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

3aUW9. Spatial coherence of high-frequency (67-kHz) acoustic fluctuations in fully developed turbulence.

Michael J. Buckingham

John R. Potter

Grant B. Deane

Marine Phys. Lab., Scripps Inst. of Oceanogr., La Jolla, CA 92093-0213

As part of ONR's high-frequency initiative, a field experiment to determine the temporal and spatial coherence of acoustic fluctuations induced by propagation through a fully developed turbulent flow has been planned in collaboration with several other research groups for late September 1994. Narrow-band measurements (67-kHz coded signals) will be taken in Cordova Channel, British Columbia, where strong, semidiurnal tidal flows (up to 1.0 m/s) create fully developed turbulence (Reynolds number (approximately equal to)10[sup 7]), and strong mixing prevents stratification (bulk Richardson number (approximately equal to)0.02). Prior experiments have established the turbulent nature of the flow and examined the horizontal arrival angle and intensity fluctuations with time. In the present experiment, a new compact acoustic array, consisting of 128 hydrophones in an elliptical configuration, is being adapted to monitor the acoustic arrivals in the vertical and horizontal, with finer spatial resolution than has previously been obtained. Amplitude and phase data will be recorded from 15 channels. Environmental data from ADCPs, turbulence meters, side-scan sonars, microstructure instruments, CTDs, etc., will be available to help interpret the acoustic results. Preliminary results of the acoustic fluctuation experiment will be presented, with an analysis of the fine-scale phase and intensity coherences, which are intimately related to the microstructure of the transmitting medium.