Advances in Microtopography Measurement of Gravel Bed Surface Structure in the Field

Field characterization of gravel-bed surface structure is important for studies on flow resistance, sediment transport and in-stream habitats. The following study presents technical developments that make obtaining highresolution digital elevation models (DEMs) from gravel beds in the field more efficient and effective. Using close-range digital photogrammetry (CRDP), only two consumer-grade digital cameras, a mounting system and a laptop are needed to start collecting data. Unlike previous photogrammetric approaches, calibration was performed in the laboratory prior to moving to the field. The calibration validity was assessed on site using a simple chequerboard. Final DEM quality was assessed with a light-weight ground-truth object to guarantee reliable information can be extracted from the measured microtopography.