Motion Characterization and Correction of Fine-scale Velocity Measurement on Wirewalker

The Wirewalker (WW), a wave-powered vertical profiling system, was developed at Scripps Institution of Oceanography. It serves as an ideal instrument to collect oceanic data because of its rapid profiling repeat time, hydrodynamically quiet operation, and long measuring duration. Recent approaches have been taken to mount Nortek Signature 1000 Acoustic Doppler Current Profiler (ADCP) on the WW looking side-ward or down-ward to measure velocity shear on fine-scales (25 cm-2 m). However, motion of WW will contaminate acoustical velocity measurement. We utilize three inertial sensors on the ADCP: accelerometer, gyroscope meter, and magnetometer, to back-calculate instrument’s motion by applying physical and mathematical models. Coherence results between beam velocity and inertial sensors show that WW motion is mainly caused by the current/surface wave and unbalanced buoyancy force of the package. Translation motion induced by the surface wave is corrected by integration of accelerometer at ~0.1 Hz band. Rotation motion caused by the unbalanced buoyancy is extracted by considering WW as a solid body rotation at ~0.6 Hz band. The results suggest that platform motion is a major consideration when dealing with observational data at fine scales and help us better understand WW’s performance in order to make further improvements.