Reduced-order Kalman filter for RLG SINS initial alignment

A closed-loop reduced-order Kalman filter is utilized to perform initial alignment of ring laser gyroscope strapdown inertial navigation system. The observability of the system with different measurement models were analyzed in detail. Navigation algorithm in alignment is modified to feedback continuously for the closed-loop system. The feasibility of this solution is verified through simulation and experiments. It is shown that the initial covariance of Kalman filter can influence the speed of initial alignment significantly because the covariance can not reflect the true state of the azimuth very well. At the beginning of alignment, Kalman filter must make a very conservative guess at the initial value of azimuth angle. If not, initial alignment will be accomplished at a low speed.