Estimation of the Ocean Surface Irradiance Reflectance from Measurement of Ocean Color

Ocean surface irradiance reflectance (R_w), defined as the ratio of upward to downward irradiance just above the sea surface (E_u(0+)/E_d, dimensionless), accounts for a significant part of the ocean surface albedo (OSA), which describes the portion of incident solar energy absorbed by the ocean. Estimation of R_w from ocean color measurements would allow for a synoptic view of OSA over global oceans that is seldom addressed in the literature and further contributes to a better understanding of the heat budget in the ocean and the atmosphere-ocean interactions. In this study, we proposed a convenient algorithm to estimate R_w from remote sensing reflectance (R_rs, in sr^-1) by simply integrating R_rs of all surface orientations over the upper hemisphere. R_rs is the ratio of water-leaving radiance (L_w) to E_d, and the angular R_rs of all surface orientations can be estimated from inherent optical properties based on the approach of Lee et al. (Appl. Opt. 50, 3155-3167 (2011)). The robustness of the algorithm was confirmed by the validation against in-situ measurements at the CERES Ocean Validation Experiment (COVE) site in the Atlantic Ocean. The proposed algorithm was later applied to the Visible Infrared Imaging Radiometer Suite (VIIRS) monthly binned R_rs product and yielded reasonable distribution of R_w in global oceans. At last, the potential links between R_w and primary production, sea surface temperature anomalies, and extreme climate events, such as the El Niño and La Nina, in the past decades were discussed based on time-series R_w products derived from VIIRS data.