## 4 Result and Discussion
### Comparison of Reconstructed Electron Density at 00:00, 06:00 and 12:00  
The background electron density and the reconstructed electron density applying MART0 and MART1 are compared in Figures 6-11, and the displayed layer in the longitude-altitude plane in the 3D figures in Figures 6, 8 and 10 are the electron density at the latitude 3.35\({}^{\circ}\). Figure 6: _Cont._  
As is shown in Figure 6a, the electron density increases with altitude to the maximum at about 300 km of the F layer in the ionosphere; then, it decreases with altitude, which is a common p. For a given longitude-altitude plane, the electron density does not change much at the latitude-longitude plane, but this is not the same with the reconstructed IED by MART0 in Figure 6b. The electron density obtained by MART1 shown in Figure 6c is more similar to the background electron density both in the peak value and in the variation trend in three dimensions of the 3D ionospheric electron density. As is shown in the 3D image, it can be inferred that the reconstructed electron density obtained using MART1 is better. In order to more visually compare the electron density reconstructions within all voxel curves in the IED in all voxels of the background, the initial and reconstructed IEDs applying MART0 and MART1 are shown in Figure 7a, and the curves in Figure 7b show a profile of the IED at the same fixed spot of the above IEDs in the same order as curves in Figure 7a. The transformation of the 3D electron density to the 1D electron density can be seen in Figure 7a in the order of height; the clusters represent the electron density of a latitude-longitude plane at the same altitude. Thus, taking an overall view of Figure 7a, the horizontal axis represents the height in large scale. Figure 6: 3D ionospheric electron density of (**(a)** background, **(b)** MART0, **(c)** MART1) at 00:00. Figure 7: IED comparison of (**(a)** voxels, **(b)** profiles) at 00:00. Figure 8: 3D IED of ((**a**) background, (**b**) MART0, (**c**) MART1) at 06:00. Figure 9: IED comparison of ((**a**) voxels, (**b**) profiles) at 06:00. As can be inferred, the MART1 reconstructed IED is more similar to that of the background in both figures. The Ads of MART0 and MART1 are 1.0973 \(\times\) 10\({}^{10}\) and 9.1450 \(\times\) 10\({}^{9}\), and the RMSEs are 1.9595 \(\times\) 10\({}^{10}\) and 1.6653 \(\times\) 10\({}^{10}\), respectively. Therefore, a better reconstruction result is achieved by MART1. The background and reconstructed IED at 06:00 are shown in Figure 8.  
Comparing Figure 8b,c with the background electron density values, respectively, it is clear from these longitude-height profiles given in the figures that the electron density results obtained from the MART1 reconstruction is much more similar to the background electron density image, especially in the first and second longitude-height sliced plane  
Figure 11: IED comparison of ((**a**) voxels, (**b**) profiles) at 12:00. Figure 10: 3D IED of ((**a**) background, (**b**) MART0, (**c**) MART1) at 12:00.  
in the figures. In the first plane, at the height of the maximum electron density, there is a trend of decreasing electron density with increasing longitude, and the reconstructed electron densities by MART1 in Figure 8c follow the same trend as in Figure 8a, showing the background electron densities at longitudes smaller than about 85.8\({}^{\circ}\). In the range shown in the second profile, its electron density trend, the value of the maximum, is closer to the background electron density. The maximum value and its color bar show that the maximum value is also closer to that of the background electron density map. Therefore, from the 3D electron density map, we can see that MART1 has better reconstructed electron density results.