Underwater Flash Lidar for Cultural Heritage Site Preservation

Regular monitoring of archaeological sites is crucial due to threats from human interference, meteorological events, invasive species, and climate change. Underwater sites in shallow waters are challenging to monitor regularly due to risks of collision with submerged rocks or structures. Autonomous vehicles like unmanned surface vehicles (USVs), unmanned aerial vehicle (UAVs), and remotel operated vehicles (ROVs) equipped with 3D imaging sensors offer reliable, safe, and cost-effective solutions for surveying these areas. This study introduces a USV equipped with a flash lidar for underwater applications. Preliminary measurements were conducted at Les Argilliez, a UNESCO World Cultural Heritage site which is facing erosion and an invasive mussel species. Regular 3D mapping is being performed to analyze changes in lakebed morphology and wooden pile structure and placement. The lidar system, enclosed in a watertight cylinder, uses direct-time-of-flight to measure depth with a 128x128 pixel array and adjustable field of view (FoV). Test campaigns demonstrated the lidars effectiveness in capturing detailed 3D point clouds of the lakebed and wooden posts, allowing measurement of width, length, orientation, and surrounding morphology. Regular surveys will continue throughout 2025, providing an effective solution for underwater archaeological research.