Modelling 3D structure of forest canopies using terrestrial LiDAR data to evaluate remotely sensed hyperspectral response

The forest canopy is a region of vast ecological relevance constituting the bulk for photosynthetically active foliage and biomass. Canopy-radiation interactions taking place in forest canopies are fundamental in understanding forest growth, regeneration and dynamics. Light detection and ranging scanning systems, have greatly contributed to the development of comprehensive 3D models across a wide range of disciplines, and is becoming key in forest model construction. The capabilities of a phased-based FARO® LS 880HE TLS to represent the vertical distribution of canopy elements are tested in this work. An intense processing procedure for modeling forest stand in 3D was performed, including: multiple scans registration, noise correction classification and voxelization.

The second objective of this dissertation was to study canopy-radiation interaction, describing the influence of the structure of a broadleaved forest canopy on its measured spectral response. Below canopy light simulations were performed considering forest type, voxel size, and zenith angle range in the 3D model construction. This method for construction of forest 3D models from TLS was used to quantify the influence of structural changes on reflectance for an even-aged forest in Belgium. Leaf area index (LAI) and the vertical distribution of leaf area density (LAD) of the modeled forest canopy were calculated. It was found that reflectance in the near-infrared region from a forest canopy with modified LAI is comparable to the response of the same forest canopy with non-modified LAI but different vertical distribution of LAD, affecting chlorophyll and LAI related vegetation indices.

Overall, the results of this research highlighted the potential of a phased-based laser scanner in collecting detailed structural information from broadleaved forest canopies, as well as the processing techniques needed to adapting these data for creation of efficient 3D models used in radiation-interaction simulation analysis.