Editing Imaging radar (section)

{{Short description|Application of radar which is used to create two-dimensional images}}
{{distinguish|Radar display}}
[[File:TEIDE.JPG|thumb|right|A [[Synthetic aperture radar|SAR]] radar image acquired by the SIR-C/X-SAR radar on board the [[Space Shuttle Endeavour]] shows the [[Teide]] volcano. The city of Santa Cruz de Tenerife is visible as the purple and white area on the lower right edge of the island. Lava flows at the summit crater appear in shades of green and brown, while vegetation zones appear as areas of purple, green and yellow on the volcano's flanks.]]
'''Imaging radar''' is an application of [[radar]] which is used to create two-dimensional [[image]]s, typically of landscapes. Imaging radar provides its light to illuminate an area on the ground and take a picture at radio wavelengths. It uses an antenna and digital computer storage to record its images. In a radar image, one can see only the energy that was reflected back towards the radar antenna. 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.<ref name=":0">{{Cite web|title = What is imaging radar ?/jpl|url = http://southport.jpl.nasa.gov/desc/imagingradarv3.html|website = southport.jpl.nasa.gov|access-date = 2015-12-09|archive-url = https://web.archive.org/web/20161118152424/http://southport.jpl.nasa.gov/desc/imagingradarv3.html|archive-date = 2016-11-18|url-status = dead}}</ref>

Digital radar images are composed of many dots.  Each pixel in the radar image represents the radar backscatter for that area on the ground ([[terrain return]]): brighter areas represent high backscatter, darker areas represents low backscatter.<ref name=":0" />

The traditional application of radar is to [[Radar display|display the position and motion]] of typically highly reflective objects (such as [[aircraft]] or [[ship]]s) by sending out a radiowave signal, and then detecting the direction and delay of the reflected signal. Imaging radar on the other hand attempts to form an image of one object (e.g. a landscape) by furthermore registering the intensity of the reflected signal to determine the amount of [[Scattering#Electromagnetics|scattering]]. The registered electromagnetic scattering is then mapped onto a two-dimensional plane, with points with a higher reflectivity getting assigned usually a brighter color, thus creating an image.

Several techniques have evolved to do this. Generally they take advantage of the [[Doppler effect]] caused by the rotation or other motion of the object and by the changing view of the object brought about by the relative motion between the object and the back-scatter that is perceived by the radar of the object (typically, a plane) flying over the earth. Through recent improvements of the techniques, radar imaging is getting more accurate. Imaging radar has been used to map the Earth, other planets, asteroids, other celestial objects and to categorize targets for military systems.