## 4 Results and Discussion
### Influence of Satellite Distribution on the Detection Rate
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Station**} & \multicolumn{2}{c}{**Sun**} & \multicolumn{3}{c}{**Distant-Satellites**} & \multicolumn{3}{c}{**Near-Satellites**} \\ \cline{2-9}  & **Az/\({}^{o}\)** & **El/\({}^{o}\)** & **SVID** & **Az/\({}^{o}\)** & **El/\({}^{o}\)** & **SVID** & **Az/\({}^{o}\)** & **El/\({}^{o}\)** \\ \hline NNOR & 80.9 & 77.1 & G13 & 272 & 45 & G11 & 5 & 52 \\  & & G23 & 215 & 66 & G20 & 140 & 65 \\ \hline \multirow{2}{*}{PERT} & 78.9 & 76.3 & G13 & 275 & 45 & G11 & 7 & 52 \\  & & G23 & 217 & 66 & G20 & 140 & 65 \\ \hline \multirow{2}{*}{SUNM} & 279.8 & 66.6 & G25 & 145 & 45 & G20 & 210 & 60 \\  & & G31 & 140 & 35 & G23 & 230 & 32 \\ \hline \multirow{2}{*}{TIDB} & 301.2 & 68.5 & G25 & 135 & 47 & G20 & 220 & 70 \\  & & G31 & 135 & 40 & G23 & 243 & 45 \\ \hline \multirow{2}{*}{PIMO} & 169.9 & 52.4 & G19 & 20 & 29 & G11 & 210 & 80 \\  & & G27 & 305 & 70 & G13 & 230 & 20 \\ \hline \multirow{2}{*}{CCJM} & \multirow{2}{*}{196.3} & \multirow{2}{*}{38.0} & G03 & 50 & 40 & G11 & 230 & 50 \\  & & G19 & 10 & 55 & G16 & 120 & 30 \\ \hline \multirow{2}{*}{KUNM} & \multirow{2}{*}{151.8} & \multirow{2}{*}{36.0} & G08 & 325 & 50 & G11 & 135 & 60 \\  & & G28 & 310 & 28 & G27 & 300 & 80 \\ \hline \end{tabular}
\end{table} 
Table 6: Location information of the Sun and selected satellites at seven stations at 03:30:00 (UTC) on 13 December 2006.  
interference. Accordingly, this phenomenon leads to a difference in the detection rates at different GNSS frequencies in subsequent experiments. Figure 10: The \(C/N_{0}\) values of different GNSS systems at IGS station HARB during an intense L-band SRB event that occurred on 6 September 2017. The sampling period was 30 s. The elevation mask angle was \(10^{\circ}\). Figure 9: Influence of satellite distribution on the detection rate for 4 typical intense L-band SRB events in Table 5.  
Figure 11 shows the detection results at different frequencies for different systems. The detection performance at GPS L2 is the best of all systems. Specifically, the detection rates at GPS L2 of the flux ranges \(\geq\) 1 kSFU are 100%, with a low false alarm rate. Moreover, the detection performance at GLONASS G2 is second only to that at GPS L2 and achieves 100% on the condition of flux ranges \(\geq\) 3 kSFU. Overall, a comparison of Figures 10 and 11 shows that the more obvious the response to the SRB system is, the better the detection performance is. The detection thresholds of GPS L1 L5, GLONASS G1, and GALILEO E1 E5, under the condition of a detection  
Figure 11: Detection results of different GNSS systems at various frequencies during an intense L-band SRB event that occurred on 6 September 2017.  
rate above 80%, are 8-9 kSFU, 8-9 kSFU, 8-9 kSFU, 8-9 kSFU, and 7-8 kSFU, respectively, indicating worse performance than other frequencies and systems. However, the responses of the \(C/N_{0}\) values of GPS L5 and GALILEO E5 to SRB is still evident, which appears to contradict the above trend. Through ample analysis, we found that the data of GPS L5 and GALILEO E5 from the IGS contain few satellites that can be observed simultaneously (the values vary from 4 to 6 and 5 to 8, respectively). Hence, the values of \(N_{sat}=3\) and \(N_{station}=2\) from the optimization in Sections 4.1 and 4.2 are not suitable for GPS L5 and GALILEO E5. Through specific experiments, the optimal values for \(N_{sat}\) and \(N_{station}\) for GPS L5 are 2 and 2, respectively. For GALILEO E5, the values are 1 and 4, respectively. Although we modified the optimal values for \(N_{sat}\) and \(N_{station}\) for GPS L5 and GALILEO E5 to adapt to their smaller number of satellites and obtain better performance, the detection performance still appears to be unsatisfactory, as shown in Figure 11. The reason is that the core step of the proposed method is the comparison of multiple satellites and multiple stations, and thus, a reduction in the number of satellites can have a great impact on the detection results. [PERSON] et al.