In May 2014, the MIT Laboratory for Autonomous Marine Sensing Systems (LAMSS) participated in the BAYEX'14 experiment with the goal of collecting full bistatic data sets around proud spherical and cylindrical targets for use in real-time autonomous target localization and classification. The BAYEX source was set to insonify both targets, and was triggered to ping at the start of each second using GPS PPS. The MIT Bluefin 21 in. AUV Unicorn, fitted with a 16-element nose array, was deployed in broadside sampling behaviors to collect the bistatic scattered data set. The AUV's Chip Scale Atomic Clock was synchronized to GPS on the surface, and the data was logged using a PPS triggered analog to digital conversion system to ensure synchronization with the source. The MIT LAMSS operational paradigm allowed the vehicle to be unpacked, tested and deployed over the brief three-day interval available for operations. MOOS-IvP and acoustic communication enabled the group to command AUV mission changes in situ based on data collection needs. During data collection, the vehicle demonstrated real-time signal processing and target localization, and the bistatic datasets were used to demonstrate real-time target classification in simulation. [Work supported by ONR Code 322OA.]

The Arctic Ocean is undergoing dramatic changes, the most apparent being the rapidly reducing extent and thickness of the summer ice cover. As has been well established over prior decades, the environmental acoustics of the ice-covered Arctic is dominated by two major effects: the highly inhomogeneous ice cover, and the monotonically upward refracting sound speed profile, the combination of which forces all sound paths to be exposed to strong scattering loss and the associated loss of coherence. In some portions of the Arctic Ocean, however, inflow of warm Pacific water has created the so-called “Beaufort Lens,” a neutrally buoyant high sound velocity layer at 70-80 meter depth, which has dramatically altered the acoustic environment, creating a strong acoustic duct between approximately 100 and 300 m depth. This duct has the potential of trapping sound out to significant ranges (80-100 km) without interacting with the ice cover, resulting in much higher coherence and signal preservation. Acoustic noise measurement results collected with a vertically suspended array during ICEX 2016 illustrate the spatial and temporal noise properties in the presence of this acoustic duct at different depths. Comparisons of the ICEX 2016 data are also made with modeled Arctic noise data. [Work supported by ONR and DARPA.]