A Flexible INS Correction on Method-Based Continuous and Sparse Gravity Matching Positions

Gravity-aided inertial navigation system (GAINS) is a significant technique in underwater long-endurance passive navigation. In addition to gravity matching process, comprehensive correction is also a crucial step by implementing the gravity matching results fusing with inertial navigation system (INS) for navigation reset and INS accumulation error correction in GAINS. Due to the uneven distribution of the gravitational field and gravity feature suitability real-time changes, the matching position output frequency is difficult to fix after credibility evaluation and error elimination. The gravity matching results covered continuous or sparse frequency at different filtering periods and ranged from 3 min to 10 h, which meant in-coordinate interval characters. In this article, a flexible INS correction method (FICM) for GAINS covering the improved Kalman filtering and multipoint comprehensive correction is presented to improve filtering navigation stability. After an adaptive navigation state judgment, for continuous gravity matching positions, an extended Kalman filter (EKF) was adopted; for sparse matching results, a multipoint comprehensive correction method would be used to estimate INS gyro drifts for navigation reset-based INS error accumulation characteristics in long endurance. The hardware-in-the-loop simulation and marine dynamic experiments in the South China Sea demonstrated that compared with the commonly used filter navigation methods, the FICM could effectively suppress the accumulated INS uncertainty and drift error with a high-precision navigation result, regardless of continuous or sparse gravity matching position.