Radar
An illustration of a space shuttle, with its payload doors open, sending and receiving radar signals

Imaging radar works by bouncing a radio signal off the ground. Image Credit: NASA

      a device that sends out radio waves and picks them up again after the waves strike another object and bounce back



Sentences:
Radar is used to help predict weather and measure waves of the ocean.

Police officers can tell how fast a car is going by using a radar device.



More Information:
http://spaceplace.nasa.gov/en/kids/srtm_makemap3.shtml   →
http://southport.jpl.nasa.gov/desc/imagingradarv3.html   →
http://southport.jpl.nasa.gov/html/sat_animation.html   →
http://science.nasa.gov/headlines/y2008/29feb_radarmoon.htm   →