NAME

     vspstk  - do VSP nmo correction and binned stack

SYNOPSIS

     vspstk [ -Nntap ] [ -Ootap ] [ -vvfil  ]  [  -Hwhdrwrd  ]  [
     -tststep  ]  [  -ffrac ] [ -sxsrcx ] [ -sysrcy ] [ -dxdx ] [
     -xminxmin ] [ -xmaxxmax ] [ -rms ] [ -int ] [ -ave ] [  -owt
     ] [ -T ] [ -V ] [ -? ]

DESCRIPTION

     vspstk does a  offset/depth  dependent  NMO  correction  and
     binned stack for offset VSP data. One or more offsets can be
     processed in one data set as long as the offsets fall  along
     a  line (i.e. no areal shooting or crooked line shooting). A
     pass is made through the data to determine  all  the  source
     X,Ys   and   a   line   is   fit  through  these  points.  A
     rotation/translation transformation is done on  the  coordi-
     nates  so  that  the  programs  coordinate  system X-axis is
     aligned along the line of shooting. Small Y deviations along
     this line can be tolerated.

     The following header words must be  in  each  trace  header:
     sonde  depth in GrpElv, source point X in SrPtXC, and source
     point Y in SrPtYC. If these words are not in place you  can-
     not  run  this  code  (unless you fake in some values on the
     command line).

     The NMO correction is done using a very simple  ray  tracing
     operation assuming flat layers defined by the input velocity
     function. This defines a travel time map and an offset  map.
     The  travel  time  map is used to do the NMO correction; the
     offset map is used to properly bin-stack the corrected data.

     Note: because of the type of ray tracing this  code  becomes
     more  and  more  expensive  to run the greater the number of
     entries in the velocity file. Velocity functions should  not
     exceed 10 to 20 entries.

     vspstk gets both its data and its  parameters  from  command
     line  arguments.  These arguments specify the input, output,
     name of the velocity function file, and operational  parame-
     ters.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing  -N. No piping in is allowed since two passes on
          the data are made.

     -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).

     -v vfil
          Enter the name of  the  file  containing  the  velocity
          function  to  use.  This file must either (1) contain 2
          columns: time & velocity (as many as you wish) or,  (2)
          be  in TDFN card column format. Interval, RMS, or aver-
          age velocity may be input.

     -Hw hdrwrd
          Enter the trace header mnemonic where the  sonde  depth
          is  stored.  This  must  be  a  positive  depth (ft,m).
          Default = GrpElv

     -ts tstep
          Enter the time step with which to  resample  the  input
          velocity  function.  Most  velocity functions have less
          that 10 entries. If this is not resampled  to  a  finer
          interval  in  time  the final output will have a stair-
          step appearance due to the thick layes used in the  ray
          tracing.  Resampling  up  to 20 - 30 layers makes for a
          much smoother mute  line  on  the  output.  Default  is
          250ms. Entering any negative value turns the resampling
          off.

     -f frac
          Enter the tolerance for the ray tracing (ft,m). The ray
          tracing  is  an  iterative  one  and needs to know when
          close is clos  enough  -  this  defines  "close".  This
          should be significantly less than the bin size. Default
          = 5.

     -sx srcx
          Enter the X-origin of the well (ft,m). Default = 0

     -sy srcy
          Enter the Y-origin of the well (ft,m). Default = 0

     -dx dx
          Enter the horizontal bin size for the stacking  process
          (ft,m).  No default. This with xmin and xmax below will
          define the  number  of  output  traces,  i.e.  nbins  =
          (xmax-xmin)/dx

     -xmin xmin
          Enter the minimum horizontal stacked offset relative to
          the well (can be negative). Default = 0.

     -xmax xmax
          Enter the maximum horizontal stacked offset relative to
          the well. Default = none

     -rms Enter the command  line  argument  '-rms'  if  velocity
          function  is  rms.  Default is rms (i.e. if none of the
          velocity type flags appear).

     -int Enter the command  line  argument  '-int'  if  velocity
          function is interval.

     -ave Enter the command  line  argument  '-ave'  if  velocity
          function is average.

     -owt Enter the command line argument '-owt' if velocity file
          contains one-way time, else 2-way time is assumed.

     -T   Enter the command line argument '-T' if  velocity  file
          is TDFN format.

     -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

     gets very expensive to run for large  (  >20  )  numbers  of
     time-velocity pairs in the velocity file.

SEE ALSO

     vspvel

AUTHOR

     Paul Gutowski & Mike Mueller

COPYRIGHT

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