1
DIFFERENTIAL GUIDANCE DEVICE USING ACTIVE LASER IMAGERY
The invention relates to the domain of guidance systems for interception delivery systems of the missile, rocket or shell type, designed, for example, to neutralise designated targets.
The object of the invention is to ensure the precision guidance of low-cost, short-range, small-lethal-radius delivery systems, with a radius typically less than or equal to 3 m, or requiring impact on the target or on a vulnerable part of the target, in a range extending to the short-range domain of ground-air defence (i.e. 6-10 km), without excessive sophistication of the firing station. Lethal radius is understood to mean the radius defining the zone of the space (sphere) in which the action of the delivery system is severely damaging to any object or individual located in this zone.
In the current state of the art, the precision of the guidance of a delivery system is provided by implementing either a homing system or a beamriding system (with no sensor on the delivery system), or a passive infrared or radar differential guidance system, or a guidance system based on a cross-localisation between two sensors.
Homing solutions have the disadvantage of incurring a high cost, a cost which consequently makes the delivery system concerned too expensive in relation to certain asymmetric threats to which they are intended to respond. An asymmetric threat is understood here to mean a threat, a missile, whose cost is deemed to be particularly low if one considers the damage that it can cause and the price of the means to be implemented to arm oneself against it.
The disadvantage of the use of beamriding solutions lies in the implementation of a guidance tunnel (corridor) centred on the target or offset at a predefined angle in relation to said target. A guidance of this type entails

2
the implementation of a tight control (i.e. with a low tolerance) of the delivery system guidance axis, or the combination of the line of sight and the guidance axis, on the position of the target. It also requires the performance and maintenance of a fine harmonisation, a narrow parallelism, between the line of sight and the guidance axis. These two constraints are generally met at the cost of a substantial sophistication of the firing station (stabilisation device) and through the provision of a preventive maintenance kit (i.e. tools and the associated procedure) allowing this harmonisation to be controlled if it is likely to have degraded (substantial temperature deviation, vibrations and impacts due to the movement, etc.) and to be restored if a degradation is detected.
Passive infrared differential guidance solutions effect the remote control of the delivery system (hyperfrequency, laser, wire, etc. uplink) and localise its angular position by means of the infrared camera furthermore serving to track the target. However, with low-cost, small-calibre delivery systems, this localisation is not straightforward, as the delivery systems have a small infrared signature. The actual transmission of the delivery system must then be increased by integrating an active transmitter (pyrotechnic or electronic light source), as, for example, in the patent application EP 1 925 902, which has the consequence of rendering the structure of the delivery system more complex, thereby increasing its cost price. Furthermore, the passive infrared differential guidance precision is generally derived from the resolution of the cameras used, which is linked to the diffraction. Consequently, the higher the precision requirement, the greater the diameter of the optical systems implemented to effect the guidance must be, especially if the wavelength is greater. This requirement thus necessitates the implementation of specific optical systems (optical systems with a very small field), thereby similarly increasing the cost of the firing station.
Radar differential guidance solutions effect the remote control of the delivery system (hyperfrequency uplink) and require both the implementation

3
of a target-tracking radar comprising an integrated device for localisation of the delivery systenn and the implementation on the delivery system of a transmitter whose signal can be localised by the radar. Solutions of this type, which require the implementation of specific and costly sensors and components both on the firing station and on the delivery system, are generally adopted for top-of-the-range systems only, in particular systems whose performance is virtually unaffected by atmospheric conditions. They do not therefore represent an appropriate solution for low-cost delivery systems.
Cross-linked solutions for their part effect the remote control of the delivery system (hyperfrequency, laser, wire, etc. uplink) and the localisation of the target and of the delivery system with two different sensors. These are solutions which, on the whole, require the maintenance between the two sensors of a harmonisation that is sufficient to ensure the guidance precision. Furthermore, as a general rule, these solutions do not meet the requirement for a guidance with high angular precision so the harmonisation error is found directly on the guidance precision.
One object of the invention is to propose an effective, low-cost solution, compared with existing solutions, to the problem outlined above.
For this purpose, the subject-matter of the invention is a differential guidance device, using active laser imagery, to guide an interception delivery system towards a target detected and designated by a main sensor to which it is linked, said device moreover being mechanically linked to positioning means allowing its line of sight axis to be oriented in two axes, horizontal and vertical. The device according to the invention mainly comprises an active laser imager, transmitting a localisation laser signal, associated with a dual deviation indicatorconfigured to allow simultaneous localisation of the designated target and the interception delivery system, and to determine the differential angular deviation measurement 9 between the direction corresponding to the target and the direction corresponding to the

