FR3134470A1 - Infrared surveillance system for military aircraft and military aircraft, in particular a missile, equipped with such a system - Google Patents

Abstract

Optronic system for monitoring a space surrounding a military aircraft (100), comprising an electronic processing unit (1), infrared optronic sensors (2) connected to the electronic processing unit (1) and at least one monitoring unit. inertial measurement (3) connected to the electronic processing unit (1). The electronic processing unit (1) is arranged to: receive from each optronic sensor (2) a plurality of image signals corresponding to images captured successively for a predetermined duration; register the images relative to each other based on inertial positioning data provided by the inertial measurement unit (3); trigger an alert when several of the images include, after registration, the same zone having an intensity greater than a predetermined threshold. Aircraft equipped with such a device and method for monitoring an aircraft. ABSTRACT FIGURE: Fig. 1

Description

Infrared surveillance system for military aircraft and military aircraft, in particular a missile, equipped with such a system

The present invention relates to the field of optical monitoring of the environment of a military aircraft and more particularly of a missile or a military aircraft such as a fighter.

BACKGROUND OF THE INVENTION

It is known to equip missiles and combat aircraft with optronic surveillance devices.

The most elaborate devices, often placed at the front of the aircraft, include for example a daytime vision sensor for long-distance identification (40 km) and an infrared sensor with sensitivity in the length bands of 3 to 5 µm and 8 to 12 µm wave to detect targets at long distances. These frontal surveillance devices are used for self-protection of the aircraft (detection of enemy missiles for example) or for attack (target detection).

For self-protection, the images provided by the sensor are processed to search for, for example, the thermal trace of hot gases ejected by the missile at least at the time of its departure (we speak of the “feathers” of the missile) or of hot parts of the missile, more particularly on the fuselage. In the image, this thermal trace takes the form of an area or spot, which can be the size of a single pixel, having an intensity greater than an alert threshold. The alert threshold is relatively low to be able to detect a missile departure as far away as possible but must be significantly higher than the image noise to avoid the multiplication of false alarms. Image processing is therefore relatively delicate.

OBJECT OF THE INVENTION

The invention aims in particular to provide an optronic system for improved monitoring of the environment of a missile or a military aircraft.

• recevoir de chaque capteur optronique une pluralité de signaux image correspondant à des images capturées successivement pendant une durée prédéterminée ;
• recaler ensemble les images les unes par rapport aux autres, dans un repère commun à tous les capteurs, à partir de données de positionnement inertiel fournies par l’unité de mesure inertielle ;
• déclencher une alerte lorsque plusieurs des images comprennent après recalage une même zone ayant une intensité supérieure à un seuil prédéterminé.

For this purpose, according to the invention there is provided an optronic system for monitoring a space surrounding a military aircraft, comprising an electronic processing unit, optronic sensors connected to the electronic processing unit and at least one measuring unit. inertial connected to the electronic processing unit. The optronic sensors have a predetermined individual field and are arranged to be fixed on the aircraft so as to have an overall field corresponding substantially to the space to be monitored. The electronic processing unit incorporates a processor and a memory containing a program having instructions arranged for:

• receive from each optronic sensor a plurality of image signals corresponding to images captured successively for a predetermined duration;
• register the images together in relation to each other, in a reference frame common to all the sensors, from inertial positioning data provided by the inertial measurement unit;
• trigger an alert when several of the images include, after registration, the same zone having an intensity greater than a predetermined threshold.

The military aircraft can be a combat plane, a missile or other and the space to be monitored can be for example 360° or 180°. Thus, when the aircraft is moving, the images of the series of images provided by each optronic sensor are offset relative to each other due to the fact that each optronic sensor is fixed relative to the aircraft and that the aircraft moved in space. This shift depends on the time interval between each image, the speed of the aircraft and the movements it has made. Therefore, the same element of the landscape scanned by a sensor, such as for example a thermal trace of missile departure in the case of infrared sensors, will not be exactly positioned in the same place in the images of the series, even if the displacement of the aircraft would be minimal between two images, which complicates the detection of this element of the landscape. The inertial data are used to determine the speed of the aircraft and the movements made between the images in order to be able to register the images captured with each other in a reference point common to all the sensors and thus make the same elements of the landscape coincide with each other (including the missile thermal traces) visible on several captured images. This makes it possible to highlight the thermal traces of interest by eliminating the noise which is present randomly from one image to another. The detection is therefore more precise.

The invention also relates to an aircraft equipped with such an optronic system, the aircraft comprising a structure on which the optronic sensors are rigidly fixed and distributed.

