WO1995014948A1

WO1995014948A1 - Infrared scanner apparatus

Info

Publication number: WO1995014948A1
Application number: PCT/AU1994/000734
Authority: WO
Inventors: Raymond Peter Johnson; William Frederick Woods; Shaun Garner
Original assignee: The Commonwealth Of Australia
Priority date: 1993-11-26
Filing date: 1994-11-25
Publication date: 1995-06-01

Abstract

An electromagnetic scanner, particularly which uses a mechanical scanning arrangement comprising a wedge (10) rotating in front of and about the radiation axis (12) of a radiation focusing arrangement, lens (13), producing a conical scan. Translation or rotation of the apparatus containing the rotating wedge (10) and lens (13) produces a two-dimensional scan of the radiation scene. Further electronic processing of the detector signal providing digital information (Figs. 3, 4 and 5) which is compiled into a viewable image by associating successive digital data values with a row and column position of a frame store. The radiation image is stored in a frame store during compilation and updated with each scan of the rotating wedge (10). Further image stabilization techniques are possible.

Description

INFRARED SCANNER APPARATUS

This invention relates to electromagnetic (EM) radiation scanners and in particular to imaging and mapping scanners.

PRIOR ART

There exist a great variety of imaging devices a small proportion of which are of the scanning type. Typically scanners comprise a radiation focusing means and a detector both of which are designed to operate within a selected band of the electromagnetic radiation spectrum.

Scanners are passive devices designed to view a portion of a scene comprising an object or view, and focus that portion on to a detector which transduces the radiation collected into an electrical signal representative of that portion of the image. A variety of electronic means are available to process many transduced signals and construct from them an image of the scene which is unique to the radiation spectrum at which the detector is designed to operate.

According to the invention imaging scanners described in this specification provide sufficient resolution at low cost so as to be usable in many radiation bands for equally many applications such as for example surveillance, remote sensing and specialist applications such as power line aerial surveillance.

Furthermore, when the information gathered by the scanner described in this specification is combined with geographic co-ordinate information the scanner becomes a mapping instrument. Imaging devices which generate sequential frames of information such as television or continuous film cameras are not ideal for mapping applications because any one recorded frame represents an area rather than a point on the surface of the earth. According to the invention the scanner described in this specification can be optimised for operation in, for example, the ultraviolet, visible, near and long wave infrared portions of the EM spectrum. Changing the characteristics of selected elements of the scanner for the particular portion of the spectrum of interest does not require a change to the basic scanning mechanism whereas prior art scanners would require a completely new mechanism.

This specification uses a military example of an imaging scanner application which is optimised for the infrared portion of the EM spectrum. However, it will be realised by those skilled in the art that the concepts described are applicable to other ranges of the EM spectrum and the physical arrangements described only need minor adjustments in their arrangement or how they are used to make them useful in other scanning applications as well as mapping applications.

The problems of the prior art are described in particular detail with respect to a military application but reference is also made to problems common to related civilian and commercial applications both in regard to the particular EM range used and the scanning techniques used for imaging and mapping applications.

There already exist a large variety of imaging infrared scanners in the medium-range weapon seekers field and parallel fields of surveillance (for large area or long range) .

In particular, with regards medium range seeker applications one such seeker uses a small array of Infrared (IR) detectors operating in the 8-12 micro-metre waveband, typically brought into operation after a human operator has identified a potential target. This arrangement requires relatively high scan rates (eg 30Hz) to provide flicker free images for comfortable observation by the human operator. Typically, the field-of-view is small (eg 3° x 3°) and the preferred field-of-regard is provided by slewing the imager in a high quality gimbal arrangement. Thus in this example a small field-of-view is enlarged to include a larger field-of-regard using a precision mechanical gimbal arrangement.

In a further scanner arrangement applicable to medium-range seekers a field-of-view of (eg 15° x 11.5°) and a scan rate (eg 30Hz) is provided using a 120 element linear array used in a push-broom mode with electronic serialisation in one axis and typically a nodding mirror scan in the other axis. The typical means to widen the field-of-regard is to increase the scan angle with a precision mechanical gimbal arrangement.

