FR3005359A1 - METHOD AND DEVICE FOR PROTECTING LOW-ALTITUDE AIRCRAFT AGAINST SOLID AIR MISSILE - Google Patents

Abstract

Protective method for aircraft operating at low altitude vis-à-vis ground / air missiles comprising a step of detection of passive approach (1) of threat designation to develop raw tracking towards these threats, a detection step active (2) triggered from the raw designation provided by processing the passive detection, a step of processing the respective detection data (3,4), passive and active, to extract respectively raw trackings and accurate trackings from previous detections and positioning information of the aircraft (8), and a step of managing these data (5) by fusion to form a hierarchy of these threats leading to the development of a threat processing order, a choice of countermeasures according to this order, and parameter values adapted for its deployment.

Description

The present invention relates to the protection of aircraft operating at low altitude, including helicopters, and relates to a method and a device for protecting such aircraft vis-à-vis ground / air missiles.

The protection of aircraft, especially those operating at low altitude, has changed significantly in recent years because, in addition to remote-controlled radar or laser beam missiles, most of the ground-to-air threat (over 90%) is currently missiles, with terminal guidance performed by an infrared homing device. In the medium term, specialized weapons systems will be able to implement multi-mode firing lines (radar, laser and infrared). Effective protection of the helicopter or low-level aircraft therefore requires the ability to detect the firing pattern of weapon systems and hostile weapons fired taking into account the potential multiplicity of threat components, and with sufficient notice to implement an adequate response (maneuvering, decoying, jamming, ...). Threats against helicopters or low-flying aircraft are generally classified as Short-Range Ground / Air 20 (SACP), and Very Short-Range (Short SATCP) ground-to-air threats. For example, current SACPs and SATCPs with radar, laser, infrared or combined radar / laser guidance have typical ranges from 3.5 km (infrared guidance) to 7 km (radar and / or laser guidance). Other guiding techniques (for example of the filo or fibroguidage type), used on other weapon systems, may possibly be used by missiles likely to threaten a helicopter or an aircraft. The use of these guidance techniques does not fundamentally modify the characteristics of the missile, in particular its signature in the field of radar waves (electromagnetic, abbreviated EM). The main characteristics of the missile trajectories are as follows: the missiles with infrared terminal guidance have a flight consisting of an initial phase of acceleration (called the "boost phase" in English terminology) of a duration of order of 2 to 3 s bringing them to a speed of about 400 to 500 m / s, followed by a so-called cruise flight phase for 5 to 6 s, and finally, more often, of a flight phase (not powered) called free flight of very short duration (1 to 2 s), - the laser guided missiles or radar have a flight consisting of a boost phase of a duration of the order of 2 at 3 s driving them at speeds of the order of 1000 to 1200 m / s, followed by a free flight phase of duration of the order of 6 to 15 s. Given their overspeed relative to the aircraft, all these missiles are almost directed towards their target from the moment of firing, the trajectory followed being almost rectilinear during the guiding phase. It results in a direction of arrival of the missile contained in an angular domain which extends in 360 ° field and in site on ± 10 ° (in inertial reference carried). However, the evolution of the danger to the aircraft could come from "pull-up" missiles, that is missiles fired in the vertical plane with a far elevation of the line joining the firing line. to the target. This mode of fire leads to initially divert the missile of its target, then to make him make a maneuver to resume a normal trajectory of interception. Thus for a SACP missile with a longer flight time than that of a SATCP missile, it is possible to modify the flight profile so as to reach the aircraft with a higher elevation angle than that of the advanced SATCP missiles. As far as decoying is concerned, infrared (IR) pyrotechnic decoys are increasingly being replaced by omnidirectional jammers with modulated infrared sources, for example arc lamps or cesium flash lamps. But these lamps are not very effective vis-à-vis the imaging missiles and consume significant electrical power (several kW), and are, like IR decoys, indiscreet making the aircraft easily detectable. This has led to the development of directional focus scramblers as described in the article by Burt Keirstead et al, entitled "Integrated Avionics" of the Journal of Electronic Defense, Vol. 15, No. 5. Laser-directed directive jammers, which substantially reduce pupil size and consumption, especially when pumped by diodes, are currently the most effective for jamming imaging-guided missiles.

Optimum management of countermeasures, avoiding excessive consumption of lures and untimely maneuvers, requires an accurate and rapid assessment of the danger to the aircraft, as well as an optimal implementation of the countermeasures.

