Under sea-ice acoustic noise and propagation measurements in the Thethys Bay (Ross Sea, Antarctica)

Underwater acoustic measurements have been recently carried out in Tethys Bay (Ross Sea, Antarctica) during the XXIX Italian Antarctic Expedition to investigate the environmental noise and to support acoustic propagation studies in the area. Tethys Bay is a small, deep cove close to the Antarctic Italian base Mario Zucchelli Station (Baia Terra Nova -74°42' S e 164°07' E), covered with sea-ice for most of the year. During the period of the experiment (November 2013) the pack-ice had an almost constant thickness of about 2.2 m, so that the measurements were performed deploying the instruments into the sea from holes having 1.3 m diameter drilled in the pack ice. They were located along the bay axis at a distance of about 500 m each other. The sea depth was around 200 m except for the hole close to the coast, were it was only 25 m. An hydrophone RESON TC 4032 was located in the outermost hole and measurements were collected at 0, 20 and 45 m depth. The measurements were repeated each time moving the acoustic source, a transceiver transmitting FSK pulses at 11 kHz, in the other three holes. During the experiment, sound speed profiles, sea temperature and salinity, currents, as well as the main meteorological parameters were continuously measured. The acquired passive acoustic measurements evidenced that the signal was generally dominated by different sounds from seals. Finally, the collected data-set and results from preliminary analysis of sound intensity attenuation is presented. The matching between the measured data and data obtained through numerical ray-tracing models of the under-ice acoustic propagation is discussed, pointing out the physical parameters that primarily impact on the attenuation.