Sound propagation over an isolated seamount off the Canadian west coast
Keywords:acoustic wave propagation, underwater sound, seamount, Canadian west coast, propagation loss, sound sources, 230-Hz CW projector, explosives, hydrophones, multipath propagation loss, downslope reflections, sound-channel axis
AbstractAcoustic shadowing, reflection, and enhancement near an isolated seamount have been studied by examining the results of an experiment carried out to measure the propagation loss over Dickins Seamount off the Canadian west coast. Two types of sound sources were used: a 230-Hz CW projector towed at depths of 18 and 184 m; and 0.82-kg explosives detonated at depths of 24 and 196 m. The receiving system had hydrophones spaced in depth from 329 to 633 m. In the acoustic shadow region, the propagation loss for the shallow sources increased by 15 dB over the loss measured in the absence of the seamount. Examination of the multipath propagation loss for the shots revealed that the received signals consisted of two arrivals. The first and dominant pulse was determined to be a diffracted wave while the subsequent group of weaker pulses was attributed to a series of bottom and surface reflections. Strong reflections from the seamount were observed when the shallow CW source was 3 to 5 km from the seamount peak. For source positions closer to the peak, these reflections changed to downslope reflections resulting in an enhancement of the directly received energy. Only minimal effects were observed in the results for the deep sources because most of the source energy propagated along the sound-channel axis above the seamount peak.
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