Active camouflage



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.

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) by counterillumination.

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
Active camouflage provides concealment in two ways:
 * 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.

Active camouflage has its origins in the diffused lighting camouflage first tested on Canadian Navy corvettes including HMCS Rimouski during World War II, and later in the armed forces of the United States of America in the Yehudi lights project, and of the United Kingdom.

In research
Current systems began with a United States Air Force program which placed low-intensity blue lights on aircraft as counterillumination camouflage. As night skies are not pitch black, a 100 percent black-colored aircraft might be rendered visible. By emitting a small amount of blue light, the aircraft blends more effectively into the night sky.

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.

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.

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.

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.

In animals
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. Bioluminescence is common among marine animals, so counterillumination camouflage may be widespread, though light has other functions, including attracting prey and signalling.

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.

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. For example, the tropical flounder Bothus ocellatus can match its pattern to "a wide range of background textures" in 2–8 seconds.