4
interception delivery system. The pointing of the device in the direction of the target is effected here by the positioning means to which it is linked.
According to one particular embodiment, the device according to the invention furthermore comprises an optical amplifier device, mounted on the interception delivery system and configured to allow amplification of the laser echo reflected by the latter.
According to a different particular embodiment, the device according to the invention furthermore comprises a laser telemeter allowing determination of the respective distances of the target (Dtarget) and the interception delivery system (Ddeiivery system), the direction pointed by the telemeter being determined by the dual deviation meter; the distances of the target and the interception delivery system being transmitted to means responsible for guiding the interception delivery system towards the target.
According to one particular embodiment of the device according to the invention, the active imager is configured in such a way as to effect, between two consecutive transmissions, the acquisition of a plurality of successive temporally offset images, the acquisition times and the duration of each acquisition allowing the definition of acquisition windows separated from one another, the distance corresponding to a given image being a function of the time interval separating the time of opening of the temporal window during which the image was captured from the time of transmission.
According to one variant of the preceding particular embodiment, the dual deviation indicatoris configured in such a way as to transmit to means responsible for the guidance of the interception delivery system towards the target both the delivery system-target differential deviation measurement and the distance corresponding to the temporal window on the basis of which the transmitted differential deviation measurement was calculated.

5
According to one particular embodiment, tlie device according to the invention furthermore comprises ancillary guidance means configured to take into account the information relating to the azimuth, the angle of sight and the distance of the designated target, supplied by the detection system, and to effect the guidance of the interception delivery system towards the target during the flight phase in which it is located outside the field of the imager.
According to one particular embodiment, the device according to the invention is configured to effect a multi-target interception. For this purpose, it comprises a plurality of ancillary guidance means, each being configured in such a way as to provide the guidance of an interception delivery system towards a given target. The device according to the invention is furthermore designed in such a way as to be able to be oriented successively towards each of the designated targets and implemented in such a way as to simply provide the final guidance of the corresponding delivery system towards the target concerned.
According to one particular embodiment, the device according to the invention furthermore comprises means associated with the imager allowing a direct optical guidance of the interception delivery system by the device.
According to one variant of the preceding particular embodiment, the optical guidance means are laser beam remote control means which comprise a laser source integrated into the active imager, the beam of which covers the field of the active imager, and configured in such a way that the divergences of the illumination laser beam of the active imager and of the remote control laser beam are identical or similar.
According to one variant of the preceding particular embodiment, the laser imager comprises only one single transmission source. The latter is

6
used both to effect the transmission of the signal serving to illuminate the zone imaged by the device and to effect the transmission of the remote control beam of the interception delivery system, the transmission of the illumination signal and the transmission of the remote control signal being alternated in time.
According to one particular implementation of the variant of the preceding particular embodiment, the imager furthermore being equipped with a wavelength-agile laser transmitter, the transmission of the remote control commands is effected on a wavelength differing from the wavelength of the transmission of the localisation signal.
The characteristics and advantages of the invention will be more readily understood from the description which follows, based on the attached figures, in which:
- Figures 1 and 2 are synopses showing the structure of the device according to the invention, in its general form;
- Figure 3 is a diagram illustrating a first method for effecting the measurement of the target and delivery system distances by means of the device according to the invention;
- Figure 4 is a diagram illustrating a second method for effecting the measurement of the target and missile distances by means of the device according to the invention;
- Figure 5 is a diagram illustrating a first implementation variant of the device according to the invention, in which the latter comprises a laser telemeter;
- Figure 6 is a diagram illustrating a second implementation variant of the device according to the invention, in which the latter is configured to effect by itself the measurement of the target and delivery system distances;
- Figures 7 and 8 are illustrations of two implementation variants of the

