The FLuorescence EXplorer (FLEX) mission is the eighth mission in the Earth Explorer programme, (part of ESA'sLiving Planet Programme). It comprises a satellite for the global monitoring of steady-statechlorophyll fluorescence in terrestrial vegetation.[12] Leaf photosynthesis releases energy not required in the biochemical process in the form of light in wavelength between 640 and 800 nanometres.[3]
After more than 70 years of basic and applied research in chlorophyll fluorescence, it is now established that fluorescence is a sensitive indicator ofphotosynthesis in both healthy and physiologically perturbed vegetation that can be used to monitor croplands and forests.[3]
Fluorescence is a powerful non-invasive tool to track the status, resilience, and recovery of photochemical processes, and provides important information on overall photosynthetic performance with implications for relatedcarbon sequestration. The early responsiveness of fluorescence to atmospheric, soil and plant water balance, as well as to atmospheric chemistry and human intervention in land usage, makes it a useful biological indicator in improving the understanding ofEarth system dynamics.
FLEX will encompass a three-instrument array for measurement of the interrelated features of fluorescence, hyperspectral reflectance, and canopy temperature.
ESA-developed Earth observation missions
The program will involve a space and ground-measurement program of 3-years duration and will provide data formats for research and applied science.
In November 2015, ESA has selected FLEX as the agency's eighthEarth Explorer mission.[13]
In November 2016, ESA has selected Italian companyLeonardo to build the main instrument (FLORIS) for the FLEX satellite.[14]
In 2018, during the first FLEXSense campaign, the OLCI instruments of theSentinel-3B satellite was reprogrammed to operate in a mode simulating the future cooperations with FLEX and a parallel aerial campaign used aircraft-based observations to demonstrate aspects of the FLORIS instrument functionality.[15]
In January 2019, ESA has selectedThales Alenia Space as the prime contractor for the satellite and to oversee the development of the FLORIS instrument by Leonardo.[16]
In summer 2019, the second FLEXSense campaign took place, with operations closely following the 2018 campaign.[15]
In January 2022, ESA has signed a contract withArianespace for a joint launch of FLEX andAltius onVega C.[17]
In December 2023, Thales Alenia Space selected the UK’sNational Satellite Test Facility for the satellite's first comprehensive assembly, integration and test campaign.[18]
In 2024, theFraunhofer IOF inJena was exhibiting the double-slit assembly, which it had developed for the FLORIS instrument, at SPIE Photonics West inSan Francisco.[19]
In August 2025, the FLORIS instrument has been joined to the FLEX satellite platform atThales Alenia Space inCannes.[20]
^Kraft, S; Del Bello, U; Bouvet, M; Drusch, M; Moreno, J (2012). "FLEX: ESA's Earth Explorer 8 candidate mission".2012 IEEE International Geoscience and Remote Sensing Symposium. pp. 7125–7128.doi:10.1109/IGARSS.2012.6352020.ISBN978-1-4673-1159-5.S2CID7603157.
^Kraft, S; Bézy, J.-L; Del Bello, U; Berlich, R; Drusch, M; Franco, R; Gabriele, A; Harnisch, B; Meynart, R; Silvestrin, P (2013). "FLORIS: Phase a status of the fluorescence imaging spectrometer of the Earth Explorer mission candidate FLEX". In Meynart, Roland; Neeck, Steven P.; Shimoda, Haruhisa (eds.).Sensors, Systems, and Next-Generation Satellites XVII. Vol. 8889. pp. 88890T.doi:10.1117/12.2032060.S2CID128624334.
^Drusch, Matthias; Moreno, Jose; Del Bello, Umberto; Franco, Raffaella; Goulas, Yves; Huth, Andreas; Kraft, Stefan; Middleton, Elizabeth M; Miglietta, Franco; Mohammed, Gina; Nedbal, Ladislav; Rascher, Uwe; Schuttemeyer, Dirk; Verhoef, Wout (2017). "The FLuorescence EXplorer Mission Concept—ESA's Earth Explorer 8".IEEE Transactions on Geoscience and Remote Sensing.55 (3):1273–1284.Bibcode:2017ITGRS..55.1273D.doi:10.1109/TGRS.2016.2621820.S2CID5267592.
^Stoll, M.P; Buschmann, C; Court, A; Laurila, T; Moreno, J; Moya, I (2003). "The FLEX-Fluorescence Explorer mission project: Motivations and present status of preparatory activities".IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477). Vol. 1. pp. 585–587.doi:10.1109/IGARSS.2003.1293850.ISBN978-0-7803-7929-9.S2CID56932583.
^Rascher, Uwe; Gioli, Beniamino; Miglietta, Franco (2008). "FLEX — Fluorescence Explorer: A Remote Sensing Approach to Quantify Spatio-Temporal Variations of Photosynthetic Efficiency from Space".Photosynthesis. Energy from the Sun. pp. 1387–1390.doi:10.1007/978-1-4020-6709-9_299.ISBN978-1-4020-6707-5.
^Harnisch, Bernd; Kraft, Stefan; Bézy, Jean-Loup; Drusch, Matthias; Bouvet, Marc; Del Bello, Umberto (2017). "Fluorescence imaging spectrometer concepts for the Earth explorer mission candidate flex".International Conference on Space Optics — ICSO 2012. p. 72.doi:10.1117/12.2309086.ISBN9781510616172.S2CID125313615.
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