Thermal contrast detailing for inflatable decoy targets

Improved thermal contrast detailing for inflatable decoy targets is provided by providing the decoy with gas permeable skin panels for surface areas which would be at a higher temperature relative to other surface areas on the actual target represented by the decoy. Heated, pressurized air is provided to the decoy and escapes through the gas permeable panels making those panels hotter than adjoining gas impermeable panels. The target decoy may also be rigid. Thermal contrast may also be achieved by using chilled, pressurized air. The invention may also be used for providing any thermal radiance area-source.

BACKGROUND OF THE INVENTION 
The present invention relates generally to military decoys, and more 
particularly to an inexpensive inflatable thermal target decoy. 
Military decoys are primarily used for either of two purposes. One is 
simulating full size military targets to mislead an enemy. The other, and 
more common, purpose is to simulate military targets for target practice. 
Target decoys should be inexpensive, convenient and realistic. A presently 
popular construction method for making target decoys that simulate a 
complex target in three dimensions, and which can be quickly deployed from 
a compact package and later quickly dismantled, is to use balloon-like 
inflatable membranes. An important requirement for such decoys is that 
they present a realistic thermal image to thermal imaging surveillance. To 
provide thermal contrast detailing, and thus make a deceptively realistic 
thermal signature for the inflatable decoy targets, the prior art has 
generally placed electric resistance heater panels on the decoys to 
simulate engine covers or other outside surface components that normally 
would be proportionally warmer than the rest of the decoy surface. These 
thermal panels generally double the cost of the inflatable decoy. Passive 
solar heating has also been used for daytime applications. 
The prior art includes a variety of other methods for simulating thermal 
signatures on a decoy. While these other methods apparently have not been 
used in combination with an inflatable decoy, their teachings could be 
applied to inflatable target decoys. For example, U.S. Pat. No. 4,279,599 
to Marshall et al teaches the use of an etched flat metal plate where the 
etched surface is more emissive than its surrounding unetched area and, 
from solar heating of the plate, presents a deceptively warmer surface 
area. Where sufficient sunlight is not available to heat the plate, 
Marshall et al teaches attaching an electric contact heater to the back of 
the plate. 
Another example of a prior art teaching that could be adapted to produce 
deceptive thermal signatures on an inflatable decoy is U.S. Statutory 
Invention Registration (SIR) H308 to Tutin et al. The Tutin et al SIR 
teaches, as part of the use of a fabric-covered frame aircraft decoy, 
mixing metal particles with the fabric paint to increase the infrared and 
radar signatures of the decoy over its entire surface. 
The prior art also includes using pyrotechnics to produce a deceptive 
thermal signature. 
Unfortunately, all of the prior art, both that now used and that which may 
be adapted in the future, are add-on solutions, increasing complexity and 
cost. None of the prior art teachings take advantage of some inherent 
feature of inflatable decoys to provide deceptive thermal signatures. Such 
a solution would be simpler, more convenient and less expensive. 
Thus it is seen that there is a need for an inflatable decoy that provides 
a deceptive thermal signature without the need for expensive and 
complicated add-on apparatus. 
It is, therefore, a principal object of the present invention to provide an 
inflatable decoy target that utilizes its inherent supply of pressurized 
air to help produce thermal contrast detailing over the surface of the 
decoy. 
It is another object of the present invention to provide different methods 
for heating the pressurized air used to enhance the thermal contrast. 
It is a further object of the present invention to provide a general method 
for making thermal radiance area sources and patterns. 
It is a feature of the present invention that only a single heat source, or 
heater, is needed for each decoy. 
It is a further feature of the present invention that the heater is 
separate from the decoy and can thus provide heat to more than one decoy 
at the same time. 
It is an advantage of the present invention that the separate heater is not 
destroyed with the decoy. 
It is a further advantage of the present invention that the heater can be 
integrated with the inflation blower, and the same inflation blower can be 
used with both heated and nonheated inflatable decoys. 
It is another advantage of the present invention that its fabrication will 
be a straightforward and inexpensive modification to already existing 
inflatable decoy construction methods. 
