The study of urban areas by remote sensing is currently in significant development thanks to the availability of
new high spatial resolution cameras (metric and decimetric scale). However, at those resolutions, the measured signal is
complex to analyse, mainly because of the 3D structure of the scene (inducing sunny and shady areas) and of the spatial
variability of the urban materials. As in the shady areas the signal is predominantly due to aerosol scattering, a precise
characterisation of those particles is required.
Today, no efficient method has been implemented to characterise urban aerosols directly from remote sensing at
this scale. In order to develop such a method, based on the transitions between sunny and shady areas, we need to have a
clear idea of the properties of urban aerosols and to assess their impact on the relative contributions of the different
components of the signal.
To this end, a statistical study of urban aerosols optical properties is first conducted. Data obtained for several
years from 161 urban AERONET stations are processed and exhibit a huge variability of those properties. A
phenomenological study is carried out afterwards with a 3D direct radiative transfer code, AMARTIS. It allows to assess
the significant impact of those particles on the signal for an urban canyon, in the sun and especially in the shade where
up to 90% of the signal can be due to atmospheric scattering. It shows the necessity to model correctly all the
components of the signal to be able to retrieve efficiently the aerosols.