Comparisons of simultaneous signal reception over long range among hydrophones with unlike acoustic geometries

Abstract

Propagation measurements were made to six hydrophones installed offshore Bermuda at depths from 430 to 2450 fm. Four were bottomed onslope or at basin depth; two were suspended, one at the sound channel axis and one 30 m above the deep bottom. Both impulse sources (charges detonated at 18 and 240 m) and a continuous wave (cw) transducer towed at 120 m were used. The 800-nm track began 40-nm south of Bermuda at midpoint of the ensemble of hydrophones and ended off St. Thomas beyond the Puerto Rican Trench. The bottom receiver at 430 fm had the lowest transmission loss; the deep basin hydrophone the highest. Arrival order identification from shot processing for all hydrophones showed performance depended on the degree to which the local bottom slope enabled a receiver to intercept both up and downcoming ray paths. Suspension per se was not significant. Energy partition among arrival orders indicated one arrival carried about 50% of received signal strength. About five arrivals were needed before 90% of the total signal was collected, suggesting broad ocean coverage is unavoidably linked to coping effectively with multipath propagation. [Work supported by NavElecs.]