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

The mission aims to produce the first global map of fluorescent light spectra from vegetation. This faint glow is given off by photosynthesis as plants convert carbon dioxide into molecular chains of carbon using the energy from absorbed photons and cannot currently be measured directly from space. This will be possible thanks to 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, 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 450 kg, it will be dual-manifested for launch on Europe’s Vega vehicle from the Guiana Space Centre in 2022-2023.

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, INRA, CNRM, LEMP).