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The prestack Gaussian beam scheme is implemented
as common-shot profile migration, the implementation of which is
similar to that of finite difference depth migration.
All the frequency components of all surface recorded seismograms are
downward continued as in the poststack case. The final migrated reflectivity
image is obtained after application of the imaging condition to the downward
continued wavefields , as in conventional migration
(Claerbout, 1976, 1985; Reshef and Kosloff, 1986).
When each surface seismogram
is taken as a source and migrated separately, the reflectivity image is the
wavefield of Equation (17) evaluated at *t*=*t*_{d} at each depth point,
where *t*=*t*_{d}
is the arrival time of the direct wave from the source to the depth points
(*x*,*z*). The reflectivity image is formed by superposition of
the contributions of all surface seismograms.

** Next:** Surface and crosswell seismic
** Up:** Mo: Gaussian beam
** Previous:** A smooth v(x,z) background
Stanford Exploration Project

11/17/1997