Numerical Weather Predictions for GPS Positioning
When 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 baselines lengths where the differential effect of the signal delay from the neutral atmosphere is significant, these global models of the signal delay are not sufficiently accurate, and this is especially the case during abnormal weather conditions.
This paper describes a new approach where numerical weather predictions (NWPs) are introduced in the GPS data processing instead of 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. For the tests described in this paper, the signal delays are determined as a zenith delay through the NWP combined with a mapping function. This approach is useful for kinematic and shorter static GPS applications. The paper describes the theory of the method, and the applicability of the method is evaluated by analysing position accuracies obtained by introducing NWP-derived signal delays in kinematic and static processing of GPS data. Improved position accuracies are obtained for most of the test scenarios, indicating that the method does have a potential.
KeywordsGPS positioning numerical weather predictions (NWP) tropospheric delay
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- 1.Beutler, G., E. Brockmann, R. Dach, P. Fridez, W. Gurtner, U. Hugentobler, J. Johnson, L. Mervart, M. Rothacher, S. Schaer, T. Springer, R. Weber (2000). Bernese GPS Software. Astronomical Institute, University of Berne.Google Scholar
- 3.Brunner, F. K., M. Gu (1991). An improved model for the dual frequency ionospheric correction of GPS observations. Manuscripta Geodaetica, 16:205–214.Google Scholar
- 4.Cannon, M. E. (1997). Carrier Phase Kinematic Positioning: Fundamentals and Applications. In Geodetic Applications of GPS, Lecture Notes for Nordic Autumn School edited by Bo Jonsson. Number 16 in Reports in Geodesy and Geographical Information Systems, National Land Survey of Sweden.Google Scholar
- 5.Hopfield, H.S. (1969). Two-quartic Tropospheric Refractivity Profile for Correcting Satellite Data. Journal of Geophysical Research, 74(18): 4487–4499.Google Scholar
- 6.Jensen, A. B. O., M. E. Cannon (2000). Performance of Network RTK Using Fixed and Float Ambiguities. Proceedings of the 2000 National Technical Meeting of the Satellite Division of the Institute of Navigation (ION NTM 2000). Pages 797–805.Google Scholar
- 7.Jensen, A. B. O. (2002). Numerical Weather Predictions for Network RTK. Publication Series 4, volume 10. National Survey and Cadastre — Denmark.Google Scholar
- 8.Johansson, J. M. (1997), Modelling of the Earth Atmos-sphere in Space Geodetic Applications. In Geodetic Applications of GPS, Lecture Notes for Nordic Autumn School edited by Bo Jonsson. Number 16 in Reports in Geodesy and Geographical Information Systems, National Land Survey of Sweden.Google Scholar
- 9.Langley, R. (1996). Propagation of the GPS Signal. In Kleusberg, A. and P. J. G. Teunissen (eds) GPS for Geodesy, Lecture Notes in Earth Sciences. Springer-Verlag.Google Scholar
- 10.Mendes, V. B. (1999). Modelling the neutral-atmosphere propagation delay in radiometric space techniques. Ph.D. dissertation. Report number 199. Department of Geodesy and Geomatics Engineering, University of New Brunswick, Fredricton.Google Scholar
- 12.Pany, T., P. Pesec, G. Stangl, (2001). Atmospheric GPS Slant Path Delays and Ray Tracing Through Numerical Weather Models, a Comparison. Physics and Chemistry of the Earth. 26A(3):183–188.Google Scholar
- 13.Saastamoinen, J. (1973). Contributions to the Theory of Atmospheric Refraction. Bulletin Geodesique. Printed in three parts, 105:279–298, 106:383–397, 107:13–34.Google Scholar
- 14.Sass, B. H., N. W. Nielsen, J. U. Jorgensen, B. Amstrup, M. Kmit (2000). The Operational HIRLAM System at DMI. Scientific Report 00-26. Danish Meteorological Institute. CopenhagenGoogle Scholar
- 15.Schueler, T. (2001). On Ground-based GPS Tropospheric Delay Estimation. Ph.D. thesis, Universitdt der Bundeswehr, München.Google Scholar
- 16.Seeber, G. (1993). Satellite Geodesy. Foundations, Methods and Applications. Walter de Gruyter.Google Scholar
- 17.Vedel, H., K. S. Mogensen, X.-Y. Huang (2001). Calculation of zenith delays from meteorological data, comparison of NWP model, radiosonde and GPS delays. Physics and Chemistry of the Earth, 26A(6–8):497–502.Google Scholar