Precise Navigation of USV Based on PPP-RTK/MEMS in the Offshore Environment

High-precision position, velocity and attitude information is the premise for the unmanned surface vehicle (USV) to perform various tasks. The traditional navigation technology of USV is to combine RTK (real-time kinematics) with MEMS (micro-electromechanical system). In order to avoid bi-directional communication of RTK/MEMS, a loosely coupled PPP (precise point positioning)-RTK/MEMS navigation method is proposed in this contribution, where the un-combined PPP-RTK positioning model and advanced time-differenced carrier-phase (TDCP) velocity determination model is adopted. When the reference stations are far away from the user, i.e., more than 55 km, the centimetre-level positioning results can be achieved and especially 99% horizontal error is less than 10 cm. Compared with the TDCP-only centimetre-per-second-level velocity accuracy, the proposed method can increase to accuracy of the order of millimetres per second. In terms of attitude determination accuracy, the roll and pitch are better than 0.1 degrees and yaw is better than 0.5 degrees, showing a similar performance to the nominal accuracy. Therefore, the proposed PPP-RTK/MEMS integration method can be a promising USV navigation solution in the offshore area.