Unmanned Scanning

Gottfried Mandlburger et al.: A case study for detection and modelling of submerged deadwood from UAV-borne topo-bathymetric LiDAR point clouds 01.12.2021

Alluvial forests constitute an important and ecologically sensitive habitat. Diseases of endemic tree species like ashes have increased the amount of dead wood in alluvial forests in Austria in the recent past (Kessler et al. 2012). During seasonal flood peaks, the increased discharge carries deadwood stems into the active river channels, where they are floating downstream until either natural or artificial barriers (river bends, bridge piers, hydropower stations, etc.) stop their movement. On the one side, stranded driftwood plays an important role in aquatic ecosystems, e.g. as shelter for juvenile fish stages, but on the other side, it can cause severe problems like log jams potentially resulting in flooding of residential areas. For these reasons, monitoring of the volume and distribution of driftwood within rivers and lake outlets is an important topic from both an ecologic and socio-economic point of view. In the recent past, airborne topo-bathymetric LiDAR (Light Detection And Ranging) has gained increased importance for mapping the littoral zone of both coastal and inland water areas. Bathymetric LiDAR uses short laser pulses in the green domain of the electro-magnetic spectrum for measuring objects above and below the water table.
In this case study the authors present early results of using 3D point clouds acquired with a survey-grade topobathymetric laser scanner for detecting and modelling submerged driftwood. They demonstrate that stems and even branches are well recognizable in the point cloud and that the achieved point density and measurement precision allows derivation of the driftwood skeleton parameters like tree length and diameter. This enables quantitative analysis of submerged biomass.

UAV-based data acquisition was carried out by Skyability GmbH, www.skyability.com, using a RIEGL VQ-840-G topo-bathymetric laser scanner.

The presentation (DOI 10.34726/wim.1979) was given during the SilviLaser Conference 2021 and is available in the SilviLaser Proceedings at the reposiTUm.