Infrared camouflage device

Details Infrared camouflage device Infrared camouflage device

2000-11-20

2003-09-02

Loney, Donald J. (Department: 1772)

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Structurally defined web or sheet

Including components having same physical characteristic in...

C428S919000

Reexamination Certificate

active

06613420

ABSTRACT:

BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German patent document 199 55 608.3, filed Nov. 19, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an infrared (IR) camouflage device for land targets, especially suitable for camouflaging military objects, such as land vehicles, against thermal imaging devices and infrared guidance heads.
In thermal camouflage an attempt is made to adjust the heat radiation emitted by an object to be camouflaged to the level of the thermal background; that is, to influence the temperature of the observable surfaces by design measures, such as heat damping, isolation, and back ventilation. While improvements are known in the area of active signature (for example for internal heat sources, such as motor, drives, energy assemblies), no satisfactory solutions have been provided by these measures relative to solar (passive) heat signature, since the temperature response of military objects as a rule differs sharply from that of a natural background. Proposed solutions for compensating for these deviations by active heating or cooling are described for example in German patent document DE 32 17 977 A1 and are less practical, especially in view of their high energy consumption.
Other known techniques are aimed at achieving signature reduction, not by influencing the actual surface temperature, but by changing the emission behavior of the surface. It is known that heat radiation of a body is determined not only by its temperature but also by the thermal emissivity &egr; of its surface. The use of low emission surface layers for infrared camouflage is known, and is described for example in German patent document DE 30 43 381 A1 and European patent document EP 0 123 660 A. One problem with this type of camouflage with low emission camouflage agents is that when the thermal emissivity &egr; is reduced, the infrared reflectivity &rgr; theoretically rises according to the formula &rgr;=1−&egr;. Hence, an increased reflection of ambient radiation takes place. This overlaps the natural emission so that the heat radiation (and therefore the observable radiation temperature when the thermal emissivity is reduced) depends to an increasing degree on the temperatures of the reflected ambient areas (ground temperature, sky temperature). Reflections from areas of the sky close to the zenith have proven to be especially critical since their radiation temperatures differ considerably, depending on the cloud cover, and can also heavily influence the signature. A known effect of low emission camouflage means is the observation of “cold spots”, i.e., areas with a low radiation temperature compared with the background temperatures due to the reflection of cold areas of the sky.
In order to take this fact into account, European patent document EP 0 250 742 A1 discloses a device with which thermal emissivity can be controlled. The heat radiated from an object is adjusted within wide limits as desired with very slight energy demand by controlling the shares of heat reflection and emission. A substantial reduction of contrast of the thermal radiation relative to the background is possible. However, the high cost of making such systems and the necessity for additional measurement and regulating devices are disadvantages.
When using low emission infrared camouflage means, the geometric features of the object to be concealed have to be taken into account. Distinctions must be made in particular between:
Surfaces Areas inclined toward the ground
Surfaces that are horizontal oriented or inclined toward the sky
Surfaces that are vertical oriented or slightly inclined toward the sky (up to 25° relative to vertical).
Basically, these areas require different embodiments of camouflaging means. For areas that are predominantly inclined to the ground, the known low emission camouflage agents with a permanent thermal emissivity that is as low as possible are used, since the ground temperatures located in front of the object will be reflected, independently of the observation point. The radiation temperature of the ground is generally identical to the rest of the thermal background. By transferring this temperature to the object to be camouflaged, a high reduction of contrast can be achieved with a corresponding camouflage effect. In this case, known LE (low emission) camouflaging agents can be used, such as for example, low emission paint (“LEP”) or low emission polymer foil (“LEF”).
For areas with predominantly horizontal alignment the known low emission camouflage agents cannot be used directly. The problem is that these areas, if they can be seen, always reflect predominantly sky temperatures near the zenith. Because these sky temperatures are very low, and can vary considerably depending on the cloud cover, reflected heat radiation is extremely dependent on the cloud cover. In many cases, horizontal areas that are provided with low emission camouflage means will be “cold spots” when, by reflection of the cold sky, the natural emission is overcompensated. Low emission behavior is desired only to the extent that increasing solar heating of the surface necessitates a reduction of the thermal radiation.
Similar problems exist in areas that are directed upward (angle to the horizontal less than 65°). They can reflect the sky radiation as well.
The situation in camouflage of essentially vertical surfaces (this includes surfaces inclined slightly to the sky—up to 25° relative to the vertical) is a mixture of the already-described conditions in the horizontal or the upwardly directed areas on the one hand and areas inclined to the ground on the other. Depending on the observation angle, the heat radiation reflected at the camouflage agent comes primarily from areas near the ground or from the sky radiation. The problem is that even small changes in the observation angle (or equivalently, small changes in inclination of the area, for example with moved camouflaged objects) can cause a sharp change in the radiation temperature of the object.
Hence, the object of the invention is to provide an effective camouflage device for object surfaces that are aligned essentially vertical without costly measurement and regulating devices.
Another object of the invention is to provide a camouflage arrangement in which the percentage of the reflected radiation that comes from sky radiation or ground radiation remains constant over a range of angles of inclination which is as large as possible.
These and other objects and advantages are achieved by the camouflage arrangement according to the invention, which breaks up the surface into areas inclined to the ground and areas inclined to the sky, with an area as large as possible of the radiation reflected at the camouflage device coming from the ground and the smallest percentage being reflected from the sky radiation or from only warmer sky areas near the horizon. This can be accomplished according to the invention by a surface structure that consists exclusively of two groups of partial areas, with the partial areas of the first group being directed downward and forming angles &agr; between 5° and 45° with the vertical and the partial areas in the second group being aligned upward and forming angles &bgr; between 50° and 85° with the vertical, with &agr;+&bgr; being <90°. The partial areas within each group can have different angles &agr; and &bgr;.
The total surface of all the upwardly aligned partial areas is advantageously less than the total area of all of the downwardly directed partial areas, and the structural sizes of the surface structure lie especially between 12 &mgr;m and 1 cm, preferably between 100 &mgr;m and 1 mm.
The structural sizes are chosen in an especially advantageous embodiment so that they are larger than the wavelength of infrared radiation and smaller than the wavelength of radar radiation. A size range suitable for the purpose is that between 20 &mgr;m and 1 mm. This ensures that the radar radiation cross section will not be i

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