Phase-Difference Approach for GNSS Global Ionospheric Total Electron Content Mapping

The paper proposes an ingenious method for global ionospheric total electron content (TEC) mapping based on a phase-difference approach to the analysis of phase measurements of GNSS signals at a pair of coherent frequencies on a distributed network of ground-based receivers of the global IGS network. The proposed approach uses the representation of the ionosphere as a thin layer with the TEC distribution given by a truncated expansion into a series of spherical harmonics in the Sun-synchronous geomagnetic coordinate system. The expansion coefficients are determined by the least squares technique with a TEC positivity constraint, which is implemented by solving the corresponding linear complementarity problem. The proposed method does not require estimation of the differential code biases of both satellites and receivers, which makes it possible to combine data from various GNSS, such as GPS, GLONASS, and Galileo, within a single algorithm. The results of testing the proposed method on synthesized observation data using the real geometry of GNSS satellites, IGS receivers, and the ionosphere given by the NeQuick2 model, are presented. The results of comparing the real global ionospheric maps obtained by the proposed method and the maps of the CODE center are reported.