Nonlinear spectral mixing: quantitative analysis of laboratory mineral mixtures
- Poulet F, S. Erard
- J. Geoph. Res.,
Natural geological surfaces may have various mineralogical compositions and physical properties. Reflectance spectra, obtained from heterogeneous surface are complex nonlinear function of particle size, abundance, material opacity and type of surfaces (e.g. dust, sand, bedrock, where particles are mixed at different scales) . Spectral mixtures can be registered at different scales: from microscopic (in the laboratory) to meter (field) and kilometer scale (planetary surfaces). The choice of mixture end-members is scale dependent, when rock is observed in microscopic scale single minerals are the end-members. At this scale being in intimate contact with each other, minerals produce spectral intimate mixtures, which have non-linear behavior . The behavior of intimate mixtures mostly was studied from powdered samples, which enable to produce mixtures with known proportions and compositions. However intimate mixtures of natural surfaces are less known. In natural environments mixtures can be composed from diversity of different rock types with various proportions and grain sizes. Mixture constituents can vary from dust with extremely small particles to large boulders or rocks with continuous lattice. At the field scale we are dealing with macroscopic mixtures. Some of the theories claim that these mixtures are supposed to have linear behavior, because the specimens are not in intimate contact with each other. Therefore, probability of a photon’s being spread among the representatives of a mixture is dependent only on contribution area of each constituent specimen . Though, investigations showed that macroscopic mixtures are complex and have non-linear behavior. Here we try to observe macroscopic spectral mixtures of natural surface scenarios and present preliminary results of primary observations.