Underwater Deadwood and Vegetation from UAV-borne Topo-Bathymetric LiDAR

GIM International recently published an article about the usage of the RIEGL VQ-840-G topo-bathymetric laser scanner for detecting and modelling submerged deadwood and vegetation.

Deadwood acts as an important underwater habitat but also poses a threat to bridges, hydroelectric power plants and riverside buildings. Underwater vegetation is a proxy for climate change in general and global warming in particular. In this context, UAV-borne topo-bathymetric laser scanning constitutes a promising tool for accurately capturing and modelling these small-scale objects in high spatial resolution.

Sensor

The RIEGL VQ-840-G is an integrated topo-bathymetric laser scanning system including a factory-calibrated IMU/GNSS system and a camera. The lightweight, compact VQ-840-G LiDAR can be installed on various platforms, including UAVs. The laser scanner comprises a frequency-doubled IR laser, emitting pulses of about 1.5ns pulse duration at a wavelength of 532mrad and a pulse repetition rate of 50–200kHz. Onboard time-of-flight measurement is based on online waveform processing of the digitized echo signal. In addition, the digitized waveforms are stored on disc for offline waveform analysis. The depth performance of the instrument is in the range of more than 2 Secchi depths.

3D point cloud of submerged bunch of willow tree branches coloured by class ID (red)