NAME

     dafd2d  - whiten 2D amplitude (in Kx-Ky)  spectrum  of  time
     slices from program fftxy

SYNOPSIS

     dafd2d [ -Nntap ] [ -Ootap ] [ -expexp  ]  [  -titaper  ]  [
     -bballast ] [ -? ]

DESCRIPTION

     dafd2d does a simple amplitude whitening of the output  from
     program fftxy in a manner simliar to its trace cousing dafd.
     A taper, the shape of which is altered by a power  exponent,
     is  applied  to  the interior of the amplitude spectrum such
     that the higher wavenumbers  are  increasingly  boosted.  At
     some  point this trend stops and as the wavenumbers continue
     to increase a down-weighting taper  is  applied  around  the
     edges of the spectrum. The phase spectrum is untouched.

     dafd2d gets both its data and its  parameters  from  command
     line  arguments.   These  arguments  specify  the taper, the
     exponent, and the bias at zero wavenumber.

  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.  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).

     -t itaper
          Enter the % of the full radius over which to apply  the
          taper.  The  full  radius  is  defined  for the largest
          ellipse which can be inscribed within the dimensions of
          the  Kx  and Ky axes. Within this % radial distance the
          weight  applied  to  the  amplitude   spectrum   is   [
          (full_radius  - r)/full_radius ] ** exp, where r is any
          determined radius less than the full radius  and  where
          exp  is  the  powering exponent. Outside the taper zone
          the last interior weight is multiplied by  (full_radius
          -  r)/full_radius  which  approaches  zero  at the full
          radius. Outside the full radius the weights are set  to
          zero. Default = 75


     -exp exp
          Enter the powering exponent for the interior  weighting
          function. Default = 1

     -b ballast
          Enter the bias to be added to the weighting function at
          Kx  = Ky = 0. This is to avoid zeroing out the spectral
          origin. Default = 0.0

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

EXAMPLE

      fftxy -Ninput | \
      dafd2d -t50 | \
      fftxy -Ooutput -R
     where the middle portion of the wavenumber  amplitude  spec-
     trum is boosted by the default power of 1.

BUGS

     unknown

AUTHOR

     Paul Gutowski, socon 422-3146, pgutowski@trc.amoco.com

COPYRIGHT

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