Active camouflage

Many cephalopods such as this cuttlefish can change color rapidly for signalling or to match their backgrounds.

Active camouflage or adaptive camouflage 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.[1]

Active camouflage is used 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 counterillumination, with the use of bioluminescence.

Military counterillumination 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 panels or coatings that can vary their appearance.

Definition

Illustrating the concept: active image capture and re-display creates an "illusory transparency", also known as "computer mediated reality" or "optical camouflage"

Active camouflage provides concealment either[2] by making an object not merely generally similar to its surroundings, but effectively invisible through accurate mimicry, and by changing the appearance of the object as changes occur in its background.

In research

Active camouflage has its origins in Second World War studies of counter-illumination. The first of these was the so-called diffused lighting camouflage tested on Canadian Navy corvettes including HMCS Rimouski. This was followed in the armed forces of the United States of America with the airborne Yehudi lights project, and of the United Kingdom.[3] The Yehudi lights project placed low-intensity blue lights on aircraft. As night skies are not pitch black, 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 night sky, and the aircraft is able to fly closer to its target before being detected.

Active camouflage may now develop using organic light-emitting diodes (OLEDs) and other technologies which allow for 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.[4]

An invisibility cloak using active camouflage by Susumu Tachi. Left: The cloth seen without a special device. Right: The same cloth seen through the half-mirror projector part of the Retro-Reflective Projection Technology.

Active camouflage technology exists only in theory and proof-of-concept prototypes. In 2003 researchers at the University of Tokyo under Susumu Tachi created a prototype active camouflage system in which a video camera images the background and displays it on a cloth using an external projector.[5]

Phased array optics (PAO) 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.[6]

In 2011, BAE Systems announced their Adaptiv infrared camouflage technology. It uses about 1000 hexagonal panels to cover the sides of a tank. The panels are rapidly heated and cooled to match either the temperature of the vehicle's surroundings, or one of the objects in the thermal cloaking system's "library" such as a truck, car or large rock.[7]

In animals

See also: List of camouflage methods and Category:Animals that can change color
Counterillumination camouflage of the firefly squid, Watasenia scintillans uses bioluminescence to match brightness and colour of the sea surface above.

Active camouflage is present in several groups of animals including cephalopod molluscs, fish, and reptiles.

There are two mechanisms of active camouflage in animals: Counterillumination camouflage, and color change.

Counterillumination camouflage is the production of light to blend in against a lit background. In the sea, light comes down from the surface, so when marine animals are seen from below, they appear darker than the background. Some species of cephalopod, such as Abralia veranyi and Watasenia scintillans, produce light in photophores on their undersides to match the background.[8] Bioluminescence is common among marine animals, so counterillumination camouflage may be widespread, though light has other functions, including attracting prey and signalling.


Four frames of a peacock flounder show its ability to match its coloration to the environment.

Color change permits camouflage against different backgrounds. Many cephalopods including octopuses, cuttlefish, and squids, and some terrestrial reptiles including chameleons and anoles can rapidly change color and pattern, though the major reasons for this include signalling, not only camouflage.[9][10]

Active camouflage is also used by many bottom-living flatfish such as plaice, sole, and flounder that actively copy the patterns and colors of the seafloor below them.[11] For example, the tropical flounder Bothus ocellatus can match its pattern to "a wide range of background textures" in 2–8 seconds.[12] Similarly, the coral reef fish, the seaweed blenny can match its coloration to its surroundings.[13]

See also

References

  1. ↑ Kent W. McKee and David W. Tack (2007). "Active Camouflage For Infantry Headwear Applications" (PDF). HumanSystems: iii.
  2. ↑ Kent W. McKee and David W. Tack (2007). "Active Camouflage For Infantry Headwear Applications" (PDF). HumanSystems: 1.
  3. ↑ "Naval Museum of Quebec". Diffused Lighting and its use in the Chaleur Bay. Royal Canadian Navy. Retrieved January 19, 2012.
  4. ↑ Kent W. McKee and David W. Tack (2007). "Active Camouflage For Infantry Headwear Applications" (PDF). HumanSystems: 10–11.
  5. ↑ Time magazine: Invisibility
  6. ↑ Wowk B (1996). "Phased Array Optics". In BC Crandall. Molecular Speculations on Global Abundance. MIT Press. pp. 147–160. ISBN 0-262-03237-6. Archived from the original on 27 February 2007. Retrieved 2007-02-18.
  7. ↑ "BBC News Technology". Tanks test infrared invisibility cloak. BBC. 5 September 2011. Retrieved March 27, 2012.
  8. ↑ "Midwater Squid, Abralia veranyi". Midwater Squid, Abralia veranyi (with photograph). Smithsonian National Museum of Natural History. Retrieved November 28, 2011.
  9. ↑ Forbes, Peter. Dazzled and Deceived: Mimicry and Camouflage. Yale, 2009.
  10. ↑ Wallin, Margareta (2002). "Nature's Palette" (PDF). Nature's Palette: How animals, including humans, produce colours. Bioscience-explained.org. pp. Vol 1, No 2, pages 1–12. Retrieved November 17, 2011.
  11. ↑ Sumner, Francis B. (May 1911). "The adjustment of flatfishes to various backgrounds: A study of adaptive color change". Journal of Experimental Zoology 10 (4): 409–506. doi:10.1002/jez.1400100405.
  12. ↑ Ramachandran, V.S. and C. W. Tyler, R. L. Gregory, D. Rogers-Ramachandran, S. Duensing, C. Pillsbury & C. Ramachandran (29 February 1996). "Letters to Nature". Rapid adaptive camouflage in tropical flounders. Nature (journal). pp. 379: 815–818. doi:10.1038/379815a0. Retrieved January 20, 2012.
  13. ↑ Bester, Cathleen. "Seaweed blenny". Ichthyology. Florida Museum of Natural History. Retrieved 2015-01-06.

Bibliography

External links

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