In yet a further scanner arrangement again applicable to medium-range seekers, Sprite detector technology as it is known, uses a nodding mirror scan in combination with a rotating disc containing reflecting elements to provide the second scan axis. This arrangement provides a narrow field of view, which is widened by using a mechanical gimbal arrangement to extend, in particular, the horizontal field- of-view in combination with electronic scanning and memory storage techniques.

In other application areas IR detectors use a wide variety of array and single IR detector arrangements.

In one example, two-dimensional staring arrays comprise an arrangement in which the whole of the focal plane of an optical system is covered by detectors sensing all parts of the radiation field in parallel. These types of array have high sensitivity and mechanical simplicity where the required field-of-view may only be one or two degrees and where signal integration times must be short i.e. well suited to anti¬ aircraft applications. However, enlarging the field-of-view will require a very much more complicated or less efficient optical system and enlarged array size and the only practical approach to enlarging the field-of-regard is to provide a mechanical gimbal arrangement. It is also known in particular in a military environment that staring array seekers are designed to continuously receive radiation energy from all parts of the scene of a combat environment and some counter measures are likely to damage parts of the array or result in a distortion of the image provided by the equipment.

In a further example, a push broom scanning array uses a single axis long linear array which in a mid-range scanning application provides a potentially wide horizontal field-of- view when used in combination with a horizontal mechanical gimbal arrangement, while a relatively short array provides a typically smaller vertical field-of-view. Such an arrangement is however, susceptible to damage due to some particular counter measures. For example, the serialisation mechanism of the array may be damaged such as to completely disable the detector. Even the failure of a single detector will distort the image by not producing one of the scan lines of the displayed image.

Thus the invention in its basic form or enhanced form should provide images largely free or a minimisation of many of the problems of the prior art, such as, the effects of aberrations, stray radiation due to inadequate cold shielding, the requirement for complex anamorphic aspheric mirrors, image narcissus, and banding and zoning due to detector or scan mismatching. Some of these deficiencies in conventional imagers, while tolerable to a human viewer, cause severe degradation to the efficiency of automatic target recognisers. To address at least some of the issues and problems of current Imaging Infrared (IIR) scanners it was considered that particular attention to mechanical scanning techniques and sensor selection was crucial to providing a low cost, practical and effective device particularly suited to the military application to be described but also the many commercial applications such a device would make possible.

A radiation image may be formed by mechanically scanning a field-of-view in a minimum of two axes using either a single radiation detector or an array of radiation detectors. This approach offers relatively low sensitivity since the detector spends only a very short time sampling the radiation from portions of the field-of-view, but has the advantage of reducing the susceptibility of the sensor/s to counter measures and increases the overall reliability of the device since redundancy of the sensor can be built-in at very low incremental cost.

As discussed previously mechanical scanning can be complicated by using multiple axis precision built mechanical gimbal arrangements or alternatively various quality and cost combinations of nodding mirrors and spinning multifaceted reflectors.

The mechanical scanning technique of this invention comprises an example of the category of scanners which use an asymetric element which rotates about the radiation axis of the radiation collection system to produce a variant of an annular scan as opposed to focusing and reflecting elements translating or rotating to produce linear scans.

In particular, the scanning mechanism of this invention comprises a radiation transmissive wedge rotating in front of a primary radiation focusing means and about the radiation axis of the primary radiation focusing arrangement to produce a conical scan. In the embodiment described an advantage of this scanning mechanism comprises the low complexity of the spherical refracting components since: the detector is on the primary radiation axis which minimises the effects of aberrations; the focusing elements are mechanically separate from the scanning device so as to isolate the system focus from the scanning device; and the apparatus can be produced using consistent cylindrical symmetry about the radiation axis simplifying manufacture and tolerance requirements. A scan of a scene without translation provides a conical scan which typically can be translated into a circular scan in a frame store which can be made to represent an image of the radiation scene. A rotating wedge radiation transmission element produces a conical scan of the radiation scene.

