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                               PROCESS STACK

Parameters, alphabetically:
header    lprint      new

Document Date: 17 April 2007
    August 2002 - remove zeroing of trace header words 19 & 21 (x-coords)
    July 2004 - Changed HEADER preset from NORMAL to FIRST
    August 2005 - Add parameter NEW.
    May 2006 - Changed NEW prest to 1 - NEW STACK ALGORITHM
    Feb 2007 - Compute the rp coodinates (source + receiver ) / 2 and
              store on header words 19 & 20 and zero 21 & 22

PROCESS STACK adds consecutive traces, completing the sum when the 
special SIOSEIS end-of-gather flag (header word 51 set to -1) is
detected.  The end-of-gather flag may be set by PROCESS GATHER,
processes INPUT or DISKIN parameter NTRGAT, or PROCESS HEADER.

The summed trace is scaled or averaged by the number of live trace
samples contributing to each stacked trace.  i.e. mute times are
accounted for, as well as the number of live traces in the summation.

PROCESS STACK honors trace length changes within the gather as well
as changes of the deep water delay with the gather.

Some of the SEG-Y trace headers are modified by PROCESS STACK.

The rp number is always set to the rp number of the first trace of
the gather.  The rp trace number is always 1.

The SIOSEIS end-of-gather flag, SEG-Y long header word 51, is set to 1.

The number of stacked traces (cdp or fold) is set SEG-Y short word 17.

See PROCESS STK for median stack.
--------- ----------

HEADER - The type of header replacement.  
       = FIRST, The SEG-Y trace header of the first trace of the
         gather is used for the stacked trace.
       = NORMAL, Same as FIRST but is addition the shot number, the 
         shot trace number, and the trace range are set to 0.  
       = LAST, The above header values are taken from the last trace
         of each gather.
         Preset = NORMAL

NEW    - A YES/NO switch.  Yes indicates that the "new" stacking
         algorithm is to be used.  Only non-zero values are included
         in the stacked trace average.  Process stack has always honored
         process MUTE and SMUTE zeroing, but NMO DSTRETCH and DESPIKE
         zeroes were not honored.  The new algorithm assumes that modern
         recording and process is done in floating point and a zero
         amplitude only happens when a sioseis process intentionally sets
         it to zero.
         PRESET = YES        e.g.   new no.


END    - Terminates the parameter list.

Copyright (C) 1992 The Regents of the University of California
Go to the list of seismic processes.      Go to SIOSEIS introduction.