A Radiative Transfer Simulator for DSCOVR/EPIC and Its Application to a Sensitivity Study of Cloud Property

The NOAA Deep Space Climate Observatory carries the Earth Polychromatic Imaging Camera (EPIC) that acquires the sunlit Earth from sunrise to sunset in 10 narrow spectral bands ranging from 317 nm to 779 nm. One of the primary applications of the EPIC images is to study cloud properties, including cloud mask, cloud top height, cloud geometric thickness, and optical depth. In addition, a significant portion of all the EPIC images is affected by sun glints that interferes the cloud mask determination and cloud property retrieval. In order to facilitate the remote sensing algorithm development, we have built a radiative transfer tool that can simulate the EPIC radiance for flexible atmospheric conditions. Spectral bands include 388, 443, 552, 680, 688, 764, and 779 nm. Major gas absorptions are incorporated, which includes water vapor, CO₂, CH₄, O₂, ozone, and NO₂. We use the Atmospheric Radiative Transfer Simulator (ARTS) to calculate the absorption cross section for each gas component with the absorption line parameters from the high-resolution transmission molecular absorption database (HITRAN). Gas absorption data for ozone and NO₂are supplemented from other sources. The gas absorption coefficients are then computed and integrated into multiple scattering radiative transfer solution. We have used this radiative transfer package to systematically explore the capability of cloud property retrieval using the EPIC images. Our sensitivity shows that it is promising to ease the impacts of sun glint to the cloud masking by using oxygen A and B band measurements centered at 764 and 688 nm. In addition, the use of EPIC images for cloud top height and geometric thickness will be presented.