Optical model of a conifer shoot

Abstract

Description of the entire structure of a conifer shoot, which forms a radiation scattering pattern, has been challenging, and the previous respective components of radiative transfer models for conifer stands were rather coarse. The progress of 3D scanner technology made it possible to collect high-density point clouds of Norway spruce shoots and describe the shoots’ geometrical shape and parameterization in full detail in this paper. The skeleton of shoots was created using custom clustering of point clouds for detecting separate needles. Needles and shoot twigs were modeled as circular cylinders, with their inclination and azimuth corresponding to the shoot skeleton.Specular reflection of incident radiation on the convex surface of needles in the border stripe of the shoot’s silhouette was found to be directed to the forward hemisphere, which increases the ratio of forward to backward scattering of radiation in a shoot. This allows multiple collisions of incident photons inside the same shoot and in the neighbor shoots in deeper layers of the crown layer in a forest, which increases the probability of incident photons being trapped in shoots and crowns of needle-leaf trees.