NAME

     fftar -  High-resolution F-K spectral  analysis  of  seismic
     gathers

SYNOPSIS

     fftar [ -Nntap ] [ -Ootap ] [ -ipcr ] [ -V ] [ -h ] [ -? ]

DESCRIPTION

     fftar Performs high-resolution spectral analysis for seismic
     gathers.  It  first does an FFT along the time dimension, it
     takes the FFT-time  output  and  performs  a  complex  high-
     resolution  spectral  analysis  using an autoregressive (AR)
     model.
     fftar gets both its data and  its  parameters  from  command
     line  arguments.  These arguments specify the input, output,
     the order of autoregressive modelling and verbose  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'.

     -O otap
          Enter the output data  set  name  or  file  immediately
          after typing -O.  The output data set also requires the
          full path name (see above).

     -ip ip
          Enter the order of the autoregressive  (AR)  modelling.
          The default is equal to half the number of traces minus
          1.

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

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

DISCUSSION

     This  program  performs  a  high-resolution   2-D   spectral
     analysis of seismic gathers. Most of the resolution power of
     this program is apparent when using small number of traces ,
     for  instance less than 30. The program starts with perform-
     ing an  FFT  in  the  time  dimension,  then  applies  high-
     resolution  autoregressive  spectral  analysis  (AR) to this
     output. The spectral output has  a  similar  data  structure
     like  the  F-K  spectral  analysis  output. The order of the
     autoregressive (AR) analysis has to be less  than  half  the
     number of traces. Since the true order of the AR analysis is
     unknown, it is best to start with low ip order, for instance
     6  or 8 and slowly test increasing it, until optimal resolu-
     tion is obtained. Unfortunately there is no explicit way  to
     set the order ip appriori.

BUGS

     None known up to this point

AUTHOR

     Anthony Vassiliou (socon 422-3749)

COPYRIGHT

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