In this section I test the nonlinear iteration outlined in section
on the Mississippi Canyon data. I ran only one
nonlinear iteration. Since the velocity model is already quite nicely
determined, I did not do residual velocity analysis after the first run of
LSJIMP. However, I did recompute the crosstalk weights and the reflection
coefficients for each of the four multiple generators.
The updated crosstalk weights are shown in Figure ,
at CMP 55 of 750. The most notable difference after the nonlinear update is the
infill of the near offsets. Although invisible in this case, the nonlinear
update also allows us to model crosstalk energy below twice the onset of the
first seabed multiple, which would be 7.5 seconds. This ability is very
important for data recorded in shallower water.
![]() |
Figure compares the weighted data residual at CMP 55
of 750 before and after the nonlinear update. The Figure is split in half along
the time axis as explained earlier in section
. The
most striking differences are highlighted with ovals. As mentioned earlier, the
R1 pure multiple and R2 seabed pegleg overlap over most of the 2-D line, which
inhibits estimation of R1's reflection coefficient. Although I do not show the
updated R1 reflection coefficient, Figure
implicitly
illustrates the beneficial change. The event highlighted in ovals on the
residual panels, which has three visible peaks, does not have that wavelet shape
in the raw data. Crosstalk between the overlapping events and an improperly
high R1 reflection coefficient cause the event to be ``manufactured'' in the
LSJIMP result. By better estimating the R1 reflection coefficient, the event is
not present in the residual, and thus, not manufactured by LSJIMP. Other that
this event, however, the differences between the two panels are minimal.
![]() |
Figure compares the LSJIMP estimated primaries at CMP
55 of 750 before and after the nonlinear update. The Figure is split in half
along the time axis as explained earlier in section
.
Ovals highlight the same regions as were highlighted in Figure
. The differences between the two estimated primary
panels are quite subtle; the difference panel on the right is more
englightening. Notice how the manufactured event discussed earlier is better
suppressed after the nonlinear update.
![]() |
Finally, Figure shows the stack of the LSJIMP
estimated primaries after the nonlinear update. The Figure is directly
comparable with Figure
. Again, the differences are
quite subtle. Notice an improvement in the removal of deep, salt-related
multiple events, like BSPLTS.
![]() |