Three color infrared camouflage system

A three-color camouflage system comprises layers of camouflage material hng low, intermediate and high thermal emissivities in the infrared spectral range, and appearing black, green and brown in the visible spectral range. The camouflage surface is structured in such manner that there is color adaptation to the natural background in the visible spectral range, as well as adaptation to the natural background in thermal emissivity in the infrared spectral range so that targets cannot be recognized with infrared sensing devices. Thermal emissivity in the infrared spectral range is controlled by superimposing layers of intermediate and high emissivity onto a basic low emissivity camouflage layer and providing perforations in these layers allowing the low-emissivity layer to be seen. High-emissivity areas are provided by perforations allowing the high-emissivity surface of the object being camouflaged to be seen. Alternatively, spots of high emissivity are superimposed on the three camouflage layers to provide areas of high emissivity. This camouflage system may also be used in the construction of decoys.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to camouflaging means and a method for disguising 
the visible and infrared image of military targets which may be 
substantially warmer than their surroundings by having been exposed to the 
sun, or in which heat may be produced by internal combustion engines, 
electric motors, generators, or transformers. 
2. Description of Prior Art 
Camouflage materials providing protection in the visible spectral region 
(wavelength from 400-700 millimicrons) by color adaptation to the 
background are well known to the art. However, most currently used 
camouflage paints, irrespective of their color in the visible spectral 
region, tend to have high emissivities in the infrared spectral regions 
from 3 to 5 and from 8 to 14 microns. (No significant infrared radiation 
is propagated over long distances outside these two "windows" because of 
absorption by water vapor and carbon dioxide contained in the atmosphere.) 
The emissivities of such paints tend, on average, to be significantly 
higher than those of most naturally occurring backgrounds. Therefore, 
targets painted with such paints can be clearly detected by imaging 
devices operating in the infrared spectral ranges. Moreover, many such 
targets have heat sources such as internal combustion engines, electric 
generators and motors which create a temperature contrast with the natural 
background which further enhance the detectability of such targets by 
means of infrared sensing devices. To provide protection against sensing 
devices operating in the infrared spectral regions, camouflaging materials 
with controlled electromagnetic emissivities in the infrared regions as 
well as in the near-by radar region have been proposed. 
U.S. Pat. Nos. 4,560,595 and 4,615,921 provide a thin metallic randomly 
deformed camouflage layer covered by two different plastic materials 
having different emissivities in the infrared region, simulating the 
surrounding terrain. U.S. Pat. No. 4,495,239 provides camouflage nets and 
thermal insulation mats using pigments for the visible and near infrared 
spectral region, and a binder with high transparency to radiation in the 
infrared range, providing low emissivity in that range, as well as in the 
radar range from 3 to 3000 GHz. U.S. Pat. No. 4,142,015 provides a layer 
of insulating foamed plastic, applied to the surface of the target to be 
camouflaged, that varies randomly to blur the visual and thermal image of 
the target. U.S. Pat. No. 2,294,675 provides a coating composition having 
a dark color in the visible spectral range and a low emissivity in the 
infrared range. 
The methods and apparatus provided heretofore for disguising military 
targets both in the visible and infrared spectral ranges suffer from the 
drawback that the effective emissivity of the camouflage material in the 
infrared ranges cannot readily be closely adapted to that of the 
surroundings from which the target should be indistinguishable when viewed 
by infrared detection equipment. Moreover, the thermal "signature" of such 
targets resulting from internal heat sources such as internal combustion 
engines, exhaust pipes, electric motors or generators, or transformers, 
cannot readily be disguised by known methods. 
The object of present invention therefore is to provide means and a method 
for structuring the camouflaging surface in such manner that there is both 
color adaptation in the visual range and an effective emissivity in the 
infrared range which can be designed to simulate that of virtually any 
natural background, and which can furthermore be designed to disguise hot 
regions of the target which would ordinarily be clearly discernible with 
infrared detection devices. 
SUMMARY OF THE INVENTION 
The present invention provides camouflaging means fastened to the surface 
of a military target to be camouflaged which includes a material having a 
high emissivity (0.7-0.9) in the visible spectral range, thus appearing 
black to the human eye, and a low emissivity (about 0.1) in the infrared 
spectral range; a second material superimposed upon the first material in 
irregularly-shaped patches which appears green in the visible spectral 
range and which has an intermediate emissivity (0.5-0.7) in the infrared 
spectral range; and a third material superimposed upon the first material 
in irregularly-shaped patches which appears brown in the visible spectral 
range and which has a high emissivity (0.7-0.9) in the infrared spectral 
range. The irregularly-shaped patterns thus created on the camouflaging 
surface are designed to simulate naturally occurring backgrounds. For 
equipment of the United States Army, the patterns are in accordance with 
Technical Manual 43-0139, "Painting Instructions for Army Materiel," Troop 
Support Command (TROSCOM) Publications. The proportions are 44% green, 41% 
black and 15% brown. 
