There is noise or the connection can even break – the cellular network is significantly affected by precipitation. This begs the question: Can this problematic effect also be used? Apparently yes: German researchers are currently establishing a rain measurement system using the mobile network. The clever system has now passed the practical test in Germany: the team was able to create high-resolution rain maps based on the effects of precipitation on the radio links. It is now planned to use the method in Africa, among other places.
“Raindrops are about as large as the wavelength of the microwave radiation of the radio links operated at a frequency of 15 and 40 gigahertz, so they strongly attenuate the radiation in this frequency range,” explains Harald Kunstmann from the Institute for Meteorology and Climate Research – Atmospheric Environmental Research (IMK-IFU ) in Garmisch-Partenkirchen. The following applies: The more it rains, the greater the drop in performance between two antennas. Kunstmann and his colleagues take advantage of what can cause headaches for telecommunications companies: “We have developed a completely new method for measuring rain from the interaction between weather events and human technology. If a cellular network is available, we don’t need a new infrastructure or additional ground staff, ”says Kunstmann.
On the trail of the rain signature
The scientists emphasize that the sensitivity of the measurement process is just as high as that of the classic method with precipitation pots. “The detection limit is a rain rate of one millimeter per hour, and the data are available with a time lag of only one minute,” says co-author Christian Chwala from IMK-IFU. The researchers have now proven that the method delivers what it promises: They are presenting the first nationwide rain measurement using the new method. “We measured the current weakening of 4,000 radio links in Germany every minute for a year. The resulting data set is unique in the world due to its resolution and size, ”says Chwala.
In addition to the classic methods of data analysis, the researchers used artificial intelligence (AI) to filter out the rain signal from the precipitation-related weakening of the radio links between the cell phone towers. “Other factors such as wind or the sun can also cause the signal to weaken slightly. With the help of our AI, we were able to recognize when a weakening was due to rain, ”says co-author Julius Polz from the IMK-IFU. “We have now trained them so that we can do without calibration using traditional methods of rain measurement.”
Little effort and fast information transfer
The great advantage of the system is that it provides information about local rainfalls with only a minimal delay. On the other hand, the tightly knit network of cell phone masts enables high regional coverage with measurements without great effort. The new procedure could therefore quickly warn of floods in mountain regions, for example. “Above all, however, the method has great potential for countries in which there are few or no weather stations or rain radar devices, but a dense mobile network is available,” emphasizes Kunstmann. In regions such as West Africa, for example, the measurement method could help to obtain more precise precipitation information for water management, say the scientists. As they report, the first system for nationwide precipitation recording using the cellular network is now being set up in Burkina Faso.