Two-dimensional angle of arrival fluctuations

Abstract

Angle of arrival fluctuations are one manifestation of acoustic propagation through a turbulent flow. Here the two-dimensional angle of arrival distribution for a 670-m acoustic path through a high Reynolds number flow in a tidal channel is examined and its origin and relationship to the flow field is determined. Over scales greater than the variability due to turbulence, a solution of the ray propagation equation explains the effect of advection on the horizontal arrival angle. The rapidly fluctuating two-dimensional angle of arrival distribution shows a degree of scatter consistent with the level of turbulent intensity. After removal of effects due to the finite aperture, orthogonal components are correlated during strongly sheared flow implying that the turbulence is weakly anisotropic over the measured scales. This anisotropy is discussed in terms of the cross stream velocity gradients ∂v/∂x′ and ∂v/∂z′, where (x′,z′) are perpendicular diagonal coordinates.