Effect of hydrodynamic variations on sound transmission across a geostrophic flow

Abstract

A previously developed environmental-acoustics model for sound speed in a geostrophic flow is used to examine refracted/bottom-reflected (RBR) ray transmissions between a bottom-mounted source and receiver, in a direction perpendicular to the current flow. It is shown that explicit current effects may be assumed to be negligible, but that implicit effects of current on sound speed are significant. Ray geometry, travel time, spreading loss, and the total acoustic field associated with RBR transmissions are examined in detail. A numerical example is presented which models propagation studies over the Miami-Bimini installation across the Florida Straits. It is found that acoustic phase and amplitude are significantly affected by variations in the current. Finally, current is related to measured transport fluctuations, and a comparison is made between theoretical and experimental phase variations. Good qualitative agreement is achieved which clearly illustrates the importance of current (transport) variations on cross-current propagation, and demonstrates that the strong experimental correlation between environmental and acoustic properties can be modeled successfully using environmental-acoustics models.