In-Motion Coarse Alignment for SINS/USBL Based on USBL Relative Position

The accuracy of initial attitude calculated from initial alignment has an important influence on the performance of SINS/USBL integrated navigation system. Currently, two main problems need to be overcome for SINS to complete the in-motion coarse alignment assisted by USBL system. 1) As SINS cannot obtain accurate initial attitude during the initial alignment phase, so USBL system can only provide the relative position in acoustic frame, but not the precise absolute position in navigation frame. 2) The outliers contained in the USBL raw data will seriously affect the performance of coarse alignment. In this paper, an in-motion coarse alignment method for SINS/USBL using the relative position of USBL is creatively proposed. Firstly, after constructing the apparent displacement vector from the relative position provided by USBL system and the output of IMU, an in-motion vector observation model is constructed. Secondly, the proposed method can suppress the influence of outliers in USBL raw data based on the advantages of displacement vector. Finally, the experimental results of the simulation and field tests show that the proposed method can not only complete the in-motion coarse alignment with favorable performance, but also effectively suppress the influence of the outliers in USBL data on the coarse alignment.
Note to Practitioners
—This paper was motivated by the problem of rapid in-motion coarse alignment for the SINS/USBL integrated navigation system in an underwater environment. Due to the failure of GNSS signals in underwater environments, the existing in-motion coarse alignment algorithms assisted by GNSS position/velocity are no longer applicable. In this paper, an in-motion coarse alignment method assisted by USBL relative position is proposed for SINS in underwater environments. In this article, we compare and analyze the differences between the principle of USBL positioning and GNSS positioning. Based on the characteristics of USBL positioning principle, the displacement vectors are extracted from the relative position of USBL for coarse alignment in this paper. The designed method can effectively suppress the impact of noise and outliers in USBL data on coarse alignment performance. The results of the simulation and field tests indicate that the method investigated in this paper is feasible in practical engineering.