Many Greyhound buses sweep the road ahead with a radar beam, which warns the driver if there is an obstacle in his path.

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And in the image of Moscow-Sheremetyevo airport, the flat concrete surfaces of the runways appear as black lines because the radar beam has been very efficiently reflected away from the satellite.

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The trailer-mounted radar is a "phased array" type - it scans the sky with a narrow beam which flicks between thousands of locations each second.

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