Low-cost sensor records river level – ScienceDaily


Researchers at the University of Bonn have developed a method that allows the water level of rivers to be monitored around the clock. The cost effective sensor is suitable for example for district level flood warning systems. The study was published in the journal Water Resources Research.

There is a wide range of methods for determining the level of a watercourse – from very simple methods (by gauge or staff gauge) to advanced radar solutions. But they all have a problem: most gauges can be damaged by direct exposure to a high water level, many don’t allow for continuous monitoring, remote reading is difficult or they’re simply too expensive.

However, at Wesel in the Lower Rhine, a measuring device that does not have these defects has already been in service for two years: it is cost-effective, reliable and capable of continuously transmitting the water level to the assessment center via mobile communications. In principle, this means that this sensor is suitable for providing a densely distributed network for flood and drought warning systems.

“The core of the device is a low-cost GNSS receiver and antenna,” explains Dr. McCann Kareghar of the Institute of Geodesy and Geoinformatics at the University of Bonn. This is a sensor that can conventionally determine its location with an accuracy of several meters. It does this using US GPS satellites and their Russian GLONASS counterparts. “However, the satellite signals can also be used to measure the height of the GNSS antenna above the river surface,” says Caregar.

The reflected signals provide information on the water level

This is because the waves transmitted by the satellite are partially captured by the antenna. The remainder is reflected from the nearby environment (in this case the water surface) and reaches the receiver via bypass. This reflex part travels longer. When it is superimposed on the received signal directly, it forms certain patterns called interference. Can be used to calculate the distance between the antenna and the water level.

“We can attach a GNSS antenna to any structure, whether it’s a bridge, a building, a tree, or a fence by a river,” Karegar explains. “From there, he can measure the river level around the clock without contact – within 1.5 cm on average. However it is less likely to be damaged during severe flood events.” The accuracy of the method does not match that of the radar-based sensor. However, it is quite sufficient for its intended use. At just under 150 euros, the device is also much cheaper than its advanced counterpart.

GNSS antenna connected to a microcomputer called a Raspberry Pi. “The device is about the size of a small smartphone; yet it has enough power to calculate water levels from raw data,” says Professor Dr Kristen Larsson of the Institute of Geodesy and Geoinformatics. Thanks to its flexibility and low power consumption, microcomputers are very popular among hobbyists, who use them to achieve a wide variety of projects. It can be powered by solar cells and then works completely autonomously. It can also transmit its data over the mobile network.

Reproduction information online

“The software we wrote is open source,” Larson explains. So anyone can use it for free. The researchers also make all information about their project available on the Internet. So interested parties can easily reproduce the measuring device.

However, this process has one drawback: it is only suitable for rivers with a width of at least 40 meters. “This is the smallest radius over which the antenna can receive the reflected satellite signal,” says Carrigar. “If the waterway is very narrow, most of the reflected signals are coming from the ground.” But the participants plan to further improve their evaluation code. They hope they can get reliable results for smaller rivers like the Ahr in Germany, which suffered severe flooding in 2021.

Participating institutions and financing:

In addition to the University of Bonn, the Federal University of Rio Grande do Sul in Brazil participated in the study. The project was funded by the German Research Foundation (DFG), the National Council for Scientific and Technological Development of Brazil (CNPq), and the State Research Funding Agency of Rio Grande do Sul (Fapergs).

Story source:

Materials Introduction of Bonn University. Note: Content can be modified by style and length.



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