Abstract
Recent developments in unmanned aerial vehicles (UAVs) have resulted in high-resolution digital elevation models (DEMs) of vulnerable coastal environments, including beach–foredune topography. If performed repetitively, they can offer an excellent tool to determine the spatial and temporal changes in the sediment budget, which may be required for proper land management. However, the quality of a UAV, slope parameters, and vegetation significantly influence DEM accuracy. The aim of this study is to compare precise GPS-RTK transects across a section of the South Baltic coast in Poland with those obtained from a DEM based on high-resolution and high-accuracy images obtained by a wind-resistant, high-quality fixed-wing UAV during beyond visual line of sight operation (BVLOS). Different land cover classes, slope inclination, and general curvature, as well as surface roughness, were taken into consideration as possible factors influencing the uncertainty. The study revealed that marram grass greatly affects the accuracy of the UAV-derived model and that the uncertainty of the UAV-derived DEM increases together with increasing slope inclination and, to a lesser degree, with increasing general slope curvature. We showed that sediment budget determinations with the use of a UAV-based DEM are correct only where grass cover is sparse, in our study, up to 20% of the area.
Highlights
Foredunes are characterized by diversified relief with annual changes ranging between a few centimeters and 1–2 m (Nolet et al 2018)
The uncertainty of digital elevation models (DEMs) processed from the point cloud data is spatially distributed regarding land cover classes and three terrain variables
We showed that dense marram grass significantly lowers the accuracy of the Unmanned aerial vehicles (UAVs)-derived model and that the greatest absolute elevation differences between UAV-derived DEMs and GPS-real-time kinematic (RTK) measurements are obtained for slope overgrowth by high grass
Summary
Foredunes are characterized by diversified relief with annual changes ranging between a few centimeters and 1–2 m (Nolet et al 2018). Some previous studies have been performed to estimate a foredune sediment budget based on elevation data surveyed with GPS-RTK along transects oriented perpendicular to the coastline and crossing foredune ridges (Vespremeanu-Store and Preoteasa 2007; Delgado-Fernandez 2011), sometimes together with the analysis of aerial photography (Rader et al 2018). Unmanned aerial vehicles (UAVs) allow the acquisition of high-resolution DEMs of vulnerable coastal environments, including beach–foredune topography. If performed repetitively, they can offer an excellent tool to determine the spatial and temporal changes in the sediment budget, which may be Estuaries and Coasts (2020) 43:1939–1955 required for proper land management. There are numerous disturbing factors responsible for DEM inaccuracy, most importantly, the quality of UAVs, slope inclination, and vegetation
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