7
device according to the invention, in which the latter is configured to effect the remote control of the delivery system;
- Figure 9 is an illustration relating to an application of the device according to the invention, allowing a high-precision target distance measurement to be effected, and facilitating the interworking of a plurality of devices.
As schematically illustrated notably in Figures 1 and 2, the solution provided consists of a device intended to be associated with a main sensor, this main sensor being able, for example, to consist of a sensor integrated into a standard fire control, or a - possibly remote - surveillance and tracking sensor.
A standard fire control itself comprises, in a conventional manner, a main sensor comprising detection means 13, for example an optical, infrared or radar tracking camera, and positioning means 15 allowing orientation of the line of sight axis in two axes, horizontal and vertical. The initial pointing of the fire control towards a target is carried out on the basis of an external object designation (for example a surveillance radar, an optronic surveillance device, a look-out, etc.).
A surveillance and tracking sensor (for example a multi-functional radar or high-speed optronic surveillance) is a sensor allowing successive detection of targets in a substantial angular domain (for example 360° in azimuth and from 10° to 40° in angle of sight), then to carry out the tracking thereof, i.e. to localise the target precisely (for example to within a plurality of milliradians) and with a sufficiently high frequency (for example 10 to 40 Hz). This precision and this refresh rate allow direct orientation of the "dual axes" (horizontal and vertical) of positioning means towards the target, these means themselves being linked to the device according to the invention.
The device according to the invention consists mainly of an active laser imager 11 associated with a dual deviation indicator12. This deviation

8
indicatoris configured to allow simultaneous localisation of the target 16 and the delivery system 17 and, more precisely, to determine the differential angular deviation measurement 0 between the target 16 and the delivery system 17 responsible for intercepting it. The device according to the invention thus allows the guidance of the delivery system 17 towards the target 16 with a high precision without excessive sophistication of the fire control or the delivery system.
As shown in Figure 2, the differential deviation measurement 9, 121, between the target 16 and the delivery system 17 thus determined is intended to be associated with measurements 21 of the target and delivery system distances, obtained, furthermore, to produce, with the aid of the means 22, remote control commands allowing guidance of the delivery system 17 towards the target 16 or to a vulnerable part of the target. These remote control commands may themselves be transmitted to the delivery system via a conventional hyperfrequency or laser uplink, indicated by the broken-line arrow 23 in the figure.
According to the application concerned, the target and interception delivery system distances are measured in different ways, directly with the aid of the means constituting the main sensor, a tracking radar or a surveillance and tracking radar, for example, or by an additional sensor, a laser telemeter 51, for example, as shown in Figure 5 presented below.
According to one particular embodiment, the device according to the invention may also comprise a passive optical device intended to be mounted on the delivery system 17 and allowing the amplification of the laser echoes reflected by the delivery system.
Thus, in the case of a standard fire control, a typical firing sequence implements the different means which interwork with the device according to the invention on the basis of the following principle:

9
- the acquisition and rough tracking of the target are carried out by the main tracking sensor 13-15, for example a radar or a camera 13, mounted on a mechanical pointing device 15, for example a turret or sight unit.
- the processing means 14 of the main sensor process the signal 131 originating from the sensor 13, a video image 18 for example, to determine the angular position of the target on the basis of the echo reflected by the latter and thus to initiate then maintain an angular tracking loop linked to the pointing device 15.
In the case of an association with a surveillance and tracking sensor, the pointing device 15 is pointed directly using the measurements of the sensor.
- then, in the case of a standard fire control as in the case of an
association with a surveillance sensor, as soon as the target 16 enters the
field of the active imager 11 of the device according to the invention, a fine
angular tracking of the target 16 or a chosen part of the target is instigated by
the latter. For this purpose, the image 19 of the target, obtained by the active
imager 11, is processed by the deviation indicator12 of the device according
to the invention. The signal 111, corresponding to the image 19 processed by
the deviation meter, is formed on the basis of the echo 26 of the laser signal
24 transmitted by the imager 11 and reflected by the target 16, in accordance
with the operating principle of an active laser imager.
Then, if a firing decision is taken, an interception delivery system is sent towards the target and the following guidance phases are implemented:
- a first phase, initial phase, of guidance of the delivery system 17
(missile, etc.) towards the zone located in the field of the active laser imager
11 is provided by the guidance device associated with the main sensor, and
forming the fire control system. This device may, for example, be a remote
control device 22, linked to the telemetry system of the main sensor,
transmitting navigation commands 23 to the delivery system 17 as shown in
Figure 2, or may also comprise an ancillary device linked to the sensor, a

