## 2 GNSS RO Event Simulation and Assessment Approaches
### Experimental Programs  
Numerical simulation experiments of RO events were conducted by using the above-mentioned TLE orbit data of the GNSS transmitting and LEO receiving satellites to quantitatively analyze the following scientific questions under the existing multi-GNSS conditions.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Satellite ID** & **Inclination/(\({}^{\circ}\))** & **RAAN/(\({}^{\circ}\))** & **Eccentricity** & \
\begin{tabular}{c} **Argument of** \\ **Perigee/(\({}^{\circ}\))** \\ \end{tabular} &
\begin{tabular}{c} **Mean** \\ **Anomaly/(\({}^{\circ}\))** \\ \end{tabular} & **Height/(km)** \\ \hline BDS-3 (C59) & 1 & 226.6 & 0.0003 & 356.3 & 149.4 & 35,787 \\ BDS-3 (C38) & 56 & 56.9 & 0.0019 & 191.9 & 341.8 & 35,787 \\ BDS-3 (C19) & 55.4 & 123.8 & 0.0012 & 293.4 & 66.5 & 21,528 \\ GPS (13) & 55.5 & 169.8 & 0.0048 & 53.4 & 307.1 & 20,182 \\ COSMOS (2425) & 64.8 & 255.3 & 0.0024 & 342.9 & 16.3 & 19,129 \\ GSAT (E11) & 56.8 & 31.2 & 0.0004 & 31.7 & 328.3 & 23,222 \\ IRIDIUM (109) & 86.4 & 129.2 & 0 & 92.1 & 268.1 & 778 \\ COSMOS (2361) & 82.9 & 112.9 & 0.0032 & 129.8 & 43.7 & 989 \\ NNSS (19) & 89.9 & 242.6 & 0.0171 & 349.6 & 10.2 & 1069 \\ QZSS (184) & 42.4 & 269.3 & 0.0758 & 269.1 & 89.6 & 35,787 \\ QZSS (189) & 0.02 & 188.6 & 0.0002 & 271.7 & 154.3 & 35,787 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main orbital elements of representative transmitting satellites from their TLE data files.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Satellite ID** & **Inclination/(\({}^{\circ}\))** & **RAAN/(\({}^{\circ}\))** & **Eccentricity** & \
\begin{tabular}{c} **Argument of** \\ **Perigee/(\({}^{\circ}\))** \\ \end{tabular} &
\begin{tabular}{c} **Mean** \\ **Anomaly/(\({}^{\circ}\))** \\ \end{tabular} & **Height/(km)** \\ \hline RS01 & 93.6 & 151 & 0.0001 & 90 & 30 & 600 \\ RS02 & 93.9 & 215 & 0.0001 & 90 & 150 & 600 \\ RS03 & 94.6 & 330 & 0.0001 & 90 & 270 & 600 \\ RS04 & 95.5 & 183 & 0.0001 & 90 & 90 & 600 \\ RS05 & 96.6 & 245 & 0.00 To what extent can the multi-GNSS integration increase the number of RO events and their global coverage fraction for a single polar-orbit LEO satellite?  
An RO constellation with how many polar-orbit LEO satellites can achieve the Spire/GPS occultation detection capability and thus can meet the GNWP's basic requirements in terms of the RO event number, timeliness, and global coverage fraction?  
In the GNSS RO event simulation, the receiving satellites were divided into 6 groups, i.e., the single traditional meteorology LEO satellite (MET), 3-satellite constellation (RS01-03, 3 RS), 6-satellite constellation (RS01-06, 6 RS), 9-satellite constellation (RS01-09, 9 RS), 12-satellite constellation (RS01-12, 12 RS), and 100-satellite constellation (100 RS), while the transmitting satellites were divided into 3 groups i.e., single GNSS systems of BDS-3 (30 satellites), GPS (30 satellites), and multi-GNSS (251 satellites). Then, GNSS RO systems combined with the abovementioned receiving and transmitting satellite groups were simulated, long time series of GNSS RO events were calculated by using the methods described in Section 2.1, and the ID number, latitude, longitude, and time of each RO event were stored in occultation tables for statistical analysis.  
Specifically, the comparison of the MET/multi-GNSS and MET/BDS-3 RO system performance could be used to analyze the detection capability improvement of multi-GNSS for a single polar-orbit LEO satellite. The comparison of the 3 RS/multi-GNSS, 6 RS/multi-GNSS, 9 RS/multi-GNSS, 12 RS/multi-GNSS, and 100 RS/GPS RO systems were used to analyze the detection capability of the polar-orbit LEO satellite constellations under the existing multi-GNSS status.