EP1202021B1 - Apparatus for boresighting a laser transmitting channel with a passive observing channel - Google Patents

Apparatus for boresighting a laser transmitting channel with a passive observing channel Download PDF

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Publication number
EP1202021B1
EP1202021B1 EP01402722A EP01402722A EP1202021B1 EP 1202021 B1 EP1202021 B1 EP 1202021B1 EP 01402722 A EP01402722 A EP 01402722A EP 01402722 A EP01402722 A EP 01402722A EP 1202021 B1 EP1202021 B1 EP 1202021B1
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Prior art keywords
detector
harmonization
laser
scene
det
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German (de)
French (fr)
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EP1202021A1 (en
Inventor
Christian c/o Thales Intellectual Propert Pepin
Francois-Xavier c/o Thales Intel. Prop. Doittau
Jean-Claude c/o Thales Intell Prop Fontanella
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Thales SA
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Thales SA
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41G—WEAPON SIGHTS; AIMING
    • F41G3/00—Aiming or laying means
    • F41G3/32—Devices for testing or checking
    • F41G3/326—Devices for testing or checking for checking the angle between the axis of the gun sighting device and an auxiliary measuring device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41G—WEAPON SIGHTS; AIMING
    • F41G3/00—Aiming or laying means
    • F41G3/14—Indirect aiming means
    • F41G3/145—Indirect aiming means using a target illuminator

Definitions

  • the invention relates to a device for the harmonization between a laser emission path and a passive path of observation. harmonization consists in making the optical axes of these paths parallel so that they have a common line of sight.
  • the invention applies in particular to target designation systems comprising a telemetry laser path or of illumination and a passive way of observation with an imaging detector to visualize and continue the target. It also applies to active / passive imaging systems having a laser emission path scanning and a passive imaging path. More generally, it applies to any system for which it is necessary to harmonize the transmission channel laser and the passive way of observation.
  • the target designation by laser is advantageously carried out thanks to a 'pod' (this term meaning nacelle in Anglo-Saxon language) arranged in external carriage of the aircraft.
  • a 'pod' this term meaning nacelle in Anglo-Saxon language
  • he can have an observation channel including a visible imaging detector and / or an infrared detection imaging detector, in band II or III, to locate the target, as well as a laser path, whose optical axis can be separated or confused with that of the observation channel, emitting for example in the near infrared and 'locked' on the way observation.
  • This lock assumes the perfect 'alignment' between the two pathways, ie the perfect parallelism of their optical axes or not), then defining the same line of sight.
  • This harmonization must can be controlled during a mission.
  • the harmonization between the illumination laser and the line of sight of the imaging detector can be realized in different ways and in particular, when the detector has a spectral band compatible with the length of the laser, by re-injecting some of the energy emitted by the laser into the entrance pupil of the imaging detector.
  • the position of the image of the spot laser thus obtained with respect to the center of the field of the imaging detector indicate the harmonization error.
  • the means used to perform reinjection returns the light according to the incident direction, for example using a corner cube mirror.
  • Figure 1 illustrates in a simplified diagram an example of harmonization device according to the prior art.
  • the axis observation path optical ⁇ i (in solid line in FIG. 1) comprises in this example a afocal afocal device, an OBJ focusing objective to form the image of a scene on a DET imaging detector, for example a Silicon detector operating in the visible and near infrared.
  • the way ⁇ l axis laser (short and long alternating dotted line) includes a laser LAS of illumination emitting in the near infrared.
  • An MEL mixer whose the transmission and the reflection are adapted to the wavelength of the laser while transmitting the maximum of the flux emitted by the scene, allows superimpose the two lanes.
  • the harmonization scheme includes in this example a cube corner CCB and a set of mirrors 11, 12 placed on the track laser, upstream of the mixer MEL, one of the two mirrors being movable in rotation (mirror 11).
  • the mirror 11 is oriented so as to send to the cube corner CCB the laser pulse that is is thus reinjected into the imaging pathway ⁇ i (optical path indicated in dashed line in Figure 1).
  • a shutter (not shown) for cutting the flow coming from the scene, is closed during the phase of harmonization and the image of the laser pulse on the imaging detector can be visualized in order to determine the harmonization defects corresponding to the deviations angle between the line of sight of the detector and the position of the the laser image.
