Development of a Practical Coherent Acoustic Doppler Current Profiler

The practical feasibility of developing a Coherent Acoustic Doppler Current Profiler (ADCP) with spatial resolution and range comparable to those of commercially available incoherent systems but with much smaller velocity measurement variance is being studied. This improvement in measurement accuracy will reduce required averaging times, thus permitting the observation of short time-scale currents (i.e. internal wave breaking) which are beyond the capabilities of available incoherent ADCP's. Several strategies have been analysed and tested. Among them, transmission of coded acoustic pulses combined with coherent signal processing techniques has been given special attention. This approach may allow the measurement of watermass velocities with high accuracy without the range limitations of conventional pulse-to-pulse coherent systems due to velocity ambiguity and pulse-to-pulse decorrelation. Several schemes based on this approach have been analysed and their relative merits assessed.