Geostationary Environmental Monitoring Spectrometer (GEMS) status, preliminary results and validation campaign

Abstract

The Geostationary Environment Monitoring Spectrometer (GEMS) instrument onboard the GEO-KOMPSAT-2 (GK2B) satellite was launched successfully in February 2020. After GEMS started operation in Geostationary Earth Orbit (GEO), in-orbit testing (IOT) was performed for several months to calibrate and validate the entire ground system and fine tune the developed retrieval algorithms of the atmospheric pollutants according to the actual space environment. Since the IOT period, the Environmental Satellite Center under the National Institute of Environmental Research (ESC NIER) has been in charge of GEMS operation scheduling and data release to the public on its website (https://nesc.nier.go.kr). GEMS is the world’s first geostationary instrument that observes air quality, on an hourly basis during daylight, over Asia from Japan in the east to part of India in the west. The UV-visible spectrometer with sub-nm spectral resolution (0.2 nm sampling and 0.6 nm FWHM) and high spatial resolution (3.5 x 8 km or 7 x 8 km) measures the column amounts of atmospheric aerosols and other gaseous pollutants (O3, NO2, SO2, HCHO and AOD). GEMS will enable better understanding of the formation and diurnal cycle of air pollution, long-range transport of air pollutants, and distribution and chemical processes of emission sources. In this study, we present details of the GEMS mission including instrumentation, observation schedule and the initial comparison results with ground-based measurements from Pandoras and AERONET and other satellite products (TROPOMI, OMI, etc.). We also introduce GEMS validation campaigns of GMAP2021 and SIJAQ, and the international GEMS Validation Team. The GEO AQ constellation (GEMS, TEMPO, and Sentinel-4) and polar-orbiting satellites (OMI, OMPS, TROPOMI, etc.) will provide significant synergies beyond the limits of measurements and understanding of air quality.