IMPROVING THE VERTICAL RESOLUTION OF IONOSPHERIC TOMOGRAPHY WITH GPS OCCULTATIONS

We combine GPS/MET data from 29 occultations and IGS ground data colle cted from 160 stations around the world to perform stochastic tomograp hy of the ionosphere with a 4x20x20 global grid of voxels extending fr om 200 to 650 km above the mean surface of the Earth. A correlation fu nctional approach that limits the spatial high frequency content of th e images is used, and a Kalman filter is applied in the time direction . The combination of ground and occultation data and the use of smooth ing techniques is robust enough for vertical resolution in this four-l ayer model analysis. We discuss the role of noise on the choice of the correct range of eigenvalues in the inversion problem, and the impact of occultation data, showing that ground data alone is insufficient f or vertical resolution even in a three-layer, noise-less simulation.