Conference Agenda

FLEX (FLuorescence EXplorer) is ESA’s 8th Earth Explorer mission and its development is coming to an end with the completion of the satellite, the ground segment and the preparations for a launch in September 2026.

Major milestones have been achieved in the past months with the testing and delivery of the flight hardware of the FLORIS instrument and the satellite platform in 2025. A successful calibration and characterisation campaign in the first half of 2025 confirmed the expected instrument performances. The delivery of FLORIS and its mating with the satellite platform mid-2025 marked the start of the satellite integration and test phase which is ongoing and will finish by end-April 2026. Preparations on the ground segment are all progressing nominally and will be ready in time for launch. All launcher activities are on track and the launch campaign in CSG/Kourou (French Guiana) is about to start end June.

The status of the FLEX mission development progress and its finalisation for a launch early September 2026 will be provided including an overview on the 3-month in-orbit Commissioning Phase activties.

The FLEX instrument Performance Simulator (FIPS) is a software allowing the simulation of synthetic raw data representative of the FLEX instrument radiometric, spectral and geometric performances. The FIPS simulates the optical performance of the instrument telescope and the two spectrometers. Particular emphasis was put in simulating the straylight performance of the instrument. The full acquisition chain from detectors to onboard data generation is also simulated allowing the generation of instrument source packets.

The Ground Processor Prototype (GPP) processes both synthetic and real instrument Earth Observation data, from the instrument source packet up to the Level 1B user product. The processing includes dark signal removal, smearing correction, non-linearity correction, straylight correction, absolute radiometric calibration and flat field equalization. The resulting Level 1B product includes geolocated top-of atmosphere radiances, associated data quality information and uncertainty estimates. In addition, also included are meteorological data and instrument characteristics required for further processing of the data to the Level 2.

The GPP is also designed to process data from the instrument whilst operating in various calibration modes. This functionality will enable in-flight characterization and calibration of the instrument.

The instrument radiometric calibration will be performed in-flight using a Sun diffuser. It will be further monitored and validated using regular observations of the Moon and deep convective clouds. The non-linearity of the instrument detector chain will be characterized on ground and then verified in-flight using natural targets at various level of signal and associated instrument integration times.

The in-flight spectral characterization will be based on the measurements of atmospheric absorption features as well as solar absorption lines observed on the onboard sun diffuser.

The absolute geometric performance will be monitored and corrected for through spatial feature matching of nominal EO data with a database of georeferenced high spatial resolution (30 m) images. The spatial co-registration between the high resolution and low spectral resolution spectrometers will be ensured by spatial feature matching between the two spectrometers’ data.

The ESA FLEX (Fluorescence Explorer) mission aims to study the photosynthetic activity of terrestrial vegetation by measuring Sun-Induced Fluorescence (SIF) emission and key biophysical variables for required to interpret the SIF signal. The potential applications of FLEX mission products range from advancing our understanding of the carbon cycle to supporting food security and water quality monitoring. To achieve these objectives, a large consortium of scientific experts and industrial partners forms the Data Innovation and Science Cluster (DISC). The FLEX DISC aims to develop and industrialize the Level-1C and Level-2 data processing algorithms, conduct calibration & validation activities, and provide a collaborative platform for mission data exploitation by experts and end-users.

With the first development phase of the Level-2 Processor completed, the product definition and data processing algorithms are reaching a mature and stable state. FLEX Level-1C products consist of approximately 3-minute acquisition slices (~1300x150 km²) containing top-of-atmosphere radiances from FLORIS, OLCI, and SLSTR instruments, all projected onto a common working frame (the FLORIS-HR focal plane). Each Level-1C product is accompanied by comprehensive metadata, including spectral characteristics, uncertainty estimates, geometry, and meteorological information. Level-2 products contain bio- and geo-physical variables projected in UTM coordinates using Sentinel-2 gridding. Key variables include surface apparent reflectance and at-surface solar irradiance, fluorescence emission spectra, classical biophysical parameters (leaf area index, leaf chlorophyll content, leaf carotenoid content, fraction of absorbed photosynthetically active radiation), as well as photosynthesis-related variables such as electron transport rate, fAPAR by Chlorophyll, fluorescence quantum efficiency, regulated energy distribution.

As the project enters Phase 2, the focus shifts towards maximizing algorithm accuracy and robustness, further industrializing the processing chain, and preparing for commissioning rehearsals ahead of launch.

In this presentation, we review the current status of the FLEX DISC activities, describe the characteristics of the mission products, and present the latest algorithm validation results. This contribution complements other presentations that focus on specific aspects of the data processing algorithms. Participants in the FLEX Fluorescence Workshop are expected to gain first-hand insight into the FLEX mission products, supporting their readiness for mission exploitation by end users.

The ESA FLuorescence Explorer (FLEX) mission will provide unique observations of sun-induced chlorophyll fluorescence, opening new opportunities for understanding vegetation functioning, photosynthesis, and ecosystem responses to environmental stress. To prepare the scientific community for the exploitation of FLEX data products, the FLEX Data, Innovation and Science Cluster (DISC) has developed the FLEX Collaborative Platform (CP), a cloud-based environment designed to support data access, processing, calibration, validation, and scientific analysis.

This contribution will present the FLEX Collaborative Platform as a key enabler for FLEX data exploitation, bridging the gap between algorithm development, operational processing, and scientific research. The platform provides access to FLEX products and auxiliary datasets, integrated development environments (e.g. Jupyter notebooks and containerised processing tools), and scalable computing resources, allowing users to work close to the data. By adopting a cloud-native and reproducible approach, the CP supports transparent and traceable scientific workflows throughout the FLEX mission lifecycle.

We will describe the architecture and core services of the FLEX CP, with particular emphasis on the design of workflows relevant to the fluorescence community. These will include: (i) interactive exploration of FLEX Level-2 products and derived variables; (ii) reprocessing of FLEX datasets using updated processing chains or algorithm variants; and (iii) integration of in-situ measurements for calibration and validation activities. Practical examples will illustrate how scientists can combine FLEX data with external datasets to assess product quality, perform comparative analyses, and support downstream applications.

By providing a common, cloud-based environment for data access, processing, and validation, the FLEX CP underpins a wide range of scientific studies addressed in this workshop, including vegetation stress detection, ecosystem functioning, and multi-mission data analysis. Beyond individual use cases, the FLEX CP fosters collaboration between scientists, algorithm developers, and validation teams by providing a shared environment for experimentation and knowledge exchange. This contribution will discuss how the FLEX CP supports the mission readiness ahead of launch and facilitates early science activities by lowering the barrier to data access and advanced processing.

The FLEX Collaborative Platform represents a strategic component of the FLEX ecosystem, ensuring that the community can efficiently exploit fluorescence observations and maximise the scientific return of the mission.

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