Acoustic scattering strength of turbulence generated waves in a shallow water flow

This work examines an airborne method of ultrasonic characterization of the dynamically rough water surface in an shallow water flow. A new experimental setup has been developed and tested in a 12 m long, 450 mm wide laboratory flume. This equipment includes a source of a 45 kHz airborne wave, microphone array, and an array of wave probes. It has been shown experimentally and theoretically that the directivity of the ultrasonic wave scattered by the dynamically rough water surface can be related directly to the roughness correlation function which can be measured non-acoustically. It is shown that the form of the roughness correlation function is determined unambiguously by the scale and intensity of the turbulence processes in the flow. The proposed acoustic method is accurate, remote, and rapid. It can be used to relate the spectral and statistical characteristics of the rough flow surface to the scale and intensity of the turbulent flow structures which cause the water surface to appear rough.