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 | Prediction error filters to enhance differences |  |
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The bit precision limiting
scheme used in the previous section should either have a relatively
uniform, or somewhat unpredictable, amplitude effect. A more interesting
test is to apply both difference detecting methodologies on a problem
where the locations of the differences are well known.
PSPI migration
accurately handles non-overturning waves when the velocity in a given
depth layer is constant. When velocity varies laterally the accuracy
decreases as a function of propagation angle. The Marmousi
example has significant lateral velocity variation and many
steeply dipping events. As a result the image quality varies with
the number of reference velocities that are used. Figure 9
shows the effect of changing the number of reference velocities
used in the migration.The rows represent migrating with a PSPI migration
using one, three, and seven reference
velocities. The left column is the migrated image, the center panel
is the result of using the PEF method for detecting differences. The right
panel shows the result of using the histogram matching.
In this case, the PEF approach proves to be better at identifying differences
in the images. Note how the PEF approach highlights the steeply
dipping features, where the PSPI approximation breaks down. With increasing
number of reference velocities only steeper dipping features are displayed.
The histogram approach seems to simply highlight the major features in
the image, showing limited preference towards large dips. Figure 10
shows the total differences as a function of the number of reference velocities.
Note how the effect of increasing the number of reference velocities is
much more pronounced in the PEF case.
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big-v
Figure 9. The rows represent migrating with a PSPI migration
using one, three, and seven reference
velocities. The left column is the migrated image, the center panel
is the result of using the PEF method for detecting differences. The right
panel shows the result of using the histogram matching.
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v-graph
Figure 10. A graph of the differences detected by
the PEF (solid line) and histogram matching (dashed line) scheme.
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 | Prediction error filters to enhance differences |  |
![[pdf]](icons/pdf.png) |
Next: Planewave migration
Up: R. Clapp: PEF enhancement
Previous: Precision
2007-09-18