|
ARTICLES
Anti-aliased
Kirchhoff 3-D migration
By D. E. Lumley, J. F.
Claerbout, and D. Bevc
A significant degradation
in the quality of Kirchhoff migration images can arise when
the migration operator summation trajectory is too steep for
a given input seismic trace spacing and frequency content.
This phenomenon is called ``operator aliasing'' and is strictly
distinct from and independent of data aliasing. Unfortunately,
the conditions which lead to significant operator aliasing
are common in most 3-D Kirchhoff migration work, due to the
sparse and irregular nature of 3-D acquisition geometries,
and the need to minimize the size of 3-D migration input data
volumes.
We anti-alias the migration
operators ``on the fly'' with N-point triangle filters. Using
a Z-transform representation, we reduce each N-point triangle
filter operation to an efficient three-point filter operation,
with the added minor overhead of a causal and anticausal integration
of the input trace data prior to migration. Our anti-aliased
migration is computationally efficient since it requires about
the same number of floating point operations as a conventional
Kirchhoff migration, and is conservative in its memory use
since it does not require storage of multiple trace-data copies
to implement the anti-aliasing. Our anti-aliased migration
is accurate in that it applies local anti-alias filters separately
for each of the many migration operators which pass through
a given input data point.
We demonstrate our method
with a 3-D implementation on a massively parallel Connection
Machine CM-5, and compare our new anti-aliased Kirchhoff migration
to a conventional aperture-weighted Kirchhoff migration in
an application to a 3-D marine seismic data example. Our results
indicate that our anti-aliasing method greatly enhances the
3-D resolution of steep salt-sediment interfaces and faults,
and suppresses false reflections caused by conventional Kirchhoff-migration
aliasing artifacts. Our method is applicable to other space-time
Kirchhoff operations such as NMO velocity-stacking and DMO.
64th Ann. Internat. Mtg.,
Soc., Expl. Geophys., Expanded Abstracts, 1282-1285, (1994).
56th Ann. Internat. Mtg.,
European Assoc. Expl. Geophys., (1994)
|
