Abstract
Earth’s reflectivity is among the key parameters of climate research. National Aeronautics and Space Administration (NASA)’s Earth Polychromatic Imaging Camera (EPIC) onboard National Oceanic and Atmospheric Administration (NOAA)’s Deep Space Climate Observatory (DSCOVR) spacecraft provides spectral reflectance of the entire sunlit Earth in the near backscattering direction every 65 to 110 min. Unlike EPIC, sensors onboard the Earth Orbiting Satellites (EOS) sample reflectance over swaths at a specific local solar time (LST) or over a fixed area. Such intrinsic sampling limits result in an apparent Earth’s reflectivity. We generated spectral reflectance over sampling areas using EPIC data. The difference between the EPIC and EOS estimates is an uncertainty in Earth’s reflectivity. We developed an Earth Reflector Type Index (ERTI) to discriminate between major Earth atmosphere components: clouds, cloud-free ocean, bare and vegetated land. Temporal variations in Earth’s reflectivity are mostly determined by clouds. The sampling area of EOS sensors may not be sufficient to represent cloud variability, resulting in biased estimates. Taking EPIC reflectivity as a reference, low-earth-orbiting-measurements at the sensor-specific LST tend to overestimate EPIC values by 0.8% to 8%. Biases in geostationary orbiting approximations due to a limited sampling area are between − 0.7 % and 12%. Analyses of ERTI-based Earth component reflectivity indicate that the disagreement between EPIC and EOS estimates depends on the sampling area, observation time and vary between − 10 % and 23%.
Highlights
Earth’s reflectivity characterizes the fraction of incident solar radiation that the sunlit Earth reflects back to space
We started with analyses of variations in the Earth Polychromatic Imaging Camera (EPIC) scattering function, Pλ, at λ = 680 nm and λ = 780 nm (NIR) derived from Deep Space Climate Observatory (DSCOVR) EPIC images acquired on 23 August 2016
This is an anomalous day in the sense that the EPIC observed almost the entirety of South America free of clouds, a rare event
Summary
Earth’s reflectivity characterizes the fraction of incident solar radiation that the sunlit Earth reflects back to space It is among the key variables in remote sensing, Earth’s energy budget studies and climate models [1,2,3,4,5]. Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging SpectroRadiometer (MISR) onboard Terra and MODIS onboard Aqua, these low-earth-orbiting (LEO) satellite sensors provide Earth’s spectral reflectivity at 10:30 and 13:30 LST, respectively. It takes 1–2 days for MODIS and 9 days for MISR to provide global coverage of the Earth at instrument-specific LSTs. National Oceanic and Atmospheric Administration (NOAA)’s Geostationary Operational Environmental Satellite East (GOES-East) acquires almost complete sunlit images of North and South America and most of the Atlantic Ocean and the Pacific Ocean basin. Their specification is critical to understanding the feedback mechanisms within the land–atmosphere–ocean system that strives to achieve dynamic equilibrium in response to perturbations of the Earth’s radiation budget
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