NAME

     velcoh  - examines seismic records for the dips  having  the
     highest coherency

SYNOPSIS

     velcoh [ -Nntap ] [ -OSotaps ] [ -OCotapc  ]  [  -vvel  ]  [
     -dsdmin  ] [ -dedmax ] [ -dnnsearch ] [ -dxdx ] [ -wtnrows ]
     [ -wxncols ] [ -rsnrst ] [ -renred ] [ -V ] [ -? ]

DESCRIPTION

     velcoh point by  point  in  both  time  and  space  examines
     seismic  records  for  the  dip having the highest coherency
     within a moving rectangular window.  A range of dips defines
     a  range  of  slopes  within the moving window.  The program
     starts at the smallest (or most negative) slope and computes
     the  coherency  for  linear  events for all positions of the
     moving window.  The slope is stepped up the the  process  is
     repeated  but  the  new  coherency  is checked to see if has
     increased over the old value at each window position.  If it
     has  the  old  coherency  is replaced by the new value.  The
     search process is repeated for all slopes.  Since  the  pro-
     cess  looks  for linear events within the window the size of
     the window should be small  compared  to  the  input  record
     itself to avoid significant event curvature.

     The final result is two records: the first is  a  record  of
     dips  at  every  sample and trace; the second is the maximum
     coherency of those dips.

     velcoh gets both its data and its  parameters  from  command
     line  arguments.  These arguments specify the input, output,
     the analysis window, the start and end dips and  the  number
     of  dips, the velocity of the shot/receiver medium, and ver-
     bose printout, if desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N unless the input is from a pipe in which case
          the -N entry must be omitted.  This input  file  should
          include the complete path name if the file resides in a
          different directory.  Example -N/b/vsp/dummy tells  the
          program to look for file 'dummy' in directory '/b/vsp'.

     -OS otaps
          Enter the dips output data set name or file immediately
          after  typing  -OS.   This  output file is not required
          when piping the output to another process.  The  output
          data set also requires the full path name (see above).

     -OC otapc
          Enter the  coherency  output  data  set  name  or  file
          immediately  after  typing  -OC.  This output cannot be
          piped except inside IKP where it is sent to the 3  out-
          put connector.

     -v vel
          Enter the shot/receiver velocity in m or  ft/s.   There
          is  no  default and failure to include this on the com-
          mand line will cause the program to stop.

     -dx dx
          Enter the trace spacing (ft,m).  No default.

     -ds dmin
          Enter the starting dip value (degrees).   This  can  be
          negative.  Default = -90.

     -de dmax
          Enter the ending dip value (degrees).  Default = +90.

     -dn nsearch
          Enter the  number  of  steps  between  dmin  and  dmax.
          default  =  21.   This number along with the dip angles
          and velocity establishes a range of slownesses of  con-
          stant  increment  from smallest to largest.  Each slow-
          ness along with the sample interval and  trace  spacing
          gives  a  slope  within the scanning window along which
          the coherency is calculated.

     -wt nrows
          Enter the time  scanning  window  dimension  (samples).
          Default = 10

     -wx ncols
          Enter the spatial scanning window  dimension  (traces).
          Default = 10

     -rs nrst
          Enter start record number.  Default value is the  first
          record.

     -re nred
          Enter end record number.  Default value is last record.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -?   Enter the command line  argument  '-?'  to  get  online
          help.   The program terminates after the help screen is
          printed.

BUGS

     Unknown

AUTHOR

     Original code by Lynn Kirlin, University  of  Victoria,  BC;
     mods by Paul Gutowski

COPYRIGHT

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