Comparison of Four Acoustic Doppler Current Profilers in a High Flow Tidal Environment

Acoustic Doppler Current Profilers (ADCPs) are commonly used across a range of disciplines for flow measurements in fluvial, coastal and offshore environments. As with any measurement instrument, calibration and assessment of the accuracy of ADCP outputs is of high interest to many users, but in most cases the data is not independently verified. The accuracy of the measurements is of particular importance to the emerging tidal stream energy industry, since available power is proportional to velocity cubed. This paper describes the methodology of a field study conducted to compare flow velocity measurements from five collocated ADCPs. The velocity magnitude and direction results from four of the ADCPs are compared and contrasted in the paper. The most significant result from this study is the mean pairwise difference of depth and time averaged speed of up to 0.19 m s−1 between two collocated instruments on one frame. The differences in results between instruments highlight the issues of instrument accuracy and of spatial variability of flow conditions