Through-water terrestrial laser scanning in hydraulic scale models: proof of concept

ABSTRACT

River engineering research demands increasingly high-resolution topographic data of both exposed and submerged surfaces. Detecting the topography through water is challenging in real world applications and in hydraulic laboratories. For hydraulic scale models, non-intrusive and accurate methods are needed to detect the dynamics of the river bed and its morphology without model draining. The Leica ScanStation P15 terrestrial laser scanner was tested for dry surface and through-water laser scanning. An existing procedure was adapted to reduce the distortion caused by refraction at the air/water interface. A series of tests with flow depths smaller than 0.15 m indicated an accuracy of less than 1.4 mm, resulting in a method that can be applied in hydraulic scale models with a movable bed. A sensitivity analysis revealed that the angle of incidence is the most sensitive parameter whereas the refractive index is a robust parameter. A strong decay in accuracy was observed for angles of incidence larger than 60° due to uncertainties in the flow depth. The major limitations for an application in the laboratory are high turbidity and water surface deformations that lead to an inaccurate detection of the water surface.

Keywords:

• Experimentation
• hydraulic scale model
• morphodynamics
• refraction
• terrestrial laser scanning (TLS)

Acknowledgements

The authors would like to thank Professor Andreas Wieser and his team of the Institute of Geodesy and Photogrammetry, ETH Zurich for the valuable input and discussions.