Séminaire
At global scale, photosynthesis is the largest process of carbon sequestration. The estimation of the amount of carbon exchanged between atmosphere and vegetation is crucial for predicting the evolution of atmospheric CO2. However, the current observations of land surfaces allow to characterize the state of the vegetation (cover, light interception, biomass) but rather poorly its functioning.
Although the light energy absorbed by plants is mainly used to drive the photosynthetic mechanisms, a small amount is lost through fluorescence emission (ChlF). As ChlF competes with photochemical conversion, its variations are closely related to variations of photochemical yield. ChlF is a rich signal whose kinetic variations, spectral characteristics as well as its dependency to excitation light are widely used in photosynthesis research at the leaf level. Hence, ChlF appears as a good candidate to assess vegetation status at large or global scales using remote sensing techniques.
Research in the field of canopy level fluorescence remote sensing has grown significantly in recent years thanks to the development of passive method. They are based on the use of the abrupt spectral changes in solar illumination for discriminating chlorophyll fluorescence from reflected light by the vegetation and allow long-range measurements. Recent publications showed for the first time global maps of sun-induced fluorescence and several satellite mission claims to be able to measure the fluorescence.
In this seminar we will present the principles of fluorescence measurements, some results obtained during measurement campaigns at canopy level and the issues on the interpretation of the measured signal for its use in productivity models.
MP Lefebvre (01.44.27.27.99)