Simulation de la fluorescence de la végétation mesurée depuis une orbite géostationnaire

Abstract : This thesis is about remote sensing of the chlorophyll fluorescence to monitor the vegetation from space. Recent work shows that the diurnal variation of the chlorophyll fluorescence is the most discriminative criterion to assess vegetation physiological state, especially water stress. To ensure several measurements in a day, a geostationary orbit is considered. We created a passive imager to assess the diurnal cycles of fluorescence in the O2-A absorption band. It employs an interferential filter wheel as in the case of the Goci satellite, but providing higher resolution. After proof of concept, we have been facing difficulties defining the fluorescence yield at canopy scale. Indeed, the complexity of vegetation structure takes part in the radiative transfer within the vegetation cover. It is therefore impossible to define in all cases a fluorescence yield working for passive measurement. Nevertheless, we propose proxies to approach it in some cases. Modelling the radiative transfer of fluorescence enabled us to show the accessibility of the fluorescence yield for covers with high leaf density and horizontal leaf distribution. This modelling has been extended in order to simulate geostationary measurements in O2-A and O2-B bands. The results show the possibility to measure in the O2-A band with an uncertainty of less than 10 % on fluorescence fluxes and a temporal repeatability lower than one hour to monitor diurnal cycles of vegetation fluorescence, in order to detect a stress. In favourable cases, measurement in the O2-B band could be envisaged.
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Submitted on : Tuesday, March 14, 2017 - 12:45:52 AM
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Camill Rhoul. Simulation de la fluorescence de la végétation mesurée depuis une orbite géostationnaire. Interfaces continentales, environnement. Université Paris-Saclay, 2016. Français. ⟨NNT : 2016SACLX097⟩. ⟨tel-01488881v1⟩

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