High‐frequency propagation in a turbulent flow

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≊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 floa...