  • this harmonization scheme presents a number of number of disadvantages that lead to modest performance.
  • cube corner imperfections related to defects in realization lead to harmonization errors.
  • corner of cube is placed in front of the pupil common to the laser pathways and of observation, as is the case in Figure 1, it can not cover part of this pupil (for reasons of congestion), an image of the laser pulse on the relatively dimension detector significant and limited harmonization accuracy.
  • the of laser energy is not uniform throughout the pupil, the fact of not covering the entire pupil can lead to harmonization errors.
  • the effect of aberrations degrades the image and may induce a positional error of his barycentre.
  • the present invention proposes a very harmonizing device precise does not have the disadvantages of the prior art. It consists of visualize using the same imaging detector used to image the scene, the image of the laser pulse retroreflected by the scene itself and no longer by a cube corner. To do this, the invention uses a detector specific that can operate in two modes, an imaging mode classic and a harmonization mode in which the flow from the retroreflected laser pulse can be detected in the streaming stream by the scene.
  • the device according to the invention makes it possible to harmonize in a real situation, since the laser spot imaged on the detector is the same as that which will follow, for example, a laser guided weapon. It also allows to avoid the use of a mixer whose specifications are between the laser path and the observation path.
  • FIG. 2 represents, to illustrate the invention, the overall architecture of an optronic imaging and target tracking equipment in the Air / Ground configuration, equipped with a harmonization device according to an exemplary embodiment.
  • the different subsystems shown in the figure are mounted in a rigid support structure (optical bench equipped not shown) which is itself installed inside an envelope carried by an aircraft.
  • the equipment comprises a transmission channel (of optical axis ⁇ l) of a laser pulse emitted by a laser transmitter LAS whose wavelength is compatible with the target illumination function to be performed, with its optical COL collimation to obtain a low divergence beam in the ⁇ l direction.
  • the laser emission path is distinct from the imaging path, which makes it possible to limit the backscattered laser flux in the imaging path. But it is possible to design a system in which the emission laser pulses are injected into the imaging path, at the afocal portion of the optics of the imaging path.
  • FIG. 2 it is a 'Cassegrain' type optical, made by means of two mirrors M1, M2.
  • a dichroic mirror M3 separates the observation path into an infrared path, of axis ⁇ i IR and a visible / near infrared path of axis ⁇ i VIS .
  • These two paths are respectively equipped with a DET IR sensitive imaging detector in the infrared and a DET VIS sensitive imaging detector in the visible and near infrared range, in which the optical focusing OPT form the image of the scene in each of the spectral bands.
  • the opto-mechanical assembly is mounted and adjusted at the factory so that the axes ⁇ l and ⁇ i are parallel.
  • this parallelism does not generally remain valid with sufficient accuracy in operational use, given the environmental constraints borne by the equipment, which induce axis movements, especially at the laser level. It is therefore necessary to harmonize in flight.
  • the device for the harmonization between the ⁇ l axis laser pathway and the ⁇ i axis observation pathway comprises a rapid laser pulse detector DET IMP , which makes it possible to determine the instant of arrival of the laser pulse retroreflected by the scene on the detector (s) of the observation channel and delivering a signal S.
  • the fast detector DET IMP is positioned in a focal plane of the OPT multispectral optics through a mirror M 4 taking part of the flow on the visible-near-infrared path. It further comprises a harmonization detector forming one of the imaging detectors (in the example of FIG.
  • the harmonization detector controlled by the control means MCD, can operate in two modes, a conventional imaging mode and a harmonization mode in which the flow from the laser pulse retroreflected by the scene can be detected. in the continuous stream diffused by the scene, thus making it possible to detect harmonization defects.
  • the harmonization detector includes a set of photosensitive zones in the spectral band of the laser resignation.
  • the MCD means control the harmonization detector in imaging mode or in harmonization mode. They receive the S signal issued by the rapid detector, and allow, in harmonization mode, the operation of the harmonization detector according to two phases. In first phase of waiting, the electrical charges resulting from the conversion photons received by the photosensitive zones are integrated so almost continuous with a sufficiently short integration time for enable detection of the flux from a retroreflected laser pulse by the scene in the continuous stream broadcast by the scene.
