## Materials and Methods
### Equipment and Data Collection Methods  
The particle size of the droplets produced by the nozzle and the deposition distribution were two main parameters in this study, the water was used instead of pesticide. The experiment was conducted under the pressure of 0.2 MPa with the environmental temperature at \(25\pm 2\)\({}^{\circ}\)C and the relative humidity of \(55\pm 5\%\). Spray particle size analyzer (NKT Analysis Instrument, Shandong, China, PW180-B) was used to measure the droplet size, the measurement range was 1-1000 \(\upmu\)m and the repeatability error was kept within 1%. According to the commonly used UAV spraying flight attitude, spray heights were set to 1 m, 1.5 m, and 2 m.  
As shown in Figure 3, the deposition was measured by several 100 mL measuring cylinders, the center of the upper surface of each measuring cylinder was the position of each measuring point. The experiment put measuring cylinders along the centerline, the time for collecting was 5 min, and the collection repeated for three times. Since the external diameter of the100 mL measuring cylinder was 65 mm (the distance between the centers of two adjacent measuring cylinders is the same as the value of external diameter), we set the distance between each measuring point at the same spray height as 65 mm. the inner diameter of measuring cylinder was 27 mm, and we can get the area of spray for each measuring cylinder, the conversion formula of measured volume and deposition was obtained as follows:  
\[\beta_{dep}=\frac{V}{0.25\pi d^{2}} \tag{1}\]  
where \(\beta_{dep}\) is the deposition (mL/cm\({}^{2}\)), \(V\) is the measured volume (mL), \(d\) is the inner diameter of the measuring cylinder (cm). The droplet size was measured by passing the laser of particle size analyzer through the measuring point accordingly, and vertically, each experiment collected 60 data of the same measuring point as a group and every test repeated for three times, 60 data were averaged as one measuring value for one measuring point. The 50% effective deposition determination method was used to determine the spray span of TEEJET XR110015 VS nozzle [32]. According to the ASAE standard S341.3, the two-point distance between half of the maximum deposition on both sides was defined as the effective spray span. The deposition was measured in 29 horizontal positions (14 different measuring point on both sizes and one center point) at each height, the measuring cylinders were placed along the center line just as shown in Figure 3, every test was repeated for three times. After this experiment, the spray spans were determined for each height, 1040 mm for 1 m, 1300 mm for 1.5 m, and 1430 mm for 2 m accordingly. The spray span showed symmetry along the spray height direction (axis \(x\)). Figure 3: Schematic diagram of droplet size and deposition distribution measuring x, vertical axis; y, horizontal position; h, spray height. According to preliminary experiment, the spray height remained the sets before (1 m, 1.5 m and 2 m), the measuring points were set along the horizontal line and the interval is 65 mm, the maximum horizontal position were set to \(\pm\)520 mm, \(\pm\)650 mm and \(\pm\)715 mm for each spray height. Additionally, we selected three most commonly used spacing of nozzles in UAV spraying for twin nozzles experiment (0.5 m, 0.6 m, and 0.7 m). The distribution diagram of measuring points was shown in Figure 4, the VMD values and deposition values obtained from these measuring points were shown in Table 1. As shown in Figure 4a, the first experiment was to measure the droplet size at each measuring point of the single nozzle, the study took the center of the nozzle as the zero point of the \(y\)-axis and collected data of all measuring points within the maximum horizontal position on both sides, group A in Table 1 represents the VMD values obtained by this experiment.