Phase fluctuations and horizontal refraction of low‐frequency sound signals in shallow water in presence of internal waves.

Abstract

Fluctuations of the sound pulse phase front propagating approximately perpendicular to the direction of motion of a train of intensive internal waves in the experiment Shallow Water 2006 (SW06) are studied. Acoustic data received by a horizontal/vertical line array (WHOI‐Shark array) during 3 h are analyzed. Low‐frequency modulated signals with a carrying frequency of 300 Hz were transmitted, propagating approximately along coastal line at the source‐receiver distance of 20 km. During this time, a train of intense internal waves (Rosey) was moving toward the New Jersey coast. Internal waves were being monitored by the ship radars (aboard R/V Sharp and R/V Oceanus) and by the thermistor chains. It is shown that phase fluctuations of the acoustic pulses arise with the appearance of internal waves at the source‐receiver acoustic track and they correspond to horizontal refraction of the sound pulses. For the low‐frequency sound pulses, modal decomposition of received signals is used both for the processing of experimental data and for the theoretical analysis. Experimental data are compared with theoretical estimation of horizontal refraction. [Work was supported by ONR code 321OA and by CRDF, Grant BP3C10].