ESTIMATION OF THE CHLOROPHYLL FLUORESCENCE LIFETIME OF PLANT CANOPIES- VALIDATION OF A DECONVOLUTION METHOD BASED ON THE USE OF A 3-D CANOPY MOCKUP

Fluorescence or backscattered signals measured over a plant canopy aft er a picosecond laser shot (nadir viewing) are composed of elementary contributions coming from different illuminated leaves, branches, twig s, and the soil background. They are affected by time delays, dependin g on their levels within the canopy. The global signals measured are t hen rather complex and depend on canopy architecture and fluorescence characteristics Also, an amplitude decorrelation exists between fluore scence and backscattered signals, due to the difference existing betwe en reflectance and fluorescence properties of plant canopy components. For this reason it was necessary to develop a specific method for ret rieving the mean fluorescence lifetime of a complex plant canopy under field condition. In a first step, the position and the reflectance ch aracteristics of each reflecting canopy element is determined from the deconvolution of the backscattered signal. In a second step, the para meters obtained are introduced into the fluorescence function in order to determine the mean fluorescence lifetime. The validity of the deco nvolution method has been tested for numerous situations, using simula ted laser shots on a 3-D canopy mockup. The results obtained show a ve ry good agreement between estimated and input parameters. (C) Elsevier Science Inc., 1996.