Acoustic travel-time perturbations due to shallow-water internal waves and internal tides in the Barents Sea Polar Front: Theory and experiment

During August 1992, a combined acoustics/physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the Barents Sea Polar Front in the region near Bear Island. Oceanographic observations from shipboard hydrography and moored sensors allowed the construction of the internal wave frequency spectrum for the area. A rapidly sampled tomographic section from a 224-Hz, 16-Hz-bandwidth acoustic source to a 16-element vertical receiving array enabled the monitoring of travel-time fluctuations over the internal wave frequency band. To describe the measured acoustic fluctuations, theoretical expressions have been developed for the travel-time variances which are functions of the internal wave oceanographic field, the local acoustic propagation characteristics, and the acoustical system’s properties. Both ray and mode theory expressions are generated, as the experiment was performed in shallow water and both ray and mode arrivals were resolvable. Comparison of the theory with the data shows generally good agreement. However, due to the fact that the internal wave study is a secondary objective of this experiment, the data are not of the quality eventually hoped for. Directions for future research in this area are outlined and discussed.