BRIEF DESCRIPTION OF THE INVENTION

In a preferred feature of the invention a radiation scanning apparatus for producing a radiation image comprising:

at least one radiation detector means for providing a signal representative of a portion of a radiation scene detected by said detector,

a primary radiation focusing means for focusing incoming radiation on said at least one radiation detector means having a radiation axis,

a secondary radiation element having a radiation axis and comprising at least two planar surfaces forming a wedge shape providing a predetermined field-of-view of said radiation scene which is positioned between said scene and said primary focusing means and such that said radiation axis of said primary radiation focusing means is coincident with said radiation axis of said secondary radiation element wherein said secondary radiation element is rotatable about said coincident radiation axes to focus a conical scan of a predetermined field-of-view of said radiation scene on to said at least one radiation detector means, and

lateral translation means for laterally translating said radiation scanning apparatus across said radiation scene, whereby

said translated conical scan detected by said detector provides a two-dimensional representation of said radiation scene.

In yet a further preferred feature of the invention a radiation scanning apparatus has a rotation means for rotating said radiation scanning apparatus about an axis orthogonal to said coincident radiation axes across a predetermined field-of-view of said radiation scene, whereby

said rotated conical scan detected by said detector means provides a two-dimensional representation of said radiation scene.

In yet a further preferred feature of the invention a radiation scanning apparatus has a secondary scanning mechanism having a rotating mirror located in front of said secondary radiation element and rotatable, about an axis orthogonal to said radiation axis and arranged to reflect a predetermined field-of-view of said radiation scene into said radiation scanning apparatus.

In yet a further preferred feature of the invention a method of generating a scanned radiation image comprising the steps of:

(a) providing a radiation scanning apparatus as described; (b) assigning to each position in said frame store a digital signal value corresponding to one or more of the nearest samples of said radiation scene as said radiation scanning apparatus traces a descending semicircular arc over said radiation scene and which is representative of a portion of a radiation scene, and

(c) laterally translating or rotating said radiation scanning apparatus orthogonal to said radiation axis at a rate which matches the adjacency of successive horizontal locations in said frame store of a respective row of said radiation image stored in said frame store.

BRIEF DESCRIPTION OF THE FIGURES

In order that the invention may be more clearly understood and readily carried into effect a preferred form of the optical scanning apparatus will now be described by way of example only with reference to the accompanying figures in which:-

Fig. 1 depicts a diagrammatic representation of the scanning apparatus;

Fig. 2 depicts a mechanical representation o*f the scanning apparatus;

Figs. 3a, 3b and 3c depict a pictorial representation of a scanned pixel storage technique;

Fig. 4 depicts a more detailed pictorial representation of the scanned pixel storage techniques during a slow linear scan of the field-of-view;

Fig. 5 depicts a time lapsed version of the technique in Fig. 4; Fig. 6 depicts a functional block diagram of the apparatus;

Fig. 7 depicts a panoramic scanning arrangement; and

Fig. 8 depicts an example of an aerial mapping procedure.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The invention will be described with particular details relevant to a configuration suitable for use in gliding weapons and Remotely Piloted Vehicles. However, it will be clear to the person skilled in the art that the invention is useful in a large variety of other applications having the common requirement of a typically low cost image scanning mechanism and method of image creation. A mapping application will also be described where the scanning apparatus output is combined with geographic co-ordinate information as it is stored for later processing, viewing and analysis or on the fly imaging or mapping as is sometimes required.

Directional guidance apparatus of varying sophistication comprises a major portion of the cost of a gliding weapon and typically the damaging munitions are a relatively inexpensive part of the cost of the weapon.

Imaging guidance apparatus provide a means by which the weapon can discriminate between the actual target and decoys readily used by the target. An imaging infrared seeker apparatus is designed to provide assistance to the controller of the weapon to discriminate between for example sea going vessels and high flux infrared and laser point sources used as decoys by prospective targets as well as providing an image suitable for automatic or human intervention guidance of the weapon from its arrival in the target area until it strikes the target. Since a target may move in an unpredictable fashion during the flight time, the field-of-view provided for further processing must initially, after arrival in the target area, be as wide as possible, typically kilometres across. After initial acquisition of the target the mid-course guidance system (typically having a field-of-view which is not as wide) can improve the directionality of the weapon.

However, to accommodate directionality errors a wider and generally larger area of scan can overcome these types of errors by allowing for the continuous re-calculation of the location of the target and correction of the direction of the weapon.

The embodiment describes an imaging infrared seeker apparatus but whenever the term optical is used in this description it will be apparent to the person skilled in the art that equivalent elements in the ultraviolet and visible electromagnetic radiation ranges are able to be used with a suitable scanner implementation and its application.

