## 4 Effect of Different Highly Heterogeneous LEO Constellations on CIT  
In order to investigate the influence of different altitude heterogeneous LEO constellations on CIT, we combine different altitudes and different numbers of LEO satellite plans to form different altitude heterogeneous LEO constellations. According to the spatial distribution of rays in Figure 2, it can be seen that for LEO satellites with different altitudes, the number of voxels they pass through is different, and the shape of the rays from the ground-based GNSS station to the LEO satellites can be regarded as an inverted cone, so that the lower the altitude, the more lower elevation angle rays it produces. Meanwhile, according to the gain of the CIT results above, for the low altitude LEO satellites, the percentage of  
Figure 9: Percentage RMS gain of the CIT results from GNSS and GNSS combined with varying numbers of LEO satellites at different altitudes, compared with the NeQuick2 model, across altitudes on 19 March 2024. RMS gain increases with the increase of the number of LEO satellites. According to this feature, we can set the number of LEO satellites in lower orbits higher than the number of LEO satellites in higher orbits, and a total of six different combinations can be designed, as shown in Table 3; LEO192 is used as a reference to demonstrate the effectiveness of other plans to reconstruct the IED. Consistent with Figures 6 and 7, we counted the bias and RMS distributions of the CIT results of the six plans with the NeQuick2 model in time and altitude, as shown in Figures 10 and 11. From Figure 10, we can see that the six plans present basically the same bias distribution, but planB has a large negative deviation from 350 km to 550 km compared to the other plans, while the positive deviation is larger than that of the other plans at around 300 km. It is also clear from Figure 11 that planB has a large  
We counted the RMS distribution of the CIT results at altitude for the different plans and GNSS, as shown in Figure 12. As can be seen in Figure 12, there is a significant improvement in the CIT results after applying the different schemes compared to GNSS only, and at the peak electron density altitude (~300 km), the different schemes achieve the same improvement, with a reduction in the RMS from 2.80 \(\times\) 10\({}^{11}\) el/m\({}^{3}\) to ~2.03 \(\times\) 10\({}^{11}\) el/m\({}^{3}\). At 550 km altitude, the smallest RMS values exist for the six plans, with both GNSS + LEO192 and planA reducing the RMS to 0.25 \(\times\) 10\({}^{11}\) el/m\({}^{3}\). Below 250 km, the RMS for the six plans is close to that of the GNSS, with no significant improvement. Based on the CIT statistics for the different plans, we calculated the percentage RMS gain for each plan versus GNSS-only observations, as shown in Figure 13. In terms of overall gain, the RMS gain of all six plans exceeds 25%, with planB having the smallest RMS gain of 27.31% and planA having the largest RMS gain of 32.42%. At 100-300 km, planE has the largest gain of 13.59%. Compared with planD, planE only reduces 15 LEO satellites at an altitude of 1000 km, which is consistent with the results in Figure 9, further illustrating that the addition of LEO satellites in high orbits does not enhance the CIT effect. At 300-500 km, planD has the largest gain of 39.55%, and planB has the smallest gain of 31.16%. PlanB has only 96 LEO satellites at 300 km altitude, which is much lower than the other plans, resulting in the smallest RMS gain for this plan at altitudes below 500 km. In 500-800 km, the RMS gain of GNSS + LEO192 is the largest, 50.19%, and the RMS gain of planA is 49.79%, which is close to the result of GNSS + LEO192. Also, this altitude interval is the altitude range with the largest RMS gain, and the RMS gains of all six plans are more than 44%. At 800-1000 km, the RMS gain of GNSS + LEO192 is the largest, and in this interval, according to the results in Figure 9, increasing the number of LEO satellites in the 800 km altitude can improve the accuracy of the CIT results.