## 3 Results
### Average Electron Density Profile Comparison
These are the same profiles used in Figure 3 which show close agreement in the bottomside E-region after the profiles are shifted in altitude to match at \(fmin\). Figure 7 shows the average EDPs for Gakona. The GNSS-RO profiles generated at Gakona were the least aligned on average of the four sites, with the ionosonde densities larger than the RO densities at all altitudes above \(fmin\). The average ionosonde profile has a flat E-region with a sharp increase in \(N_{e}\) with altitude from \(fmin\) to \(lnmE\). The GNSS-RO profiles were better at showing an E-region peak than at all other sites, with a nearly vertical average profile at a higher altitude and slightly lower \(N_{e}\) than the ionosonde profile. The average altitude shift was the second largest at 3.9 km, and once shifted, the average EDPs are only well aligned for a small range above \(fmin\). The GNSS-RO profiles gradually increase in altitude as \(N_{e}\) increases, whereas the ionosonde profile is much flatter. Despite the shift, there is still a large separation between the profiles near \(hmE\). Finally, Figure 8 shows the average EDPs for Fortaleza. Unlike the previous sites, Fortaleza was the only site where the standard deviation of the GNSS-RO profiles was larger than the ionosonde profiles. Additionally, the average ionosonde profile has a more gradual increase in \(N_{e}\) with altitude than the average ionosonde profile at the other sites and still has a positive slope above average \(hmE\). The GNSS-RO \(N_{e}\) is larger than the unshifted ionosonde \(N_{e}\) at \(hmE\), also unlike the other sites. In the comparison with the shifted ionosonde profile, the average EDPs show reasonable agreement from \(fmin\) for the lower part of the E-region but have a large separation in \(N_{e}\) at \(hmE\). The GNSS-RO profile gradually increases and does not have a clear E-region peak in the average profile. Figure 5: Average unshifted and shifted EDPs at Hermanus for GNSS-RO and ionosonde measurements showing general agreement between \(fmin\) and \(hmE\). The average density was calculated in 1 km increments and is shown with standard deviation uncertainties. Error bars are used for ionosondes and shading is used for GNSS-RO. Figure 6: Average unshifted and shifted EDPs at I-Cheon for GNSS-RO and ionosonde measurements showing agreement near \(fmin\) and a continual growth with altitude for the GNSS-RO observations that is not observed for the ionosondes. An average EDP comparison was also performed for each site between the GNSS-RO and FIRI average profiles. The shifting process was only performed for comparisons with ionosondes; thus, there is only one comparison for each site between the GNSS-RO and FIRI, shown in Figure 9. The average \(fmin\) and unshifted \(hmE\) measured by the ionosondes for each site are included for reference. The GNSS-RO and FIRI average EDDs are similar for each site, thus they will all be discussed together. Unlike the ionosonde profiles, the average FIRI profiles are slightly higher in altitude than the GNSS-RO profile. It is clear to see from the shaded FIRI standard deviation area ridge in altitude below \(fmin\) that there are profiles with either a double ledge or a ledge below \(fmin\). This ridge is least prevalent at I-Cheon and occurs most prominently at Gakona and Fortaleza. The variability between the GNSS-RO and FIRI profiles at Gakona and Hermanus is low. However, the GNSS-RO profiles at I-Cheon and Fortaleza are at a lower altitude than the FIRI and have a large separation in \(N_{e}\) at \(hmE\). The GNSS-RO profiles are in good agreement overall with Hermanus and Gakona, with little separation between the profiles from \(fmin\) to \(hmE\), and show poorer agreement at Fortaleza and I-Cheon. The key takeaway from the comparison with the FIRI profiles is the performance at relatively low electron densities and altitudes, with a strong agreement in the D- to E-region transition at all sites.