Impact of Radiometric Water Vapor Measurements on Troposphere and Height Estimates by GPS

P. Haefele, L. Martin, M. Becker, E. Brockmann, J. Morland, S. Nyeki, C. Matzler, M. Kirchner

Abstract:	The Measurement of Alpine Tropospheric Delay by Radiometers And GPS (MATRAG) project was designed to study the limits of precise GPS height determination and to answer the question of how radiometric water vapor measurements can contribute to this and to the GPS estimation of tropospheric delays. The measurements with Water Vapor Radiometers (WVR) and GPS were conducted at dedicated stations in Central Switzerland in September 2003. In this paper we will first concentrate on the technique of radiometry itself with the goal of assessing the calibration and stability of different types of WVRs. Results of simultaneous measurements of several instruments were used to determine the accuracy of state-of-the-art devices. They are consistent at the 1.2 kg/m2 level with an uncertainty of ± 0.5 kg/m2. The validation of GPS-derived tropospheric estimates – namely the zenith total delays – by WVR is presented in the second part of this paper, where we find a mean difference between GPS and WVR results of about 4.5 ± 5.3 mm. The last part of the paper focuses on the analysis of two particular baselines within the triangle Zimmerwald, Bern and Jungfraujoch. This triangle with height differences of about 3,000 m and short baselines of 10 and 50 km was observed simultaneously by WVR and GPS. The analysis of these baselines was accomplished with various strategies and different levels of a-priori information for the GPS estimation, i.e. introduction of meteorological observations and / or WVR wet delays. Resulting biases in estimated station heights of up to 2 cm are studied as well as station height repeatabilities of 3 to 5 mm and estimated tropospheric delays. The observed biases are mainly introduced by the WVRs, whereas the elevation cut-off dependent height offsets are caused by commonly known GPS error sources such as Multipath and antenna phase center variations.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2289 - 2302
Cite this article:	Haefele, P., Martin, L., Becker, M., Brockmann, E., Morland, J., Nyeki, S., Matzler, C., Kirchner, M., "Impact of Radiometric Water Vapor Measurements on Troposphere and Height Estimates by GPS," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2289-2302.
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