10
beamriding system on which the delivery system automatically adjusts its trajectory.
- a second phase, which begins when the delivery system 17 enters the field of the active imager 11 and during which the deviation indicator12 performs the acquisition and tracking of the delivery system 17. The delivery system is localised thanks to its echo 26 which, as previously mentioned, may be amplified by a passive echo amplifier device, for example a retroreflector.
- a final phase during which the tracking of the target 16 and the guidance of the delivery system 17 towards the target are directly controlled by the device according to the invention. The guidance of the delivery system 17 towards the target 16 is effected by measuring the delivery system-target differential deviation measurement, 0, and by sending navigation commands to the delivery system 17 using, for example, the hyperfrequency or laser remote control means 22, associated with the firing system, until the interception. These remote control commands are produced using, in particular, the relative angular positions of the target 16 or a particular zone of the target and of the delivery system 17, determined by the deviation indicator 12 processing the image 19 produced by the active laser imager 11. Alternatively, the guidance of the delivery system towards the target can be effected by implementing an ancillary laser guidance (beamriding) device controlled by the device according to the invention.
Advantageously, the device according to the invention thus allows a very precise guidance of an interception delivery system 17 towards a target 16, without the need for substantial modifications of the protection system (main sensor and fire control) with which it is associated, or on the interception delivery system 17 implemented by this system. The addition of the device according to the invention to a system of this type therefore allows, in a simple manner and at low cost, a significant increase in the guidance precision of the delivery system 17 towards its target 16.

11
Thus, for example, an active laser Imager whose field covers 5 milliradians and having a sensor with a 500-point resolution allows a theoretical precision of the differential angular deviation measurement 0 of 10 microradians. Assuming the quality of the optical system limited by diffraction and a laser illumination at 1.5 microns, the diameter of the optical system would be around 200 mm, which does not constitute a major integration difficulty.
Furthermore, active laser imagers being sensors increasingly used for different applications such as remote identification (maritime, border surveillance, etc.), the techniques associated with active laser imagery (solid-state lasers, InAsGa image sensors) are undergoing rapid development. Consequently, through mass effect, the cost of such imagers is constantly falling.
Similarly in an advantageous manner, the guidance effected here being a differential guidance, a fine stabilisation of the line of sight of the system is not necessary in order to obtain a high guidance precision. It suffices only that the target 16 and the delivery system 17 remain in the field of the active imager 11. An electronic stabilisation is, however, conceivable in order to guarantee an ease of visualisation for an operator possibly wishing to visualise the captured images.
Furthermore, it must be noted that, the high resolution of the active imager 11 allowing a precise guidance of the delivery system 17, the device according to the invention is particularly well-suited to guidance of low-cost, small-lethal-radius delivery systems 17, or the guidance of delivery systems whose effectiveness requires impact with the target 11. The possibility of reaching a high-vulnerability point of the target 16 in such a way as to increase the effectiveness of the firing thus allows the use of delivery systems 17 carrying lighter loads and, consequently, minimisation of the collateral damage that may be caused in the interception zone.

12
As previously mentioned, tlie guidance may furtiiermore be facilitated by the implementation of a retroreflector (tube corner or other) on the delivery system 17, in order to amplify the signal reflected by the latter. Insofar as simple solutions furthermore exist that enable the performance of this reflector function by one of the devices mounted on the delivery system, for example with a hyperfrequency or laser remote control receiver, this addition allows localisation of the delivery system to be facilitated without causing a significant increase in the cost of this delivery system.
The use of the device according to the invention is thus advantageously economical in terms of implementation.
It must be noted that, as well as enabling the performance of the angular measurement function for which it is normally implemented, the device according to the invention may, in certain particular embodiments, be configured to carry out measurements of the target and delivery system distances. In fact, the sensor of the active laser imager 11 of the device generally has a sensitisation and desensitisation control, the very short switching time of which allows the imager to be rendered sensitive only during one or more successive temporal windows separated in time as from the time of transmission of the localisation signal 24. Each temporal window corresponds to a distance interval whose position is a function of the propagation speed of the transmitted wave. Thus, for example, a temporal window of 500 ns corresponds in terms of propagation to a distance interval of 150 m.
As shown in Figure 3, a distance search can thus be carried out by considering a series of active images obtained by effecting the offset of an analysis window (temporal window) 31, from one image capture to another. The distance measurement method then consists in offsetting in time, with each transmission of the localisation signal 24, the reception temporal window, and in testing for each captured image the presence of the object, target or delivery system, in the image concerned. Then, if the object

