Annual Cycle of MODIS Albedo, Nadir BRDF-Adjusted Reflectance and BRDF Products

The MODerate resolution Imaging Spectroradiometer (MODIS) BRDF/Albedo Products (MOD43B) have been available to the public since July 2000. For the first time, an annual phenological cycle of these MODIS products is available for use by climate and biogeochemical modelers. Model parameters describing the Bidirectional Reflectance Distribution Functions (BRDF), measures of the albedo, and Nadir BRDF-Adjusted Reflectances (NBAR) have all been upgraded to a provisional status (from November 2000 onward). The operational MODIS BRDF/Albedo algorithm relies on multidate, atmospherically corrected, cloud-free surface reflectances and a semiempirical kernel-driven bidirectional reflectance model (RossThickLiSparseReciprocal) to determine parameters describing the BRDF of the global land surface. These one kilometer gridded parameters (for seven spectral bands and three broad bands) are then used to determine the global directional hemispherical reflectance ("black-sky albedo") at local solar noon, and the bihemispherical reflectance ("white-sky albedo") for each 16-day period. Global spectral NBARs (at the mean solar zenith angle of the observing period) are also computed to provide surface reflectances that have been corrected for view angle effects. Due to the consistency of this product over time, NBARs are particularly useful in capturing the phenological signal of the underlying surface vegetation. Thus annual sequences of the NBAR Product serve as the primary input for the MODIS Land Cover Product (MOD12Q). The MODIS BRDF/Albedo products are currently globally available at 1km and 5km resolutions and a 1/4 degree resolution version will soon be released. The annual temporal sequences will be presented as well as a discussion of the evaluation and reprocessing efforts that are underway.