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Earth as a Proxy Exoplanet: Simulating DSCOVR/EPIC Observations Using the Earth Spectrum Simulator

Gu, Lixiang and Zeng, Zhao-Cheng and Fan, Siteng and Natraj, Vijay and Jiang, Jonathan H. and Crisp, David and Yung, Yuk L. and Hu, Yongyun (2022) Earth as a Proxy Exoplanet: Simulating DSCOVR/EPIC Observations Using the Earth Spectrum Simulator. Astronomical Journal, 163 (6). Art. No. 285. ISSN 0004-6256. doi:10.3847/1538-3881/ac5e2e.

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Analyzing time-resolved disk-integrated spectral images of the Earth can provide a baseline for future exoplanet characterization. The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) provides ∼5000 full-disk sunlit Earth images each year in ten wavelengths from the ultraviolet to the near-infrared. A whole-disk radiative transfer model can improve our understanding of the temporal variation of Earth’s disk-integrated reflected radiance (“light curves”) at different wavelengths and create a pool of possible observations of Earth-like exoplanets. We use the two-stream-exact-single-scattering line-by-line radiative transfer model to build the Earth Spectrum Simulator (ESS) and reconstruct DSCOVR/EPIC spectral observations. Atmospheric effects, such as scattering by air molecules, clouds, aerosols, and gaseous absorption, are included. Surface contributions are treated using appropriate bidirectional reflectance distribution functions. We simulate ∼300 images in each channel for observations collected in 2016, with a spatial resolution of ∼2000 pixels over the visible disk. ESS provides a simultaneous fit to the observed light curves, with time-averaged reflectance differences typically less than 7% and root-mean-square errors less than 1%. The only exceptions are in the oxygen absorption channels, where reflectance biases can be as large as 19.55%; this is a consequence of simplified assumptions about clouds; especially their vertical placement. We also recover principal components of the spectrophotometric light curves and correlate them with atmospheric and surface features.

Item Type:Article
Related URLs:
URLURL TypeDescription
Gu, Lixiang0000-0002-3089-3706
Zeng, Zhao-Cheng0000-0002-0008-6508
Fan, Siteng0000-0002-3041-4680
Natraj, Vijay0000-0003-3154-9429
Jiang, Jonathan H.0000-0002-5929-8951
Crisp, David0000-0002-4573-9998
Yung, Yuk L.0000-0002-4263-2562
Hu, Yongyun0000-0002-4003-4630
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 December 19; revised 2022 February 19; accepted 2022 March 14; published 2022 May 20. This work was supported by the National Natural Science Foundation of China under grant 41888101. All computations were done at the High-performance Computing Platform of Peking University. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Y.L.Y. was supported in part by a Virtual Planetary Laboratory grant from the University of Washington. S.F. acknowledges funding support from CNES. We acknowledge funding support from the NASA Exoplanet Research Program NNH18ZDA001N.
Funding AgencyGrant Number
National Natural Science Foundation of China41888101
University of WashingtonUNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Subject Keywords:Spectrophotometry; Radiative transfer; Exoplanets; Exoplanet surface variability; Exoplanet atmospheres; Exoplanet astronomy; Habitable planets; Earth (planet); Exoplanet atmospheric composition; Exoplanet atmospheric variability; Exoplanet surface characteristics; Exoplanet surface composition
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Spectrophotometry (1556); Radiative transfer (1335); Exoplanets (498); Exoplanet surface variability (2023); Exoplanet atmospheres (487); Exoplanet astronomy (486); Habitable planets (695); Earth (planet) (439); Exopl
Record Number:CaltechAUTHORS:20220523-165124000
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Official Citation:Lixiang Gu et al 2022 AJ 163 285
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114880
Deposited By: George Porter
Deposited On:24 May 2022 17:09
Last Modified:24 May 2022 17:09

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