Assessment of DGPS-Derived Aircraft Trajectories by Comparison with Continuous Kinematic GPS Positioning

Larry D. Hothem, Carlos L.V. Aiken and Mamadou Balde

Abstract:	In May 1991 and May 1992, near Phoenix, Arizona, USGS conducted airborne Global Positioning System (GPS 1 experiments). The experiments demonstrated the application of GPS to determine coordinates for the camera exposure stations of airborne photogrammetry. Each experiment included at least three separate missions with observations performed between about 10:00 AM and 2:00 PM. The flight altitudes were approximately 6000 meters. Data were collected at one-second intervals with dual-frequency receivers on the aircraft and at four or more ground stations. During the 1991 experiment, the separation between each of four ground stations and the center of the project area were approximately 20, 100, 550 and 600 km. The data collected simultaneously in 1992 involved seven ground stations located about 20, 100, 200, 505, 550, 930, and 1010 km from the project's center. The observables collected in 1991 included C/A code pseudorange, Ll carrier phase, and L2 codeless carrier phase. In 1992, the data sets contained the additional observables of Ll and L2 P-code pseudoranges and L2 full-wavelength carrier phase measurements. The ground station tracking data, supplemented by additional data from CIGNET (Cooperative International GPS Network) stations located in North America, were processed by multi-station orbital adjustment methods. These solutions yielded coordinates with an internal consistency at the 5 cm level and ties to an earth-centered global reference frame. The coordinates from these solutions were fixed in the differential GPS (DGPS) and kinematic solutions for the aircraft trajectories. The aircraft data were processed with several independently developed post-processing software packages. To obtain estimates for the internal consistency of the aircraft coordinates, we compared results from solutions using different ground stations for the fixed reference. We estimated the accuracy for the carrier smoothed DGPS-derived aircraft trajectories by comparing with the few cm-level continuous kinematic coordinate data. Several factors influenced the accuracy of the DGPS-derived aircraft trajectories. These included satellite geometry, number of satellites observed, multipath, orbital accuracy, distance between the aircraft and the reference station, and robustness of the processing algorithms. Initial estimates for the DGPS-derived aircraft coordinate data ranged within 3 meters rms.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	1079 - 1090
Cite this article:	Hothem, Larry D., Aiken, Carlos L.V., Balde, Mamadou, "Assessment of DGPS-Derived Aircraft Trajectories by Comparison with Continuous Kinematic GPS Positioning," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 1079-1090.
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