Spectral unmixing is the procedure by which the measured spectrum of a mixed pixel is decomposed into a collection of constituent spectra, or endmembers, and a set of corresponding fractions, or abundances, that indicate the proportion of each endmember present in the pixel. Endmembers normally correspond to familiar macroscopic objects in the scene, such as water, soil, metal, or any natural or man-made material. Unmixing provides a capability that is important in numerous tactical scenarios in which subpixel detail is valuable
(Keshava., 2015) A Survey of Spectral Unmixing Algorithms. Lincoln laboratory journal.