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The program that
I used to migrate the data implements the common-azimuth
downward continuation operator presented in previous reports
by Biondi and Palacharla
.
The continuation operator is derived
in the frequency-wavenumber domain,
but, because it is applied to depth migration,
it is implemented using a mixed space-wavenumber
domain migration scheme.
In particular, I implemented the method using a straightforward
generalization of phase-shift plus interpolation (PSPI) Gazdag and Sguazzero (1984)
to common-azimuth migration
because of its simplicity and computational efficiency;
other choices, such as split step Stoffa et al. (1990)
would have probably been just as effective.
The design a frequency-space (Fx)
representation of the common-azimuth downward continuation operator
would be a worthwhile effort,
after common-azimuth migration has been proven effective
and accurate to image a wide-class of 3-D data sets.
The results of multi-line 2-D migrations were computed by a simple
modification of the common-azimuth migration program;
the well known 2-D double square root operator
Claerbout (1985) was substituted
for the common-azimuth operator.
The multi-line 2-D migration program is slightly faster than the
full 3-D program.
Because it propagates energy only along the in-line direction,
it does not require repeated forward and inverse FFTs along the cross-line
midpoint axis to take into account
the velocity variations along the cross-line direction.

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Stanford Exploration Project

11/11/1997