Quality Assurance of Airborne Lidar Bathymetry Products for Shoreline Mapping

Accurate and consistent shoreline determinations play a major role in coastal management and are necessary for federal and state boundaries. Delineations along this dynamic margin are dependent upon the stage of tide and are demarcated by tidal datums such as Mean High Water (MHW) and Mean Lower Low Water (MLLW). Current shoreline mapping is dominated by passive-sensor aerial and satellite imagery in the visual and infrared part of the spectrum. The limitations of this passive-sensor technology include the requirement of day-time acquisition, optimal weather conditions, and variations introduced by individual operator interpretation that lead to shoreline products with results that cannot be reproduced. Airborne lidar bathymetry (ALB) is an active remote- sensing technology utilized world-wide for coastal-zone applications to measure bathymetry and topography. This study investigates ALB technology as a potential tool for supporting shoreline mapping. Data for this study was acquired by the United States Army Corp of Engineers (USACE) during a survey of Gerrish Island, ME and Portsmouth Harbor, NH using a SHOALS-3000 system. Shoreline determinations from the USACE lidar dataset are obtained by a newly-devised computerized process using various algorithms that distinguish land and water. This work aims to assess the environmental sensitivity of the algorithms and determine if the reliability of the shoreline determination is affected by changes in seafloor composition. The study area includes a variety of shoreline types such as rocky, sandy, and human-altered. The algorithm-derived land-water interfaces are compared and analyzed with each other and against the reference shoreline constructed from the orthorectified aerial imagery simultaneously collected with the ALB data. The results are reviewed to assess the consistency of the shoreline vector in representing actual shoreline features as a function of algorithm and shoreline composition. The evaluation includes analysis of the resolution, accuracy, reliability, and quality of the shoreline determinations