generated images, the illumination has been modelled to closely agree with the average circadian illumination from April until September, corresponding to a midlatitude northern hemisphere growing season. The illumination has been composed of a combination of direct and diffuse light calculated from $350$ to $2500$nm with a $10$nm interval. The citrus trees and weeds of the orchard scenes (see paragraph \[sec:orchard\]) and the trees of the forest scene (see paragraph \[sec:forest\]) have been constructed as triangular meshes by implementing the algorithm introduced in [@Weber1995]. Their material properties have been described by a bidirectional scattering distribution function (BSDF) model [@Stuckens2009].

### Orchard scenes {#sec:orchard}

The fully calibrated virtual citrus orchard developed in [@Stuckens2009] has been used to create two different orchard scenes: (*i*) an orchard consisting of citrus trees and a soil background, leading to two-endmember mixtures and (*ii*) an orchard consisting of citrus trees, a soil background and weed patches, leading to three-endmember mixtures. Each orchard scene consists of $20\times20$ pixels, with a pixel size of $2\textrm{m}\times2\textrm{m}$. The exact per-pixel abundances are known for the three components, as well as the reference spectral signatures. More precisely, for the soil endmember, the pure spectral signature consisted of the fully sunlit soil 