Publications

The GPS radio occultation experiment within the German geoscience CHAMP (Challenging Minisatellite Payload) satellite mission has been activated now for more than 3 years. More than 250,000 occultation measurements are expected as of April 2004. Since the life time of the CHAMP satellite is predicted to last longer than 2007, the first and unique long-term set of GPS occultation data is anticipated. GFZ provides results of an operational occultation data analysis via the Information System and Data Center (ISDC). The results are available at different processing levels: atmospheric excess phase data, bending angles and vertical profiles of refractivity. Due to the ambiguity of dry and wet component to the refractivity, the bending angles and refractivity profiles are currently used to provide additional information for the data assimilation to improve the numerical weather forecast. First impact studies already demonstrated the ability of the CHAMP refractivity data to improve the global forecasts. The temperature profiles, provided at ISDC, are calculated assuming that the air is dry. The resulting dry temperature profiles are almost identical with the real temperature at altitudes above 10 km, where the wet component of the refractivity can be neglected. However, vertical profiles of the tropospheric temperature and water vapor can only be derived using ancillary atmospheric information from e.g. meteorological analyses (either temperature or water vapor). Tropospheric water vapor and temperature profiles are derived using the improved version (005) of GFZ’s operational refractivity profiles, which will be provided via ISDC by about mid 2004. The Full Spectrum Inversion (FSI) technique is used for the data analysis in the lower troposphere. To combine the measurements with the ancillary meteorological information in a statistically optimal way an operational 1Dvar retrieval code is used for the water vapor profiling. The results are validated with ECMWF analyses and radiosonde data.

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Heise, S.; Wickert, J.; Beyerle, G.; Schmidt, T.; Kaschenz, J.; Healy, S. B.; v. Engeln, A.; Reigber, C. (2004): GPS radio occultation with CHAMP: Operational derivation of vertical water vapor profiles. 1st General Assembly European Geosciences Union (Nice, France 2004).