Shallow water station keeping of AUVs using multi-sensor fusion for wave disturbance prediction and compensation

An important capability for autonomous underwater vehicles (AUVs) is station keeping. Station keeping is the ability of a vehicle to maintain position and orientation with regard to a reference object. In shallow water this mission most likely will be disrupted by the large wave induced hydrodynamic forces acting on the vehicle. To counter this problem, knowledge of these wave induced disturbances is critical to allow for the design of a control system that will enable the vehicle to accurately navigate and position itself. The ability to develop a so called "predictive" control strategy for underwater vehicles is limited by the methods available to measure and predict the wave induced disturbances. Surface vessels may employ remote sensors such as acoustic probes, lasers or short wavelength radar to determine future disturbances, but this remote sensing is not feasible in a low cost underwater vehicle. AUV control system design is limited to the use of on-board sensors for disturbance prediction. We present the design of a sliding mode controller (SMC) that employs multi-sensor data fusion for wave disturbance prediction/estimation. Using data obtained from the vehicle's Doppler, acoustic Doppler velocimeter (ADV) and motion package, a dynamic filter is developed that will fuse the information from the various sensors and provide the controller with an estimate of the wave induced disturbance, thus allowing the vehicle to station keep in both heading and position with far greater accuracy.