G. B. Larsen

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 project: 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.

The GPS Occultation Sensor for NPOESS

The Global Positioning System Occultation Sensor (GPSOS) is a precision GPS instrument carried by the NPOESS spacecraft. It measures primarily the electron density profile and scintillation parameters of the ionosphere. The measurements are obtained by tracking signals of GPS satellites that are observed to rise or set through the atmosphere while recording the signal amplitude and phase.

GPS Atmosphere and Ionosphere Methods used on Ørsted Data and Initial Application on CHAMP Data

The launch of the Orsted satellite started a range of activities to verify GPS occultation measurements of the Earth atmosphere and ionosphere based on observations of GPS signal delay from a low Earth orbiting satellite. The Orsted satellite followed the GPS/MET satellite experiment as the second mission in space to perform these types of measurements. Now the CHAMP satellite and also the SAC-C satellite are producing GPS occultation measurements in large numbers in long time-series and the data are just available since November 2001. The aim of this paper is to present an overview of the retrieval techniques used on the observations with the TurboRogue receiver on Orsted and the results obtained both for the atmosphere and ionosphere. The results of CHAMP occultations using orsted processing tools will be presented and compared with Orsted.