NAME

     swak  -  Statistical Wavelet Amplitude Kalculation.

SYNOPSIS

     swak [ -Nfile_in ] [  -Ofile_out  ]  [  -Wfile_wavelet  ]  [
     -tstarttstart  ]  [  -tendtend  ]  [ -tskiptskip ] [ -start-
     linetstartline ] [ -endlineendline ] [ -skiplineskipline ] [
     -fminfmin  ]  [  -fmaxfmax ] [ -dfdf ] [ -twindowtwindow ] [
     -ptaperptaper ] [ -pcpc ] [ -V ] [ -? ]

DESCRIPTION

     swak This program estimates the amplitude of a time  varying
     wavelet   by  performs  a  spectral  decomposition  on  user
     selected lines of a 3-D seismic data cube. Next,  it  calcu-
     lates the inverse of the wavelet spectrum, or spectral scal-
     ing factor for each time and frequency sample. This  scaling
     factor is used in program tune3d to remove the effect of the
     source wavelet from reflector tuning analysis.

     swak gets both its data and its parameters from command line
     arguments.   These  arguments specify the input, output, the
     spectral analysis window, the percent of  cosine  taper  and
     verbose printout, if desired.

  Command line arguments
     -N file_in
          Enter the input 3-D seismic cube file name  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/export/data2/migrated.data tells the program to look
          for file 'migrated.data' in directory '/export/data2'.

     -O file_out
          Enter the output file immediately after typing -O  that
          will  contain  the time variant spectrum of the seismic
          wavelet. There will be one  output  trace  for  seismic
          frequency  analyzed.  The first seismic record contains
          the wavelet spectrum, the second  seismic  record  con-
          tains  the  scaling  factor,  or inverse of the seismic
          wavelet spectrum with preconditioning using the  factor
          pc.   The  output  data set also requires the full path
          name (see above). If output is to a pipe, the -O option
          must be omitted.

     -W file_wavelet
          Enter the (optional) output wavelet analysis data  file
          name  immediately   after typing -W. These wavelets may
          be subsequently  analyzed  using  conventional  Fourier
          analysis to quantify their spectral content.

     -tstart tstart
          Enter the global start time  of the spectral decomposi-
          tion.  (Default tstart = trace start).

     -tend tend
          B Enter the global end time of the spectral  decomposi-
          tion.  (Default tend = trace end).

     -tskip output sample rate
          Enter  the  desired  output  sample  rate.    (Default:
          tskip=dt, the input sample rate).

     -startline startline
          Enter the starting line to be analyzed. You must  enter
          enough lines such that the spectrum of the reflectivity
          is white.  (Default startline fR = 1).

     -endline endline
          Enter the ending line to be analyzed.  You  must  enter
          enough lines such that the spectrum of the reflectivity
          is white.  (Default endline fR = the last record in the
          input data set).

     -skipline skipline
          Enter the line skip incremen in the analysis. You  must
          enter  enough  lines  such  that  the  spectrum  of the
          reflectivity is white.  (Default skipline fR = 1).

     -twindow twindow
          Enter the full length of the sliding analysis window to
          be  used in spectral decomposition. This window will be
          centered about each input sample. (Default = 96 ms.)

     -fmin fmin
          Enter the minimum  frequency  to  be  analyzed  in  Hz.
          (Default: fIin=1000./window).

     -fmax fmax
          Enter the maximum  frequency  to  be  analyzed  in  Hz.
          (Default: fIax=80Hz).

     -df df
          Enter the frequency increment for  analysis.  (Default:
          df=.5*1000./window,  or  twice  as  fine as the Nyquist
          increment for the analysis window).

     -ptaper ptaper
          Enter the percent cosine taper to  be  applied  to  the
          analysis wavelet.  (Default: ptaper= 20%)

     -pc pc
          Enter the percent prewhitening used  in  inverting  the
          wavelet spectrum. If the maximum amplitude of the spec-
          trum, w(f) at a given time for all frequencies is given
          by wmax, then scale(f)=1./(w(f)+pc*wmax), such that the
          output reflectivity spectrum generated by  tune3d  will
          vary between 0. and 255. (Default: pc=10%).

     -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.

BUGS

     no known bugs.

See Also:

           tune3d, spec, rwspec

REFERENCES

     Partyka, G. A., Gridley, J. M., Mims, C. V.  and  Lopez,  J.
     A., 1995, The tuning cube: Interpretational aspects of spec-
     tral decomposition, Amoco Geos. Tech. Bull. F95-G-46.

CONTRACT AGREEMENT

     This product is brought to you by Research  Agreements  D97-
     2548  (The  Coherency  and Spectral Decomposition Cubes, 2nd
     Quarter Deliverable). Thank you for your support.

AUTHORS:

     Kurt J. Marfurt (6/1997).

COPYRIGHT

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