Photogrammetric determination of water profiles

Project title

Optical triangulation methods for temporal resolved determination of water profiles in hydraulic models

Description

The measurement of water surfaces is a key task in the field of experimental hydromechanics. Established techniques are usually gauge-based and often come with a large instrumental effort and a limited spatial resolution. The Institute of Photogrammetry and Remote Sensing at the TUD-Dresden, in cooperation with the Federal Waterways Engineering and Research Institute (BAW), initialised a project to develop and implement a method to measure water-surface profiles contactless with high temporal and spatial resolution.

We chose a method based on the well-known laser light sheet projection technique. While the original approach is limited to surfaces with diffuse reflection properties, the developed technique is capable of measuring on reflecting instationary surfaces. Contrary to the traditional way, the laser line is not observed on the object. Using the properties of water, the laser light is reflected on to a set of vertical planes. The resulting laser pattern can be observed by a camera and measured by subpixel operators.

A calibration based on known still water levels provides the parameters for the determination of water level and gradient for dynamic experiments.

Due to the principle of measuring the reflected laser line rather than the projected one, the accuracy can be nearly doubled. In experiments a standard deviation of 0.03 mm for water level changes could be achieved. The measuring rate is just limited by the frame rate of the camera.

A complete measuring system together with a graphical user interface was developed for the BAW.