A spectral fitting model for chlorophyll fluorescence retrieval at global scale

Chlorophyll sun-induced red and far-red fluorescence retrieval from space was recently proposed as a possible candidate for monitoring the vegetation status at global scale. Due to the very weak fluorescence emission signal in comparison to the reflected signal, detection is possible by performing radiance measurements in some of the atmospheric absorption bands where solar radiation is strongly attenuated while fluorescence is minimally influenced by this energy loss. To obtain an accurate retrieval of any information in the O₂A and O₂B absorption bands, we used high spectral resolution forward modeling and fitting. All the efforts were focused to determine the possibility of an accurate fluorescence retrieval at the VIS-NIR fluorescence Imaging Spectrometer (FIS) resolution (2 cm^-1) of the ESA FLEX mission. In the case we present, we used MODTRAN5 at the maximum spectral resolution, i.e. 0.1 cm^-1 for the radiation simulations and simulated fluorescence and reflectance at canopy level.