# UAV Communication Recovery under Meteorological Conditions
## 3 Methods
### UAV Coverage Radius with Elevation Angle under Different Weather Conditions
3.1 Influence of \(R_{\rm rain}\), \(R_{\rm fog}\), and \(R_{\rm snow}\) on the Maximum Coverage Area of the UAV  
The relationships between the UAV maximum coverage area and the rainfall rate, the liquid water density, and the snowfall rate in the four regions are illustrated in Figure 8, Figure 9, and Figure 10, respectively. Each discrete marker point represents the UAV's maximum coverage area calculated based on the corresponding rainfall rate, liquid water density, and snowfall rate, respectively. Moreover, the solid and dashed lines show the fitting curves for the frequencies of 28 GHz and 71 GHz, respectively. Additionally, to visually demonstrate the impact of the rainfall rate on the UAV coverage area, we present the change in the maximum coverage area of the UAV caused by the rainfall rate and its 3D plot in the four regions at a frequency of 28 GHz, as shown in Figure 11. These figures reveal that the maximum coverage area of the UAV in each region decreases as the rainfall rate, the liquid water density, or the snowfall rate increases. Additionally, it is evident that the coverage areas of the UAV at 28 GHz are larger than those at 71 GHz in all four regions. Moreover, the extent of the decrease in the maximum coverage area of the UAV for each region is summarized in Table 8. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Region 1 Weather** & **Regions 2–4** & **28 GHz** & **71 GHz** \\ \hline \multirow{3}{*}{Region 1 Snow} & Region 2 & 13.30\% & 13.01\% \\ \cline{2-4}  & Region 3 & 23.74\% & 23.20\% \\ \cline{2-4}  & Region 4 & 34.49\% & 33.86\% \\ \hline \multirow{3}{*}{Region 1 Fog} & Region 2 & 12.99\% & 12.83\% \\ \cline{2-4}  & Region 3 & 23.25\% & 22.96\% \\ \cline{2-4}  & Region 4 & 33.90\% & 33.57\% \\ \hline \multirow{3}{*}{Region 1 Rain} & Region 2 & 12.23\% & 12.08\% \\ \cline{2-4}  & Region 3 & 21.83\% & 21.62\% \\ \cline{2-4}  & Region 4 & 32.25\% & 31.93\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Percentage reduction in maximum coverage radius in snow, fog, and rain conditions for Regions 2 to 4 relative to Region 1. Figure 8: UAV maximum coverage area versus rainfall rate in four regions. Figure 10: UAV maximum coverage area versus snowfall rate in four regions. Figure 9: UAV maximum coverage area versus liquid water density in four regions. Based on Table 8, we found that in the four regions, for rain, the reduction in the coverage area at 28 GHz is 183,640, 128,676, 91,418, and 62,006 m\({}^{2}\) larger than that at 71 GHz, respectively. For fog, the reduction in the coverage area at 28 GHz is 12,149, 7802, 4999, and 3142 m\({}^{2}\) larger than that at 71 GHz, respectively. Meanwhile, for snow, the reduction in the coverage area at 28 GHz is 3369, 2136, 1424, and 918 m\({}^{2}\) smaller than that at 71 GHz, respectively. Therefore, when the frequency is 28 GHz, rain and snow have the largest and smallest effects on the UAV's coverage area, respectively. When the frequency is 71 GHz, rain and fog have the largest and smallest effects on the coverage area of the UAV, respectively. In contrast to the significant impact of the rainfall rate on the maximum coverage area of the UAV, the effects of the liquid water density and snowfall rate are less pronounced. By closely examining and comparing Figures 8-10, we observe that the maximum coverage area of the UAV decreases exponentially with the rainfall rate and snowfall rate in Figures 8 and 10. However, the maximum coverage area of the UAV in Figure 9 exhibits a linear decreasing trend with respect to the density of liquid water. The expressions derived for the fitted curves in these three figures are discussed in Section 4.1. Figure 11: The change in the maximum coverage area of the UAV caused by the rainfall rate and its 3D plot in four regions (Freq = 28 GHz).