13
concerned is detected in an innage, the position of the window corresponding to this image (the position of the centre of the image for example) is attributed to the object. The precision of the distance measurement obtained is then more or less equal to the width of the window 31.
However, this precision may be improved, as shown in Figure 4, by effecting a temporal oversampling. Thus, for example, if the window 31 is offset, with each laser pulse, only by a fraction of its temporal width (i.e. its duration), for example half of its width, as shown by the chronogram in Figure 4, the domain of uncertainty 41 of the measurement is then reduced and the position of this same measurement is increased (multiplied by 2 in the example shown in Figure 4).
It must be noted that the distance search thus effected may, of course, be accelerated by not carrying out a simple systematic exploration through successive offsets of the time of capture. For this purpose, different well-known methods can be implemented, notably search by dichotomy, or search by successive applications of different temporal windows of different sizes, arranged according to a Gray code, for example.
Thus, according to the switching capacities of the active laser imager 11 used and the type of windowing that the processing means 12 associated with it can implement, the precision obtained in the distance measurement effected by the device according to the invention may be sufficient to supply the target and delivery system distances necessary for the guidance. In a configuration of this type, the device according to the invention is capable on its own of performing both the target and delivery system angular trackings and the guidance of the delivery system 17 towards the target 16. Recourse to a different telemetry means, the telemeter of the system if the latter comprises one, or the addition of a laser telemeter, for example, is thus not necessary.
It must be noted that the use of image capture temporal windows (i.e. monitoring windows) advantageously allows an improvement in the contrast

14
of the image of the target, on the one hand by separating it from the background noise (by carrying out the desensitisation of the sensor following the return of the target echo) and, on the other hand, by eliminating the atmospheric diffusion of the transmitted signal 24 on any haze or smoke (by carrying out the desensitisation of the sensor before the return of the target echo). These familiar windowing techniques are generally used for their sensitivity-increasing effects. The temporal windowing may furthermore be used to effect a selective capture in a window to improve the localisation of the delivery system 17 by placing its echo in a temporal window centred on a time corresponding to a distance estimated by real-time simulation of the path of the delivery system.
It must also be noted that, prompted by the identification and recognition functions, the very high resolution of the active laser imager advantageously allows the implementation of the device according to the invention, beyond the operation of guidance of the delivery system 17 towards the target 16, to evaluate in a very precise manner the degree of success of the interception performed and the possible change in the target 16 following interception (confirmation of target hit, state of the damage). If needed, an integration and re-adjustment over a plurality of successive images enables improvement in the quality of the visualised image.
It must also be noted that the laser transmitter and the sensor that make up the active laser 11 are generally capable of operating over the entire field covered by the imager, at refresh rates significantly greater than the video frequency, which is a frequency of several hundred Hertz, for example. However, the refresh rate of the image 19 is generally limited by the output rate (in pixels/s) of the sensor. Nevertheless, some imagers are equipped with sensors that can be configured in such a way as to transmit, on command, only certain zones of interest of the overall image. Then, if the zones of the image 19 containing the target 16 and the delivery system 17

15
are defined as the zones of interest, the transmission frequency can be significantly increased. A much higher transmission rate can then be obtained, for example several thousand Hertz.
Thus, with a laser imager comprising a sensor offering these possibilities and an appropriate image processing, the device according to the invention can be configured to present a very wide tracking and guidance bandwidth allowing the interception of specific targets, for example fast-moving or manoeuvring targets. It should be remembered here that a manoeuvring target is a target that performs changes with significant lateral accelerations (i.e. sharp turns in everyday language) with the aim of escaping the defence or making the interception by a defence delivery system more difficult.
The duration of the high-frequency operation can furthermore be limited to a determined phase of the interception of the target 16, for example the end of the interception. This therefore provides a multi-purpose device, capable of covering both the imaged field with a standard refresh rate of the captured image 19 and a more restricted field with a very high refresh rate of the captured image 19.
In order to respond notably to certain particular applications, the device according to the invention can adopt particular embodiments. Some of these embodiments are presented in the text below.
Thus, in a first embodiment, shown in Figure 5, the device according to the invention is supplemented with a laser telemeter. According to the invention, this telemeter is configured to supply the target and delivery system distance information with a precision and frequency sufficient to produce precise kinematic data, notably allowing the fine guidance of the delivery system 17 towards the target 16, even in the event of manoeuvres or substantial movement of the latter, a moving target being defined as a target moving in a direction more or less perpendicular to the line of sight axis of the imager (lateral movement as opposed to a radial movement). In the event of

