NAME

     dft  - module to compute  amplitude  and  phase  spectra  by
     discrete   Fourier   Transform   and   perform  the  inverse
     transform.

SYNOPSIS

     dft [ -Nntap ] [ -Ootap ] [ -nsins ] [ -neine ] [ -rsirs ] [
     -reire  ] [ -siwst ] [ -eiwed ] [ -fminmin freq ] [ -fmaxmax
     freq ] [ -fintfreq interval ] [ -taper% cosine taper ] [  -G
     ] [ -V ] [ -? ]

DESCRIPTION

     dft computes amplitude and phase spectra for the input  data
     as  per  the  input  parameters.   The conventional discrete
     Fourier transform is used  (rather  than  the  Fast  Fourier
     Transform)  so  that  the  frequency sample increment can be
     arbitrarily specified. The output  is  either  amplitude  or
     phase.  Output  data consists of amplitude and phase spectra
     in normal sis format. The user can extract  the  values  and
     plot  with USP program sis_xa and xgraph.  The sample inter-
     val is in the output data line header and  can  be  read  as
     Hertz.

     dft gets both its data and its parameters from command  line
     arguments.   These  arguments specify the input, output, the
     start and end records and traces, start and  end  times  for
     windows,  frequency  end points, frequency increment, window
     tapering, if desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing  -N.   If piping in this command line entry will
          be omitted.  The 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).

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

     -re ire
          Enter the end record number.   Default  value  is  last
          record.

     -ns ns
          Enter start trace number.  Default is  first  trace  of
          record.

     -ne ne
          Enter end trace number.  Default value is last trace of
          record.

     -s iwst
          Enter start  time  of  window  for  harmonic  analysis.
          Default is the start of the trace.

     -e iwed
          Enter end of window for harmonic analysis.  Default  is
          end of trace.

     -taper taper
          Enter percent cosine taper to apply to window. 100%  is
          full cosine taper and 0% is no taper.   Default is 10%.

     -fmin min freq
          Enter  beginning  frequency  for   harmonic   analysis.
          Default is 0 Hz.

     -fmax max freq
          Enter ending frequency for harmonic analysis.   Default
          is Nyquist frequency.

     -fint freq interval
          Enter frequency increment in Hz.  Default is 1 hz.

     -G   Enter the command line argument  '-G'  to apply a Gaus-
          sian taper.  This option overrides the cosine taper and
          needs no percent value input.

     -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.

EXAMPLE 1:

DISCUSSION:

     This code was born  out  of  program  samps.   However  spec
     allows the user to pipe in and out at will.

BUGS

     No bugs known at present.

SEE ALSO

     timfreq, freqtim, samps, fk, specal, ampspec, fft2da, fftxy,
     rwspec, mesa,spec, rwdft

AUTHOR(S):

     James M. Gridley, with much help from a variety of folks and
     in cooperation with Greg Partyka.

COPYRIGHT

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