Modeling the Directional Reflectance (BRDF) of a Corrugated Roof and Experimental Verification

Remotely sensed images with a pixel size of about 1 m can nowadays be acquired by airborne scanners and in the near future also by high resolution satellites. With such a high spatial resolution, remotely sensed data of urban areas can resolve structures like a roof into the different surface segments with different inclinations, e.g. in the case of a gabled roof. We have measured the BRDF (Bidirectional Reflectance Distribution Function) effects thoroughly on a roof covered with corrugated (sinusoidally shaped) roof tiles and on a sample of flat roof tiles. We modeled the shape of the corrugated tiles by a cosine function and assumed that every infinitesimal surface patch of the roof tile has a BRDF proportional to the BRDF of the flat roof tile. Model results and measurements agree well. The most critical parameters are the ratio height over wavelength of the sinusoidal roof tiles and the intensity of the specular peak of the surface patch. It is possible to retrieve these parameters from the measurements.