WO2006064261A1

WO2006064261A1 - Imaging system and method

Info

Publication number: WO2006064261A1
Application number: PCT/GB2005/004879
Authority: WO
Inventors: Jeremy Lynn Hinton
Original assignee: Bae Systems Plc
Priority date: 2004-12-17
Filing date: 2005-12-16
Publication date: 2006-06-22
Also published as: GB0427779D0

Abstract

The invention relates to a photographic imaging system in which data relating to typical features or objects that might appear in a landscape (e.g. buildings) are entered into a database for comparison with such features or objects as may be photographed. Comparison leads to cancellation of those features or objects from a resultant image, thereby retaining only data relating to features or objects which are not typical or which are moving.

Description

IMAGING SYSTEM AND METHOD

This invention is concerned with imaging techniques and is particularly concerned with a method of detecting and recording of images of objects, and thus identifying their location, that are either unusual in a particular environment or whose position has unexpectedly altered in an environment.

Range gating image location techniques are well known for providing a technique which finds particular, though not exclusive use in the military field for the detection of hostile military targets by aerial overflying either by manned or unmanned aircraft.

Hitherto, range gating techniques have used active coherent electromagnetic sources such as lasers which can be used to produce a dispersed radiation that can be used to reflect energy back to a camera (typically a CCD based on CMOS technology). Such systems are disclosed for example in EP 0363735, EP 0468175 and US Patents 4862257, 4964721 and 4967270; these systems can be regarded as active systems because they rely upon an active energy source to illuminate a target. However, with continually increasing sophistication in modern stealth techniques to provide both defensive and concealment capability, military equipment can now incorporate stealth technology to counter detection by such methods.

The present invention, on the other hand, relies on passive detection of objects such as military targets, in so far as the invention is designed instead to sense energy which is reflected or radiated from a target by natural light or the simply by its mere presence in an area or environment of interest, be that open terrain, an urban environment or elsewhere. The invention is based upon the principle that the object being sought will have a different physical profile and other characteristics that can differentiate it from its surroundings. By way of example may be instanced tanks, armoured cars, missile batteries, VTOL aircraft or artillery pieces which will have a very different profile and characteristics from buildings when located in an urban environment, whether or not viewed in the optical range of the spectrum and will produce a different signature therefrom when viewed in either the optical or the infrared range of the spectrum. Aerial photography has been used previously to this end, both in the optical and infrared portions of the electromagnetic spectrum. However the problem with such an approach is to identify objects of interest from the surrounding environment. This is particularly problematic in landscapes which can be categorised as urban or in landscapes where trees can conceal the presence of a hostile vehicle or missile battery for example. Though, such objects may have different proportions and thermal emissivity characteristics from their surroundings, these are not immediately apparent from aerial photographs Similarly, unless heavily camouflaged, such military equipment also will have a very different signature from surrounding terrain in a rural or desert environment. However, such a signature will not necessarily be immediately apparent without some indication as to the contour, shape and size of such an object. This is not a problem that has a ready or simple solution. Instead, the applicants have developed another approach, and, rather than seeking to identify such objects directly, they have developed the present invention based on an opposite approach, which is namely to eliminate from any imagery, those objects that can reasonably be expected to be present in an environment. The present invention seeks to achieve this by providing a system which passively records or includes a record of typical characteristics of an environment and combines recorded image data to enable features such as dimensions of objects to provide or be compared with a database of such information so that, against the information provided by such a database, objects that are present in a similar environment and do not match criteria established by the database can be identified. Such a database can be constructed from an actual record of the environment and terrain in question or can be constructed from a hypothetical knowledge of typical characteristics. For example, in open rural country such as is found in temperate zones, expectation would be that trees having a height say of above 6 metres and rising to higher than 10 metres would be present, with buildings in rural communities such as farms, villages etc. rising to about 8 - 10 metres. In terrain such as typifies warmer climates, such as throughout the Middle East, flat roofed buildings can be easily modelled also and the characteristics thereof similarly identified.

Any or all such criteria are then entered into the database and, in any subsequent analysis carried out by a method according to the present invention, features in a landscape that match those stored in a database can then be eliminated from such a survey as features of minimal interest.

