GLOBAL RETRIEVAL OF BIDIRECTIONAL REFLECTANCE AND ALBEDO OVER LAND FROM EOS MODIS AND MISR DATA - THEORY AND ALGORITHM

This paper describes the theory and the algorithm to be used in produc ing a global bidirectional reflectance distribution function (BRDF) an d albedo product from data to be acquired by the moderate resolution i maging spectroradiometer (MODIS) and the multiangle imaging spectrorad iometer (MISR), both to be launched in 1998 on the AM-I satellite plat form as part of NASA's Earth Observing System (EOS). The product will be derived using the kernel-driven semiempirical Ambrals BRDF model, u tilizing five variants of kernel functions characterizing isotropic, v olume and surface scattering. The BRDF and the albedo of each pixel of the land surface will be modeled at a spatial resolution of I km and once every 16 days in seven spectral bands spanning the visible and th e near infrared. The BRDF parameters retrieved and recorded in the MOD IS BRDF/albedo product will be intrinsic surface properties decoupled from the prevailing atmospheric state and hence suited for a wide rang e of applications requiring characterization of the directional anisot ropy of Earth surface reflectance. A set of quality control flags acco mpanies the product. An initial validation of the Ambrals model is dem onstrated using a variety of field-measured data sets for several diff erent land cover types.