Location: Qiankun Bay, Yellow River, China
Date: April of 2020
Equipment: ME120 USV, Hydro-tech MS400P small multibeam echo sounder system
User: National Natural Resources Second Topographic Survey Team
Background
With a total length of 5,464 km, the Yellow River is the second-longest river in China. As running through the Loess Plateau during the middle journey and carrying much sand and dust, it is then becoming the most sediment-laden river in the world. Yellow river runs through 9 cities of China and is affecting the daily lives of tens of thousands of people live alongside the river.
Monitoring the changes of underwater terrain and studying the pattern of river evolution can provide important data support for river management and flood control, to better protect the ecology of the watershed.However, due to technical limitations, it has not been meticulously mapped. To this end, not long ago, the Second Topographic Survey Team of the Ministry of Natural Resources used intelligent equipment such as unmanned aerial vehicles and unmanned surface vessels to carry out integrated multi-element topographic surveys in the Qiankun Bay section of the Yellow River.
Figure 1. Qiankun section of the Yellow River
Survey Process
The waters in the survey area are complex, with rapid currents and many shallows. With traditional measurement methods, it’s difficult to install survey equipment and rent a suitable workboat. Operating on water also poses high risks to personals.In this case, the underwater topographic survey was carried out using OceanAlpha’s ME120 autonomous surface vessel platform equipping a multi-beam sounding system.The ME120 USV adopts a modular design that its three pieces can be quickly disassembled and assembled. It can work automatically and sail into super shallow water areas as 0.45 meters. All these advantages enable it to be well adapted to operations in such complex waters.
Figure 2. Satellite picture of the survey area
The transducer and sound velocity meter of the multi-beam system was installed in the lifting mechanism of the USV. Through the USV shore-based control base station, the lifting mechanism can be remotely controlled to raise or lower the wet end equipment. There is no need for personnel to stay on board for retracting operations. The lifting mechanism reduces the risk of equipment damage and better guarantees the safety of personnel.After the equipment was installed and debugged quickly at the dock, the unmanned vessel was then launched and started to work seamlessly.
Figure 3. Multi-beam transducer and sound velocity meter are installed on the lifting mechanism.
Figure 4. Personnel install and debug equipment at the dock.
According to the real-time measured water depth and multi-beam span, the surveyor set up parallel survey lines and inspection lines with the base station software from the dock. The USV navigated according to the survey line instructions, and the collected data was sent back to the shore-based control terminal in real-time.
Figure 5. The interface of USV control software
Figure 6. ME120 USV navigates autonomously to perform mapping task
Survey Result
The data collected by MS400p MBES installed on ME120 deliveres high quality and clear reflects of the topography of the river. The ME120 was also equipped with a high-precision inertial navigation system, which provides strong support for the seamless splicing of multi-beam data and UAV data. After analysis and processing, the team obtained high-quality integrated above water and underwater data of the Qiankun section.
Figure 7. The result of above water and underwater integrated mapping
Figure 8. Partial view of integrated mapping result
Figure 9. Rendering of underwater depth
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