SvalFLEX

About the project

In September 2026, ESA launched FLEX (FLuorescence EXplorer) in tandem with Sentinel-3C. The satellite carries the FLORIS spectrometer, which measures sun-induced chlorophyll fluorescence (SIF) — the faint light plants themselves emit while photosynthesising. The goal is global maps of photosynthetic activity and plant stress, roughly monthly at 300 m resolution, across at least three growing seasons.

ESA has opened its calibration and validation (cal/val) programme to research groups contributing ground-, UAV- and airborne-based measurements. SvalFLEX contributes field data from Svalbard's Arctic tundra — a short-season, low-stature, fragmented ecosystem that makes a demanding but important test of how well FLEX captures photosynthesis at high latitudes.

WP1 - Field data

Field validation data is collected in Adventdalen valley, close to Longyearbyen. A FLoX spectrometer, deployed since 2019, continuously records canopy spectral reflectance and sun-induced fluorescence (SIF). In addition to the FLoX sensor, ten cal/val racks across various vegetation types measure NDVI, climate, and parameters such as the Photochemical Reflectance Index (PRI) and Photosynthetically Active Radiation (PAR). Also in Adventdalen, Leaf Area Index (LAI), Leaf Chlorophyll Content (LCC), vegetation cover and biomass are measured by hand. Campaigns are timed to FLEX overpasses and repeated through the short Arctic growing season to capture phenological change.

WP2 - Remote sensing data

An airborne version of the FLoX spectrometer (AirFloX), mounted on an Unmanned Aerial Vehicle, directly samples spatial variability across the full footprint of a FLEX pixel. A regularly scheduled passenger aircraft equipped with a HySpex high-resolution hyperspectral imager is based at Longyearbyen Airport, near Adventdalen. These routine flights map the entire valley, complemented by time series from Sentinel-2 and Sentinel-3. These datasets bridge the gap between plot-level field measurements and FLEX's 300 m pixel footprint, supporting spatial upscaling across the tundra's patchy vegetation cover.

WP3 - Validation

Field and remote-sensing data are combined for statistical comparison against FLEX's Level 2B fluorescence retrievals (e.g. F687, F760) and Level 2C vegetation products (LAI, fAPAR, LCC), validating FLEX data in tundra ecosystems.