High-accuracy measurements of snow Bidirectional Reflectance Distribution Function at visible and NIR wavelengths – comparison with modelling results

摘要

High-accuracy measurements of snow Bidirectional Reflectance DistributionFunction (BRDF) were performed for four natural snow samples with aspectrogonio-radiometer in the 500–2600 nm wavelength range. Thesemeasurements are one of the first sets of direct snow BRDF values over a widerange of lighting and viewing geometry. They were compared to BRDF calculatedwith two optical models. Variations of the snow anisotropy factor withlighting geometry, wavelength and snow physical properties were investigated.Results show that at wavelengths with small penetration depth, scatteringmainly occurs in the very top layers and the anisotropy factor is controlledby the phase function. In this condition, forward scattering peak or doublescattering peak is observed. In contrast at shorter wavelengths, thepenetration of the radiation is much deeper and the number of scatteringevents increases. The anisotropy factor is thus nearly constant and decreasesat grazing observation angles. The whole dataset is available on demand fromthe corresponding author.