These and other objects, features and advantages of the Present invention 
will become apparent as the description of certain representative 
embodiments proceeds. 
SUMMARY OF THE INVENTION 
The present invention provides a target decoy which includes an integral 
method for providing thermal contrast detailing. The unique discovery of 
the present invention is that thermal contrast detailing can be provided 
simply by making part of the fabric forming an inflatable decoy out of gas 
permeable fabric and inflating the decoy with heated air, so that the 
heated air escapes through the gas permeable fabric, thus transferring 
thermal energy, or heat, to the fabric, and making the gas permeable 
fabric surface area warmer than that of the gas impermeable parts of the 
decoy. 
Accordingly, the present invention is directed to an inflatable decoy 
comprising sheet material forming a bladder that, when filled with a gas, 
will inflate into a preselected shape, wherein at least one preselected 
part section of the sheet material is made of gas permeable material. The 
inflatable decoy may include means for supplying to the bladder heated, 
pressurized gas, whereby the heated gas escapes through the gas permeable 
material so that the surface area of the gas permeable material becomes 
warmer than the rest of the surface area of the decoy. The means for 
supplying heated, pressurized gas may be the exhaust of an internal 
combustion engine. The inflatable decoy may alternately include means for 
supplying to the bladder chilled, pressurized gas, whereby the chilled gas 
escapes through the gas permeable material so that the surface area of the 
gas permeable material becomes cooler than the rest of the surface area of 
the decoy. 
The invention is also directed to a rigid decoy comprising an outer surface 
having a preselected three-dimensional shape, wherein at least one 
preselected part section of the outer surface is gas permeable. The rigid 
decoy may include means for supplying to the inside of the decoy heated, 
pressurized gas, whereby the heated gas escapes through the gas permeable 
material so that the surface area of the gas permeable material becomes 
warmer than the rest of the surface area of the decoy. The rigid decoy may 
also include means for supplying to the inside of the decoy chilled, 
pressurized gas, whereby the chilled gas escapes through the gas permeable 
material so that the surface area of the gas permeable material becomes 
cooler than the rest of the surface area of the decoy. 
The invention is further directed to a method for providing thermal 
radiance area-sources, and thermal contrast detailing over a surface area, 
comprising the steps of providing a material having a back and a front, 
wherein the material comprises gas permeable and gas impermeable regions 
between corresponding front part surface areas and back part surface 
areas, and supplying heated, pressurized gas to the back part surface 
areas of gas permeable regions, whereby the heated gas passes through the 
gas permeable regions and corresponding front part surface areas, so that 
those front part surface areas of the material become warmer than the 
front part surface areas of the gas impermeable regions of the material. 
The material may be sheet material. The material may also be fabric. The 
method may alternately include supplying chilled, pressurized gas to the 
back part surface areas of gas permeable regions so that the corresponding 
front part surface areas become cooler than the front part surface areas 
of the gas impermeable regions of the material.

DETAILED DESCRIPTION 
Referring now to the FIG. 1 drawing, there is shown a perspective view of 
an inflatable decoy 10 and a schematic source 12 of heated, pressurized 
air 14. Inflatable decoy 10 may, of course, have the shape of any desired 
target, but in this example has roughly the three-dimensional shape of a 
tank. Tank decoy 10 may be made by gluing together, or otherwise 
attaching, skin panels of different shapes to form a bag or bladder having 
a preselected shape, in this example that of a tank. Most of the skin 
panels forming tank decoy 10 are made of a gas impermeable fabric so that, 
in the case of a conventional inflatable decoy, after initial inflation 
only a small volume of air needs to be continuously supplied to maintain 
internal air pressure, and the desired shape of decoy 10. Because most gas 
impermeable fabrics, and their accompanying seams, leak, even only 
slightly, a pressurized air source is generally left connected to the 
decoy to maintain its pressurization and shape. Skin panels 18 and 20, 
however, are made of gas permeable fabric. Skin panel 18 is made of a 
lightweight woven fabric that has not been conventionally sealed with a 
plastic sealant backing. Skin panel 20 is made with conventional gas 
impermeable fabric that has been fabricated with many small holes as an 
example alternate means for making a gas permeable skin panel. 