Accordingly, the present invention provides a passive method of detecting the presence of an object by aerial imaging where the object has specific characteristics relative to its terrain, the method comprising digitally mapping and recording data relating to the topography of the terrain and objects typically to be found in that terrain when observed from any specific altitude above that terrain, photographically acquiring a first digital image of that terrain in which any such object may be located, digitally storing said first image, photographically acquiring a second digital image of said terrain from a position in close proximity to that at which the first image is acquired, and digitally comparing the first image with the second image to provide a composite image, comparing the composite image with said data to identify any object that does not correspond to typical objects to be found in that terrain.

In carrying out a method according to the present invention, the step of digitally mapping and recording data preferably comprises creating a first set of data relating to said topography and objects as observed from a first aerial position, digitally creating a second set of data relating thereto as observed from a second aerial position adjacent to said first position, and correlating the first set of data with the second set of data to produce a database thereof.

In carrying out a method according to the present invention, the step of digitally mapping and recording data to produce said database may be repeated n times to produce a library of such databases. Such mapping may be carried out while the aircraft is moving at a constant airspeed. If the photographic images are then acquired at regular intervals, then successive images can be compared to isolate and identify objects that appear in that terrain. - A -

The steps of digitally mapping an environment and of photographically acquiring images can be are carried out optically during daylight and can be replaced or enhanced by photographically acquiring images are carried out in the infrared range of the spectrum. The step of digitally mapping and recording data relating to the topography of a terrain and of objects typically to be found in such an environment may be carried out to include data relating to the appearance of objects when viewed at an acute angle relative to the horizontal

The present invention further provides a passive method of detecting the presence of an object by aerial imaging where the object has specific characteristics relative to its terrain, the method comprising digitally creating a first set of data defining the topography of that terrain and of objects typically to be found in that terrain when observed from altitude above that terrain, creating from the first set of data a plurality of subsets of data representative of said terrain as seen from one or more defined altitudes above the terrain and of any such object as may typically be found therein; digitally storing said first set of data, photographically acquiring a digitised image of said environment from a known altitude; and digitally comparing the digitised image with an appropriate selected subset of the first set of data to provide a resultant image, in which all data in the digitised image that corresponds to data from the selected subset is eliminated so that only data relating to any untypical object in the terrain remains in the resultant image.

The present invention further provides a range gating system for aerial detection of any object in a terrain, the system comprising a camera arranged to be mounted on an aircraft, processor means for processing digitised data received from the camera, memory means for storing said digitised data, database means storing a database of data which defines a terrain to be overflown by an aircraft fitted with the system and data which defines characteristics of objects that can be expected to be present in that terrain, the database means being connected to the processor means, comparator means connectθd to the database means and to the memory means for comparing the digitised data with the database of data, and means for cancelling the digitised data where this corresponds to data stored in the database, to provide a resultant set of data. The aircraft will typically be an unmanned guided aircraft and may be fitted with target acquisition systems linked to the range gating system of the invention so that, for example, artillery can be directed at any target object.

There now follows a detailed description, which is to be read with reference to the accompanying drawings, of a method according to one embodiment of the present invention and of a system for implementing that method. It is to be clearly understood that the selected embodiments illustrate the invention by way of example only.

In the accompanying drawings:-

Figure 1 is a diagrammatic and schematic illustration of a system according to the present invention;

Figure 2 is a diagrammatic illustration of the manner in which the system of Figure 1 might be used according to one embodiment of the present invention;

Figure 3 is an aerial photograph of a first view of an urban environment such as that in which the present invention might be employed;

Figure 4 is an aerial photograph of a second view of the same urban environment as is shown in Figure 3 but taken approximately half a second later;

Figure 4A is a map showing the correspondence between the photographs of Figures 3 and 4 with all standard details and features removed in accordance with a method according to the present invention.

Reference is firstly made to Figure 1 , which shows functionally how a system according to the present invention operates in the field when mounted in an aircraft indicated schematically by a dashed line 10. As already stated above, the system is passive and based upon the elimination of unnecessary information from consideration. To this end, the system can be initialised in several ways, based upon information that is available. In one embodiment, the system comprises a database that can be digitally created as a library of data that relates to characteristics of features such as buildings, or natural features such as trees, that are likely to be found in terrain such as that over which the aircraft is traversing.

