Monitoring Onion Crops Using UAV Multispectral and Thermal Imagery: Preliminary Results

Agriculture constitutes one of the most important fields where Remote Sensing is employed, particularly in the aspects related to precision agriculture (PA). PA means a management strategy that aims at carrying out agronomic interventions in compliance with the actual crop needs and the biochemical and physical characteristics of the soil. PA analyses and manages the spatial variability of the field to optimize profitability, sustainability, and protection of agro-ecological services. The present paper shows the potentiality of coupling multispectral and thermal imagery acquired by an unmanned aerial vehicle (UAV) in monitoring crops. A case study in onion crop (Cipolla rossa di Tropea IGP) is provided. Multitemporal surveys were carried out by means of a fixed-wing UAV, equipped with a multispectral camera Sequoia Parrot (R-G-RedEdge-NIR) and a quadcopter equipped with a thermal camera Flir Vue Pro 640 R. Prior to proceeding with UAV surveys, soil characteristics were analysed on the basis of systematic sampling. According to the characteristics of thermal cameras, aluminum is used as the material of control targets with their size identified clearly in the thermal images. UAV multispectral imagery was calibrated with a panel with known reflectance, and verified with a spectroradiometer (Apogee Ps-300) on bare soil and vegetation. With regard to thermal ground truths, wet and dry panels/surfaces have been used as references, measuring their temperature before and after UAV thermal flights by means of a handheld infrared thermometer.