  • a second reading phase triggered by the signal S received from the fast detector at moment of detection of a retroreflected laser pulse by the scene, the integrated charges at the moment of detection of said pulse are set in sequence in order to detect in the image thus obtained the position of the corresponding laser spot. Examples of detectors applicable to harmonization device according to the invention will be described in more detail in the following.
  • optical filtering means FLT IMP and FLT HAR whose transmissions are centered on the spectral band of the emission laser, are respectively positioned in front of the pulse detector DET IMP and, during the harmonization phase, in front of the Harmonization detector (DET VIS in the example of Figure 2), to improve the detectivity of these detectors at the wavelength of the laser.
  • the filtering means FLT IMP are fixed, while the filtering means FLT HAR are advantageously removable in order to be removed in conventional imaging mode, outside the periods of operation in harmonization mode.
  • the harmonization device further comprises calculating means MCL making it possible to calculate, from the position of the laser spot in the image, the harmonization defects between the axis ⁇ i of the channel of FIG. observation and that ⁇ l of the laser emission path, these defects corresponding to angular deviations ⁇ x, ⁇ y between the center of the image and the position of the laser spot, image of the laser pulse retroreflected by the scene through the OPT optical focusing.
  • FIG. 3A thus illustrates, by an example, the position of the IML laser spot in the image, and the deviations ⁇ x, ⁇ y between the IML laser spot and the center of the IMC image corresponding to the ⁇ i axis of the line of sight of the harmonization detector.
  • the center of the IMC image corresponds to the tracking center and the correction of the harmonization error then consists, for example, in electronically moving the automatic tracking center of the opposite value of the measured difference.
  • the filtering means FLT HAR are removed and the point of the target on which the imaging detector is hung is then merged, as shown in FIG. 3B, with the IML impact point of the laser pulse.
  • the harmonization device thus makes it possible very precise alignment between the line of sight of the laser and the reference center of the imaging detector of the observation channel because it directly uses the image of the laser spot formed on the observed scene, this which allows to have the best possible resolution. It allows to obtain a very precise harmonization between the illumination laser and the position of the point pursued automatically on the scene, allowing for a very large impact accuracy of the ammunition in case of laser guided weapon fire, or a very high accuracy of location for equipment observation or surveillance.
  • the use of multispectral optics common to the two near-infrared and infrared channels allows the equipment to have this very precise harmonization capability both in operation. by day in night operation. Indeed, the harmonization device can operate by day, even very brightly, thanks to the use of the specific harmonization detector, and it can also operate at night.
  • the harmonization detector near infrared imaging detector in the example of FIG. 2 is used during the harmonization phase to locate the laser spot on the stage, as described previously, while the infrared detector performs for example the pursuit of the target continuously, without being disturbed by the harmonization phase.
  • the correction is applied automatically to the position of the tracking center of the infrared detector DET IR , making it possible to carry out the harmonization permanently, at each shot.
  • the infrared tracking By day, in order not to disturb the pursuit of the target, it is also possible to carry out the infrared tracking, with perhaps a slightly less good resolution, while the near infrared detector is used to perform the harmonization .
  • the harmonization phase it is possible to return to near-infrared tracking by operating the harmonization detector in conventional imaging mode, in order to possibly benefit from the best resolution inherent to this spectral band.
  • harmonization detectors which, together with the pulse detector, allow the operation of the device according to the invention.
  • a prime example is to use as a detector of harmonization an imaging detector with integration and transfer type CCD (initials of "Charge Coupled Device” in English terminology), precisely located in the focal plane of the focus lens of the observation path, and comprising a set of photosensitive zones in silicon (or “pixels” according to Anglo-Saxon terminology), organized in a generally square matrix, typically 100x100 pixels.
  • CCD integration and transfer type
  • pixels photosensitive zones in silicon
  • Use of a photosensitive material in the visible and near infrared spectrum, by example Silicon is particularly suitable for the detection of a laser emitting in the near infrared, like the Nd: YAG laser, at 1.06 ⁇ m.
  • the CCD detector is controlled by the means of MCD command so as to operate in a mode of conventional CCD operation when the harmonization detector is in imaging mode and according to a mode called "treadmill" when the detector is in harmonization mode.
