First experience with near real-time water vapor estimation in a German GPS network

The GeoForschungsZentrum (GFZ) has started together with three other resear ch centers of the German Helmholtz Association the "GPS Atmosphere Sounding " Project (GASP) on using ground-based (Subproject I) and space-based (Subp roject 2) GPS observations for applications in the numerical weather predic tions, climate research and space weather monitoring, which this paper focu sses on. The Subproject 1 comprises all necessary components - data links a nd handling, path delay estimation, conversion to water vapor. The GPS and meteorological data are transmitted in hourly batches to the GFZ since Dece mber 1998 and processed with GFZ EPOS software. First experiences with near real-time analysis have been obtained and the operational precision determ ination of water vapor within local GPS networks has been demonstrated with an accuracy of better than 2 mm with a standard deviation at the level of better than I mm. Densification of the test network is progressing from 10 to 100 sites, requiring new analysis strategies. (C) 2001 Published by Else vier Science Ltd.