A primary goal of NASA�s Earth observation efforts is the long term monitoring of key biophysical variables and the production of long term and consistent parameters for modeling studies. The MODIS BRDF/Albedo products have been embraced by the modeling community since the launch of the first MODIS on board the Terra platform. The products have thus far been validated to a stage-1 (over a small number of well calibrated sites) and the high quality primary algorithm has been shown to produce consistent global land surface albedo quantities over a variety of land surface types and snow cover. The MODIS algorithm relies on multi-date, cloud-free, atmospherically-corrected surface reflectances from both Terra and Aqua and a linear kernel-driven BRDF model to obtain realistic measures of the land surface reflectance anisotropy. These anisotropy model parameters can then be used to obtain various measures of surface albedo (intrinsic quantities such as directional hemispherical reflectance and bihemispherical reflectance as well as the actual surface albedos comparable to field instrument observations). In addition, the BRDF model information can be used to correct surface reflectances to a standard viewing geometry, and Nadir BRDF-Adjusted Reflectances (NBAR)are routinely provided as a standard MODIS product.
The MODIS BRDF, NBAR and Albedo products are currently available globally, every 8 days (based on the last 16 days) at a 500m resolution in 10 degree boxes in a sinusoidal projection. In addition, for ease of use in modeling, the products are provided in global fields at a 0.05 degree resolution in a geographic lat-lon projection. In collaboration with the MODIS Atmosphere Team, snow-free, gap-filled versions of these products have also been produced and are being enthusiastically used as initialization fields by a number of modeling efforts.
As surface albedo is a key radiative and biophysical quantity, a variant of the MODIS heritage algorithm is also being implemented by the NPP/NPOESS effort to provide daily surface albedo. However, refinements will be needed to accurately couple the MODIS era surface albedo and anisotropy quantities with the less robust VIIRS daily solutions to provide long term climate quality records of albedo and anisotropy.
Thus the primary aims of this proposal are to continue to maintain, refine, and validate the MODIS albedo and reflectance anisotropy products and to evaluate, refine, and prepare for the validation of the proposed VIIRS anisotropy and daily albedo products. Furthermore, through continued active participation in both the MODIS and NPP Science Teams, as well as the Radiative Measurement Team, we will develop the strategies necessary to bridge the MODIS and VIIRS observing periods and to provide a long term consistent record of the Earth's reflective character for climate, biogeochemical and weather-prediction modeling efforts.
