PECULIARITIES OF SOUND PROPAGATION OVER THE CONTINENTAL SHELF IN BASS STRAIT

摘要

Measurements of the transmission loss of airgun signals from an offshore seismic exploration survey were made in 2011 in the western part of Bass Strait, Australia, as part of an 8-month sea noise monitoring and blue whale tracking program supported by Origin Energy. The measurements were made using an array of four autonomous sea noise recorders equipped with single hydrophones and deployed on the seafloor on the continental shelf not far from the continental slope. The distances from the hydrophones to the airgun array varied from 38 km to nearly 75 km. A review of the airgun signals received on the hydrophone array revealed that their waveform and spectral characteristics were atypical of a low-frequency impulsive signal propagated in shallow water over the continental shelf. The acoustic energy in the received signals was noticeable only in three relatively narrow frequency bands below 40 Hz. Moreover, airgun shots from some seismic transects were not detected in sea noise recordings. An explanation of such peculiar sound propagation in this area of the strait is suggested in this paper based on results of numerical modelling and some supplementary data on seafloor properties.