Effect of canopy structure on sun-induced chlorophyll fluorescence

We investigated the impact of canopy structure on chlorophyll fluorescence properties. For this purpose, we developed SpectroFLEX, an instrument for quantitative measurements of canopy fluorescence in O2A and O2B atmospheric absorption bands. The fluorescence emission of a natural grass canopy was compared with the leaf level fluorescence spectrum acquired simultaneously. It was found that the red-to-far-red fluorescence ratio decreased by a factor of two from the leaf to the canopy level. In addition, this ratio decreased under high light conditions. FluoSAIL simulations were conducted to study the impact of canopy density and geometry on this decrease. This effect has been attributed to a preferential re-absorption of red fluorescence emission during radiative transfer within the canopy compared to far-red emission.