GB1605368A

GB1605368A -

Info

Publication number: GB1605368A
Application number: GB4605273A
Authority: GB
Priority date: 1973-10-02
Filing date: 1973-10-02
Publication date: 1994-06-22
Anticipated expiration: 1989-10-02

Description

PATENT SPECIFICATION ( 11)1605368

( 21) Application No 46052/73 ( 22) Filed 2 Oct 1974 ( 31) Provisional Application No 46052/73 ( 32) Filed 2 Oct 1973 ( 44) Complete Specification Published 22 June 1994 ( 51) In L Cl 5 ( 52) Index at Acceptance G 02 B 26/10 31781 17/42 17/87 H 4 D DLAA DLPA D 72 X D 730 D 735 D 745 D 750 D 773 D 775 D 783 G 2 J JB 7 WX UIS 52139 ( 19) ( 72) Inventors: John David Bannister, James Wilfred Lyons ( 54) IMPROVEMENTS IN OR RELATING TO AIRBORNE TRACKING, RANGING AND GUIDANCE SYSTEMS I/We BRITISH AEROSPACE PU Bu LC LI Mrr ED comp AN Y, a British Company organised under British Aerospace (Nominated Company) Order 1980 and British Aerospace (Appointed Day) Order 1980, of 100 Pall Mall, London SW 1 Y HR do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following

statement -

This invention relates to airborne tracking, ranging and guidance systems, and more particularly infra-red/laser devices.

A modern combat aircraft is usually required to be capable of satisfying a number of mission specifications if it is to justify its existence For example, air-to-air combat capability is demanded from the same air-frame as is designed to meet a ground attack requirement In addition to introducing conflicting basic structural design and configuration philosophies, multi-missions demand equally different weapon system requirements In the air-to-air role, target search is the main requirement associated with computing facilities for calculating optimum interception trajectories once lock-on has been achieved For the air-to-ground role a ranging device is a desirable asset for achieving high weapon-delivery accuracy.

_ O Such a dual role has previously been fulfilled using radar capable of operating in more than one mode but various limitations exist concerned with size and weight Hence with a limitation on antenna dish diameter, for example, target detection ranges are barely adequate especially in low level environments where ground clutter is present and therefore is is desirable to adopt an alternative system which overcomes these various shortcomings.

Recently, developments have taken place in laser systems which make them suitable for airborne applications and, in the military field, particular emphasis has been placed on their use as air-to-ground ranging devices to improve weapon delivery accuracy However the basic combination of the laser ranger and its corresponding scanning head receiver offers an even greater flexibility of operation which is not attainable with a radar of similar weight and size It is possible to envisage several operating modes for a laser system and, by way of example, the following have been considered, 1) Use of the scanning head receiver as a search sensor for airborne targets.

2) Use of the scanning head receiver as an 55 acquisition sensor for ground targets when operated in conjunction with the laser rangefinder.

3) Use of the laser rangefinder and receiver as a simple fixed beam terrain-following system 60 4) Use of the laser rangefinder in conjunction with the search sensor and/or a pilot helmet sight as a ranging device for air-to-air guns and missiles.

5) Use of the laser rangefinder and receiver 65 in conjunction with a pilot helmet sight or display marker as a device for updating the aircraft navigation system relative to identification points of known co-ordinates.

6) Use of the scanning head receiver in 70 conjunction with appropriate detector(s) to provide a day and night imaging capability.

It is, therefore, an object of the present invention to overcome shortcomings of existing systems by achieving an improved laser sensor 75 unit able to fulfil one or more operating modes.

Accordingly, the invention provides a combined laser ranging device and scanning head receiver apparatus sharing common optics, wherein the scanning aperture for incident target 80 radiation comprises both reflecting optics and refracting optics having a common optical axis and a common focal point and receiving different respective portions of the incident radiation, and a laser source projects a laser 85 ranging beam along said optical axis through the scanning aperture and is steered in space by angular movement of the scanning head about said focal point By this means, harmonisation of both transmitter and receiver functions is 90 ensured The target radiation received may be focused on to semi-conductor detector elements which, in turn, generate a voltage being a function of target radiation The processed signals can then be either displayed to the pilot 95 or used to activate other devices according to the particular operating mode of the sensor.

