Announcement of opportunity for FLEX cal/val

With this AO, ESA invites research groups and individuals worldwide to contribute to cal/val efforts supporting the FLEX mission.

What is FLEX?

FLEX is ESA’s eighth Earth Explorer mission, an earth observing science mission developed under the ESA FutureEO Programme. The mission is planned for launch in late 2026. FLEX is the first mission designed to measure vegetation fluorescence from space on a global scale. By detecting the faint glow emitted by plants during photosynthesis - known as solar-induced chlorophyll fluorescence (SIF) - and other quantitative physiological indicators, FLEX will provide a unique perspective on plant health, stress, and productivity. 

These quasi-direct measurement of plants’ photosynthetic activity are critical to better understanding vegetation functioning and the global carbon and water cycles.

FLEX will carry the FLORIS (FLuORescence Imaging Spectrometer) instrument, which operates in the 500–780 nm spectral range with high spectral resolution. 

These observations will occur over a swath width of 150 km with a spatial resolution of 300 m. FLEX will fly in a sun-synchronous orbit with an altitude of 814.5 km, an inclination of 98.65°, and a repeat cycle of 27 days. It is expected that it will orbit ahead of a Sentinel-3 satellite in order to collect complementary measurements over the same location within 6 - 15 seconds of each other.

This AO is an open call to contribute to cal/val activities of FLEX products, starting from the commissioning phase (Phase E1) and throughout the operational phase (Phase E2). 

ESA welcomes participation from all interested institutions and individuals involved in vegetation monitoring, plant physiology, remote sensing, and related fields. Cal/val activities are expected to cover a range of ground-based, Unmanned Aerial Vehicle (UAV), airborne, and modelling efforts that will support the validation of FLEX products and contribute to improved understanding and interpretation of SIF and other advanced FLEX products.

Funding:

ESA will not provide financial support through this call. Funding for activities conducted under this AO shall be secured through national or institutional sources. If relevant to apply, please contact the Norwegian Space Agency (Vigdis Lonarvigdis.lonar@spaceagency.no) to discuss your project idea and possibilities for funding.

If relevant to apply, please contact the Norwegian Space Agency (Vigdis Lonar: vigdis.lonar@spaceagency.no) to discuss your project idea and possibilities for funding.

Evaluation of proposals:

All proposals submitted in response to this AO will be reviewed by the ESA FLEX cal/val Scientific Committee. All participants will be informed via email following the conclusion of the evaluation process.

The following criteria will be used in the evaluation of all proposals:

• Relevance of the proposed project to FLEX cal/val activities
• Quality of the proposed project
• Collaborative benefit derived from participating as a FLEX cal/val team member
• Feasibility and probability of success

More information and documentation.

How to apply?

1. Go to the ESA User Services Portal

2. Register or log in to EO Sign In - Users are recommended to provide their institutional email address when registering a new account

3. After logging in, complete and submit your FLEX Cal/Val project proposal

4. The proposal will be assessed by the ESA FLEX Cal/Val scientific committee. You will be notified via email of the evaluation outcome after the opportunity closes.

Deadline: The deadline for submission is 31 August 2025.