## 4 Experiment
### Analysis of Experiments Results
#### 4.4.3 Droplet Deposition at the Boundary of Operation Units  
In order to verify the sensitivity of the designed variable spray system, the sampling bands are set up to collect droplet deposition. The sampling bands are located 1 m and 2 m away from the operation unit boundary line. The droplet deposition amount of the units 1-4 of the first sortie was selected for analysis. And the test data are shown in Table 5. In Table 5, S4, S10 and S16 are the acquisition bands at the demarcation line of the operation unit. S3, S5, S9, S11, S15 and S17 are the numbers of acquisition band numbers which are 1 m away from the demarcation line on both sides of the demarcation line. S2, S6, S8, S12, S14 and S18 are the numbers of acquisition bands which are about 2 m away from the demarcation line on both sides of the demarcation line. S7, S13 and S19 are the numbers of acquisition bands located in the central position of the operation unit respectively. The layout of the sampling zone from S2 to S19 is in accordance with the method shown in Figure 16.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Unit** & **Prescription Value (L-hm\({}^{-2}\))** & **Sampling Band** & **Deposition (ug-cm\({}^{-2}\))** \\ \hline \multirow{2}{*}{1} & & S2 & 22.58 \\ \cline{3-4}  & 7.5 & S3 & 21.89 \\ \hline Boundary & & S4 & 20.63 \\ \hline \multirow{4}{*}{2} & & S5 & 35.68 \\ \cline{3-4}  & & S6 & 39.43 \\ \cline{3-4}  & & S7 & 39.21 \\ \cline{3-4}  & & S8 & 40.28 \\ \cline{3-4}  & & S9 & 38.64 \\ \hline Boundary & & S10 & 39.46 \\ \hline \multirow{4}{*}{3} & & S11 & 27.64 \\ \cline{3-4}  & & S12 & 23.64 \\ \cline{3-4}  & 7.5 & S13 & 24.06 \\ \cline{3-4}  & & S14 & 21.96 \\ \cline{3-4}  & & S15 & 22.68 \\ \hline \end{tabular}
\end{table}
Table 5: Droplet deposition at the boundary of operational unit.  
Figure 21: Droplet depositions in various sorties: (**a**) first sortie; (**b**) second sortie; (**c**) third sortie; (**d**) fourth sortie.  
The diagram of droplet deposition in operation units 1-4 is shown in Figure 22.  
It is known from Table 5 and Figure 22, when the UAV flies over the boundary band, the prescription interpretation system is interpreted to get the prescription value of the next operation unit and sent to the variable spray control system. The variable spray control system regulates the flow rate of the spray system according to the spraying prescription value. From Table 5, the droplet deposition at the boundary is similar to that of the working unit. The droplet deposition at the 1 m position behind the boundary is between the values at the center of the two working units. For example, the variation rates of the droplet deposition at S5, S11 and S17 are 63%, 29.95% and 217.67% respectively. On the other hand, the deposition of droplets on the acquisition belt, which are 2 m away from the demarcation line, is similar to that on the central line of the operation unit. Since the plant protection drone flies at 4 m/s during the test, the new prescription value is received. When the target value of the spray volume change value is about 2 m, the operation time of the system is 0.4s from receiving to square value to arriving at the target value of flow. Which reflects the sensitivity of the system. From Table 5 and Figure 22, it can be seen that the droplet depositions in the four operation units 1-4 vary with the prescription value. The normalized ratio of the droplet deposition in the center line of operation units 1-4 is 1:1.79:1.07:5.93, and the ratio of prescription value for these four operation units is 1:5:1:7. Due to the drift and adherence of droplets to fuselage, the actual deposition value is smaller than the prescription value, but the ratio is consistent, which reflects the effectiveness of variable spray system. The above analysis shows that the PWM-PID variable spray system designed based on the prescription can quickly adjust the flow according to the prescription map. The system has certain sensitivity and stability.