Author(s): Stephane Bertin; Heide Friedrich; Patrice Delmas; Edwin Chan
Linked Author(s): Heide Friedrich
Keywords: Remote sensing; Stereo-photogrammetry; Gravel-bed; DEM; Roughness; Image processing
Abstract: There is a need for high-resolution topographical data of riverine gravel-beds for hydraulic studies. To date, there is no readily affordable and deployable technique to collect these data, especially over submerged topographies. Terrestrial laser-scanners and proprietary stereo-photogrammetric systems, with associated commercial software, allow exposed gravel-beds to be represented as high-resolution Digital Elevation Models (DEMs), both in the laboratory and in the field. Some measurements, yet sparse, were obtained through-water. However, either the necessary equipment (hardware/software) or the complexity of the methodology restrained the applicability of the findings. For stereo-photogrammetry to be used in hydraulic research, the promise of a versatile technique, which can be adapted to varied experiments, with quick high-resolution data acquisition, warranted further development. In this paper, a low-cost stereo-photogrammetric system, and its application for gravel-bed studies, is presented, together with an internal performance evaluation. The setup and its principle of operation, which make use of digital consumer cameras and non-commercial photogrammetric process steps, differ from previous photogrammetric systems employed for gravel-bed morphology characterization. The developed system is used in laboratory experiments measuring a water-worked gravel-bed made of fine sediment particles (D50 of 7-mm). A variety of DEMs with 0. 5-mm ground resolution, obtained over the same gravel-bed with variable surface coverage and water depth, is presented and the extracted metrics are compared. The presented photogrammetric system shows promise in the advent of a new method for gravel-bed topography measurement at the grain-scale, which allows data to be obtained with minimum disturbance.