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.