Known protection systems develop a missile alert detection function associated with a so-called countermeasure reaction function. The missile warning detectors currently comprise, in a conventional manner, a radar warning detector, sometimes associated with a laser alert detector both operating in passive listening to detect, analyze, identify and develop the direction finding of the received transmissions. The countermeasure function is ensured by the use of infrared (IR), electromagnetic (EM) lures and / or by performing a backup maneuver. Some missile approach radars allow the detection of SATCP and SACP missiles. A radar of this type is specialized by a judicious choice of the emission frequency band, the waveform, the characteristics of the antennas and the processing algorithms, notably providing for distance, radial velocity and theoretical duration before impact. Its main advantage is the detection safety it provides, which results in a low rate of false alarms (abbreviated to TFA). However, this solution has the major disadvantage of not being sufficiently discrete because of the need for a permanent EM emission for panoramic monitoring. In addition, angular measurements suffer from poor resolution as a result of diffraction of the emission lobes. The need to refine the measures by implementing specialized filtering and tracking algorithms results in a critical increase in the time taken to acquire the threat. The response times can not be respected, especially in the case of the 30 SATCP threats. Thus, in many cases, the radar emission technique is not satisfactory for accurately and rapidly locating the priority threats to be treated, in particular those corresponding to a missile fired against the aircraft.

Another limitation of this radar technique comes from the development of the threat with very low EM signature. Moreover, the increasingly widespread appearance of purely optronic acquisition and fire control systems (in the optical, TV or infrared spectral bands) implies that the missile can only be detected from the moment it was fired, without any warning information of the passive component EM necessary for the detection of the firing line. To counter this type of threat, passive optronic detection has developed. Two main techniques exist: the Io IR detection, based on the detection in the spectral band II (3-5 pm) of the emission of the jet of the missile during its propulsed phase, and the detection of the jet in the ultraviolet (abbreviated UV). The IR detectors have a good sensitivity and a good resolution, making it possible to obtain satisfactory ranges (class 10 km) on the jet of the missile; their main drawback is the high probability of false alarm (high TFA) resulting from the large number of parasitic sources in band II. This defect requires the implementation of a very elaborate target extraction processing, including in particular adapted spatial filtering, variable detection thresholding and rejection of fixed targets. On the contrary, UV detectors display a great insensitivity to false alarms. The level of production of the backdrop and the landscape is almost zero in the day, in the UV spectrum less than 290 mm wavelength. This leads to simple extraction treatments. However, these sensors can only be used with a short range (a few kilometers), and only on the missile propulsion phase. Their performance depends on the weather conditions in which missile fire is carried out. The choice of the type of detection to equip the aircraft, active detection and / or passive radar, supplemented by a detection of laser alert, passive IR and / or UV detection, is performed according to the characteristics (altitude, altitude, altitude, altitude, altitude). ) of the mission dedicated to the aircraft. This results in a significant complexity of the processing due to the need, for the chosen optronic detection type, to be able to cope with all the spectral contrast situations between the missile and the environment. Under these conditions, the response may not be effective in speed and accuracy, especially for "silent" threats, that is to say without EM emissions. The invention aims to overcome the aforementioned drawbacks by making it possible to bring the automatic implementation of a fast, reliable and triggered reaction to an optimum instant. For this purpose, the invention proposes a missile warning detection built around an IR passive optronic detection, or IR and UV combined, combined with an active detection, radar or laser, operating in "slave" mode of detection. optronics. The approach followed draws on the complementarity of the information provided by each detections and a processing allowing the fusion of this information to obtain the best possible knowledge of the threat in the minimum time necessary for the protection announced. More specifically, the object of the invention is a protection method for aircraft operating at low altitude vis-à-vis ground / air missiles comprising a step of passive optronic detection of missile threats to develop angular tracking operations. direction of these threats, an active detection step triggered from the angular designation provided by passive detection processing, a processing step of the respective passive and active detection data, respectively to extract complete and accurate readings from previous detections and positioning information of the aircraft, and a step of managing these data by merging to form a hierarchy of these threats. This prioritization step leads to the development of a threat processing order, a choice of countermeasure according to this order, and parameter values adapted for its deployment. The active detection, which may be a radar or laser detection, is activated only on prior designation of the only direction of the track coming from the passive detection component (in IR or IR spectral band associated with UV, called the optronic band). and therefore with sufficient discretion to minimize the risks of interception of the active issue. This arrangement makes it possible to carry out an active panoramic detection without this type of detection resulting in an increase in the threat linked to the transmission of the device intended to protect it. To optimize the processing, an additional step consists in integrating into the data merging step a step dedicated to eliminating false alarms. Suitable and associated countermeasures can be chosen between infrared or radar decoy, and / or infrared lamp or directional radar interference. Multireal laser scrambling, particularly suited to the method according to the invention, can be used in preference to lamp-directed interference. The invention also relates to a protection device for implementing said method. This device is preferably in the form of a modular monobloc structure means stacked in successive layers consisting of passive and active detectors, missile locating means 15 and detection data processing means. This stack allows a simplification of the architecture of the installation by significantly reducing the number of interconnections between the detection means, treatment and countermeasure, and by corollary reduction of the size and weight of the device. self-protection 20 complete. In addition, it is possible to use this layered structure to insert other applications (radar, laser telemetry, ...) or for extensions (detection of flashes of helicopter blades, passive direction finding radar radar emission , ...). The various extensions are advantageously integrated in successive layers so as to preserve the monoblock shape of the assembly. Preferably, the detection, location, processing, power source and countermeasure control means are interconnected by a single and fast link so as to establish optimized information exchanges. In the case where a protection for aircraft, operating in particular at low altitude is sought, the device according to the invention comprises a mobile frame and a fixed frame. The mobile frame comprises the active detection means (for example radar) and an inclined scanning mirror for diverting the input flow to the passive optronic detectors located in the fixed frame which also houses the processing means. In the case where only the protection of helicopters is sought, such helicopters conventionally comprising a rotor with blades rotated about an axis by known means, the detectors are fixed to the axis of rotation of the rotor, preferably to above it in order to benefit from a better visibility, to ensure a permanent 360 ° sweep in the field. The device also comprises means for developing a threat processing order based on a hierarchy of threats resulting from the tracking data, and means for triggering a countermeasure adapted to the processing order. The coupling of the detectors to the rotor has a double advantage: it makes it possible to ensure an omnidirectional coverage in the field with the aid of a reduced number of sensors; it also eliminates blade effects with optimal positioning sensors, fixed relative to the blades and as their optical sighting axes are arranged between the blades. According to one particular embodiment, the protection device comprises means for activating the active detection on demand, on internal or external stress, to confirm the missile angular tracking and to determine missing parameters of speed of approach and distance of the threats to be transmitted to data fusion means. The passive detection can be carried out by an IR detector 25 associated or not with a UV sensor. Active detection can be performed by a laser and / or radar technique. In an exemplary embodiment, the countermeasure is a diode pumped multi-phase laser jammer, particularly adapted to the protection device according to the invention, the triggering means of this jammer comprising pre-pointing means. Another countermeasure may consist of decoying means, the triggering means then comprising means for determining the ejection of these decoys at a given instant and with optimum chronometry.

