Innovative 3D Imaging Tools for Assessing Damages To Coral Reef Habitats Caused By Grounding Events

On November 6, 2015, a National Oceanic and Atmospheric Administration (NOAA) National Data Buoy Center (NDBC) weather buoy was reported to be stranded on Neva Shoal, southeast of Kapou (Lisianski) Island in the Northwestern Hawaiian Islands (NWHI). The buoy mooring consisted of 13.72 m of 2.54 cm chain, 365.76 m of 2.54 cm wire, and nearly 2,438.40 m of 2.54 cm nylon mooring line. The buoy broke free from its assigned station 394.29 km northeast of Honolulu on March 10, 2013. The buoy continued to transmit information and drifted northeast before reversing course and drifting into Papahānaumokuākea Marine National Monument (PMNM) where it ran aground on the Neva Shoal in about 12.19 m of water in an area of high coral cover. Following the initial stranding in November 2015, the buoy moved more than 1.93 km in a southwesterly direction, most likely caused by larger swell events. The intermittent movement was due to a portion of the mooring being still attached to the buoy and dragging along the benthic substrate. The total damage caused by the dragging chain was significant and spread over a large spatial area. The buoy was recovered by the F/V Lady Alice on May 26, 2016. Researchers on the NOAA Rapid Assessment and Monitoring Program expedition surveyed the reef locations where the buoy was stranded after the removal of the buoy. Researchers were able to visit the last two recorded locations at which the buoy was stranded on May 7 and 8, 2016. Overlapping imagery was collected from the areas exhibiting damage from the buoy mooring. The images were processed using Structure-from-Motion photogrammetry to create 3D reconstructions of the affected coral reef habitats. The resulting 3D models and orthophotomosaics were analyzed with geospatial software to accurately quantify the impacts from the buoy stranding at these two locations. Utilizing this innovative methodology provides a useful visual and quantitative method for assessing the impacts and damage associated with grounding damage on coral reef habitats.

Key Words

Weather buoy, grounding, coral reef, reef damage, damage assessment, 3D reconstruction, structure-from-motion, 3D mapping, Northwestern Hawaiian Islands, Papahānaumokuākea Marine National Monument, Hawaiʻi