Characteristics of Low-Frequency Ambient Noise in Shallow Water With a Heterogeneous Bottom Structure

Abstract— The characteristics of low-frequency noise fields in shallow-water acoustic waveguides with a heterogeneous bottom structure in the presence of waterlike areas are analyzed through numerical experiments. Two seabed models are considered: an idealized one with a linear change in the sound speed in the bottom along one of the Cartesian coordinates and a realistic one where the sound speed in the bottom depends on all three coordinates. The second model is close to the real situation in one shallow-water area of the Kara Sea. Noise fields from distributed near-surface sources (surface waves) and a point source (ship noise) are studied. Calculations are performed using the wide-angle parabolic equation method. Averaged horizontal and vertical directivity patterns of the surface wave noise field are obtained, as well as average intensity values depending on the sound frequency and position of the receiving vertical array. Spatial dependence of the local source noise level is constructed for bottom areas with different properties. The possibility of detecting areas with a waterlike bottom by recording the noise of a moving vessel with a stationary vertical acoustic array is demonstrated. In the case of distributed sources, it is shown that the averaged noise characteristics weakly depend on the sound speed in the bottom.