In the context of ongoing climate change, many scientific, political, economic, and societal issues depend on our knowledge of the functioning and CO2 balance of terrestrial ecosystems. To date, three complementary approaches are used: in situ monitoring, modeling, and remote sensing.
RS has already demonstrated its ability to monitor the dynamics of the biochemical and structural attributes of the vegetation, but its potential to provide information on the physiological state and responses of terrestrial ecosystems to abiotic factors remains to be studied. Currently, two physiological mechanisms of photosynthesis regulation are directly linked to observable optical signals from space:
1-The xanthophyll cycle involved in non-photochemical quenching (NPQ), which is the main process used to protect cells in environments in which light energy absorption exceeds the capacity for light utilization by leaves. This process can be informed by the Photochemical Reflectance Index (PRI), calculated from reflectance in narrow spectral bands at 531 nm and 570 nm and
2- Chlorophyll fluorescence induced by the sun (SIF) which is accompanied by a detectable emission of light.
The ESA has approved the FLEX mission, the first satellite mission dedicated to the measurement of SIF and PRI, in order to map photosynthesis on a global scale at a weekly time step. However, the quantification of photosynthetic from space is not directly feasible.
The main objective of this thesis project is to integrate the current knowledge on NPQ, PRI and SIF mechanisms into a new leaf-scale model of NPQ/PRI and SIF and to implement this new model into the ecosystem-scale model CASTANEA – a process-based model simulating forest functioning in terms of CO2, water, energy exchanges and forest growth developed by EV team of ESE Lab [Dufrêne et al. 2005; Davi et al. 2005; Guillemot et al., 2014).
The development of the leaf scale model will benefit from the advances made in FluorMODleaf model, developed by Yves Goulas’ team at the LMD Lab. [Pedros et al.2010]. The calibration and validation of the unified “optical-ecophysiological” CASTANEA-SIF-NPQ-PRI ecosystem model, coupling the optical responses of the vegetation to its ecophysiological functioning, will rely mainly on SIF, LIF (Laser Induced Fluorescence) and reflectance data acquired since 2021 on the Fontainebleau-Barbeau ICOS Forest site (http://www.barbeau.universite-paris-saclay.fr/index-fr.html). This model will serve not only as a predictive model but also as a conceptual framework for interpreting PRI and SIF signals under the control of various other factors.
Candidates :
Masters in Terrestrial Environmental Physics; remote sensing; Ecology and Biophysics… Experience of studies on terrestrial ecosystems, structure and functioning of the vegetation, etc.? Quantitative skills: remote sensing, modeling, coding language, data processing.
For more Information about the topics, contact Directeur de thèse :
kamel.soudani@universite-paris-saclay.fr
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