Sound propagation in a continuously stratified laboratory ocean model

Abstract

The propagation of sound in a density-stratified fluid is examined in an experiment with a tank of salty water whose density increases continuously from the fluid surface to the tank bottom. Measurements of the height dependence of the fluid density are used to calculate the height dependence of the fluid salinity and sound speed. The height-dependent sound speed is then used to calculate the refraction of sound rays. Sound propagation in the fluid is measured in three dimensions and compared with the ray analysis. This study provides a basis for laboratory modeling of underwater sound propagation in the fluctuating stratified oceans.

Acoustic vortices in inhomogeneous media

“…2(c)], which is identified from the singular point of the phase distribution. The singular trajectory is compared with a horizontally emitted eigenray from a point source (black dashed line), which is an arc of a circle c 0 /G in a linearly stratified medium [35]. The results show that the singular trajectory does not lie on the eigenray of the point source.…”

“…We start by simulating the propagation of ultrasonic vortex fields in a linearly stratified fluid, where the sound speed is c = c 0 − Gz, such as that considered in Refs. [35,38]. The gradient is as large as G = 58 m/s per mm, which enhances the stratification effect in a short propagating distance (that saves the simulation load).…”

“…When considering practical situations or applications, the media commonly have spatially varying parameters in various areas. For example, in deep ocean environments, the sound speed is a function of depth, resulting from temperature and salinity stratification, and pressure variation [34,35]. In biomedical ultrasound, the sound speed has a large variation crossing tissues (see, e.g., Refs.…”

“…Experimental work to validate the behaviors would be valuable. One may use the setup of the ultrasound tank experiment in a stratified fluid [35], where the gradient is two orders smaller than the first example but several orders larger than oceans.…”