Comprehensive Validation of the FORMOSAT-7/COSMIC-2 Electron Density Profiles and Its Application to Space Weather

The FORMOSAT-7/COSMIC-2 (F7/C2) mission can provide near 4,000 soundings per day of the Earth's ionosphere by the TriG GNSS Radio occultation System (TGRS) onboard each satellite. The TGRS can receive signals from GPS as the FORMOSAT-3/COSMIC, and additional from GLONASS to increase measurements. In this paper, comprehensive validations of ionospheric electron density profiles, and results of data assimilation system are reported. First, co-located observations are used for self-comparison to prove that the payload is operating normally. Moreover, F2 region peak density (NmF2) and peak height (hmF2) estimated from ionosonde are served as a reference to evaluate the quality of data. The difference of electron density between Jicamarca and F7/C2 reveals a stable bias from 100 to 300 km altitude with slight overestimate. F7/C2 profiles are also highly correlated with worldwide ionosonde soundings, the correlation coefficients for NmF2 and hmF2 are 0.94 and 0.84, respectively. The bias of NmF2 and hmF2 are around 104/cm3 and few kilometers, which indicates F7/C2 measurements are accurate and stable. Even the F7/C2 satellites received signals at the lower orbital altitudes, they can obtain consistent performance of measurements. These dense observations can shorten the data accumulation period to reproduce three-dimensional ionospheric structure and make near real-time monitoring of ionospheric conditions possible. In addition, the data assimilation system is applied to analyze the impacts for ionospheric forecast. The results show significant improvement of the electron density distribution. Detailed validation and investigation are reported in this paper to prove that the profiles retrieved from F7/C2 are reliable and suitable for operational space weather applications.