16
significant movement and manoeuvres, the determination of the target kinematics and consequently the guidance of the delivery system in fact require target distance measurements with much greater precision than those which the device allows to be obtained.
As shown in the synoptic diagram in Figure 5, the addition of a laser telemeter 51 to the device according to the invention advantageously allows an operating configuration to be conceived for which the main tracking sensor with which the device according to the invention is associated allows instructions to be produced allowing the tracking of the target with the aid of a rough pointing device.
In this configuration, the active laser imager 11 transmits a laser illumination 24, a luminous wave allowing the generation of an image of the target 16 and of the delivery system 17. The laser telemeter 51 for its part transmits laser pulses 52 allowing measurement of the distances of the target 16 and the delivery system 17, indicated by the double dotted arrows 512 and 513, on the basis of the echoes 53 and 54 reflected by the target and by the delivery system respectively. The means 12 associated with the imager 11 are configured here not only to effect the differential deviation measurement between the target 16 and the delivery system 17, but also to integrate the distance information 511 supplied by the telemeter in such a way as to produce guidance information to guide the delivery system 17, said information being transmitted to the delivery system 17 by the remote control transmitter 22.
It must be noted that the laser telemeter 51 is initially pointed at the target, in the same way as the active laser imaging device according to the invention, thanks to rough pointing effected by the system with which it is associated. For this purpose, during its integration on the rough pointing means, it is subject to an operation of alignment with the active laser imaging device according to the invention.

17
In a second embodiment, the device according to the invention is associated with ancillary low-cost guidance means managed by the detection system, 13-15, with which the device is associated, for example a beamriding guidance system. The function of these supplementary guidance means is to effect the guidance of the delivery system 17 towards the target 16 during the flight phase in which it is located outside the field of the imager 11. The guidance is then effected on the basis of the distance, line of sight and azimuth information supplied by the main sensor of the detection system, IS¬IS. In this configuration, the device according to the invention is used only for the final interception phase, for which the precision and bandwidth requirement is the greatest. This implementation allows more optimised trajectories to be obtained (moving target, etc.). It also allows the system to be made capable of carrying out multi-target interceptions through the implementation of a plurality of ancillary, co-located guidance devices and through the sequential management of the device according to the invention to effect successive interceptions. Furthermore, the device according to the invention thus implemented advantageously allows the guidance of the delivery system to be made independent, to a large extent, from the main sensor with which it is intended to be associated.
In a different embodiment, the device according to the invention is linked to a precise surveillance sensor, for example a multifunctional radar, or to an optronic surveillance system which performs the target detection and tracking function and allows direct pointing of the device. The use of a rough tracking sensor is then no longer necessary, insofar as the rough pointing device can then be controlled by the target measurements (line of sight and azimuth deviation measurements, or line of sight, azimuth and distance deviation measurements) carried out by the precise surveillance sensor. The target will then appear in the field of the active laser imaging device according to the invention without the need for an intermediate acquisition phase by a tracking sensor.

18
It must be noted that the absolute deviation measurements of the target, i.e. the angular deviation between the position of the target and the axis of the active laser imaging device, obtained by the deviation measurement associated with the active laser imaging device, can be used to control the rough pointing device in a more precise manner than permitted by the deviation measurements of the surveillance sensor.
It must furthermore be noted that, in the case of the acquisition of the target is provided in advance by an optronic surveillance sensor, i.e. without distance information, the loopback of the rough pointing onto the absolute deviation measurements of the target advantageously allows pointing of a laser telemeter harmonised with the active laser imaging device according to the invention.
In a further different embodiment, the active imager 11 of the device according to the invention comprises a wavelength-agile laser source, or is able to transmit localisation light signals on two different wavelengths. Furthermore, the device according to the invention here comprises a retroreflector device equipped with an interferential band-stop filter intended to be mounted on the delivery system 17, the role of which is to block the reflection of the signal carried by one of the two wavelengths. The echo of the delivery system 17 can thus be discriminated from possible jamming echoes (countermeasures) transmitted by the target 16, the discrimination being effected through comparison between the two images produced with two different chromatic illuminations. The use of an active (laser) means can in fact be detected by the target 16, provided that it is equipped with a warning sensor. Said target may then implement countermeasure means, such as, for example, the retroreflector stream being able to hinder the tracking and therefore the guidance of the delivery system 17. A jamming of this type is particularly effective during the final phase, when the temporal

