ORIGINAL RESEARCH article
Front. Remote Sens.
Sec. Multi- and Hyper-Spectral Imaging
This article is part of the Research TopicEarth Observations from the Deep Space: 10 Years of the DSCOVR MissionView all 20 articles
NISTAR Measurements Confirm Basic Aspects of EPIC-Derived Global-Scale Dayurnal Variability in Earth's Reflected Radiation
Provisionally accepted
- 1Goddard Institute for Space Studies (NASA), New York, United States
- 2NASA Langley Research Center, Hampton, United States
- 3L-1 Standards and Technology, Inc., Manassas, VA, USA, Manassas, United States
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A unique model/data comparison capability is made possible by the unique viewing geometry from NASA's DSCOVR Mission Lissajous orbital location around the Lagrangian L1 point. The key point of this unique location is the large orbital inclination relative to the perpendicular of the Sun-Earth line-of-sight. This circumstance enables periodic Sun-Earth-Satellite phase angle shifts ranging from 2-degrees to 12-degrees with repeating ~3-month periodicity. At such extreme phase angles, backscattered radiation for spherical cloud-top particles is strongly phase angle dependent, but not for irregular-shaped ice particles. Also key, are the near-hourly high-resolution EPIC images that have been converted to radiative solar fluxes by extensive use of ancillary satellite data and CERES-based ADMs. These EPIC-derived SW fluxes, integrated over the Earth's sunlit hemisphere, constitute the EPIC Composite dataset of 1-day resolution global-scale reflected SW fluxes, which have been shown to agree well with CERES reflected SW fluxes. Using the EPIC data as a template, the DSCOVR satellite ephemeris enables aggregation of climate GCM run-time output over the sunlit hemisphere with the same viewing geometry as EPIC. Generating the GCM-equivalent global-scale SW flux dataset, together with the EPIC data, forms the basis for a new paradigm in model/data comparisons. The key advantages of this DSCOVR-style approach are the (1) identical space-time sampling with identical viewing geometry and complex, but identical averaging over the diurnal cycle between observations and climate GCM output data, (2) preservation of short-period variability at 1-day resolution due to the Earth's rotation, and (3) self-consistent weather noise suppression by identical averaging over the sunlit hemisphere. Early examples of the EPIC data variability drew concerns from colleagues worried that the variability in the EPIC data might be modeling noise. There is no other way to resolve this concern but to find another data source that shows the same degree of variability. The definitive comparison to NISTAR measurements presented in this study unequivocally confirm that the global EPIC-derived variability is indeed real, and not a data artifact.
Keywords: Anisotropy parameter, Backscattered radiance, Dayurnal cycle, EPIC-NISTAR, Global-scale variability, phase angle, Planetary albedo, radiation budget
Received: 24 Aug 2025; Accepted: 26 Dec 2025.
Copyright: © 2025 Lacis, Russell, Carlson, Su and Yu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Andrew A Lacis
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