Initial Results of GPS-LEO Occultation Measurements of Earth’s Atmosphere Obtained with the GPS-MET Experiment

The radio occultation technique, which has been repeatedly proven for planetary atmospheres, was first utilized to observe Earth’s atmosphere by the GPS-MET experiment (launched in April 1995), in which a high performance GPS receiver was placed into a low-Earth orbit. During certain phases of the mission, more than 100 occultations per day are acquired. A subset of this occultation data is analyzed and temperature in the neutral atmosphere and electron profiles in the ionosphere are obtained. Comparing about 100 GPS-MET retrievals to accurate meteorological analyses obtained from the European Center for Medium-range Weather Forecasting at heights between 5–30 km, temperature differences display biases of less than 0.5K and standard deviations of 1–2K in the northern hemisphere, where the model is expected to be most accurate. Furthermore, electron density profiles obtained for different geodetic locations and times show the main features that are expected in the ionosphere.