In another particular embodiment, the protection device may also contain the device processing and management means that develop the maneuver commands for the aircraft. Other characteristics and advantages of the invention will become apparent during reading of the detailed description which follows, illustrated by the appended figures which represent respectively: FIG. 1, a functional block diagram of the protection method comprising active detection EM ( radar); FIGS. 2 and 2a, an exploded view and an external view of a modular missile warning structure of the helicopter protection device according to the invention; and FIG. 3 is a view from above of the optronic and radar axes of sight of a device according to the invention; - Figure 4, an example of adaptation of the protection device 15 according to the invention in the case of an aircraft. The functional flowchart of FIG. 1 shows that the protection method according to the invention is organized around a passive detection 1, in the conventional optronic detection bands of the IR thermal radiation, and possibly UV combustion of the jet of the propellant of the 20 missile to be detected, coupled with an active detection 2, radar or laser, respective processing 3 and 4 of these passive and active detections, to deliver an alarm information to a management 5, and a link 6 compatibility between detections and interface with a countermeasure command 7 (abbreviated CM). The spectral bands of operation of the passive detection are conventionally the IR band II, covering the spectrum 3-5pm, and the UV band of solar irradiance called "solar blind" in English terminology, of radiation detection of the combinations resulting from the combustion of propellants. The passive detection processing 3 simultaneously takes into account the signals resulting from the IR and UV detections, in the case of a dual optronic detection. It realizes the extraction of the sources of emission in the form of "plots" (image-points likely to be a missile), the analysis and the follow-up of the course of these plots, elaborated classically on the basis of criteria of spatial parameterization, temporal and radiometric, and the directional extraction of missile tracks. Passive detection processing 3 designates information management alarms corresponding to the detected missiles. Two known types of treatment can be advantageously implanted and performed simultaneously. The first treatment, called short-range detection, corresponds to an objective of highlighting nearby missiles with a reaction time as short as technologically possible. The second, long-range detection process corresponds to a remote missile focus objective. It therefore takes into account more stringent detection conditions than in the previous case. This aspect is compensated by taking into account the parameterization criteria over a longer time, which makes it possible to eliminate the false alarms induced by the lowering of the thresholds in detection. This last treatment is therefore equivalent to the introduction of an additional step of eliminating false alarms. As for the active detection processing 4, treatment type said "radar pulse Doppler" in English terminology, it consists in extracting 20 measurements of speed and distance of the most mobile targets at the time of its release. This known treatment is based on the use of coherent waves, the frequency analysis of which provides speed information by identification of a component due to the Doppler effect, and whose temporal analysis provides distance information. The information management 5 mainly provides two related functions, implemented by application of digital processing: a compatibility function that makes it possible to manage compatibility signals exchanged between the passive and active detection processes, and an interface function between These detection processes and a central countermeasure control 7. The interface function also processes positioning information of the aircraft 8 (roll condition, altitude, rotor position in the case of the helicopter application, etc.). .), intended to identify the relative positioning of the passive detections. This identification makes it possible to locate in the direction of the alarms in connection with the passive detection processing 3.

