The number of people who own mobile phones is rising, fast. The number of people in the world who own a traditional rain gauge is not. Luckily for lovers of meteorological data, though, it seems that the proliferation of phones has created a new, roundabout way to figure out an area's rainfall: by measuring how much a cellphone signal degrades on its trips between the phone and the cell tower.
The heavier the rain, and the larger the raindrops, the more your cell signal degrades. It's not enough interference to prevent people from completing calls during a thundershower, usually, but it's noticeable. In a study out this week in the journal Proceedings of the National Academy of Sciences, Dutch scientists say this is the key to turning our phones into mobile rain gauges. If you know a phone's signal strength on a clear day, and you can measure how much of the signal gets lost from bouncing off raindrops, you can figure out how much rain is falling between the phone and the tower.
One such data point wouldn't be much use. But the world is bursting with devices constantly chatting with area cell towers, and by measuring the signal loss for all of them, scientists can create a fairly accurate map of precipitation. Study leader Aart Overeem from the Royal Netherlands Meteorological Institute led a team that collected 12 days of cellphone-rain data to create a weather map for all of The Netherlands, then compared it to the numbers from traditional rain gauges. Overeem called the result "quite accurate."
Could tallying the rainfall by cell signal go beyond a quirky finding and become a useful way to gather meteorological data? The researchers suggest that their technique might be useful somewhere such as Africa, where phone ownership rates are exploding but there are comparatively few accurate rain gauges, or as a way to confirm or correct radar images. The scientists just have to convince the carriers to give up the data about your phone signal.
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