Our co-pending patent application 46051/73 describes the evolution and one embodiment of a scanning head receiver for use in the practical 100 realisation of the present invention The head is scanned about the focal point in pitch and azimuth, in addition to possessing a roll stabilisation facility, thus enabling the laser mo 1 605 368 beam to be refracted in the scan direction The fundamental problem with this arrangement is the location of suitable detectors since ideally the detector unit and laser should be co-located.

In the preferred embodiment, practical considerations recommended the adoption of a fixed detector unit mounted transversely near the system optical axis, and the use of a fixed reflecting surface, because of the limited space available, and the need for multiple connections to and from the detector Therefore, in the preferred embodiment, the system makes use of a collimating lens located in front of the focus so that the overall optical system becomes afocal In principle, the detector units may then be placed anywhere in the collimated beam but the desirability of locating the laser optical axis co-incident with the scanning head axis makes it advantageous to use a 450 reflector element and a transversely aligned detector unit The collimating lens is so shaped that radiation incident on it, received and focused by the scanning head, is diverged to form a beam of radiation parallel in itself and to the system optical axis The re-direction of the radiation on to the detector is by means of one or more prisms, dependent upon the number of separate detector units employed A small modification to the facing at the centre of the prism allows the laser beam to pass through with low loss.

On reception, some energy is lost due to the presence of this discontinuity at the prism centre but, as this is in the same ratio as the cross sectional areas of the laser beam and the collimated incident energy, losses are of the order of only 1 %.

A number of possible detector arrangements are available which fulfil the requirements of the various roles proposed for the multi-mode sensor The use of a self-scanned matrix detector to meet all the roles is discussed in our co-pcnding patent application No: 46247 f 73.

With that arrangement a single reflecting prism and detector unit are used.

An alternative arrangement is considered where air-to-air search and laser ranging use a separate detector unit from that used for the imaging requiremen L The invention may be better understood by reference to the following description of a preferred embodiment, given by way of example and with reference to the accompanying drawings; in which:Figure 1 shows diagrammatically an optical arrangement for a multi-mode laser sensor.

Figure 2 is a sectional side elevation of a total laser sensor assembly.

Figure 3 is an end view in the direction of the arrow 3 of Figure 2.

Figure 4 shows diagrammatically an aircraft installation.

Figure 5 shows the spectrum of infra-red radiation from a typical target and sun background radiation.

Figure 6 shows a cruciform arrangement for a dual channel detector assembly.

Figure 7 is a diagram illustrating the use of the detector of Figure 6 in tracking a targe.

In Figure 1, incident radiation 2 received by the scanning head 1 passes through a filter 80 70 on to a main dish reflector 81 and also through lenses 20, 19 The radiation reflected by the dish reflector 81 is further reflected by a sub-dish or flat plate reflector 82, and the beams from both the sub-dish 82 and the buses 20, 19 are 75 convergent on a focal point 3 which is located on the scan axis 4 and serves as the centre of rotation of the scanning head However, this radiation is collimated by a lens 5 located just forward of the focal point 3 and passes by way 80 of a convex focusing lens 6, a concave focusing lens 7 and a convex collimating lens 8 into a dichroic prism 9 where the received energy is deflected substantially at right angles through a convex lens 10 which focuses it on to the 85 appropriate detector In the described arrangement two detectors are used, one 11 for air-to-air search and laser ranging, and the other 12 for imaging, both contained in suitably cooled dewar flasks 13 90 For this arrangement the prism 9 is two-way in function having cemented interfaces 14 which are sensitive to wavelength and hence direct the appropriate radiation on to the correct detector.

Associated with the imaging role is the 95 desirability of, once having spotted the target, zooming in in order to enhance recognition.

This facility is provided by concave/convex lenses 6 and 7, in effect a telephoto lens unit, which are movable in a rearward direction to 100 give optical magnification variable from unity to four.

Since the optical system comprising the scanning head, collimating unit and telephoto lens is basically afocal, the focal length of the 105 system is determined by the final lenses 10 which focus the deflected incident radiation on to the detectors The field of view for each detector unit is determined by focal length and detector size and typical fields of view do not 110 exceed 200.

The laser source 17 is located on the main axis of the system beyond the dichroic prism 9.

The basic laser beamwidth 15 is of the order of m R but, particularly for air-to-air tracking and 115 terrain following, variation of this figure is desirable This is achieved using a simple translating lens 16 located in front of the laser source 17 and which may also be used for laser beam dispersion when necessary during certain 120 operating modes.

