Impact of Sentinel-5 SWIR Detector Persistence on Trace Gas Retrievals

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.