## 3 Case Study and Experimental Results
It confirms initial suppositions about worse ground performance due to the natural unstructured conditions of the crop. In general terms, it improves the average signal quality in 19%. The SNR has been also computed for each node, likewise the average SNR for each WSN within each parcel. In Figure 13 the average SNR values over a given time are shown on the left column, and the mean values during that period can be observed on the right column. The analysis of \begin{table}
\begin{tabular}{|c|c|c|c|} \hline
**Parcels** & **Average dispersion [m]** & **Signal quality [\%]** & **Packets lost [\%]** \\ \hline A & 10 & 80.3 & 4.1 \\ B & 20 & 73.2 & 6 \\ C & 30 & 59.9 & 6.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Signal quality and packets lost during the remote sensing mission for each cluster. \begin{table}
\begin{tabular}{|c|c|c|c|c|} \hline
**Parcels** & **Flight height [m]** & **Signal quality [\%]** & **Packets lost [\%]** & **Nodes covered** \\ \hline A & 10 & 95.2 & 0.8 & 100\% \\ A & 20 & 93.9 & 1.7 & 100\% \\ A & 30 & 84 & 1.1 & 100\% \\ B & 10 & 93.8 & 1.2 & 100\% \\ B & 20 & 90.2 & 1.3 & 100\% \\ B & 30 & 83.7 & 1.4 & 91\% (10/11) \\ C & 10 & 95 & 0.9 & 100\% \\ C & 20 & 91 & 1 & 100\% \\ C & 30 & 87.4 & 3 & 100\% \\ \hline \end{tabular}
\end{table} 
Table 2: Signal quality and packets lost during the remote sensing mission for each cluster. those plots have shown that SNR mean values are higher when using Ground-Air WSN link compared to using the Ground WSN, making the presence of the relay elevated node advisable. Table 3 shows values from the aerial robot (_i.e._, dynamic node) acquired during the survey over the parcels. The waypoints are optimal points where the aerial robot passes over and they have to be set up previously to define the mission. Furthermore, the update time represents the time that the aircraft needs to stay above ground in order to obtain the signal from the target cluster. It should also be noted that the quality of the signal and the count of lost packets shown in Table 3 refer to the communications between the dynamic node and the emitter ground node. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|} \hline
**Parcels** & **Time** & **Way-point** & **Update Time** & **Battery** & **Quadrotor speed** & **Signal quality** & **Packets lost** \\ \hline \multirow{3}{*}{A} & 17 h:45 m:14 s & 40 \({}^{\circ}\)06\({}^{\circ}\)49.48’N & \multirow{3}{*}{71 s} & \multirow{3}{*}{12.51 V} & \multirow{3}{*}{5 m/s} & \multirow{3}{*}{92.3\%} & \multirow{3}{*}{2\%} \\  & 08/12/2010 & 03 \({}^{\circ}\)17\({}^{\circ}\)05.09’W & & & & \\ \cline{1-1} \cline{5-7} \multirow{3}{*}{B} & 17 h:47 m:32 s & 40 \({}^{\circ}\)06\({}^{\circ}\)46.85’N & \multirow{3}{*}{83 s} & \multirow{3}{*}{12.37 V} & \multirow{3}{*}{5 m/s} & \multirow{3}{*}{89.7\%} & \multirow{3}{*}{3\%} \\  & 08/12/2010 & 03 \({}^{\circ}\)17\({}^{\circ}\)04.14’W & & & & & \\ \cline{1-1} \cline{5-7} \multirow{3}{*}{C} & 17 h:50 m:43 s & 40 \({}^{\circ}\)06\({}^{\circ}\)39.36’N & \multirow{3}{*}{76 s} & \multirow{3}{*}{12.02 V} & \multirow{3}{*}{5 m/s} & \multirow{3}{*}{96\%} & \multirow{3}{*}{1\%} \\  & 08/12/2010 & 03 \({}^{\circ}\)17\({}^{\circ}\)07.10’W & & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Values from the aerial robot (_i.e._, dynamic node) survey mission. Figure 13: Average SNR obtained for the WSNs from each parcel. From top to down, A, B, C, respectively. As previously mentioned, the experiments were performed both in the morning and afternoon. Since the climate has considerably changed during this season, we had the opportunity to validate our system at different wind speeds. Table 4 shows the parameters and results from those experiments, monitoring the battery status after the experiments and the overall duration of the aerial vehicle trajectory. In both experiments the quadrotor speed was set to 5 m/s and both experiments were made with full charged batteries. In the morning (Experiment 1) with regular wind speeds, the mission was carried out more quickly than in the afternoon (Experiment 2).