# Rain Monitoring with Polarimetric GNSS Signals: Ground-Based Experimental Research
## 3 Results and Discussion
### Statistical Results in 2016  
For statistical and comparative analysis, the minimum elevation of every GPS satellite is set to 2\({}^{\circ}\) and the length of their data is set to one hour. Then, by calculation, it is found that the observing time of G8, G10, G11, G15, G16, G21, G26, G28, G29 is not long enough to get one-hour data, while data from other 12 GPS satellites (G1, G3, G7, G9, G12, G13, G22, G23, G24, G25, G27, G30) can be used to analyze. Their data from no-rain days is also calculated by the above processing algorithm. Some statistical results are shown in Figure 14.  
Figure 12: Examples of phase shift from two rainy days compared with radar reflectivity and path-averaged rain rate calculated from radar reflectivity: (**a**) on 27 June 2015; (**b**) on 10 August 2015; (**c**) sky plot of G22 at this selected time. Figure 13: Case of accumulated phase shift on 10 August 2015 compared with accumulated rainfall observed from four weather stations and calculated from radar, respectively: (**a**) comparison results with data from four weather stations; (**b**) comparison results with data from Jurong weather station and radar. From Figure 14, it is obvious that their standard deviations of the four GPS satellites' data are small and stable, which is well consistent with the features of G22 and G27 from 2015. Besides, the other satellites' data has the same characteristics. In order to compare, their statistical results for the no-rain days are displayed in Table 1.  
Since each satellite has its own orbit, their maximum elevations with the same minimum elevation (\(2^{\circ}\)) and lasting the same time (one hour) are different, which can be seen in Table 1. Besides, obviously in Table 1, other statistics, such as maximum, minimum and mean standard deviations are reported. Statistical results on no-rain days show that the maximum standard deviation of all the satellites is 3.36 mm (G7), the minimum is low to 0.69 mm (G23), and the mean value of standard \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Satellite**} & **Minimum** & **Maximum** & **Maximum Standard** & **Minimum Standard** & **Mean Standard** & **Number of** \\  & **Elevation (\(\circ\))** & **Elevation (\(\circ\))** & **Deviation (mm)** & **Deviation (mm)** & **Deviation (mm)** & **Rainfall Cases** \\ \hline G1 & 2 & 22.4 & 3.28 & 1.24 & \(1.98\) & 4 \\ G3 & 2 & 26.5 & 2.40 & \(1.01\) & \(1.55\) & 3 \\ G7 & 2 & 11.2 & 3.63 & 1.08 & 2.0 & 2 \\ G9 & 2 & 24.3 & 2.57 & 1.13 & 1.62 & 3 \\ G12 & 2 & 26 & 2.87 & 1.15 & 1.73 & 3 \\ G13 & 2 & 20.8 & 2.75 & 1.34 & 1.96 & 4 \\ G22 & 2 & 25 & 2.77 & 1.03 & 1.63 & 1 \\ G23 & 2 & 18.4 & 2.48 & 0.69 & 1.59 & 1 \\ G24 & 2 & 23.2 & 2.82 & 1.19 & 1.81 & 1 \\ G25 & 2 & 26.7 & 2.57 & 1.03 & 1.63 & 1 \\ G27 & 2 & 20.7 & 2.81 & 1.49 & 2.17 & 2 \\ G30 & 2 & 17.2 & 2.54 & 0.94 & 1.67 & 2 \\ \hline \end{tabular}
\end{table} 
Table 1: Statistical results of different GPS satellites. Figure 14: Statistical characteristics of four GPS satellite data in all no-rain days: (**a**) G1; (**b**) G12; (**c**) G22; (**d**) G27. deviations from different satellites is less than 2.2 mm, with the majority within 2 mm. Besides, the samples from different satellites for statistics are all more than 80 (no-rain days). Compared with the results in [PERSON] et al. (2018), these standard deviations here are almost the same, some even better, which demonstrates the consistency of observed data on no-rain days and the reliability of phase shift background values. This also reveals the stability of experimental equipment and feasibility of the data processing algorithm. In Table 1, rainfall cases refer to the cases obtained by matching the phase shift of rainy day with the rain gauges. In these cases, rainfall information is detected by rain gauges. Here, some cases are shown in Figure 15.  
Figure 15: _Cont._  
In Figure 15, R1, R2, R3, and R4 represent the correlation coefficient between accumulated phase shift and accumulated rainfall from Lishui, Danyang, Jintan and Jurong weather stations, respectively.