Fig. 1 depicts the basic elements of a scanning apparatus which provides a conical scan of an object emitting or reflecting electromagnetic energy (not shown but nominally located off to the left of the page) . A conical scan of the object is achieved with a high speed circular motion of a secondary optical element, wedge 10, which is located with respect to two criteria. The first is that the wedge is located forward of the primary optical element a simple doublet lens 13. The second is that the axis of rotation (in this example shown as 11) of the wedge 10, corresponds to the primary optical axis 12 of the primary optical element 13, which focuses incoming radiation onto a radiation detector 14. All optical elements are coated to minimise surface reflections over the desired radiation passband. A scan of the radiation scene is achieved when a linear translation or rotation is imparted to the scanning apparatus. A rotational translation of the scanning apparatus is achievable in a number of ways . In the example of a gliding weapon to which the device is attached, the gliding direction can be changed so that the primary optical focus direction is moved both lef and right (zero gimbal arrangement), or a gimbal may provide this movement independent of the weapon's trajectory (single gimbal arrangement), or two gimbals may provide not only left and right rotation but upwards and downward rotation in a dual gimbal arrangement.

If the scanning apparatus is used in fixed or mobile equipment a rotational scan can also be provided using a flapping mirror located forward of the secondary optical element.

A rotation of the apparatus increases the field-of-view and is shown schematically as arrowed line 15 in Fig. 1.

As will be described later in the specification, the portions of the radiation image captured by the detector 14 are transformed into rectilinear co-ordinates as almost always is required for a display device or is further processed so as to enhance the radiation image. The transformation into rectilinear co-ordinates is performed either at the time so that immediate image information is available or the information is collected, stored and processed later.

Typically in a munitions application real time processing is necessary, but in a commercial application image processing can be delayed. To achieve real time results the signal from the detector 14 is input to a frame store or, subsequent to display, the signal either in raw form or in frame store form can be sent to a storage means for later analysis or replay. Appropriate processing of the raw form of radiation image data can provide increased resolution of the image in comparison to an image or mapping which is processed on the fly, because there is sufficient time to implement more detailed data analysis. However, as processing speed and algorithms associated with image signal processing improve the resolution of the image provided in real time will improve.

A difficult problem faced by most imaging infrared seekers in a vibration-prone environment, is the reduction of sightline jitter to less than one frame store location dimensions which is dependent on the combination of detector size and the focal length of the radiation focusing elements. This problem is prominent in prior art seeker apparatus because prior seekers rely on mirrors supported in bearings and any angular play in the bearings results in the sightline being deviated by twice the mirror deviation. Similar problems befall most scanning apparatus used on a mobile platform.

In order to reduce this effect the scanner arrangement of this invention uses a refracting wedge, which is insensitive to small angular movements. This is achieved by ensuring that the optical radiation path through the wedge is coincident with the central axis of the bearings within which the wedge rotates. Furthermore, with this arrangement different wedge drive means are possible, however, a wedge drive motor which also has its axis coincident with the optical path is preferable.

The only moving part in the scanner is the rotating optical wedge assembly 10 at the front of the arrangement as shown in Fig. 2.

A compact annular brushless motor 16 drives the wedge 10 which is supported by two ball races 17 and 18. Both motor and ball races must allow the optical radiation path 12 to pass along their coincident axes. This is achieved by using an annular electric motor and large diameter bearings. An alternative embodiment may use an off axis electric motor and a belt-driven wedge.

Other infrared detector embodiments, may have 0.5 to 1 milliradian resolution which are sensitive to 8-12 micron radiation, while yet another embodiment may use a small detector or a detector array to improve resolution as well as increasing detector signal generation speed, sensitivity and detector redundancy in the case of a detector array.

Fig. 2 depicts in particular a scanner apparatus which consists of a 50mm aperture F/l optical system with a joule- thompson cooled mercury cadmium telluride photoconductive detector 14. The embodiment depicted has a single infrared detector with 2 milliradian resolution and is sensitive to 3- 5 micron wavelength electromagnetic radiation.

A magnetic or optical pick-up 19 provides picture synchronisation information by detecting the passage of optical or magnetic markers 20 on a disc 21 attached to the rotating component. Pixel sampling pulses are derived directly or indirectly by spacing the markers in an appropriate manner.

