ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aUW9. High-frequency propagation in a turbulent flow.

David M. Farmer

Daniela Di Iorio

Ward Cartier

Inst. of Ocean Sci., 9860 W. Saanich Rd., Sidney, BC V8L 4B2, Canada

As part of the new ONR-initiative in moderate-to-high-frequency acoustics, a pilot experiment will be carried out in a shallow tidally forced channel in September 1994 to compare acoustic variability with direct measurements of turbulent velocity and sound-speed fluctuations. The acoustic configuration will consist of a linear array of four sources on one side, and four receivers on the other (f=67.5 kHz, L(approximately equal to)700 m), together with a single source and receiver for reciprocal transmission. Separation of reciprocal transmission from reception of the other four sources allows a repetition rate for all sources of 5 Hz. The spatial filter will be applied to the acoustic data so as to focus the measurement on the central portion of the channel, at which location a moored turbulence sensor (R. Lueck) will be deployed at the same depth as the acoustic path. Supplementary measurements will be acquired with a multiple frequency backscatter sonar, moored current meters, and pressure gauges, and a neutrally buoyant float to measure the larger scale turbulent motions (E. D'Asaro, APL-UW and D. Veenstra, IOS). The experimental work will be discussed in the context of prior studies of forward scattering from turbulence and preliminary results will be presented.