A comparison of current profiles collected from bottom- and buoy-mounted instruments

Current profiles collected using a Nortek Aquadopp profiler mounted in an AXYS Technologies TRIAXYS wave buoy are compared to coincident measurements from nearby bottom-mounted instruments. A 2014 experiment conducted in the Chesapeake Bay with 0 - 3 m waves and 0 - 1 m/s currents suggested that observed discrepancies of 200-400 mm/sec could be due to inadequate resolution of rapid buoy movements and subsequent improper transformation of acoustic Doppler beam data to geographic coordinates. A second, similar experiment was run in 2015-2015 with 4 Hz attitude/acceleration data provided in real time, and high frequency data logged for post-processing and analysis. Mean errors were reduced to ~50 mm/sec, but showed a bias towards overestimating southward velocity. This bias was proportional to vertical shear and increased with depth; several possible explanations were detailed and discarded. While the substantial improvement in performance is notable and the implemented acceleration measurement improvementsshould be made operational, there is research remaining to understand the observed behavior.