By “rigidly fixed”, we mean that the optronic sensors are not orientable relative to the structure of the aircraft, which simplifies the arrangement of the sensors and increases the acquisition speed since the images are not obtained by a scanning movement of optronic sensors.

• recevoir de chaque capteur optronique une pluralité de signaux images correspondant à des images capturées successivement pendant une durée prédéterminée ;
• recaler ensemble les images des différents capteurs les unes par rapport aux autres, dans un repère commun à tous les capteurs, à partir de données de positionnement inertiel fournies par l’unité de mesure inertielle ;
• déclencher une alerte lorsque plusieurs des images comprennent, après recalage dans le repère commun à tous les capteurs, une même zone ayant une intensité supérieure à un seuil prédéterminé.

The invention also relates to a method for monitoring a space surrounding a military aircraft provided with optronic sensors and at least one inertial measurement unit which are connected to an electronic processing unit, the optronic sensors having a predetermined individual field and being fixed on the aircraft so as to have an overall field corresponding substantially to the space to be monitored, the method comprising the steps of:

• receive from each optronic sensor a plurality of image signals corresponding to images captured successively for a predetermined duration;
• register together the images of the different sensors in relation to each other, in a reference frame common to all the sensors, from inertial positioning data provided by the inertial measurement unit;
• trigger an alert when several of the images include, after registration in the reference point common to all the sensors, the same zone having an intensity greater than a predetermined threshold.

Other characteristics and advantages of the invention will emerge on reading the following description of a particular and non-limiting embodiment of the invention.

Reference will be made to the attached drawings, including:

there is a schematic view of a location device according to the invention;

there is a schematic top view of an aircraft equipped with a location device according to the invention;

there is a schematic bottom view of this aircraft;

there is a schematic side view of this aircraft.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figures 2 to 4, the invention is described here in application to the monitoring of the space surrounding an aircraft, generally designated 100, having a structure 101 (the cell or fuselage) and wings 102, the other parts of aircraft 100 not being mentioned here. The aircraft 100 carries a monitoring device in accordance with the invention.

Also with reference to the , the monitoring device according to the invention comprises an electronic processing unit 1 connected to six optronic sensors 2 and to six inertial measurement units 3 each arranged in the vicinity of one of the optronic sensors 2. In the figures, the numerical reference 2 is associated with the letters: “fu” to designate an optronic sensor 2 oriented towards the front and upwards, “ru” to designate an optronic sensor 2 oriented towards the rear and upwards, “fd” to designate an optronic sensor 2 oriented towards the front and down, “rd” to designate an optronic sensor 2 oriented towards the rear and the bottom, “ll” to designate an optronic sensor 2 positioned laterally and oriented to the left, “lr” to designate an optronic sensor 2 positioned laterally and oriented to the right. In the figures, the numerical reference 3 is associated with the same letters as the optronic sensor 2 in the vicinity of which the inertial measurement unit 3 is fixed.

Each optronic sensor 2 here is a sensor made of a material sensitive to wavelengths between approximately 3 and 5 µm (MWIR band) and between approximately 8 and 12 µm (LWIR band). Indeed, sensitivity to the MWIR band makes it possible to detect combustion gases (from missiles or planes and more generally from any aircraft) which include a lot of carbon dioxide emitting at a wavelength of 4.2 µm. Sensitivity to the LWIR band makes it possible to more effectively detect missiles whose engines have been stopped and missiles and aircraft approaching from the front. The sensor is for example made of mercury-cadmium telluride (HgCdTe) or of a material having a periodic structure of “superlattice” type layers presenting sensitivity in the bands concerned. Each optronic sensor 2 is here a focal plane array detector or FPA, has a predetermined individual field here of 105° by 84°, and has a resolution of 2560 pixels by 2048 pixels ( we recall that an optronic sensor is composed of a plurality of elementary detectors adjacent to each other and that a pixel, from the English "picture element", designates such an elementary detector). Each pixel is formed by a photodiode and a well accumulating electrical charges according to the photons it receives. These electrical charges are periodically extracted in the form of an elementary signal. All of the elementary signals extracted at a given instant from the elementary detectors of an optronic sensor 2 form an image signal. The frame frequency of the optronic sensors 2 is preferably between 50 and 100 Hz.