The collimated laser beam 15 passes forward through the dichroic prism 9 from the reverse side thereof via a small notch 18 set into the prism interface The beam continues forward 125 through the telephoto optics into the forward collimating lens 5 where it diverges from the focal point 3 until it passes through the twin lenses 19 and 20 This gives the final transmitted beam diameter Angular movement 130 1 605 368 of the scanning head, and consequently the lenses 19, 20, about the focal point 3 serves to steer the laser beam in space.

The optical elements must be capable of handling signals over a wide optical bandwidth.

To cover the required bands and produce low aberration optical elements, a material such as arsenic trisulphide, magnesium fluoride or zinc selenide glass is desirable, as is lens coating to reduce surface reflections.

Referring to Figures 2 and 3, showing one detailed embodiment of the invention, the optical scanning head 21 is mounted for pivotal movement in pitch within an azimuth gimbal ring 22 by means of bearings disposed within torque motor and resolver 23 and 24, respectively The azimuth gimbal ring 22 is similarly mounted for pivotal movement in azimuth within a roll casing 25 by means of bearings incorporated in torque motor and resolver 26 and 27 For rotation about the roll axis, the roll casing 25 extends rearwardly for mounting within a fixed casing 30 by means of bearings 28 and 29 The bearing 29 seats around a cylindrical boss portion 31 of the fixed casing having a forwardly extending flange 32 on which is mounted the detector array and optical assembly 33 previously described with reference to Figure 1 This assembly comprises a tubular sleeve 34 at the forward end of which, and centred close to the scan axis 4, is carried the collimating lens 5 movable fore and aft to a limited extent by means of a threaded sleeve 35 for adjustment relatively to the focus point 3 and scan axis 4.

The tubular sleeve 34 houses the telephoto system lenses 6 and 7 which are movable fore and aft therein by suitable operating means This movement is transmitted by locating pegs 36 on the lens holders 37 and 38 passing through axial slots in the tubular sleeve 34 to engage in helical grooves in respective outer sleeves 39 and 40 having operative connection to servo motors.

The tubular sleeve 34 further houses the fixed collimating lens 8 and the dichroic prism 9 and provides side branch mountings for the focusing lenses 10 for direction of the collimated energy on to the detector elements 11 and 12 contained within the cooling dewar flasks 13.

The laser beam 15 emanating from the laser unit 17 is collimated by passing through the lens 16 as already described Lens adjustment fore and aft for beam width variation and dispersion is by means of a threaded lcns carrier 41 mounted within the cylindrical boss 31 and engaging an anti-backlash gear train 32 driven by a lens motor 43 mounted on the front ring 46 of an inner main frame 44 which also supports the roll motor 47, roll synchro 48 and telephoto lens motors 49.

This inner main frame also carries the laser unit 17 and associated modulators, ranging and target marking amplifiers for all roles, and a detector cooling system A rear ring 51 of the main frame 44 provides support for modulators 52, a fan 53 and a coolant pump 45 The inner main frame 44 is isolated by anti-vibration mounting means 55 from an outer support structure 56 This structure carries a rear 70 pressure dome 57 incorporating an air-to-air heat exchanger 58, a liquid-to-air heat exchanger 59 and a reservoir 60 The pressure dome forms the rear end closure of a canister 61, the opposite or forward end being closed by a 75 hemispherical optical dome 62 This dome 62 completely surrounds the scanning head 21 and may be designed as a MAKSUTOV corrector to further reduce residual aberration.

A typical aircraft installation is shown in 80 Figure 4 in which the laser sensor is situated close to the fuselage nose 63 The pressurised canister 61 of the sensor is enclosed within a fairing 64 whose lines correspond to the fuselage profile 65 This fairing is mounted by 85 means of spigots 66 on a machined ring 67 forming the front boundary of the air-frame structure, the fairing being held in place by suitable quick release fasteners The sensor can be withdrawn on side rollers running on tracks 90 attached within the fuselage (not shown) By moving the unit sufficiently far forward the electrical and cooling systems may be readily disconnected The hemispherical dome 62 is protected by eyelid shutters 68 operated by dual 95 actuators 69 and linkages 70 mounted on the sensor canister The shutters 68 may incorporate wiping pads for cleaning of the dome surface.

