INVERSION OF GPS METEOROLOGY DATA

The GPS meteorology (GPS/MET) experiment, led by the Universities Corp oration for Atmospheric Research (UCAR), consists of a GPS receiver ab oard a low earth orbit (LEO) satellite which was launched on 3 April 1 995. During a radio occultation the LEO satellite rises of sets relati ve to one of the 24 GPS satellites at the Earth's horizon. Thereby the atmospheric layers are successively sounded by radio waves which prop agate from the GPS satellite to the LEO satellite. From the observed p hase path increases, which are due to refraction of the radio waves by the ionosphere and the neutral atmosphere, the atmospheric parameter refractivity, density, pressure and temperature are calculated with hi gh accuracy and resolution (0.5-1.5 km). In the present study, practic al aspects of the GPS/MET data analysis are discussed. The retrieval i s based on the Abelian integral inversion of the atmospheric bending a ngle profile into the refractivity index profile. The problem of the u pper boundary condition of the Abelian integral is described by exampl es. The statistical optimization approach which is applied to the data above 40 km and the use of topside bending angle profiles from model atmospheres stabilize the inversion. The retrieved temperature profile s are compared with corresponding profiles which have already been cal culated by scientists of UCAR and Jet Propulsion Laboratory (JPL), usi ng Abelian integral inversion too. The comparison shows that in some c ases large differences occur (5 K and more). This is probably due to d ifferent treatment of the upper boundary condition, data runaways and noise. Several temperature profiles with wavelike structures at tropos pheric and stratospheric heights are shown. While the periodic structu res at upper stratospheric heights could be caused by residual errors of the ionospheric correction method, the periodic temperature fluctua tions at heights below 30 km are most likely caused by atmospheric wav es (vertically propagating large-scale gravity waves and equatorial wa ves).