Cellular rain gauges

Knowing where and how hard rain is falling is important not only for determining whether to take an umbrella, but also for managing water resources, improving precipitation models, anticipating flooding, and assessing climate. Yet many parts of the globe lack good data, whether from weather radar or from rain gauges. (Gauge prevalence is less than half what it was a decade or two ago.) Meanwhile, the world is being increasingly covered by cellular communications networks, and radio signals broadcast between cell towers have been proposed as a new means of monitoring rainfall: At common communications frequencies (roughly 7–40 GHz), the attenuation of signals transmitted from one cell tower to another is mainly due to absorption and scattering by raindrops along the path. Such attenuation data are typically gathered by cellular companies every 15 minutes or so to monitor the stability of their networks. Armed with attenuation data from a Dutch telecom for 2400 network links, Aart Overeem, Hidde Leijnse, and Remko Uijlenhoet at Wageningen University and the Royal Netherlands Meteorological Institute have now dynamically mapped rainfall over all the Netherlands. For each link, the researchers extracted the spatially averaged rainfall intensity during each 15-minute interval, compensating in real time for such systematic issues as water films on the cell-tower antennas. The plotted intensities correlate well with radar imaging and can identify and track individual storms. (A. Overeem, H. Leijnse, R. Uijlenhoet, Proc. Natl. Acad. Sci. USA, in press.)—Richard J. Fitzgerald