On the alignment of platform and strapdown systems

After a brief review of the principles of the gyrocompassing loop in an inertial navigation system for the initial alignment of the platform this method is applied to a strapdown system. Test results are presented based on simulated and on realistic sensor signals for different motions of the base. The speeding-up of the gyrocompassing loop is discussed as introduction to the application of Kalman filtering for the alignment of platform and strapdown systems. The proposed method results in simple formulas for the covariance and the gain which can be easily implemented in a computer. As compared to the gyrocompassing alignment for platform and strapdown systems the proposed method is faster. Its sensitivity to acceleration measurement errors due to bias shift and vehicle motions decreases with elapsed time while it remains constant in the gyrocompassing procedure. The theory is again exemplified for the sensor signals and base motions mentioned above.