Comparison of INS transfer alignments through observability analysis

Transfer alignment provides a rapid and effective way how to align and calibrate an inertial navigation system (INS) using the accurate information of other INS. However, in the previous literatures, it is found that not every transfer alignment algorithm is efficient in any environments. In this paper, the conventional velocity matching algorithm and the rapid velocity and attitude matching algorithm are compared in several typical environments by observability analysis. It is explained in theory, in this paper, why the velocity matching algorithm could estimate azimuth misalignment under constant velocity maneuver, but the velocity and attitude matching algorithm could not. At the same time, this paper analyzes the influence of sway and acceleration maneuvers to improve the observability of the two transfer alignment algorithms. Since GPS can provide the velocity and attitude information of vehicle, the accurate information used in transfer alignment can be replaced by the corresponding information from GPS in order to reduce the cost. However, the errors of velocity and attitude provided by GPS are larger than by accurate INS. So the estimation errors caused by external sensor errors must be considered if using GPS as the external sensor. At the end of this paper, the estimation errors of azimuth angle of the two algorithms due to the unobservable states and the errors of external sensor are deduced using the control-theoretic approach and proved by simulation, respectively.