Combining pressure and particle velocity sensors for seismic processing

This work discusses the combination of pressure and particle velocity measurements in a single sensing element for underwater seismic applications. In such applications the sensing elements, usually pressure sensors arranged in linear arrays (streamers), receive from the bottom layered structure replicas of a broadband signal generated by a seismic source. In spite of careful setup of sound-receiver geometries, the useful replicas for bottom characterization are contaminated with other replicas, particularly surface reflected ones (ghosts). Since, single pressure sensors are omni-directional it is difficult, if not impossible, to filter out the nuisance replicas at sensor level. However, sensors composed by collocated or closely located pressure and vector field measurements can achieve spatial selectivity. Herein, we analyze the spatial filtering capabilities of various pressure-pressure, particle velocity-particle velocity and pressure-particle velocity combinations in light of seismic applications for narrow band signals. Simulations with the OASES code show that narrow band spatial filtering characteristics of the various combinations can be extended to broadband signals. These results were verified for experimental data acquired by 10 cm apart vector sensors measuring pressure and particle velocity in the 800-1250 Hz band, during the Makai Experiment 2005 sea trial, off Kauai I., Hawaii (USA).