## 3 Methodology  
Intense L-band SRBs can affect the GNSS observation data in a large area near the subsolar point, including through a decrease in \(C/N_{0}\), an increase in Geometric Dilution Precision (GDOP) and positioning error. In the worse cases, it can also lead to the loss of lock. The \(C/N_{0}\) shows the most obvious reaction to intense L-band SRBs, especially when an event is not severe. Figure 1 shows the solar X-ray flux measured by the Geostationary Operational Environmental Satellite (GOES) Solar X-ray Imager during an X3.4-level X-ray solar flare on 13 December 2006. According to the data, the flare occurred from 02:14 to 02:57 (UTC), and the peak time was 02:40 (UTC). This solar flare was accompanied by an intense L-band SRB that had a profound impact on the performance of GPS. Figure 2 shows the L-band (1415 MHz) solar radio emission power observed at station Sagamore Hill in America during this SRB event. The data were obtained from the radio solar telescope network (RSTN), and the sampling frequency was 1 Hz. This SRB event occurred between 02:20:00 and 04:45:00 (UTC), and the peak flux value reached 1.1 \(\times\) 10\({}^{5}\) SFU, which was more than 1000 times of the normal value (\(<\)100 SFU). We select stations CEDU and ALIC in Australia as well as stations TWTF and KUNM in China to analyze the influence of the SRB on the \(C/N_{0}\) on 13 December 2006. The solar elevation angles of the four stations were 80.7\({}^{\circ}\), 84.9\({}^{\circ}\), 42.5\({}^{\circ}\) and 36.0\({}^{\circ}\), respectively. Figure 3 shows the decrease in the \(C/N_{0}\) of different satellites at each station for the GPS L1 frequency. The data were provided by the International GNSS Service (IGS), and the sampling period was 30 s. Figure 3 shows that the \(C/N_{0}\) of each station decreased to varying degrees during the SRB. Figure 1: Solar X-ray flux measured by the Geostationary Operational Environmental Satellite (GOES) Solar X-ray Imager during the solar flare that occurred on 13 December 2006. The flare occurred from 02:14 to 02:57 (UTC), and the peak time was 02:40 (UTC). The sampling period was 3 s. The solar X-ray flux data were provided by the National Geophysical Data Center ([[https://satdat.ngdc.noaa.gov/sem/goes/data/](https://satdat.ngdc.noaa.gov/sem/goes/data/)]([https://satdat.ngdc.noaa.gov/sem/goes/data/](https://satdat.ngdc.noaa.gov/sem/goes/data/)), accessed on 6 January 2021). \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{\(L_{n}\)=10\(\cdot\)lg(\(P_{n}\)), dBW} & \multicolumn{5}{c}{**Rate of the Solar Radio Emission Flux (k), SFU**} \\ \cline{2-7}  & **1** & **10\({}^{2}\)** & **10\({}^{3}\)** & **10\({}^{4}\)** & **10\({}^{5}\)** & **10\({}^{6}\)** \\ \hline \(0<\beta<5\) & \(-187.1\) & \(-167.1\) & \(-157.1\) & \(-147.1\) & \(-137.1\) & \(-127.1\) \\ \hline \end{tabular}
\end{table} 
Table 3: Rate of the solar radio emission flux. Figure 3: The \(C/N_{0}\) values at the GPS L1 frequency for International Global Navigation Satellite System Service (IGS) stations CEDU (**a**), ALIC (**b**), TWTF (**c**) and KUNM (**d**) during the intense L-band SRB event that occurred on 13 December 2006. The solar elevation angles of the four stations were 80.7\({}^{\circ}\), 84.9\({}^{\circ}\), 42.5\({}^{\circ}\) and 36.0\({}^{\circ}\) respectively. The sampling period was 30 s.  
Figure 2: Solar radio flux at 1415 MHz observed at station Sagamore Hill provided by radio solar telescope network (RSTN) during the intense L-band solar radio bursts (SRB) event that occurred on 13 December 2006. The sampling frequency was 1 Hz, and the burst period was mainly approximately 02:30, 03:30 and 04:00 (UTC). The influence of the SRB on the \(C/N_{0}\) of the GNSS receiver increased with increasing solar elevation angle, which is consistent with the conclusions in the literature [18]. Station ALIC and station CEDU in Australia were closer to the subsolar point, and consequently, their \(C/N_{0}\) values showed a stronger decline.