High-Precision LBL/INS Round-Trip Tightly Coupled Navigation Based on Constrained Acoustic Ray-Tracking and RTS Smoothing

In long baseline (LBL)/inertial navigation system (INS) round-trip tightly coupled navigation, the traditional tightly coupled method exhibits the function model mismatch and the observation distance error. To address this issue, we proposed a high-precision LBL/INS round-trip tightly coupled navigation based on constrained acoustic ray-tracking and Rauch-Tung-Streibel (RTS) smoothing. Specifically, the method develops the system and measurement models tailored for LBL/INS round-trip tightly coupled navigation to improve the state estimation accuracy of the filter. A novel round-trip acoustic ray-tracking based on the depth constraint is then introduced to reduce the distance observation errors. Additionally, the measurement model is transformed into the local Cartesian coordinate system to facilitate acoustic round-trip ray-tracking. Finally, RTS smoother is utilized to enhance the smoothness of the navigation results. The simulation test results demonstrate that the proposed methods outperform the traditional method, with a reduction of 35.6$\%$ and 67.0$\%$ in the three-dimensional root mean square (3D-RMS) value of the navigation errors, respectively. In the field experiment, the proposed methods display a decrease of 11.7$\%$ and 38.8$\%$ in the 3D-RMS value in contrast to the traditional method, respectively. These findings indicate that the proposed methods exhibit superior accuracy, stability and availability compared to the traditional method.