Described as "an electronic question and answer system", it sends a radar signal to any unidentified target to which a friendly will respond automatically with a coded reply.

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In the Madagascan data, for example, the choppiness of the waves in the open stretches of the Indian Ocean can be contrasted with the smooth reflection of the radar signal from the enclosed, calm waters of the Baie de Diego.

BBC: German TanDEM-X satellite returns first images

Because tunnels block a radar signal, trains rely largely on hard-wired equipment like the box beside the track, which helps drivers and dispatchers talk to each other and controls a machinelike traffic signal, giving the drivers basic commands to stop and go.

NEWYORKER: Boss Rail

As soon as a helicopter goes beyond the 80-mile zone covered by land-based radar, its signal is picked up by the offshore platforms, with the data then returned to the airport.

BBC: Helicopter location system begins

By picking up this return signal, the radar probe's own antenna collects information about the crystal and, thus, the physical state of the tyre.

ECONOMIST: MONITOR

The Patriot missile homes on an electronic signal "painted" on the target by the radar, and relays its position in relation to the target back to the radar and on to the control centre.

BBC: Fact file: Patriot missile defence

Over the next few months, MOS broke above this trendline, negating any short side opportunity, but I kept them on my radar knowing that MOS lagging the general market was a huge signal that could not be ignored.

FORBES: POT Is Going Up In SMOKE