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I illustrate the migration of multiples with one shot. In Figure
I display the source function on the left panel,
and the recorded wavefield on the right panel. The
recorded wavefield is the superposition of primaries and multiples.
The migration result for this shot location is shown in Figure
a.
Figure displays the source function and the
up-going wavefield for the migration of multiples. As proposed in the
preceding section, the source function is not impulsive but areal.
The recorded wavefield contains the surface-related multiples only.
The migration result is shown in Figure b and
compares favorably with the output of the migration of primaries.
It is interesting to note that the water-bottom is illuminated with
a wider aperture when multiples are used. As illustrated in Figure
, for a given receiver Rn, the primary illuminates
the reflector in ra at a closer location to the source in S
than does the multiple in rb. Therefore, for one given shot, the
multiples migrate with a wider aperture but with smaller angles.
As a final result, I display in Figures c and
d
the different illumination patterns for both the impulsive and areal
sources ().
These maps are obtained by simply computing the amplitude
(squared) of the down-going wavefield at each depth and for each
frequency. These Figures illustrate the aperture and illumination
effects of the multiples.
shotprim14
Figure 4 Shot-profile
migration of the primaries. Left: Impulsive source function. Look
closely at offset 0. meter and time 0. second to see
the impulse. Right: Recorded primaries and multiples.
shotmig14
Figure 5 Shot-profile
migration of the multiples. Left: Areal source function. Right:
Recorded multiples only. The source function is plotted upside-down
to represent the computation involved by the time-reversed process.
compil14
Figure 6 Migration results and
illumination maps of the down-going wavefields for the imaging of
multiples and primaries. (a) Migration of the primaries. (b) Migration
of the multiples. (c) An illumination map for the impulsive source.
(d) An illumination map for the areal source.
Next: Migration of the survey
Up: A synthetic data example
Previous: The Amoco dataset
Stanford Exploration Project
6/7/2002