Water level sensors serve an important purpose in rivers, warning of floods and unsafe recreational conditions. A new one is claimed to be not only more robust and reliable than others, but also considerably less expensive.

According to scientists at Germany's University of Bonn, conventional water level sensors suffer from one or more limitations – they get damaged in floods, they're difficult to read remotely, they don't measure water levels continuously, or they're too costly. Led by Dr. Makan Karegar, the researchers developed an alternative that doesn't have such problems.

The device takes the form of an antenna that is installed adjacent to a river, out of the water. It continuously receives GPS and GLONASS satellite signals – part of each signal is received directly from the satellite, while the rest is received indirectly, after it's been reflected off the river's surface. The further down the surface is relative to the antenna, the longer the distance the reflected radio waves end up traveling.