Fluctuations of resolved acoustic multipaths at long range in the ocean

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Abstract
A phase-coded signal centered at 220 Hz with 64-ms resolution was transmitted at 10-min intervals between an acoustic source moored at 2-km depth and a bottom-mounted receiver at ∠3-km depth and at ∠900-km range. A variety of fluctuation statistics (pulse and cw) are computed for three resolved multipaths from a 32-day record. The fluctuations are compared with theoretical predictions based on internal wave scattering. Some measurements agree with theory; measurements that disagree differ by amounts that are statistically significant but not large. Uncertainty of the internal wave energy level could account for some discrepancies. Some theoretical results are very sensitive to small changes of the second derivative of the mean sound-speed profile. There are substantial fluctuations at frequencies below those that can be accounted for by internal waves.