Estimating flow velocities of the water column using the motion response of an Autonomous Underwater Vehicle (AUV)

The WVAM method is a nonacoustic method to calculate the velocity components of a turbulent water column using the motion response of an Autonomous Underwater Vehicle (AUV) without the aid of an Acoustic Doppler Current Profiler (ADCP). This study analyses water velocity measurements estimated using the WVAM method as a function of the turbulence level of the environment by testing the method in an estuary that exhibits strong tidal currents (around 2 m/s). The uncertainty of this method at different water column conditions was computed by comparing the velocity measurements from the WVAM method with those obtained from the AUV mounted ADCP. The WVAM method determines the water velocities by comparing the motion response of the vehicle when operating within turbulent and calm water environments respectively. The motion of the vehicle in the calm water environment was obtained by conducting simulations of the vehicles in calm water under the same control commands executed during the field experiments in turbulent conditions. A reduction in the accuracy of the method in rougher water environments was observed due to the hydrodynamic coefficients of the simulation model reaching their nonlinear range limits. A possible strategy to overcome this limitation and improve the WVAM method´s ability to accurately estimate the flow field in the vicinity of AUVs operating in highly turbulent environments is also provided.