Azimuth Error Suppression Method Based on the Rotation Modulation and Acoustic Navigation Assistance for Polar Grid SINS

The grid strapdown inertial navigation system (SINS) can conquer the orientation problem caused by the meridian convergence in the polar region, but azimuth errors of the grid SINS still exist. The navigation error characteristic is analyzed based on the grid SINS mechanization. According to the error analysis, the azimuth error of the grid SINS will accumulate with time and it is hard to be estimated in polar regions because of the low observability. To improve the orientation accuracy, an azimuth error suppression method based on the rotation modulation and acoustic navigation assistance is proposed in this paper. The grid SINS mechanization is modified to update without longitude and avoid the influence from the longitude error amp. As the latitude increased, the compass effect decreased, which leads to the reduction of azimuth errors observability. So the rotation modulation, which chooses the azimuth axis as rotation axis, is employed to restrain the azimuth errors caused by the horizontal inertial measurement devices, and simultaneously improve the observability of azimuth errors. Then the azimuth errors accumulate with time and will increase the nonlinearity of system, and together with the velocity and position navigation information from acoustic measurement units, the nonlinear filter model is designed to further estimate and suppress the azimuth errors. Finally the simulation results show that with the rotation modulation and acoustic navigation assistance the proposed method in this paper can suppress the accumulated azimuth errors of the grid SINS effectively when working in the polar regions, and prove that the scheme has practical engineering application value.