The operation of decoy 10 is simple. Heated, pressurized air source 12 
supplies heated air 14, or any suitable heated gas, to decoy 10 at a rate 
sufficient to replace, in addition to normal leakage, the air, or gas, 
lost through gas permeable panels 18 and 20. 
Heated air 14 escaping through skin panels 18 and 20 transfers part of its 
thermal energy, or heat, to the skin panels so that those surface areas of 
the decoy become warmer than the rest of the decoy. In this particular 
example embodiment, the skin panels will appear to be typical engine 
covers to thermal imaging surveillance or targeting apparatus. 
It should be noted that the escaping hot or warm air has a relatively low 
emissivity, and that it is the heated or warmed skin panels which emit 
significant thermal radiation. 
It should also be noted that it is generally unnecessary that the heated 
skin panels reach the same temperature that a real, for example, engine 
cover, only that there be a sufficient contrast between the thermal 
emissivity from the gas permeable surface areas and the gas impermeable 
surface areas. 
In one test, a bag shaped test target was constructed of fiber-reinforced 
plastic drop-cloth material and included a six by six inch hole covered by 
a patch of lightweight woven synthetic fabric. The test target was first 
pressurized with ambient temperature air, and then with heated air. 
Thermal radiation measurements, in degrees C. (8-12 microns, 
emissivity=1), yielded readings of, with ambient pressurized air, bag=18.4 
and patch=19.7; and, with heated pressurized air, bag=19.1 and patch=36.1. 
Heated, pressurized air may, of course, be supplied from a variety of 
sources. A particularly good source would be the exhaust from a small 
internal combustion engine. The heater and blower may be integrated, or a 
separate heater may supply heated air to a blower. 
A variety of useful enhancements and variations of the disclosed invention 
will readily appear to those with skill in the art of the invention. For 
example, reflective paint can be applied to the backs of the gas 
impermeable skin panels to enhance the thermal contrast by further 
limiting the amount of heat transferred to the gas impermeable panels. 
Also, more elaborate openings may be utilized that can be variably opened 
and closed so that a thermostatic control may be utilized to create 
preselected thermal signatures. 
Another variation of the described invention is to use chilled air instead 
of heated air, so that the gas permeable areas will become cooler, and 
thus present a cooler thermal image to thermal imaging surveillance. Air 
source 12 may be viewed as a source of chilled, pressurized air for this 
embodiment. 
Those with skill in the art of the invention will also see that the listed 
advantages of using a separate pressurized air source as the source of 
heat will also work for rigid decoys. Most rigid decoys are also hollow 
and need only have added skin panels of gas permeable material to achieve 
the same useful results. The heated air may be delivered by either 
supplying to the inside of the entire decoy, or be ducted to the specific 
locations. Decoy 10 may be viewed as having a rigid structure for this 
embodiment. 
Those with skill in the art of the invention will further see that its 
teachings are ideally suited to fabricate very large scale, or 
architectural, decoys. 
Those with skill in the art of the invention will also see that its 
teachings extend to a general method for providing thermal radiance 
area-sources and thermal contrast detailing over a surface area. The 
general method can be used to provide thermal optical definition patterns, 
greybody and blackbody thermal optical calibration sources, and the like. 
The disclosed thermal target decoy successfully demonstrates the use of an 
adaptation of an inherent feature of Prior art apparatus to provide 
features that previously required more complex additional components. 
Although the disclosed apparatus is specialized, its teachings will find 
application in other areas where apparatus will benefit from reduction of 
parts and simplification. 
It is understood that various modifications to the invention as described 
may be made, as might occur to one with skill in the field of the 
invention, within the scope of the claims. For example, the claimed 
bladder may comprise either a plurality of individual bladders, or a 
single large manifold. Therefore, all embodiments contemplated have not 
been shown in complete detail. Other embodiments may be developed without 
departing from the spirit of the invention or from the scope of the claims 
.