Expected retrieval accuracies of bidirectional reflectance and albedo from EOS-MODIS and MISR angular sampling

This paper reports expected accuracies of bidirectional reflectance and albedo retrievals from the angular sampling provided by NASA's upcoming moderate resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR) on the EOS-AM-1 satellite platform. A numerical discrete ordinates method radiative transfer model by Myneni is used to simulate bidirectional reflectances for combined MODIS and MISR angular sampling as a function of latitude and time of year for six different bidirectional reflectance distribution function (BRDF) types (land cover types) in the red and near-infrared wave bands. These simulated observations are then inverted using three different simple BRDF models scheduled for use in the future operational MODIS and MISR BRDF/Albedo Products: the reciprocal Ambrals, the modified Rahman-Pinty-Verstraete (RPV), and the modified Walthall BRDF models. Bidirectional reflectance and albedo retrievals are studied not only at the mean solar zenith angle of observation but extrapolated to arbitrary other Sun zenith angles as well. The in fluence of loss of observations to clouds is also examined. Results show that albedo may be retrieved with 2 to 8% median accuracy using either the Ambrals or the modified RPV model for any solar zenith angle for any MODIS/MISR sampling and that the accuracy of predicted nadir view reflectance is also mostly within a 10% error margin. For the Myneni forward model used, the Ambrals model may be slightly more accurate. The empirical modified Walthall model clearly performs worse than the two semiempirical models. Error distribution histograms allow assessing the overall accuracy to be expected from the planned MODIS BRDF/Albedo Product.