Measurement and modeling of downslope acoustic propagation loss over a continental slope

Measurements of propagation loss were obtained in an experiment to study downslope acoustic propagation over the continental slope off the Canadian west coast. The propagation was strongly influenced by the bathymetry and a downslope enhancement was observed at a receiver in the deep sound channel for shallow explosive charges deployed over the continental slope. The maximum enhancement was observed for sources near the edge of the continental shelf at a range of about 110 km, where conversion to low-loss water column propagation paths by bottom interaction occurred at a depth approximately equal to the sound channel axis. The propagation loss measured for these sources was as much as 15 dB less than that estimated for propagation over a flat ocean bottom, and was equivalent to levels recorded for sources at only 25–30 km. The data were interpreted by examining the structure of the signals received from the charges deployed over the slope, and by using ray theory to determine the propagation paths. The range dependence of the propagation loss was modeled using a wide-angle parabolic equation method with a realistic geoacoustic model of the environment which included sound speed, density, and attenuation profiles. The model results were in excellent agreement with the measured values over the entire frequency band of the measurements.