GPS ground station data for CHAMP radio occultation measurements

The role of GPS ground station data for the CHAMP Atmospheric Profiling exp eriment is discussed. The profiling activities at GeoForschungZentrum Potsd am (GFZ) are briefly described and first results of the occultation process ing system are presented. The atmospheric excess phase of the occultation l ink between the CHAMP and the GPS satellite is derived by a double differen ce method using ground station data. The influence bf ground station data o n the accuracy of the derived atmospheric profiles is discussed. A relation ship between the temperature errors at several heights resulting from error s in atmospheric excess phase is given, e.g. an error of 1 mm/s in the time derivative of the excess phase results in a temperature error of 1 K at 30 km. Furthermore, a study was performed to estimate the required data rate of the ground station measurements. In particular the influence of the Sele ctive Availability (SA) termination on May 2, 2000 is emphasized. We conclu de that the acquisition rate can be reduced from 1 Hz to 0.1 Hz without los s of information, Simulations of the CHAMP occultation experiment show that the joint Jet Propulsion Laboratory, Pasadena (JPL) & GFZ "high rate & low latency" network enables the processing of globally distributed occultatio n events with a highly redundant number of ground stations. Latency aspects are studied in view of the future task of providing atmospheric occultatio n data for operational weather forecast. (C) 2001 Elsevier Science Ltd. All rights reserved.