thumb|[[Cephalopod molluscs such as this cuttlefish can change color rapidly for signaling or to match their backgrounds.|alt=Photograph of a camouflaged cuttlefish]]

Active camouflage, adaptive camouflage, or chameleonizing is camouflage that adapts, often rapidly, to the surroundings of an object such as an animal or military vehicle. In theory, active camouflage could provide perfect concealment from visual detection.

Active camouflage occurs in several groups of animals, including reptiles on land, and cephalopod molluscs and flatfish in the sea. Animals achieve active camouflage both by color change and (among marine animals such as squid) by counter-illumination, with the use of bioluminescence.

Military counter-illumination camouflage was first investigated during World War II for marine use. More recent research has aimed to achieve crypsis by using cameras to sense the visible background, and by controlling systems that can vary their appearance, such as coatings, or variable temperature infrared panels using the Peltier effect.

In animals

thumb|[[Counter-illumination camouflage of the firefly squid, Watasenia scintillans uses bioluminescence to match brightness and color of the sea surface above.|alt=Drawing showing principle of squid counter-illumination camouflage]]

Active camouflage is used in several groups of animals including cephalopod molluscs, Bioluminescence is common among marine animals, so counter-illumination may be widespread, though light has other functions, including attracting prey and signaling.

Color change

thumb|Four frames of a [[peacock flounder show its ability to match its coloration to the sea bed around and beneath it.|alt=Photographs of a fish changing its coloration to match background]]

Color change permits camouflage against different backgrounds. Many cephalopods including octopuses, cuttlefish, and squids, and some terrestrial amphibians and reptiles including chameleons and anoles can rapidly change color and pattern, though the major reasons for this include signaling, not only camouflage. Cephalopod active camouflage has stimulated military research in the United States.

Active camouflage by color change is used by many bottom-living flatfish such as plaice, sole, and flounder that actively copy the patterns and colors of the seafloor below them. For example, the tropical flounder Bothus ocellatus can match its pattern to "a wide range of background textures" Similarly, the coral reef fish, the seaweed blenny can match its coloration to its surroundings.

In research

Active camouflage provides concealment by making an object not merely generally similar to its surroundings, but effectively invisible with "illusory transparency" through accurate mimicry, and by changing the appearance of the object as changes occur in its background. The Yehudi lights project placed low-intensity blue lights on aircraft. As skies are bright, an unilluminated aircraft (of any color) might be rendered visible. By emitting a small, measured amount of blue light, the aircraft's average brightness better matches that of the sky, and the aircraft is able to fly closer to its target before being detected.

Possible technologies

Active camouflage may now develop using organic light-emitting diodes and other technologies which allow images to be projected onto irregularly shaped surfaces. Using visual data from a camera, an object could perhaps be camouflaged well enough to avoid detection by the human eye and optical sensors when stationary. Camouflage is weakened by motion, but active camouflage could still make moving targets more difficult to see. However, active camouflage works best in one direction at a time, requiring knowledge of the relative positions of the observer and the concealed object.

Phased-array optics would implement active camouflage, not by producing a two-dimensional image of background scenery on an object, but by computational holography to produce a three-dimensional hologram of background scenery on an object to be concealed. Unlike a two-dimensional image, the holographic image would appear to be the actual scenery behind the object independent of viewer distance or view angle.

Military prototypes

thumb|upright=1.4|An armoured vehicle fitted with [[Adaptiv infrared side panels, switched off (left), and on to simulate a large car (right)

In fiction

Active camouflage technology, both visual and otherwise, is a commonly used plot device in science fiction stories. The Star Trek franchise incorporated the concept ("cloaking device"), and Star Trek: Voyager depicts humans using "bio-dampeners" to infiltrate a Borg Cube without the antagonists realizing they are there. The eponymous antagonists in the Predator films also use active camouflage. In many video games, such as the Halo series, Deus Ex: Human Revolution, and the Crysis series, players can obtain and use cloaking devices.

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See also

  • Cloaking device
  • Cloak of invisibility
  • Penetration aid
  • Snow camouflage – color change with the seasons
  • Stealth technology

References

  • "Multi-perspective background simulation cloaking process and apparatus ", United States Patent & Trademark Office
  • "Scientist show off 'invisible coat'", The Sydney Morning Herald, 30 March 2003
  • Phased Array Optics
  • "Thermal and Visual Camouflage System Patent No 6,338,292 ", United States Patent & Trademark Office

fr:Camouflage (militaire)#Camouflage optique