Determining the Daytime Earth Radiation Budget from DSCOVR

The Deep Space Climate Observatory (DSCOVR) platform provides a unique perspective for remote sensing of the Earth. With the National Institute of Standards and Technology Advanced Radiometer (NISTAR) and the Earth Polychromatic Imaging Camera (EPIC) onboard, it provides full-disk measurements of the broadband shortwave and total radiances reaching the Earth-Sun Lagrange-1 (L-1) position.Because the satellite orbits around the L1 spot, it continuously observes a nearly full Earth, providing the potential to determine the daytime radiation budget of the globe at the top of the atmosphere. The NISTAR is a single-pixel instrument that measures the broadband radiance from the entire sunlit side of the Earth, while EPIC is a spectral imager with channels in the ultraviolet and visible ranges.

The Level 1 NISTAR shortwave radiances are filtered radiances. To determine the daytime TOA shortwave and longwave radiative fluxes, the NISTAR measured shortwave radiances must be unfiltered first. We will describe the algorithm used to un-filter the shortwave radiances. These unfiltered NISTAR radiances are then converted to the full disk shortwave and daytime longwave fluxes, by accounting for the anisotropic characteristics of the Earth-reflected and emitted radiances. These anisotropy factors are determined by using the scene identifications determined from multiple low Earth orbit and geostationary satellites matched into the EPIC field of view. Comparison of the fluxes from NISTAR with those from CERES synoptic product indicates that the NISTAR SW fluxes are about 12% larger than those from CERES, and the NISTAR LW fluxes are about 6% larger than those from CERES.

The narrowband EPIC radiances are converted to broadband radiances using the narrowband-to-broadband regression relationships developed from collocated MODIS and CERES data. These EPIC broadband radiances are then used to derive EPIC SW fluxes using the same methodology as for NISTAR. The agreement between the EPIC SW fluxes and the CERES SW fluxes are within 2%.