GB2274154A

GB2274154A - Modifying the infra-red appearance of a body

Info

Publication number: GB2274154A
Application number: GB8927403A
Authority: GB
Inventors: Ian Hunter
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1989-12-04
Filing date: 1989-12-04
Publication date: 1994-07-13
Anticipated expiration: 2009-12-04
Also published as: GB2274154B; GB8927403D0

Abstract

A ships infra-red appearance is modified by determining the infra-red image of the ships surroundings and reflecting infrared radiation from its surroundings by reflector means pivotable about pivot points 9 to cause the ship to merge into its surroundings. Because the reflector means are pivotable the way in which the ships infra-red appearance is modified can be controlled and the infra-red appearance can be made to correspond to the ships background when viewed along the line of sight of a likely threat, thus making it difficult to detect by a heat-seeking missile. The reflector means may be coated with bands of material translucent to infra-red radiation but opaque to visible radiation, to make it inconspicuous, and may comprise an inflatable envelope with a reflective surface. <IMAGE>

Description

Modifying the Infra-red APPearance of a Body This invention relates to modifying the infra-red appearance of a body, particularly but not exclusively modifying the infra-red appearance of a ship to prevent its detection by a missile or other weapons system.

Heat seeking missiles have been developed which combine an infra-red detector with a degree of computer intelligence and memory. Such missiles seek out not simply just a hot body, but a body producing an infra-red appearance of a target which has been programmed into the missile's memory. Such a missile would ignore devices such as decoy flares fired from a ship and fly to the ship as intended.

According to a first aspect of the invention, there is provided a method of modifying the infra-red appearance of a body comprising: reflecting infra-red radiation from the body's surroundings from infra-red reflector means provided on the body.

By so reflecting radiation, the infra-red appearance may be disrupted or altered to such an extent that the body when viewed through an infra-red detection system would not be recognisable and a missile for instance would not recognise the body as a target and consequently miss the body.

Preferably, the infra-red appearance of the body would be modified so as to correspond at least in part to infra-red emissions from the body's background.

By modifying the appearance of the body to correspond to the background, the presence of the body will be difficult to detect when viewed by an infra-red detector.

The background will preferably, be the background when the body is viewed along a particular line of sight. The particular line of sight will be that appropriate to a direction likely to contain a threat. Such a threat may be an enemy's weapon system, a missile or a pilot wearing night vision equipment.

Preferably, the line of sight is that of a detected threat. The threat may be detected by a radar system or visually, the line of sight of the threat identified and the background appropriate to that line of sight selected.

If the missile is a sea skimming missile its line of sight of a ship for instance would be such that the ship's background would be mostly sky. Therefore, the ships infra-red appearance would be modified to match that of the sky. For a missile approaching at a high altitude the ship's background would be mostly sea and accordingly the ship's infra-red appearance would be modified to match that of the sea.

Typically, the method comprises providing a plurality of movable reflector means on the body, determining the infra-red appearance of the surroundings, determining the infra-red emission from the body due to its temperature and moving the reflector means so as to reflect the infra-red emission of the surroundings such that when viewed from a distance, the infra-red appearance of the body comprises a mixture of its own emission due to the temperature and the reflected emission of the surroundings.

Avantageously, the method comprises determining the infra-red appearance of the background; determining the unmodified infra-red appearance of the body and positioning the reflector means so as to reflect infra-red radiation from the surroundings.

By determining the infra-red appearance of the background and the unmodified infra-red appearance of the body, the body's infra-red appearance may be modified to closely match that of the background.

Preferably, the modified infra-red appearance comprises a mixture of the unmodified appearance and the reflected radiation.

The reflected radiation may be from the sky, sea or land according to the background and the body's unmodified infra-red appearance.

According to a second aspect of the invention there is provided apparatus for modifying the infra-red appearance of a body comprising: reflector means arranged on the body so as to reflect infra-red radiation from the body's surroundings.

Such apparatus can be used in the method described above.

Preferably, the reflector means is arranged such that the reflected radiation modifies the body's infra-red appearance so as to correspond to the appearance of the body's background as mentioned previously.

Advantageously, means are provided for varying the amount of infra-red radiation reflected. This allows the modified infra-red appearance to be varied to closely correspond to the appearance of the background whatever the ambient conditions.

