Ingesting GPS-derived TEC data into the International Reference Ionosphere for single frequency radar altimeter ionospheric delay corrections

Abstract

At the University of New Brunswick (UNB), we have developed the capability to independently produce hourly global total electron content (TEC) maps from Global Positioning System (GPS) data. UNB's hourly GPS-derived global TEC maps can be ingested directly into a modified version of the International Reference Ionosphere 1995 (IRI-95) model and augmented with a plasmaspheric electron content model to update its coefficient sets. We present a technique to provide improved IRI-95 predictions by using the modified model as a sophisticated interpolator between hourly GPS-derived TEC updates. The updated IRI-95 coefficient sets will make it possible to provide ionospheric delay corrections for various applications including single frequency radar altimeter missions such as the upcoming Geosat Follow-On mission. Since the spacecraft will be orbiting “inside” the ionosphere, our GPS-updated IRI-95 electron density profile will allow us to integrate the electron densities up to the spacecraft altitude to remove the bias imposed by the ionosphere. This would not be possible using GPS-derived TEC alone since it provides integrated electron content up to the altitude of the GPS satellites (20,200 km). In this paper, we present results based on 3 days' worth of global GPS data (33 International GPS Service for Geodynamics (IGS) stations) at a medium solar activity time (year 1993) and 3 days' worth of global GPS data (74 IGS stations) at a low solar activity time (year 1995). We also compare our updated IRI-95 predictions using UNB's global TEC maps and the original IRI-95 predictions, against TOPEX/Poseidon (T/P) dual frequency altimeter-derived TEC data. Based on 3 days' worth of global GPS data during the medium solar activity time in 1993, the results show that there was better than a 9 TECU level (1 sigma) agreement in the total electron content on a global scale with the T/P-derived TEC data using the UNB technique. For the 1995 low solar activity time, our results agreed with the T/P data at better than the 5 TECU level (1 sigma). These results suggest than our method may be viable for providing ionospheric delay corrections for future single frequency altimeter missions.