Study of non-linear mixing in hyperspectral imagery — A first attempt in the laboratory

Non-linear spectral mixing occurs due to multiple reflections between different materials inside a single pixel. Studying such effects from satellite-borne or airborne images does not enable to control the parameters intervening in the mixing such as the variability of materials reflectance, viewing and illumination angles, BRDF, adjacency and topographic effects. Therefore, in this paper, we discuss the possibility to study non-linear mixing in the laboratory by the construction of a model imaged by a hyperspectral camera. We first study the case of a flat miniature scene; this experimental set-up enables to retrieve linear mixing results with a relative error of about 5-6%. Then, we reproduce the topographic effects responsible for the non-linearity of the mixing by adding some reliefs in the scene. We can then notice that the reflectance of the pixel is no more equal to the weighted average of the materials reflectance so that the non-linear effects due to reliefs are outlined. We finally apply the bilinear unmixing algorithm to improve unmixing results.