Assessment of optimal flying height and timing using high-resolution unmanned aerial vehicle images in precision agriculture

This paper shows some practical experiences of using unmanned aerial vehicles-based platform for remote sensing in supporting precision agriculture mapping. There have been studies on unmanned aerial vehicles used to calculate plant water stress; however, the scientific reports of drone images that are used to predict best time and height are rare. The trial was conducted during 2020, in a five-year-old Anji tea plant experimental field, where drone captures images in a different time series of 27 flights during experimental days. This work aims to (1) investigate the appropriate thermography timing and altitude based on unmanned aerial vehicles remote sensing, (2) conduct a quantitative and qualitative study of various thermal orthomosaics and photographs, (3) establish workflow for high-resolution remote sensing application. All flights were operated at 3 m/s flying speed. Flights were performed during the testing day at about 09:00 h, 11:00 h, and 13:00 h. The drone images were taken at relative flying heights of 25 m, 40 m, and 60 m each day. The relationship between canopy temperature and plant-based variables was also established. The results reported that flights at 11:00 h and 60-m altitude orthomosaic could provide the best relation and accurate canopy temperature. On the other hand, the high relationship between stomatal conductance and canopy temperature was R-2 0.98 at 11:00 h. The selection of optimal timing and altitude can provide rapid and reliable canopy temperature information. Overall, high resolution with low-altitude unmanned aerial vehicles images proved good relationship in order to assess the canopy temperature.