  • mode imaging the CCD detector acquires the scene (conversion of photons received in charge then integration into potential wells of charges released proportionally to the illumination received for a period of time predetermined integration, typically of the order of 20 msec), then the loads are transferred in column and sampled by multiplexing line to line to form sequential signals that form the signal of visualization (reading phase of the image), and this, during the acquisition of the next image.
  • a sensitivity calculation shows that in the absence of noise due at the back of the stage, the system detects laser pulses with good performance.
  • the contribution of solar irradiance significantly disrupts the signal, even after filtering around the wavelength of the laser, because the time of integration of the image is long before the duration of the pulse.
  • the "treadmill" mode described in patent FR 2 740 558 in the name of the applicant, allows the detection of the flow from the laser pulse retroreflected by the scene into the continuous flow broadcast by the scene.
  • Figure 4 shows a diagram of a mode of operation of a CCD detector in treadmill mode.
  • it is a so-called frame transfer detection array, which conventionally comprises an image zone 40 and a memory zone 41.
  • the image zone consists of 4x4 photosensitive zones (or pixels ) Pi and the memory area forms a CCD multiplexing circuit, composed of elementary memories Mi, realized in integrated CMOS circuitry.
  • the detector further comprises an output register R and an amplification stage A. It is controlled by the control means MCD of the device according to the invention, connected to the rapid pulse detector DET IMP .
  • the treadmill mode operation applied to a frame transfer CCD matrix is divided into two phases: a detection waiting phase and a reading phase after detection.
  • the signal S delivered by the fast detector DET IMP is zero, reflecting the absence of pulse.
  • the CCD is in continuous transfer at high speed, which results in a very short integration time (typically 250 ⁇ sec) compared to the integration time in imaging mode. Thanks to the high rate of vertical transfer, the acquisition of the background signal is reduced to a minimum time, hence the minimum associated noise, allowing the detection of very low level pulse.
  • the transfer of lines at high speed is then continued until the image zone is brought into the memory zone, then the memory zone is read at a normal cadence, the reading phase comprising the transfer of charges to the multiplexing circuit integrated in the detector and to the output register R to form, after amplification by the amplification stage A, corresponding to a visualization signal SV to the desired video standard.
  • the calculation means MCL of the device according to the invention which can be made by a processor common to the MCD control means, allow to calculate, from the position of the pixel (s) illuminated in the image by the laser pulse, harmonization defects corresponding to the angular differences between the axis of the line of sight of the Harmonization detector and the axis of the laser emission path.
  • the frame transfer detector can be substituted, as illustrated in FIG. 4, with a so-called "full frame array” detector, in which the pixels occupy almost the entire surface of the array and in which the transfer takes place. is said per line, the charges of the same line being simultaneously transferred line by line.
  • the operation in treadmill mode comprises a first waiting phase during which the transfer is at a high rate, then a reading phase after a pulse has been detected by the fast detector DET IMP .
  • a detector can be adapted to the device according to the invention. It is a matrix of photo-detectors, each photo-detector being connected to a read circuit of the MCD control means of the matrix by an input circuit which ensures for the photodetector that him is coupled, the functions of polarization and integration of the photoelectric signal, the reading circuit allowing the multiplexing of the signals issued for forming a video signal.
  • this matrix described in patent FR 2 762 082 in the name of the applicant, it is possible to detect a laser pulse short in the continuous stream broadcast by the scene.
  • the matrix of photo-detectors is adapted to form the device harmonization detector according to the invention can operate in a conventional imaging mode and according to a harmonization mode.
  • the operation of the photodetector array comprises, as previously, two phases, a detection waiting phase, during which the photoelectric signal generated by each photodetector is continuously integrated, and a phase of detection. reading of the image, after detection by the rapid detector DET IMP of the laser pulse retroreflected by the scene.
  • the waiting phase comprises for each photodetector a succession of very short integration cycles (of the order of one microsecond). During each integration cycle, the photodetector integrates only an infinitesimal amount of charge that is transferred to a buffer memory and held until the end of the next cycle and then discarded without prior reading if no signal from the fast detector is not detected.
