Horizontal refraction and sound fluctuations caused by internal waves packets in shallow water

Abstract

The subject of the paper is to consider the propagation of a low-frequency sound field in shallow water in the presence of solitonlike internal waves (SLIW). It is assumed that SLIW spread approximately across the stationary acoustic trace. The problem of sound propagation is considered within the framework of 3-D model of the shallow water. The theory of ‘‘horizontal rays and vertical modes’’ is applied to take into account influence of horizontal refraction due to SLIW. As shown in the paper SLIW can lead (periodically in time) to ‘‘focusing’’ and ‘‘defocusing’’ of the horizontal rays or, in other words, to the periodic appearance of ‘‘horizontal waveguide.’’ Estimations of the sound fluctuations due to SLIW demonstrate that the amplitude of fluctuations can reach up to 10–20 dB (between moments of the ‘‘focusing’’ and ‘‘defocusing’’). The next effect conditioned by internal waves is horizontal filtering of vertical modes, where we have separate focusing and defocusing rays, corresponding to different vertical modes at different points of horizontal waveguide. The results presented in the paper can be used as the basis of remote sensing of the internal waves packets in shallow water. [Work supported by RFBR, Grant 97-05-64878.]