Azimuth-dependent ocean bottom cable receiver coupling to the seafloor

Abstract

Inconsistent horizontal receiver coupling to the seafloor causes measured signal differences on both horizontal receiver components. To explain this inconsistency, we considered distinct coupling parameters, the damping ratio and resonance frequency, for the receiver inline and crossline directions. Our approach combined these coupling parameters with the azimuth angle between an airgun shot and the receiver geometrically and used two visualization methods to show spatially dependent receiver coupling, based on correlation and root-mean-square amplitudes. We developed finite-element method simulation results together with field data from one ocean bottom cable (OBC) in very soft biosediment. The simulations provided an insight to the difference between perfectly coupled ideal receiver response and poor coupling. From the field data, we compared OBC receiver coupling for trenched and untrenched cable. Our results revealed that the field data had an azimuth-dependent response pattern with amplitude decay and time shift on the untrenched inline component, which we can reproduce with our simulations. Azimuth-dependent receiver coupling indicated that the inline and crossline receiver components were connected by the direction of the traveling wave, and trenching the cable will reduce the azimuth-dependent coupling effects.