ESA’s Fluorescence Explorer (FLEX) is designed to provide new information on vegetation functioning, plant stress and the links between photosynthesis and the carbon and water cycles from space. Flying in tandem with Copernicus Sentinel-3, FLEX combines solar-induced fluorescence (SIF) products with complementary information on vegetation optical properties, surface temperature and atmospheric conditions at 300 m x 300 m spatial resolution.

Following its successful launch on 15 September 2026, FLEX entered its commissioning phase, during which instrument performance, calibration, product quality and end-to-end data processing are assessed and consolidated. These activities are essential to establish the scientific readiness of the mission and to prepare the transition towards routine operations and full scientific exploitation.

This session will provide a forum for presenting and discussing the first results from FLEX commissioning and early mission operations. Particular emphasis will be placed on instrument and data performance, in-flight calibration and characterisation of the FLORIS instrument, and the evaluation of Level-1 and Level-2 products using in-situ validation observations. Contributions addressing FLEX-specific retrieval performance and sensitivity to e.g. atmospheric and surface conditions are welcome.

The session will also include validation of the first FLEX products using ground-based, airborne and independent satellite observations, field campaigns, and other reference datasets. Studies exploiting the tandem configuration with Sentinel-3, including cross-comparisons and synergies between the two missions, are encouraged.

First scientific analyses based on FLEX observations are also welcome, including investigations of spectrally resolved SIF, vegetation functioning and environmental stress. This includes contributions addressing methodologies, datasets and modelling approaches supporting the interpretation and future exploitation of FLEX data.

The session aims to bring together the FLEX mission, calibration and validation, processor development and science communities at a key stage in the mission lifecycle. It will provide an opportunity to review early mission performance, discuss lessons emerging from commissioning, identify remaining challenges, and define priorities for the transition towards routine scientific exploitation of FLEX data.