The Charles Stark Draper Laboratory, Inc.

William A Drohan

J Arnold Soltz

Glenn Mamon

A method and apparatus for surveying ground terrain from an airborne vehicle is disclosed. According to the method and apparatus, an inertial measurement unit, a position tracking device, and a terrain altimeter are carried by the airborne vehicle in a known vector relationship to one another. The inertial measurement unit provides continuous accelerometer data from which a first determination of vehicle position can be made. Simultaneously, data from the tracking device representative of the position of the tracking device relative to cooperating reflection means on the ground, if within sight of the airborne vehicle, provides, in combination with gimbal angle sensor outputs from the inertial measurement unit, an independent determination of the position of the vehicle. The two position measurements, when available, are continuously compared in real time on board the vehicle and error corrections are generated therefrom by estimation theory. The generated error corrections are stored and updated in real time and error correction signals are preferably provided to at least the inertial measurement unit to correct errors due, for example, to drift in the unit. The airborne vehicle can thereby be out of sight of the cooperating reflection means for substantial time durations without substantially degrading the accuracy of the position information. Corrected positional information, which includes the generated error corrections, and the correlated output of the terrain altimeter are stored to provide a profile of the region over which the vehicle flies. In preferred embodiments of the invention, both the position tracking device and the terrain altimeter are laser devices.

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Bedford, MA, United States of America

William A Drohan