NAME

     dskft - Apply a Wavenumber Disk Filter to  a  Seismic  Depth
     Section

SYNOPSIS

     dskft [-Nntap] [-Ootap] [-VTvtap] [-Itype]  [-DXdx]  [-DZdz]
     [-F1f1] [-F2f2] [-F3f3] [-F4f4] [-V] [-h] [-?]

DESCRIPTION

     dskft is a program to filter a seismic  depth  section  with
     bandpasses defined as radial disks in the wavenumber (kx,kz)
     domain.  The program computes the parameters of  the  radial
     disks from user supplied frequency (Hz) parameters.

     The primary use of this program is to filter  out  low  fre-
     quency  wavelet  stretch  resulting from far offset prestack
     migration without simultaneously eliminating  low  frequency
     reflection  data  (i.e.,  in the (kx,kz) domain the low fre-
     quency stretch noise will build up along the kx=0  axis  and
     can readily be removed with a circular (radial) filter).

     The program steps in dskft are:
     1)  Read depth section  - USP seismic dataset.
     2)  Read velocity field - USP seismic dataset.
     3)  Read filtering parameters.
     4)  Stretch depth section from variable velocity
         background to a constant velocity background.
         The constant velocity used is determined by
         the program.
     5)  Fourier transform data into the (kx,kz) domain.
     6)  Filter data using a radial pass filter to remove
         low and/or high wave number components from the
         data.
     7)  Inverse Fourier transform data to the (x,z) domain.
     8)  Unstretch depth section back to the original
         velocity background.

  Command line arguments
     -N ntap
          Enter the filename of the input  dataset  after  typing
          -N.  Input dataset should be a seismic depth section.

     -O otap
          Enter the filename of the output dataset  after  typing
          -O.

     -VT vtap
          Enter the filename of the velocity dataset after typing
          -VT.   This  is  a  USP-formatted  dataset where sample
          values are interval velocities.


     -I type
            1 = zero inner ring  (filter out low frequencies)
            2 = zero both inner and outer rings (recommended)
            3 = zero outer ring  (filter out high frequencies)

     -DX dx
          This value is the input trace spacing (ft or meters) of
          the depth section.

     -DZ dz
          This value is the input depth  sample  spacing  (ft  or
          meters) of the depth section.

     -F1  -F2  -F3  -F4 f1  f2  f3  f4
          The four filter  points  (in  Hz)  in  the  trapezoidal
          filter.  No default.

     -V   Enter a -V for a verbose printout.

     -h   Enter -h for online help. Program will terminate  after
          printing this.

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

SEE ALSO

     mbs, startjob, beginjob, endjob, piestkt

BUGS

     None known.

AUTHOR

     Mary Ann Thornton, Ron D. Coleman

COPYRIGHT

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