MULTI-FLEX: towards a strategy for fluorescence monitoring at multiple scales within the context of the FLEX/S-3 tandem mission

Living Planet Fellowship research project carried out by Marco Celesti.

The future FLEX/Sentinel-3 tandem mission will provide unique information on vegetation dynamics by exploiting Sun-induced fluorescence and reflectance at the unprecedented spatial scale of 300m x 300m. This magnified view into the photosynthetic machinery will enhance our ability to face the actual and future challenges related to food production and to the interactions between natural ecosystems and the climatic and biogeochemical Earth system. Towards the FLEX mission, a lot of technical and scientific development is ongoing in order to build up the knowledge necessary to translate this spectral information into a meaningful and concrete way to retrieve photosynthesis from space. Within this context, the ATMOFLEX project started in February 2018 with the main aim of collecting Sentinel-3A measurements and collocated ground observations characterizing the state of the atmosphere for an extended period of time. As a core objective of ATMOFLEX, several sites have been instrumented with state-of-the-art hyperspectral spectroradiometers continuously measuring over the vegetation. Moreover, for a limited period of time, Sentinel-3B OLCI data in a FLEX-like configuration will be acquired, together with airborne acquisition with the FLEX airborne demonstrator (HyPlant). This will bring the unique opportunity of a multi-scale, multi-platform dataset acquired with fluorescence-capable devices, over a coherent time and geographical frame.
This project is focused in exploiting the potential of fluorescence and reflectance to describe photosynthetic dynamics, by exploiting the dataset acquired within the ATMOFLEX project, developing a flexible tool built on physically based RTMs for retrieving information about vegetation biophysical/biochemical parameters and Sun-induced fluorescence, capable of dealing with multiple spectral and spatial resolution data. High level parameters retrieved from model inversion such as the fluorescence quantum efficiency will be compared with simpler fluorescence- and reflectance based metrics proposed to track vegetation photosynthetic dynamics or to correct for mixed pixel problems arising at the spatial scale offered by satellite observations.
Apart from contributing to the development of an innovative approach for a coupled retrieval of fluorescence and vegetation parameters, the direct benefit of this approach would be to enrich the dataset of the ATMOFLEX sites with consistent data that can be further exploited at a later stage. Moreover, the multi-scale approach proposed in this project will improve our understanding of the link between punctual measurements performed on the ground and satellite observation in the context of the future FLEX cal/val activities, a fundamental step towards the creation of robust and reliable products out of the mission.