1. A method for spectral demixing, the method comprising: obtaining empirical spectroscopic data representing a plurality of frequencies of electromagnetic energy that has interacted with a specimen; accessing a computer readable representation of a hierarchal spectral cluster tree representing a spectral library; demixing, with data on each of a plurality of levels of the hierarchal spectral cluster tree, foveated spectroscopic data derived from the empirical spectroscopic data; identifying at least one node in the hierarchal spectral cluster tree as corresponding to the empirical spectroscopic data; and outputting an endmember abundance assessment of the specimen corresponding to at least the at least one node.