19
windowing is no longer discriminating between the target and the delivery system.
In a further different embodiment, the device according to the invention comprises a laser receiver/responder intended to be mounted on the delivery system 17. This embodiment, more costly than the preceding one, advantageously allows further improvement in the resistance to the countermeasures that may be implemented by the target 16. In particular, it enables a temporal discrimination between the jamming echoes (countermeasures) despatched by the target 16 and the echo of the delivery system 17. It also enables the creation of a downlink (delivery system-guidance system link) that can be used to implement various other functions, for example telemetry functions.
In a different embodiment, shown in Figure 6, the device according to the invention comprises an imager 11, itself comprising a laser transmitter capable of transmitting pulses with a high frequency and a sensor configured to produce images with a high production frequency, as described above. The processing means 12 associated with the imager 11 are for their part configured in such a way as to be able to measure both the target/delivery system differential deviation measurement, as shown by the chronogram 61 and the respective distances of the delivery system 17 and the target 16, the distance search being effected, for example, as shown by the chronogram 62, through successive applications of different temporal windows of different sizes, arranged according to a particular code.
The production of high-frequency images thus obtained allows an updating of the images that is sufficient to alternate the determination of the delivery system-target differential deviation measurement (with two temporal windows centred on the distances of the delivery system 17 and the target 16), and the performance of search and distance measurement tasks, with no significant adverse effect on the guidance performance.

20
In a different embodiment, shown in Figure 7, the uplink comprises a laser source integrated into the imager, the beam of which covers the field of the active imager. The function of this second laser source is to implement the remote control link 73 of the delivery system 17 (uplink). In this embodiment, made possible insofar as the divergences of the illumination laser beam 71 of the active imager and of the remote control laser beam 72 are similar or identical, the projection optical system is advantageously shared. This embodiment thus advantageously allows a reduction in the number of optical paths necessary for the guidance and provides, by design, the alignment of the two paths.
In a further different embodiment, shown in Figure 8, a variant of the preceding embodiment, the laser imager 11 comprises only one single transmission source which is used to effect both the transmission of the signal 24 serving to illuminate the zone imaged by the device and the transmission of the remote control commands 81 necessary for the guidance of the delivery system. The transmissions used for the illumination 24 and those used for the remote control 73 of the delivery system 17 are then alternated in time, as shown in the figure.
In the case where the imager 11 is equipped with a wavelength-agile transmitter, the transmission of the remote control commands 73 can furthermore be effected on a different wavelength.
Finally, in a different embodiment, the device according to the invention may comprise an imager 11, itself comprising a laser transmitter configured to generate, on command, for the purpose of deterrence, a laser beam in a visible wavelength in such a way as to cause a glare or alert the pilot or crew of a potentially hostile aircraft 16 (potential target to be intercepted) to the imminence of the despatch of an interception delivery system 17 to meet it.

21
This transmission on a visible wavelength may, for example, be obtained either by implementing a wavelength-agile laser, or by inserting a non-linear optical element (for example a frequency-doubling or frequency-tripling crystal) into the beam of the laser transmitter of the device.
It must be noted that, regardless of the embodiment considered, the device according to the invention is intended to be linked to a surveillance and interception system wherein it allows a significant improvement (and at low cost) in the relative localisation precision of an interception delivery system 17 in relation to a declared target 16 that must be intercepted in the most effective manner possible, and the guidance of the delivery system 17 towards this target 16. A surveillance and interception system may therefore comprise one single device according to the invention, co-located with the main sensor of the system.
Alternatively, as shown in Figure 9, it may comprise a plurality of devices according to the invention 91 (two devices I and II in the figure), separated from one another, one of the devices being, for example, co-located with the main sensor of the system. A configuration of this type is advantageously adapted to cases where the precision of the distance measurement must be maximum, as, for example, when the target to be intercepted comprises a shell moving in front of the system, a target for which the interception must entail the impact of the delivery system on the target. The guidance precision to be achieved is then on a centimetre scale.
In such a case of use, the device according to the invention is used in a plurality of specimens (two or more) occupying, in relation to one another, positions that are known as precisely as possible. The angular measurements (a and (3) carried out by the different devices, of which the relative positions (distance D) are known with precision, are jointly exploited here by the system in such a way as to precisely determine the distance of the target through simple triangulation, as shown in Figure 9.

