Estimation of instantaneous TOA albedo at 670 nm over ice clouds from POLDER...

Sun, W., N. Loeb, and S. Kato (2004), Estimation of instantaneous TOA albedo at 670 nm over ice clouds from POLDER multidirectional measurements, J. Geophys. Res., 109, D02210, doi:10.1029/2003JD003801.

An algorithm that determines the 670-nm top-of-atmosphere (TOA) albedo of ice clouds over ocean using Polarization and Directionality of the Earth’s Reflectance (POLDER) multidirectional measurements is developed. A plane-parallel layer of ice cloud with various optical thicknesses and light scattering phase functions is assumed. For simplicity, we use a double Henyey-Greenstein phase function to approximate the volumeaveraged phase function of the ice clouds. A multidirectional reflectance best-fit match between theoretical and POLDER reflectances is used to infer effective cloud optical thickness, phase function and TOA albedo. Sensitivity tests show that while the method does not provide accurate independent retrievals of effective cloud optical depth and phase function, TOA albedo retrievals are accurate to within ~3% for both a single layer of ice clouds or a multilayer system of ice clouds and water clouds. When the method is applied to POLDER measurements and retrieved albedos are compared with albedos based on empirical angular distribution models (ADMs), zonal albedo differences are generally smaller than ~3%. When albedos are compared with those on the POLDER-I ERB and Cloud product, the differences can reach ~15% at small solar zenith angles.

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Radiation Science Program (RSP)