In considering the application of this system to the multi-mode role, Figure 5 shows that the 100 radiance from an air-borne target is seen to peak in the 4-5 micron band The radiation is made up of that emitted from the hot metal parts of the aircraft and that due to CO 2 emission from the jet plume A narrow band filter 71 is used in 105 the receiver to maximise the target signal relative to background radiation The scattered sunlight dominates below 2 microns and a second narrow band filter 72 samples this radiation The filter characteristics are chosen so 110 that laser radiation of around 1 micron is also detected by this channel.

A dual channel detector element is therefore used and in a known element the detector is made up from two layers of material each 115 having different characteristics The preferred embodiment of this detector arrangement is shown in Figure 6 and is of cruciform appearance, the front layer 73, representing one channel, being a germanium semi-conductor for 120 radiation in the 1 micron band but substantially transparent to radiation in the 4 micron band.

The second layer 74, representing the second channel, and typically indium antimonide, de Lects radiation in both wavebands and hence 125 this channel of the detector is responsible for extracting the target signals By combining the two channel outputs in opposition, substantial cancellation of the background returns can be achieved 130 1 605 368 The cruciform detector is made up of a number of individual semi-conductor elements the size of each detector element being determined by the desired elemental field of view and the f-number of the optical system.

When a target return is present it falls only within one detector element whereas background radiation is detected by all the elements The background signal level in each element of a channel may differ because of spatial variation in radiation and hence an estimation of the background signal is usually achieved by averaging the response of all detector elements in the channel By using integrated circuit techniques, well within the state of the ar, each detector channel can be processed separately thus enabling elements to be gated in or out of the processing system and the cancellation scheme to be implemented.

Imaging can be achieved by using a separate detector matrix, e g of Mercury Cadmium Telluride, sensitive in the 8-13 micron region.

The application of this system to the various operating modes will now be summarised.

For Mode I the laser rangefinder is nonoperative and the receiver head scans a volume of airspace searching for possible airborne targets which will be supposed present when a signal appears above the receiver amplitude threshold At this stage only the vertical or longitudinal row 76 of the detector elements of Figure 6 is in use but when the target is declared genuine by the processing system, a tracking mode is entered, the detector side elements 77 now being gated into the signal processing circuitry The scanning head is now nutated, thereby causing the focused incident energy to execute a circular motion about the centre of the detector cross array, as indicated at 79 in Figure 7 If the target is aligned with the optical axis, the receiver processes a train of uniformly spaced pulses If the target is positioned off axis, the pulse train becomes frequency modulated, the degree and phase of modulation indicating the target position relative to the boresight The demodulated signal can be used to provide correction signals to the tracking servos The background rejection system can still be operative during the tracking phase and as the tracking range reduces the target signal increases relative to general background radiation Since the magnitude of each signal can be individually monitored it is possible to determine the situations in which the cancellation system can be gated out and the target detector layer 74 permitted to operate independently The front detector layer 73 is then free to act as the receiver element for the laser ranger.

Mode 2 differs little from existing systems and there are two ways of operation The pilot may identify the ground target through the canopy and manoeuvre his aircraft such that he can position an aiming marker by means of his head-up display.

The scanning head receiver is then directed in a narrow search field about the defined vector The laser range finder, sharing common optics with the receiver, is thus directed at the target and the scattered radiation is detected by the receiver By appropriate coupling of the 70 return signals to the servos of the scanning head the device can be made to lock on to the identified target The laser used for ranging purposes operates in the micron band and hence the background cancellation detector mentioned 75 for the search mode can be employed as the basic detector for the air-to-ground role.

An alternative method is to illuminate the target by a remote laser on the ground in which case only the sensor receiver is operative, the 80 scanner executing a space volume search On acquiring the target the sensor again enters a tracking mode.

The proposed method of terrain following, Mode 3, uses a laser system whereby the laser 85 beam is depressed through a fixed angle relative to the aircraft flight vector, the beam nominally illuminating the terrain at a present reference range Ranges to the terrain which differ from this reference value cause appropriate pitch rate 90 demand signals.

Because the pulse repetition frequency (pr f) of current lasers is limited ( 10/sec being typical) fully scanned terrain following is not envisaged but by increasing the beam depression 95 angle after hillcrest clearance improved performance is achieved.

