Near real-time water vapor estimation in a German GPS network-first results from the ground program of the HGF GASP project

For the ground-based part of the GPS Atmosphere Sounding Project (GASP) the near real-time monitoring of integrated water vapor with a delay of 1.5 ho urs was demonstrated for 35 sites and the data retrieval for 46 sites is al ready in progress. Comparisons to postprocessed results as well as validati on with independent techniques and models show that an accuracy of 1-2 mm i n the precipitable water vapor could be achieved. To make this possible als o software for Ultra Rapid orbit predictions (10-20 cm accuracy) and interp olation within surface meteorological data from synoptic networks (0.3hPa a ccuracy) were developed. (C) 2001 Elsevier Science Ltd. All rights reserved .