FLEX (FLuorescence EXplorer) is the eighth ESA Earth Explorer orbital technology demonstration mission and was selected in 2015.

FLEX will employ a specialized spectrometer to measure fluorescent light from vegetation produced by photosynthesis. The mission—a world first with ambitious science goals planned for 2025—aims to generate global maps of this light from land surfaces and coasts with a spatial resolution of 300 metres and a 27-day repeat cycle.

The faint glow from chlorophyll is given off by photosynthesis as plants convert carbon dioxide into molecular chains of carbon using the energy from absorbed photons. Quantifying photosynthesis by observing this glow is the aim of FLEX’s main instrument, FLORIS (FLuORescence Imaging Spectrometer), designed by the Leonardo consortium, which will sense light in a frequency band between 500 nm and 880 nm.

Science teams are studying plant fluorescence with a view to gaining a better understanding of how photosynthesis effects the way carbon moves between vegetation, the atmosphere and the water cycle.

FLEX’s readings will be correlated to those from the European Sentinel-3 satellite, with which it will operate in tandem to provide unique environmental context by taking advantage of its optical and thermal sensors.

The mission’s precise science goals will be to:

• Qualify fluorescence measurements for studying photosynthesis and compare them to other methods.
• Understand temporal and spatial variations and compare them with more precise field measurements.
• Identify and characterize the effects of different types of stress—like drought, heatwaves, cold and wind—on plant fluorescence and photosynthesis.
• Open new avenues and applications for observation of plant fluorescence, notably for agriculture.

The FLEX satellite will be assembled by Thales Alenia Space. Weighing 460 kg, it will be dual-manifested for launch on Europe’s Vega-C vehicle from the Guiana Space Centre in 2025.

How CNES is contributing

CNES has been involved in the project from the outset, notably supporting the research laboratories contributing to the mission. The LMD dynamic meteorology laboratory is leading science efforts on the subject in France, working alongside several other French laboratories (LSCE, ESE, CESBIO, INRAE, CNRM, OHP, IMBE and LEMP).