The next ESA mission FLEX will provide innovative hyperspectral spatial data such as sun-induced fluorescence (SIF) at a high spatial resolution (300 m). The use of new satellite observations for scientific studies concerning the monitoring of crop production, requires algorithms to transform "SIF" products from the FLEX mission level 2 to higher level products such as gross primary production or an early indication of stress (L3 level and above). But the international scientific community currently lacks coupled fluorescence-photosynthesis measurements at the canopy scale as well as detailed and validated models on which to base the assimilation of spatial fluorescence data. Indeed, although efforts to develop inversion models and procedures have been undertaken by ESA as part of the preparatory studies, these remain limited for the following reasons:

- The radiative transfer model adopted by ESA, SCOPE (van der Tol et al., 2009) does not incorporate dynamic modelling of canopy development, and therefore cannot be used for the assimilation of the time series produced by FLEX.

- The SCOPE model does not have a soil water balance sub-model, which limits its use under stress conditions.

- SCOPE is based on a turbid approach to radiative transfer in the canopy, and is therefore ill-suited for studies of structural and geometric effects on the fluorescence signal, necessary to deconvolve these from physiological effects.

- The fluorescence/photosynthesis coupling scheme of SCOPE is based on laboratory leaf measurements for only a few plant species, and too few actual canopy fluorescence data exist at present to allow validation of the fluorescence on a larger scale.

In this global context, the objectives of this PhD work concern the comparison and the synergy of different techniques for detecting, for monitoring and for modelling the effects of water stress on crop production mainly in agricultural contexts (field crops, olive groves). Thanks to a previous TOSCA funding (ECOFLUO and HYFLEX projects) an innovative and operational tool for in situ remote sensing of fluorescence at canopy level over crop sites has been developed. It will be deployed in two different equipped sites (one crop site in the SW part of France, on crop site in India and probably one crop site in Tunisia) which are part of research networks (ICOS site, ANR HiDRATE, PEPR Faircarbon). These field campaigns will allow to get physiological measurements of plant water status at canopy level and SIF observations in the meantime. These data will then be integrated into canopy models (direct-mode) and to develop inversion and assimilation procedures for spatial fluorescence data to quantitatively estimate canopy photosynthesis (at local and global scales). 

This work will benefit from collaborations already established either through the funding of research projects funded by TOSCA, ANR HiDRATE and from skills within CESBIO on 3D radiative transfer as well as knowledge in plant ecophysiology.

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For more Information about the topics and the co-financial partner (found by the lab !);

contact Directeur de thèse - valerie.le-dantec@univ-tlse3.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 14th, 2025 Midnight Paris time !