12 Platform one August/September 2023 | Uncrewed Systems Technology Researchers in Germany have developed a technique for more accurate mapping of lakes and rivers by uncrewed systems (writes Nick Flaherty). Surveying inland bodies of water precisely is a challenging task for authorities and port operators, who have to provide up-to-date maps of riverbeds and port facilities. The researchers, at the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation (IOSB), have therefore developed an easy-to-operate, uncrewed vessel that autonomously surveys bodies of water such as rivers, lakes and harbours above as well as below the surface, and produces corresponding 3D maps. 3D reconstruction of the river banks is generated by combining cameras and a Lidar scanner, while the sonar can map depths of up to 100 m. The project is based on a commercial USV connected to a central control station on land. GPS satellite navigation, acceleration and angular rate sensors as well as a doppler velocity log sensor enable the vessel to feel its way incrementally along the bottom of the body of water autonomously. The data from the various sensors is merged to guide the navigation system. For mapping above water, laser scanners and cameras are used in combination with mapping software developed at Fraunhofer IOSB, enabling the devices to reconstruct high-precision 3D models of the surroundings. In turn, the underwater mapping is carried out with the help of a multi-beam sonar, which is integrated into the sensor system and creates a complete 3D model of the bed. “Our navigation system is semiautomatic, in that the user needs only to specify the area to be mapped,” said Dr Janko Petereit, a scientist at the Fraunhofer IOSB. “The surveying process itself is fully automatic though, and the data is evaluated using just a few clicks of the mouse.” The first step is to specify the area to be surveyed; the software uses that information to calculate the route. The USV autonomously evades obstacles detected by the laser scanner and sonar. During a mission, a quick 3D model, including dynamic objects such as moving vessels, is generated in real time for navigation purposes. A second, high-precision 3D model is computed by the software after data evaluation, capturing both the floor of the body of water and the scene above the water surface, while also ignoring moving objects. Tests of the vessel took place on a number of lakes. The operational prototype is currently being used by the Smart Ocean Technologies research group at Fraunhofer in other projects that focus on underwater and surface robotics. In addition to autonomy algorithms, autonomous shipping also requires highly accurate maps, which are not always available at present. “Currently, manual surveys are only conducted every 1 or 2 years, and provide far less accurate results than our 3D models, so the condition of the waterways is not optimally captured,” Dr Petereit said. “River surveys will therefore need to be conducted far more often in the future and with a higher level of detail, which our system offers in a cost-effective way.” Mapping 3D surveys simplified The Fraunhofer researchers have developed an easy-to-use way to map lakes and rivers accurately
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