Deriving CERES fluxes from geostationary radiances

The Clouds and Earth's Radiant Energy System (CERES) provides broadband radiance measurements in the three spectral ranges: total (0.3-100.0 micron), shortwave (0.3-0.5 micron), and atmospheric window (8.0-12.0). The scope of this research deals with shortwave radiation and how the CERES mission derives TOA fluxes. Since the CERES instrument provides radiances, fluxes must be derived by an Angular Distribution Model (ADM). The ADM analyzed here was created using data from the Tropical Rainfall Measuring Mission satellite (TRMM) in Rotating Azimuth Plane Scan (RAPS mode) to capture scene types for a multitude of solar, azimuth, and satellite zenith angles. An empirical model was constructed by pairing these geometric zenith angles with various scene identifications, provided by the Moderate-resolution Imaging Spectroradiometer (MODIS), such as cloud area fraction, cloud phase, optical depth, and surface type.

The CERES experiment releases several products with differing spatial and temporal resolutions. To improve upon the temporal resolution of the CERES sun-synchronous orbit path, geostationary satellite data are often merged to fill temporal gaps. Since geostationary satellites often have more bands as well as smaller spectral bands than CERES. The geostationary visible channel radiance must first be converted to a broadband radiance and then to a broadband flux, which is accomplished using the CERES ADMs. There are no scene data from MODIS and thus geostationary scene data must be used. This research seeks to quantify potential biases and errors introduced by passing geostationary measured and derived scenes into the CERES ADM.