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                                PROCESS DMO

Document Date:  1 November 1991

Process DMO, Dip Move Out, applies a phase filter in Omega-K domain to 
correct for move-out when dip is present.  Typically, NMO is used to 
produce a zero-offset section which is then migrated to produce a final 
image.  However, if dips exist, then the mapping of seismic data using 
the NMO equation is dip dependent, and causes subsurface smear updip 
away from the midpoint.  To mitigate this problem, dip moveout algorithms 
have been developed to allow all dips to stacked simultaneously without 
up-dip smear.  The algorithm used in process DMO is the EXACT LOG DIP 
MOVEOUT formulation by LINER and assumes constant velocity.

The traces input to DMO must be sorted by offset distance (range), which 
may be accomplished with process SORT with the SORT parameters lkey1 10 
FLAG51 -1, the "end-of-sort" flag.

This DMO algorithm has "stretch" problems which may be a alleviated in 
the time domain using process LOGST1 in the time domain before process 
tx2fk and "unstretching" it in the time domain after DMO and FK2TX LOGST2.

PROCESS DMO requires the data to be transformed into the FK (frequency-
wavenumber) domain using process TX2FK.  The data may be converted back to 
the time domain after DMO using FK2TX.

A typical DMO processing sequence is:
      procs sort diskin nmo logst1 tx2fk dmo fk2tx logst2 diskoa end

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DELTAX - The distance between traces, also called the group spacing.  

WINDOW - The type of window to apply before computing the FFTs.
       = HANN, Hanning window.
       = RECT, Rectangular or box car window (no window).
         Preset = RECT

OFFSET - The source-receiver offset (range) which if invoked will override 
         header value.  This is only useful when only one offset is input 
         to DMO and the header value must be overridden.
         Preset - none

Copyright (C) 1991 The Regents of the University of California
ALL RIGHTS RESERVED. Written by Graham Kent, September 1991
Go to the list of seismic processes.      Go to SIOSEIS introduction.