REMOTE DETECTION OF PHYSIOLOGICAL DEPRESSION IN CROP PLANTS WITH INFRARED THERMAL IMAGERY

The infrared thermal imagery was measured concurrently with physiological status in stressed and non -stressed corn and wheat canopies. Thermal images were obtained with an infrared thermography system from a distance of 5 to 20 m. Each thermal image, composed of 512(H) X240(V) pixels with a sensitivity of 0.05°C, was recorded in a video tape every 8 seconds in the field, and analyzed in a laboratory later. A root-reducing treatment was used for simulating environmental stresses, which treatment was carried out by cutting a root system with a thin metal plate at the depth of 20 cm, but brought little apparent change in plant stands. Photosynthesis, transpiration and stomatal conductance in the stressed canopy were depressed, which were accompanied with an inverse change in the canopy surface temperature. The maximum difference in mean surface temperatures of the stressed and non-stressed parts of the canopy was no less than 4.2°C in corn and 3.1°C in wheat. Gaussian distribution of spatial temperature frequency in the stressed part shifted toward higher temperature from that of non-stressed part of the canopy, which was visualized clearly on the pseudo color thermal image while no visible changes were observed directly from the distance. The infrared imagery was effective, especially, for detecting physiological depression or for comparing various canopies in their physiological status on a remote and real-time basis. © 1990, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.