ATMOSPHERIC SOUNDING WITH CHAMP: GPS GROUND STATION DATA FOR OCCULTATION PROCESSING

Abstract

The double difference technique is the standard processing method of challenging minisatellite payload (CHAMPs), global positioning system (GPS) occultation data to correct for satellite clock errors. In order to apply this technique, the implementation of a global fiducial GPS ground network is required. This network (“High Rate and Low Latency Network”) was installed jointly by GeoForschungsZentrum Potsdam (GFZ) and Jet Propulsion Laboratory (JPL) in preparation of the CHAMP occultation experiment and is operated jointly by both institutes. Presently (June 2001) it consists of 28 stations (18 funded and operated by JPL, 10 by GFZ). Aspects of utilizing the ground station data for the GPS occultation processing are discussed. The network configuration allows for occultation data processing with about ∼3.5 ground stations per occultation event. The global distribution of that redundancy is found to be irregular. The network fulfills low latency requirements imposed by numerical weather prediction (NWP) systems. For the first time reduced acquisition rates of 1/5, 1/10 and 1/30 Hz compared to the current standard 1 Hz were applied to GPS occultation data processing. For the three resulting sets of 1400 vertical dry temperature profiles (using 1/5, 1/10 and 1/30 Hz, respectively) it was shown that the mean and standard deviation of the dry temperatures in relation to corresponding meteorological analyses are almost identical in relation to those of a referencing 1 Hz data set.