The camouflaging layers are attached to the surface of the equipment and to 
each other by adhesives. 
Perforations in the green and brown patches allow portions of the black 
material to be seen. Additional perforations through the black, green and 
brown materials allow thermal radiation from the equipment being 
camouflaged to pass through to the surroundings. In an alternative 
embodiment of this invention, small spots of material having high 
emissivity in the infrared range are applied to the camouflaging surface 
in place of the additional perforations. 
As a further alternative, brown and green camouflage layers may be applied 
to the target surface and black camouflage material may be superimposed in 
continuous, randomly-shaped patches, or in small spots by a sputtering 
technique. 
The technique of this invention by which both the visible and infrared 
appearance of an object can be controlled may also be used in the 
construction of two-dimensional and three-dimensional decoys simulating 
military and other targets.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
The camouflaging means of this invention provides conventional color 
adaptation in the visible spectral range. Irregularly-shaped black, green 
and brown patterns mimic foliage and soils. For equipment of the United 
States Army, the patterns are in accordance with Technical Manual 43-0139, 
"Painting Instructions for Army Materiel," Troop Support Command (TROSCOM) 
Publications. The proportions are 44% green, 41% black and 15% brown. 
Other color combinations may be chosen to mimic desert and snowy 
environments. 
In the infrared spectral regions from 3 to 5 and from 8 to 14 microns of 
wavelength, the emissivity of the camouflaging surface is controlled by 
mixing low-emissivity areas with high-emissivity areas, whereby a wide 
range of average emissivity may be achieved by the suitable choice of area 
ratios. The average emissivities of the camouflaging means in the infrared 
spectral regions are chosen to correspond to emissivities in the same 
spectral regions found in the natural environments in which the 
camouflaged targets will operate. 
The basic camouflage material used in this invention is a layer having a 
high emissivity (0.7-0.9) in the visible spectral range, thus appearing 
black to the human eye, and a low emissivity in the infrared spectral 
ranges (about 0.1). Nickel oxide and black stainless steel are most 
suitable for this purpose; such materials are commercially available. This 
layer is bonded to the surface of the equipment by adhesives. 
Superimposed on this first basic layer are additional layers, such as 
fabric patches of irregular shape being dyed or pigmented to appear green 
and brown in the visible spectral region and having intermediate to high 
emissivities in the infrared spectral regions. These green and brown 
layers are bonded to the base layer by adhesives. 
The darkness or brightness of these green and brown fabric patches in the 
visible spectral range may be varied by providing small perforations, 
regularly or randomly spaced, through which the visually black underlying 
surface may be seen. The human eye, rather than perceiving these small 
black spots as such, mixes them and perceives them as different shades of 
dark and light green and brown. The size of these perforations may range 
from 1 to 3600 square millimeters each, and the area occupied by these 
perforations in any given section of camouflage surface may range from 1 
to 25 percent of the total area. 
An analogous kind of mixing of dark and light takes place in the infrared 
spectral regions. The small perforations in the green and brown layers 
permit the low-emissivity base layer to be seen. The effect is to lower 
the effective average emissivity in any given region of the camouflage 
surface to a level between that of the intermediate-to-high values of the 
unperforated layers and that of the low-emissivity base layer. 
An additional method of varying the average effective emissivity of the 
green and brown layers, as well as that of the black base layer, consists 
of providing spots of high emissivity. This is accomplished by two 
alternate means: 
(a) small perforations through the camouflaging layers are provided which 
are too small to see individually on infrared imaging equipment but which 
allow radiation from the target surface, which has a high emissivity in 
the infrared range, to pass through all the camouflage layers, creating 
local regions of higher average emissivity; 
(b) small spots of high emissivity, e.g. spots of epoxy paint, are applied 
to the camouflaging layers, these spots again being too small to be 
perceived as individual spots on infrared sensing equipment but conferring 
on the local area a higher average emissivity which is perceptible to 
infrared sensors. The color of these spots in the visible spectral range 
should preferably be green or brown. 
