Flight Evaluation of Precision Code Differential GPS for Terminal Area Positioning

B. David McNally, David N. Warner Jr., Daniel M. Hegarty, Thomas A. Schultz, Richard Bronson

Abstract:	A Precision Code (P-Code) Differential GPS (DGPS) system has been developed and flight tested at the NASA Ames Research Center. Airborne equipmen& installed in a NASA twin turbo-prop aircraft (Beechcraft King Air 200), includes a 5 channel GPS receiver (Rockwell/Collins RCVR3A), an inertial navigation unit (Litton LN-93). and a real-time computer system. Ground equipment, installed in a mobile reference station, includes an identical receiver and real-time computer. Differential corrections to satellite range and range rate measurements are computed and filtered in the ground reference system, and then uplinked to the aircraft at a rate of 1 set per second. Airborne satellite range and range rate data are fast differentially corrected and then used to compute aircraft position and velocity using an 8 state extended Kalman filter. INU data are used to propagate the DGPS solution between the 1 second GPS epochs. The airborne DGPS solution drives standard approach guidance instruments in the cockpit. This paper presents the results obtained during a flight-test evaluation of real-time P-Code DGPS positioning accuracy for terminal area flight operations. Final approaches were flown from 4-7 miles out at 120 knots. The aircraft was laser tracked during each approach to determine its “true” position. Positioning accuracy for approaches flown during periods of good satellite geometry (PDOP I 6) was 0.1 f0.9m (1 sigma) laterally, and -0.8 f 3.3m (1 sigma) vertically. Pilots commented that the DGPS-based guidance appeared smooth and visually accurate.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	557 - 570
Cite this article:	McNally, B. David, Warner, David N., Jr., Hegarty, Daniel M., Schultz, Thomas A., Bronson, Richard, "Flight Evaluation of Precision Code Differential GPS for Terminal Area Positioning," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 557-570.
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