On the Use of Close-Range Digital Stereo-Photogrammetry to Measure Gravel-Bed Topography in a Laboratory Environment

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 scanners-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 field. . Some measurements, yet sparse, were 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 variedvaried experiments, with quick high-resolution data acquisition, warranted further development. In this paper, a low-coststereo-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 (D 50 of 7-mm ). A variety of DEMs with 0.5 -mm ground resolution, obtained over the same gravel-bed and with variable surface coverage 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 to be obtained with minimum disturbance .