Mapping Beaches with Lasers: Operational Considerations for Accurately Quantifying Small-Scale Morphological Changes Over Large Spatial Domains Using Mobile Terrestrial Lidar

Properly quantifying coastal change hazards, including flooding and erosion risk from major storm events, relies on up-to-date, high-resolution morphology data across large spatial extents. Airborne lidar scanning (ALS) provides extensive coverage (10-1000 km) with minimal data occlusion, but also demands significant resources for deployment and may lack the temporal (annual or greater) and spatial resolution (1 to 10s of pts/m²) necessary to adequately map the evolution of coastal features at scales relevant to the forcing conditions. In addition, it can be difficult to accurately extract bare earth surfaces from these sparse ALS point clouds along heavily vegetated coastal foredunes, providing challenges for addressing small morphologic signals such as wind-driven dune growth. Mobile terrestrial lidar scanning (MTLS) offers the potential to cover a medium to large spatial extent (10-100 km) but with higher density (100s to 1000s of pts/m²) and faster mobilization times which enable more frequent sampling. These spatio-temporal scales provide new opportunities to yield process-insights into beach and dune morphodynamics at the ~meter to regional scale. For example, these data can resolve seasonal and spatial patterns in dune grasses on the foredune face and their relation to dune growth rates. These 4D measurements provide a new, previously unavailable, dataset that can help fundamentally advance dune eco-morphodynamics and evaluate coastal morphology change models. In this work, we explore MTLS data collection strategies to optimize data quality along a stretch of coastline with vegetated foredunes on the Outer Banks, NC. Forward driving speed, 2D and 3D scanning modes, pulse repetition rate, and horizontal and vertical angular resolution were among the operational and acquisition parameters that were tested to determine the optimal MTLS sampling regime to capture the bare earth and dune grass properties while maintaining accuracy and efficiency.