A Multi-Parameter Global Electron Density Model (GEDM) From GNSS Radio Occultation Data

The precise 3-D ionospheric electron density (IED) modeling is in general difficult due to costly and insufficient observations in the ionosphere. The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission has provided a significant opportunity for estimating the IED profile during the past 15 years. In this article, a precise empirical 3-D global electron density model (GEDM) from COSMIC GNSS radio occultation (RO) data is developed based on Fourier expansion and principal component analysis (PCA) and evaluated with independent datasets. Each profile is described by five essential parameters: the mean scale height Hm, bottom and topside slopes of the scale height (a1 and a2), peak density of the F2 layer (NmF2), and height of the F2 layer peak density (hmF2). The GEDM model can provide IED at any local time (LT) (0–24 h), F10.7 (70–150 sfu), Kp (0–9), latitude (90°S–90°N), longitude (180°W–180°E), and altitude, especially in the F region. The model is validated by the incoherent scatter radar (ISR), International Reference Ionosphere (IRI)-2020, K-Band Ranging system (KBR) of the Gravity Recovery and Climate Experiment (GRACE), and the Global Ionospheric Map (GIM) TEC in 2010 and 2014. The results show that the GEDM model has preferable reliability and consistency with respect to the independent observations and the IRI-2020 model. The statistical error of the GEDM model is lower than that of the IRI-2020, particularly in the mid-latitude region. Furthermore, the GEDM model is capable of precisely capturing typical ionospheric features, such as the equatorial ionization anomaly (EIA), winter anomaly, and the annual anomaly.