• un premier capteur optronique 2fu débouche sur une surface supérieure de la structure 101, ici en avant du cockpit, et est orienté vers l’avant de l’aéronef 100 ;
• un deuxième capteur optronique 2ru débouche sur la surface supérieure de la structure 101, ici en arrière du cockpit, et est orienté vers l’arrière de l’aéronef 100 ;
• un troisième capteur optronique 2fd débouche sur une surface inférieure de la structure 101 et est orienté vers l’avant de l’aéronef 100 ;
• un quatrième capteur optronique 2rd débouche sur la surface inférieure de la structure 101 et est orienté vers l’arrière de l’aéronef 100 ;
• un cinquième capteur 2ll et un sixième capteur 2lr débouchent sur des surfaces latérales opposées de la structure 101 et sont orientés sur un axe transversal de la structure 101 respectivement vers la gauche et vers la droite.

The optronic sensors 2 are rigidly fixed to the cell 101 of the aircraft 100 as follows:

• a first optronic sensor 2fu opens onto an upper surface of the structure 101, here in front of the cockpit, and is oriented towards the front of the aircraft 100;
• a second optronic sensor 2ru opens onto the upper surface of the structure 101, here behind the cockpit, and is oriented towards the rear of the aircraft 100;
• a third optronic sensor 2fd opens onto a lower surface of the structure 101 and is oriented towards the front of the aircraft 100;
• a fourth 2nd optronic sensor opens onto the lower surface of the structure 101 and is oriented towards the rear of the aircraft 100;
• a fifth sensor 2ll and a sixth sensor 2lr open onto opposite side surfaces of the structure 101 and are oriented on a transverse axis of the structure 101 respectively towards the left and towards the right.

This positioning makes it possible to combine the individual fields of the optronic sensors 2 to obtain an overall field of 4π steradians covering the entire space surrounding the aircraft 100.

Each inertial measurement unit 3 (commonly called IMU from English "inertial measurement unit") comprises, in a manner known in itself, accelerometers and gyroscopes or gyrometers making it possible to determine linear and angular movements relative to the axes of a reference mark. Each inertial measurement unit 3 is fixed to the same part of the structure 101 as one of the optronic sensors 2, in the immediate vicinity thereof, to detect the movements of the part of structure 101 to which the optronic sensor 2 is fixed . The fact of fixing an inertial measurement unit 3 on the same part of structure 101 as the associated optronic sensor 2 and in the immediate vicinity thereof makes it possible to limit the possible relative movements of the inertial measurement unit 3 of the optronic sensor 2 associated which could result for example from an elastic deformation of the structure 101. Each inertial measurement unit 3 is arranged to provide electrical signals, called here positioning signals, representative of inertial attitude data (orientation of the support in the space around the axes of the reference frame) and inertial movement data of the cell part 101 to which the inertial measurement unit 3 and the associated optronic sensor 2 are fixed. More precisely, inertial data has the form of quaternions.

The electronic processing unit 1 comprises a calculation component, such as a processor, and at least one memory containing at least one program executable by the calculation component. The electronic unit can be produced in the form of an integrated circuit, an FPGA circuit, or an electronic card comprising a substrate provided with conductive tracks and electronic components connected to the conductive tracks. The program contained in the electronic processing unit 1 includes instructions arranged for:

- control the acquisition of image signals by each optronic sensor 2 and more generally control each optronic sensor 2;

- recover the inertial data contained in the positioning signals coming from each inertial measurement unit 3 and perform calculations on this inertial data;

- associate the inertial data of each inertial measurement unit 3 with the image signals of the optronic sensor associated with it so that at each instant of capture corresponds an image and inertial positioning data,

- carry out processing of the image signals supplied by each optronic sensor 2.

More precisely, the processing carried out includes, for each optronic sensor 2 and the associated inertial measurement unit 3, the steps of:

- control the acquisition of image signals by each optronic sensor 2 for a predetermined duration;

- realign the images in relation to each other, in a single reference point common to all optronic sensors, from the inertial data provided by the inertial measurement unit 3 associated with the optronic sensor 2 having provided said images to be realigned.

Finally, for all the optronic sensors and on the images assembled in the single reference mark common to all the optronic sensors, the processing includes the step of triggering an alert when several of the images include, after registration, the same zone having a higher intensity at a predetermined threshold.

• à chaque instant t chaque capteur optronique n fournit une image notée image_capteur(n)_instant(t) ;
• le recalage de ces images à chaque instant t dans un repère commun à tous les capteurs fournit une « macro-image » telle que

By way of illustration, with a number N of optronic sensors 2:

• at each instant t each optronic sensor n provides an image denoted image_sensor(n)_instant(t);
• the registration of these images at each instant t in a reference point common to all the sensors provides a “macro-image” such that

• le traitement est réalisé sur une série de macro-images, correspondant à des instants successifs, recalées les unes par rapport aux autres dans le repère commun.