The low-speed linear scan may be readily provided by mounting the whole scanner in a one-axis gimbal 22, or by utilising the gimbal typically required for stabilisation. Alternatively, strapdown operation without gimbals (zero gimbal arrangement) is feasible by using vehicle body motion to provide the linear component as previously described.

In other embodiments, the horizontal scan may be implemented by a nodding mirror external of the wedge. Fig. 7 depicts a further scanning mechanism consisting of a mirror 23 angled at approximately 45 degrees to the primary optical axis 11 and rotates 24 in the same direction as the rotating prism 10. This enables the sensor to have a panoramic field of view of up to 360 degrees in one axis.

For example, the scanning mechanism may be oriented vertically with a field of view of 10 degrees. This enables the secondary scanning mechanism to survey a 10 degree swath about the entire horizon of 360 degrees on a repeating basis, or alternatively to selectively rotate over a smaller portion of the horizon of particular interest.

Typically, other infrared imaging apparatus such as those which use a mirror arrangement cause a rotation of the scanned image, which has to be corrected by a further complex prism mechanism. The invention exhibits rotational symmetry, therefore, the problem of image rotation is very simply correctable by advancing or retarding the scanner sampling pulses electronically or by repositioning the information in the frame store and leaving the sample rate the same.

The technique of obtaining a rectilinear picture is illustrated in Figs. 3a, 3b, 3c, 4 and 5. The sensor field of view is divided into rectilinear rows and columns of nominally square pixels of dimensions approximately equal to the spatial resolution of the detector Fig 3a. However, as depicted in Figs. 4 and 5 the scanned pixels are of substantially circular form which is largely a result of the shape of the detector and the scanner optics .

Each pixel of the image corresponds to an address in a frame store. As the scan advances on a descending semicircular arc, the radiation field as represented by a detector signal output is sampled at approximately 100kHz. As the scan crosses each horizontal row a detector signal is given a digital value by an analog to digital converter. This implies that samples are taken non-uniformly in time about the periphery of the scanned circle. Alternately samples may be taken uniformly and redundant data discarded. The digitised sample of a portion of the radiation scene viewed at that time is associated with the horizontally closest frame store location in that row and stored in that location in the frame store. Alternatively, the value stored in a frame store may be a weighted average of several adjacent sampled detector signal values or a weighted average of a number of sample values in the vicinity of a predetermined frame store location. In this embodiment the height of the view created by the scan is approximately 10° of the field- of-view. However, the general rule is that the height of the view is twice the deviation angle of the wedge.

The horizontal scan rate can be controlled so that the scanner has moved by approximately one frame store location when the next similar semicircular scan is being performed. Ideally, a complete image will be built up in the frame store without overlapping or missing frame store locations. The ascending semicircular arcs may be used to construct a second image of the field, time-delayed slightly from the first or may be used to overwrite the current image. The two images may be presented sequentially or combined for presentation to a target recognition system or for viewing by an operator.

As shown in Fig. 4 each frame store location or pixel represents the sensor signal output selected one pixel apart vertically and as the wedge rotates in the direction 30 there is also a slow horizontal scan (rotation) in the direction 40, which provides pixels representative of the sensor signal output to the right of the first circular scan. Fig. 5 depicts the build up of pixels after the start of the sixth scan assuming that the horizontal scan rate is uniform and coordinated as best it can be with the frame store/pixel locations required to build up the image.

Fig. 6 depicts a functional block diagram of the scanner head 50; signal processor 60 and monitor 70. The wedge 10 is spun by the motor 16 in front of the focusing means 13 which directs the incoming radiation onto detector 14. In this example a pre-amplifier 52 is used to boost the detector signals. The signal output from the detector is representative of a portion of the radiation scene and is provided to an Analog to Digital converter 62 which provides a digital representation of the radiation scene which is associated with a location/pixel in a frame store 64. The controller 66 controls the speed of rotation of the wedge by controlling the speed of the motor 16 and synchronises the rate at which the detector is sampled with the analog to digital converter 62 which is entered into the frame store 64. In one application the radiation image can be provided to the monitor 70. Also shown is a data storage device 68 which can be used to store complete or partial frame store contents or alternatively it could store successive digital representations of the radiation image for later processing. In a further version of the apparatus, global positioning data can be encoded 72 onto the detector signal digital representations and used at a later time to analyse the image in a mapping application.

