Monitoring Earth's photosynthesis from space

3 minute read 

Scientists from NPL are playing a critical role in ensuring the quality and reliability of data from the European Space Agency’s (ESA) Fluorescence Explorer (FLEX) mission,  which successfully launched this week aboard a Vega-C rocket from Kourou, French Guiana.  

FLEX is ESA's first mission dedicated to measuring vegetation fluorescence, providing unprecedented insights into plant photosynthesis, vegetation health and the global carbon cycle. The mission will help scientists understand how actively plants are functioning, rather than simply how green they appear, improving our understanding of the exchange of carbon, water and energy between land surface and the atmosphere. 

At the heart of the mission is the FLORIS (Fluorescence Imaging Spectrometer) instrument, a state-of-the-art hyperspectral spectrometer that measures sunlight reflected from vegetation and the extremely faint fluorescence signal emitted by plants during photosynthesis. Observing across the visible and near-infrared spectrum at very high spectral resolution, FLORIS is capable of detecting subtle changes in plant activity, stress and productivity that cannot be observed by conventional Earth observation satellites. FLEX will fly in tandem with the Sentinel-3 satellites, combining FLORIS measurements with complementary observations of surface reflectance, land surface temperature and atmospheric properties to generate a unique picture of ecosystem health at a global scale.  

NPL works as part of the FLEX Data Innovation and Science Cluster (DISC), playing a key role in preparing for the mission's operational phase. NPL is responsible for the validation of the FLEX surface reflectance and at-surface irradiance products, helping to ensure that measurements derived from the satellite are accurate, traceable and scientifically robust. NPL has also provided guidance on the development and implementation of uncertainty estimates within the FLEX products themselves and for their validation activities, ensuring confidence in the quality of the mission data and the scientific conclusions drawn from them.  

The NPL team has developed validation methodologies, uncertainty frameworks and operational tools that will underpin product quality assessment throughout the mission. Through work in other projects, NPL has developed key reference sites and networks (HYPERNETS and INSIF) that are the key infrastructure enabling the SI-traceable validation for FLEX. As part of this effort, the NPL team recently installed a new HYPERNETS site in a grass field at Wytham Woods in Oxford. These SI-traceable networks are critical for the validation of surface reflectance as well as other downstream satellite products.    

Looking ahead, NPL will produce the operational validation reports for the FLEX surface reflectance products during commissioning and throughout the mission lifetime. These independent assessments will provide evidence of product performance and measurement quality, helping ESA and the wider scientific community maximise the value of the mission's observations. 

Listing image credit: ESA