Author(s): Mariann Szilágyi, Márton Zsugyel, Tamás Krámer, András Rehák and Sándor Baranya
Linked Author(s):
Keywords: vegetation patch; UAV; large-scale particle tracking velocimetry; LSPTV; Lagrangian survey
Abstract:
The physical interaction of aquatic vegetation with flow and sediment has long been investigated as it affects ecological conditions around submerged macrophytes, determines the effectiveness of shore protection by vegetation, and governs the natural evolution of vegetation patches through enhanced sedimentation. Tower-based imaging techniques such as large-scale particle tracking velocimetry (LSPTV) and particle imaging velocimetry (LSPIV) have been used in the field to survey the surface velocity field and reveal Lagrangian coherent flow structures. However, the surveyed extent is severely limited by the field of view of the camera, and accuracy suffers at low angles. In contrast, the high viewpoint of Unmanned Aerial Vehicles (UAV) offers the opportunity to extend the spatial coverage in shorter campaigns. In this paper, we explore the applicability and resolution of UAV video recordings to describe the effects of patchy vegetation on flow patterns in a shallow lake. Primary aim of this research is to establish and introduce a LSPTV-based measurement methodology of shallow lake currents near to vegetation patches. A cloud of 30 tracer disks have been seeded and tracked with a downward looking camera in the vicinity of a patch of Schoenoplectus lacustris. Video frames were georeferenced automatically. Tracer particles were identified by a blob search algorithm, and they were matched across the frame sequence using a simple distance criterion. As a result, velocity fields were determined with neither instantaneous, nor stationary characteristics. This surface velocity distribution is adequately close to the depth-averaged velocity distribution which was determined by data acquired from previous vertical flow profile measurements. The pilot results prove that UAV-based LSPTV offers a new insight into hydrodynamics through the resulting trajectories and Lagrangian velocity distributions.
Year: 2019