Elimination of free-surface related multiples without need of the source wavelet

This paper presents a new, wave-equation based method for eliminating the e ffect of the free surface from marine seismic data without destroying prima ry amplitudes and without any knowledge of the subsurface. Compared with pr eviously published methods which require an estimate of the source wavelet, the present method has the following characteristics: it does not require any information about the marine source array and its signature, it does no t rely on removal of the direct wave from the data, and it does not require any explicit deghosting. Moreover, the effect of the source signature is r emoved from the data in the multiple elimination process by deterministic s ignature deconvolution, replacing the original source signature radiated fr om the marine source array with any desired wavelet (within the data freque ncy-band) radiated from a monopole point source. The fundamental constraint of the new method is that the vertical derivativ e of the pressure or the vertical component of the particle velocity is inp ut to the free-surface demultiple process along with pressure recordings. T hese additional data are routinely recorded in ocean-bottom seismic surveys . The method can be applied to conventional towed streamer pressure data re corded in the water column at a depth which is greater than the depth of th e source array only when the pressure derivative can be estimated, or even better, is measured. Since the direct wave and its source ghost is part of the free-surface demultiple, designature process, the direct arrival must b e properly measured for the method to work successfully. In the case when the geology is close to horizontally layering, the free-su rface multiple elimination method greatly simplifies, reducing to a well-kn own deterministic deconvolution process which can be applied to common shot gathers (or common receiver gathers or common midpoint gathers when source array variations are negligible) in the tau -p domain or frequency-wavenum ber domain.