## 4 Results and Discussion
### Detection of a Single Satellite  
The data from station NNOR on 13 December 2006 are used for the detection of a single station. The detection period is 00:00:00-10:00:00 (UTC), and the time of the peak solar radio emission power is approximately 03:30:00 (UTC), with a solar incident angle of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ID** & **Latitude/\({}^{\circ}\)** & **Longitude/\({}^{\circ}\)** & **Country** \\ \hline ISPA & 110 W & 27 S & Chile \\ AREQ & 72 W & 16 S & Peru \\ BOGT & 75 W & 4 N & Colombia \\ MDO1 & 105 W & 30 N & USA \\ CHPI & 45 W & 22 S & Brazil \\ CRO1 & 65 W & 17 N & USA \\ KOUR & 53 W & 5 N & Guyana \\ NNOR & 116 E & 31 S & Australia \\ PERT & 115 E & 31 S & Australia \\ SUNM & 153 E & 27 S & Australia \\ TIDB & 148 E & 35 S & Australia \\ PIMO & 121 E & 14 N & Philippines \\ CCJM & 142 E & 27 N & Japan \\ KUNM & 102 E & 25 N & China \\ GUAM & 144 E & 13 N & Guam \\ USUD & 138 E & 36 N & Japan \\ TSKB & 140 E & 36 N & Japan \\ DARW & 131 E & 12 S & Australia \\ TOW2 & 147 E & 19 S & Australia \\ RABT & 7 W & 33 N & Morocco \\ MAS1 & 16 W & 27 N & Spain \\ SFER & 7 W & 36 N & Spain \\ VILL & 4 W & 40 N & Spain \\ YEBE & 4 W & 40 N & Spain \\ KOKB & 160 W & 22 N & USA \\ TLSE & 1 E & 43 N & France \\ MPAR & 30 E & 0 N & Uganda \\ HARB & 27 E & 25 S & Africa \\ EBRE & 0 E & 40 N & Spain \\ MATE & 14 E & 40 N & Italy \\ MAT1 & 14 E & 40 N & Italy \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The ID, latitude, longitude and country of the IGS stations used in the experiments. 77.1\({}^{\circ}\). All satellites observed at the peak time are detected separately using the method described in Section 3.1. The valley period common to at least \(N_{sat}\) satellites is judged as the detection result of a single station. In this section, different values of \(N_{sat}\) are compared and analyzed. Figure 5 presents the detection rates corresponding to different \(N_{sat}\) for GPS. At both the L1 and L2 frequencies, the detection rate decreases with increasing \(N_{sat}\) for any flux range due to the increasingly severe restriction. Moreover, regardless of the value of \(N_{sat}\), the detection rate at the L2 frequency is significantly higher than that at the L1 frequency. A possible reason for this is that flux or power density at different frequencies of GNSS may have a big difference even for the same L-band SRB event [22]. In the case of \(N_{sat}=5\), only a few flux ranges have a detection rate of \(\geq\)80%. For GPS L1, only 8-9 kSFU and 9-10 kSFU reach 80%; for GPS L2, only 1-2 kSFU, 4-5 kSFU, 7-8 kSFU, 8-9 kSFU, and 9-10 kSFU reach 80%. Overall, the detection rate is quite low in the case of \(N_{sat}=5\). Figure 5: Detection rate of GPS L1 and L2 at IGS station NNOR during an intense L-band SRB event that occurred on 13 December 2006. The histogram shows the number of samples in each flux range. Conversely, in the case of \(N_{sat}\) = 2, the detection rate at both frequencies reaches the highest for all the flux ranges due to the less severe restriction. However, the detection rates of GPS L1 and L2 in the range of 0-100 SFU reach 12.87% and 51.82%, respectively. Note that the flux density under normal circumstances is below 100 SFU, and thus, the detection rate of this range represents the false alarm rate. As mentioned above, the false alarm rate is much higher in the case of \(N_{sat}\) = 2. Furthermore, in the case of \(N_{sat}\) = 3 or \(N_{sat}\) = 4, the detection rate in the range of 0-100 SFU is close to 0, with higher reliability. Regarding GPS L1, for the ranges of 5-6 KSFU, 7-8 KSFU, 8-9 kSFU, and 9-10 kSFU, the detection rate of \(N_{sat}\) = 3 is equivalent to that of \(N_{sat}\) = 4. However, the detection rate of \(N_{sat}\) = 3 is significantly higher than that of \(N_{sat}\) = 4 when the flux is lower. Regarding GPS L2, for the range of 0.1-1 kSFU, the detection rate of \(N_{sat}\) = 3 is slightly higher than that of \(N_{sat}\) = 4, with a difference of 6.15%, and the detection rates of the other ranges are equivalent.