The Environmental Trace Gases Monitoring Instrument-II (EMI-II) onboard the Gaofen-5B satellite provides high-resolution hyperspectral measurements in the ultraviolet range, enabling the retrieval of total ozone column (TOC) at regional to global scales. In this study, an optimized TOC retrieval algorithm for EMI-II is developed and comprehensively evaluated over the Yangtze River Basin. The algorithm integrates several improvements, including a refined spectral calibration with pseudo-absorption cross sections to correct wavelength shifts and stretches, and a region-specific air mass factor (AMF) look-up table generated using the SCIATRAN radiative transfer model. Validation against ground-based Brewer and Dobson spectrophotometer data from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) shows that the optimized retrieval achieves a correlation coefficient exceeding 0.9 and a mean bias within ±5%. Cross-comparisons with the TROPOspheric Monitoring Instrument (TROPOMI) and Geostationary Environment Monitoring Spectrometer (GEMS) products further demonstrate the reliability and consistency of the EMI-II retrievals. The results confirm that EMI-II provides accurate and stable TOC measurements across diverse surface and atmospheric conditions in China. This study establishes a validated retrieval framework that enhances the scientific application potential of Chinese environmental satellites for atmospheric monitoring and supports the development of future ozone observation missions.
Cheng et al. (Fri,) studied this question.