Monitoring the 3 dimensional ionospheric electron distribution based on GPS measurements

In the last decade GPS has become a valuable tool for determining various ionospheric and neutral atmospheric parameters. The presently existing global and regional networks of GPS ground stations (e.g. regional surveying offices, International GPS service IGS) open the opportunity to establish monitoring systems to estimate ionospheric and tropospheric/stratospheric key-parameters (e.g. electron content, temperature, water vapour) on a regular base. Here first results of a 3 dimensional ionospheric electron density monitoring system applied for the European region are reported. The system is generally based on continuous GPS derived TEC measurements from the dense European IGS network and uses model assisted (IRI, Gallagher model) iterative algebraic methods to solve the inversion problem. Nevertheless, even in dense GPS networks the available number of measurements are inevitably sparse, and the combination of ground-based measurements gives not fully satisfying vertical resolution. Therefore ionosonde and radio occultation data, as those of CHAMP, have been used to improve the image reconstruction.