Fundamental Data Records (FDRs) are instrumental in advancing our understanding of Earth systems and for addressing societal challenges effectively. These long-term records contain uncertainty-quantified, calibrated and geo-located multi-instrument/multi-platform satellite sensor data spanning several decades to support climate-related applications. While certain applications may directly integrate these products, FDRs primarily serve as foundation for generating higher-level Thematic Data Products (TDPs) and Essential Climate Variables (ECVs), which provide valuable insights into a wide range of natural processes and events.

Rooted in the synergy of historical and contemporary satellite data, the generation of FDRs has been recognised as an essential part of ESA activities. ESA's dedication to FDRs dates back to 2019, with the launch of two pathfinder projects: FDR4ALT and FDR4ATMOS.

These projects, using data from ESA's legacy Heritage Space remote sensing satellites (ERS-1, ERS-2 and Envisat), have focused on altimetry, radiometry and atmospheric composition applying modern analysis to historical data assets and generating well-characterised, multi-mission, long-term time series of calibrated and quality-controlled Earth Observation (EO) sensor data (Level-1), and geophysical parameters (Level-2).

The two projects inherit the legacy of the EU-funded FIDelity and Uncertainty in Climate Data Records from Earth Observations) project, ensuring the meticulous characterisation of uncertainty through Metrological guidelines.

The successful completion of both the FDR4ATMOS and FDR4ALT projects has paved the way for follow-on activities, which are now underway for the period 2024-2026, to further improve the quality and extend the coverage of the products. Additionally, ESA has embarked on other FDR activities, reinforcing its commitment to harnessing Earth observation data for scientific advancement and societal benefit.
 

FDR4ALT

The Fundamental Data Records for Altimetry (FDR4ALT) project exploits measurements acquired by the altimeter and radiometer instruments onboard the ERS-1, ERS-2 and Envisat ESA Heritage Space satellites, to generate both Fundamental Data Records and Thematic Data Products, supporting long term data exploitation across various Earth surfaces. The FDR and TDP datasets resulting from the FDR4ALT project have recently been made available to users and are freely accessible via the ESA Online Dissemination Service.

In February 2024, ESA initiated a follow-up phase of the project for three additional years, to further enhance the quality and extend the coverage of the products. Key activities include revising the processing baseline with Research & Development on land ice, inland waters, ocean and atmosphere, while also computing updated orbits for ERS and investigating ERS-2 data after the failure of its on-board tape recorder.
 

FDR4ATMOS

The Fundamental Data Records for Atmospheric composition (FDR4ATMOS) project uses the datasets from GOME/ERS-2 and SCIAMACHY/Envisat nadir-looking measurements, with the aim of generating cross-instrument Level-1 products.

The current focus is on spectral windows in the Ultraviolet-Visible-Near Infrared regions for the retrieval of atmospheric parameters, including ozone (O3), sulphur dioxide (SO2), and nitrogen dioxide (NO2) column densities, and cloud properties. The datasets will be made available to users by the second half of 2024.

FDR4ATMOS activities have been officially extended for three years to include GOME-2 data in collaboration with EUMETSAT, promising harmonised data sets and a comprehensive lunar model.
 

FDR4AVHRR

The Fundamental Data Record for Advanced Very-High-Resolution Radiometer (FDR4AVHRR) project was kicked off in January 2024, after a series of activities aimed at addressing the AVHRR instrument datasets.

The project is geared towards generating an FDR product (comprising reflectance and brightness temperatures for all AVHRR channels), derived from the AVHRR Local Area Coverage (LAC) archive maintained by ESA and encompassing observations over the European region from NOAA and EUMETSAT satellites, spanning the timeframe from 1981 to 2023.

Furthermore, the project will explore the feasibility of extending the FDR coverage to selected regions worldwide, such as areas in Africa and South America.
 

FDR4ATSR

The Fundamental Data Records for Along Track Scanning Radiometers (FDR4ATSR) project seeks to generate an FDR product specifically tailored for the ERS-1/2 ATSR-1/2 and Envisat AATSR instruments. This product will be aligning calibration standards with the continuous updates of the Copernicus Sentinel-3 SLSTR protocols, thereby ensuring continuity and compatibility across missions, and meeting the primary goal of supporting the ESA CCI (Climate Change Initiative) LST (Land Surface Temperature) products.

Philippe Goryl, Head of Sensor Performance, Products and Algorithm Section within ESA’s Ground Segment Department, says, “The FDR4 projects represent a strategic investment by ESA to harness the wealth of data from various Earth observation satellite missions, both past and present. They embody ESA's commitment to multidisciplinary research and maximise the scientific benefit of the individual mission data assets, within ESA's Heritage Space Programme framework”.