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, which are gaining increased attention due to their socio-economic and ecological importance. 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.


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.

RIEGL VQ-840-G topo-bathymetric Laser Scanning System mounted on Skyability Octocopter UAV in front of Pielach River study area.

Study Area and Dataset

The study area is located at the tailwater of the pre-Alpine Pielach River, a tributary of the Danube River in Lower Austria. The study site is located in a Natura 2000 natural conservation area and the gravel bed river features a meandering course with frequent geomorphic changes in response to flood peaks. The area has been surveyed twice with the RIEGL VQ-840-G, first in November 2021 using the scanner mounted on an octocopter UAV operated by the Austrian service provider Skyability, and second in February 2022, when the scanner was mounted on a helicopter platform.

Both missions showed that the capture of submerged topography and the detection of complex features such as deadwood and submerged vegetation are possible in high detail. Based on the automatic classification of 3D points, it is now possible to quantify parameters of submerged deadwood (stem length and width) and littoral vegetation (vegetation height and volume).

Read the full article here.

About the authors:

Dr. Gottfried Mandlburger

Gottfried Mandlburger studied geodesy at TU Wien, where he also obtained his Ph.D. in 2006. After finishing a 3-years research stay at the University of Stuttgart (2017-2019), he returned to TU Wien in 2020, where he is currently working as senior researcher and lecturer at the research division Photogrammetry within the Department of Geodesy and Geoinformation. In November 2021 he obtained his venia docendi in Photogrammetry for his habilitation thesis on “Bathymetry from active and passive Photogrammetry”. His main research areas are airborne topographic and bathymetric LiDAR from both manned and unmanned platforms, multimedia photogrammetry, bathymetry from multispectral images, DTM modelling, topographic data management, and scientific software development. He is awardee of ISPRS (U.V. Helava Best Paper Award 2019) and ASPRS (John I. Davidson President’s Award 2019) for recent publications on bathymetry from active and passive photogrammetry.

About David Monetti and Skyability

David Monetti holds a DI from the TU Vienna. He is currently CEO at Skyability GmbH, a drone service provider based in Austria. He manages daily business and research projects funded by the Austrian national funds. His product development activities focus on lidar systems; using lidar on different platforms like ULS, MLS or TLS have turned it into a tool used daily which now creates the best obtainable digital twin of a target of interest. For more than a year now David is also responsible for implementing lidar-bathymetry at Skyability. His research activities and 5+ years hands-on work have turned him into a true expert in the field.

Skyability is an Austrian full-service provider for drone services. The company was founded in 2015 and covers a wide range of services. These include services in the areas of UAV surveys, drone laser scanning, terrestrial laser scanning, thermography and much more. Public institutions like energie Burgenland, ÖBB INFRA, Wiener Netze and companies like FALCO wood industry and Porr are among Skyability’s customers.


About Martin Pfennigbauer and RIEGL

Dr. Martin Pfennigbauer holds a PhD in electrical engineering from Vienna University of Technology. He has been employed by RIEGL Laser Measurement Systems since 2005, presently as Chief Research Officer. His special interest is the design and development of Lidar instruments for surveying applications, with a focus on rangefinder design, waveform processing and point cloud analysis.

RIEGL is an international leading provider of cutting-edge technology in airborne, mobile, terrestrial, industrial and unmanned laser scanning solutions for applications in surveying.

RIEGL has been producing LiDAR systems commercially for over 40 years and focuses on pulsed time-of-flight laser radar technology in multiple wavelengths.

RIEGL’s core Smart-Waveform technologies provide pure digital LiDAR signal processing, unique methodologies for resolving range ambiguities, multiple targets per laser shots, optimum distribution of measurements, calibrated amplitudes and reflectance estimates, as well as the seamless integration and calibration of systems.

RIEGL’s Ultimate LiDARTM 3D scanners offer a wide array of performance characteristics and serve as a platform for continuing Innovation in 3D for the LiDAR industry.

From the first inquiry, to purchase and integration of the system, as well as training and support, RIEGL maintains an outstanding history of reliability and support to their customers.

Worldwide sales, training, support and services are delivered from RIEGL’s headquarters in Austria and in the USA; main offices in, Japan, China, Australia, Canada and the UK; and a worldwide network of representatives.


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