The main objective of this proposal is to document, monitor and improve the accuracy of a set of key land surface variables including the MODIS directional surface reflectance (MOD09), MODIS vegetation indices NDVI and EVI (MOD13), MODIS surface BRDF and BRDF corrected surface reflectance/spectral albedo (MOD43), and MODIS longwave surface radiation variables, surface temperature and spectral emissivity (MOD11). In addition to general routine maintenance of this set of variables (products), the following activities will be performed to ensure its further refinement: (1) validation of the radiative transfer (RT) approaches underlying some of products operational algorithms; (2) theoretical estimation of the accuracy of the products based on the accuracy of input parameters (e.g., atmospheric variables, calibration uncertainties); and (3) verification of the performance of products operational algorithms for a large number of sites (e.g., AERONET, radiosonde) and conditions. Significant preliminary work has already been done to justify these activities and determine future directions of the proposed research. The vector version of the 6S RT code used for the production of MOD09 has been elaborately validated against other RT codes (including benchmarks) and experimental measurements, with the overall accuracy better than 0.7%. A realistic estimate of uncertainties and their influence on the MOD09 product has been generated and verified for a number of AERONET sites. Finally, the performance of the Collection 5 algorithms for 2003 was evaluated for 150 AERONET sites, totaling more than 4000 cases.
