Evaluating Total Column Ozone from GK-2A/AMI and GK-2B/GEMS for Atmospheric Correction of GOCI-II

Accurate atmospheric correction is essential for generating reliable ocean color products from the Geostationary Ocean Color Imager-II (GOCI-II).In particular, gaseous absorption correction requires precise total column ozone (TCO) information, as uncertainties in TCO directly affect ozone transmittance and can propagate to errors in remote sensing reflectance (Rrs).Since GOCI-II does not provide its own ozone measurements, external TCO datasets from the co-orbiting geostationary sensors Geo-Kompsat-2A/Advanced Meteorological Imager (GK-2A/AMI) and Geo-Kompsat-2B/ Geostationary Environment Monitoring Spectrometer (GK-2B/GEMS) must be employed.This study evaluates the performance of AMI- and GEMS-derived TCO as input data for GOCI-II atmospheric correction.One year of AMI and GEMS TCO products (2024) was spatially mapped onto the GOCI-II Local Area grid and assessed against the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis.Statistical metrics -including correlation coefficient (R), root mean square error (RMSE), and bias-were used to quantify accuracy.The results indicate that both AMI and GEMS show strong correlation with ERA5, but AMI exhibits lower RMSE and smaller bias, with more spatially uniform differences across the domain.GEMS, while also highly correlated with ERA5, shows a larger negative bias and stronger spatial and seasonal variability.To investigate the impact on gaseous absorption correction, ozone transmittance, and preliminary Rrs differences were compared using AMI- and GEMS-based TCO inputs.AMI consistently produced smaller transmittance and Rrs deviations relative to ERA5, suggesting that AMI provides more stable TCO for GOCI-II atmospheric correction.Overall, this study demonstrates that AMI TCO is more suitable as the primary input for GOCI-II gaseous absorption correction.These findings provide a basis for selecting optimal ozone inputs for geostationary ocean color processing and contribute to improving the consistency of long-term GOCI-II ocean color records.