GPS GLONASS SENSING OF THE NEUTRAL ATMOSPHERE - MODEL-INDEPENDENT CORRECTION OF IONOSPHERIC INFLUENCES/

Radio occultation sensing of the terrestrial atmosphere can be perform ed by using signals from Global Positioning System (GPS) or Global Nav igation Satellite System (GLONASS) satellites, which are received by s atellites in low Earth orbit. The signal transmitted from a GPS/GLONAS S satellite, when occulted, suffers propagation effects in the ionosph ere and atmosphere, including carrier and group phase shifts and ray p ath bending. Those propagation effects give direct information on the refractivity of the medium of occultation. In order to sense the neutr al atmosphere only, we have to carefully correct for the ionospheric c ontribution to the propagation effects whose influences are poorly kno wn at present time. In this paper, we provide a straightforward method for model-independent correction of the ionospheric effects based on the correction of the ionospheric bending angle rather than correction of the optical path lengths, as done by previous studies. Using the p resented correction, the accuracy of retrieved temperature profiles of the atmosphere is better than 1 K up to heights of some 55 km during typical ionospheric conditions. The formalism can easily be implemente d in on-line analyses of phase data obtained by the radio occultation technique. This promising technique may thus in fact become an extreme ly valuable tool for supporting climate monitoring as well as weather and climate modeling and prediction.