  • the DCM control means When a laser pulse is detected by the fast detector, the DCM control means trigger in each photodetector the summation of the signal being integrated with the contents of the associated memory cell, thereby preventing any loss of information.
  • Each memory cell then contains a negligible signal from the back of the scene, with the exception of that associated with the photodetector having received the laser pulse and for which the background signal is dominated by the detected signal coming from the pulse.
  • the MCD control means then trigger the second phase corresponding to the reading, at a normal rate (typically a few milliseconds) of the contents of the memories, delivering an image from which the position of the laser spot on the harmonization detector can be known. formed of the matrix of photo-detectors.
  • the calculation means MCL then make it possible to evaluate the harmonization defects.
  • the MCD control means In imaging mode, the MCD control means generate a much longer integration time for each photodetector (from the order of the millisecond, for example), then trigger the reading phase, thus allowing to obtain a normal image of the scene.
  • the matrix of detectors is more complex, and more expensive, at implement that the "treadmill" detector because each photo-detector has its own circuit for integrating loads (circuit input).
  • it has several different CCD detector advantages.
  • the choice of photo-detectors, preferably of the type photo-voltaic allows to adapt to other laser wavelengths resignation.
  • the sensors made on InGaAs, InSb or HgCdTe will be privileged and may, depending on their nature and depending on the desired performance, work strongly, little or no cooled.
  • HgCdTe or AsGa multiwell quantum well detectors strongly cooled, will be preferred.
  • the material chosen for the detector is compatible with imaging in the infrared band, it is not necessary to add a second infrared imaging detector, as this is the case in the example of Figure 2, unless we want a total simultaneity between harmonization and imaging modes.
  • the use of a photodetector matrix as harmonization detector allows also, in harmonization mode, to limit the photodetectors used to those located near the center of the detector field (windowing of the matrix centered on the line of sight of the observation channel).
  • harmonization detectors described above are preferred examples for the implementation of the harmonization system according to the invention, it is not limited to these examples.
  • Other detectors imagery are possible if, in addition to their imaging function, they can, in a particular mode of operation, and associated with a fast pulse detector, detect a laser pulse in a flow of continuous background, in order to proceed with the harmonization between the emission laser and the way of observation in real conditions, ie thanks to the impulse laser retroreflected by the scene itself.
  • the detection surface of the fast detector DET IMP can be reduced with respect to the total field of the image, by centering it on the axis of the line of sight of the signal path. 'observation. Indeed, the probability of detection of the retroreflected impulse by the scene during the harmonization procedure is maximum in the central part of the field.
  • the sensitive area of the detector By reducing the sensitive area of the detector, its detectivity is increased, which further improves the performance of the harmonization device.
  • the harmonization device further comprises electronic means for high-pass filtering of the signal delivered by the pulse detector DET IMP , making it possible to cut off the signal corresponding to the luminous flux generated by the backscattering on the atmosphere of the emitted laser pulse.
  • a laser pulse is emitted to the scene and the stream retroreflected by the scene is detected as described above, in order to calculate possible harmonization errors.
  • the function of the pulse detector is to detect the moment of arrival of the retroreflected pulse on the harmonization detector in order to trigger the reading phase of the image on which the laser impact appears.
  • FIG. 5 thus represents, in one example, the shape of the signal delivered by the fast detector as a function of time. The origin of the times corresponds to the moment of emission of the laser pulse.
  • the signal S 1 corresponding to the flux backscattered by the atmosphere extends for a predetermined time T 1 , the duration of which is correlated with the distance over which the laser pulse can be backscattered towards the equipment.
  • This time which may be a few tens of microseconds, is significantly greater than the time T 2 of the signal S 2 corresponding to the duration of the pulse retroreflected by the scene.
  • the electronic filtering means of the device according to the invention thus make it possible to cut the low frequency spurious signal S 1 and to keep only the useful signal S 2 corresponding to the pulse retroreflected by the scene.
  • Another way to overcome this is to provide at the output of the rapid detector DET IMP electronic means for inhibiting the signal delivered by the pulse detector for a predetermined time after the emission of a laser pulse, and corresponding to the luminous flux generated by the backscattering on the atmosphere of the emitted laser pulse.
  • This inhibition time during which the delivered signal will not be taken into account by the MCD control means, may be a few tens of microseconds for example.