Preferably, the reflector means comprises at least one reflector pivotably mounted on the body and the amount of infra-red radiation reflected is varied by pivoting the reflector means in at least one plane.

By making the reflector pivotable, the part of the body's surroundings reflected can be controlled and hence the modified infra-red appearance can be varied.

In a particular preferred embodiment the reflector means is arranged to pivot in two mutually orthogonal planes. Thus the amount of infra-red radiation reflected can be varied to a greater extent than would be possible if the reflector means were to be pivotable in one plane only.

The reflector means could be pivoted hydraulically, electro-mechanically, pneumatically or even manually.

In some applications it may be preferable to vary the amount of infra-red radiation reflected, by obscuration of some or all the reflector means. Such obscuration could be achieved by removable screens or adjustable blinds.

Preferably, the reflector means reflects substantially only infra-red radiation. This is preferable because it would be undesirable in most applications to reflect visible radiation which would make the body's presence conspicuous to possibly hostile observers.

Advantageously, the reflector means is at least partly coated with a material which is substantially translucent to infra-red radiation but substantially opaque to visible radiation. The coating will therefore allow the use of reflector means with conventional reflective surfaces without making the body conspicuous.

Preferably, the material is applied over part of the reflector means to produce bands of alternately coated and non-coated surfaces. It is preferable to apply the material in this way to avoid making the reflector means visually conspicuous which would be the case if all of the surface was coated with the material for this would make the surface black. At a distance away from the reflector means the strips will become indistinct resulting in the reflector means appearing an inconspicuous grey.

Graphite is preferred as the coating material because it can be conveniently applied to most reflective surfaces.

By graphite it is meant the diamond form of graphite which being crystalline is durable.

In some embodiments of the invention it may be advantageous for the reflector to comprise an inflatable envelope having a reflective surface.

This would be advantageous where, because of the limitations of space, the reflector means needed to be stored until deployed. Such deployment could be rapidly achieved by inflating the envelopes with gas from compressed gas cylinders either automatically or manually.

The apparatus conveniently comprises means for determining the infra-red appearance of the body and the background, an output from said means being used to control the amount of the infra-red radiation reflected by the reflector means.

The means might be a single infra-red detector or a plurality of detectors. In the case where only one detector is used, it is necessary for it to be able to scan both the body and its surroundings. In the case of a plurality of detectors, separate detectors could be directed to provide signals representative of the infra-red appearance of the body or surroundings at distinct portions.

A specific embodiment of the invention will now be described with reference to the accompanying drawing in which: Figure 1 is a sketch showing a simplified temperature distribution of a ship; Figure 2 is a cross section through a reflector means in accordance with the invention; Figure 3 is a frontal elevation of the reflector means shown Figure 2; Figure 4 shows a reflector means attached to part of the ship; Figure 5 is a schematic diagram of an infra-red appearance control system in accordance with the invention; Figure 6 shows a ship viewed from a high altitude; and Figure 7 shows reflectors reflecting the sea and sky.

A typical temperature distribution of a ship is shown in Figure 1. The temperatures shown are relative to the ambient air temperature. The ship 1 has a hull 2 at a temperature of 2 0K above ambient and a superstructure 3 varying from 50K to 20 0K above ambient.

The various parts of the ship 1 will emit infra-red radiation according to their temperature and the well known Planck's Law. The ship 1 will therefore have a relatively intense infra-red appearance in comparison with the much cooler sky and sea.

An approaching missile with an infra-red detector called a FLIR (forward looking infra-red) of typical resolution will resolve detail 2 meters apart at a distance of 10 km from the ship 1. At this range, nothing within the 2 meters will be resolved, only the total power emission will be detected.

Mounted on the hull 2 and the superstructure 3 are reflector means one of which is shown in Figure 2. It comprises an aluminium plate 4 coated on its rear surface with the conventional paint layer 5 and on its front surface PVDF (polyvinylidene fluoride) itself coated with a high reflectivity, low emissivity silvering 7. Graphite stripes 8 are applied to the silvering 7 to make the reflector means visually less conspicuous. The graphite stripes 8 are more clearly shown in Figure 3.

In this case, the reflector means have dimensions of 0.1 x 0.2 meters and are attached at suitable places on the ship 1 by means of brackets 10 as shown in Figure 4. The brackets have actuators (not shown) which pivot the reflector means about pivot points 9. The dimension's of the reflectors can be varied according to requirements.

