DVL-Aided In-Motion Coarse Alignment for Underwater Vehicles With Latitude Uncertainty

To solve the in-motion alignment problem of underwater vehicles with latitude uncertainty, a Doppler velocity log (DVL)-aided coarse alignment method is proposed in the article. The in-motion coarse alignment with latitude uncertainty is formulated as an optimization problem, and the objective function in quaternion-based velocity increment form is presented. Firstly, the coarse estimate of attitude quaternion is conducted to obtain a rough attitude reference through taking the position matrix as an unknown constant matrix. Secondly, the influences of vehicle's linear motion on the estimate of the attitude quaternion are analyzed in detail. Then the angular rate related to vehicle's linear velocity, which causes the large yaw error in the coarse estimation stage, is eliminated from the gyroscope outputs. Moreover, a more accurate latitude estimate and attitude quaternion are achieved by using the corrected gyroscope outputs into the determination of attitude quaternion, completely separating the linear motion from the vehicle's in-motion condition. The results of simulation and experiment demonstrate that the proposed method can overcome the interferences of vehicle's linear motion, and verify its effectiveness to solve the in-motion coarse alignment with latitude uncertainty.