Validation of CERES Science Team-derived MODIS cloud properties using ground-based measurements at the DOE ARM SGP site

To validate the NASA CERES-derived MODIS cloud macrophysical and microphysical/optical properties, we have collected ~5 years of collocated Terra satellite-ARM surface observations during the March 2000-July 2004 period, and ~2 years of collocated Aqua satellite-ARM surface observations during the May 2002-July 2004 period at the ARM SGP site. The surface data were averaged over a 1-hour period centered at the time of the Terra and Aqua overpass the SGP site, the corresponding CERES-MODIS cloud properties were averaged in a 30-km x 30-km box centered on the ARM SGP site. The ground-based measurements and retrievals taken over the ARM SGP site are used as “cloud-truth” data set in the validation of the CERES Science Team-derived MODIS day and night cloud retrieval algorithms. All cloud samples used in this study are single-layer overcast clouds. From this comprehensive data set, we will provide a statistically reliable validation for this climate type with enough independent samples to assess the errors for a variety of cloud types and their dependence on the diurnal cycle and seasonal changes. In addition, we will investigate the dependencies of the CERES-MODIS cloud retrievals on solar zenith, viewing zenith, scattering, and relative azimuth angles.