Flash lidar for underwater cultural heritage mapping

Abstract Documenting and monitoring submerged cultural heritage sites require high-resolution mapping under challenging conditions. Acoustic sensors like multi-beam echo sounders (MBES) efficiently cover large areas but provide limited lateral resolution and can suffer from multipath and surface-reflection artefacts in shallow water. Passive optical approaches like underwater photogrammetry yield fine detail but demand extensive acquisition time, favourable water conditions, and surface features for 3D reconstruction. We evaluate a time-of-flight (ToF) flash lidar deployed from unmanned surface vehicles across three archaeological sites: Les Argilliez (Switzerland), Roseninsel (Germany), and Epidaurus (Greece). The system records dense point clouds with centimetric resolution at speeds matching acoustic surveys. Repeatability, accuracy, and point cloud completeness were quantified, and lidar-derived depths were compared with single-beam echo sounder (SBES) reference data. Flash lidar captures fine-scale structural details, independent of ambient illumination, reducing the operational gap between acoustic and optical methods, enabling high-resolution mapping and monitoring of underwater cultural heritage sites.