Azimuthal coupling computations for transmission loss caused by shelf internal waves

Abstract

The amplitude of an acoustic field propagating through a stratified continental shelf water column in the presence of an internal wave packet is azimuthally dependent when referenced to the direction of propagation of the internal wave packet. Internal wave packets propagating across the continental shelf give rise to a highly directional wave-number spectrum of the continental shelf sound velocity field. FOR3D [D. Lee, G. Botseas, and W. L. Siegmann, J. Acoust. Soc. Am. 91, 3192–3202 (1992)], a three dimensional, one-way acoustic propagation model, has been modified to model internal waves in shallow environment on various computational platforms. It allows azimuthal coupling in the propagation, so that horizontal variation of the field may be observed. Results of numerical solutions are presented for propagation through synthesized internal wave packets [D. Tielburger, S. Finette, and S. Wolf, J. Acoust. Soc. Am. 101, 789–808 (1997)] in order to demonstrate the dependence of properties of the acoustic field as a function of range and bearing from the source and internal wave packet. These will also be compared to models that do not take into account azimuthal coupling. [Work supported by the Office of Naval Research.]