About the FLEX Bridge Study

The FLEX Bridge Study has advanced the work of the PS Study and PARCS projects by addressing priorities identified in these studies
and in ongoing FLEX preparatory activities.  The goal was to optimize approaches for SIF retrievals and applications in assessment of
photosynthesis & stress status in terrestrial vegetation, including development of a calibration/validation strategy for FLEX products.

FLEX Bridge has formed a foundation for subsequent science & applications development during mission development and deployment.
The study consolidated follow-on activities leading up to the User Consultation Meeting held on 15-16 September 2015 in Krakow, Poland.
Following comprehensive assessment by ESA's Earth Science Advisory Committee, FLEX has been selected as the Earth Explorer 8 mission.

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 address priorities identified by previous studies and in ongoing FLEX preparatory activities.
  • To optimize the fluorescence retrieval algorithm developed under the PARCS project.
  • To optimize the photosynthesis retrieval model (SCOPE v1.53) and its related algorithm developed under the PS Study.
  • To consolidate and develop retrievals for additional Level 2 data products.
  • To further exploit applications in photoynthesis modelling & stress detection.
  • To develop a calibration/validation strategy for FLEX products.

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.

A key finding so far is the inherent value of having both the red and the far-red fluorescence emission peaks for applications.  This underscores the unique advantages of FLEX and its optimized FLORIS sensor.  Visible plant colour doesn't matter to fluorescence.

The PS Study Project

The Photosynthesis Study was one of three parallel study activities conducted during Phase A/B1 assessment of the FLEX candidate mission.

The study provided guidance on how to best utilize the fluorescence signal retrieved under PARCS (The “Performance Analysis and Requirements Consolidation Study”).

It also complemented the FLUSS Study (“atmospheric corrections for FLUorescence Signal and Surface pressure retrieval over land”) activity, which helped define atmospheric correction requirements to compute top-of-canopy radiances from observed top-of-atmosphere radiances.

FLEX Bridge has advanced these works.

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

Read the FLEX Report for Mission Selection  HERE.

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