Assessment of Ocean Color Products From the New Generation Himawari-8 AHI Geostationary Satellite and Its Application in the Calculation of the Photosynthetically Active Radiation

Hourly Himawari-8 (H8) Advanced Himawari Imager Level 3 Ocean Color (L3 OC) products have been recently released; however, a thorough evaluation and uncertainty analysis of L3 OC data spanning full disk, as well as applicability to studies on photosynthetically active radiation (PAR) have not yet been conducted. This study evaluates the accuracy of L3 OC products, including normalized water-leaving radiance (Lwn) at 470, 510, and 640 nm, Chlorophyll-a concentration (Chlor-a), aerosol optical thickness (AOT) at 510 nm, and Ångström exponent (AE), by comparing them to ground-based measurements obtained from Ocean Color Component of the AErosol RObotic NETwork (AERONET-OC). Our results demonstrate a general agreement with the ground-based measurements, especially Lwn510. Chlor-a and AOT510 also demonstrate an overall consistency, whereas AE shows a larger discrepancy. Uncertainty analysis shows that Lwn remained accurate under different conditions, although increased uncertainties were observed in turbid water and periods of severe air pollution. Spatial analysis revealed that the distribution of L3 OC and Aqua-MODIS L2 OC products were strongly correlated. Lwn and Chlor-a in the Yellow and Bohai Seas exhibit seasonal variations, with both parameters decreasing in summer and increasing in winter. The impact of aerosols and Chlor-a on PAR calculations was investigated by developing a sophisticated algorithm for estimating PAR under clear-sky conditions using a coupled radiative transfer (RT) model. An analysis of the May 2021 dust event in the Southern Yellow Sea, which exhibited an AOT of 0.82, showed a notable increase in Chlor-a levels —one to two days later, while the average daytime PAR forcing was −42.469 W/m2 under clear-sky conditions.