Figure 1

Figure 2

On Figure 1, I display the input shot gather, with the description of the recording parameters. The water-bottom multiples are easily visible: they are separated by lags of 0.5 seconds. Next to the input shot-gather, I also display a first attempt of removal of these multiples, with a method I describe in this report (Darche, 1990). It consists in doing a Burg-type adaptive processing in the domain, after a slant-stack transform. This process is especially useful to have a good estimate of the velocity curve of the primaries: a velocity analysis of the input gather only reveals velocity picks due to the strong multiples. However, I don't consider it as optimal in this case, because the multiples are not efficiently removed at far offsets. The velocity curve obtained from the first multiple removal enables us to perform the NMO correction of the input gather, and the result is also displayed on Figure 1.

Then, I transform the NMO-corrected data to the *t _{0}*-

On Figure 2, we can notice three basic topics. First, due to the
stretch at far offsets, the water-bottom reflection does not focus around
*p*=0, because of the stretch of the far-offsets after NMO correction.
Then, the water-bottom multiples are clearly visible at 1 and 1.5 second,
with two peaks around . I isolated the region in which I
find the multiples with a thick boundary line. Finally, no major event
is visible after 2 seconds.

I isolate the water-bottom multiples by putting to 0 the values *U*(*t _{0}*,

Figure 3

The multiples have been efficiently removed.
Some major events, especially after 1.5 seconds, have been emphasized.
I think a problem can come from the definition of the multiple region:
if we take it too wide (in *p*), we localize the energy of the remaining
events in a narrow band of the *t _{0}*-

Finally, I advise *not* to work directly with the region defining
the *primaries* on Figure 2. Effectively, it appears that
the water-bottom reflection, especially, should be described by a wider
range of *p*-parameters than the one I used: the modeling operator could
not restitute it entirely, and it would be modified in the process. This
is due in particular to the stretching at far-offsets, to the mute,
and also to refracted arrivals. On the
other hand, the multiples are known to be approximately parabolic,
and their energy is concentrated in the region I defined, so we are sure
to restitute them entirely.

1/13/1998