## 3 Results
### The Results of Ground Drift  
For the impact of different wind speeds of 2, 4, and 6 m/s on the ground drift at four liquid pressures to be compared, all drift treatments and sample collection were conducted by the same operators. As shown in Figure 5, the overall variations were similar under different pressures and wind speeds. The deposition amount at each sampling location in the main deposition area of 2-15 m was increased with increasing wind speed, except for \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Liquid Pressure/Bar** & **D\(\
u_{0.1}\)/\(\mu\)m** & **D\(\
u_{0.25}\)/\(\mu\)m** & **D\(\
u_{0.5}\)/\(\mu\)m** & **D\(\
u_{0.75}\)/\(\mu\)m** & **D\(\
u_{0.9}\)/\(\mu\)m** & **\(\Delta_{s}\)** \\ \hline
0.2 & 59.39(0.0045) & 83.37(0.0027) & 124.46(0.0089) & 202.27(0.0073) & 275.67(0.0073) & 1.74 \\
0.3 & 54.54(0.0046) & 71.09(0.0113) & 101.71(0.0097) & 147.75(0.0103) & 236.07(0.0318) & 1.78 \\
0.4 & 53.21(0.0214) & 65.18(0.0124) & 88.84(0.0061) & 127.01(0.0073) & 193.42(0.0146) & 1.58 \\
0.5 & 49.67(0.0120) & 63.34(0.0147) & 85.95(0.0117) & 121.05(0.0050) & 186.69(0.0058) & 1.59 \\ \hline \end{tabular}
\end{table} 
Table 1: Droplets size distribution (mean (standard deviation)) under four different liquid pressures. the location at 15 m at a pressure of 5-bar, in which the deposition amount of the wind speed condition of 4 m/s was greater than that of the wind speed condition of 6 m/s. Because the nozzle pressure is one of the decisive factors of the flow rate, the deposition amount at most sampling locations in the main deposition area increased with the increasing pressure. In addition, the maximum values of drift deposition at pressures of 4 bar (9.88 \(\mu\)L) and 5 bar (10.42 \(\mu\)L) were obviously higher than those at pressures of 2 bar (3.10 \(\mu\)L) and 3 bar (5.83 \(\mu\)L). The curve shape of the deposition distribution at the 4-bar pressure resembled that at the 5-bar pressure due to a similar \(PDF_{N}\) of droplet size distribution. The deposition amount of different drift areas was obtained by the integration of sampling locations within the designated area, as shown in Table 2. For most drift areas, larger wind speeds had the highest deposition amount for all liquid pressures. Generally, the liquid pressure of 5 bar was associated with a higher deposition than that of the liquid  
Figure 4: The probability integral distribution function of droplet size (\(PDF_{N}\)) at four pressures of 2, 3, 4, and 5 bar, whose flow rates are 486.94, 606.87, 696.78, and 822.64 mL/min, respectively. Figure 5: Ground deposition drifting downwind. (**a**) drift deposition of 2 bar, (**b**) drift deposition of 3 bar, (**c**) drift deposition of 4 bar, and (**d**) drift deposition of 5 bar. Distance is from the Unmanned Aerial Vehicles (UAV) test platform. pressure of 4 bar, followed by the liquid pressure of 3 bar, then 2 bar and this rule was most obvious in the areas of 2-6 m and 6-10 m. We observed that the highest deposition of 8698.682 uL, on condition when the wind speed was 6 m/s and the liquid pressure at 5 bar, was 7.12 times as much as the lowest deposition amount of 1222.371 uL, on condition that the wind speed was 2 m/s and the liquid pressure was 2 bar in the area of 2-6 m.  
To study the relationship between the deposition amount of all areas and total drift amount, the drift ratio (the percentage of deposition amount for each area to total drift amount in the same treatment) was introduced. The drift ratios of T3 (pressure of 4 bar, 56.91%) and T4 (pressure of 5 bar, 54.85%) were higher than those of T1 (pressure of 2 bar, 49.37%) and T2 (pressure of 3 bar, 49.45%) under the wind speed of 2 m/s. The drift ratio of T7 (a pressure of 4 bar, 49.15%) was higher than those of T5 (pressure of 2 bar, 41.44%) and T6 (pressure of 3 bar, 44.67%) under a wind speed of 4 m/s. The drift ratios of T11 (a pressure of 4 bar, 44.03%) and T12 (a pressure of 5 bar, 47.32%) were higher than those of T9 (pressure of 2 bar, 34.48%) and T10 (a pressure of 3 bar, 34.60%) under a wind speed of 6 m/s.