Integrated Acoustic Observing System for the Arctic

In DAMOCLES the first acoustic tomography experiment has been carried out in the Fram Strait from 2008–2009 using one acoustic source and one acoustic array. Travel time was recorded at eight receivers between 100 and 900m and preliminary analysis of travel time data has been performed. Through inversion techniques, internal ocean temperature will be retrieved over distance of 130 km. The travel time data will be assimilated into the TOPAZ ice-ocean forecasting system in hindcast mode. The main objective of ACOBAR is to establish a multipurpose acoustic system in the Fram Strait for tomography, navigation/positioning of gliders and floats under the ice, and communication with underwater units. When the triangle of transceivers is deployed in 2010, average temperature will be available from 6 tracks of acoustic travel time measurements. Three tracks provide reciprocal travel times and current velocities can be derived. The system will transmit both RAFOS signals for navigation and tomographic signals. For the high Arctic, it is recommended to design and implement a cost-efficient, multi-purpose infrastructure for tomography, navigation/positioning of gliders and floats under ice, and standard oceanographical moorings in the Arctic (Dushaw et al. 2009). The implementation of multi-purpose acoustic observing system will build on experience from the previous acoustic tomography experiments in the central Arctic Ocean (Gavrilov and Mikhalevsky, 2006) and the regional acoustic system currently under implementation in the Fram Strait within ACOBAR. The ultimate goal is to assimilate the observations into ice-ocean models in order to provide improved monitoring and forecasting of the sea ice and ocean conditions. Furthermore, the acoustic infrastructure can be used for monitoring of ambient noise and marine mammals in the polar regions. The anticipated increase of human activities in the Arctic will lead to higher noise levels, e.g. from fishing vessels, oil and gas installations, seismic exploration and ship transportation. The observing system can therefore be used to assess the impact of increasing ambient noise levels on marine mammals.

References Dushaw, et al. 2009. A Global Ocean Acoustic Observing Network. OceanObs 2009 Community White paper. Gavrilov and Mikhalevsky, 2006. "Low-frequency acoustic propagation loss in the Arctic Ocean: results of the Arctic Climate Observations using Underwater Sound experiment", J. Acoust. Soc. Amer., v.119 (6).