Normal mode coupling in a waveguide with a range-dependent sound speed profile in the bottom

Sound propagation in shallow water over the bottom with a varying impedance is considered in the coupled normal mode approach. Water depth is assumed to be constant. Bottom roughness is not taken into account. Range-dependent impedance is only associated with the spatial variability of sound speed in the bottom. The results of 3D seismic survey conducted in the Kara Sea are taken as an input data for sound propagation modeling. Numerical simulations show that the typical horizontal gradients ~0.4 s^-1 of the bottom sound speed provide mode coupling.