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

• Published in: Optics express 2022-09, Vol.30 (20), p.36176-36189
• Main Authors: Yu, Xiaolong, Lee, Zhongping
• Format: Article
• Language: English
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.469201

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.