Radiance coming from shaded areas in urban scene

This paper is devoted to the analysis of the signal that is measured by optical remote sensors when they acquired data over a shaded part of an urban scene. For such a target, the signal is much lower than for others, as there is no direct downward irradiance. In this work, a simple urban scene is considered that introduces a shaded area. The signal observed by a high spatial resolution satellite sensor over a normal panchromatic band (500-700 nm) is computed thanks to an adapted radiative transfer code (AMARTIS) able to deal with ground topography and heterogeneity. The signal is analyzed and it appears that environmental effects play a significant role. Moreover, because of the scattering effects happening for shorter wavelengths, it is also shown that a widening of the band against 440 nm improves by about 10% the difference of signal coming from two different ground types (for whose the difference of reflectance is constant and equal to 0.1). This demonstrates that widening may be beneficial to observations in shadow because of scattering effects mainly. A more realistic scene is also considered, each part of which is associated with realistic spectral behavior. This latter simulation simply shows the importance of the thematic in the choice of the band, as it is determinant to the relevancy or the widening