Knowledge of terrain clearance height directly beneath the aircraft is a desirable parameter This can be measured with either a 100 radio altimeter or the laser beam switched to the vertical position, although this latter facility is outside the scope of the present system In the receiver, since no tracking requirements exist in this mode, the scanning head is stationary and 105 only the front central detector element 78 of the cruciform is used For manoeuvring flight, aircraft bank angle and speed are used as parameters to determine the required angular deflection of the laser beam to enable a terrain 110 following capability to be retained in turning flight The beam is turned inwards towards the centre of the turning circle and the fixed angle and the preset reference range are correspondingly adjusted 115 Mode 4 In operating mode 4 the laser ranger is used in the air-to-air role During approach to the target the infra-red search sensor is locked on to the emitted radiation in the 4 micron band, the 1 micron detector element being in a 120 standby condition It is anticipated that the laser beam will be adequately spoiled during this phase to ensure that target coverage occurs for the tracking areas associated with the search sensor Once the target is illuminated by the 125 laser, return signals are present in the 1 micron channel and range signals are generated The target range can be displayed to the pilot indicating the nature of armament to be used.

The fundamental problem with the use of a 130 1 605 368 laser in the air-to-air role is pointing the narrow beam at the target Since the laser shares optics with the seeker, once the latter is locked on, the tracker system will ensure adequate pointing accuracy for laser target illumination and the system will continue to follow the target movement In operating Mode 5 the purpose is to use the laser ranger and receiver in a manner wherein it is slaved to a pilot helmet sight or target marker on the pilot's head-up display In this way range information can be obtained on any target selected by the pilot If the target is a landmark whose known co-ordinates have previously been inserted in the navigational computer it is only necessary for the pilot to identify the land-mark, direct his sight-line at it and press the up-date button to insert instantaneous aircraft position into the computer In this mode the laser sensor operates in a manner similar to the air-to-air ranging role, except that no target lock-on is required since the up-date information is transferred immediately the return signal from the identification point is received.

In operating Mode 6 the receiver is used in a passive mode for imaging either at near IR.

wavelengths where it is dependent on reflected scene illumination for its operation (Low Light T.V) or at mid I R wavelengths where inherent thermally generated energy is the source of radiation (Forward Looking Infra Red).

A line array or matrix detector is required for imaging, the resolution being determined by the number of elements that can be accommodated on the detector unit In addition each elemental detector has to be individually processed It will be advantageous to image in the near I R (i e.

up to 1 micron) and mid I R bands (i e 3-5 microns) This will enable dual spectral band operation with its consequent contrast enhancement to be achieved Alternatively imaging can be accomplished at 8-13 microns as used on current FLIR devices.

Claims

WHAT WE CLAIM IS:-

1 A combined laser ranging device and scanning head receiver apparatus sharing common optics, wherein the scanning aperture for incident target radiation comprises both reflecting optics and refracting optics having a common optical axis and a common focal point and receiving different respective portions of the incident radiation, and a laser source projects a laser ranging beam along said optical axis through the scanning aperture and is steered in space by angular movement of the scanning head about said focal point.

2 Apparatus according to Claim 1, wherein the target radiation received is focussed on to one or more semi-conductor detector elements which generate an electric voltage being a function of target radiation.

3 Apparatus according to Claim 2, having fixed detector elements, and wherein a collimating lens is located in front of said focal point so that the overall optical system becomes afocal.

4 Apparatus according to Claim 3, wherein said optical system incorporates a movable telephoto or zoom lens combination.

Apparatus according to Claim 2 or Claim 3 or Claim 4, wherein the detector elements are displaced transversely from the optical axis and the radiation is deflected laterally on to them by a reflecting prism located on the optical axis.

Our co-pending patent application 46051/73 describes the evolution and one embodiment of a scanning head receiver for use in the practical 100 realisation of the present invention The head is scanned about the focal point in pitch and azimuth, in addition to possessing a roll stabilisation facility, thus enabling the laser This front page Is a reprint to rectify errors introduced in the course of reproduction DIVISION G 1 1 605 368 Photo-electric target tracking British Aerospace Public Limited Company 2 Oct 1974 46052/73 Heading GI lAlso in division H 3-H 5 l A combined laser ranging device and scanning head receiver share common optics, the scanning aperture for incident target radiation comprises both reflecting and refracting optics having a common optical axis and a common focal point and receiving different portions of the incident radiation, and a laser sources projects a laser ranging beam along the common optical axis through the scanning aperture and is steered in space by angular movement of the scanning head about the common focal point In the embodiment scanning head 1 (scan axis 4) includes the optical arrangement shown, and a dichroic prism 9 with cemented interfaces 14 sensitive to wavelength for directing infra-red and visual radiations to detectors 11, for infra-red air-to-air search and laser ranging, and 12, for imaging.

