NAME

     stack3d  - stack 3d data having variable  length  (trcs/rec)
     records

SYNOPSIS

     stack3d [ -Nntap ] [ -Ootap ] [ -d2negd2neg ] [  -d1negd1neg
     ] [ -d2posd2pos ] [ -d1posd1pos ] [ -pwpower ] [ -H ] [ -B ]
     [ -D ] [ -sem ] [ -swt ] [ -BC ] [ -S ] [ -L ] [ -V ] [ -? ]

DESCRIPTION

     stack3d will sum all selected traces within a 3d gather  and
     output single summed trace for that gather regardless of the
     number of traces per record (i.e. the number of traces in  a
     given  DI/LI  gather.  This type of output results from run-
     ning the quick disk sort sisort3d.

     stack3d will continue through all records of a 3d  data  set
     and  will  produce  an output file containing the composited
     gathers.  The output data set will consist of N  traces  per
     record  and  M  records, where N and M are the dimensions of
     the X-Y survey grid (i.e. the number of bins in the X and  Y
     directions  given  by  the 3d prep program pr3d).  Whether N
     refers to the X or Y directions (i.e. LI sort or DI sort) is
     entirely  dependent  on  the upstream presort3d and sisort3d
     operations).   Options are available to output  the  stacked
     data  in user specified traces per record groups and to nor-
     malize the data according to number of optionc.

  Command line arguments
     -N ntap
          Enter the full path name of  the  file  containing  the
          data set.  If not specified, input is expected to be on
          standard input. The program will give an error  message
          if  the input file is read protected.  If no input file
          is given, and there is no standard input,  the  program
          will hang.  (default is standard input )

     -O otap
          Enter the full path name for the output  file.  If  not
          specified,  standered output is expected to be on stan-
          dard output. The program will give an error message  if
          the  output  file  is  being written to a write protect
          directory.  (default is standard output )

     -d2neg d2neg
          Far trace distance to use:  negative  side  of  spread.
          (default  = largest negative distance ).  Note: must be
          a negative number.

     -d1neg d1neg
          Near trace distance to use: negative  side  of  spread.
          (default = smallest negative distance ).  Note: must be
          a negative number.

     -d1pos d1pos
          Near trace distance to use: positive  side  of  spread.
          (default = smallest positive distance )

     -d2pos d2pos
          Far trace distance to use:  positive  side  of  spread.
          (default = largest positive distance )

     -pw power
          Enter nth root stacking power.   The  samples  of  each
          trace  in  the  gather  are first raised to the 1/power
          power before summing.  After  all  the  traces  in  the
          gather have been summed the result is the raised to the
          power power.  (default = 1)

     -H   If present,  calculate  stack  using  Hamming  weights,
          w(x)=0.54+0.46*cos(y),     where    where    y=2*pi*(x-
          xcenter)/(xspread).

     -B   If present, calculate  stack  using  Blackman  weights,
          w(x)=0.42+0.5*cos(y)+0.08*cos(2y),   where   y=2*pi*(x-
          xcenter)/(xspread).

     -D   If present, calculate stack using distances as weights.

     -swt If present, output semblance weighted stack

     -sem If present output semblance values across gathers (sem-
          blance stack?)

     -BC  If present data  are  assumed  to  be  3D  CDP  gathers
          without  proper  CDPBCX & CDPBCY header values but with
          the source & receiver XYs all filled in.   The  program
          then computes an average CDP XY from these values.

     -S   If present generate weights to reflect  the  number  of
          live traces in the gather (constant for all times).

     -L   If present generate weights to reflect  the  number  of
          live samples at each time.

     -V   Verbose mode.  All parameters from the command line and
          lineheader will be sent to standard error output.

     -?   Query mode.   With  this  flag,  stack3d  will  send  a
          description  of the command line arguments to the stan-
          dard error output and stop.

BUGS

     No trap for  running  program  without  an  input  file  and
     nothing in the standard input.

NOTE 1:

     The power of the stack array can be  significantly  enhanced
     for  coherent  noise  rejection by using various weights and
     tapers on the gathers. An excellent summary of the technique
     can be found in the book by Gijs Vermeer,  Seismic Wavefield
     Sampling , SEG press, 1990. Specifically, long period multi-
     ple  rejection can be improved by tapering (using the -H, -B
     options) and by weighting the data by  the  source  receiver
     distance  (the  -D option). At present, application of these
     weights may cause some attenuation of the total power in the
     mute zone.

AUTHORS

      Original version by K. B. Taylor and R. B. Herrmann,  Saint
     Louis  University.  (1986),  P. R. Gutowski, Amoco Research.
     Major rewrite and weighting options by K.  J.  Marfurt,  APR
     (1992).

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.