Droplet deposition characteristics of plant protection UAV spraying at night

Abstract

The spraying technology of plant protection UAVs is developing rapidly. Although they can spray autonomously at night, the application performance under meteorological conditions at night still needs to be evaluated. In this research, the droplet deposition characteristics of nighttime and daytime spray of a P20 UAV with different operating parameters were compared. Specifically, the number of droplets deposited in different parts of the plant was evaluated. The results showed that under the same operating parameters the application time had a significant effect on the number of droplets deposited and coverage rate, the droplets number and coverage rate for the nighttime application were 43.47% and 37.21% higher than that by the daytime application. In terms of the droplets deposition in different parts of cotton plants, for the nighttime application, the proportions of the droplets on the upper, middle and lower layer to the total droplet number in the vertical direction of the plant were 41.24%, 35.71% and 23.05%, respectively and those were 43.09%, 33.99% and 22.91% for the daytime application. There were more droplets deposited on the middle and lower layer of the plants when spraying at night than those in the day. Additionally, the deposited droplets on the backside of the leaf account for 21.92% of the total droplets on a leaf for the nighttime application on average, while it was 20.23% for the daytime application, this proportion did not exceed 25% within all treatments. In the daytime, the droplet deposition effect was better at the flight speed of 3.0 ~3.5 m/s and flight height of 1.5~2.0 m, while for the nighttime application the best parameters were the flight speed of 3.0~4.5 m/s and the flight height of2 m. The deposition amount and penetration of droplets of the nighttime application were better than that during the daytime, and the optimal operating speed at night is also faster, so spray at night can help to improve UAV operating efficiency.