Sun-induced fluorescence: A new tool for precision farming

Abstract

Results of ground based experiments on spectral reflectance of dock leaves using a ZEISS spectrometer MCS501 UV-NIR with 2.5 nm resolution clearly show the well known induction kinetics of chlorophyll fluorescence when dark adapted leaves were exposed to continuous illumination. This observed feature demonstrates the origin of the transient behavior of reflectance caused by natural or sun-induced fluorescence. The time constant of the decline of sun induced chlorophyll fluorescence is identical to the time constant obtained simultaneously using a PAM (Pulse Amplitude Modulation) fluorometer. Results of airborne measurements with the sensor ROSIS (Reflective Optics System Imaging Spectrometer) demonstrate for the first time that sun induced chlorophyll fluorescence can be derived from airborne hyperspectral reflectance data. The new method presented here uses the spectral absorption feature of atmospheric oxygen at 762 nm, which fits better with the wavelength of chlorophyll fluorescence than the Fraunhofer absorption line at 656 nm. The results from ROSIS show maps of sun-induced chlorophyll fluorescence of green vegetation. New spatial and temporal features are observable on agricultural fields supporting the hypothesis that information on photosynthesis and plant stress may be extracted in the future from areal observation of sun-induced fluorescence.