Acoustic angular scattering by macro- and micro-scale turbulent vortices and sound speed heterogeneities

A stochastic ray-based analysis of the angular scattering of sound by ocean macro- and micro-scale turbulence is presented where the observable is angle of arrival (AOA) variance. Macro-scale processes, which are two-dimensional (horizontal plane), involve the ocean eddy field, with scales from a few kilometers to several tens of kilometers. On the other hand, micro-scale turbulence processes are three-dimensional, with scales from centimeters to a few meters. Both processes are critical to understanding the transport of ocean properties. It is shown that AOA variance observed in the direction of the ray path not only is sensitive to index of refraction fluctuations (temperature) but also is sensitive to the fluid vorticity field (∇→×u→). This result differs from established AOA theory using the paraxial approximation and looking in the direction of the wavenumber, where the index and flow field in the direction of the wavenumber are the scattering structures. It is demonstrated that a reciprocal transmission experiment with vector-sensor receivers can be used to separate index of refraction and vorticity contributions to the AOA moment equations. At the macro-scales, experimental options are mostly impractical, but at micro-scales, potential mid- to high-frequency configurations in bottom boundary layers appear possible.