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Horizontal Anisotropy and Seasonal Variation of Acoustic Fluctuations Observed During the 20102011 Philippine Sea Experiment

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Technical Report

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Naval Postgraduate School Monterey United States

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The anisotropic ocean environment will lead to variability of ocean acoustic travel time. The variability of travel times comes from several ocean dynamical processes, including eddies, internal tides, and stochastic internal waves. This study analyzes time series of travel time from the Philippine Sea 20102011 experiment conducted by the Scripps Institution of Oceanography. In this experiment, a pentagonal array of acoustic transceivers of radius 600-km transmitted 250 Hz pulses for the purpose of observing acoustic variability at multiple time and space scales. Using filtering methods, this study separates variability in travel time in bands associated with eddies, internal tides, and stochastic internal waves. The observed fluctuations in the internal wave band are compared to a simple theoretical model. The result of the research shows that over the year, eddies induce the largest amount of variability. Internal tides and internal waves show comparable fluctuations. There is some seasonal variability. Eddies and internal waves show fluctuations that are fairly isotropic across the array, while internal tides give highly anisotropic fluctuations. This anisotropy is related to the strong directionality of the internal tides that emanate from the Luzon Strait.

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