Bearings-only measurements for INS aiding: the three-dimensional case

The theory behind inertial navigation system (INS) aiding using passive, bearings-only measurements of an unknown ground object is developed. Passive, bearings-only measurements provide an effective means to aid an INS, but only the two-dimensional case was previously considered. This paper addresses the complexities of moving from two-dimensional to three-dimensional space. Stand-alone, bearings-only measurements of an unknown ground object are shown to yield estimates of the aircraft´s aerodynamic angles, viz., the angle of attack and sideslip angle, which in turn are used to aid the INS. Using the synergy of INS state and passive, bearings-only measurements, a powerful navigation algorithm is developed.