In one of many alternative versions of the apparatus the visual image can be adapted for viewing on a pilot^'s or vehicle driver^'s heads-up display.

In an enhanced version of the infrared imaging apparatus, image stabilisation is provided by using the signals from an inertial sensor 74 attached to the scanner to electronically calculate and compensate for the motion of the scanner apparatus which is independent of any deliberate translation or rotation or it may incorporate those types of motions as well. The inertial sensor may provide analog or digital output which are input to the Analog to Digital converter 62 or the processor 64 respectively. The picture produced by the scanner can then be stabilised electronically without requiring the scanner itself to be mechanically stabilised. Thus using relative movement co-ordinate correction to the detector signal data obtained from the detector the digital signal data value can then be associated with the most appropriate frame store location. For example, the frame store location for a detected signal may be calculated by adding the displacements due to, say, accumulated elevation and azimuth movement since an earlier predetermined time and as quantified by an inertial sensor apparatus . In one example any gaps in the frame store data when they occur, may be filled in with signal data interpolated from neighbouring samples or frame store locations . This electronic inertial movement correction stabilisation technique is particularly well suited to the embodiment described since it has a sufficiently low data accumulation rate for the necessary stabilisation computations to be performed between scanner sampling pulses and when the sensor signal outputs are recorded.

For example, it has been found that, an aircraft fitted with a non-mechanically stabilised scanning apparatus solidly mounted to its fuselage, which uses electronic stabilisation techniques can produce an infrared record of the terrain below the flying aircraft which is geometrically accurate to the same quality as a fully stabilised line scanning apparatus . A further image correction or stabilisation technique is useable with the invention, using an electronic correlation technique to compare the image obtained by the leading half of the conical scan with that obtained by the trailing half of the conical scan in order to derive the inertial motions of either the sensor itself, or the target itself, or the relative motion between target and sensor. These derived inertial rates (in azimuth, elevation, and roll), can be used either subsequently or in real time to correct the image without the assistance of any other inertial sensors .

Using this technique, before image data is placed in the frame store, the frame store location is modified by adding displacements due to, say, the cumulative elevation, azimuth, and roll movements which give the highest correlation between the two halves of the image. A conical scan is particularly well suited to this stabilisation technique because the overlaps between the two halves of the image are well distributed in both time and space, so that the probability of spurious correlations is reduced.

For example, it has been found possible to produce a geometrically accurate image using signals from an unstabilised sensor located in a moving vehicle. Also, a fixed scanner could be positioned so as to ecord movement of vehicles on a road, and produce a geometrically accurate image of any vehicle crossing at a reasonably uniform speed through its field-of-view.

With or without the types of stabilisation described above, aerial reconnaissance and surveillance over land is possible. One method of using the scanner described in this specification uses a translation by forward motion of the sensor platform and a vertical orientation of the scanner to provide a swath-like scan of the ground. One example of an application of such a mapping technique is the monitoring of electricity power transmission lines for hot spots. This configuration is a combination of mapping and image collection techniques.

Heretofore, the identification of hotspots along power transmission lines has been a time consuming, expensive and typically inconclusive task. Prior methods have included visual checking of the lines which requires trained and experienced spotters observing the line from an aircraft, then the further confirmation of the hot spot is necessary using expensive fixed object infrared radiation detection systems.

Using a configuration of the invention having a relatively narrow field-of-view, the scanner can be mounted and orientated to provide a swath-like scan across the ground as the aircraft flies quickly along the line providing an image of the transmission lines along their length. Ideally, the radiation image at a location in each frame store is correlated to a global positioning coordinate and for images of interest, i.e. those containing infrared radiation levels above a predetermined level, more detailed analysis can be carried out by way of image enhancement techniques on the images collected in real time or more sophisticated analysis conducted on the ground at a later time.

Preferably, a real time analysis of infrared radiation levels can be undertaken during the aircraft reconnaissance of the transmission lines. The scanner can be mechanically redirected over areas of interest even while in the process of initial surveillance or electronic scanning techniques such as for example, those described below can also be utilised.

