Sound phase and amplitude fluctuations in an anisotropic ocean.
Alexander, Charles Homer
Thornton, Edward B.
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Sound of constant amplitude and frequency was transmitted simultaneously in three orthogonal beams over a distance of 1.5 meters in the upper ocean. Time records of the resulting phase and amplitude fluctuations of the sound beams were studied by means of auto and cross spectral analysis and correlation. The time lag between corresponding peaks of the phase fluctuation autocorrelation functions of vertical and horizontal beams indicate movement of inhomogeneities between the sound fields due to water particle motion caused by surface wave action. Envelope correlation times of the phase fluctuations are found to be approximately one-half as great in the mixed layer as in the thermocline, and are greater in the vertical than in the horizontal direction in the thermocline. Anisotropy in the thermocline is also indicated by the variance of phase fluctuation being greater for sound paths in the horizontal than in the vertical direction. The autocorrelation functions of amplitude and phase fluctuations in any one direction are similar.
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