Performance characterization of a remote acoustic Doppler current profiling sonar

Monostatic acoustic Doppler technology is being evaluated for application to NOAA's mission requirements for the measurement of upper ocean current profiles. As part of that evaluation, a shipboard current profiling sonar, developed in 1978 under contract to NOAA by Thomson-CSF, was tested on the Blake Plateau. The system includes a four-beam 300-kHz “Janus geometry” hull-mounted transducer, and associated microprocessor-based electronics. The system estimates vertical current profiles in the upper 100 m by detecting the mean Doppler shift in volume-backscattered pulses at multiple ranges. Although no “sea truth” was available, agreement between mean ship' speed inferred from the acoustic Doppler measurements and Loran-C was good. The variance in time series of orthogonal components of current at specified depths is discussed as a function of transmission characteristics and ship's speed. The variance reduction with averaging indicates a random noise-type dependence when averaging of up to 10–20 observations. As more observations are averaged, the decrease in variance is limited, suggesting that an optimum averaging window can be tailored to the operating environment.