Development of the operational atmospheric correction algorithm for the COCTS2 onboard the Chinese new-generation ocean color satellite

After the two operational polar-orbiting ocean color satellites HY-1C and HY-1D launched in 2018 and 2020, respectively, China launched the new-generation ocean color observation satellite (named as HY-1E or HY-3A, hereafter called HY-1E) on 16 Nov. 2023. The second-generation Chinese Ocean Color and Temperature Scanner (COCTS2), one of the major payloads onboard the HY-1E, can daily observe global ocean color and sea surface temperature. In this study, we developed operational ocean color retrieval algorithms for the HY-1E/COCTS2 and preliminarily examined their performances. Firstly, the operational atmospheric correction algorithm was established based on look-up tables generated by vector radiative transfer model for coupled ocean-atmosphere system (PCOART), and cross-calibrated by the SNPP/VIIRS-retrieved ocean color products. Then, we proposed a cross-calibration method for correcting the radiance response difference along the viewing angles, and obtained the viewing correction functions for each channel. The results showed that the determination coefficient of the linear relationship between cross-calibration simulated radiance at the top-of-atmosphere and HY-1E/COCTS2 measured radiance was larger than 0.95, indicating the good linear response of the HY-1E/COCTS2. Based on the established atmospheric correction algorithms, the HY-1E/COCTS2 data were processed to generate the daily global products of remote sensing reflectance (<i>R</i>_<i>rs</i>) and chlorophyll-a concentration (<i>Chl</i>) and were validated by the in-situ data and the synchronous products from Aqua/MODIS and SNPP/VIIRS. The mean absolute percentage errors referring to the in-situ data from AERONET-OC were 14.287% (412 nm), 13.341% (443 nm), 8.0623% (490 nm), 9.1882% (520 nm), 17.836% (565 nm), 58.474% (620 nm), 63.229% (665 nm) and 61.552% (681 nm), and the ocean color products derived by HY-1E/COCTS2 were consistent with the products from Aqua/MODIS and SNPP/VIIRS, indicating the good performance of HY-1E/COCTS2 to monitor global ocean color environment.