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.
In August 1992, a coastal ocean tomography experiment was conducted in the Barents Sea over the steep northwestern slope of the Bear Island Trough, about 100 km east of Bear Island. The oceanographic objective of the experiment was to study the dynamics of the polar front and its vicinity using both acoustic tomography and traditional hydrographic techniques. The acoustic objective was to study the effects of the front and other coastal oceanography on the acoustic propagation. These objectives are strongly coupled, in that to effectively perform an inverse for the ocean features, one must first obtain a good understanding of the ‘‘forward problem.’’ In this paper, the effect of the strong frontal interface is examined, including its corrugations (‘‘interleaving’’ features), internal tides, and internal waves on the observed acoustic propagation. Effects on both the modal and ray propagation pictures will be examined, using both theoretical predictions and experimental data.
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