A new radar system that could track a vehicle through buildings is being developed by military scientists at the US Defense Advanced Research Projects Agency (DARPA).
The remote-controlled airborne detection system known as "spy in the sky" is a multipath exploitation radar (MER), which uses buildings as mirrors to identify a target vehicle from radar reflections, according to the Times Of India.
A scientist at DARPA said the new radar system sees around corners and down into "urban canyons".
According to a DARPA spokesman, MER is expected to be compatible with the radar systems currently used to track vehicles.
The reflected radar is expected to cover more ground than a line-of-sight system making it possible to monitor a city of about 1,000km² with just three airborne radars.
The MER uses Ku-band radar with frequencies between 12GHz-18GHz and produces distinct signatures for apparently similar vehicles, by detecting slight differences, including the angle of an aerial or a wing mirror.
The 3D model of a city required for the reflection pattern could be created using LIDAR, the usual optical surveying technology carried on aircraft.