Editing Radar (section)

===Radar signal===
[[File:3D Doppler Radar Spectrum showing a Barker Code of 13.jpg|thumb|250px|3D Doppler radar spectrum showing a [[Barker code]] of 13]]
{{further|Radar signal characteristics}}
A radar system has a [[transmitter]] that emits [[radio wave]]s known as ''radar signals'' in predetermined directions. When these signals contact an object they are usually [[Reflection (physics)|reflected]] or [[scattering|scattered]] in many directions, although some of them will be absorbed and penetrate into the target. Radar signals are reflected especially well by materials of considerable [[electrical conductivity]]—such as most metals, [[seawater]], and wet ground. This makes the use of [[radar altimeter]]s possible in certain cases. The radar signals that are reflected back towards the radar receiver are the desirable ones that make radar detection work. If the object is ''moving'' either toward or away from the transmitter, there will be a slight change in the [[frequency]] of the radio waves due to the [[Doppler effect]].

Radar receivers are usually, but not always, in the same location as the transmitter. The reflected radar signals captured by the receiving antenna are usually very weak. They can be strengthened by [[Amplifier|electronic amplifiers]]. More sophisticated methods of [[signal processing]] are also used in order to recover useful radar signals.

The weak absorption of radio waves by the medium through which they pass is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as [[visible light]], [[infrared light]], and [[ultraviolet light]], are too strongly attenuated. Weather phenomena, such as fog, clouds, rain, falling snow, and sleet, that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapour, raindrops, or atmospheric gases (especially oxygen) are avoided when designing radars, except when their detection is intended.