Acoustic propagation in a continental slope ocean environment
Date
1985
Authors
Dosso, Stanley Edward
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Abstract
The analysis and interpretation of experiments carried out to study acoustic propagation in a continental slope ocean environment are presented in this thesis. Measurements of the propagation loss in 1/3-octave bands from 25 to 630 Hz were obtained for propagation both up and down the continental slope in experiments off the west coast of Vancouver Island. The propagation was strongly influenced by the ocean floor bathymetry. A slope enhancement effect (decreasing loss with range) was observed for sound propagating down the continental slope. The maximum enhancement occurred for sources near the edge of the continental shelf, with measured losses as much as 16 dB less than those estimated for propagation over a flat ocean bottom. The slope enhancement effect was greatest at the high frequencies. In contrast, large losses were measured for propagation up the continental slope, particularly at high frequencies. The propagation loss for sources near the base of the slope exceeded that estimated for a flat ocean bottom by as much as 15 dB.
The parabolic equation method, which is well suited to modelling low-frequency propagation in a range-dependent environment, was used to model both the downslope and upslope propagation measurements. A treatment of the effects of density variations in the sub-bottom layers was added to the model in this thesis. The results of several test cases indicate that this addition leads to significant improvements in the model predictions. The losses calculated for propagation down the slope were in excellent agreement with the experimentally measured values. The model calculations for propagation up the slope exhibited the correct range-dependent behavior, but differed in level from the measured values which include losses due to three-dimensional effects that cannot be accounted for by the model used in this work. These results indicate that the "variable-density" parabolic equation method can accurately model the acoustic propagation in a continental slope environment.