Unmanned aircraft system-based lidar survey of structures above and below the water surface: Hilo Deep Draft Harbor Breakwater, Hawaii

Abstract

With recent advancements in unmanned aircraft system (UAS) technology, along with the miniaturization of airborne laser scanning systems, capabilities of unmanned laser scanning (ULS) systems have increased. Traditional terrestrial laser scanning surveys provide high density point clouds (hundreds - thousands of pts/m2) of a focus area, but have limited field-of-view and line-of-sight due to the constrained static nature of the system. While airborne and mobile laser scanning platforms relieve many of these limitations, lower point density (airborne), confined operation pathways (mobile), and higher operational costs become a factor. Here we present results from ULS data acquired over the Hilo Deep Draft Harbor Breakwater in Hawaii in June 2018. Inspecting the breakwater for failures and instabilities is of vital importance for Hilo. At three kilometers length and exposure to open ocean, a terrestrial laser scanning survey of the breakwater is not possible. Airborne and mobile laser scanning are not ideal due to reduced point densities and site access, respectively. In June 2018, using a RIEGL RiCOPTER with VUX laser system, the authors collected highresolution data over the above water breakwater extents. For below water surfaces, a Riegl BDF-1 bathymetric depth finder was operated from the same UAS, used to generate profiles of subaqueous surfaces of the breakwater. These bathymetric transects supplement the detailed topographic data collected above water on the breakwater. We discuss the operational concerns in both project planning and acquisition phases, as well as detailed analysis of the resulting data, used for a rigorous structure inspection program.