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Description

L'invention concerne un dispositif pour l'harmonisation entre une voie d'émission laser et une voie passive d'observation. L'harmonisation consiste à rendre parallèles les axes optiques de ces voies afin qu'elles aient une ligne de visée commune. L'invention s'applique notamment aux systèmes de désignation de cible comportant une voie laser de télémétrie ou d'illumination et une voie passive d'observation avec un détecteur d'imagerie permettant de visualiser et de poursuivre la cible. Elle s'applique aussi aux systèmes d'imagerie active/passive comportant une voie d'émission laser à balayage et une voie d'imagerie passive. Plus généralement, elle s'applique à tout système pour lequel il est nécessaire d'harmoniser la voie d'émission laser et la voie passive d'observation.The invention relates to a device for the harmonization between a laser emission path and a passive path of observation. harmonization consists in making the optical axes of these paths parallel so that they have a common line of sight. The invention applies in particular to target designation systems comprising a telemetry laser path or of illumination and a passive way of observation with an imaging detector to visualize and continue the target. It also applies to active / passive imaging systems having a laser emission path scanning and a passive imaging path. More generally, it applies to any system for which it is necessary to harmonize the transmission channel laser and the passive way of observation.

Dans des conditions d'environnement sévères, notamment de température et de vibration, la désignation de cible par laser est avantageusement effectuée grâce à un 'pod' (ce terme signifiant nacelle en langue anglo-saxonne) disposé en emport externe de l'aéronef. Il peut comporter une voie d'observation comprenant un détecteur d'imagerie visible et/ou un détecteur d'imagerie à détection infrarouge, en bande II ou III, permettant de localiser la cible, ainsi qu'une voie laser, dont l'axe optique peut être séparé ou confondu avec celui de la voie d'observation, émettant par exemple dans le proche infrarouge et 'verrouillée' sur la voie d'observation. Ce verrouillage suppose le parfait 'alignement' entre les deux voies, c'est à dire le parfait parallélisme de leurs axes optiques (confondus ou non), définissant alors une même ligne de visée. Cette harmonisation doit pouvoir être contrôlée en cours de mission.In severe environmental conditions, including temperature and vibration, the target designation by laser is advantageously carried out thanks to a 'pod' (this term meaning nacelle in Anglo-Saxon language) arranged in external carriage of the aircraft. he can have an observation channel including a visible imaging detector and / or an infrared detection imaging detector, in band II or III, to locate the target, as well as a laser path, whose optical axis can be separated or confused with that of the observation channel, emitting for example in the near infrared and 'locked' on the way observation. This lock assumes the perfect 'alignment' between the two pathways, ie the perfect parallelism of their optical axes or not), then defining the same line of sight. This harmonization must can be controlled during a mission.

Dans un équipement Air/Sol pour guidage laser de munitions par exemple, l'harmonisation entre le laser d'illumination et l'axe de visée du détecteur d'imagerie peut être réalisée de différentes façons et notamment, lorsque le détecteur possède une bande spectrale compatible de la longueur d'onde du laser, en réinjectant une partie de l'énergie émise par le laser dans la pupille d'entrée du détecteur d'imagerie. La position de l'image de la tache laser ainsi obtenue par rapport au centre du champ du détecteur d'imagerie indiquera l'erreur d'harmonisation. Pour procéder à l'harmonisation entre les voies, il est nécessaire que le moyen utilisé pour effectuer la réinjection renvoie la lumière selon la direction incidente, par exemple à l'aide d'un miroir en coin de cube.In an Air / Ground equipment for laser ammunition guidance by example, the harmonization between the illumination laser and the line of sight of the imaging detector can be realized in different ways and in particular, when the detector has a spectral band compatible with the length of the laser, by re-injecting some of the energy emitted by the laser into the entrance pupil of the imaging detector. The position of the image of the spot laser thus obtained with respect to the center of the field of the imaging detector indicate the harmonization error. To achieve harmonization between routes, it is necessary that the means used to perform reinjection returns the light according to the incident direction, for example using a corner cube mirror.

