New Visible to Broadband Shortwave Conversions for Deriving Albedos from GOES-8 Over the ARM-SGP

The radiation budget at the top of the atmosphere (TOA) is a quantity of fundamental importance to the Atmospheric Radiation Measurement (ARM) Program. Thus, it is necessary to measure the radiation budget components, broadband shortwave (SW) albedo and outgoing longwave radiation, as accurately as possible. Measurement of TOA broadband albedos over the ARM surface sites has only been possible since the advent of Clouds and the Earth’s Radiant Energy System (CERES; Wielicki et al. 1998) in 1998. Prior to the availability of CERES data, it was necessary to infer the SW albedo from the visible (VIS) channel on the Geostationary Operational Environmental Satellite (GOES) imager by applying a narrowband-to-broadband (NB-BB) conversion (Minnis et al. 1995). Broadband TOA albedos have been derived from GOES-7, GOES-8, and GOES-10 data since 1994 (Khaiyer et al. 2002) as part of the National Aeronautics and Space Administration (NASA) Langley cloud and radiation products for the ARM Southern Great Plains (SGP) domain (Available at: http://wwwpm.larc.nasa.gov/SGP/arm-sgp.html or at the ARM data center). The current NB-BB shortwave relationship (Minnis and Smith 1998) is based on GOES-6 VIS radiances and Earth Radiation Budget Experiment (ERBE) broadband fluxes taken during October 1986. This relationship has an uncertainty of 0.02 in the albedo, which is corresponds to a 10% root mean square (rms) error (Doelling et al. 1999), and tends to underestimate the albedo, especially for clear scenes (Rapp et al. 2002). The uncertainties in the NB-BB conversion can be eliminated by using the SW radiances measured by CERES. However, the improved spectral coverage by CERES comes at the price of reduced temporal sampling. CERES data are only available once or twice a day during 8 months of 1998, twice per day since March 2000 and four times per day since August 2002. GOES data are available every 15 or 30 minutes. To retain the temporal coverage of GOES and reduce the spectral conversion errors, it is necessary to develop an improved method for converting GOES VIS radiances to SW albedos.