Modeling underwater sound propagation in an arctic shelf region with an inhomogeneous bottom

The seabed data from the Kara Sea (a part of the Arctic Shelf) are used to build a low-frequency (up to 250 Hz) acoustic waveguide model and study sound propagation in this region. A 30-m deep, well-mixed, and homogenous water layer over a flat seafloor is considered. The seabed's acoustic model is based on the spatial distribution of a sound speed recorded during a three-dimensional seismic survey in the Kara Sea, as well as density data from core sample analysis. One of the region's most distinctive features is the presence of large areas (up to several tens of square kilometers) where the bottom sound speed is close to that in water. In such a setting, the normal mode approach is applied to the sound propagation problem. The overall acoustic field is made up of propagating and leaky modes, which include quasi-modes. Numerical simulations show a high spatial variability of attenuation in the waveguide, 1.5 to 20 dB/km at 137 Hz. Even if the water depth is constant and the seafloor is uniform and smooth, mode coupling and horizontal refraction can occur owing to the bottom inhomogeneities. For higher modes, the predicted angle of refraction is up to 10°.