Assessing the consistency of optical properties measured in four integrating spheres

Abstract

ABSTRACTLeaf optical properties (LOPs) determine the radiation regime of vegetation, thus being key input parameters in leaf and canopy radiative transfer models. It is of great importance to know the uncertainties originating from the LOP measurements. The most common approach to measure LOP uses integrating spheres. They allow measurements of both directional-hemispherical reflectance factor (R) and transmittance factor (T). However, sphere’s design, inner surface coating and measurement protocol differ among the spheres’ models and manufacturers. Our main goal was to evaluate the consistency of optical properties measured in four integrating spheres (Dualsphere, Labspehre, ASD, and Li-cor). Our test samples were three Spectralon® panels, four artificial materials and leaves from six common broadleaf tree species. Results showed that spectra measured in the four integrating spheres were generally similar in the spectral region between 400 and 1600 nm. The average standard deviation computed among the spectra of all samples measured in all spheres was around 0.023 (and varied between 0.005 and 0.044). Statistically significant differences were detected mainly between Dualsphere and Li-cor spheres.