The orientation of the reflector means is controlled by a control system which is shown in Figure 5 including radiometers 11, 12 and 13. The radiometer 11 is a scanning radiometer arranged to have a high degree of freedom of movement so that it can scan a number of areas of the sea or sky and the radiometers 12 and 13 are fixed to view the sky and sea respectively. The outputs of the radiometers 11, 12, 13 are passed to a Sky/Sea IR (infra-red) Data Acquisition sub-system 14 which has the necessary logic to convert the data from the radiometers into a computer compatible form. The sub-system 14 also has memory for the storage of the data prior to outputting it to the next stage of the system.

Futher radiometers 15, 16 and 17 are arranged to view various parts of the ship 1 and their outputs are passed to a Ship IR Data Acquisition sub-system 18 which performs a similar function to the sub-system 14 previously described.

The outputs from the sub-systems 14 and 18 therefore represent the infra-red appearance of the sky, sea and ship. These outputs are passed to an IR Appearance Control Computer 19 to which is also input Threat Data. The Threat Data is provided by a radar system (not shown) which has identified a possibly hostile object which might be an aircraft or missile approaching the ship 1. This data will include the altitude, range and bearing of the object from which the IR Appearance Control Computer 19 derives the line of sight of the object.

From the derived line of sight, the background against which the ship 1 will be viewed is determined. The infra-red appearance of this background is determined by comparison with the data provided by sub-system 14. The way in which the ship's infra-red appearance is to be modified is then calculated with reference to the infra-red appearance of the ship 1 provided by the sub-system 18.

In the case of a low flying missile, the ship will have a background as shown in Figure 1, that is, the background will consist mostly of sky. For cloudless sky the infra-red appearance will correspond to its temperature which is about 230 0K at the horizon, colder above the horizon. Therefore the ship 1 will contrast greatly with the infra-red appearance of the sky, the ship 1 being relatively hot and hence bright in comparison with the sky which will be dark. In this case the reflector means 25 to 29 will be pivoted by the actuators 20 to 24 in response to signals from the IR Appearance Control Computer 19 to reflect the sky, as shown in Figure 4, in the direction of the approaching object to produce a modified infra-red appearance which to the missile will closely match that of the background.

In the case of a high flying missile the ship 1 will have as its background the sea as shown in Figure 6.

Although the sea is warmer than the sky, there will exist a large enough temperature difference between the sea and the ship 1 to give a large enough contrast between their infra-red appearances for the missile to direct itself at the ship 1. The reflector means in this case will be orientated to reflect the sea and partly sky as shown in Figure 7.

The amount of sky temperature reflected relative to that of the sea depends on the temperature of that part of the ship to which the reflectors are fixed. For reflectors fixed to the funnel, which is the hottest part of the ship, the amount of sky temperature reflected is greater than would be reflected by reflectors on the ships hull 2. The infra-red from the sky can be though of as "cooling" down the ship's infra-red appearance.

By so modifying the ship's infra-red appearance the missile will fail to detect the ship 1 or fail to associate the infra-red appearance with a ship and so fly in a different direction.

In some circumstances of course the infra-red appearance will have to "warmed up" for instance when the ship 1 has as its background land. In such a case the reflector means will be adjusted to reflect infra-red radiation from the land or from some other relatively warm source.

In alternative embodiments of the invention the radiometers could be replaced by one radiometer arranged to scan both the ship, sky and sea.

The reflector means could be provided as part of the structure of the ship but of course the reflector means would be fixed and any adjustment would have to be provided, if considered necessary, by shutters arranged to obscure the reflector means.

As an alternative to using radiometers thermometers and anenometers could be used to measure the prevailing condition and a typical infra-red appearance for the body under those conditions could be accessed from a memory storing a number of such appearances.

Claims

1. A method of modifying the infra-red appearance of a body comprising: reflecting infra-red radiation from the body's surroundings from infra-red reflector means provided on the body.

2. A method as claimed in claim 1 wherein the infra-red appearance of the body is modified so as to correspond at least in part to infra-red emissions from the body's background.

3. A method as claimed in claim 2 wherein said background is the background when the body is viewed along a particular line of sight.

