Under-ice shallow-water sound propagation and communication in the Baltic Sea

Sound propagation under ice in the Baltic is of interest for military as well as civilian purposes. Important questions are, for example, how sonar systems are affected by ice in shallow waters and how marine mammal life under ice is affected by ship traffic. Changing climate and increasing ship traffic are factors of great concern also in the Arctic region. Modeling results for sound propagation under ice in the Baltic Sea are presented for low as well as high frequencies. The sound propagation is influenced by bottom as well as ice-cap interaction in these shallow waters. The low- and high-frequency modeling is performed with wavenumber and ray models, respectively. Both types of models are amended to include a solid ice layer on top of the water column. In addition, the modeling efforts are extended to study the performance of an underwater communication system developed at FOI. The modeling results are evaluated using data from sea trials in the Gulf of Bothnia under ice-covered and ice-free conditions.