Investigation of the Effects of Viewing/Solar Geometry on Satellite-Retrieved Stratus Cloud Properties over the ARM SGP Site Using Two Concurrent Geostationary Satellites

Because data coverage by the CERES and MODIS instruments aboard Aqua and Terra is increasingly intermittent away from the poles, the change in radiative and cloud properties between overpasses must be accounted for. This is done via interpolation using data from geostationary satellites. CERES-GEO (CGEO) cloud properties are retrieved based on a bi-spectral method which has been shown by numerous studies to be biased under certain viewing/solar geometry conditions. This study attempts to quantitatively estimate the biases and uncertainties of the CGEO retrieved cloud microphysical properties due to various sub-pixel scale cloud heterogeneities and the dependence of CGEO cloud retrievals on solar zenith and scattering angles. In order to achieve this, 16 years of both GOES East and West CGEO data and surface data from the ARM SGP site are collocated. The concurring satellite retrievals provide different viewing/solar geometry conditions for the same clouds, while the surface data provides the baseline. A basic statistical evaluation of the CGEO cloud properties for low-level stratus clouds is performed, in addition to an investigation of possible bias/error as a function of viewing/solar geometry and sub-pixel level heterogeneity in the clouds.