Multispectral measurement of scattering-angular light distribution in apple skin and flesh samples

Knowledge of the optical properties of apple tissues such as skin and flesh is essential to better understand the light-tissue interaction process and to apply optical methods for apple quality inspection. This work aimed at estimating the anisotropy factor of thin skin and flesh samples extracted from three apple cultivars. The scattering-angular light distribution in each tissue sample was measured at four wavelengths (λ=633, 763, 784, and 852 nm), by means of a goniometer setup. Based on the recorded angular intensity I(θ,λ), the effective anisotropy factor g_eff of each tissue type was first estimated using the mean statistics applied to the random variable cos θ. Next, the measured data were fitted with three predefined and modified phase functions-Henyey-Greenstein (p_MHG), Gegenbauer kernel (p_MGK), and Mie (p_Mie)-in order to retrieve the corresponding anisotropy factors g_MHG, g_MGK, and g_MMie. Typically, the anisotropy factors of skin and flesh amount to 0.6-0.8 in the above-mentioned wavelength range.