Field goniometer measurements were obtained to examine the angular variation in the reflectance of direct beam, diffuse and global radiation from two types of SpectralonTM panel. The results indicate that optical grade (99% reflective) and grey (20% reflective) SpectralonTM exhibit different non-Lambertian properties with respect to direct beam irradiance. The angular variation in the reflectance of diffuse radiation by the panel appears independent of the panel type but varies with the diffuse to global (D : G) irradiance ratio, especially at large solar zenith angles. The combined effect of the angular response to direct beam and diffuse radiation is that panel reflectance of the global flux shows only slight variation with angle for solar zenith angles up to 55 for optical grade SpectralonTM. For larger solar zenith angles panel reflectance increases markedly with angle.
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Document Type: Research Article
Natural Environment Research Council Equipment Pool for Field Spectroscopy, University of Southampton, Southampton, SO17 1BJ, UK
Department of Geography, University of Southampton, Southampton SO17 1BJ, UK
Publication date: 2000-10-15
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