Chaff (radar deception)
Table of contents
the name “chaff” is a military name, which resulted from the fact that this means was used first with an air raid over Berlin chaff during the Second World War. At the British Air Force chaff had the cover name Window, in the USA them Chaff (chaff) are called. The war opponents of the Second World War had developed, did not dare chaff about at the same time it first however not to use it in order not to tell to the opponent the secret.
composition and physics
the chaff consist of conductive threads of different length. In former times Stanniol became - strip used, today concerns it usually metal-vaporized breath-thin artificial fibers. They are distributed on different way in air. If a radar jet meets the material, the threads work like small dipole antennas and send a part back of the radiation , if their length corresponds with the wavelength of the radar jet, i.e. a multiple of the half wavelength has. The radar device receives then a Falschecho. In today's combat aircraft therefore for camouflage the wavelengths of the arriving radar signals are measured and cut as a function of it the chaff and distributed in air. Modern radar facilities are to be disturbed thereby however only very limited, among other things because they are able to determine by the Doppler effect the speed of the object. Since the chaff in air are very fast braked, its echoes can be filtered electronically.
it gives different procedures of the chaff employment. From an airplane the material can be thrown off like a curtain, which radar facilities can hardly penetrate. Thus activities can be camouflaged. A defensive possibility of the chaff employment consists of firing in case of an attack of missiles or airplanes individual smaller chaff clouds with rockets or other projectiles in order to direct the attack on these wrong goals. In the time of the cold war large American bombers had radar receivers, which could measure the wavelength of the opposing radar facilities, as well as chaff cutters, which cut from kilometer-long, rolled up tin-foil tape chaff of the suitable length.
Also today chaff as well as Flares are a component of the defensive preventive measures of modern combat aircraft. Flares are heat producing infrared - decoys and against guided weapons with infrared goal searching system are discharged.
In July 2005 and March 2006 wrong pictures in the weather radar observation arose. Became during periods of approx. 10 hours of rain shade observes, although there was no cloudy appearance. It is partly accepted that these phenomena are to due to military attempts with chaff over the North Sea. , a sceptical comment 
chaff are not only used, in order to be deceptive radar device. They are used also in the atmosphere research for the investigation of hoists in the upper atmosphere. For this chaff are brought by elevator research rockets into the appropriate layers and their flight paths with radar are pursued. In this way easily high-atmospheric air flows can be measured.