Cross-Validation of GEMS Total Ozone from Ozone Profile and Total Column Products Using Pandora and Satellite Observations

This study presents a comprehensive validation of total ozone columns from ozone profile (O3P) and total ozone column (O3T) products measured by the Geostationary Environment Monitoring Spectrometer (GEMS), through comparisons with Pandora, Ozone Mapping and Profiler Suite (OMPS) and TROPOspheric Monitoring Instrument (TROPOMI). O3P version 3.0 demonstrates reduced dependence on viewing geometry compared to version 2.0, whereas the O3T product shows a consistent offset between versions (v2.0 vs. v2.1). In comparison with Pandora, O3P exhibits seasonal bias patterns similar to those seen in TROPOMI and OMPS, ranging from −2% in summer to +5% in winter. However, O3T maintains abnormally persistent negative biases across seasons and times of day, along with a long-term degradation of 2–3% from 2021 to 2024. These findings suggest that O3T biases likely result from uncorrected radiometric biases rather than algorithmic limitations. Validation metrics further highlight inconsistencies in O3T, including a lower regression slope (~0.95) in the mid-latitude and higher root mean square errors in the low-latitude (~5%), compared to the other products (near 1.0 and 1–3%, respectively). Overall, O3P outperforms TROPOMI and OMPS across most validation metrics in mid-latitudes and performs similarly at low latitudes.