All-Sky Top-of-Atmosphere albedo estimation over ocean based on MODIS

Abstract

Top-of-atmosphere (TOA) albedo is a significant factor for Earth energy budget, climate change and environmental change. As tremendous regional and global changes happened over ocean, more details for the ocean monitoring need to be provided. However, there were still no high-spatial resolution TOA albedo products over ocean. In this study, all-sky TOA albedo estimation over ocean was proposed based on Moderate Resolution Imaging Spectroradiometer (MODIS) data. Instead of building angular dependent models, direct retrieval models between TOA reflectance and TOA albedo was developed based on extensive radiative transfer simulations under clear sky and cloudy sky, covering thousands of ocean and atmosphere types. Three-Component Ocean Water Albedo model was involved to take account for the ocean surface anisotropy at different wind speed, wind direction and chlorophyll conditions while Modtran was utilized to simulate different atmospheric conditions. Our results showed good agreement with the Clouds and the Earth's Radiant Energy System based on a global comparison on August, 4, 2011, with RMSE = 0.055 under cloudy sky and RMSE = 0.015 under clear sky. MODIS-based products provide more spatial details due to higher spatial resolution, which will be a good data source for regional environmental and climatic research.