Comment on egusphere-2025-6328

Abstract

Abstract. Launched in August 2025, the Sentinel-5 (S5) mission aims to enhance greenhouse gas monitoring by working alongside existing Copernicus satellites, such as the Sentinel-5 Precursor. S5 is equipped with shortwave-infrared (SWIR) grating spectrometers that provide operational daily retrievals of CH4 and CO, while the coverage of the SWIR region also makes S5 measurements sensitive to atmospheric CO2. One particular challenge for S5 is the persistence effect in its SWIR mercury-cadmium-telluride (MCT) detectors, which can introduce scene-dependent radiometric biases when the signal at a detector pixel changes between consecutive readouts, as occurs in scenes with along-track brightness variations. This study quantifies persistence-induced biases for CH4, CO, and the CH4/CO2 proxy ratio using the operational RemoTeC CH4 retrieval algorithm, an also examines persistence errors for a potential CO2 product. We simulate realistic scenes over regions like the Nile Delta, California's Central Valley, and the Lusatian lignite district, which exhibit the spatial radiance variability relevant for persistence effects. Across these scenes, the induced biases remain small, with typical amplitudes below 0.12 % for CH4, 0.10 % for CO2, 0.34 % for CO, and 0.06 % for the CH4/CO2 proxy. However, localized outliers reaching up to 1.59 % for CH4, 1.55 % for CO2, 4.01 % for CO and 0.71 % for the proxy constitute a substantial fraction of the CO and the proxy performance targets, and exceed those defined for CH4 and CO2. Our findings suggest that targeted post-filtering, such as omitting coastal and land–water interface pixels, can effectively reduce the most significant outliers in the persistence bias, thus aligning the retrieval biases with the required mission performance.

Authors 5

1. Mari C. Martinez-Velarte Aachen SRON Space Research Organization Netherlands

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Space Research Organization Netherlands

2. Jochen Landgraf Aachen SRON Space Research Organization Netherlands

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Space Research Organization Netherlands

3. Ben Veihelmann

   European Space Research and Technology Centre

   Affiliation as printed

   ESA-ESTEC, Noordwijk, The Netherlands

4. B. Sierk

   European Organisation for the Exploitation of Meteorological Satellites · European Space Research and Technology Centre

   Affiliation as printed

   ESA-ESTEC, Noordwijk, The Netherlands

   now at: EUMETSAT, Eumetsat Allee 1, 64295 Darmstadt, Germany

5. Tobias Borsdorff corresponding Aachen SRON Space Research Organization Netherlands

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Space Research Organization Netherlands