The management 5 transforms, by the processing of the positioning information 8, the alarm information obtained by passive detection processing 3 in angular locations of these alarms. The compatibility function manages, from the designations of the passive detection, the triggering of the active detection 2 in the form of activation requests, these requests can be of internal origin, or possibly external to the detection system that is ie either automatically or at the pilot's request. The merging of the locations and the measurements made by the processing of the active detection 4 is managed by the compatibility function. The management 5 then extracts missile tracks and classifies the threats according to a threat processing order. The criteria for developing the tracks may vary according to the nature of the alarms: the alarms are conventionally filtered according to their content and by application of appropriate decision logic tests, known per se. Control signals are developed according to this order and transmitted, as part of the interface function, to the central control 7 of CM. This "missile track" information is intended for the central countermeasure control 7 for a reaction adapted according to the means of countermeasure provided for or residing on the aircraft. The interface with this central control of countermeasure 7 can be achieved via a single link. Furthermore, the information management 5, coupled with the central control of CM 7, can also receive designations corresponding to electromagnetic threats, as well as data from the navigation unit of the aircraft which make it possible to compensate for the influence of the movements in the information processing. Active detection processes depend on the type of measurement used, radar or laser. For radar detection, this processing consists in extracting the information of speed and distance of the highly mobile targets present in the lobe of the radar at the moment of the triggering of the measurement. The treatment is derived from Doppler modulated pulse radar treatments. At each activation of the radar, at the request of the information management 5, the active detection processing 4 delivers the detections obtained. As for the active laser detection processing, it can also consist in extracting the distance and velocity information by temporal and frequency processing of modulated pulses of the telemetered threats, in the image of the treatment carried out for the detection in the field of EM waves. (radar). The invention also relates to a protection device for implementing the method that has just been described, including in particular a rotating missile warning module, composed of passive (IR and UV domain) and active (EM domain) detectors. or laser) and positioning means of the aircraft, and coupled to detection data processing and management means grouped in a processor, and a single link connection means between the elements of the detection module, and between module, power source and CM means. The warning module is in the form of a one-piece structure comprising a stack of elements dedicated to the detection and processing functions, and arranged in successive layers, so as to reduce the number of interconnections. Such a structure also has the advantage of being open to the integration of other elements for ancillary applications (radar, laser telemetry, etc.) or for extensions, for example: an annex radar antenna for detection flashing of the blades in the case of a helicopter application, using the same basic resources as those of the missile detection; Radial direction-finding goniometry blocks remote and grouped. Preferably, the detection and processing means are connected to one another and to the other intervening elements, supply source and CM means, by a single and fast link, so as to establish time-optimized information exchanges. of reaction. The stacking structure specifically promotes the implementation of such a connection. For example, a high speed bidirectional serial link providing minimum reaction times and carried on a common optical medium enables optimized information exchanges between the passive and active detection detectors, the navigation central for localization. missile, the management and data processing processor, and a multiraies laser jammer as a means of CM. The processor can also develop parameter values for the aircraft to perform countermeasure maneuvers, these values being communicated to the navigation commands in the form of signals conveyed by the common medium and presented to the pilot. The alert detection module comprises passive detection means IR, preferably associated with UV detection means. The combination of these two spectral observation windows indeed allows optimized reliability of the missile presence information with a minimal reaction time, corresponding to a range of distance where the countermeasure remains effective. In known manner, the detection in IR can be carried out in two ways: by sensitive strips in band II (3-5 preferably integrated in a bispectral type detection system, in order to facilitate discrimination in distance, between targets and false alarms due mainly to the reflections of the sun on the ground and on clouds, whose distance remains fixed; - with static matrices with a large number of sensitive elementary detectors in the band II, which makes it possible to improve the reliability but requires a more complex target extraction process Passive UV detection may be based on the use of sensors comprising a light intensifier A preferred countermeasure means is a steerable laser jammer in a wide omnidirectional sector, successively pointed towards the detected threats, as designated by the data management processor as being to be processed in p To do