Clear-sky and surface narrowband albedo variations derived from VIRS and MODIS Data

Satellite remote sensing of clouds requires an accurate estimate of the clear-sky reflectance for a given scene for detecting clouds and aerosols and for retrieving their microphysical properties. Knowing the spatial and angular variability of clear-sky albedo is essential for predicting the clear-sky radiance at solar wavelengths. The Clouds and the Earth's Radiant Energy System (CERES) Project uses the visible (VIS; 0.63 µm) and near-infrared (NIR; 1.6 or 2.13 µm) channels available on same satellites as the CERES scanners. Another channel often used for cloud and aerosol, and vegetation cover retrievals is the vegetation (VEG; 0.86-µm) channel that has been available on the Advanced Very High Resolution Radiometer (AVHRR) for many years. Generally, clear-sky albedo for a given surface type is determined for conditions when the vegetation is either thriving or dormant and free of snow. This paper presents a complete analysis of the CERES spectral clear-sky reflectances to determine the variations in clear-sky top-of-atmosphere (TOA) albedos for both snow-free and snow-covered surfaces for four spectral channels on MODIS using 5 and 3 years of Terra and Aqua data, respectively, and 3 years of data from two channels on the TRMM VIRS instrument. The surface albedos are derived using a radiative transfer parameterization of the impact of the atmosphere, including aerosols, on the observed reflectances. The results should be valuable for improved cloud retrievals and for modeling radiation fields.