[...] The technology 'sees' the shapes made when radio waves emitted by mobile phone masts meet an obstruction. Signals bounced back by immobile objects, such as walls or trees, are filtered out by the receiver. This allows anything moving, such as cars or people, to be tracked. Previously, radar needed massive fixed equipment to work and transmissions from mobile phone masts were thought too weak to be useful.
The system works wherever a mobile phone can pick up a signal. By using receivers attached to mobile phone masts, users of the new technology could focus in on areas hundreds of miles away and bring up a display showing any moving vehicles and people.
An individual with one type of receiver, a portable unit little bigger than a laptop computer, could even use it as a 'personal radar' covering the area around the user. Researchers are working to give the new equipment 'X-ray vision' - the capability to 'see' through walls and look into people's homes.
[...] The system, used alongside technology which allows individuals to be identified by their mobile phone handsets, will mean that individuals can be located and their movements watched on a screen from hundreds of miles away.
pretty light on technical details, but it sounds like it uses shadows between the viewer and any cell phones in the area to build up a volume map? I think the "x-ray" comment must mean they're using signal attenuation as a clue to density of intervening structures? With enough sample points (enough cell phones moving around behind the area) you might have enough data to build a map...
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