Multipath propagation loss measurements over an isolated seamount

Abstract

The interaction of low‐frequency sound with an isolated seamount has been studied by examining the multipath propagation. The data were collected during a shot run carried out over Dickins Seamount in the northeast Pacific. 1.8‐lb SUS charges were detonated at depths of 21 and 188 m along a 130‐km track beginning near a receiver suspended at a depth of 329 m, 60 km from the seamount. The multipath propagation loss was measured in 13 octave bands from 25–400 Hz. The results for both source depths indicate a region of decreased propagation loss (enhancement) before the seamount where a strong reflection is observed, and a region of shadowing beyond the seamount. In the shadowing region there are only two significant arrivals observed, and the relative arrival time remains constant with increasing shot range. The strength of these arrivals reaches a maximum when the source is about a convergence zone beyond the seamount. The shadowing effect is frequency‐dependent, with the propagation loss increasing at low frequencies. These observations are interpreted in terms of a simple model to account for the effects of the seamount.