DRONE USE IN RAPID ASSESSMENT OF HURRICANE JOAQUIN COASTAL IMPACT ON SAN SALVADOR ISLAND, BAHAMAS

Drones provide a rapid and effective method for evaluating the effects of storms on coastal environments. High resolution aerial imagery can be collected using drones in specified localities to meet the needs of researchers and/or local communities. Compared to conventional aerial image collection (as seen in Google Earth, Google Maps, etc.), aerial imagery collected by drones can yield much higher resolution, enabling more subtle storm-generated coastal changes to be documented and analyzed. Additionally, collecting and processing drone imagery data is much less expensive and more readily accessible than conventional methods of acquiring aerial imagery.

Hurricane Joaquin made landfall in the Bahamas in October 2015, and a team of researchers visited San Salvador in January 2016 to investigate the coastal effects of the hurricane on the island. Drone imagery was collected to support research on storm-generated changes in coastal boulder ridges, erosion and overwash of sandy beaches, and more. The imagery collection process, including set up, took less than an hour for areas of up to 0.2 square kilometers. Mobile applications were used for flight planning and autonomous missions to capture geo-tagged images with sufficient overlap to generate an orthomosaic. Pix4D photogrammetry software was used to process the series of individual geo-tagged images taken by the drone to produce an orthomosaic, point cloud, and Digital Surface Model (DSM) for each flight. The 2.0 cm resolution orthomosaic can be used as a detailed base-map image for geological investigations, and the aerial perspective unveils patterns or features not easily detected in ground-based surveys. Researchers also can determine elevation and volume change of features, such as sand erosion or boulder movement, within the imaged area using the DSM. Imagery collected in January 2016 will be used both as an assessment of the effects of Hurricane Joaquin and as a baseline data inventory for comparison with future drone imagery to learn more about coastal processes and storm-related changes on San Salvador.