Lightweight dual-wavelength bathymetric LiDAR for accurate seabed mapping

Abstract

Mapping of small and shallow water bodies is still done primarily in a manual, labour-intensive process. The Fraunhofer Institute for Physical Measurement Techniques IPM developed and evaluated a new compact and lightweight airborne laser-scanning system targeted at topographic and bathymetric surveys which can greatly increase the efficiency and precision. The sensor weighs less than 4 kg and can therefore be operated on many commercially available drones without special permissions according to current regulations. This is a decisive aspect in achieving the necessary operational capability and economic efficiency of such a system. To optimally address the intended use case, our sensor simultaneously emits green and infrared light. This allows for precise separation of water surface and seabed and is especially beneficial for increasing precision in shallow water regions and accurately detecting the shoreline. For sophisticated data analysis, the system records and saves the full signal waveform using high-speed analog-to-digital converters. To ensure a safe operation and reduce the required safety measures, the system is designed as a class 2M laser product. This is achieved through expanding and collimating the outgoing laser beam to approximately 50 mm in diameter and therefore reducing the light intensity. A downward-facing palmer scanner deflects the beam in a near-elliptical shape at approximately 15 • off nadir. The system has been tested and evaluated at a quarry lake in turbid water conditions. The result is a high-resolution ground model which demonstrates the benefits and feasibility of a compact bathymetric scanner and highlights the potential for further research in this field.