New approaches in global ionospheric determination using ground GPS data

Since 1 June 1998, the group of Astronomy and Geomatics of the Polytechnic University of Catalonia (gAGE/UPC) is contributing to the international pro ject of defining an ionospheric product (Total Electron Content, TEC) from the data gathered by the permanent ground GPS receivers of the Internationa l GPS Service (IGS) network. The strategy and algorithms related to such a preliminary product, its calibration with synthetic observations generated from the International Reference Ionosphere (IRI), and the comparison with TOPEX TEC data are presented. Finally, these methods are applied combining ionosonde with ground GPS data, in order to obtain the vertical structure o f the free electron distribution. (C) 2000 Elsevier Science Ltd. All rights reserved.