Messung der spektralen Reflektionsfunktion (BRDF) ausgewaehlter Oberflaechen bei natuerlicher Beleuchtung

The spectral bidirectional reflectance distribution function (BRDF) of selected artificial surfaces was measured under natural illumination. Data were obtained with a spectrometer in the wavelength range 600 nm - 900 nm with a spectral resolution of 5 nm, using 61 spectral bands. The samples were placed on a goniometer, which allowed to set all the desired angles of incidence and reflection. A Spectralon panel (made by Labsphere Inc., Boulder, Colerado) was used as a reference target for determining the incoming irradiance. The BRDF of this Spectralon panel was measured in the laboratory. The BRDF of the Spectralon panel is not lambertian, however it obeys Helmholtz's theorem of reciprocity. For the in situ measurements, an additional measurement was made for each conbination of angles with the samples being shadowed, in order to eliminate the influence of sky light. 6 out of 9 samples could be fitted to a function which was developed by Walthall et al. (1985) and modified by Liang and Strahler (1994). In this work, the function was extended by a specular peak, increasing the number of free parameters to 7. The diffuse part of the BRDF of the samples does not vary in a systematic way. The intensity of the specular peak grows with increasing zenith angles. (orig.)Available from TIB Hannover: RR 839(18-96) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman