NAME

     qnmo  - apply/remove moveout correction  using  the  quartic
     moveout equation

SYNOPSIS

     qnmo [ -Nntap ] [ -Ootap ] [ -vvtap ] [ -rsirs ] [ -reire  ]
     [ -nsns ] [ -nene ] [ -svvrs ] [ -evvre ] [ -S ] [ -R ] [ -T
     ] [ -E ] [ -B ] [ -V ] [ -XY trace ] [ -? ]

DESCRIPTION

     qnmo performs moveout correction by  means  of  the  quartic
     moveout  equation.  It  should be used when the conventional
     hyperbolic moveout equation becomes inaccurate due  to  high
     offset-to-depth   ratios,  structural  complexities,  and/or
     anisotropy. The quartic moveout is described by two  moveout
     parameters  (V2  and V4) in addition to the vertical arrival
     time t(0):

     t(r(i))     =     sqrt[t(0)**2     +     (r(i)/V2)**2      -
     (r(i)/V4)**4/t(0)**2],

     r(i) is the distance from the source for the i-th trace.

     The values of V2 and V4 should be calculated by routine vel-
     quar2  as  functions  of the vertical time t(0). Output file
     otap generated by velquar2 is used as  input  velocity  file
     vtap  in  this  code.  File  vtap  has the form of two-trace
     records: the first is V2 vs time t(0); the second is  V4  vs
     time.

     qnmo is based on routine tvdnmo and retains  many  functions
     of this code. For instance, moveout is applied/removed using
     quadratic interpolation; the user may choose to output  data
     from  before  or  after  the  last  sample cross-over in the
     moveout map (the default is to output data  from  after  the
     last cross-over point only) etc.

     The arguments are to be taken from the command line; reason-
     able  default  values  are  set up. If no input file name is
     given, the data are expected to be on  the  standard  input.
     File vtap must be specified.

  Command  line arguments
     -N ntap
          The full path of the file containing the data  set.  If
          ntap  is  not specified, input is expected on the stan-
          dard input.

     -O otap
          The full path of the output  file  which  contains  the
          moveout-corrected gathers. Default: standard output.

     -v vtap
          The full path of the file containing the moveout param-
          eters.  The  file  should  be generated by routine vel-
          quar2. vtap has SIS format and contains two traces  per
          each  record:  V2  vs  time  and V4 vs time. The sample
          interval and number of samples should be  the  same  as
          for the trace data. There is no default.

     -rs irs
          First record for processing (default = 1)

     -re ire
          Last record for processing (default = last)

     -ns ns
          First trace for processing (default = 1)

     -ne ne
          Last trace for processing (default = last)

     -sv vrs
          First velocity record to process (default = 1)

     -ev vre
          Last velocity record to process (default = last)

     -E   If present, data associated with  the  portion  of  the
          moveout map below the last sample cross-over point will
          be output.

     -T   If present, data associated with  the  portion  of  the
          moveout map above the last sample cross-over point will
          be output (problems may be  encountered  if  there  are
          more than one sample cross-over present).

     -S   If present, apply internal trace header statics (before
          nmo).

     -R   If present, remove normal moveout.

     -B   If present, input  velocity  function  is  expected  in
          decreasing shot order.

     -XY trace
          If present, the normal moveout sample map for the trace
          requested  will be output to a file name qnmo_fcn. This
          file may be accessed by xgraph for a plot of the  func-
          tion.

     -V   Flag for verbose output. The trace  header  information
          and the values used for processing are listed.

     -?   Enter argument '-?' to get online help.

BUGS

     Unknown

SEE ALSO

     velquar2, tvdnmo.

REFERENCES

     Taner, M.T., and Koehler, F., 1969, Velocity spectra - digi-
     tal  computer  derivation and applications of velocity func-
     tions:  Geophysics, 34, 859-881.

     Tsvankin, I., 1991, Nonhyperbolic moveout  revisited:  Amoco
     Production Company Research Department Report T91-E-17.

AUTHOR

     I.  Tsvankin  (USP  version  P.  G.  A.  Garossino),   Amoco
     Research, Tulsa, October 1992.

COPYRIGHT

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