A new technique mapping submerged beachrocks using low-altitude UAV photogrammetry, the Altınova region, northern coast of the Sea of Marmara (NW Türkiye)

Abstract

High-resolution aerial imagery captured from low altitudes enables the detailed reconstruction of the geomorphological features of submerged beachrocks and the quantification of their topographic complexity. These coastal deposits serve as vital indicators for estimating past sea-level positions and deformation, contributing to our understanding of climate and tectonic processes across various temporal and spatial scales. This study focuses on submerged beachrocks identified in the nearshore coastal area of Tekirdağ city (Altınova), and the existing knowledge regarding such geological formations is limited.

Situated in the tectonically active western Marmara region, the coastal zone of The Tekirdağ-Altınova is influenced by the North Anatolian Fault Zone (NAFZ), which has significantly shaped the coastline over time. Utilizing unmanned aerial vehicle (UAV) data, we successfully isolated submerged beachrocks from other coastal deposits, identifying them at depths of 2 m below current sea level and extending approximately 5 km along the coast. This identification was facilitated by integrating high-resolution aerial imagery with morphological analysis techniques, specifically employing structure-from-motion photogrammetry to generate a dense point cloud for bathymetric mapping.

The utilization of cost-effective UAV imagery facilitated the efficient monitoring of beachrocks. Geographic information systems (GIS) and the TerraceM application were employed to analyze the high-resolution bathymetry data (with a 5 cm resolution), enabling the precise estimation of shoreline angles and associated errors. These shoreline angles, which correspond to the past sea levels high stand, were mapped using swath profiles oriented perpendicular to the isobaths. Our findings reveal that the majority of submerged beachrocks exhibit shoreline angles between ∼ −0.7 m and −1.1 m. This study presents innovative methodologies for mapping the height and spatial distribution of beachrocks, as well as for reliably estimating reliable uplift rates in the nearshore area of Tekirdağ-Altınova.