this, the processor provides the jammer, from the missile track calculation, all the elements necessary for his command: - data of the threat to be rallied: deposit, site, distance, relative speed; 35 - time remaining before the theoretical impact; - type of threat identified by reference to a database on the threats contained in the management 5 and including the relevant information (missile trajectory, duration of the thruster, nature of the associated fire control, etc.) to optimize the sequence of against -measure by laser scrambling; - start time and duration of the appropriate scrambling sequence. By way of nonlimiting example, an alert detection module comprising the detection and processing elements according to the invention, adapted more particularly to the helicopter application and using an active radar detection, is illustrated by the exploded view represented In this example, the stacked detection and processing elements constitute a revolution module installed above the rotor and fixed on the rotor head to rotate in solidarity with the blades. This assembly comprises, around a cylindrical structure 11 serving as a frame: an active detection radar antenna 12 protected by a radome 13 fixed directly on the structure 11; two optronic IR and UV detectors, 14 and 15, installed in opposition and orthogonal to the axis of the electromagnetic antenna 12; a semi-cylindrical feed 16, fixed on the structure 11; a semicylindrical radar EM transmitter 17, also fixed on the structure 11, facing the power supply stage; a set of plug-in EM radar receiver modules 18, with a synthesizer; a set of cards 19 for pretreatment and electromagnetic (EM), optronic (IR and UV) and peripheral processing, accessible from a door 20 and pluggable on a motherboard 21 equipped with an internal stirring modem 22; an ancillary axial omnidirectional antenna (for radio links) 23, surmounting the whole of the equipped structure 11. As illustrated in the diagram of FIG. 2a, the assembly once mounted is in the form of a cylinder of diameter (I) equal to 500 mm and height H equal to 200 mm, the ratio H / c1) having been determined by the search for the best compromise between: 3005 3 59 14 - limiting the centrifugal acceleration levels, in particular to the periphery of the crown, - optimize the clearance of the radar antenna and optronic detectors, 5 - control the centering of the rotating mass and its inertia, - limit installation constraints at the top of the rotor. This cylinder rests on a mast 60 to 80 cm high, the assembly being fixed on the rotor plane by means of a cylindrical ring of great flatness and adapted to the rotor plane of the helicopter. As for the UV passive detections ("Solar Blind" strip abbreviated SB for short) and IR (band II 3-5 j_tm) are performed by detectors of known type. In the spectral band of operation of the radar antenna, the missile signatures are significant, for example in L-band. The opening angle of the radar beam is usually several tens of degrees. It is also sized to have all the necessary resources to ensure in extension, by adding the specialized omnidirectional antenna, the detection of flashes of blades of hostile helicopters. According to the positioning adopted, the main axes of electromagnetic and optronic radiation of the device are established between the blades, for example in the vicinity of the bisectors of the axes of the blades, thus ensuring an optimal "visibility" for the detection. As illustrated in FIG. 3, which represents a top view (bearing plane) of an A-axis helicopter rotor and equipped with a device according to the invention. The optronic sighting axes AO and AR radar, arranged between the blades Pi, form an offset angle .AG deposit. The main lobe The radar emission is also shown. The radar device angularly covers the entire field at the site of the optronic bar described above, the carrier frequency being high or low. If the carrier frequency used is high (W band for example), the radar antenna is more in-line than the field of the array and the antenna beam is then quickly oriented by a suitable device 35 described below; When the carrier frequency is low (L-band for example), the opening in site of the radar antenna naturally covers the field of the bar and no pointing device is necessary. The radar emission is pulsed with a pulse duration which results from the speed of rotation of the blades. For example, for an emission lobe L of width equal to about 60 ° in L-band, the radar illumination time is equal to about 25 ms when the speed ve is equal to the standard value 400 rpm. Under these conditions, the precise angular location of the target lo is provided by the optronic device, while the distance and the speed of the target are delivered by the radar device. The triggering of this emission takes place as soon as there is IR or UV detection, but with a systematic delay At with respect to this detection. This delay corresponds at least to the processing time of the optronic information. The delay corresponds to the angular offset AG, in the bearing, of the line of sight of the radar transmitter AR relative to the axis reference AO given by the optronic detector, IR or UV. This delay has a value such that, at the time of the radar emission, the direction of this emission is pointed at the missile detected, taking into account the rotation of the detection module. The delay At is therefore related to the drive speed of the rotor ve by the elementary relation AG = At. Ve In these conditions, the radar emission takes place only in the direction of the missile and is discrete, since it is triggered only on Presumption of target in IR or UV. The radar emission starts when the presumed target enters the radar beam and ceases when it leaves. The show is thus as short