Velocity errors associated with using short pulse lengths in a 150-kHz acoustic Doppler current profiler

Results from three deployments of an RD instruments RD SC0150 acoustic Doppler current profiler (ADCP) are presented. Simultaneous measurements with a ship-mounted (Ametek Straza) ADCP and moored Aanderaa current meters during a deployment on Georges Bank show that the three systems resolved the main features of the dominant tidal flow, but with some rate discrepancies. Examination of the discrepancies indicates that the RDI data were degraded by transmit skew errors, Doppler tracking problems in the presence of high shear and low backscatter, and other minor instrument problems. The resulting inaccuracies were exacerbated by the use of short pulse lengths. Large vertical and error velocities in the Georges Bank data set accounted for some, but not all, of the degradations. Spatial structures in the near-future flow field and degradation of the (paddle-wheel) Aanderaa rate measurement also contributed to the discrepancies