Acoustic scattering from fluid turbulence.

Abstract

There has been considerable interest in the oceanographic community in whether it is possible to use high-frequency acoustic echo sounders to measure ocean microstructure. A laboratory program, the ocean acoustics turbulence study (OATS), has been developed to examine the nature of such scattering and to compare results with that of a model recently proposed by Goodman (1990). The fundamental theory underlying the model is Bragg scattering, which results in the scattered pressure field proportional to the Fourier transform of the temperature field. A small heating element is used to generate a buoyant turbulent plume. Such a relationship could allow the prediction of the three-dimensional turbulent wave-number spectrum provided a sufficiently wide dynamic range in Bragg wave-number space were measurable. By performing scattering experiments over a very wide range of angles (ϑ=5° to ϑ=160°) and frequencies (250 kHz to 1.4 MHz) it is possible to infer such a composite spectrum. Preliminary results indicate a turbulent wave-number spectrum of classical form (−11/3 power law) in agreement with that expected for a fully developed turbulent field.