TABLE OF CONTENTS Alignment is the process whereby the orientation of the axes of an inertial navigation system is determined with respect to the reference axis system. The basic concept of aligning an inertial navigation system is quite simple and straight forward. However, there are many complications that make alignment both time consuming and complex. Accurate alignment is crucial, however, if precision navigation is to be achieved over long periods of time without any form of aiding.
In addition to the determination of initial attitude, it is necessary to initialise the velocity and position defined by the navigation system as part of the alignment process. However, since it is the angular alignment which frequently poses the major difficulty, this chapter is devoted largely to this aspect of the alignment process.
In many applications, it is essential to achieve an accurate alignment of an inertial navigation system within a very short period of time. This is particularly true in many military applications, in which a very rapid response time is often a prime requirement in order to achieve a very short, if not zero, reaction time.
There are two fundamental types of alignment process: self-alignment, using gyrocompassing techniques, and the alignment of a slave system with respect to a master reference. There are various systematic and random errors that limit the accuracy to which an inertial navigation system can be aligned, whichever method is used. These include the effects of inertial sensor errors, data latency caused by transmission delays, signal quantisation, vibration...
