Radar jamming and deception is a form of electronic countermeasures that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blanket the radar with signals so its display cannot be read are normally known as jamming, while systems that produce confusing or contradictory signals are known as deception, but it is also common for all such systems to be referred to as jamming. There are two general classes of radar jamming, mechanical and electronic. Mechanical jamming entails reflecting enemy radio signals in various ways to provide false or misleading target signals to the radar operator. Electronic jamming works by transmitting additional radio signals towards enemy receivers, making it difficult to detect real target signals, or take advantage of known behaviors of automated systems like radar lock-on to confuse the system. Various counter-countermeasures can sometimes help radar operators maintain target detection despite jamming. Mechanical jamming Mechanical jamming is caused by devices that reflect or re-reflect radar energy back to the radar to produce false target returns on the operator's scope. Mechanical jamming devices include chaff, corner reflectors, and decoys. Chaff is made of different length metallic strips, which reflect different frequencies, to create a large area of false returns in which a real contact would be difficult to detect. Modern chaff is usually aluminum-coated glass fibers of various lengths. Their extremely low weight and small size allow them to form a dense, long-lasting cloud of interference. This cloud is only effective in the range cell that it occupies. The slow movement of the chaff (compared to a flying target) makes it easily discriminated, based on the lacking Doppler shift. Ships, on the other hand, can benefit greatly from a slow-moving chaff cloud. The cloud is released within the resolution cell of the ship and moves with the wind in one direction. The ship then escapes in another direction. The decoy (chaff cloud) should have a larger radar cross-section (RCS) than the target, so the radar tracks it. Corner reflectors have the same effect as chaff but are physically very different. Corner reflectors are many-sided objects that re-radiate radar energy mostly back toward its source. An aircraft cannot carry as many corner reflectors as it can chaff. Decoys are maneuverable flying objects that are intended to deceive a radar operator into believing that they are actually aircraft.