Under-ice acoustic communication in the Nansen Basin

An underwater acoustic experiment has been performed in the Nansen Basin (eastern Arctic) at $\mathbf{84}^{\circ}$ North. Channel probe signals and communication packets were transmitted in the 4–8 kHz band, with under-ice signaling over ranges of 10, 20 and 40 km. The measurements reveal a peculiarly sparse impulse response with two arrival groups, separated by 1–2 s, with contributions from surface duct arrivals, refracted paths, and bottom-reflected sound. A high propagation loss is counterbalanced by a low ambient noise level, yielding a useful SNR at all ranges. The main challenge for communications is the long impulse response, which causes a packet to collide not only with other packets transmitted over the same link, but also with itself. Some packets are lost because of these collisions, but there are also packets that are correctly received twice. Communication is possible over 40 km at a regular modem source level.