Using a ground-piercing radar sensor aboard the Mars Reconnaissance Orbiter, a team of scientists created 3-D maps of an equatorial region known as Elysium Planitia and the channels that run underneath the plains.

NPR: Radar Reveals Apparent Buried Channels On Mars

In testing of the full CT2WS kit, absent radar, the sensor and cognitive algorithms returned 810 false alarms per hour.

ENGADGET: DARPA threat detection technology uses a camera to see targets, software and soldier brains to identify them

The latest version has new sensor capabilities, employing Multi-Platform Radar Technology for improved surveillance .

CENTERFORSECURITYPOLICY: The Future of Unmanned Flight

The Predator comes equipped with radar, seven video cameras, an infra-red sensor and a powerful zoom.

BBC: US-Mexico border: Efforts to build a virtual wall

Moreover, improvements in sensor technology and computer networks mean that the system would not need a large radar in central Europe.

ECONOMIST: A slightly warmer relationship between the West and Russia

Not only does the drone likely use advanced coatings and materials to make it difficult to detect by radar, but the drone also likely has the U.S.'s most-cutting-edge sensor technology, including sophisticated cameras and listening devices.

WSJ: Iran Says It Shot Down Unmanned U.S. Plane