As urban area’s expand, our planet grapples with a relentless environmental challenge: air pollution. Remote sensing satellites play a critical role in monitoring air pollution, and a constellation of three geostationary ultraviolet-visible satellite instruments will soon be in orbit to revolutionise the way scientists observe air quality. 

A constellation of geostationary satellite ultraviolet-visible spectrometers aims to improve air quality datasets in the Northern Hemisphere, as detailed at the 2024 General Assembly of the European Geosciences Union (EGU). ESA is supporting data accuracy through ongoing cooperation with satellite providers. 

The Committee on Earth Observation Satellites (CEOS) are behind this so-called “Geo-Ring” constellation, which plans to provide air quality related trace gas and aerosol observations in the Northern Hemisphere. 

Geo-Ring includes the Geostationary Environment Monitoring Spectrometer (GEMS) instrument on-board GEO-KOMPSAT-2B (launched February 2020), NASA’s TEMPO Earth Venture Instrument mission (launched April 2023), and the European Union’s Copernicus Sentinel-4 mission (expected to be launched in 2025).

A designated session on Geo-Ring at EGU 24 brought together atmospheric scientists and remote sensing experts to discuss recent and future plans for the constellation. The range of topics during this full day of oral and poster presentations covered everything from data calibration and validation to retrieval algorithms and intercomparison of datasets.

The GEMS instrument, of the Korean Aerospace Research Institute (KARI) GEO-KOMPSAT-2B satellite, monitors atmospheric gases over Asia. It joined the portfolio of ESA’s Third Party Mission (TPM) programme in late 2020.

The instrument is a geostationary scanning ultraviolet-visible spectrometer that can provide high spatial and high temporal resolution measurements of ozone, its precursors, and aerosols.  

As part of the TPM programme, Earthnet supports data quality assessment, data characterisation, calibration and validation and cross-calibration activities.  

Improving the accuracy of these data is the aim of a successful, ongoing cooperation between ESA and the Korean National Institute of Environmental Research (NIER).  

Korean GEMS scientists have been included in ESA’s GEMS validation activities, and a further, recent memorandum of intent between ESA and the NIER outlined continued cooperation in the calibration and validation of GEMS data.  

The linking element between the geostationary satellites is the polar orbiting Copernicus Sentinel-5P satellite. Co-located Sentinel-5P measurements with each geostationary satellite are being used as a transfer standard between the geostationary satellites that cover different geographical regions. 

Cross-calibration and validation between GEMS and the Tropospheric Monitoring Instrument (TROPOMI), on-board Copernicus Sentinel-5P, are essential to improving the accuracy of data products of air pollution gases.

The cooperation between ESA and NIER allows exchange of data and hopes to support joint ground-based calibration campaigns and the use of common calibration sites. The aim is to also foster product and methodologies harmonisation, as well as improve the development of future applications and interoperability across missions.