We measure the Bi-directional reflectance distribution function (BRDF) of ooid sand layers with three particle size distributions (0.5–1mm, 0.25–0.5mm and 0.125–0.25mm) and layer thicknesses on a reflecting mirror to determine the influential depth in the optical region at wavelengths of 658 nm (red), 570 nm (green) and 457 nm (blue). The hemispherical reflectance (albedo) was used as an indicator of BRDF changes between different layers. Measurements are carried out on both dry and water wetted grains. The results indicate that for both dry and wet and all size distributions, the influential depth is at most 2mm.
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