The navigation potential of ground feature tracking for aircraft navigation

Inertial Navigation System (INS) aiding using bearing - only measurements of stationary ground features is investigated. The objective is to quantify the navigation information obtained by tracking ground features over time. The answer is provided by an analysis of the attendant observability problem. The degree of INS aiding action is determined by the degree of observability provided by the measurement arrangement. The latter is strongly influenced by the nature of the available measurements - in our case, bearing measurements of stationary ground objects - the trajectory of the aircraft, and the length of the measurement interval. It is shown that during wings level flight at constant speed and a fixed altitude, and when one known ground object is tracked, the observability Grammian is rank deficient and thus full INS aiding action is not available. However, if at least two known ground features are simultaneously tracked the observability Grammian is full rank and all the components of the navigation state vector are positively impacted by the external measurements.