In the present invention, a new method is disclosed for the coarse alignment of strapdown inertial navigation system (INS), along with estimation of the INS systematic errors. This is achieved using an accurate external positioning system such as the global positioning system (GPS) and gravity disturbances obtained from the Earth gravitational models (EGMs) such as EGM2008 during the time of INS initialization. First, a new method for transformation of INS-sensed acceleration from the sensor frame to the navigation frame using gyro output data is disclosed. Then, using the new method of transformation and considering the effects of the INS systematic errors on the obtained gravity disturbances during highly dynamic motion, new techniques are developed for both INS coarse and fine alignments, which are based on minimizing the variations of obtained gravity disturbance vector in the navigation frame. The present coarse and fine alignments can be performed for each of two cases when the INS is stationary or moving.
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