Vector Fidelity of OBC Data and Seafloor Coupling of the Vertical Component

摘要

Ocean-bottom cables (OBCs) are the most practical andrneconomic means of deploying seismic sensors on the sea floor.rnHowever, differences in coupling of the three-component (3C)rndata and impulse responses of the measuring devices canrnprevent a proper combination of the vector wavefields duringrnprocessing of 3D converted-wave (PS-wave) surveys,rnparticularly for the horizontal components. Since hydrophonesrnare perfectly coupled to the fluid medium, their response is anrnoptimal reference of true compressional-wave (P-wave)rnreflectivity. Operators can be designed from common-receiverrngathers for removal and evaluation of vertical coupling effects.rnA least-squares operator design is applied to data from thernGulf of Mexico to minimize the difference between thernhydrophone and vertical responses after taking into accountrnwater-trapped energy.rnAnother way of doing this is by applying the equation ofrnmotion and minimizing the down-going energy in a windowrncontaining only primary reflections (see Schalkwijk et al.,rn1999). Picking such a window may be difficult for long sourcernsignatures, or when operating in shallow water. A similarrncalibration approach based on a window containing up-goingrnenergy from critically refracted waves does not suffer fromrnthese shortcomings. This method is demonstrated on a realrndata set from the North Sea and is shown to give good results.