Forecasting the weather requires huge quantities of data. many of these data are collected by high-tech means such as satellites and radar, and then crunched by some of the world’s fastest supercomputers into predictions that are far more accurate than they were 20 years ago. but low-tech tools are important too—especially old- fashioned rain gauges, which are nothing more than tubes with funnels fixed to places such as rooftops. each technique has its upsides and downsides. radar and satellites can cover swathes of land, yet they lack detail. gauges are much more accurate, but the price of that accuracy is spotty coverage. now, though, aart overeem of the royal netherlands meteorological institute and his colleagues reckon they have come up with another way to keep an eye on the rain. it offers, they believe, both broad coverage and fine detail. best of all, it relies on something that is already almost omnipresent—the mobile-phone network. their scheme starts from the observation that rain can make it harder for certain sorts of electromagnetic radiation to travel through the atmosphere. measure this impedance (and scrub out any other sources of variation) and you can measure how rainy it is. the researchers do not measure the strength of mobile-phone signals themselves. instead, they piggyback on something that mobile networks already do, and measure the strength of the microwave links that base stations use to talk to each other.
