Acoustic propagation through a low Mach number, stratified flow.

Abstract

Propagation of sound in an oceanic waveguide in the presence of a low Mach number, stratified flow is investigated. Equations for the wavenumber integration (WI) and normal mode (NM) approaches are simultaneously derived in a single formulation. When hydrodynamic shear stress and acoustic azimuthal coupling are negligible, the effect of current can be accounted for by a simple modification of existing WI and NM codes. A current layer is then shown to act as a wave-number filter which, in some cases, cannot be modeled using an equivalent sound-speed profile. Broadband numerical simulations show very good agreement between independently modified versions of OASES and KRAKEN. Applications to tomography are eventually discussed. The acoustic field for smooth current profiles can be derived as a function of the medium-at-rest mode set, making a broadband inversion possible. [Work supported by ONR.]