The perforations and spots of high emissivity may again range from 1 to 
3600 square millimeters each and have areas in any given section of the 
camouflaging surface ranging from 1 to 25 percent of the total area. 
The variations in local average emissivity created by the methods described 
disrupt what otherwise would be perceived by infrared imaging devices as a 
conspicuously uniform object in a natural background having random 
variations in infrared radiation intensity. Hotspots on the target, such 
as diesel engines, exhaust pipes, motors, generators, and transformers, 
which would normally be detected by infrared sensors as areas of high 
infrared radiation, are camouflaged with the basic low-emissivity layer, 
perforations or spots of high emissivity being purposely omitted to 
maintain a low average emissivity. 
Referring to FIG. 1 of the drawings, there is shown in schematic form a 
cross section of the camouflaging layers. Bonded to the surface of the 
target 1 is a thin layer 2 having high emissivity (0.7-0.9) in the visible 
spectral range and low emissivity in the infrared spectral region (about 
0.1). Superimposed on this base layer are layers of a second camouflaging 
material 3 and a third camouflaging material 4, appearing green and brown, 
respectively, in the visible spectral region. Perforations 5 in the green 
camouflaging layer 3 allows the base layer 2 to be seen. Similar 
perforations are provided in the brown camouflaging layer 4. A second type 
of perforation 6 allows the surface of the target 1 to be seen. 
FIG. 2 illustrates an alternate embodiment of the invention in which, 
instead of the second type of perforation, spots 7 of high-emissivity 
material, such as epoxy paint, are applied to the camouflaging surface. 
FIGS. 3A and 3B illustrate a typical view of a camouflaged surface. For 
equipment of the United States Army, the patterns are in accordance with 
Technical Manual 43-0139, "Painting Instructions for Army Materiel," Troop 
Support Command (TROSCOM) Publications. The proportions are 44% green, 41% 
black and 15% brown. 
The control of emissivity in the infrared spectral range by means of 
performations and high-emissivity spots as used in this invention is 
illustrated by the following numerical examples. 
EXAMPLE 1 
A portion of a brown layer having an emissivity of 0.8 in the infrared 
spectral range has regularly spaced circular perforations 2 mm in diameter 
(about 3 sq. mm. area) which constitute 20% of the area and through which 
the low-emissivity base layer (emissivity 0.1) may be seen. The average 
emissivity in this area is 0.8.times.80%+0.1.times.20%=0.66. 
EXAMPLE 2 
A portion of a green layer having an emissivity of 0.5 has 2 mm diameter 
regularly spaced circular perforations through which the equipment surface 
(emissivity 0.95) may be seen. The perforations constitute 25% of the 
total area. The average emissivity is 0.5.times.75%+0.95.times.25%=0.61. 
EXAMPLE 3 
A portion of the black base layer having an emissivity of 0.1 in the 
infrared spectral range has circular 3 mm diameter spots of high 
emissivity paint (emissivity 0.95) constituting 20% of the area. The 
average emissivity is 0.1.times.80%+0.95.times.20%=0.27. The color of the 
spots in the visible spectral range is green. 
EXAMPLE 4 
A portion of a green layer (emissivity 0.5) has circular 2 mm diameter 
spots of high-emissivity paint (emissivity 0.95) representing 15% of the 
area. The average emissivity is 0.5.times.85%+0.95.times.15%=0.57. The 
color of the spots in the visible spectral range is green. 
It is thus apparent that by the appropriate choice of perforations and 
high-emissivity spots, the emissivity of the camouflage surface in the 
infrared spectral range can be varied to simulate the infrared emissivity 
patterns of naturally occurring backgrounds. 
High-temperature parts of the target such as exhaust pipes, which would 
normally be observed as high-emissivity regions of a target by infrared 
sensing devices, can be "toned down" by the choice of low-emissivity 
camouflage layers which make such high-temperature parts blend in with the 
background. 
As a further alternative, brown and green camouflage layers may be applied 
to the target surface and black camouflage material may be superimposed in 
continuous, randomly-shaped patches, or in small spots by a sputtering 
technique. 
The technique of this invention by which both the visible and infrared 
appearance of an object can be controlled may also be used in the 
construction of two-dimensional and three-dimensional decoys simulating 
military and other targets. 
While there have been described what at present are considered to be the 
preferred embodiments of this invention, it will be obvious to those 
skilled in the art that various changes and modifications may be made 
therein without departing from the invention and it is therefore intended 
to cover all such modifications and changes as fall within the spirit and 
scope of this invention.