Multitemporal monitoring of Posidonia oceanica banquettes using UAV photogrammetry

Abstract. Posidonia oceanica banquettes represent key coastal features in the Mediterranean, providing ecosystem services such as shoreline protection, sediment retention, and carbon storage. Despite their ecological importance, their spatial and temporal dynamics remain poorly quantified due to the lack of standardized monitoring approaches. This study presents a UAV-based photogrammetric methodology for the multitemporal analysis of banquette morpho dynamics, integrating NRTK-supported surveys, Structure-from-Motion processing, and uncertainty-aware DEM differencing. The method was applied to Maurizio Vitale Beach (Culuccia Island, Sardinia, Italy), a protected and low-impact coastal environment, using four UAV surveys acquired between 2022 and 2025. High-resolution Digital Elevation Models (DEMs) were generated and compared to quantify volumetric changes across seasonal and interannual timescales. Results show a highly dynamic system, characterized by alternating phases of erosion, redistribution, and accumulation. Seasonal analysis (June–October 2024) revealed moderate volumetric losses (−41.3 m³), mainly affecting the seaward edge, with localized deposition in inner sectors. Interannual comparison (2022–2024) highlighted a more pronounced net loss (−74.2 m³). Conversely, the 2024–2025 analysis showed significant recovery, with widespread accretion (+95.8 m³), indicating strong temporal variability. The proposed approach proved effective in capturing both horizontal and vertical changes, distinguishing between boundary retreat and surface lowering processes. These results demonstrate the potential of UAV photogrammetry as a reliable and scalable tool for standardized banquette monitoring, supporting coastal management strategies and contributing to the objectives of the POSEIDON project.