The Effect of Tropospheric Propagation Delay Errors in Airborne GPS Precise Positioning

Virgilio Mendes, J. Paul Collins, and Richard Langley

Abstract:	When operating in an airborne environment, test results have shown that ambiguity resolution is particularly sensitive to errors in the tropospheric delay models applied to the carrier phase observations. Since the aircraft is at a higher altitude than the ground-based reference station, the model must accurately represent the relative tropospheric delay caused by the altitude difference. In kinematic applications, the zenith tropospheric delay can be determined with prediction models such as Saastamoinen’s using pressure, temperature, and humidity measurements. This zenith delay is then mapped to other elevation angles using mapping functions such as those of Ifadis or Niell. This paper highlights the performance of several widely used tropospheric delay models, including the model currently proposed for the FAA’s WAAS. The accuracy of this model is assessed by (1) comparisons with ray tracing through an extensive set of radiosonde data, covering different latitudes, and (2) analyzing position solutions and the carrier phase observation residuals of GPS flight tests. We conclude that (1) the tropospheric delay error is mainly due to the inaccuracy of the zenith delay determination, and (2) a combination of a zenith delay model with the Niell or Ifadis mapping functions yields improved solutions, as compared to the currently proposed WAAS model.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1681 - 1689
Cite this article:	Mendes, Virgilio, Collins, J. Paul, Langley, Richard, "The Effect of Tropospheric Propagation Delay Errors in Airborne GPS Precise Positioning," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1681-1689.
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