Each detector is in a cooled Dewar flask 13 In the imaging role a zoom lens system 6, 7 is employed Variation of laser beam width is achieved by a lens 16 To cover the required radiation bands with low aberration the optical materials may be arsenic trisulphide, magnesium fluoride or zinc selenide glasses, and lenses are coated to reduce surface reflexions A constructional embodiment is described Figs 2, 3 (neither shown), in which the scanning head is pivotable in pitch within an azimuthal gimbal ring, the latter being pivotable in azimuth; rotation about the roll axis is also arranged In an aircraft installation the laser section of the apparatus is near the nose of the fuselage Figs.

4 a, b (neither shown); a forward hemispherical glass dome is provided and is protected by "eyelid" shutters which may incorporate pads for wiping the surface of the dome.

Detection, Fig 5 Some radiation bands of interest are as shown in Fig 5 A detector made from two layers of material having different characteristics is employed, is of cruciform appearance and the front layer 73 being elements of germanium semi-conductor for 1 micron band radiation but substantially transparent to 4 micron band radiation; the second layer 74, typically of indium antimonide elements, detects radiation in both bands The effective element sizing is such that a target echo falls within one detector element only whereas background radiation is detected by all elements The imaging detector is a separate mercury cadmium telluride matrix, sensitive to the 8-13 micron band Modes of operation In mode 1 the laser rangefinder is inoperative and scanning for airborne targets is effected utilizing a receiver amplitude threshold; only the column 76 of the cruciform detector is utilized until the target is found to be "genuine" when row 77 is employed also and thereafter nutation by a subdish enables angular tracking utilizing the fact that receiver pulse outputs are unequally spaced when the target is off-axis In mode 2 a visually-identified ground target is tracked and its range found; or a remote laser on the ground illuminates the target and the scanner searches and tracks i L Mode 3 is terrain-following utilizing pulsing of the laser radar, and the laser radar may additionally be used for heightfinding In mode 4 the infra-red passive sensor aims the apparatus onto an airborne target and the laser system is then rendered operative for ranging Mode 5 slaves the laser radar to a pilot's helmet sight or a target marker on a pilot's display, for any target selected by the pilo L In mode 6 low-light television or midinfra-red band imaging is employed.

/o 2 2i_(continued on next page) 2i.

DIVISION H 3-H 5 1 605 368 Photo-electric target tracking British Aerospace Public Limited Company 2 Oct 1974 46052/73 Heading H 4 D lAlso in division(s) G 1 l A combined laser ranging device and scanning head receiver share common optics, the scanning aperture for incident target radiation comprises both reflecting and refracting optics having a common optical axis and a common focal point and receiving different portions of the incident radiation, and a laser sources projects a laser ranging beam along the common optical axis through the scanning aperture and is steered in space by angular movement of the scanning head about the common focal point In the embodiment scanning head 1 (scan axis 4) includes the optical arrangement shown, and a dichroic prism 9 with cemented interfaces 14 sensitive to wavelength for directing infra-red and visual radiations to detectors 11, for infra-red air-to-air search and laser ranging, and 12, for imaging.

