Integration Scheme for SINS/GPS System Based on Vertical Channel Decomposition and In-Motion Alignment

Accurate alignment and vertical channel instability play an important role in the strap-down inertial navigation system (SINS), especially in the case that precise navigation has to be achieved over long periods of time. Due to poor initialization as well as the cumulative errors of low-cost inertial measurement units (IMUs), initial alignment is not sufficient to achieve required navigation accuracy. Concerning this problem, in the paper, misalignment error is dynamically modeled and in-motion alignment is provided based on position and velocity matching. It is revealed that, using misalignment error, orientation estimation can be properly corrected. Moreover, to prevent the instability effects of the vertical channel, decomposed SINS error model is derived. In the decomposed SINS error model, the navigation states in the vertical channel are separated from those in the horizontal plane. Two-step estimation process is developed for the integration of the aforementioned SINS error dynamics with the measurements provided by global positioning system (GPS) and fifteen-state SINS/GPS mechanization is presented. The assessment of the proposed approach is conducted in airborne test.