The Impact of different Leaf Surface Tissues on active 3D Laser Triangulation Measurements

Laser scanning devices used for plant phenotyping have shown their ability to penetrate the plant surface. This results in an interaction with the leaf tissue and in absorption of the emitted laser. The use of the intensity of reflection, measured from the backscattered laser ray, enables a more profound analysis of the geometric accuracy as well as an inspection of the plant's physiological condition. We show the comparison of two triangulation-based 3D laser scanners with different wavelengths, 658 nm (red) and 405 nm (blue), providing the intensity as additional information. By analysing the interaction of both laser sensors with separated leaf tissue contents it is possible to locate the origin of the measured signal and to evaluate the geometric accuracy of the point cloud. Furthermore, differences in the physiology of the plant as well as surface altering plant diseases like powdery mildew can be identified using the intensity of reflection. The use of the combination of a blue and a red laser scanner for high precision 3D imaging of the plant surface is shown, as well as its applicability for the analysis of plant tissue composition, the stage of leaf senescence and for a detection of plant diseases is demonstrated. Finally, the intensity of the red laser showed a high interpretability regarding the tissue composition while the blue laser provided a high geometric accuracy.