22 CLAIMS
1. Differential guidance device using active laser imagery to guide an
interception delivery system (17) towards a target (16) comprising a
main sensor (13, 15) linked to said device and positioning means
(15),
characterized in that the main sensor (13-15) is suitable for detecting and designating the target (16),
in that said device being mechanically linked to positioning means (15) allowing orientation of its line of sight axis towards the target (16) in two axes, horizontal and vertical, and in that it mainly comprises an active laser imager (11) transmitting a localisation laser signal (24), associated with a dual deviation indicator (12) configured to allow simultaneous localisation of the designated target (16) and the interception delivery system (17) and to determine the differential angular deviation measurement 9 between the direction corresponding to the target (16) and the direction corresponding to the interception delivery system (17).
2. Device according to Claim 1, characterized in that it furthermore comprises an optical amplifier device, mounted on the interception delivery system (17) and configured to allow amplification of the laser echo (26) reflected by the latter.
3. Device according to one of Claims 1 or 2, characterized in that it furthermore comprises a laser telemeter (51) allowing determination of the respective distances of the target (Dtarget) and the interception delivery system (Ddeiivery system), the direction pointed by the telemeter being determined by the dual deviation indicator; the distances of the target (16) and the interception delivery system (17) being transmitted

23
to means (22) responsible for guiding the interception delivery system towards the target.
4. Device according to one of Claims 1 or 2, characterized in that the active imager (11) is configured in such a way as to effect, between two consecutive transmissions (24), the acquisition of a plurality of successive temporally offset images, the acquisition times and the duration of each acquisition allowing the definition of acquisition windows separated from one another, the distance interval corresponding to a given image being a function of the time interval separating the time of opening of the temporal window during which the image was captured from the time of transmission.
5. Device according to Claim 4, characterized in that the dual indicator(12) is configured in such a way as to transmit to means (22) responsible for the guidance of the interception delivery system towards the target both the delivery system-target differential deviation measurement and the distance corresponding to the temporal window on the basis of which the transmitted differential deviation measurement was calculated.
6. Device according to any one of Claims 1 to 5, characterized in that it furthermore comprises ancillary guidance means configured to take into account the information relating to the line of sight, the azimuth and the distance of the designated target (16), supplied by the detection system (13-15), and to effect the guidance of the interception delivery system (17) towards the target (16) during the flight phase in which it is located outside the field of the imager (11).
7. Device according to Claim 6, configured to effect a multi-target interception, characterized in that it comprises a plurality of ancillary

24
guidance means, each being configured in such a way as to provide the guidance of an interception delivery system towards a given target, the device according to the invention itself been configured to be oriented successively towards each of the designated targets and implemented in such a way as to simply provide the final guidance of the corresponding delivery system towards the target concerned.
8. Device according to any one of the preceding claims, characterized in that it furthermore comprises means associated with the imager (11) allowing a direct optical guidance of the interception delivery system by the device.
9. Device according to Claim 8, characterized in that the optical guidance means are laser beam remote control means (73) which comprise a laser source integrated into the active imager (11), the beam of which covers the field of the active imager, and configured in such a way that the divergences of the illumination laser beam (71) of the active imager (11) and of the remote control laser beam (72) are identical or similar.

10. Device according to Claim 8, characterized in that, the laser imager (11) comprising only one single transmission source, the latter is used both to effect the transmission of the signal (24) serving to illuminate the zone imaged by the device and to effect the transmission of the remote control beam of the interception delivery means, the transmission of the illumination signal (24) and the transmission of the remote control signal (73) being alternated in time.
11. Device according to Claim 10, characterized in that, the imager (11) being equipped with a wavelength-agile laser transmitter, the transmission of the remote control commands (81) is effected on a

25
wavelength differing ftorn l:lie wavelength of the transmission of the locaiisation signal (24),
Dated this 23/04/2012 ' --'"^
(NEHA SRIVASTAVA)
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S |