NAME

     iangle -  Calculate Incident angles from AVOMIG Output

SYNOPSIS

     iangle [ -N1ntap1 ] [ -N2ntap2 ] [ -Ootap ]  [  -rsirs  ]  [
     -reire ] [ -ampminampmin ] [ -V ] [ -? ]

DESCRIPTION

     iangle extracts incident angles from avomig results and out-
     puts them in an usp dataset format. These angles can them be
     processed and analyized for AVO (RDA) effects.

     avomig outputs two sets of migrated offsets, relative ampli-
     tude  preserved  offsets  and  relative  amplitude preserved
     offsets multiplied by the  incident  angle  (raised  to  the
     fourth  power,  for display convience).  Incident angles are
     estimated in avomig through a stationary  phase  calculation
     which finds a specular point of tangency between ray derived
     travel times and the input common offset seismic data.

     iangle divides the two sets of migrated offsets,  tests  for
     a  meaningful  angle  calculation, and outputs these results
     (in degrees) as a USP format file.  A value of 90 degrees is
     used  as  a  flag  for  no significant data being found or a
     meaningless angle was calculated.

     iangle gets data and parameters from command line arguments.
     These arguments specify the input and output trace data.

  Command line arguments
     -N1ntap2
          Enter the {relative amplitude migrated} data  set  name
          or  file immediately after typing -N.  This 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 subdirectory  'vsp'
          stored in directory b.

     -N2ntap2
          Enter the {relative amp migrated * cos( angle)  **  4)}
          input  data  set  name or file immediately after typing
          -N.  This 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 subdirectory 'vsp' stored in directory b.

     -Ootap
          Enter output data set name or  file  immediately  after
          typing  -O.  This output file is not required when pip-
          ing the output to another process.  The output data set
          also requires the full path name (see above).

     -rs irs
          first record to process.         (default = 1)

     -re ire
          last record to process.          (default = all)

     -ns ns
          first trace in record to process. (default = 1)

     -ne ne
          last trace in record to process.  (default = all)

     -ampmin ampmin
          minimum absolute amplitude to  extract  angle  informa-
          tion.  (default = 1E-20) statistics (default = 0)

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

     -?   Enter this (or '-?' if you are running in  c-shell)  to
          get  online  help.   The  program  will terminate after
          printing a list of parameters.

BUGS

     - unknown

SEE ALSO

     iangle avomig smedian off2ang

AUTHOR

     W. P. May, 1995

COPYRIGHT

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