About the FLEX Photosynthesis Study

The Photosynthesis Study targetted the linkage between solar-induced chlorophyll fluorescence and photosynthesis in terrestrial vegetation.
During FLEX operation, it would be desirable to map actual photosynthesis by measuring from space fluorescence emission.

The study developed and implemented a photosynthesis model based on state-of-the-art existing modules incorporating chlorophyll fluorescence.
In addition, a simpler prototype algorithm to derive photosynthesis was developed from the model and/or empirical data.

Click HERE to read or download the Final Report.

Click HERE to read or download the Final Reports.

About FLEX

FLEX will be the first mission designed to monitor the photosynthetic activity of the terrestrial vegetation layer using a completely novel technique:  measuring the chlorophyll fluorescence signal that originates from the core of the photosynthetic machinery!  This method will provide a new way to assess the dynamics of actual photosynthesis through sun-induced fluorescence, which offers a great advancement over current capabilities that can detect only potential photosynthesis as derived in passive reflectance measurements by conventional land surface monitoring satellites.  Read more HERE and HEREHERE too...  And HERE !!


It is already well known that plant photosynthesis is a sensitive indicator of environmental perturbations such as excessive ozone, pollutants, cold or heat stress, and deficiency of nutrients or water.  Currently, vegetation stress is poorly described in numerical models.

The capacity of fluorescence to track photosynthetic strain and recovery could be valuable in gauging the integrity of vegetative carbon sinks and the likelihood for sustained growth and carbon assimilation.

The responsive feature of fluorescence also supports practical applications such as agronomic crop improvement and forest vegetation assessment in the face of climatic instability.

To watch a video demonstration of Chlorophyll Fluorescence, click HERE.


Scientific Objectives of the Study

  • To assess the quality of fluorescence-derived photosynthesis data against classical optically-based methods (i.e. from fraction of absorbed photosynthetically active radiation times Light Use Efficiency).
  • To address in more detail temporal and spatial scaling issues (from towers to satellite footprints).
  • To identify and characterize the effects of different types of stress on fluorescence and photosynthesis (especially drought and freezing air temperatures).
  • To indicate potential applications of the novel fluorescence observations.

Upon absorption of a photon of light energy, chlorophyll transitions to an excited state known as singlet chlorophyll (1Chl*), which can contribute energy either for photochemistry, heat release, or fluorescence emission or for the production of triplet chlorophyll (3Chl*).

Photosynthesis Photosynthesis
Gina Mohammed / P&M Technologies

The Potential

The potential of fluorescence to indicate the presence of stress before damage is visible and possibly irreversible is a major aspect to be considered in the usage of FLEX measurements.  In contrast, reflectance changes often are detectable only in dramatic or advanced cases of physiological strain.

And leaf colour matters to reflectance.  Because FLEX takes a different approach by measuring the fluorescence that plants give off as they photosynthesise, a plant's visible colour will no longer be problematic.

Other Links to FLEX

The Photosynthesis Study was part of the package of parallel study activities needed for proper assessment of the FLEX candidate mission.

The study results now provide guidance on how to best utilize the type of fluorescence signal retrieved under PARCS ("Performance Analysis and Requirements Consolidation Study").

The study also complemented the FLUSS Study ("atmospheric corrections for FLUorescence Signal and Surface pressure retrieval over land") activity, which was to define an optimal atmospheric correction strategy to compute top-of-canopy radiances from the observed top-of-atmosphere radiances.

Click HERE to see a list of Publications journal papers & conference presentations resulting from the PS Study.

About the European Space Agency...

The European Space Agency (ESA) is Europe's gateway to space, with the mission to shape the development of Europe's space capability and ensure that investment in space delivers benefits to the citizens of Europe and the world.  ESA undertakes programmes and activities far beyond the scope of any single European country, keeping Europe at the forefront of global space activities.  Today it launches satellites for Earth observation, navigation, telecommunications and astronomy, sends probes to the far reaches of the Solar System, and cooperates in the human exploration of space.

For further information, please visit www.ESA.int