On the Average Field Intensity and Individual Modes of a Low-Frequency Sound Signal in a Shallow Waveguide with a Statistically Rough Bottom Boundary

For a low-frequency sound signal propagating in a horizontally inhomogeneous waveguide in shallow water, the influence of a fluctuating interface between the water layer and fluid bottom sediments was studied based on statistical modeling using the cross-sectional method. The modeling was carried out for hydrological conditions in many situations corresponding to the shallow shelf zones of the Russian Arctic seas. A specific feature of these water areas is the presence of an almost homogeneous water layer on poorly consolidated bottom sediments with various characteristics, including a high degree of gas saturation. The dependence of the average intensity of the sound signal and its individual modes on the parameters of the problem has been studied: the characteristic scale of fluctuations of the interface and impedance of this interface, which determines its penetrable properties. It is shown that the influence of bathymetric fluctuations on the average intensity of acoustic modes has its own characteristics versus the influence of random volumetric inhomogeneities of the sound speed in the water layer and sediments, established earlier. Thus, bottom roughness of a relatively small scale leads, on average, to increased attenuation of a sound signal when propagating in a waveguide, and this can occur at relatively short distances from the source. An increase in the reflectivity of a rough bottom boundary weakens the effect of increased sound attenuation so that for typical values of sound speed in the bottom, attenuation at distances of 10–20 km from the source differs little from that for an undisturbed horizontal boundary.