Abstract:

First GPS radio occultation (RO) measurements aboard the U.S.- German GRACE-B (Gravity Recovery And Climate Experiment) satellite were recorded on July 28 and 29, 2004, providing globally distributed vertical profiles of refractivity, temperature and specific humidity. The profiles show excellent agreement with meteorological analyses. Almost no refractivity bias is observed between 2 and 30 km, the standard deviation is between 1 and 2% within this altitude interval.

The GRACE satellite clock stability is significantly improved in comparison with CHAMP (CHAllenging Minisatellite Payload). This allows for the application of a zero difference technique for precise analysis of the GRACE occultation data. A next campaign was performed between September 23 and 30, 2005 and confirmed the results of the first measurements. A continuous activation of the GRACE occultations would immediately double the number of available precise atmospheric soundings daily and would make a first operational multisatellite occultation mission reality.