;

• the processing is carried out on a series of macro-images, corresponding to successive instants, aligned with each other in the common reference frame.

The reference common to the optronic sensors 2 is obtained for example by designating one of the inertial measurement units 3 as “master” and by choosing the reference of this master inertial measurement unit as the common reference. The other inertial measurement units 3 are aligned, in a manner known in itself, on the mark of the “master” inertial measurement unit.

We recall that the registration makes it possible to make the same elements of the landscape (including thermal missile traces) which would be visible on several captured images but at different locations of the images taking into account the movements of the aircraft 100 between the captures coincide with each other. . This registration is possible because the inertial data makes it possible to determine the difference in position in space and the difference in orientation in space of each optronic sensor 2 between two successive images. The predetermined threshold is of the order of magnitude of the noise: it is the use of several images which makes it possible to reveal that the area in question is an area of interest. The registration thus makes it possible to replace the images in the same fixed reference point which is not that of the wearer.

In practice, the program of the electronic processing unit 1 implements the following steps:

- sum the image signals obtained during the predetermined duration by registering them from the inertial positioning data so as to obtain a result signal;

- search in the result signal for one or more portions of interest having an amplitude greater than the predetermined threshold.

Thus, during operation of the device of the invention, the signals corresponding to the same scene visible in the images of the series are accumulated to form a result signal. Even if the portion of interest of each image signal, representative of the presence of a thermal trace, is of low amplitude, the result signal will include a corresponding portion of interest whose amplitude will be the sum of the amplitudes of the portions of interest of all image signals. This temporal accumulation amounts to making the optronic sensor comparable to a fictitious sensor stabilized in space and having an increased well depth. In addition, since the noise is random, it is attenuated in relation to the portion of interest in the result signal. The accumulation of image signals thus makes it possible to demonstrate that several images included, after registration, the same zone having an intensity greater than the fixed threshold.

Note that in the case of a missile targeting the aircraft 100, the missile is on a collision course so that it appears during most of its course at the same heading relative to the aircraft. This is why it is possible to use a relatively low detection threshold and several images to detect it efficiently. We find ourselves in much the same situation with a distant plane.

Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

In particular, the monitoring device according to the invention may have a structure different from that described.

It is possible not to have an inertial measurement unit per sensor. Preferably, we will ensure that no sensor is more than one meter away from an inertial measurement unit.

In a less efficient embodiment than that described, it is possible to use the inertial unit of the aircraft to register the images with each other by assuming that the cell does not deform or within acceptable limits in relation to the desired detection sensitivity.

Optronic sensors can be sensitive to only one of the two wavelength bands mentioned or to other wavelength bands than those mentioned.

Other materials than those mentioned are possible, in particular indium antimonide (InSb).

It is also possible to use quantum well infrared photodetectors.

We can use quaternions in inertial data but also Euler angles and rotation matrices.

It is also possible to combine sensors from the infrared domain and sensors from the visible domain.

Other sensor sizes can be used, for example (in pixels): 640 by 640, 1280 by 1280, 1600 by 1600, 2000 by 2000, 2560 by 2048, 4000 by 4000, 5120 by 5120, or others.

The number and position of optronic sensors may differ from those indicated above. Preferably, the optronic sensors are n in number and each have a field substantially equal to 1/n of the space to be monitored.

• mettre un seuil relativement bas sur chaque image, ce qui engendre un nombre élevé de plots dont une grande part correspond à du bruit ;
• filtrer les plots « bruit » par rapport aux plots « cible » en utilisant la statistique. Selon l’approche statistique, si dans une zone restreinte de quelques pixels autour d’un plot d’intérêt dans une image, il y a, dans un premier nombre prédéterminé d’images suivantes, un deuxième nombre prédéterminé de nouveaux plots qui dépassent le seuil, alors le plot d’intérêt est vraisemblablement un plot « cible ». Par exemple, on considère que si dans une zone restreinte de quelques pixels autour d’un plot, il y a, dans les 5 prochaines images, au moins 3 nouveaux plots qui dépassent le seuil, alors le plot initialement considéré est vraisemblablement un plot « cible ». On dit couramment que l’ensemble des plots est mis en piste ici en 3/5 (3 plots détectés sur 5 acquisitions).

