Remote Sensing of Plants by Streak Camera Lifetime Measurements of the Chlorophyll a Emissionα

Summary The possibility of time resolved chlorophyll a fluorescence measurements using an intensified and gatedstreak camera was demonstrated on different plants at a distance of 40-80 m. The investigations, carried out in various experimental conditions: different target geometries (one planar leaf, tilted leaves, sparce foliage, separated levels of leaves), variable slit widths (0.1 to 1 mm) of the camera and measurements at different weather conditions have shown a good reproducibility of the results. The decay profiles were analyzed in order to obtain the best fit between the experimental curves and those obtained by convoluting the experimental response function R exp ( t ) with the theoretical emission law F( t ) modelled by a sum of two or three exponentials. The mean value T m of the chlorophyll fluorescence lifetimes was determined for each experimental condition. For example for poplar leaves measured in October 1993, t m was equal to = 0.8 ns in the morning, decreased strongly to = 0.4 ns in midday and then slowly increased to 1.21 ns in the night.