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C

C-Band Radar

A radar operating in the 3900 to 6200 megahertz range whose wavelength is generally accepted as 5 centimetres.

CAPPI

Description


2D-map containing the representative reflectivity for the horizontal plane (layer) placed at a predefined altitude. A set of maps for various heights may be given inside of the same product.

Notes

• The parameter filling of cones can optionally be omitted.

Chaff


Chaff is a radar countermeasure in which aircraft or other targets spread a cloud of small, thin pieces of aluminium, metallised glass fibre or plastic, which either appears as a cluster of secondary targets on radar screens or swamps the screen with multiple returns.

Modern armed forces use chaff (in naval applications, for instance, using short-range SRBOC rockets) to distract radar-guided missiles from their targets. Most military aircraft and warships have chaff dispensing systems for self-defense. An intercontinental ballistic missile may release in its midcourse phase several independent warheads, a large number of decoys, and chaff.

Chaff can also be used to signal distress by an aircraft when communications are not functional. This has the same effect as an SOS, and can be picked up on radar. It is done by dropping chaff every 2 minutes.

US Navy Chaff

Problems caused in weather radar products

Chaff is frequently released by military aircraft during exersices. On the radar display it is usually seen as narrow bands of high reflectivity. Sometimes these chaff echoes may have a distance for hundreds of km. The width of the bands depends on the range from the radar and the amount of diffusion time.

Example Image

Chaff

Circular Polarization

Electromagnetic radiation in which the electrical field rotates uniformly about the direction of propagation. The effect is to reduce return signals from spherical targets, which eliminates some precipitation targets from the radarscope. Usually found on Air Traffic control radars.

Clear air echo


Radar returns from cloud and precipitation-free (optical clear) air. Clear-air echos are caused by Bragg scatter and insects. Bragg scatter comes from small-scale fluctuations of the refractive index (i.e. turbulent fluctuations of humidity).

Coherent Radar

A radar, such as a pulse Doppler, in which phase of the transmitted energy is preserved for comparison with the phase of returned energy to determine target motion.

Coherent Signal

A signal which contains information in both its phase and amplitude.

Constant altitude reflectivity


2D-map containing the representative reflectivity for the horizontal plane (layer) placed at a predefined altitude. A set of maps for various heights may be given inside of the same product.

Notes

• The parameter filling of cones can optionally be omitted.