The high spatial resolution TROPOspheric Monitoring Instrument (TROPOMI) launched in 2017 onboard the Sentinel-5 Precursor (S5P) platform provides important information on global volcanic and anthropogenic SO2 emissions, with an unprecedented level of details. More recently, the Geostationary Environmental Monitoring System (GEMS) was launched onboard the GEO-KOMPSAT-2B satellite in February 2020. GEMS has the unique capability of sensing SO2 over Asia at hourly resolution, offering great perspectives in monitoring and understanding emission process and pollution transport in the atmosphere. GEMS is the first satellite sensor of a geostationary constellation with the European (Sentinel-4) and US (TEMPO) counterparts.
In a recent study (Theys et al., 2021), we proposed an approach called Covariance-Based Retrieval Algorithm (COBRA), different from the classical Differential Optical Absorption Spectroscopy (DOAS). Application of COBRA to TROPOMI SO2 column retrievals leads to a significant reduction of the retrieval noise and biases as compared to the TROPOMI operational (DOAS-based) SO2 product. COBRA even reveals new emission sources in long-term averaged SO2 maps.
In this presentation, we apply COBRA for the retrieval of SO2 from GEMS spectra. The resulting SO2 vertical columns are presented and evaluated against different satellite data sets (GEMS L2 SO2 operational product, and TROPOMI SO2 COBRA and operational products) and ground-based measurements. While GEMS measures the same location several times per day, it is crucial to understand the retrieval bias and how it varies under varying observation geometry. This aspect and possible corrections will be discussed extensively.
Theys, N., Fioletov, V., Li, C., De Smedt, I., Lerot, C., McLinden, C., Krotkov, N., Griffin, D., Clarisse, L., Hedelt, P., Loyola, D., Wagner, T., Kumar, V., Innes, A., Ribas, R., Hendrick, F., Vlietinck, J., Brenot, H., and Van Roozendael, M.: A Sulfur Dioxide Covariance-Based Retrieval Algorithm (COBRA): application to TROPOMI reveals new emission sources, Atmos. Chem. Phys., 21, 16727–16744, https://doi.org/10.5194/acp-21-16727-2021, 2021.