Retrieval of red spectral albedo and bidirectional reflectance using AVHRR HRPT and GOES satellite observations of the New England region

Abstract

As a prototyping exercise for the moderate‐resolution imaging spectroradiometer (MODIS) albedo/BRDF product, we demonstrate the retrieval of bidirectional reflectance distribution functions (BRDFs) and red spectral albedo measures for the New England region, United States, from merged AVHRR and GOES radiances at a 1 km 2 (nominal) spatial scale. These data were acquired during a 25‐day period in early fall 1995. The spatial pattern of BRDF retrievals shows that urban, suburban, and interurban regions exhibit directional scattering that is well modeled by the geometric optics of shadow casting. The directional reflectance of more continuous forest areas is better described by volume‐scattering mechanisms. Spectral albedos are larger in urban and suburban areas than in forested regions, as might be expected from the strong absorption of leaves in the red wave band. The red spectral albedo generally increases with solar zenith angle, as has been noted in ground measurements of broadband albedo. A number of technical limitations discussed constrain the absolute accuracy of retrieved albedos presented here, although the spatial patterns of albedo and the consistency of the BRDF shapes inspire confidence. These limitations will largely be overcome with application of our algorithm to data from the MODIS and MISR instruments on the EOS AM‐1 platform.