Use of Numerical Weather Prediction Fields for the Improvement of Tropospheric Corrections in Global Positioning Applications

A. Jupp, S. Healy, M. Powe, J. Owen, J. Butcher

Abstract:	The modernisation of GPS and the introduction of Galileo will result in tropospheric errors becoming an increasingly significant proportion of the GNSS user's error budget. This paper examines the potential of Numerical weather Prediction (NWP) to provide a tropospheric correction service to the GNSS user. When radio waves propagate through the atmosphere they are delayed and their path is refracted or bent due to gradients in the three-dimensional refractive index field. Such physical effects cause "tropospheric delays" which are difficult to model because of variations in the atmospheric state, particularly water vapour. Typically, a GNSS user's tropospheric corrections are based on a climate model, but by definition such models are based on a mean atmospheric state and thus residual errors will occur. A short-range forecast from a NWP model should provide a better representation of the neutral atmosphere than a model based on climate. This suggests that a tropospheric correction derived from NWP fields should reduce tropospheric errors. This paper investigates the spatial and temporal properties of meteorological features on the tropospheric errors experienced by GNSS users. The potential for the provision of an NWP based real-time service for positioning applications is investigated on a regional and global scale. Strategies for dissemination of tropospheric corrections are discussed and the trade-off between accuracy and correction service bandwidth described. The technique of lossy image compression of tropospheric zenith delay maps is proposed which substantially reduces the quantity of data: to such an extent that the broadcast of a tropospheric correction service through a satellite navigation system becomes a viable proposition.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	377 - 389
Cite this article:	Jupp, A., Healy, S., Powe, M., Owen, J., Butcher, J., "Use of Numerical Weather Prediction Fields for the Improvement of Tropospheric Corrections in Global Positioning Applications," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 377-389.
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