Differential acoustic bearing as a technique to study internal waves

Abstract

Measurements have been made of the effect of internal waves on acoustic bearings near the island of Hawaii. The research platform FLIP was instrumented with a 30‐element vertical thermistor string (∼3‐m uniform spacing) and with hydrophone booms at depths of ∼30 and ∼90 m. The mixed layer depth was below 30 m. With a sound source at a depth of ∼30 m and a range of 1.5 nm, the bearing of the sound source was measured with the 30‐ and 90‐m hydrophones. The difference in bearings measured at the two depths is compared to the record of isotherm depths obtained with the thermistor string. The differential acoustic bearing technique is suggested as a means of measuring propagation direction and spatial coherence in the horizontal for short period (3 cph) internal waves. [Research supported by the Office of Naval Research.]