Since radars provide their own illumination, they can image regions of the world at any time of the day or night. An imaging radar works very much like a flash camera. In a radar image, one can see only the light that was reflected back toward the radar antenna. At the Earth's surface, the energy in the radar pulse is scattered in all directions, with some reflected back toward the antenna. These echoes are converted to digital data and passed to a data recorder for later processing and display as an image.
Radar transmits a pulse and measures reflected echo or backscatter.
In the case of imaging radar, the radar moves along a flight path, and the area illuminated by the radar is moved along the surface in a swath, building the image as it moves along building up a radar image using the motion of the platform. The length of the radar antenna determines the resolution in the azimuth direction of the image, or along the track of the swath that is being taken. The longer the antenna, the finer the resolution will be in this dimension. Synthetic aperture radar refers to a technique used to synthesize a very long antenna by combining echoes received by the radar as it moves along its flight track. Radar images are composed of many dots, or picture elements.