Propagation loss measurements in a region of complex bathymetry over the continental slope

Abstract

Measurements of propagation loss over a sloping bottom have been obtained in experiments on the continental slope off the west coast of Vancouver Island. Shot runs were carried out to ranges of 100 km using 18 m and 180 m SUS charges in upslope and downslope geometries. The data were processed in 1/3‐oct bands from 12.5–630 Hz. The 18‐m shots were bottom‐limited in these experiments, and the effect of the interaction with the seafloor was observed for these charges in both experimental geometries. An enhancement in the propagation loss was observed for the downslope run, with the loss decreasing by up to 10 dB for shots at the crest of the slope, whereas the loss increased with range faster than cylindrical spreading for the upslope run. Also, an optimum frequency of propagation was observed at 50 Hz for both geometries. In contrast, the propagation loss increased with both range and frequency for the deeper shots. The measurements have been modeled using a wide‐angle parabolic equation method which is capable of accounting for the interaction with the sloping bottom. The modeled results provide an accurate description of the features observed in the measurements.