Global ionospheric total electron content mapping using the global positioning system

Space-based radio navigation systems such as the Navstar Global Positioning System (GPS) can provide us with a unique opportunity to study the effect of the ionosphere as the signals propagate from the satellites to the GPS receivers.; Based on a modified version of UNB's DIPOP software package, I developed an algorithm to produce regional or global total electron content (TEC) maps on an hourly basis using dual frequency-GPS observations from stations of the International GPS Service for Geodynamics (IGS). The algorithm uses a spatial linear approximation of the vertical TEC above each IGS station using stochastic parameters in a Kalman filter estimation to describe the local time and geomagnetic latitude dependence of the TEC. I used a new concept to take into account the temporally and spatially varying ionospheric shell height as opposed to a commonly adopted fixed shell height. I demonstrated that the UNB algorithm was capable of modelling the diurnal variation of TEC even during a geomagnetic storm period. I also have modified the International Reference Ionosphere 1995 (IRI-95) model to update its coefficient sets using the UNB GPS-derived regional ionospheric maps, based on a 5 week long GPS campaign, in order to provide more precise IRI-95-derived ionospheric delay predictions for e.g., single frequency GPS receivers.; I enhanced the UNB algorithm to estimate ionospheric model parameters from a global set of GPS stations to independently produce hourly snapshots of the global ionosphere. The previously modified IRI-95 model as a sophisticated interpolator was used between two GPS-derived TEC updates to provide improved IRI-95 ionospheric delay predictions. During the update procedure, I enhanced the IRI-95 model with an empirical plasmaspheric electron content model.; Based on 3 days' worth of global GPS data during a medium solar activity period in 1993 (33 IGS stations for each day) there was better than a 9 TECU level (1 sigma) agreement in the TEC on a global scale with TOPEX/Poseidon-derived (T/P) TEC data. For a low solar activity 1995 data set (74 IGS stations for each day), the UNB results showed an agreement with the T/P data at better than the 5 TECU level (1 sigma).; The UNB global ionospheric TEC modelling technique in conjunction with the IRI-95 update procedure has been demonstrated to be a viable alternative to provide independently-derived ground-based ionospheric delay corrections for single frequency applications such as single frequency radar altimeter missions.