Validation of the GPS TEC maps with TOPEX data

Abstract

The existence of a worldwide IGS (International GPS Service) permanent network of dual frequency receivers, makes feasible the computation of Global Ionospheric Maps (GIM's) of vertical Total Electron Content (TEC). The GIM's computed by the IGS Associate Analisys Centers (IAAC's) are being computed in a daily basis since 1998. The comparison with other kinds of forecast GIM's (computed from the International Reference Ionosphere (IRI) model and the GPS broadcast model) show that the GPS GIM's provide better accuracy and are useful for different applications such as navigation and time transfer. In this context, the performance of both kind of models are presented in this work in order to determine the accuracy of the different Global Ionospheric Maps. This is done by comparing with the TOPEX data that provides an indepentent and precise vertical TEC determination over the oceans (at the level of few TECU) which provides a way of validating the GIM's.