Page 400 - Acquisition and Processing of Marine Seismic Data

7.6 f-k FILTERING 391

FIG. 7.25 Two semblance plots calculated from the same CDP gather (A) before and (B) after Radon velocity filter. In (A),
enclosures from first- and second-order multiple reflection amplitudes dominate the semblance plot in deeper parts, prevent-
ing the picking of primary reflection velocities. After removal of the multiples, semblance contours of primary reflections hid-
den behind the multiples become visible.

section of WEMR is almost multiple free and, recovery (TAR) or automatic gain control
in particular, the long period multiples are (AGC) must not be applied before WEMR, since
completely removed. these processes modify the amplitudes of the
WEMR is an effective multiple removal tech- seismic data and result in issues during the
nique that can be successfully applied even in modeling of the multiples by WEMR.
the areas of complex geology. Correct picking
of the seafloor arrival times and converting them
into the depth using accurate water column 7.6 f-k FILTERING
velocity is crucial in the efficiency of the method.
It is generally applied to shot gathers, and it is Multiples can arrive at the receivers at the
one of the most appropriate methods for AVO same time as the primary reflections. However,
analysis in which the relative amplitudes are moveouts of the reflection hyperbolas of both
of significant importance. Processes such as arrivals will be different since they propagate
trace balancing, deconvolution, true amplitude with different velocities, and the curvature of