Regional Sea Surface Skin Temperature Retrieval From HY-1C and HY-1D COCTS

Haiyang-1C (HY-1C) and Haiyang-1D (HY-1D) are Chinese satellites for marine observation. They operationally work to form the networking of morning and afternoon satellites, improving the capacity of coverage in the temporal and spatial dimensions. These satellites carry Chinese Ocean Color and Temperature Scanners (COCTS), containing two thermal bands with central wavelengths of 10.8 and 12.0 m and enabling sea surface temperature (SST) observations. Herein, regional algorithms for SST retrieval are developed for the South China Sea (SCS) by applying radiative transfer modeling. The SCS has unique atmospheric conditions characterized by high temperature and humidity, particularly in the central and southern regions. Atmospheric profiles sufficient to represent the atmospheric conditions of the SCS are selected. The relationship between the top-of-the-atmosphere simulated brightness temperature and the reanalysis skin SST of the selected profiles is determined. The HY1C and HY-1D COCTS SSTs in the SCS are retrieved utilizing the obtained algorithm. The HY-1C/COCTS SSTs are evaluated using the Sea and Land Surface Temperature Radiometer SST, and the HY-1D/COCTS SSTs are evaluated using the Visible Infrared Imaging Radiometer Suite SST. For the HY-1C/1D COCTS SSTs, the biases are around 0, and the standard deviations are around 0.5°C. The differences between the HY-1C and HY-1D COCTS SSTs are analyzed to further validate the accuracy of the retrieval method. The difference is 0.38°C during the day and 0.03°C at night, which indicates a diurnal warming phenomenon in the SCS.