Complex Application of Ray and Wave Approaches to Sound Field Calculations in a Narrow Waveguide on the Black Sea Shelf

Abstract

This article deals with study of combined use of ray and wave methods for assessment of underwater sound field intensity in shallow water given different types of sediments and different sound localizations. A hydroacoustic waveguide is considered with a sound velocity profile containing a narrow near-bottom and weakly pronounced near-surface sound channels. Two types of seabed are considered: silty and sandy, and two cases of source location: near-surface and near-bottom. Two approaches are used to calculate the acoustic field: the ray method and normal wave method. It is accepted that the ray method is more consistent with the high frequency range, whereas the normal wave method is more consistent with the low frequency range. It is shown that as the frequency increases, the vertical profile of normal waves concentrates in the region of global minimum on the sound velocity profile. The dispersion characteristics of normal modes and their attenuation coefficients are analyzed. It is shown that the smallest group velocity of a normal mode corresponds to the largest attenuation coefficient, which is explained by a significant interaction with the bottom. The calculated sound field levels in the water layer are used to estimate the field level of a sound source that is traumatic for benthic fauna. It is shown that in case of a sound velocity profile with two sound channels and source location on the axis of a narrow waveguide, the ray method for calculation of the pattern of sound strength decay with distance gives a systematic underestimation of the field level.