Comparison of CERES and MISR Top-of-Atmosphere Broadband Albedo

The shortwave (SW) albedo of Earth-atmosphere system is a fundamental parameter to climate modeling efforts. The Clouds and the Earth's Radiant Energy System (CERES) and the Multi-angle Imaging Spectroradiometer (MISR) on Terra satellite both seek to obtain accurate albedo of the Earth. With its angular distribution models (ADMs), the CERES SW radiances can be directly converted into broadband albedo. However, the MISR has nine different viewing cameras operating at only four narrow bands. To obtain SW albedo from MISR spectral albedo archived in the MISR Level 2 TOA/Cloud Albedo Data, a narrowband to broadband albedo conversion algorithm must be developed.

To develop a narrowband to broadband albedo conversion algorithm, we use a merged CERES-MODIS-MISR dataset in which CERES broadband and MISR narrowband radiances are stored over each CERES footprint. A linear regression of MISR narrowband radiances to CERES broadband radiance is employed to convert the MISR narrowband radiances at the nine viewing angles into broadband radiances. The narrowband and broadband reflectances at the nine viewing angles are then broadcasted to their closet neighbor viewing angles to do an integral for generic narrowband and broadband albedo relationship. It is found that the generic narrowband and broadband albedos have linear relationship and the slope of their regression line is only a strong function of solar zenith angle and its dependence on cloud and surface conditions is insignificant. The generic narrowband and broadband albedo relationship is validated by a theoretical model for overcast plane parallel cloud cases.

Using this linear relationship, MISR spectral albedo in the MISR Level 2 TOA/Cloud Albedo Data is converted into broadband albedo and compared with CERES albedo over 1o x 1o latitude and longitude region for a period of time. We will compare the CERES and MISR top-of-atmosphere broadband albedo both regionally and globally. Cloud type and land surface type will also be considered in the comparison. The bias difference between the MISR and the CERES SW albedo over different seasons will be estimated.