The characteristics and/or features of such a terrain can be acquired by actual overflying by an aircraft and conversion into digital format for storage in the database, with detail such as the characteristics of buildings, trees and other major features separately identified and logged as to their characteristics and locations.

Alternatively, where the possibility of overflying to create such a database is not sensible due to the potential hostility of the environment, the generality of the terrain can be mapped from contour maps and features such as buildings as may be expected to be present in that terrain added to the database for reference purposes as hereinafter described.

The characteristics of buildings may include typical dimensions of such buildings such as height and surface area as seen from the air together with data relating to thermal imaging of such buildings, and these may be created in the form of simple plans of such buildings. The database must also make provision for relating such dimensions and characteristics to the altitude of the aircraft carrying the equipment. Where the camera is forward ranging, or in other words is directed or can be directed forwardly, rearwardly or to the side of the aircraft to capture images of terrain ahead, to the rear or to the side of the aircraft, the database will also include programming for interpreting features or characteristics as viewed at various angles depending upon the attitude of the onboard camera and the altitude of the aircraft. Signals received from the ground, either as optical signals, infrared signals or the like are received by a camera on board the aircraft, the camera comprising one of more charge coupled devices 12 (preferably CCDs typically based on CMOS technology) which is/are connected, via a comparator/processor 14 to a memory 16 in which digital signals received from the camera are stored. The processor is adapted to convert the signals received from the camera into a format recognised by and compatible with the system on board the aircraft. These signals are then delivered to the comparator to which a database 18 is also coupled. The database, in the simplθst form of embodiment of the invention, simply includes parameters relating to features that are expected to be found within a scanned terrain such as buildings and trees. The comparator 14 then compares the data from the database 18 with that received via the camera 12 from the memory 16 and where the data from memory matches that from the database, then that data is zeroed by the processor 14 so that the only data that remains is that which relates to objects that have been scanned in the overflown terrain and are deemed by the system not to have matched criteria established by the database. In other words, say for observing an urban environment, the system simply eliminates, for example, any objects that it senses as substantially square or rectangular, such as buildings, because their parameters fall within maxima and minima stored within the database. These parameters may also include factors such as the optical reflectivity or the thermal emission properties of typical objects such as buildings. The resultant data accumulated by the system is then compiled and stored in a further memory 20 and can be fed to a HUD unit 22 in the aircraft or to a separate monitor, and via the aircraft's own communications system can be transmitted to ground control for further processing as necessary.

The manner of operation of a system according to the present invention in carrying out a method according to the invention can be seen from the example shown in Figure 2. The method requires overflying of a terrain by an aircraft 10. The aircraft carries an onboard camera as described with reference to Figure 1 and which is directed vertically downwards and digitally maps and records data relating to the topography of the terrain and objects typically to be found in that terrain when observed from any specific altitude above that terrain. In Figure 2 is shown a diagrammatic landscape in which trees are shown and these are assumed to be of a certain height and closely adjacent those trees are shown a plurality of armoured vehicles 30. For the purposes of operating the system and for carrying out the method, the trees are assumed to be of a known height range. However, the vehicles partially concealed by the trees are outside that height range. Thus, when an overflight occurs, the onboard camera captures images of the trees and the vehicles. The camera photographically acquires a first digital image of that terrain and of the objects, and then the image is digitally stored. As the aircraft moves across the terrain, the camera then photographically acquires a second digital image of that same terrain from a position in close proximity to that at which the first image is acquired. This depends upon the speed of operation of the camera and the speed of the aircraft, but optimally, the two images are taken in close proximity to one another so that a stereo image of the terrain can be compiled.

The first image is compared digitally with the second image to provide the composite image, and the composite image is compared with data compiled and stored in the database to identify any object such as the armoured vehicles shown in the drawings that does not correspond to typical objects to be found in that terrain. It will be readily appreciated that if an object is moving while two such images are taken in quick succession, then the movement of the object can be detected as easily as its actual presence can be recorded.

