Atmosphere sounding using GPS radio occultation

Introduction On July 17, 1995 the U.S. Air Force announced “ .. that today the Global Positioning System (GPS) satellite constellation has met all requirements for Full Operational Capability”. Apart from precise positioning GPS signals also can be used to derive characteristic properties of the propagation medium (neutral atmosphere and ionosphere). Onboard the Low-Earth-Orbiting MICROLAB-1 satellite (launched on April 5, 1995) GPS signals were recorded, which were transmitted by a setting GPS satellite and tangentially travelled the Earth’s atmosphere (GPS occultation measurements within the GPS/MET-Experiment, Ware et al., 1996). Globally distributed vertical profiles of atmospheric temperature, water vapor and electron density were successfully derived, the GPS radio occultation technique as an innovative remote sensing method became reality. The properties of the calibration-free atmosphere limb sounding technique (e.g. all-weather-capability, high accuracy, high vertical resolution, low cost realization) offer great potential for atmospheric and ionospheric research, improvement of numerical weather forecasts, space weather monitoring and climate change detection (e.g. Anthes et al., 2000; Hajj et al., 2000; Kuo et al., 2000; Kursinski et al., 1997).