Near Real-Time Water Vapor Monitoring in a German GPS Network and Assimilation into Weather Forecast Model

Christoph Reigber, Gerd Gendt, Galina Dick and Maria Tomassini

Abstract:	In the framework of the “GPS Atmosphere Sounding Project” (GASP) of the German Helmholtz Association operational determination of vertical integrated water vapor (IWV) in near real-time is performed since May 2000 within a dense German GPS network for applications in numerical weather predictions and climate research. The estimation of IWV with a delay of 40 minutes has demonstrated an accuracy of better than 2 mm with a standard deviation at the level of ±1 mm. This accuracy is sufficient for introducing GPS technology results into the operational weather forecast. The analysis is performed with the GFZ EPOS software in sliding 12- hour windows using parallel analysis of station clusters with the Precise Point Positioning strategy. The GASP network is steadily increasing and consists presently of approximately 100 sites. Further densification of the test network to more than 100 sites is foreseen in the next future. The NRT results are compared with the postprocessed estimates and validated using co-located instruments, namely water vapor radiometer and radiosondes. GPS observations have also been compared regularly with the output of the limited-area model of the German Weather Service to check the observation quality and to validate the model output. The comparisons indicate that the quality of the GPS results is acceptable for data assimilation purposes. Some cases of disagreement between GPS and model IWV values could be explained as shortcomings of the model due to the poor time resolution of conventional observations. This confirms the high potential of the GPS technique for the detection of rapidly evolving meteorological phenomena, e.g. frontal passages. Work is currently being carried out to use the GPS data in the forecast model and first results from assimilation experiments will be discussed.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1084 - 1093
Cite this article:	Reigber, Christoph, Gendt, Gerd, Dick, Galina, Tomassini, Maria, "Near Real-Time Water Vapor Monitoring in a German GPS Network and Assimilation into Weather Forecast Model," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1084-1093.
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