Internal wave imprint in the oceanic ambient noise

Abstract

Investigations of dependencies between the characteristics of ambient noise field and different types of hydrophysical inhomogeneities in the ocean had revealed the possibility of realization of passive acoustic tomography methods (without transmitting signal and only on the basis of a noise field). Internal gravity waves are one of such inhomogeneities. They are manifested in the ambient noise field by modulation of noise level due to variation of sound-speed profile and by noise of ‘‘suloy’’ created on the sea surface by intense internal waves. The results of complex field experiments on synchronous measurements of internal waves and ambient noises are presented and analyzed. The observations were carried out near the Mascarene Ridge in the Indian Ocean, the region of generation of large-amplitude internal waves. The interrelation between fluctuations of noise field (received by vertical array of hydrophones) and vertical displacements of thermocline caused by internal waves had confirmed the possibility of practical realization of the acoustical system for internal wave observation. It was shown that amplitudes, periods, number of modes and directions of internal wave propagation can be determined on the basis of measuring of noise fluctuations. [Work supported by Russian Foundation for Basic Research.]