Since the scan of the area is successive and swath-like, images can be stored for later normal or enhanced image analysis, as discussed above, or stored in a temporary data buffer and various data and image manipulations such as comparison of successive images can be undertaken.

Also, because the swath is imaged twice from two slightly different directions, i.e., by the leading and the trailing semicircle, it is possible to generate a three-dimensional image of the scene, refer Fig. 8. For example, the leading semicircular image can be displayed in red, the trailing semicircular image can be displayed in green, and viewing of the composite image with suitable filters, provides an image from which details such as the relative proximity of trees to power lines can be ascertained. This is but one of the many techniques available for displaying an image stereoscopically in a manner which simulates a three-dimensional representation of the radiation scene.

The abovementioned analysis techniques can provide sufficient detail of the selected radiation characteristics of the scene and/or object for assessment of a variety of scene characteristics of interest.

In the embodiment of the invention for a military gliding weapon, 128, 256 and 512-row versions of a conical scanner operating at 3-5 and 8-12 microns have been ground and flight tested, with both mirror and gimbal horizontal scanning as well as an inertially corrected version which has produced useable images and mappings. Sensitivity of the detector is about 0.015 degrees C which is a variable dependent on the spacial resolution and integration time of the apparatus.

The above scanning apparatus uses an infrared detector element. However, other detectors, say for example an ultraviolet sensitive detector, along with appropriate filters and focusing means can be designed into the scanner apparatus of this invention, flown over crops etc and valuable information can be collected for use by farmers, agronomists and other experts in their field regarding a myriad of environmental and crop characteristics not otherwise economically or easily observable by traditional methods .

In a yet further application of the scanner apparatus of the invention it is possible to scan a radiation scene and simultaneously collect radiation in a plurality of different bands of the electromagnetic spectrum so that the characteristics of the radiation scene associated with each band can be scanned or mapped simultaneously. For example, two bands of the infrared portion of the electromagnetic spectrum plus an ultraviolet band could provide information related to the different chemicals used in a crop or area of farmland. To implement a scanner having this facility, it is preferable to provide in place of the primary radiation focusing means an arrangement of lenses, mirrors and a prism element which will disperse the incoming radiation into predetermined bands of the electromagnetic spectrum and focus each wanted band of the radiation spectrum onto an appropriate detector. The processing of the detector signals will occur in the variety of manners described previously.

It will be appreciated by those skilled in the art, that the invention is not restricted in its use to the particular application described and neither is the present invention restricted in its preferred embodiment with regards to the particular elements and/or features described herein. It will be appreciated that various modifications can be made without departing from the principles of the invention, therefore, the invention should be understood to include all such modifications within its scope.

Claims

The claims defining the invention are as follows:

1. A radiation scanning apparatus for producing a radiation image comprising:

2. A radiation scanning apparatus for producing a radiation image comprising: at least one radiation detector means for providing a signal representative of a portion of a radiation scene detected by said detector,

rotation means for rotating said radiation scanning apparatus about an axis orthogonal to said coincident radiation axes across a predetermined field-of-view of said radiation scene, whereby

3. A radiation scanning apparatus for producing a radiation image comprising:

at least one radiation detector means for providing a signal representative of a portion of a radiation scene detected by said detector, a primary radiation focusing means for focusing incoming radiation on said at least one radiation detector means having a radiation axis,

a secondary scanning mechanism having a rotating mirror located in front of said secondary radiation element and rotatable, about an axis orthogonal to said radiation axis and arranged to reflect a predetermined field-of-view of said radiation scene into said radiation scanning apparatus .

4. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said primary radiation focusing means disperses said radiation on to two or more of said detectors which are receptive to different bands of the electromagnetic spectrum.

5. A radiation scanning apparatus according to claims 1 or 2 or 3 further comprising

an analog to digital converter means for transforming said radiation detector means signal into a digital data value representative of a portion of said radiation scene.

6. A radiation scanning apparatus according to claim 5 further comprising

a frame store having a plurality of locations in which said digital data values are stored as a pixel value, and

an association means for associating a digital data value representative of a portion of said radiation scene with a location in said frame store.

7. A radiation scanning apparatus according to claim 6 further comprising

a monitor for viewing said frame store output.

8. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector is a single radiation sensitive element of dimensions adapted to provide a portion of the field-of-view of said radiation scene to match the pixel size of a frame store.

9. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector is a single radiation sensitive element of dimensions adapted to provide a portion of the field-of-view of said radiation scene which is substantially similar to the pixel size of a frame store.

10. A radiation scanning apparatus according to claim 6 further comprising

a motion compensation means for providing an electronic correlation of said detector radiation signal obtained during the leading portion of the conical scan with said detector radiation signal obtained during trailing portion of said conical scan from which is derived the inertial motion of either said scanning apparatus, said target or the relative motion between said target and scanning apparatus.

11. A radiation scanning apparatus according to claim 10 further comprising

a correction means which subsequent to said conical scan of said radiation scene calculates the relative motion of said scanning apparatus in azimuth, elevation and or roll and provides these relative motion measurements to said association means for assisting the association of each digital data value representative of a portion of said radiation scene with a position in said frame store.

12. A radiation scanning apparatus according to claim 10 further comprising

a correction means which in real time calculates the relative motion of said scanning apparatus in azimuth, elevation and or roll using the difference in the data signals between said leading portion of said scan and said trailing portion of said scan about said radiation axis and provides relative motion measurements to said association means for assisting the association of each digital data value representative of a portion of said radiation scene with a position in said frame store.

13. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said primary radiation focusing means is a simple doublet arrangement.

14. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector means is primarily receptive to the infrared band of the electromagnetic spectrum.

15. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector means is primarily receptive to the 3-5 micro-metre waveband.

16. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector means is primarily receptive to the 3-5 or 8-12 micro-metre waveband.

17. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector means is primarily receptive to the optical band of the electromagnetic spectrum.

18. A radiation scanning apparatus according to claims 1 or 2 or 3 wherein said detector means is primarily receptive to the ultraviolet band of the electromagnetic spectrum.

19. A radiation scanning apparatus according to claim 5 further comprising

a geographic data signal input means which provides and associates with one or more digital data values a geographic reference value representative of the geographic location of said portion of said radiation scene.

20. A method of generating a scanned radiation image comprising the steps of:

(a) providing a radiation scanning apparatus as claimed in any one of claims 1 to 9;

(b) assigning to each position in said frame store a digital signal value corresponding to one or more of the nearest samples of said radiation scene as said radiation scanning apparatus traces a descending semicircular arc over said radiation scene and which is representative of a portion of a radiation scene, and

(c) laterally translating said radiation scanning apparatus orthogonal to said radiation axis at a rate which matches the adjacency of successive horizontal locations in said frame store of a respective row of said radiation image stored in said frame store.

21. A method of generating a scanned radiation image comprising the steps of:

(b) assigning to each position in said frame store a digital signal value interpolated from one or more of the nearest samples of said radiation scene as said radiation scanning apparatus traces a descending semicircular arc over said radiation scene and which is representative of a portion of a radiation scene, and

(c) rotating said radiation scanning apparatus about an axis orthogonal to said radiation axis at a rate which matches the adjacency of successive horizontal locations in said frame store of a respective row of said radiation image stored in said frame store.

22. A method according to claims 20 or 21 comprising the further step of:

(d) electronically stabilizing said radiation image for a scanner apparatus located on a moving platform, by calculating the relative motion of said scanning apparatus in azimuth, elevation and or roll by using information obtained from an analysis of said two halves of said image representation generated by the ascending and descending portions of said scanner apparatus, and

(e) providing the calculated relative motion measurements to said association means for the association of each digital data value representative of a portion of said radiation scene with a position in said frame store.

23. A method according to claims 20 or 21 comprising the further step of:

(d) electronically stabilizing said radiation image for a scanner apparatus located on a moving platform, by calculating the relative motion of said scanning apparatus in azimuth, elevation and or roll by using information obtained from an inertial motion sensor attached to said scanner apparatus, and

24. A method according to claims 20 or 21 for mapping a radiation scene comprising the further step of

(f) associating with each location or a group of locations in said frame store data representative of a global positioning co-ordinate of the respective portion of said radiation scene.

25. A method of processing a radiation detector means output of a radiation scanning apparatus according to claims 20 or 21 wherein said leading portion of said conical scan and said trailing portion of said conical scan of the same radiation image are displayed to each eye of a viewer in a manner to stimulate a three dimensional representation of said radiation scene.