4. A method as claimed in claim 3 wherein the line of sight in that of a detected threat.

5. A method of modifying the infra-red appearance of a body as claimed in any preceding claim comprising providing a plurality of movable reflector means on the body, determining the infra-red appearance of the surroundings, determining the infra-red emission from the body due to its temperature and moving the reflector means so as to reflect the infra-red emission of the surroundings such that when viewed from a distance, the infra-red appearance of the body comprises a mixture of its own emission due to the temperature and the reflected emissions of the surroundings.

6. A method as claimed in claim 5 comprising determining the infra-red appearance of the background; determining unmodified infra-red appearance of the body and positioning the reflector means so as to reflect infra-red radiation from the surroundings.

7. A method as claimed in claim 6 wherein the modified infra-red appearance comprises a mixture of the unmodified appearance and the reflected radiation.

8. A method substantially as herein described with reference to and as illustrated by Figures 1 to 7.

9. Apparatus for modifying the infra-red appearance of a body comprising: reflector means arranged on the body so as to reflect infra-red radiation from the body's surroundings.

10. Apparatus as claimed in claim 9 wherein the reflector means is arranged such that the reflected radiation modifies the body's infra-red appearance so as to correspond to the infra-red appearance of the body's background.

11. Apparatus as claimed in claims 9 or 10 wherein means are provided for varying the amount of infra-red radiation reflected.

12. Apparatus as claimed in claim 11 wherein the reflector means comprises at least one reflector pivotably mounted on the body.

13. Apparatus as claimed in claim 12 wherein the amount of infra-red radiation reflected is varied by pivoting the reflector means in two mutually orthogonal planes.

14. Apparatus as claimed in claim 13 wherein the amount of infra-red radiation reflected is varied by obscuration of some or all the reflector means.

15. Apparatus as claimed in any preceding claim wherein the reflector means reflects substantially only infra-red radiation.

16. Apparatus as claimed in claim 15 wherein the reflector means is at least partly coated with a material which is substantially translucent to infra-red radiation but substantially opaque to visible radiation.

17. Apparatus as claimed in claim 16 wherein the material is applied in bands.

18. Apparatus as claimed in claim 16 or 17 wherein the material is graphite.

19. Apparatus as claimed in any preceding claim wherein the reflector means comprise an inflatable envelope having a reflective surface.

20. Apparatus as claimed in any preceding claim comprising means for determining the infra-red appearance of the body and the background, output from said means being used to control the amount of infra-red radiation reflected by the reflector means.

21. Apparatus as claimed in any preceding claim wherein the body is a ship and the radiation is reflected from the sea and/or sky.

22. Apparatus substantially as herein described with reference to and as illustrated by Figures 1 to 7 of the accompanying drawings.

22. Apparatus substantially as herein described with reference to and as illustrated by Figures 1 to 7 of the drawings.

Amendments to the claims have been filed as follows CLAIMS

1. A method of modifying the infra-red appearance of a body comprising: determining the infra-red appearance of a selected region of a body's surroundings, and reflecting infra-red radiation from a selected region of the body's surroundings by controlling infra-red reflector means provided on the body.

2. A method as claimed in claim 1 wherein the infra-red appearance of the body is modified so as to correspond at least in part to infra-red emission from the body's background.

4. A method as claimed in claim 3 wherein the line of sight is that of a detected threat

6. A method as claimed in claim 5 comprising determining the infra-red appearance of the background; determining the unmodified infra-red appearance of the body and positioning the reflector means so as to reflect infra-red radiation from the surroundings.

9. Apparatus for modifying the infra-red appearance of a body comprising: means for determining the infra-red appearance of a region of a body's surroundings; and reflector means arranged on the body so as to reflect infra-red radiation from a selected region of the body's surroundings.

11. Apparatus as daimed in clairns 9 or 10 wherein means are provided for varying the amount of infra-red radiation reflected.

12. Apparatus as claimed in claim 11 wherein the reflector means comprises at least one reflector pivotally mounted on the body.

14 Apparatus as claimed in claim 13 wherein the amount of infra-red radiation reflected is varied by obscuration of some or all of the reflector means.

16. Apparatus as daimed in claim 15 wherein the reflector means is at least partly coated with a material which is substantially translucent to infra-red radiation but substantially opaque to visible radiation.

17. Apparatus as claimed in claim 16 wherein the material is applied in bands.

18. Apparatus as claimed in claim 16 or 17 wherein the material is graphite.