Wind-induced response of rice under the action of the downwash flow field of a multi-rotor UAV

Unmanned aerial vehicles (UAVs) are becoming increasingly used in agriculture. Many agricultural operations, the involving UAVs are carried out at low flying altitudes, which generates a powerful downwash flow field that changes the shape of plants. To explore the influences of the downwash flow field on the shape of plants, this paper focused on rice plants at heading stage and tested the effect of different UAV flight parameters. The single-factor tests in hover showed that the wind speed at the rice canopy reduced and turbulence intensity of the downwash flow field increased as the UAV flight altitude increased from 2 to 8 m. Moreover, it showed that the degree of rice plant deformation was closely related to the maximum velocity of the downwash flow field. The multifactor field tests showed that the area of rice deformation was shaped like a horseshoe; and the flight altitude (1.5-5 m), flight speed (1-5 m s(-1)) and payload (0-20 kg) had obvious effects on rice plant deformation with the greatest effect due to payload, followed by flight speed, and flight altitude. When the maximum wind speed was less than 3 m s(-1), the downwash flow field did not cause obvious changes to rice plant morphology. (C) 2021 IAgrE. Published by Elsevier Ltd. All rights reserved.