Effect on Kalman based underwater tracking due to ocean current uncertainty

Although it was recognized that an unmanned underwater vehicle (UUV) in reality might experience changing ocean current along its mission trajectory, most published papers related to the single beacon underwater navigation assumed a constant ocean current over the whole duration. When this assumption is against the reality, those underwater tracking models not only will fail to adequately describe the change of ocean current over the duration, but also may introduce large error to their position estimation. In this paper, by including adequate ocean current uncertainty in the process model at each discrete time, the estimated ocean current can exhibit time-varying and location-dependent characteristics. The effect on the accuracy of underwater tracking due to the inclusion of the ocean current uncertainty is investigated through a kinematic model that treats the unknown effective sound velocity (ESV) as a state variable. In addition to the Kalman filter, the performance of the corresponding Rauch-Tung-Striebel (RTS) smoother is also studied. Both simulation and filed data are used to study the effect on the accuracy of underwater tracking.