Global Mapping of the Surface Composition on an Exo-Earth using Color Variability


Left: Input map of a toy model. Three colors indicate different surface types, land, vegetation, and ocean corresponding to white, gray, and black. Right: Color composite map for the same model. The color composite is based on the retrieved components in Figure 2; the component 0, 1, and 2 correspond to green, orange, and blue, respectively.

Photometric variation of a directly imaged planet contains information on both the geography and spectra of the planetary surface. We propose a novel technique that disentangles the spatial and spectral information from the multi-band reflected light curve.

This will enable us to compose a two-dimensional map of the surface composition of a planet with no prior assumption on the individual spectra, except for the number of independent surface components. We solve the unified inverse problem of the spin-orbit tomography and spectral unmixing by generalizing the non-negative matrix factorization (NMF) using a simplex volume minimization method.

We evaluated our method on a toy cloudless Earth and observed that the new method could accurately retrieve the geography and unmix spectral components. Furthermore, our method is also applied to the real-color variability of the Earth as observed by Deep Space Climate Observatory (DSCOVR). The retrieved map explicitly depicts the actual geography of the Earth and unmixed spectra capture features of the ocean, continents, and clouds. It should be noted that, the two unmixed spectra consisting of the reproduced continents resemble those of soil and vegetation.

Hajime Kawahara
(Submitted on 8 Apr 2020)
Comments: 20 pages, 14 figures, accepted for publication in ApJ. The code is available online at this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2004.03931 [astro-ph.EP] (or arXiv:2004.03931v1 [astro-ph.EP] for this version)
Submission history
From: Hajime Kawahara
[v1] Wed, 8 Apr 2020 11:00:55 UTC (973 KB)
https://arxiv.org/abs/2004.03931
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