Sound through the internal wave field

Abstract

We review the subject of sound propagation through the random ocean internal wave field. Among the assumptions that are usually made, two are identified as not always valid: the Markov approximation and the expansion around a deterministic ray. When these approximations are valid, and the internal wave field known, acoustic phase :O.uctuations are very accurately predicted and intensity :O.uctuations reasonably well calculated. For the calculations of statistical moments of the acoustic field, the two techniques of moment equations and path integrals have been developed to a high degree, and give similar results. Among all other statistical quantities, the probability density function for intensity has received the most attention, but no satisfactory theory has been developed for this or other quantities.

Coupled mode transport theory for sound transmission through an ocean with random sound speed perturbations: Coherence in deep water environments

“…Thus the approximation of expansion about the unperturbed ray is expected to break down on the order of hundreds of kilometers, and some evidence of this has been presented by Flatt e and Vera (2003). In addition, it has been known for some time that the ray path functionals in the path integral theory do not correctly handle ray path curvature that is typical of ocean acoustic propagation (Henyey and Macaskill, 1996;Flatt e and Rovner, 2000). While corrections have been proposed for ray path curvature, they are either computationally intensive or empirical and approximate (Flatt e and Rovner 2000).…”

Analysis of multipath acoustic field variability and coherence in the finale of broadband basin-scale transmissions in the North Pacific Ocean

“…Another fundamental question in wave propagation studies is the scaling of fluctuations with acoustic center frequency, and thus we go from comparing different transmission paths to comparing center frequency differences along a given path. This is an area where there is very little theoretical knowledge, beyond results that are primarily valid at high frequencies and short range ͑Flatté et al, 1979;Flatté 1983;Henyey and Macaskill, 1996͒. Further, theoretical results focus on the fluctuations near a deterministic geometrical acoustics ray path, not the interference pattern of many such rays.…”

A review of recent results on ocean acoustic wave propagation in random media: basin scales

“…Note that the Markov approximation has not been made in our evaluation of , which is extremely important to accurate predictions [13]. This approach has also been taken by Henyey [3] in examining the validity of the Markov approximation for steeply turning rays.…”

“…Thus, (3) where , is the acoustic wavelength, and the Green's function [2] gives the vertical distance from a ray to a nearby "broken" ray having unit slope discontinuity at . is also closely linked to the variance of log-intensity ( [12], [16], in the case of full saturation, the mutual coherence function for small frequency separations can be written as The parameters , and can be interpreted as follows.…”

“…T HE preponderance of effort to understand ocean acoustic wave propagation in random media (WPRM) has been focused on relatively high acoustic frequency and short-range experiments [1]- [3]. In the 1990s, low-frequency basin-scale experiments were motivated by the desire to measure ocean climate change [4], and acoustical oceanographers undertook the design of their experiments by extrapolating the established WPRM ideas to low frequency and long range.…”