# Investigation into the Effect of Atmospheric
## 4 Results, Analysis and Discussion
### Analysis of Results  
The CNR differences of some satellites are positive and some are negative with positive being the majority in Data set 1 (see Table 7), we cannot see that the high PM\({}_{10}\), PM\({}_{2.5}\) and AQI indices in Day 1 (see Table 1) always lead to a reduction of CNR. Day 1 CNR minus Day 2 CNR would be always negative if the particulate matter had an impact on the GNSS signal propagation, which would lead to a reduction in signal strength and an increase in the noise level. In no physical and chemical circumstances would the additional particulate matter in the atmosphere increase the GNSS CNR. The overall mean values of L1 and L2 CNR differences of Data set 1 are less than those of Data set 2 (see Table 7, absolute values are considered). Since Data set 1 has great differences in PM\({}_{10}\), PM\({}_{2.5}\) and AQI indices between sidereal days (see Table 1) while Data set 2 has similar PM\({}_{10}\), PM\({}_{2.5}\) and AQI indices between sidereal days (see Table 2), we cannot find any significant impact of particulate matter on GNSS signal propagation based on the results of the data sets collected in November 2014. Data sets 3-5 have great differences in PM\({}_{10}\), PM\({}_{2.5}\) and AQI indices between consecutive sidereal days (see Tables 3-5) while Data set 6 has similar PM\({}_{10}\), PM\({}_{2.5}\) and AQI indices between consecutive sidereal days (see Table 4). Similar to the data sets collected in November 2014, the CNR differences of some satellites are positive and some are negative with positive as the majority in Data sets 3-5 collected in December 2015 (see Table 8). The CNR differences in Data set 6 are less than the CNR differences in Data sets 3-5; however, the standard deviations are similar (see Table 8). Nevertheless, all the mean values of CNR differences in Data sets 1, 3-5 are much less than 1 dBHz, which is much less significant as the multipath effect [26]. The effect of the different temperatures, pressures and relative humidity values on tropospheric delays between sidereal days in the data sets is estimated. The hourly meteorological data collected at the national air quality monitoring station at Wanli University was put in the Saastamoinen tropospheric model [5; 6], and the computed ZTDs in Days 1 and 2 and their differences of the  
Figure 9: Plots of L1 (**a**,**b**) and L2 (**c**,**d**) CNR of satellites PRN08 and PRN16 in Day 1 vs. L1 and L2 CNR of the satellites in Day 2 of Data set 6; Blue: Day 1 CNR, Green: Day 2 CNR, Red: the differences in Day 1 and Day 2 CNR. six data sets are shown in Table 9. It shows that the effect of the different temperatures, pressures and relative humidity values on tropospheric delays between sidereal days is very small, therefore, the effect of the different meteorological conditions on CNR is negligible. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Data Set 1 Great AQI Difference** & \multicolumn{2}{c}{**L1 (dBHz)**} & \multicolumn{2}{c}{**L2 (dBHz)**} \\ \hline PRN & **Mean** & **S.D.** & **Mean** & **S.D.** \\ \hline
14 & 0.059 & 0.160 & \(-\)0.056 & 0.560 \\
16 & 0.159 & 0.145 & 0.051 & 0.371 \\
18 & 0.016 & 0.191 & 0.011 & 0.809 \\
21 & \(-\)0.017 & 0.317 & 0.345 & 1.523 \\
24 & \(-\)0.009 & 0.247 & 0.100 & 1.074 \\ Overall & 0.042 & 0.090 & & \\ \hline
**Data set 2 Similar AQI** & \multicolumn{2}{c}{**L1 (dBHz)**} & \multicolumn{2}{c}{**L2 (dBHz)**} \\ \hline PRN & Mean & S.D. & Mean & S.D. \\ \hline
14 & 0.124 & 0.127 & 0.079 & 0.221 \\
15 & 0.184 & 0.196 & \(-\)0.975 & 1.085 \\
18 & 0.097 & 0.144 & \(-\)0.043 & 0.386 \\
24 & 0.157 & 0.167 & \(-\)0.702 & 0.744 \\
29 & 0.167 & 0.191 & 0.072 & 0.857 \\ Overall & 0.146 & & \(-\)0.314 & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: 95% confidence level statistical results of the L1 and L2 CNR differences of selected satellites in two consecutive sidereal days in the Datasets 1 and 2 collected in November 2014. Data with the satellite elevation angle greater than 30\({}^{\circ}\) is used.