An Acoustic System for Measuring Ocean Flows by Space-Time Scintillation Analysis

We describe an acoustic measurement system built to test several techniques for analyzing a forward-scattered sound field in the ocean. The fluctuations of the sound field contain information about the field of flow along the acoustic path. The instrument consists of a microprocessor-controlled, radio-linked transmitter with a 4-element array, a 4-element receiving array and a receiver incorporating signal processing, data logging and control electronics on a VME bus. Pseudo-random noise coding is used to enhance the signal, with the decoding being carried out in real time by a high-speed multichannel hardware correlator.The transmit and receive arrays may be configured to test spatial aperture filtering for measuring the mean flew field or to measure the structure function of the refractive-index turbulence. Dual-frequency operation is also available for differential absorption measurements. Preliminary results of a field test in a turbulent tidal channel are presented.