The dual-sensor method has had a good deal of success in attenuating water-column multiples in multicomponent seafloor surveys. The method in its simplest form has been refined by various workers to take into account some of the factors otherwise neglected. These include: (1) nonvertical incidence implying variation of reflection and transmission coefficients with angle of incidence, (2) nonvertical incidence, again, requiring provision for S waves; (3) inclusion of the significant contributions to these multiples generated at the source end and thus multiple energy arriving also from below; (4) the effect of varying water depth; and (5) significant differences in the two wavelets, both in phase and amplitude spectra. We propose to review improvements that have been made and try to develop further refinements.
There are two essentially different types of water-column reverberations: (1) those that are confined to the water layer and (2) those that follow the arrivals of primary reflections. Some preliminary numerical results are given for the second type. These show that no universal scaling factor exists that can be used to eliminate multiples of all orders by summation of hydrophone and vertical geophone traces. For the first type, however, all such reverberations arrive from above and provision just for variation of reflection and transmission coefficients with angle of incidence, perhaps in the τ-p domain, could lead to great improvement.
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