In Figures 3 and 4, including Figure 4A, are shown two images of an urban terrain which have been taken in close time-related proximity to one another. The system used had been set up to take into account the urbanisation of the terrain in so far as it had parameters relating to the typical sizes of houses and other buildings had been incorporated into the database. Figure 3 shows the initial image and Figure 4 shows a similar image taken very quickly thereafter. In Figure 4, towards the bottom right of the image, can be seen an encircled vehicle that has moved in the time elapsed between the two images being taken. The two images were then processed by the system and the resultant differential image can be seen in Figure 4A where the system has identified a vehicle only as having characteristics which are unusual in that terrain.

The manner in which images can be taken is also further exemplified by Figures 3 and 4 which show the images as being taken to one side of the aircraft and not simply from vertically above a terrain.

It will be appreciated from the above description, that though the illustrative embodiments of the invention have been described with reference to the use of optical cameras, the invention can be as readily implemented using the infrared portion of the spectrum. Thθ manner in which the differential image is recorded can of course be varied. It can for example be recorded using a co-ordinate system to pinpoint the location of any objects that are revealed by comparison of the two images, or it can be recorded as photographic image or in any other format that is required.

Claims

1. A passive method of detecting the presence of an object by aerial imaging where the object has specific characteristics relative to its terrain, the method comprising digitally mapping and recording data relating to the topography of the terrain and objects typically to be found in that terrain when observed from any specific altitude above that terrain, photographically acquiring a first digital image of that terrain in which any such object may be located, digitally storing said first image, photographically acquiring a second digital image of said terrain from a position in close proximity to that at which the first image is acquired, and digitally comparing the first image with the second image to provide a composite image, comparing the composite image with said data to identify any object that does not correspond to typical objects to be found in that terrain.

2. A method according to claim 1 wherein the step of digitally mapping and recording data comprises creating a first set of data relating to said topography and objects as observed from a first aerial position, digitally creating a second set of data relating thereto as observed form a second aerial position adjacent to said first position, and correlating the first set of data with the second set of data to produce a database thereof.

3. A method according to claim 2 wherein the step of digitally mapping and recording data to produce said database is repeated n times to produce a library of such databases.

4. A method according to any one of claims 1 to 3 wherein the steps of digitally mapping an environment and of photographically acquiring images are carried out optically.

5. A method according to any one of claims 1 to 4 wherein the steps of digitally mapping an environment and of photographically acquiring images are carried out in the infrared range of the spectrum.

6. A method according to any one of claims 1 to 5 wherein the step of digitally mapping and recording data relating to topography and objects typically to be found in an environment when observed relative to any specific altitude above that environment is effected by geometric interpolation.

7. A passive method of detecting the presence of an object by aerial imaging where the object has specific characteristics relative to its terrain, the method comprising digitally creating a first set of data defining the topography of that terrain and of objects typically to be found in that terrain when observed from altitude above that terrain, creating from the first set of data a plurality of subsets of data representative of said terrain as seen from one or more defined altitudes above the terrain and of any such object as may typically be found therein; digitally storing said first set of data, photographically acquiring a digitised image of said environment from a known altitude; and digitally comparing the digitised image with an appropriate selected subset of the first set of data to provide a resultant image, in which all data in the digitised image that corresponds to data from the selected subset is eliminated so that only data relating to any untypical object in the terrain remains in the resultant image.

8. A passive method of detecting the presence of an object by aerial imaging substantially as hereinbefore described with reference to the accompanying drawings.

9. A range gating system for aerial detection of any object in a terrain, the system comprising a camera arranged to be mounted on an aircraft, processor means for digitally processing data received from the camera, memory means for storing said digitised data, database means storing a database of data which defines a terrain to be overflown by an aircraft fitted with the system and data which defines characteristics of objects that can be expected to be present in that terrain, the database means being connected to the processor means, comparator means connected to the database means and to the memory means for comparing the digitised data with the database of data, and means for cancelling the digitised data where this corresponds to data stored in the database, to provide a resultant set of data.

10. A range gating system for aerial detection of any object in a terrain substantially as hereinbefore described with reference to the accompanying drawings.