## 4 Experiment
### Analysis of Experiments Results  
#### 4.4.1 Droplet Deposition Density Analysis  
During the experiment, the number of droplets per square centimeter of the water-sensitive paper in each sampling point was collected. The distribution uniformity of the droplet coverage tester was calculated by Equation (7). The grayscale image the water-sensitive paper after scanning is shown in Figure 19. The central sampling band of 6 working orders in the next route of the one or two sorties was selected, as shown in Table 4. When the water droplet coverage density is less than 15 per cm\({}^{2}\), it is regarded as an invalid sampling point.  
According to the data in Table 4, when the prescription values are different, the distribution of droplet deposition density is more intense in the middle and less intense on both sides. Because of the small natural wind speed during the experiment, the droplet deposition does not have obvious migration, and the peak value of deposition concentration is gathered near the sampling center line. The prescription values of operational units 1-6 are 7.5 L/hm\({}^{2}\), 15 L/hm\({}^{2}\), 7.5 L/hm\({}^{2}\), 37.5 L/hm\({}^{2}\), 15 L/hm\({}^{2}\), and 30 L/hm\({}^{2}\), and the normalized ratio of prescription value is 1:2:1:5:2:4.  
In the first sortie, the normalized ratio of effective droplet deposition density of these six operation units is 1:1.38:0.93:3.15:1.07:1.85. In the second sortie, the normalized ratio of their effective droplet deposition density is 1:1.59:1.15:1.99:1.04:2.21. The actual normalized ratio of fog droplet deposition density of these six operation units is smaller than its theoretical ratio. The main reason is that the droplet does not fall due to the drift of droplets in the process of operation. The data in the table show that the effective sampling point number is from \(-3\) to \(3\). According to the Civil Aviation Industry Standards of the People's Republic of China (MH/T1002.1-2016) with regard to the technical specifications for the quality of agricultural aviation ultra-low-capacity pesticide-spraying operations [31], it can be estimated that the actual spraying swath is about 5 m.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sortie**} & \multirow{2}{*}{**Unit**} & \multicolumn{8}{c}{**Sampling Point**} & \multirow{2}{*}{**Average**} & \multirow{2}{*}{**Coefficient**} \\  & & & & & & & & & & & & **of Variation** \\ \hline \multirow{5}{*}{First} & 1 & 6 & 16 & 19 & 29 & 44 & 31 & 23 & 14 & 9 & 25.14 & \\  & 2 & 2 & 17 & 22 & 37 & 81 & 54 & 22 & 10 & 8 & 34.71 & 38.07\% \\  & 3 & 0 & 15 & 19 & 26 & 47 & 34 & 17 & 6 & 0 & 23.43 & 32.5\% \\  & 4 & 13 & 26 & 57 & 123 & 169 & 115 & 41 & 23 & 12 & 79.14 & 237.77\% \\ \cline{2-11}  & 5 & 1 & 9 & 16 & 39 & 73 & 27 & 18 & 7 & 0 & 27 & 56.88\% \\  & 6 & 0 & 14 & 23 & 45 & 137 & 67 & 24 & 16 & 3 & 46.57 & 72.48\% \\ \hline \multirow{5}{*}{Second} & 1 & 0 & 12 & 19 & 24 & 41 & 31 & 20 & 16 & 4 & 23.29 & 59.47\% \\  & 2 & 9 & 16 & 22 & 37 & 93 & 49 & 29 & 14 & 0 & 37.14 & 28.08\% \\  & 3 & 0 & 15 & 23 & 36 & 55 & 29 & 16 & 13 & 1 & 26.71 & 73.83\% \\ \cline{1-1} \cline{2-11}  & 4 & 4 & 21 & 33 & 59 & 143 & 37 & 20 & 12 & 0 & 46.43 & 47.9\% \\ \cline{1-1}  & 5 & 1 & 6 & 15 & 23 & 69 & 31 & 18 & 7 & 0 & 24.15 & 113.54\% \\ \cline{1-1}  & 6 & 3 & 14 & 29 & 67 & 115 & 89 & 32 & 15 & 3 & 51.57 & 113.54\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Statistics of droplet coverage density.  
Figure 19: Grayscale image of water-sensitive paper.