Clear-Sky and Surface Narrowband Albedo Datasets Derived From MODIS Data

Satellite remote sensing of clouds requires an accurate estimate of the clear-sky radiances for a given scene to detect clouds and aerosols and to retrieve their microphysical properties. Knowing the spatial and angular variability of clear-sky and surface 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 near-infrared (NIR; 1.24, 1.6 or 2.13 µm) and visible (VIS; 0.63 µm) channels available on the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) to help identify clouds and retrieve their properties. 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. The surface albedos are derived using a radiative transfer parameterization of the impact of the atmosphere, including aerosols, on the observed reflectances. This paper presents the method of generating monthly clear-sky overhead albedo maps for both snow-free and snow-covered surfaces of the above 4 channels using one year of MODIS (Moderate Resolution Imaging Spectroradiometer) CERES products. These maps are used as the background to determine the variations in clear-sky top-of-atmosphere (TOA) reflectances at a given set of viewing and illumination angles. Angular, seasonal, and local variations of the overhead are characterized for all appropriate channels.