Ordnance – Shields – Shape or composition
Reexamination Certificate
1999-09-30
2002-01-15
Jordan, Charles T. (Department: 3644)
Ordnance
Shields
Shape or composition
C089S036010, C089S036070, C089S036080, C089S001110
Reexamination Certificate
active
06338292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to surface modification devices and techniques, and more particularly to a background matching camouflage system. Specifically, the invention relates to a passive optical and infrared camouflage system in which a body is heated or cooled to match background emmissivity and in which the body may be simultaneously altered optically to correspond with background colors.
2. Background of the Invention
The art of concealment by altering an object to blend with its physical surroundings and environment, i.e., camouflage, has been practiced for centuries. Initially, it was only necessary to conceal an object from the visible physical surroundings. However, as technology has developed, it has become necessary to conceal an object over multiple bands of the electromagnetic spectrum. Most notably, in addition to visible concealment, it has become necessary to conceal an object's infrared radiation (IR) to prevent thermal detection systems and the like from identifying an object based on its heat signature. Thus, modeling of camouflage effectiveness should consider both the infrared and visible spectrums.
There are three capabilities that must be addressed in a camouflage system: passive surveillance capability, active surveillance capability and high energy weapon capability. Of these, passive surveillance systems utilize electro-optical systems operating in the visible wavelength and infrared wavelength bands. Visual surveillance systems operate in the 0.4 to 0.7 micrometer portion of the electromagnetic spectrum. These systems rely on the visual, that is, that which is recognizable by the human eye. In addition, optical augmentation systems, which range from hand-held binoculars to video display terminals with zoom-in capability, may be utilized to enhance visual detection. In any event, detection mechanisms employed in visual surveillance systems employ color and/or brightness contrast to “identify” targets.
Passive systems which operate in the infrared wavelength bands, the 0.8 to 14 micrometer portion of the electromagnetic spectrum, which include the solar band, the high temperature band and the low temperature band, operate by homing-in on the contrast between the target IR signature and the IR signature of the surrounding environment.
Turning first to visible camouflage, making targets hard to find in the visible light spectrum (wavelength from 400-700 millimicrons) is primarily concerned with the development of ever more effective camouflage patterns and with techniques for characterizing the effectiveness of the camouflage for particular terrain. The techniques in use today largely involve painting, coloring, and/or contour shaping to allow an object to better blend with the surrounding environment. Other than color adaption to the background, these techniques have involved obscuring the contours of an object by covering the object with camouflage material such as nets or leaf cut tarpaulins. Such covering camouflage is good for visual concealment because the outlines of covered objects are disguised and difficult to discern from the surrounding natural environment, provided that the color scheme is harmonized with the surrounding natural environment. Thus, there are manufactured special nets for woodlands, for deserts, and for snow, all of which have very different color schemes.
However, in the visible spectrum, successful camouflage may be limited by factors including the following:
a. Camouflage patterns painted on a conventional surface are unable to change and a fixed camouflage pattern is inappropriate for the variety of backgrounds encountered in nature or otherwise man made.
b. One observer sees a military target against a rocky background while another observer sees the target against a forested background, while a third observer sees the target against a red barn. The current state of the art does not allow the military target to be effectively camouflaged for all these observers simultaneously or in real time.
c. When either the object or the observer moves, the background against which the target is seen changes, reducing the effectiveness of the camouflage pattern.
d. Most camouflage paints, irrespective of their color in the visible spectral range, tend to have high emissivities in the infrared spectral regions, wherein such emmissivities are 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.
Even the combination of several techniques may not effectively camouflage an object from detection. For example, known camouflage covering material, such as nets, generally have a very open, apertured structure. The proportionate covering of such conventional materials is only about 50-65%. This has been found to be insufficient when surfaces with high emmissivities, such as camouflage paints, are being covered because the high emissivities are still detectable through the covering's apertures. Likewise, such coverings would also be ineffective in masking warm objects against detection by thermal reconnaissance.
Turning now to camouflage in the IR spectrum, finding targets in the IR spectrum utilizes target size and apparent temperature differences between the target and the background (known as &Dgr;T), a summary measure that combines target background physical temperature difference and target background emmissivity difference. Some targets contain highly concentrated heat sources which produce very high localized temperatures. There are also targets that contain a large number of heat sources with distinctive shapes which form easily recognizable patterns. As the contrast sensitivity of solid state detectors improves, it becomes possible to discern, for example, the number of cylinders in a gasoline engine and other subtle distinctions such as a change in fabrication material or perhaps a particular type of seam.
More specifically, many targets have internal heat sources which create a temperature contrast with the natural background which further enhanced the detectability of such targets by means of infrared sensing devices. For example, a tank generates large amounts of heat in the engine compartment and exhaust pipe, as well as from electric generators and motors. When the guns are fired, their barrels become heat sinks. Friction while the tank is moving heats the rims of the drive and the idler wheels and their central bearing portions. The track also becomes heated by friction with the wheels. The bearing area between the turret and tank body can also become heated. Moreover, radiant energy from the sun may be absorbed by the steel shell of a tank during the daytime, and at nighttime such energy reradiates from the shell, providing a clear IR signature against a cool background such as trees or hills. In addition, as mentioned above, the emissivities of paints tend, on average, to be significantly higher than those of most naturally occurring backgrounds. Therefore, a tank painted with camouflage paints can be clearly detected by imaging devices operating in the infrared spectral ranges.
To mask &Dgr;T differences, some IR camouflage prior art techniques have involved the use of subsystems to alter the surface of the object, such as forcing heated or cooled air over an object to match the object's temperature to that of the surrounding environment. Of course, these subsystems themselves often have extraordinary power requirements which generate their own IR signature. Another technique has been to deploy decoy IR sources in an environment to radiate IR signatures equal to that of any specific target. More commonly, however, IR camouflage prior art techniques involve complete covering or shielding of an object with a material cover, such as a tarpaulin, in order to hide an objects IR signature.
Much effort has been expended in the determination of materials to be used to comprise the typical IR camouflage shielding.
Kinsella Michael Joseph
Reynolds Robert Fisher
Best Christian M.
Bracewell & Patterson L.L.P.
Jordan Charles T.
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