The GPS (Global Positioning System)Â radio occultation experiment onboard the GermanÂ CHAMP (CHAllenging Micro satellite payload)Â satellite was successfully started on February 11,2001. By the end of July 2001 about 16,000Â occultations were recorded. More than 80% of theÂ measurements could be processed to derive verticalÂ profiles of atmospheric temperature and specificÂ humidity. Throughout the measurement period GPSÂ anti-spoofing mode was enabled. On average, aboutÂ 230 globally distributed occultations per day wereÂ recorded.
Their distribution shows a characteristicÂ latitudinal dependence with maximum occultationÂ density at polar regions and minimum density in theÂ equatorial region. A statistical comparison of dryÂ temperature profiles, derived from CHAMPÂ measurements, and corresponding meteorologicalÂ analyses shows excellent agreement between 8 and 30 km altitude. For the Northern hemisphere the mean deviation is <0.5 K with a standard deviation of <1 K between 12 and 25 km.A single difference technique was applied to theÂ data analysis.Â
The temperature difference for an individual profile compared to the corresponding data, retrieved by double differencing, is <0.1K below 20 km and <0.5 K below 35 km altitude. Keywords. GPS radio occultation, CHAMP,remote sensing, temperature profiles
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