Application of UAV photogrammetry for the mapping of lake terraces on vegetated terrain in the Central European mixed forests zone, Ostrowskie Lake, North-Western Poland

Abstract This article presents the use of Unmanned Aerial Vehicle (UAV) photogrammetry for monitoring changes in lake shore topography. The case study focuses on Lake Ostrowskie, where the water level has been declining due to the significant influence of a subsidence sink caused by coal mining activity. The water level has declined by an estimated 4.6 m over the past 60 years. As a result of this gradual decrease, lake terraces have formed parallel to the shoreline, measuring 0.1–0.3 m in height and 0.5–20.0 m in width. UAV-derived products, such as the Digital Elevation Model (DEM) and orthomosaic, have facilitated the identification and spatial mapping of nine lake terraces which have formed since 2004. The identified terraces correspond to former shorelines, which are visible in archival orthophotomaps. The most important advantage of using UAV photogrammetry corrected with Real-Time Kinematic (RTK) field measurements is the high resolution of the resulting products, reaching 1.95 cm per pixel. Such resolutions enable the identification of vegetation height at different stages of the ecological succession, which reflect the relative age of each terrace.