Global atmospheric sounding with GPS radio occultation aboard CHAMP

Abstract

The German CHAMP (CHAllenging Minisatellite Payload) satellite provides continuously GPS radio occultation data since February 2001. The measurements are analyzed by an operational satellite orbit and occultation processing system at GFZ. In total, more than 200,000 precise globally distributed vertical profiles of refractivity, temperature and water vapor are provided as of June 2005. The operational ground infrastructure from GFZ allows for the demonstration of a rapid data analysis since February 2003. A mean delay between measurement and provision of atmospheric excess phase data of ∼4 hours is continuously reached. Results of various validation studies with data from meteorological analyzes of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the global radiosonde network indicate an excellent quality of the CHAMP data. But in the lower troposphere systematic deviations are observed, the known negative refractivity bias of the occultation data. It is most pronounced in the Tropics and is also observed by other GPS occultation instruments. The CHAMP data stimulated a number of studies to investigate the observed bias and to improve the GPS occultation data quality in the lower troposphere. First radio occultation measurements from the GRACE-B (Gravity Recovery And Climate Experiment) satellite are available for a 25 h period on July 28/29, 2004. © 2006 Springer-Verlag Berlin Heidelberg.