Effects of Tidally-Varying Sound Speed on Acoustic Propagation over a Sloping Ocean Bottom.
RENSSELAER POLYTECHNIC INST TROY N Y DEPT OF MATHEMATICAL SCIENCES
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The influence of sound-speed fluctuations on propagation of a CW signal in an ocean with a uniformly-sloping bottom and a horizontal surface is analyzed using ray theory. The mean sound-speed structure is modeled as bilinear, with bottomed source and receiver above and below the SOFAR axis, respectively. The horizontally-independent fluctuations oscillate with a 12-h period in the upper ocean. An examination is made of possible types of rays for down-slop propagation that might exist, depending on bottom-slope angle and source-receiver separation. The total acoustic field is investigated for its dependence on these parameters and time. For certain conditions when up to three rays comprise the mean total field, three patterns of time evolution are described, each of which may have significant amplitude variations. Numerically-computed examples of each type are presented. The linear relationships between phase variations of individual rays and the sound-speed fluctuations are derived. Then, formulas are developed to explain the most frequent behavior of the relative amplitude and phase of the multipath total field. Predictions from the formulas show very good agreement with the numerical calculations. Author