Nonlinear alignment method for land SINS

The gun-board Strapdown Inertial Navigation System (SINS) is discussed. To solve the problem of system non-linear caused by the large azimuth misalignment angle, a non-linear parameter estimation method based on Fast Orthogonal Search (FOS) and Kalman Filter (KF) is proposed after a detailed analysis of the model for estimation of large misalignment angle errors. The non-linear error model previously trained is used for alignment. The linear attitude error can be eliminated, and the nonlinear attitude error can be suppressed effectively. The simulation results show that the FOS/KF method can result in more alignment accuraty and real-time than the Extended Kalman Filter (EKF). With a comparison of the test results shows that the azimuth angle error is up to 14.99° when the EKF is used alone, while the azimuth angle error is within 0.8° when the FOS/KF method is used. The accuracy of estimation with FOS/KF method does not change with nonlinearity of the system and does not need coarse alignment, simplifying the alignment process and improving the carrier maneuverability effectively.