver statics file,	
	      includes application of Residual Refraction Statics	

     sustaticrrs <stdin >stdout  [optional parameters]	 		

 Required parameters:							
	none								
 Optional Parameters:							
	v0=v1 or user-defined	or from header, weathering velocity	
	v1=user-defined		or from header, subweathering velocity	
	hdrs=0			=1 to read statics from headers		
 				=2 to read statics from files		
	sign=1			=-1 to subtract statics from traces(up shift)
 Options when hdrs=2:							
	sou_file=		input file for source statics (ms) 	
	rec_file=		input file for receiver statics (ms) 	
	ns=240 			number of sources 			
	nr=335 			number of receivers 			
	no=96 			number of offsets			

 Options when hdrs=3:                                                  
       blvl_file=              base of the near-surface model file (sampled
                                  at CMP locations)                    
       refr_file=              horizontal reference datum file (sampled at
                                  CMP locations)                       
       nsamp=                  number of midpoints on line             
       fx=                     first x location in velocity model      
       dx=                     midpoint interval                       
       V_r=                    replacement velocity                    
       mx=                     number of velocity model samples in     
                                  lateral direction                    
       mz=                     number of velocity model samples in     
                                  vertical direction                   
       dzv=                    velocity model depth interval           
       vfile=                  near-surface velocity model             

 Options when hdrs=4:                                                  
       nsamp=                  number of midpoints on line             
       fx=                     first x location in velocity model      ", 
       dx=                     midpoint interval                       ", 

 Options when hdrs=5:                                                  
       none                                                            

 Notes:								
 For hdrs=1, statics calculation is not performed, statics correction  
 is applied to the data by reading statics (in ms) from the header.	

 For hdrs=0, field statics are calculated, and				
 	input field sut is assumed measured in ms.			
 	output field sstat = 10^scalel*(sdel - selev + sdepth)/swevel	
 	output field gstat = sstat - sut/1000.				
 	output field tstat = sstat + gstat + 10^scalel*(selev - gelev)/wevel

 For hdrs=2, statics are surface consistently obtained from the 	
 statics files. The geometry should be regular.			
 The source- and receiver-statics files should be unformated C binary 	
 floats and contain the statics (in ms) as a function of surface location.

 For hdrs=3, residual refraction statics and average refraction statics
 are computed.  For hdrs=4, residual refraction statics are applied,   
 and for hdrs=5, average refraction statics are applied (Cox, 1999).   
 These three options are coupled in many data processing sequences:    
 before stack residual and average refraction statics are computed but 
 only residual refractions statics are applied, and after stack average
 refraction statics are applied.  Refraction statics are often split   
 like this to avoid biasing stacking velocities.  The files blvl_file  
 and refr_file are the base of the velocity model defined in vfile and 
 the final reference datum, as described by Cox (1999), respectively.  
 Residual refraction statics are stored in the header field gstat, and 
 the average statics are stored in the header field tstat.  V_r is the 
 replacement velocity as described by Cox (1999).  The velocity file,  
 vfile, is designed to work with a horizontal upper surface defined in 
 refr_file.  If the survey has irregular topography, the horizontal    
 upper surface should be above the highest topographic point on the    
 line, and the velocity between this horizontal surface and topography 
 should be some very large value, such as 999999999, so that the       
 traveltimes through that region are inconsequential.                  

 Credits:
	CWP: Jamie Burns

	CWP: Modified by Mohammed Alfaraj, 11/10/1992, for reading
	     statics from headers and including sign (+-) option

      CWP: Modified by Timo Tjan, 29 June 1995, to include input of
           source and receiver statics from files. 

      CWP: Modified by Chris Robinson, 11/2000, to include the splitting
           of refraction statics into residuals and averages

 Trace header fields accessed:  ns, dt, delrt, gelev, selev,
	sdepth, gdel, sdel, swevel, sut, scalel
 Trace header fields modified:  sstat, gstat, tstat

 References:

 Cox, M., 1999, Static corrections for seismic reflection surveys:
    Soc. Expl. Geophys.