An investigation into the properties of the dark endmember in spectral feature space

In most multispectral image transformation methods, the position of the dark endmember is placed at the origin of the n-D spectral domain regardless of the target spectral signature. A series of field experiments under varying illumination showed that shadow-lines, which hypothetically pass through the dark endmember, never pass directly through the origin of the spectral feature space. The dark endmember so-defined is termed the ‘dark point virtual endmember’ (DPVE) and its location is assumed to be sensitive to the state of atmosphere. A conceptual radiative transfer model was derived and this demonstrated the susceptibility of the DPVE to the proportion of scattered light from the sky. Further analysis also revealed that the DPVE plays an important role in defining the lower boundary of the data distribution in spectral feature space. The results suggest that, as a signature of atmospheric effects of a scene, estimating the DPVE has potential to reduce some of the uncertainties associated with conventional dark point atmospheric correction methods.