EO Sign In Authentication (Open): This collection is openly accessible but requires users to log in with an EO Sign In account (a system used across ESA Earth Observation services) before any downloads can proceed. 

Access Steps:

1. Create or log in to EO Sign In
2. Go to the Dissemination Service or ESA MAAP Explorer.
3. Browse or search for the collection. 
4. Download product.

The dissemination service provides access to the FDR4ATMOS/ATMOS__L1B v1. 1dataset.

The data is collection based and allows data browsing and download via treeview and filename search options.

Data download is available via HTTPS, including bulk download functionality. ESA internal users can use their ESAAD account to access the HTTPS Dissemination Service.

Access to ftps://hm-atmos-ds.eo.esa.int is available via common FTP clients using implicit FTP over TLS and your own EO Sign In credentials. For internal ESA users the ESAAD account cannot be used for FTP access.

Products can also be discovered through the ESA MAAP Explorer service, which allows users to browse and download products among the available datasets from ESA and Third Party Missions and instruments, using various criteria (spatial, temporal).

Note: v01_00 products were replaced by the updated v01_01 products in Q3/2026. The dataset version is indicated in the product file name.

The Fundamental Data Record (FDR) for Atmospheric Composition dataset is a cross-instrument product resulting from the ESA FDR4ATMOS project.

The FDR [ATMOS__L1B] contains selected Earth Observation Level 1B (L1B) parameters (irradiance/reflectance) from the nadir-looking measurements of the following satellite missions:

• ERS-2 GOME
• Envisat SCIAMACHY

The data record (1995 -2012) offers harmonised cross-calibrated spectra specifically optimised for spectral windows in the Ultraviolet-Visible-Near Infrared regions for the retrieval of critical atmospheric constituents such as:

• ozone (O3),
• sulphur dioxide (SO2),
• nitrogen dioxide (NO2) column densities,
• and cloud parameters.

By reducing inconsistencies between instruments, the FDR enhances the reliability of long-term atmospheric studies.

The FDR4ATMOS v1.0 dataset was originally generated in 2023 and made available for users shortly thereafter. In 2026, a new version (1.1) was released to address a technical issue in the SCIAMACHY OBSERVATION group, where the wavelength axis (lambda variable) for all spectral channels (UV, VIS, NIR) was not monotonically increasing. The root cause of the issue was in the incorrect indexing of the lambda variable during the NetCDF writing process. Notably, the wavelength values themselves were calculated correctly within the processing chain, so scientific validity of the spectra was unaffected.

Additional corrections and updates in v1.1 include correction of SCIAMACHY PMD GEODATA and satellite geometry fields, Earth-radius units in GOME data, and updated metadata.

Users are invited to download v1.1 and update any analyses to align with the latest version.

The FDR4ATMOS products are currently considered experimental reflecting the innovative harmonisation approach and the use of a limited-sized test dataset to investigate the impact of harmonization on the Level 2 target species. Ongoing follow-on activities are further validating and refining these results.

The FDR4ATMOS product is currently being extended to include data from the MetOp GOME-2 series.

Product format

The FDR4ATMOS product introduces significant enhancements over the individual mission datasets:

• GOME solar irradiances are harmonised using a validated SCIAMACHY solar reference spectrum, solving the fast-changing etalon effects present in the original GOME Level 1B data;
• Reflectance data are provided for both GOME and SCIAMACHY. GOME reflectances are harmonised to degradation-corrected SCIAMACHY values, using collocated observations from the CEOS Pseudo-Invariant Calibration (PIC) sites;
• SCIAMACHY data are scaled to the lowest integration time within the spectral band using high-frequency PMD measurements from the same wavelength range. This simplifies the use of the SCIAMACHY spectra, which were split in a complex cluster structure (with own integration time) in the original Level 1B data;
• The harmonization process applied mitigates the viewing angle dependency previously observed in GOME UV measurements;
• All products include associated uncertainty estimates, supporting robust scientific analysis.

Each FDR product provides, within the same file, irradiance/reflectance data for UV-VIS-NIR special regions across all orbits on a single day, including therein information from the individual ERS-2 GOME and Envisat SCIAMACHY measurements.

FDR has been generated in two formats:

• L1A (ATMOS__L1A) – includes additional parameters such as harmonisation factors, PMD, and polarisation data extracted from the original mission Level 1 products. Intended for expert users and not part of the nominal dissemination.
• L1B (ATMOS__L1B) – nominal product designed for standard applications and general users.

Please refer to the README file for essential guidance before using the data.

All the new products are conveniently formatted in NetCDF. Free standard tools, such as Panoply, support quick visualisation and inspection of NetCDF files.

Note: Panoply is sourced and updated by external entities. For further details, please consult our Terms and Conditions page.

Uncertainty characterisation

A core objective of the FDR4ATMOS project was the rigorous characterization of Level 1 uncertainties for both instruments, based on metrological best practices. A comprehensive set of documentation and practical example datasets are provided:

1. General guidance on a metrological approach to Fundamental Data Records (FDR)
2. Uncertainty Characterisation document
3. Effect tables (quantitative breakdown of individual uncertainty contributions)
4. NetCDF files containing example uncertainty propagation analysis and spectral error correlation matrices for SCIAMACHY (Atlantic and Mauretania scene for 2003 and 2010) and GOME (Atlantic scene for 2003)
   reflectance_uncertainty_example_FDR4ATMOS_GOME.nc
   reflectance_uncertainty_example_FDR4ATMOS_SCIA.nc