Gravity compensation for long-duration underwater inertial navigation systems

Abstract As a core technology for autonomous navigation technology, inertial navigation offers high disturbance robustness as well as low observability. It plays a crucial role in various domains, including underwater vehicle operations. The accuracy of the inertial navigation calculation determines the precision of underwater navigation and positioning. However, owing to the non-uniformity of the gravitational field distribution of the Earth and the influence of component errors, the performance of inertial navigation degrades over long-term operation as it is influenced by the gravitational field of the Earth. Conventional inertial navigation replaces the actual gravitational field with an idealized normal gravitational field for computational simplicity. However, in complex underwater environments, such gravity-modeling approximations compromise overall solution accuracy. This study investigates the application of underwater gravity compensation in inertial navigation and examines its comprehensive influence on navigation performance, including compensation algorithms based on the spherical harmonic function model of the gravity field and gravity compensation methods for long-duration inertial navigation based on attitude damping. Simulation and experimental results demonstrated that the use of the gravity compensation method with attitude damping significantly improved the navigation solution accuracy of low-speed and long-endurance carriers. The final on-board measurement experiment results show that by adopting attitude damping for gravity compensation, the latitude accuracy of inertial navigation will increase by more than 10%, and the longitude accuracy will increase by over 60%. These findings provide theoretical support for the optimal design of inertial navigation systems and offer practical guidance for implementing gravity compensation techniques in engineering applications.