Internal-wave-induced acoustic fluctuations in a horizontally stratified medium

Abstract

Passage of an acoustic signal through an internal wave field results in the presence of amplitude and phase fluctuations at the receiver. The acoustic-internal wave interaction has been discussed previously using ray techniques [R. P. Porter, R. C. Spindel, and R. J. Jaffee, J. Acoust. Soc. Am. 56, 1426–1436 (1974)]. We report here on wave techniques describing the interaction phenomenon. The Rytov perturbation approach is applied to a horizontally stratified medium which is perturbed by the internal wave field. Statistical expressions for the acoustic fluctuations are obtained based upon a postulated internal wave model [C. Garrett and W. Munk, Geophys. Fluid Dynam. 2, 225–264 (1972)]. It is shown that for internal wavelengths comparable to acoustic ray cycle distances a resonant condition exists leading to large acoustic fluctuations. The validity and limitations of the perturbation technique applied to the horizontally stratified medium are discussed.