## 3 Effect of Fixed-Altitude Heterogeneous LEO Constellations on CIT
### Results of CIT  
Based on the distribution of the number of LEO satellites at different altitudes, we apply the RLS method to invert the global ionospheric electron density. Figure 5 shows the global distribution of IED at 300 km for GNSS and GNSS + different number of LEO  
Figure 4: Percentage gain in the number of ray-crossing voxels over GNSS differences for different altitude ranges at 00:00:00-00:00:10 UT on 19 March 2024. Figure 3: Number of ray-crossing voxels at 00:00:00–00:00:10 UT on 19 March 2024, with red, green, and blue vertical lines indicating altitudes of 300 km, 500 km, and 800 km, respectively. satellites at 300 km altitude CIT results at 00:00:00-00:00:10 UT on 19 March 2024. It can be found that the IED, inverted using solely GNSS observations, can only roughly reflect the double crest structure of the equatorial ionization anomaly (EIA), whereas the addition of 15 LEO satellites makes the double crest structure more pronounced. This shows a trend in that the northern crest is stronger than the southern crest, and the details of the EIA are gradually being portrayed in a complete way in the process of the addition of the LEO satellites. We counted the deviation and RMS of the difference between the CIT inverted IED and the NeQuick2 model value as an evaluation index, as shown in Figures 6 and 7, but only the results after the addition of the LEO satellites at the 300 km altitude are given here. From Figure 6, it can be seen that the ionospheric IED, inverted using only GNSS observations, has a positive bias with a maximum positive bias of more than \(2\times 10^{11}\) el/m\({}^{3}\) at an altitude of 200-400 km, and a negative bias with a maximum value of more than \(1\times 10^{11}\) el/m\({}^{3}\) at 400-800 km. After adding 15 LEO satellites at 300 km altitude, the range of altitude and the value of deviation become smaller, and after increasing to 192 LEO satellites, the range of positive deviation is reduced to 200-325 km. Also, the maximum value of deviation is not more than \(1.8\times 10^{11}\) el/m\({}^{3}\), the range of negative deviation is reduced to 550-800 km, and the maximum value of deviation is not more than \(0.8\times 10^{11}\) el/m\({}^{3}\). Based on the RMS distribution in Figure 7, it can be seen that there are strips with average RMS values significantly higher than \(2.5\times 10^{11}\) el/m\({}^{3}\) at 200-400 km and regions with average RMS values significantly higher than \(1.5\times 10^{11}\) el/m\({}^{3}\) at 400-600 km when only GNSS observations are used. After adding 15 LEO satellites, the average value of RMS is reduced to less than \(1.5\times 10^{11}\) el/m\({}^{3}\) at 400-600 km, and the average value of RMS is reduced to less than \(2.5\times 10^{11}\) el/m\({}^{3}\) at 200-400 km. After increasing to 192 LEO satellites, the average RMS for 400-600 km is reduced to less than \(1.0\times 10^{11}\) el/m\({}^{3}\), and the average RMS for 200-400 km is reduced to about \(2.0\times 10^{11}\) el/m\({}^{3}\). Figure 5: Global distribution of ionospheric electron density (IED) at 300 km for GNSS and GNSS + different number of LEO satellites at 300 km altitude computerized ionospheric tomography (CIT) results at 00:00:00–00:00:10 UT on 19 March 2024. IEDs for the NeQuick2 and IRI2020 models are also given.