To separate the signal from the noise, it is possible to use the summation method which has been described but other known methods are possible. So, another method includes the steps of:

• put a relatively low threshold on each image, which generates a high number of plots, a large part of which corresponds to noise;
• filter the “noise” plots compared to the “target” plots using statistics. According to the statistical approach, if in a restricted area of a few pixels around a plot of interest in an image, there is, in a first predetermined number of following images, a second predetermined number of new plots which exceed the threshold, then the plot of interest is probably a “target” plot. For example, we consider that if in a restricted area of a few pixels around a plot, there are, in the next 5 images, at least 3 new plots which exceed the threshold, then the plot initially considered is probably a "spot". target ". It is commonly said that all the plots are tracked here in 3/5 (3 plots detected out of 5 acquisitions).

The invention is applicable to any type of aircraft, whether piloted or not.

Claims (12)

Optronic system for monitoring a space surrounding a military aircraft (100), comprising an electronic processing unit (1), optronic sensors (2) connected to the electronic processing unit (1) and at least one measuring unit inertial sensor (3) connected to the electronic processing unit (1), the optronic sensors (2) having a predetermined individual field and being arranged to be fixed on the aircraft so as to have an overall field corresponding substantially to space to be monitored, the electronic processing unit (1) incorporating a processor and a memory containing a program having instructions arranged for:

• receive from each optronic sensor (2) a plurality of image signals corresponding to images captured successively for a predetermined duration;
• register together the images of the different sensors in relation to each other, in a reference frame common to all the sensors, from inertial positioning data provided by the inertial measurement unit (3);
• trigger an alert when several of the images include, after registration in the reference point common to all the sensors, the same zone having an intensity greater than a predetermined threshold.

System according to claim 1, in which the program comprises the steps of:
- sum the image signals obtained during the predetermined duration by registering them from the inertial positioning data so as to obtain a result signal;
- search in the result signal for a portion of interest having an amplitude greater than the predetermined threshold. System according to claim 1, in which the program comprises the steps of:

• put a predetermined threshold on each image to generate one or more plots;
• filtering plots corresponding to noise compared to plots corresponding to a target using a statistical approach.

System according to claim 3, in which, according to the statistical approach, if in a restricted area around a plot of interest in an image, there is, in a first predetermined number of following images, a second predetermined number new plots corresponding to pixels exceeding the predetermined threshold, then the plot of interest is probably a plot corresponding to a target. System according to claim 1, in which the optronic sensors (2) are n in number and each have a field substantially equal to 1/n of the space to be monitored. System according to any one of the preceding claims, in which the optronic sensors (2) have one of the following approximate resolutions (pixels):

• 640 by 640,
• 1280 by 1280,
• 2000 by 2000,
• 2560 by 2048,
• 4000 by 4000.

System according to any one of the preceding claims, in which the optronic sensors (2) are sensitive to wavelengths of the MWIR band. System according to claim 7, in which the optronic sensors (2) are sensitive to wavelengths of the LWIR band as well. Military aircraft (100) equipped with an optronic system according to any one of the preceding claims, the aircraft comprising a structure (101) on which the optronic sensors (2) are rigidly fixed and distributed. Military aircraft (100) according to claim 9, in which the optronic sensors (2) are positioned as follows:

• a first optronic sensor (2fu) opening onto an upper surface of the structure (101) and oriented towards the front of the aircraft (100);
• a second optronic sensor (2ru) opening onto the upper surface of the structure (101) and oriented towards the rear of the aircraft (100);
• a third optronic sensor (2fd) opening onto a lower surface of the structure (101) and oriented towards the front of the aircraft (100);
• a fourth optronic sensor (2rd) opening onto the lower surface of the structure (101) and oriented towards the rear of the aircraft (100);
• a fifth sensor (2ll) and a sixth sensor (2lr) which open onto opposite side surfaces of the structure (101) and which are oriented on a transverse axis of the fuselage.

Military aircraft (100) according to claim 10, in which the monitoring device comprises as many inertial measurement units (3) as optronic sensors (2) and each inertial measurement unit (3) is fixed to the structure (101 ) in the vicinity of each optronic sensor (2). Method for monitoring a space surrounding a military aircraft (100) provided with optronic sensors (2) and at least one inertial measurement unit (3) which are connected to an electronic processing unit (1), the optronic sensors (2) having a predetermined individual field and being fixed on the aircraft so as to have an overall field corresponding substantially to the space to be monitored, the method comprising the steps of:

• receive from each optronic sensor (2) a plurality of image signals corresponding to images captured successively for a predetermined duration;
• register together the images of the different sensors in relation to each other, in a reference frame common to all the sensors, from inertial positioning data provided by the inertial measurement unit (3);
• trigger an alert when several of the images include, after registration in the reference point common to all the sensors, the same zone having an intensity greater than a predetermined threshold.