The scanner was mounted on top of t

The scanner was mounted on top of the sample at distance of 1.65 meters. The sample was tilted using a small goniometer between angles 0⁰ and 60⁰. The Spectralon calibration plate was used to calibrate the raw intensity values. Small samples with 3000-4000 points were taken from TLS point clouds and the mean intensity value was calculated from them. Incidence angles greater than 40⁰ were measured with different geometry, i.e., to achieve incidence angles greater than 0⁰ on the horizontal sample surface, the sample were not placed directly under the scanner. In this way, we were able to tilt the sample into incidence angles greater than 40⁰ without the grains falling down because of the tilt.