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As discussed in Chapter , the cost of downward
continuing a 3-D wavefield one depth step in the Fourier domain is
proportional to . On the other hand, the cost
of imaging with equation () is proportional to
*N*_{xy} *N*_{h<<3463>>xy}.
Clearly, if the number of offsets is large, then the cost of the
imaging step may be comparable (or even greater) than the cost of the
downward continuation.
This increase in computational cost is not a problem with
shot-geophone migration. In that instance, the cost of the
imaging step (proportional to *N*_{xy} *N*_{h<<3465>>xy}), will always be
less than the cost of the downward continuation [proportional to
].

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Stanford Exploration Project

5/27/2001