as possible, for the sake of discretion. In addition, these conditions make it possible to obtain a multi-threat processing capability. During the radar illumination time, at a given rotor revolution, the emission is pulsed (radar-pulse Doppler) at a sufficient repetition frequency so that, after spectral analysis of the received signals, an unambiguous sorting in speed ground echoes and fast moving target echoes. To increase the reliability and range of the radar confirmation, the illumination can advantageously be renewed in the same direction on a few successive rotor turns (typically less than or equal to 5 revolutions). Multicible capacity, that is to say here the spatial separation of several targets simultaneously present in the same radar beam, is ensured by the resolution in distance of the radar and by the fineness of its resolution in speed. Furthermore, the countermeasure jamming means (abbreviated to CM) may be located at the same location or at a different location from that of the missile warning device, but remains decoupled from the rotation of the blades, for example by a installation at the top of the rotor, or deported on the helicopter, above the cockpit, behind the rotor or in the nose. As for the spectral band of the UV detection according to the embodiment example, it is between 0.260 and 0.285 μm to be of zero solar irradiance (called "solar blind" in English terminology, abbreviated SB), due to absorption by the ozone layer at high altitude. Any source then appears as a bright spot on a black background and it is possible, under these conditions, to detect the emission of the missile jet combustion with few false alarms. The detection threshold can then be increased in the absence of solar irradiance. The disadvantage of this band is the very low atmospheric transmission, because of the aerosol and molecular diffusion (known as Rayleigh scattering) as well as because of the absorption due to oxygen and ozone. With photocathode detectors, good performance is obtained for distances of a few kilometers, which is suitable for helicopters. A first possible UV detector is a light intensifying tube whose photocathode, in CsTe or RbTe, provides the detection and spectral selection function. A microchannel slab multiplies the emitted electrons by a factor of 2,000 and provides an easily measurable signal. The technology of light intensifier tubes is well known. Other fully solid state solutions (SiC, ternary semiconductor alloys II-VI (Cd-Zn-Te)) are also conceivable. As for the IR detection of the embodiment example, it is performed by a PZSe type strip cooled to 200 K by Peltier effect, comprising 30 elementary sensors with a pitch of 300 lm in site. The bearing width of the bar is of the order of 30 gm. The field elementary field corresponds to the desirable measurement accuracy on the missile, about 1 °. The corresponding focal length then rises to 300 mm, which gives, for a 1 μm infrared lens of diameter conventionally equal to 20 mm, a realistic aperture equal to F / 0.86. Measuring the instant of passage of the IR sensor array on the image of a missile provides the bearing coordinate by simultaneously rotating the detection module with the rotor and the blades of the helicopter. The angular measurement accuracy in the bearing is 0.1 ° and the moment of passage is measured for a duration of about 0.42 jas in the present case for a standard rotational speed of the rotor equal to 400 revolutions / min. The dimensions of this bar correspond to an instantaneous angular coverage of 0.1 ° in the bearing and 30 ° in the site, which makes it possible to detect the feather of missiles during their phase of powered flight. The scanning of the bearing space is obtained by rotating the rotor. The standard rotational speed of the rotor equal to 400 rpm results in an information refresh time of the order of 0.15 sec, satisfactory for the application. To double the refresh rate of the information, it is possible to double the number of detectors by distribution around the rotor axis. The processing of the rotor position makes it possible to directly calculate the position of the rotor directly, so that the alarms are located instantaneously in the field. In the exemplary embodiment, the treatment is conventionally performed by controlling a clock on the rotation of the rotor, thanks to synchronization pulses delivered during the passage of the rotor to a reference position. The processor delivers at all times the rotor position with respect to a local repository. It also corrects this information of the movements of the helicopter platform, to obtain an angular location in inertial mark carried thanks to the information coming from an inertial unit conventionally equipping the helicopter. The interface between the detection and processing elements of the warning device according to the exemplary embodiment with, on the one hand, the power source means and the other data exchange and countermeasure control, is realized, respectively, by a conventional rotary joint and a high-speed bidirectional optical link, the connection fixed part / moving part being performed by an optical rotary joint. On the optical data link, the discrete signals are coded and "inlaid" in a manner known per se, so that all the discrete data and signal signals can be exchanged on the single optical link, which simplifies the process. 'installation. The signals between the detection elements and the processing elements are of a discrete nature, exchanged in the sense of the amount (towards the detection elements) and / or the downward direction (towards the processing elements); these signals concern rotor position tops (upward direction) and electromagnetic compatibility (EM) and optronic (upward and downward) signals.

