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. Given that the radar pulse travels at the speed of light, it is relatively straightforward to use the measured time for the roundtrip of a particular pulse to calculate the distance or range to the reflecting object. Higher bandwidth means finer resolution in this dimension. In the case of imaging radar, the radar moves along a flight path and the area illuminated by the radar, or footprint , is moved along the surface in a swath, building the image as it does so.
Aperture means the opening used to collect the reflected energy that is used to form an image.
A synthetic aperture is constructed by moving a real aperture or antenna through a series of positions along the flight track. This focusing operation, commonly known as SAR processing, is now done digitally on fast computer systems. Synthetic aperture radar is now a mature technique used to generate radar images in which fine detail can be resolved. SARs provide unique capabilities as an imaging tool. Radar images are composed of many dots, or picture elements.