An investigation into the interaction of a grazing angle broadband spherical audio signal with the dynamically rough air–water interface of shallow flows in rivers and channels

Abstract

Laboratory measurements were made of a broadband audio signal transmitted and received at grazing angles over a range of shallow water flow regimes. Synchronous measurements of local surface fluctuation were taken using a thin-wire wave gauge positioned at the point of specular reflection. The first and second statistical moments of the acoustic intensity at the receiver are shown to be directly related to the second statistical moment of the water surface fluctuations. It was hypothesized that this relationship was due to the path-length of the dominant signal fluctuating in direct relation to the interface fluctuations at the specular reflection point. This hypothesis is corroborated by analysis of the second statistical moment of the “time-of-flight” of the surface-reflected signal, and by direct analysis of the instantaneous water surface position.