Influence of latitude in coarse self-alignment of strapdown inertial navigation systems

In this paper, a new approach for the coarse self-alignment of strapdown inertial navigation systems (SINS) is presented. This approach, here called indirect approach, consists on estimating the initial Euler angles of the SINS for a given rotation sequence, directly from the inertial sensors raw readings, to then proceed with the calculation of the corresponding direct cosine matrix (DCM), which represents the SINS initial orientation. It is demonstrated in this paper that the utilization of the proposed approach with rotation sequences 321, or 312, allows the SINS initial orientation to be accurately determined in terms of its DCM, even if the actual position of the SINS on the Earth's surface is unknown. This approach is, therefore, particularly useful in situations where the SINS position is unknown, or for safety reasons, must not be informed.