The Laboratoire d’Hydraulique* at ESTP (French School of Construction Work) is carrying out studies on soil deformation around bridge piers in the presence of natural flows (tides, rivers, etc.). For this study, researchers need to take riverbed height and shape measurements from outside the hydraulic channel, without placing sensors that could affect the flow, and that’s why they contacted us to tap into our optical metrology skills.
We carried out an experimental study to simultaneously identify and validate the most suitable technologies (stereo vision with pattern projection, fringe projection, laser profilometry), and assess their performance on samples under different conditions. One of the main difficulties in this study was the disparities between the textures to be analysed between sandy riverbeds or clay riverbeds. Various wavelengths and experimental conditions were used to obtain an optimal light/material interaction mode for all substrates, while taking into account the turbidity of flows that limit visibility. We also had to take into account additional optical deformations caused by changes in the environment, particularly air/water flows.
Researchers carried out many technical tests to ultimately get reliable measurements and a 3D reconstruction of riverbeds subject to natural river flows. They did so using a structured light projection scanner (Photoneo) coupled with optical correction techniques that use simplified calibration and radius launcher calculations.
The end product delivered by R&D Vision was a system that allows the ESTP Laboratoire d’Hydraulique to take the measurements it wants using a fast, accurate, time-resolved sensor. Thanks to the sensor’s flexibility of use, it can be positioned in the strategic locations to be studied in the measuring channel.