Among animals, both insects such as the eyed hawk-moth, and vertebrates such as tree frogs possess camouflage that works in the infra-red as well as in the visible spectrum.
History
The caterpillar of the eyed hawk-moth Smerinthus ocellatus is camouflaged to match a leafy background in both visible and infra-red light.
The English zoologist Hugh Cott, in his 1940 book Adaptive Coloration in Animals, wrote that some caterpillars such as the eyed hawk-moth Smerinthus ocellatus, and tree frogs such as the red-snouted treefrog Hyla coerulea, are coloured so as to blend with their backgrounds whether observed in visible light or in infra-red.[3][4] Cott noted the importance of camouflage in the infra-red, given the ability of tactical reconnaissance to observe in this part of the spectrum:
Because such screens are effective against direct observation and ordinary photography, by no means does it follow that they will be hidden in the infra-red photograph. Comparison of aerial photographs taken simultaneously on panchromatic and infra-red plates will reveal much that before the advent of this new technique would have been adequately camouflaged...
A German-led NATO research project concluded in 2004 that while "the multispectral signatures of most military equipment can be significantly reduced by combinations of various camouflage materials", multi-spectral camouflage for individual soldiers remained lacking. The main problems identified were operational constraints such as mobility, weight, and the soldier's physiology.[6]
Camouflage
Multi-spectral camouflage can be applied to individuals, to vehicles, and to buildings. It can take the form of specialised paints or camouflage nets that provide conventional camouflage, reduce the amount of heat given off by an object, and alter the shape and size of its radar signature.[7][8][9][10][11][12] The Saab Barracuda Mobile Camouflage System provides a degree of concealment in the visible, thermal infrared, and radar parts of the electromagnetic spectrum,[13] as does the Miranda Berberys-R multispectral camouflage system from Poland.[14] Similarly, other companies such as the American-Israeli "Fibrotex" and "Ametrine", and the Greek "Intermat Defence" proposed their own products ranging from static vehicle camouflage fabric to multispectral spray paints.
An example of individual multispectral camouflage. The showcased suit provides simultaneous camouflage in the VIS and LWIR wavelengths of the electromagnetic spectrum. The soldier thermal signature matches the surrounding environment. Credits: ProApto Camouflage
Saab AB began offering a multi-spectral personal camouflage system known as the Special Operations Tactical Suit (SOTACS) as early as 2005.[15] And as of 2018, multiple countries are phasing out legacy camouflage systems with multi-spectral systems.[16][17]
In the last decade other companies developed their own individual multispectral camouflage, such as the Israeli "Polaris Solutions", the American "Relv Camo", and the Italian "ProApto". The latter specifically focuses on 3D individual camouflage, proposing multispectral Ghillie Suits designed also for amphibious operations and both tropical and arctic environments.
As this type of camouflage hinders electromagnetic radiation, radio-communications and GPS are also hindered. This can be overcome by using frequency selective surfaces, allowing specific frequencies to pass through.[19]
^Cott, Hugh B. (1940). Adaptive Coloration in Animals. Oxford University Press. p. Plate 5 shows the eyed hawk-moth caterpillar in visible and infra-red on a leafly background; Plate 6 shows a tree-frog similarly. It is clear from the plates that these animals reflect infra-red.
^Cott, Hugh B. (1940). Adaptive Coloration in Animals. Oxford University Press. p. 10.
^Nave, C.R. "The Electromagnetic Spectrum". HyperPhysics. Hosted by Georgia State University Department of Physics and Astronomy. Retrieved 30 April 2013.
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