Determination of Cloud Radiative Properties from Satellite Observations

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The treatment of satellite fields-of-view in the International Satellite Cloud Climatology Project (ISCCP) permits only two descriptive categories: either free of or contaminated by clouds. For the cloud-contaminated cases, a single-layer "effective" cloud model is then used to derive the radiative properties of the cloud, which is presumed to be spatially homogeneous plane-parallel with fixed scattering properties. An ability to distinguish either broken or uniform clouds has profound consequences for computing radiative fluxes at the surface and top of the atmosphere. The "spatial coherence method" (Coakley and Bretherton, 1982) is designed to address this problem by taking advantage of the "structure" amongst the pixels to retrieve percentage cloud cover. Using the 4 km AVHRR data, Dr. Coakley will derive empirical estimates of cloud cover and radiative properties for the Pacific and Atlantic Ocean basins from 50 degrees South to 50 degrees North. He will determine the effect of cloud geometry on its reflectivity, and assess the opacity of clouds at IR wavelengths and possible bias of the spatial coherence method. Dr. Coakley will also collaborate with ISCCP scientists to compare and contrast the results from two different approaches.