Page 459 - Acquisition and Processing of Marine Seismic Data
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450 9. VELOCITY ANALYSIS
FIG. 9.24 Semblance plots calculated from a synthetic CDP gather with different random noise levels of (A) 0%, (B) 10%,
(C) 20%, and (D) 30% with respect to the maximum reflection amplitude in the synthetic data. Increasing noise results in deg-
radation of enclosures, especially for deeper reflections.
semblance plots of a synthetic CDP gather with which may ultimately complicate the picking
and without top mute. A direct arrival and 20% of the velocity of the seabed and shallow subsur-
random noise is included in the synthetic data. face reflections. This situation causes much
Several artificial enclosures just above the sea- more drastic results in the real supergather
floor reflection appear in the semblance plot, example in Fig. 9.27. The negative effect of
