Global surface albedo from CERES/Terra surface and atmospheric radiation budget (SARB) data product

NASA's Terra and Aqua satellites provide a wealth of new data for study of the global ecosystem. Clouds and the Earth's Radiant Energy System (CERES) broadband instruments (on both Terra and Aqua) provide global maps of top-of atmosphere (TOA) radiation. CERES also integrates observations from multiple EOS instruments to derive enhanced data products. We here present gridded monthly mean broadband surface albedos, over the entire globe for five years (Mar 2000 through Dec 2004, based on the integration of TOA observations with radiation transfer calculations from a host of data sources. These products are systematically validated with independent ground-based observations at ~50 sites around the globe. Albedo maps are also compared to NASA Langley GEWEX Surface Radiation Budget group and NASA GISS/ISCCP FD data products for a limited number of coincident months. (See http://www-cave.larc.nasa.gov/cave/ for details on validation and data products.)

A number of input data streams are needed to produce the CERES land surface albedo. Higher resolution, narrowband Moderate resolution Infrared Spectrometer (MODIS) pixels are collocated within the larger broadband CERES footprints. Cloud properties are derived which are consistent with the broadband radiation. Global Modeling and Assimilation Office (GMAO) Goddard Earth Observing System (GEOS) GEOS-4 supplies atmospheric profiles; global ozone is from National Centers for Environmental Prediction (NCEP); and microwave based snow and ice maps are from National Snow and Ice Data Center. For aerosols, we use MODIS aerosol optical depth data along with the Model for Atmosphere and Chemistry (MATCH) data to supply aerosol constituent types and their vertical distribution. A surface model based on International Geosphere and Biosphere Programme (IGBP) scene types is used to supply underlying spectral shapes for both albedo and emissivity. Initial broadband surface albedo is either retrieved directly from clear sky footprints or taken from a history map of pre-processed clear sky data for cloudy skies. Over ice-free ocean, a validated coupled ocean atmosphere radiation transfer model is used to specify the surface albedo. Fast, 2-stream radiative transfer calculations are done for each footprint; and compared with CERES TOA observations.

While we use narrowband measurements like MODIS for guidance, radiative transfer calculations for land albedo are anchored to direct CERES measurements at TOA which are spectrally integrated (the same, solar broadband envelope that heats the earth). Data is collected over each month at satellite observation time (~1030 LST for Terra and ~1330 LST for Aqua) and spatially averaged within 1-degree equal angle grid boxes. These data are subsequently averaged in time providing a monthly mean. We supply a diurnal model based on a single "d-value" (following Dickinson's theory, which we assign as a function of surfacetype); this gives the albedo for any sun angle or sky condition.