Patent ID: RE42891

Claim:
A method for determining a vehicle's altitude above a predetermined reference level utilizing values of navigation quantities from one or more external sources, an altitude being referenced to the predetermined reference level unless otherwise noted, the method comprising the steps: (a) obtaining values of a plurality of external-source navigation quantities at periodic input intervals, the external-source navigation quantities including a first external-source vehicle altitude , the external source for the first external-source vehicle altitude being an inertial reference system ; (b) obtaining observations at periodic observation intervals of one or more observation quantities, at least one of the observation quantities being a function of a second external-source vehicle altitude, the second external-source vehicle altitude being referenced to the portion of the terrain beneath the vehicle, an observation interval containing one or more of the periodic input intervals; (c) deriving correction data at the periodic input intervals from the observations of step (b); (d) obtaining values of one or more corrected or computed navigation quantities at the periodic input intervals using the correction data of step (c), the one or more corrected or computed navigation quantities including a corrected first external-source vehicle attitude.