On Statistical Modeling of Acoustic Propagation Losses of Low-Frequency Sound in a Waveguide of a Shallow Sea With Developed Surface Waves

A statistical problem of the propagation and scattering of a low-frequency acoustic signal in a shallow-water waveguide with a randomly rough surface and a horizontal absorbing liquid bottom is considered. This inhomogeneous waveguide is studied using the cross-sectional method and local mode theory. To determine the mode amplitudes, a boundary value problem is formulated, which is replaced by a corresponding problem with initial conditions for the imbedding equations. The latter equations are solved without approximations using standard computational schemes, allowing for efficient modeling of the statistical characteristics of the sound signal field. This paper presents calculations of signal intensity attenuation and its fluctuations in an Arctic waveguide under developed surface waves and for two types of bottom boundary impedance. It is shown that the influence of a random surface on the intensity of a propagating signal is relatively small for paths of typical length in shallow water. Intensity losses due to fluctuations increase slowly with distance. A comparison of the results obtained using different methods for solving this statistical problem (adiabatic, WKB-approximation) reveals an observable quantitative discrepancy. It is shown that the type of the correlation function (spectrum) of surface fluctuations has little effect on the average intensity of the signal field, and attenuation is determined by the amplitude of the fluctuations and their correlation radius.