SHALLOW WATER DEPTH EXTRACTION - PROGRESS AND CHALLENGES

After several years of operations, the Optech Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) bathymeter has proven to be an accurate, cost-effective, rapid, safe and flexible method for providing depth solutions ranging from approximately 1.5 meters to 50 meters in clear water. However, this traditional method of depth measurement has limitations in very shallow water and/or turbid areas where lidar signals from the water surface and water bottom merge. Such limitations inhibit seamless lidar sounding at the land-water boundary and restrict a much broader application of laser bathymeters in inland environments as well as very shallow coastlines. Historically, various approaches have been attempted towards recovering lidar points within the very shallow water region, but with limited success. However, over the past two years very promising advances in shallow water algorithms have been made, demonstrating the depth-sounding capability of airborne lidar bathymeters in extremely shallow water as well as a seamless lidar depth solution across the land-water boundary. A demonstration survey was recently conducted along the Gold Coast of Australia. The purpose of this survey was to evaluate the performance of the SHOALS system primarily in shallow water areas, but under varying water conditions and bottom types. This survey highlights both the efficiency of Airborne Lidar Bathymetry (ALB) as well as the limitations that exist with the technology. This paper will present the data results from the Gold Coast demonstration survey in addition to offering an overview of the tools - hardware and software - used to execute the planning, acquisition and processing of data. The inherent challenge of extracting depths from merging surface and bottom signals will be discussed, as well as the challenges associated with depth extraction in turbid water. The latest progress in the endeavor to fully automate shallow water depth extraction will be presented, including results from shallow water ground truth exercises.