The signals and information exchanged on the optical link between the warning device and the central countermeasure command are: 1) in the "amount" direction from the CM central command to the missile warning device: setting signals, - EM and optronic prohibition signals, - attitude information of the helicopter, such as its roll condition, - rotor position tops. 2 °) in the "downward" direction, ranging from the missile warning device 25 to the central control of CM: missile track information, alerting device status information, EM synchronization signals - optronic synchronization signals.

According to another exemplary embodiment of the device according to the invention, this time using a laser as an active detection means. In this embodiment, the laser detector is in the form of a YAG laser rangefinder with controlled emission. It is pulsed at the repetition rate equal to that imposed by the speed ve of rotation of the blades (ve = 0.15 s / revolution), or a sub-multiple of this frequency, with a pulse duration of typically 48. las for a laser divergence of 2 mrd. The fixed telemetry wavelength can be 1.06 μm (or 1.54 ptm for eye safety). The passive detection comprises, as in the previous embodiment, a Peltier-cooled PbSe IR strip associated with a UV light intensifying tube. But, if the angular location accuracy of the threat remains sufficient for the self-protection and deployment of the CM (typically 1 °), the laser divergence is of the order of magnitude of milliradian. This then necessitates an angular accuracy of the location of the substantially finer threat to be able to direct the laser emission on the missile threat detected in IR or UV. For example, with identical optical characteristics (for example: focal length of 17 mm, aperture F / 0.8), the IR strip uses a larger number of elementary sensors, in a length / width ratio of the order of 9. , when the emitting laser divergence is 2 mrd. A difference-of-magnitude data processing between the intensities in and in + i detected by the sensors of ranks n and n + 1, of type in + 1 in and in + 1 + in sampled on 10 levels, for example, is also necessary for to know precisely the angular location of the threat, in order to point the laser source on it. The pointing in site is controlled, - classically by a single-axis mobile mirror -, according to the measurement in site made from the IR detection coming from the IR bar, with a precision of 0,5 mrd, on the detected missile and located angularly. In order to give the necessary time At to the mirror in order to be able to point the detected missile, the nominal axis of the range finder is shifted at least from AG in relation to the array in a manner similar to the embodiment of radar active detection, that is to say, such that AG At_ At At degrees, At being the ve (0,15) 4,17,10-4 (360) mechanical duration of orientation of the mirror on the maximum value of the site 30 defined from IR (or UV) detection. Under these conditions, the laser emission is discrete, only triggered in the direction of the missile, and the capacity is multimissiles, because one can telemétrer several detected missiles threats, the cadence related to the rotation of the blades. In the case where there is no rotating element on the aircraft to be protected, such as a helicopter rotor, especially in the case of aircraft, which moves at low altitude, the device according to the invention remains in a modular stack by being adapted in the following manner, with reference to FIG. 4. This adaptation does not concern the positioning detection means of the aircraft and the processing and management processor of the detection data, which are preserved without modification. The device comprises a mobile frame 41, rotating in rotation around the vertical axis Z'Z, and a fixed part 42 integral with the aircraft structure 43. The mobile frame comprises an inlet port H, an inclined mirror 44 which can also rotated around the S'S site axis, in order to exploit large s's site domains (typically 30 °), and the radar transmitter / receiver 45, occupying in this embodiment a volume of 5 X 5 X 10 cm3. This radar unit is equipped with an antenna 46 and emits a main lobe Le. The frame 41 is driven in continuous rotation (at a frequency equal to a few Hertz) by an annular drive motor 47. A JTE electric rotary joint and an optical rotary joint JTO 20 provided with position feedback sensors separate the frame. mobile and serve as power supply and data transmission links, as in the case of the previous helicopter application. The fixed frame comprises a focusing lens 48 of the incident flux Fi on a detection strip 49 through a derotation prism 50, slaved to the rotation of the mobile frame by the copying sensors. In operation, the scanned input stream Fi passes through the window H, is reflected on the mirror 44 and then focused on the detection bar 49. The bar detects in an IR or UV spectral band and the window is passing in the corresponding band.