Detecution, Fig 5 Some radiation bands of interest are as shown in Fig 5 A detector made from two layers of material having different characteristics is employed, is of cruciform appearance and the front layer 73 being elements of gennrmanium semi-conductor for 1 micron band radiation but substantially transparent to 4 micron band radiation; the second layer 74, typically of indium antimonide elements, detects radiation in both bands The effective element sizing is such that a target echo falls within one detector element only whereas background radiation is detected by all elements The imaging detector is a separate mercury cadmium telluride matrix, sensitive to the 8-13 micron band Modes of operation In mode 1 the laser rangefinder is inoperative and scanning for airborne targets is effected utilizing a receiver amplitude threshold; only the column 76 of the cruciform detector is utilized until the target is found to be "genuine" when row 77 is employed also and thereafter nutation by a subdish enables angular tracking utilizing the fact that receiver pulse outputs are unequally spaced when the target is off-axis In mode 2 a visually-identified ground target is tracked and its range found; or a remote laser on the ground illuminates the target and the scanner searches and tracks it Mode 3 is terrain-following utilizing pulsing of the laser radar, and the laser radar may additionally be used for heightfinding In mode 4 the infra-red passive sensor aims the apparatus onto an airborne target and the laser system is then rendered operative for ranging Mode 5 slaves the laser radar to a pilot's helmet sight or a target marker on a pilot's display, for any target selected by the pilot In mode 6 low-light television or midinfra-red band imaging is employed.

/i /C ' /1 /.5 (continued on next page) 2 F Al-_ L_ 2-'

6 Apparatus according to Claim 5, wherein there are two detectors located at opposite sides of the optical axis and responding to different wavelengths, and the prism has wavelengthsensitive interfaces so as to direct radiations of different wavelengths on to the appropriate detectors.

7 Apparatus according to Claim 5 or Claim 6, wherein the laser source is located on the optical axis behind the prism, and the prism has a small central region that is modified, specifically to assist the passage of the laser beam therethrough.

8 Apparatus according to Claim 2 or Claim 3 or Claim 4, wherein a dual channel detector array is employed made up of front and rear layers of material having sensitivity to different wavelength bands.

9 Apparatus according to Claim 8, wherein the dual-channel detector array comprises a plurality of detector elements arranged in two rows mutually at right angles to form a cruciform configuration.

Apparatus according to Claim 9, wherein the front layer of the detector array responds to laser beam reflected radiation.

11 A combined laser ranging device and scanning head receiver, substantially as described with reference to the accompanying drawings.

LLOYD WISE, COULY & HAIG Chartered Patent Agent, Norman House, 105-109 Strand, London, WC 2 R OAE Agent for the Applicants.

Printed by MTL Orpington, Kent 1994 Published at The Patent Office, Concept House, Cardiff Road, Newport, Gwent NP 9 IRE Further copies may be obtained from Sales Branch, Unit 6, Nine Mile Point, Cwmfelinfach, Gwent N Pl 7 HZ PATENT SPECIFICATION ( 11)1 605 368 0 cc een ttn ( 21) Application No 46052/73 ( 22) ( 31) Provisional Application No 46052/73 ( 32) ( 44) Complete Specification Published 22 June 1994 ( 5 I) IntCl ' G 02 B 26/10 3 f ( 52) Index at Acceptance H 4 D DLAA E 2 J 1 D 745 DW uis JB 7 WX 52139 Filed 2 Oct 1974 Filed 2 Oct 1973 ( 19) 781 17/42 17/87 )LPA D 72 X D 730 D 735 750 D 773 D 775 D 783 ( 72) Inventors: John David Bannister, James Wilfred Lyons ( 54) IMPROVEMENTS IN OR RELATING TO APIRBORNE TRACKING, RANGING AND GUIDANCE SYSTEMS I/We B Rr ITISH AEROSPACE PUBLIC LII Tr E co MPAN, a British Company organised under British Aerospace (Nominated Company) Order 1980 and British Aerospace (Appointed Day) Order 1980, of 100 Pall Mall, London SW 1 Y HR do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:This invention relates to airborne tracking, ranging and guidance systems, and more particularly infra-red/laser devices.

A modem combat aircraft is usually required to be capable of satisfying a number of mission specifications if it is to justify its existence For example, air-to-air combat capability is demanded from the same air-frame as is designed to meet a ground attack requirement.

In addition to introducing conflicting basic structural design and configuration philosophies, multi-missions demand equally different weapon system requirements In the air-to-air role, target search is the main requirement associated with computing facilities for calculating optimum interception trajectories once lock-on has been achieved For the air-to-ground role a ranging device is a desirable asset for achieving high weapon-delivery accuracy.

JO Such a dual role has previously been fulfilled using radar capable of operating in more than one mode but various limitations exist concerned with size and weigh Lt Hence with a limitation on antenna dish diameter, for example, target detection ranges are barely adequate especially in low level environments where ground clutter is present and therefore is is desirable to adopt an alternative system which overcomes these various shortcomings.