Anisotropic properties of long‐time intensity fluctuations of midfrequency signals in presence of intense internal waves in shallow water.

Abstract

Intensity fluctuations of sequence of midfrequency pulses radiated for 5 h in SW06 experiment were considered. Frequency band of pulses is 2–10 kHz; they were radiated by the source (R/V Knorr) with the interval about 15 s and received by four hydrophones (SHRUs) placed at the distances from 4 to 14 km and different directions (SW, SSW, NE, and NNE) from the source. During this time period, remarkable train of internal waves (amplitude of displacement up to 15 m) passed toward coastal line at the velocity of 0.6 m/s. Angles between wave front of train and acoustical tracks were about 65–80 deg. Mechanism providing sound fluctuations in this case is mode coupling (for the low‐frequency signals) or additional scattering of rays by internal waves (in high‐ or midfrequency situation). It was shown that temporal fluctuations of the sound intensity of received pulses initiated by internal waves have spectra, depending on the direction of propagation of internal wave relative acoustic track. Results of comparison of experimental data with theoretical estimations demonstrate good consistency. [This work was supported by ONR and RFBR.]