Measuring Stress Reactions of Beech Seedlings with PRI, Fluorescence, Temperatures and Emissivity from VNIR and Thermal Field Imaging Spectroscopy

Photosynthesis rate was measured during the course of a day on a pot of well-watered and a pot of drought-stressed young beech trees. At the same time, hyperspectral visible/near infrared and hyperspectral thermal images of the plants were recorded with a very high spatial resolution from a 3.8 m high platform. Time series of photochemical reflectance index (PRI), sun-induced fluorescence, temperature, and emissivity of the leaves were correlated with the photosynthesis measurements. PRI (R-2=0.72 and 0.78 for well-watered and drought-stressed group, respectively), fluorescence (R-2=0.72 and 0.40), and temperature (R-2=0.62 and 0.69) proved to be good estimators for measured photosynthesis rates, emissivity had weaker correlations (R-2=0.05 and 0.18). High resolution maps of photosynthetic activity could be produced from PRI, fluorescence, and temperature.