NAME

     qdchop  - module to apply quadrant chop dip filter

SYNOPSIS

     qdchop [ -Nntap ] [ -Ootap ] [ -llf ] [ -wwc ] [ -sist  ]  [
     -eiend ] [ -nsnss ] [ -nense ] [ -rsirs ] [ -reire ] [ -Wbwb
     ] [ -U ] [ -V ] [ -? ]

DESCRIPTION

     qdchop apples a filter to eliminate all positive  (or  nega-
     tive) dips in the space/time domain.  This is a very econom-
     ical method of chopping dip quadrants since  the  filter  is
     implemented  by  two  passes  of  a  one dimensional hilbert
     transform filter:  once spatially, and once temporally.

     By choosing the start and end traces to process the user can
     deal effectively with both sides of a split spread.  Indivi-
     dual qdchops each dealing with one side of the spread can be
     piped together.  If the spread center moves within the gath-
     ers down the line  then  even  more  qdchops  can  be  piped
     together, each one having different trace process ranges and
     also different record process ranges.

     qdchop is useful for applications  not  requiring  precision
     dip removal (for this use dipf or taupf + taupr.  qdchop has
     good rejection and this can be improved still more  by  cas-
     cading it in a pipeline.

     qdchop gets its  parameters  from  command  line  arguments.
     These arguments specify the input, output, the start and end
     traces, the processing parameters, and verbose printout,  if
     desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing  -N.   If  piping into this program do not enter
          this command line argument.   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.  If piping out of this program do not
          enter this command line argument.  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).

     -l lf
          Enter the length of the  spatial  part  of  the  2-pass
          hilbert  operation.   This entry must be odd.  The tem-
          poral filter length is set  internally  to  twice  this
          entry plus 1.  Default = 63

     -w wc
          Enter the Ross weight to  be  applied  to  the  hilbert
          filters.   The  smaller  the value the more boxcar-like
          the weights become.  This entry will be  used  for  the
          spatial  hilbert  filter (which is usually shorter than
          the temporal one).  The weight for the temporal  filter
          is  set  internally to be twice this value.  Zero means
          no Ross weight.  Default = 2.

     -s ist
          Enter the start time for the processing.   Output  data
          traces will start at this time.  Default = 0 ms

     -e iend
          Enter the end time for  the  processing.   Output  data
          traces  will  end at this time.  Default = end of input
          trace

     -ns ns
          Enter start process trace number. Traces in each record
          before  this value will be passed unprocessed.  Default
          value is the first record.

     -ne ne
          Enter end process trace number. Traces in  each  record
          after  this  value will be passed unprocessed.  Default
          value is last record.

     -rs irs
          Enter start process record number. Records before  this
          value will be passed unprocessed.  Default value is the
          first record. Remember here record numbers are  sequen-
          tial

     -re ire
          Enter end process record  number.  Records  after  this
          value  will  be  passed  unprocessed.  Default value is
          last record.

     -Wb wb
          The filter will begin at wb*Tw where Tw is the the  two
          way  travel  time  to the water bottom. For example, if
          wb=1.9 the shallow part of the section will  be  passed
          and  simple  water bottom multiples will be attenuated.
          The water bottom depths are pulled  from  trace  header
          location  WDepDP.  The  water bottom velocity is pulled
          from line header location WatVel.  A value of  wb  >  0
          overrides the -s option above. (Default wb=0.)

     -U   Enter the command line argument  '-U'  to  chop  events
          dipping  upward  away  from  the  leftmost trace (first
          trace on record).   Otherwise  the  program  will  chop
          events  dipping  downward  to the right (from the first
          trace on the record).

     -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.

SEE ALSO

      dipf, fkstrip, taupf, taupr, rmmult

AUTHOR

     P. R. Gutowski, APR, (1989). Water  bottom  tracking  option
     added by K.J. Marfurt, APR,(1992).

COPYRIGHT

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