Numerical Weather Predictions for Kinematic GPS Positioning

A.B.O. Jensen

Abstract:	When the GPS satellite signals are transmitted through the atmosphere they are affected by the media. In the neutral atmosphere the refraction is a function of pressure, temperature, and humidity along the signal path, and in the GPS positioning process this effect is normally handled by utilising global tropospheric delay models. For high accuracy differential positioning over medium size baselines, where the differential effect of the signal delay from the neutral atmosphere is significant, global models of the signal delay are not sufficiently accurate. This is in particular the case during abnormal weather conditions. This paper describes a solution where numerical weather predictions (NWPs) are introduced in the GPS data processing instead of the global tropospheric delay models. NWPs are predictions of the meteorological conditions for a given area and epoch in time, and can as such be used for estimating the tropospheric delay for a satellite signal by numerical integration along the signal path through the NWP. The signal delay determined from a NWP is often more accurate than the delay determined using a global delay model. For the tests described in this paper the signal delays are determined as a zenith delay through the NWP combined with a mapping function for mapping the signals to lower elevation angles. This new approach for estimating the tropospheric delay is expected to be more useful for kinematic GPS applications, where only one or a few data epochs are available for the positioning process, than for static applications, where the signal delay can be estimated as a part of the adjustment process based on several data epochs. The paper describes the theory of the method, and its applicability is evaluated by analysing position accuracies obtained by introducing NWP-derived signal delays in kinematic processing of GPS data. For the evaluation the high resolution DMI-HIRLAM-E numerical weather prediction provided by the Danish Meteorological Institute is used together with GPS data collected in 14 different sites in Denmark and Southern Sweden.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2285 - 2293
Cite this article:	Jensen, A.B.O., "Numerical Weather Predictions for Kinematic GPS Positioning," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2285-2293.
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