NAME

     pol2  - 2-component ground roll filtering

SYNOPSIS

     pol2 [ -Nntap ] [ -Ootap ] [ -sist ] [ -eiend ] [ -nsns ]  [
     -nene  ] [ -rsirs ] [ -reire ] [ -flfl ] [ -fhfh ] [ -nfnf ]
     [ -wlw ] [ -Tth ] [ -Sisrc ] [ -thetatheta ] [ -NRnrec  ]  [
     -DRndir ] [ -E ] [ -G ] [ -P ] [ -V ] [ -? ]

DESCRIPTION

     pol2  filters  out  ground  roll  on  2-component  data  and
     enhances the body wave motion along the principle axes.  The
     algorithm is based on a method originally due to  Archambeau
     & Flynn.  The 2-component data is frequency combed by multi-
     ple gaussian filters  resulting  in  a  ensemble  of  narrow
     passband  2-component trace pairs.  This is because the next
     step is based on the assumption  of  monochromicity  of  the
     signal.   An eigen-decomposition is then done on the sample-
     by-sample component correlation of the filtered traces  giv-
     ing an eigenvalue and the eigenvectors for each frequency as
     a function of time.  These are then used to compute  filters
     to

     a) attenuate the ground roll, and

     b) find the motion along the principle axes

     The hope is that once the ground roll has been filtered  out
     the  resulting  motion  is due to body waves only.  The last
     step is the sum the filtered/enhanced  narrow  passbands  to
     reconstitute the original bandwidth.

     pol2 gets processing controls from the command line. Reason-
     able  defaults  are  set  up.   Input data is in the form of
     standard seismic records (whatever gather) of  trace  pairs,
     where  the  first trace of each pair is the vertical and the
     second is the horizontal.  The line header is checked to see
     that header entry RATTrc has the value 2; if not the program
     exits.



  Command line arguments
     -N ntap
          Enter the full path of the  file  containing  the  data
          set.  In none is given input defaults to a pipe.  Note:
          input data consists of 3-component  data  multiplxe  d,
          i.e.,  vertical,  radial, transverse, vertical, radial,
          traansverse, etc, for t he entire  gather.   This  data
          may be generated from separate data sets using  fBmergn
          with a -m flag.

     -O otap
          Enter the output file name for the filtered traces.  In
          none  is  given  output  defaults to a pipe.  Note: the
          output data is in the same order as  the  input  (se  e
          ntap above)

     -s ist
          (integer) Start time of process in ms  (default = 0 ms)

     -e iend
          (integer) End time of process in ms  (default = end  of
          trace)

     -ns ns
          First trace in record to process (default = 1)

     -ne ne
          Last trace in record to process (default = all)

     -rs irs
          (integer) First record to process (default = 1)

     -re ire
          (integer) Last record to process (default = all)

     -fl, -fhfl,fh
          Minimum low cut and maximum high cut frequencies in  Hz
          for  gaussian narrow bandpass filters.  Default = 1.0Hz
          and 1/2 Nyquist, respectively.

     -nfnf
          Maximum number of frequency bands.   The  actual  value
          will be calculated internally and reported in the prin-
          tout file.  This is based on  the  contruction  of  the
          gaussian filters (e.g. their width, etc).  Default = 50

     -w lw
          Length of agc window in ms  (default =  500  ms).   The
          following conditions determine how the window is built

          lw = 0, center frequency of each gaussian filter deter-
     mines window length
          lw < 0, window is haved with each  successively  higher
     gaussian
          ls > 0, window length is constant

     -theta theta
          Polar  scan  angle  (deg)  with  respect  to  vertical.
          Default = 0 deg.

     -NR nrect
          Exponent to power rectilinearity filter.  Default = 2

     -DR ndir
          Exponent to power directionality filter.  Default = 2

     -S isrc
          Source type determines on which component agc  computa-
          tion is done:

          1 = V
          2 = R
          0 = V+R (resultant)

     -T thresh
          Threshold of rectilinearity filter.  Default = .95

     -P   If present, do complete polarization  filtering  opera-
          tion (rect + rotation)

     -E   If present, enhance motion  along  original  coordinate
          axes.

     -G   If present, do rectilinearity filtering only

     -V   If present give verbose printout

     -?   Query mode.  With this flag, pol2 will give a  descrip-
          tion  of  the  command line arguments and stop the pro-
          gram.

DISCUSSION

     The program makes use of the gaussian  filter  comb  wherein
     adjacent  teeth  of  the conb are positioned such that their
     overall sum leads to a flat spectrum.

BUGS

     Be careful of the octave option  (negative  number  of  fre-
     quency  bands)  that  the upper band does not exceed nyquist
     (500/sample interval)

AUTHORS

     P. R. Gutowski, Amoco Production Research Center, 1986

COPYRIGHT

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