Comparison of UAV-based digital elevation model with multi beam bathymetry for shallow water

Accurate bathymetric data is essential for marine and coastal applications, particularly in shallow water regions. Unmanned Aerial Vehicle (UAV)-based systems are recognized for their cost-effectiveness and flexibility, making them a promising alternative in shallow-water environments where Multi Beam Echosounder (MBES) systems often face limitations due to high operational costs or logistical challenges. However, the UAV-based method is influenced by refraction effects, which result in underwater objects being perceived as shallower than their actual depth, leading to a decrease in the accuracy of the bathymetric model. To address this issue, the underestimation of water depth in submerged areas caused by refraction was evaluated using a correction algorithm. This study aims to assess the accuracy and usability of the UAV-based Digital Elevation Model (DEM) for seafloor mapping. For this assessment, the UAV-based DEM from the water body was compared with high-resolution three-dimensional (3D) seafloor topography obtained from a multi beam acoustic survey conducted in the same water area. The results indicated that an accuracy of 1.2 meters (RMSE) can be achieved in relatively shallow water areas up to a depth of 5 meters, while an accuracy of 2.0 meters (RMSE) is achievable at depths of around 15 meters. The study also highlighted the direct correlation between UAV-based DEM accuracy and depth, as well as the impact of sun glint on measurement accuracy. These findings underscore the potential of UAV technology to enhance bathymetric surveying capabilities, particularly in regions where MBES is either impractical or cost-prohibitive, thereby offering a valuable tool for comprehensive mapping and coastal studies.