NAME

     tstretch - map or stretch data lying on a fixed but  irregu-
     lar depth grid to a equally sampled time grid.

SYNOPSIS

     tstretch [ -Nfile_irreg ] [ -Ofile_reg ] [  -Tfile_twt  ]  [
     -dtdteql ] [ -tmintmin ] [ -tmaxtmax ] [ -V ] [ -? ]

DESCRIPTION

     tstretch was designed to efficiently resample the output  of
     the  2D  Kirchhoff migration algorithm sammig to a regularly
     (i.e. equally) sampled grid in time using a 6 point interpo-
     lation  algorithm.  This  routine, when included in the flow
     'prepmig;vsm|vsamp|kray;sammig|tstretch' will  result  in  a
     prestack  (depth)  migration  mapped  in  time to a floating
     datum.

     tstretch gets both its data and its parameters from  command
     line arguments.  These arguments specify the input, outputs,
     and certain floating point values to  override  the  current
     restrictions to trace header integer values.

  Command line arguments
     -N file_irreg
          Enter the input irregularly sampled depth data set file
          name  (output  from  routine  sammig) immediately after
          typing -N unless data are coming  in  from  a  pipe  in
          which  case  the  -N option should not be entered. Data
          may be either common rflection point or  common  offset
          gathers  with  the  crp  number  stored in trace header
          DphInd`fR.  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 file_reg
          Enter the output regularly (equally) sampled time  data
          set file name after the -O option or, if data are going
          to a pipe, the -O option should not be entered.

     -T file_twt
          Enter the input two way traveltime map file  name  gen-
          erated  by  routine  kray  immediately after typing -T.
          kray stores the common reflection point index in  trace
          header  DphInd.  tstretch  will  use the two way travel
          trace whose crp point is closest to that of the irregu-
          larly  sampled depth trace in its depth to time conver-
          sion. This input data set requires the full  path  name
          (see above).

     -dt dt
          Enter the constant time sample increment at  which  the
          input   irregular  depth  data  are  to  be  resampled.
          (Default: The original seismic sample increment,  which
          has  been  stored in line header word OrTRCN by program
          sammig).

     -tmin tmin
          Enter the minimum time in msec  for  the  ouput  trace.
          Negative  times  may be useful when a floating datum is
          used below topography. This value  will  be  stored  in
          line header word TmFsMs. (Default: tmin=0.)

     -tmax tmax
          Enter the maximum time in msec  for  the  ouput  trace.
          (The  original seismic trace length tmax_orig is stored
          in line header  word  OrRECN  by  program  sammig.  The
          default is then tmax=tmax_orig-tmin).

     -V   Enter the command line argument '-V' to obtain  verbose
          output.

     -?   Enter the command line  argument  '-?'  to  get  online
          help.   The program terminates after the help screen is
          printed.

BUGS

     No bugs known at present.

Project Agreement.

     This algorithm predated the project agreement process. It is
     currently  supported  by  the 2-D MBS Core Product Line P96-
     2519. Thank you for your support!

SEE ALSO

     vsm, vsamp, kray, tiray, sammig, kmod, zstretch, vttd

AUTHOR

     K. J. Marfurt (APR) (1992, 1994). In honor of her  23  years
     of  service, the Mary Ann Thornton floating datum option was
     added at no cost to the BU  customers  on  the  day  of  her
     retirement (8/28/96).

COPYRIGHT

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