Multisensory methods for the reconstruction of the three-dimensional forest structure

The actual structure of individual forest stands or even larger forest areas has a decisive influence on the ecological characteristics of forests. The forest structure controls processes such as interception, absorption and distribution of energy and precipitation. In order to understand the interactions between structural features and ecological variables, detailed structural information is required, ideally also taking into account the seasonal cycle. The horizontal and vertical dimensions and thus the arrangement of the individual phytoelements in space should therefore be recorded in as much detail as possible. Changes during the transitional periods of spring and fall are particularly important for ecological studies.
The recording of the structure of tree populations has so far been limited to a few measurements and described representatively using mean values. For detailed 3D structures, these direct measurement methods quickly reach their (capacity) limits. In contrast, indirect, non-destructive methods appear extremely attractive: hemispherical photography is a method for obtaining information on the spatial distribution and relevant areas of phytoelements in forest stands. Using objectified segmentation technology, combined standard applications can be used with greater accuracy. In addition to a bias-free determination of the transmission of solar radiation at individual zenith angles, leaf tilt angle distributions and relative illuminance can also be determined simultaneously. In addition, the color information of the digital images will be used to draw conclusions about the fine structure (leaves, bark) of the forest stands. The recording and evaluation of hemispheric photos over a period of time thus enables the determination of structural information and knowledge of structural dynamics.
The project is being expanded to include additional recordings with a terrestrial laser scanner, which produces a very dense and precise three-dimensional point cloud. It is hoped that the recorded object geometry of all phytoelements will provide a basis for improved LAI determination. In addition, methods for generating three-dimensional descriptions of the vegetation structure from the point clouds are being further developed.
Further information can also be found on the project page of the Chair of Photogrammetry at TU Dresden.