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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.

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Function of Agricultural Terraces in Mediterranean Conditions - Selected Examples From the Island of Ikaria (The Southern Sporades, Greece) The aim of the research was to define the influence of agricultural terraces on slope erosion. There have been selected three plots located on the Greek island Ikaria. On the plots detailed geomorphological mapping was done, spatial relief models were created based on the measurements taken using GPS RTK, georadar profiles were made using RAMAC/GPR and the extent of destruction of terrace resistance walls was evaluated. In comparison with similar forms on other Aegean islands, Ikarian terraces are narrow and high. Their stability depends on: lihtology, slope gradient, height and spatial arrangement of particular terrace steps and the current way of their usage. It was acknowledged that the most stable are the forms created on crystalline schists and gneisses, whereas the slopes, which erode the easiest, are the terraced ones consisting of carbonate rocks. The obtained results indicate that on Ikaria similarly to numerous other regions the most significant factor facilitating erosion on the terraced slopes is the cessation of their agricultural usage.