Scheme to estimate water-leaving albedo from remotely sensed chlorophyll-a concentration

Water-leaving albedo (α_w(λ)) is an important component of the ocean surface albedo and is conventionally estimated based on remotely sensed chlorophyll-a concentration (Chl) (termed Chl-α_w). We show that estimated α_w(λ) by Chl-α_w could be significantly biased in global oceans, because there is no guarantee of closure between the modeled remote sensing reflectance (R_rs(λ)) from Chl-inferred inherent optical properties (IOPs) and the input R_rs(λ) that is used to derive Chl. We thus propose a simple and improved scheme, termed Chl-α_w_new, and show that the step to infer IOPs from Chl is not necessary, where α_w(λ) can be accurately estimated from satellite-measured R_rs(λ) and a Chl-based look-up-table (LUT) for the bidirectional relationships of angular R_rs(λ). Evaluations with both HydroLight simulations and satellite measurements show that Chl-α_w_new is equivalent to the recently developed α_w scheme based on IOPs (IOPs-α_w, [Remote Sens. Environ. 269, 112807]), where both schemes could significantly improve the estimation of α_w(λ) compared to Chl-α_w. Comparisons among Chl-α_w, Chl-α_w_new, and IOPs-α_w highlight that optical closure of R_rs(λ) is essential for accurate remote sensing of α_w(λ), while the model for R_rs(λ) bidirectionality has rather minor impacts. The impact of improved α_w(λ) estimations on the solar flux exchanges at the air-sea interface is preliminarily evaluated in this effort, where the use of Chl-α_w_new could increase the estimation of reflected solar radiation by over 68.7% in turbid waters compared to that using Chl-α_w, highlighting the necessity of incorporating accurate α_w schemes into the coupled ocean-atmosphere models, especially for regional models in coastal oceans.