Ionospheric tomography based on GNSS observations of the CMONOC: performance in the topside ionosphere

This study carries out a quantitative analysis of the performance of ionospheric tomography in the topside ionosphere, utilizing data of October 2011 collected from 260 Global Navigation Satellite System (GNSS) stations in the Crustal Movement Observation Network of China. This tomographic reconstruction with a resolution of 2° in latitude, 2° in longitude and 20 km in altitude has more than 70 % of voxels traversed by GPS raypaths and is able to provide reliable bottom parts of ionospheric profiles. Compared with the observations measured by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17 and F18) at an altitude of 830–880 km, the results show that there is an overestimation in the reconstructed plasma density at the DMSP altitude, and the reconstruction is better during daytime than nighttime. In addition, the reconstruction at nighttime also indicates a solar activity and latitudinal dependence. In summary, with respect to DMSP measurements, the daytime bias is on average from −0.32 × 105/cm3 to −0.28 × 105/cm3, while the nighttime bias is between −0.37 × 105/cm3 and −0.24 × 105/cm3, and the standard deviation at daytime and at nighttime is, respectively, 0.082 × 105/cm3 to 0.244 × 105/cm3 and 0.086 × 105/cm3 to 0.428 × 105/cm3. This study suggests that vertical ionospheric profiles from other sources, such as ionosondes or GNSS occultation satellites, should be incorporated into ground-based GNSS topside tomographic studies.