Calculations of internal-wave-induced fluctuations in ocean-acoustic propagation

Variability in the ocean sound-speed field on time scales of a few hours an d horizontal spatial scales of a few kilometers is often dominated by the r andom, anisotropic fluctuations caused by the internal-wave field. Results have been compiled from analytical approaches and from numerical simulation s using the parabolic approximation into an efficient set of algorithms for calculating approximations to internal-wave effects on temporal and spatia l coherences, coherent bandwidths, and regimes of acoustic fluctuation beha vior. These approximate formulas account for the background, deterministic, sound-speed profile and the anisotropy of the internal-wave field, and the y also allow for the incorporation of experimentally determined profiles of sound speed, buoyancy frequency, and sound-speed variance. The algorithms start from the geometrical-acoustics approximation, in which the field tran smitted from a source can be described completely in terms of rays whose ch aracteristics are determined by the sound speed as a function of position. Ordinary integrals along these rays provide approximations to acoustic-fluc tuation quantities due to the statistical effects of internal waves, includ ing diffraction. The results from the algorithms are compared with numerica l simulations and with experimental results for long-range propagation in t he deep ocean. (C) 2000 Acoustical Society of America. [S0001-4966(00)00208 -3].