Modeling of Low-Latitude Ionosphere Using GPS Data With SHF Model

The Indian ionosphere is characterized by large variations, irregularities, and equatorial anomaly conditions. Therefore, an appropriate ionospheric model is necessary for satellite-based navigation systems. An ionospheric model based on spherical harmonic function (SHF) is used for modeling. Using the basis functions and measured vertical total electron content (TEC) data, spherical harmonic coefficients are computed by a weighted least square method. Seventeen stations of GPS Aided Geo Augmented Navigation TEC data are considered in the analysis. The results of the SHF model are presented in terms of accuracy of the residual error and compared with other standard grid models. The diurnal TEC variations are well depicted using the SHF model. The summer- and autumn-equinox-season ionospheric delay variations are also presented. The results indicate that the SHF model is capable of estimating ionospheric delays well.