Effects of a surface ice cover and a bottom step on hydroacoustic wave propagation

This study investigates the effects of a semi-infinite floating ice cover and a small seabed step on hydroacoustic-wave propagation in a compressible fluid of finite depth, with particular attention to the reflected and transmitted waves and the normalized bottom pressure. The cutoff frequencies are examined, and matching equations between the open-water and ice-covered regions are established to obtain the reflection and transmission coefficients and the normalized bottom pressure. The numerical solution is verified using an energy-conservation relation. Results show that the elastic ice cover strongly reflects low-frequency hydroacoustic waves, whereas this reflection weakens as the incident frequency increases. Increasing ice thickness enhances the ice inertial effect and strengthens the wave number mismatch between the two regions, leading to stronger reflection and weaker transmission. When a seabed step is present, the local water depth is changed, which improves the wave number matching between the open-water and ice-covered regions. As a result, the reflection of hydroacoustic waves by the elastic ice cover is weakened, while transmission and normalized bottom pressure are enhanced. This effect is more evident at lower incident frequencies and for thinner ice covers. The results clarify that a seabed step weakens the reflection of hydroacoustic waves by the elastic ice cover through a local water-depth variation that adjusts the hydroacoustic wave number.