Acoustic-to-seismic coupling : properties and applications to seismic sensors

Abstract : Acoustic-to-seismic coupling is investigated using measurements of acoustic and seismic signals generated from acoustic sources. Source types used for the measurements were: pure tones, band limited pink and white noise, and broad band noise from an acoustic impulse (gun shot). The measurements showed that the frequency dependence of acoutic-to-seismic coupling was independent of source type. However, the efficiency of coupling favored certain frequency bands for a fixed source height. Dependence of the coupling on source height was also investigated. Measurements showed that the favored frequency bands were lowered as the source height was increased for frequencies below 250 Hz. Two techniques were evaluated for separating the acoustic-to-seismic coupled signature from the measured seismic signature in order to support development of methods for suppressing acoustic-to-seismic coupled background noise. Alternatively, such separation could help improve target classification. The two techniques (one using velocity measurements, the other using coherent measurements) were shown to be potentially useful for separating the acoustic-to-seismic coupled part of the seismic signature from the measured seismic signature. A theoretical approach with a simplified model of plane waves, a smooth surface, and no soil layering was not adequate to explain the measured dependence of acoustic-to-seismic coupling on frequency and source height. (Author)