Weather radars scan from hilltops and tall towers, producing rainfall maps at resolutions of hundreds of meters and several minutes. In dense urban areas — where flooding risk is highest and infrastructure is most vulnerable — this resolution is often insufficient.
This paper demonstrates that cellular base stations already function as distributed radar systems. The radio signals transmitted between towers are attenuated and scattered by rainfall. By processing these signals with standard radar techniques, the authors extract rainfall measurements at spatial resolutions of a few meters and temporal resolutions of tens of seconds — orders of magnitude finer than conventional weather radar.
The main obstacle is ground clutter. Weather radars point upward, so the only returns come from atmospheric targets. Cell towers point horizontally, so buildings, trees, and terrain contaminate the signal. The paper's contribution is the signal processing pipeline that separates weather returns from the fixed-clutter background, exploiting the fact that rainfall scattering varies in time while ground clutter does not.
The infrastructure already exists. Dense urban areas — exactly where fine-resolution rainfall data is most needed — are also where cell tower density is highest. No new hardware is required, only new processing of signals that are already being transmitted for communication.
The duality is structural: a communication network and a sensor network are the same physical system viewed from two perspectives. Every signal carries information about its channel. Whether you decode the message or decode the channel depends on what you want to know.