Brdf Measurements of Urban Surface Materials at the Ego Facility Using a Laser Source

In this paper we present a study of the BRDF characteristics of urban surface materials (e.g. roof coverings). Multiangular measurements were made at the European Goniometer Facility, Ispra, Italy. We used a linearly polarized HeNe-laser as illumination source and a spectroradiometer with a mounted polarizer as detector. Measurements were done at horizontal (s) and vertical (p) polarisation states relative to the principal plane, resulting in measurements at four different combinations of source and detector orientation (ss, sp, ps and pp). We performed a systematic study of the accuracy of BRDF measurements to determine measured deviations from the Lambertian case. Polarization effects in the principal plane are analyzed for roof covering materials as well as for a Spectralon sample of 50% reflectance. The measurements show that the reflectance from our surface materials is a combination of different components. As a first approximation they can be described by a component due to internal scattering (diffuse component) and a component that is due to specular reflection of inclined surface facets.