As in the preceding cases, the optronic detection (IR or UV) controls the pulsed radar emission. The choice of the radar transmission frequency is again the result of a compromise between the width of the radar emission lobe and the width of the scanning of the sensor array or, temporally, between the radar pulse duration and the accuracy of the angular localization of optronic detection (IR or UV).

Claims (21)

REVENDICATIONS1. Protective method for aircraft operating at low altitude vis-à-vis ground / air missiles comprising a step of detection of passive approach (1) of threat designation to develop raw tracking towards these threats, a detection step active (2) triggered from the raw designation provided by processing the passive detection, a step of processing the respective detection data (3,4), passive and active, to extract respectively raw trackings and accurate trackings from previous detections and positioning information of the aircraft (8), and a step of managing these data (5) by fusion to form a hierarchy of these threats leading to the development of a threat processing order, a choice of countermeasures according to this order, and parameter values adapted for its deployment. 2. Protection method according to claim 1, characterized in that the passive detection (1) is performed in the optronic spectral range chosen between an IR band of atmospheric transmission and this IR band associated with a UV band called "solar blind", and in that the active detection (2) is selected between a detection in the field of electromagnetic waves of the radar and the near-infrared range of the lasers. 3. Protection method according to claim 1 or 2, characterized in that a step dedicated to the elimination of false alarms is integrated in the step of merging the data. 4. Protection method according to one of the preceding claims, characterized in that the adapted countermeasures can be chosen between an infra-red wave decoy, a decoy by radar waves, and one of the previous decoy accompanied by jamming directive laser multiraies.35 5. Protective device for implementing the method according to one of the preceding claims, characterized in that it comprises a rotary modular missile warning structure (11; 41, 42) with stacked successive layers, composed of at least one passive optronic detector (14, 15, 48) and an active detector (12, 45), aircraft position detection means and a detection data processing and management processor ( 19), and that a single-link connection means connects the layers of the modular structure (11; 41,42) between them and these layers to a power source and to a central control means for counteracting measured. 6. Protection device according to claim 5, characterized in that the passive detector comprises an IR detector and / or a UV detector, in that the single link is an optical link, and in that the active detector is selected between a radar and a laser. 7. Protection device according to claim 6, characterized in that the UV detector is a microchannel light intensifying tube, and in that the IR detection is performed by a bar comprising a number of elementary sensors, a step in and a bearing width adapted to obtain an instantaneous angular coverage substantially equal to 1 ° in the bearing and 40 ° in elevation. 8. Protective device according to claim 7, characterized in that the UV detection spectral band is substantially between 0.260 and 0.285 μm. 9. Protection device according to claim 8, characterized in that the detection threshold is adjusted according to the solar illumination. 30 10. Protection device according to claim 5, characterized in that the countermeasure means are located at a location decoupled from the rotation, in that the connection between the alert module and the power source is performed by an electrical rotary joint, and in that the connection between the warning module and the countermeasure control is performed by an optical rotary joint. 11. Protection device according to claim 5, characterized in that the active detection means are constituted by a radar (12) sized to allow the extension of the layered modular structure to at least one of the following applications: a millimetric radar detection, radar detection in L spectral band, and a radar goniometer of passive radar plays. 12. Protective device according to claim 11, characterized in that the radar emission is triggered with a systematic delay At with respect to passive optronic detection, this delay dedicated to the processing time corresponding to an angular shift AG in the bearing, by relative to the deposit reference given by the optronic detector, related to the driving speed of the rotor ve by the elementary relation AG = At / ve. 13. Protection device according to claim 5, characterized in that it comprises means for activating the active detection on demand, on internal or external stress, to confirm the missile tracking and determine close-up speed parameters and remote threats to be transmitted to the data merging means. 14. Protective device according to claim 5, characterized in that the processing and management processor develop settings of countermeasure maneuvers. 15. Protection device according to claim 5, characterized in that the countermeasure means is a steerable laser jammer, successively pointed towards the detected threats, as designated by the data management processor as being to be processed. priority. 16. Protective device according to any one of the preceding device claims, applied to helicopter protection, characterized in that the revolution module is installed above the rotor and fixed on the head of the rotor to be rotation in solidarity with the blades. 17. Protective device according to claim 16, characterized in that the positioning detection is obtained by controlling a clock on the rotation of the rotor, thanks to synchronization pulses delivered during the passage of the rotor to a reference position, the processor delivering at all times the rotor position with respect to a local reference. 18. Protection device according to claim 16, characterized in that, the blades having bisecting axes and the radiation of the passive and active detectors of the main axes, the detectors are positioned so that the main axes of electromagnetic and optronic radiation are established. on the blade bisectors, the active radar emission having a main lobe which angularly covers the field in site of the optronic detection. 19. Protective device according to any one of claims 5 to 15, applied to the protection of aircraft, operating especially at low altitude, characterized in that the device according to the invention comprises a mobile frame (41) and a frame fixed (42), the movable frame comprising the active detection means (45) and a scanning mirror (44) inclined to deflect the input stream (Fi) to the passive optronic detectors (48) located in the fixed frame ( 42) which also houses the means of treatment. 20. Protective device according to any one of claims 5 to 10, using a laser range finder as active detection means, characterized in that the passive detection comprises an IR strip associated with a UV light intensifying tube, the IR bar of dimensions, number of elementary sensors and steps making it possible to obtain a measurement in situ and a measurement in bearing of the position of the detected missile covering a field of the same order of magnitude as that obtainable with a class of accuracy at least equal to . 21. Protection device according to claim 20, characterized in that the rangefinder is shifted angularly in alignment with respect to the IR array of an angle AG equal to -At corresponding to the time of Ve necessary treatment At.