## 2 Materials and Methods
### Evaluation of Spray Coverage and Penetration  
To analyze the effect of nozzle type on coverage and penetration, the agricultural spraying drone was equipped with a flat fan nozzle and an AI nozzle and sprayed with water on 6 September and 5 October 2021. The drone flew at a height of 3 m above the ground and a speed of 2 m/s during the experiment. The flight distance of single spraying was 40 m. The pressure of pump was set to 0.28 Mpa based on the nozzle recommendation [44]. The flow rate of the pump at this pressure was 1.2 L/min. The sprayed droplets were collected using water-sensitive paper (76 mm \(\times\) 52 mm, Teejet Technologies, Glendale Heights, IL, USA) [46]. Since the water-sensitive paper is sensitive to moisture, the humidity was controlled below 80% by draining the water in the rice field the day before the experiment. To minimize the effects of humidity, the paper was put out immediately prior to spraying and collected a few seconds after the drone sprayed the plant protection product. Three sampling points were symmetrically arranged along the perpendicular direction of the agricultural drone flight route with three repetitions (Figure 3). The interval distance between sampling points was 2 m. The total length of the sampling points was designed for the effective spray width. The distance between the flight center line was 10 m and, while the drone was returning, the spraying stopped. The water-sensitive paper was attached to the angle-control label stand (Figure 4). The water-sensitive paper was installed at two levels: the canopy (h\({}_{1}\) = 80 cm) and middle point (h\({}_{2}\) = 40 cm) of the crop at each sampling point. The collectors were installed at three points on the flight path. After the experiment, each water-sensitive paper was sealed in a zipper bag to block contact with moisture and delivered to the laboratory. The images of the water-sensitive paper were obtained using a red, green, and blue camera and analyzed via binarization.  
Figure 4: **(left)** Arrangement of water-sensitive paper at two height levels (40, 80 cm) and (right) appearance of angle-control label stand.  
Figure 3: Layout of flight path and collectors. The distance between groups of collectors is 10 m and the drones fly perpendicular to the wind direction.  
The coverage and penetration ratio (PR) were measured to evaluate the nozzle spray performance because the amount of agent delivered to the surface or inside the crop affects control effectiveness. Coverage refers to the ratio of the droplet deposition area on the collector to the entire collector area. The amount of deposition can be compared based on coverage (Equation (1)) [47]. The collector located at the canopy was used to analyze the coverage. The PR was measured to identify the ratio of agents to be delivered inside the crop. PR is important, especially for leafy plants, because it affects the delivery of the agent [48]. The PR was calculated using the ratio of droplet areas attached to the canopy and middle point of crops (Equation (2)). R (Version 4.2.2, The R Foundation, Vienna, Austria), a statistical analysis software, was employed to analyze the data. A two-way analysis of variance was conducted to analyze sensitive factors affecting the spray performance.  
\[\mathrm{C}=\frac{A_{D}}{A_{W}} \tag{1}\]  
\[\mathrm{PR}=\frac{\mathrm{C}_{2}}{\mathrm{C}_{1}} \tag{2}\]  
where C is coverage, \(A_{D}\) is total area of droplets deposited, \(A_{W}\) is total area of water-sensitive paper, PR is penetration ratio, \(\mathrm{C}_{1}\) is coverage of water-sensitive paper at h\({}_{1}\), and \(\mathrm{C}_{2}\) is coverage of water-sensitive paper at h\({}_{2}\).