# Evaluation of GNSS-TEC Data-Driven IRI-2016 Model for Electron Density
## 3 Results  
### Accuracy Analysis of Electron Density Profile  
#### 3.1.1 Comparison with Ionosonde Data  
As an example, the electron density profiles of the two ionosonde data are shown for the two stations in Beijing and Wuhan from 00:00 to 07:30 UT (with a time interval of 90 min) on day 8 of 2015 and day 8 of 2019, compared with the electron density profiles output from the IRI-2016 model driven by IG12 and IG-up, respectively, as shown in Figures 1-4. In particular, the black dotted line indicates the electron density profiles of the ionosonde observations, the green solid line indicates the electron density profiles output with the original IRI-2016 driven by IG12, and the red solid line indicates the electron density profiles output with the IRI-2016 driven by IG-up (upda-IRI-2016), and the figure name on each subfigure identifies the electron density profile generation and the time and place of generation. As can be seen in Figures 1-4, the electron density profiles output from upda-IRI-2016 driven by IG12 differ less from those of ionosonde in the vast majority of cases at both stations compared to IRI-2016 driven by IG12, in both low solar activity and high solar activity years. It can be seen in Figures 1-4 that the electron density in the year of high solar activity (2015) is higher than that in the year of low solar activity (2019). The electron density in 2015 is about \(1\times 10^{12}\) el/m\({}^{3}\) to \(2\times 10^{12}\) el/m\({}^{3}\) higher than that in 2019 at the same moment in terms of the ionosonde data from the Wuhan station, and both IRI-2016 driven by IG12 and upda-IRI-2016 driven by IG-up reflect that the activity of the ionosphere is affected by the solar activity. The variation of IED with height in the IRI-2016 model output is consistent with that of ionosonde in terms of the overall trend, showing an increase with height first, and then a gradual decrease after reaching the height of the peak density of the F2 layer, which is in line with the physical mechanism of the ionosphere. However, the IRI-2016 model has some differences with the ionosonde data in the electron density and NmF2 in the lower layers, and although this difference still exists in upda-IRI-2016 as well, the difference is significantly reduced compared with IRI-2016. It is therefore concludedthat the upda-IRI-2016 model driven by IG-up improves the accuracy of the calculated electron density compared to IRI-2016 driven by IG12. After completing the qualitative analysis of the electron density profiles, we proceeded to calculate the precision metrics of the bottomside electron densities using Equations (1)-(3) to analyze the precision variation of the bottomside electron densities. The precision metrics include the MAE, RMSE, and corresponding precision improvement of the difference between the electron density output from IRI-2016 and upda-IRI-2016 and the ionosonde electron density, and the specific precision metrics calculation results are shown in Table 1. The statistics include the whole year of 2015 and the first month of 2019 for both stations. Figure 1: Comparison of ionosonde electron density profiles at Wuhan station from 00:00 to 07:30 UTC on Day 8, 2015, with those output from IRI-2016 and upda-IRI-2016 driven by IG12 and IG-up, respectively. Figure 2: Comparison of ionosonde electron density profiles at Beijing station from 00:00 to 07:30 UTC on Day 8, 2015, with those output from IRI-2016 and upda-IRI-2016 driven by IG12 and IG-up, respectively. Since ionosonde cannot detect data above hmF2 and the electron density information above hmF2 is calculated based on the Chapman theory, and since ionosonde data may be missing at night. Therefore, this paper only counts the bottomside (hmF2 below) electron density profiles during the daytime (00:00\(-\)09:00 UT) when counting the electron density