Models to Estimate High Frequency Acoustic Scattering Due to Thermal Fine- and Micro-Structure of the Ocean
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION MELBOURNE (AUSTRALIA)
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Existing models to obtain intensity and phase changes of sound due to thermal fluctuations in the ocean, such as that developed by Chernov, are limited in their application. They are valid only for an isotropic medium and where the range is much greater than the correlation distance of the fluctuations. Extensions to short range and for an anisotropic medium are described here, both for the stochastic wave and ray models. Theoretical expressions obtained for acoustic fluctuations are easily evaluated. Numerical estimates are provided using stochastic wave and ray models for certain parameters of range, frequency and temperature variation, of interest in target strength measurements. These estimates indicate acoustic fluctuations for an anisotropic medium are always higher than for an isotropic media. For a range of 100 m, frequency of 100 kHz and temperature fluctuation of 0.007 C deg, the root mean square relative intensities and the root mean square phase fluctuations are on the average higher by a factor of 6, where the vertical correlation lengths are the same and the radial correlation length is about 50 times larger. Closed form expressions in the deterministic ray approximation are given to evaluate intensity and phase changes due to the mean temperature gradient. The validity of the deterministic ray theory results is discussed. Results from the stochastic wave and ray models are examined for the applicability of the stochastic ray model at high frequencies.
- Physical and Dynamic Oceanography