ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

1pAO7. Acoustic mode coupling induced by internal wave fields in shallow water.

Steven Finette

Dirk Tielbuerger

Stephen Wolf

Acoust. Div., Naval Res. Lab., Washington, DC 20375

The problem of the propagation of acoustic waves in a stochastic ocean waveguide, for which the sound-speed variability within the water column is treated explicitly as a random variable, is addressed. The sound speed is composed of a deterministic, time-independent profile and two time-dependent stochastic components representing a (linear) background Garrett--Munk internal wave field and (nonlinear) internal wave soliton packets. A high-angle elastic parabolic equation method is used to compute single-frequency realizations of the pressure field using this representation of the sound-speed fluctuations. Transmission loss and scintillation index measures are estimated for both the full field and its modal decomposition at various ranges from the acoustic source, for different source depths and for both flat and sloping bottoms. These measures are incorporated in the analysis of acoustic modal coupling induced by the internal wave fields as a function of range; results support a recent prediction [D. Creamer, submitted to J. Acoust. Soc. Am.] that the scintillation index increases exponentially with range due to the competition between mode coupling and mode stripping found in shallow water waveguides. [sup a)]Permanent address: Forschungsanstalt der Bundeswehr fur Wasserschall-und Geophysik, Klausdorfer Weg 2-24, 24148 Kiel, Germany.