Stereoscopic and velocimetric reconstructions of the free surface topography of antidune flows

Imaging methods developed to characterise the oscillatory free surface of rapid flows are presented and applied to torrential currents over sediment antidunes. The aim is to obtain high-resolution relief maps of the free surface topography. Two measurement principles are tested, both based on the imaging of floating tracers dispersed on the rapidly flowing surface. The first technique involves direct stereoscopic measurements. The second technique is indirect, and exploits a Bernoulli relation to derive surface elevations from the horizontal velocity field acquired using a single camera. Special attention is paid to error estimation and control. Relief maps obtained for various bedform patterns are presented, allowing comparison between the two techniques.