Comparison Between GPS Radio Occultation and Radiosonde Sounding Data

Global Positioning System (GPS) Radio Occultation (RO) is a new technique for obtaining profiles of atmospheric properties, specifically: refractivity, temperature, pressure, water vapor pressure in the neutral atmosphere, and electron density in the ionosphere. The data received from GPS RO contribute significant amounts of information to a range of fields including meteorology, climate, ionospheric research, geodesy, and gravity. Low-Earth orbiting satellites, equipped with a GPS receiver, track GPS radio signals as they set or rise behind the Earth. Since GPS signals are refracted (delayed and bent) by the Earth's atmosphere, these data are used to infer information about atmospheric refractivity. Before the GPS RO data are used for research and operations, it is essential to assess their accuracy. Therefore, this research provided quantitative estimates of the accuracy of GPS RO when compared with measurements of known accuracy. Profile statistics (mean, standard deviation, standard error) were computed as a function of altitude to quantify the errors. Comparing RO data with nearby (300km; 2hr) radiosonde data yielded small mean error for all of the statistical plots generated, affirming that the RO technique is accurate for measuring atmospheric properties. Comparison of RO data with sounding data from different radiosonde systems showed that the RO technique was of high enough accuracy to differentiate differences in performance of various types of radiosonde systems. The results indicated that India’s IM-MK3 radiosonde has the greatest amount of uncertainties and Australia's Vaisala radiosonde has the least amount of uncertainties.