  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.
