Abstract
This paper presents the physical basis of the EPIC cloud product algorithms and an initial evaluation of their performance. Since June 2015, EPIC has been providing observations of the sunlit side of the Earth with its 10 spectral channels ranging from the UV to the near-IR. A suite of algorithms has been developed to generate the standard EPIC Level 2 Cloud Products that include cloud mask, cloud effective pressure/height, and cloud optical thickness. The EPIC cloud mask adopts the threshold method and utilizes multichannel observations and ratios as tests. Cloud effective pressure/height is derived with observations from the O2 A-band (780 nm and 764 nm), and B-band (680 nm and 688 nm) pairs. The EPIC cloud optical thickness retrieval adopts a single channel approach where the 780 nm and 680 nm channels are used for retrievals over ocean and over land, respectively. Comparison with co-located cloud retrievals from geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites shows that the EPIC cloud product algorithms are performing well and are consistent with theoretical expectations. These products are publicly available at the Atmospheric Science Data Center at the NASA Langley Research Center for climate studies and for generating other geophysical products that require cloud properties as input.
Highlights
Since June 2015, the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) has been providing observations of the sunlit side of the Earth at the L1 Lagrangian point approximately 1.5 million km from the Earth
A geosynchronous earth orbit (GEO)–low earth orbit (LEO) composite dataset has been generated by the Clouds and the Earth’s Radiant Energy System (CERES) team at the NASA Langley Research Center by projecting the GEO–LEO retrievals to the EPIC grid (Khlopenkov et al, 2017)
Since the Lambertian-equivalent reflectivity (LER) model does not take these factors into account, it is expected that the EPIC CEP is lower in altitude than the physical cloud top; the results shown here are consistent with previous studies and theoretical predictions
Summary
Since June 2015, the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) has been providing observations of the sunlit side of the Earth at the L1 Lagrangian point approximately 1.5 million km from the Earth. A suite of algorithms has been developed for generating the standard EPIC Level 2 cloud products that include cloud mask, cloud effective pressure/height (CEP/CEH), and cloud optical thickness (COT) These algorithms use as input the observations from five EPIC channels, namely the 388 nm and the two pairs of O2 A-band (780 and 764 nm) and Bband (680 and 688 nm) reference and absorption channels. These observations provide the most cloud information content and are close to each other in observation time, which is important for reducing uncertainties resulting from temporal changes in clouds and the rotation of the Earth.
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