Influence of the excitation light angle on the vegetation fluorescence emission

zenith angle ABSTRACT: Many years of green plants fluorescence studies show, that the fluorescence could be used as an intrinsic indicator of the plant bio status. The advantage of that approach is the opportunity stress factors to be discovered before the symptoms are observed with more conventional means. Various devices have been already developed for active or passive measurement of fluorescence in laboratory and natural conditions (on-ground and air-born) and two dedicated projects (FLEXSAT—NASA and FLEX—ESA) for remote measurements of solar-induced plant fluorescence were conducted as well. The investigations in recent years have proved that the fluorescence can be remotely sensed from satellite altitudes. At the same time many factors playing significant role in the plant photosynthetic process still need to be evaluated—season/weather changes, natural conditions as heat, moisture, light exposure, plant species differences etc. The influence of the excitation light angle on the fluorescence emission was one of the experiments, which the authors have started in order to investigate the technical opportunities for registering the spatial distribution of fluorescence variations under illumination conditions, close to the natural one. In specially designed biochamber plant simples were illuminated with parallel beam at different angles, simulating changes of solar zenith angle. The paper presents the method and technical condition of the experiment, spectral images of spatial distribution of plant fluorescence at different illumination angle and results of image processing in graphical form.