The GRAS SAF radio occultation processing intercomparison project ROPIC

Abstract

Global Navigation Satellite System (GNSS) based radio occultation (RO) measurements promise to be valuable observations to supplement the data base used for numerical weather prediction, atmospheric process studies, and climate research. Especially in the latter case it is important to fully understand the influence of the particular processing (algorithms, implementations, and used parameters) on the quantities used for further studies. To assess the impact of different algorithms and implementations used to derive bending angles and refractivities and to identify possible systematic deviations three centers routinely processing RO data had been given an identical excess phase and orbit (Level 1a) CHAllenging Minisatellite Payload (CHAMP) data set comprising observations from two months. To probe the robustness and possible dependences of the processing results on atmospheric conditions the middle month of the winter and summer season 2005 had been chosen. The results after an external quality control indicate a good agreement of the data sets between 5 km and 40 km for bending angles and refractivity depending on latitude, although the Wegener Center for Climate and Global Change (WEGC) data set exhibits systematic deviations compared to Danish Meteorological Institute (DMI) and Deutscher Wetterdienst (DWD). At high altitudes, the different initialization strategies are visible in the processed data. The Radio Occultation Processing Center Intercomparison Campaign (ROPIC) was conducted by the Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) Satellite Application Facility (SAF). © 2009 Springer-Verlag Berlin Heidelberg.