The use of empirical models to investigate GPS derived total electron content

Hourly values of two months of Total Electron Content (TEC) calculated from Global Positioning System (GPS) Satellites observations of Doppler effect using a technique developed at the IROE of Florence, Italy (Ciraolo, 1993) are studied together with simultaneous measurements of Geostationary Satellite Faraday TEC obtained at a different location in Europe. These experimental data are compared with TEC values calculated by using DGR and IRI-90 empirical models of the electron density in the ionosphere based on ionospheric characteristics obtained from vertical sounding at locations near the two places where TEC from satellite observations are obtained. The results show that the correlation of experimental and model data is good in daytime. Night-time values of GPS (TEC) is not well correlated with the model calculations possible indicating that this technique sees an additional distribution of ionization from the one obtained by Faraday observations and the empirical models used. (author). 4 refs, 2 figs, 2 tabs