Advancements in dyke surveillance: an UAV-RGB-Image-based monitoring approach

This research started with the objective to document and analyse the changes between spring and summer on the dyke Quenin, an earthen structure subjected to erosion by the sea waves. As test flights, two surveys were done and some conclusions were drawn from the corresponding structure from motion (SfM) pipeline outputs, orthomosaic and digital surface model (DSM). Initially, we conducted a study to assess the achievable accuracy of topographic models with the available equipment, correction networks and flight parameters. Next, we evaluated the impact of various ground control point (GCP) and checkpoint (CP) distributions on the accuracy of the DSM to identify the optimal configuration for future monitoring missions. Finally, we were able to detect changes in topography, vegetation and shallow bathymetry using only RGB images. In terms of topography, we identified areas affected by overtopping and erosion. Vegetation changes were observed using visible band vegetation indices (VVI), although these were influenced by the site lighting conditions during the missions. Shallow bathymetry, covering depths from 0 to −5 m, was derived using well-established methods based on water colour. The main contribution of this article is to demonstrate the potential of red, green and blue (RGB) imagery acquired by unmanned aerial vehicle (UAV) for monitoring changes in topography, bathymetry, armour rocks and vegetation and to define flight parameters for future monitoring missions on the dyke.