Processing of CHAMP radio occultation data using GRAS SAF software

The developments of an operational system for processing of radio occultations from the GRAS (Global navigation satellite system Receiver for Atmospheric Sounding) receiver onboard the future Metop satellite is the primary scope of the EUMETSAT proviect: GRAS Satellite Application Facility (SAF). The planned GRAS SAF data products and processing system is discussed together with a preliminary product validation based on statistical analysis of retrieved refractivity and temperature using radio occultation data from the German CHAMP (CHAllenging Minisatellite Payload) satellite. The CHAMP data from the first 8 weeks of 2003 have been processed using the GRAS SAF retrieval system and we present the results as compared to the ECMWF. The mean difference in refractivity is approx. 0.5% with standard deviations less than 1% between 8-25 km and approximately 2% both close to the surface and at 35 km.