La figure 1 illustre par un schéma simplifié un exemple de dispositif d'harmonisation selon l'art antérieur. La voie d'observation d'axe optique Δi (en trait continu sur la figure 1) comprend dans cet exemple un dispositif afocal AFO, un objectif de focalisation OBJ permettant de former l'image d'une scène sur un détecteur d'imagerie DET, par exemple un détecteur Silicium fonctionnant dans le visible et le proche infrarouge. La voie laser d'axe Δℓ (en trait pointillé alterné court et long) comprend un laser LAS d'illumination émettant dans le proche infrarouge. Un mélangeur MEL, dont la transmission et la réflexion sont adaptées à la longueur d'onde du laser tout en transmettant le maximum du flux émis par la scène, permet de superposer les deux voies. Le dispositif d'harmonisation comprend dans cet exemple un coin de cube CCB et un jeu de miroirs 11, 12 placés sur la voie laser, en amont du mélangeur MEL, l'un des deux miroirs étant mobile en rotation (miroir 11). Pour procéder à l'harmonisation, le miroir 11 est orienté de telle sorte à envoyer vers le coin de cube CCB l'impulsion laser qui se trouve ainsi réinjectée dans la voie d'imagerie Δi (chemin optique indiqué en trait pointillé sur la figure 1). Un volet (non représenté), permettant de couper le flux issu de la scène, est fermé pendant la phase d'harmonisation et l'image de l'impulsion laser sur le détecteur d'imagerie peut être visualisée afin de déterminer les défauts d'harmonisation correspondant aux écarts angulaires entre l'axe de la ligne de visée du détecteur et la position de l'image laser.Figure 1 illustrates in a simplified diagram an example of harmonization device according to the prior art. The axis observation path optical Δi (in solid line in FIG. 1) comprises in this example a afocal afocal device, an OBJ focusing objective to form the image of a scene on a DET imaging detector, for example a Silicon detector operating in the visible and near infrared. The way Δℓ axis laser (short and long alternating dotted line) includes a laser LAS of illumination emitting in the near infrared. An MEL mixer, whose the transmission and the reflection are adapted to the wavelength of the laser while transmitting the maximum of the flux emitted by the scene, allows superimpose the two lanes. The harmonization scheme includes in this example a cube corner CCB and a set of mirrors 11, 12 placed on the track laser, upstream of the mixer MEL, one of the two mirrors being movable in rotation (mirror 11). To proceed with the harmonization, the mirror 11 is oriented so as to send to the cube corner CCB the laser pulse that is is thus reinjected into the imaging pathway Δi (optical path indicated in dashed line in Figure 1). A shutter (not shown) for cutting the flow coming from the scene, is closed during the phase of harmonization and the image of the laser pulse on the imaging detector can be visualized in order to determine the harmonization defects corresponding to the deviations angle between the line of sight of the detector and the position of the the laser image.

Dans la pratique, ce dispositif d'harmonisation présente un certain nombre d'inconvénients qui conduisent à des performances modestes. Notamment, les imperfections du coin de cube liées aux défauts de réalisation entraínent des erreurs d'harmonisation. D'autre part, lorsque le coin de cube est placé devant la pupille commune aux voies laser et d'observation, comme c'est le cas sur la figure 1, celui-ci ne peut couvrir qu'une partie de cette pupille (pour des raisons d'encombrement), entraínant une image de l'impulsion laser sur le détecteur de dimension relativement importante et une précision d'harmonisation limitée. En outre, si la répartition d'énergie laser n'est pas uniforme dans toute la pupille, le fait de ne pas couvrir toute la pupille peut induire des erreurs d'harmonisation. Enfin, dans le cas où le coin de cube n'est pas placé au centre de la pupille du détecteur, l'effet des aberrations dégrade l'image et peut induire une erreur de position de son barycentre.In practice, this harmonization scheme presents a number of number of disadvantages that lead to modest performance. Notably, cube corner imperfections related to defects in realization lead to harmonization errors. On the other hand, when corner of cube is placed in front of the pupil common to the laser pathways and of observation, as is the case in Figure 1, it can not cover part of this pupil (for reasons of congestion), an image of the laser pulse on the relatively dimension detector significant and limited harmonization accuracy. In addition, if the of laser energy is not uniform throughout the pupil, the fact of not covering the entire pupil can lead to harmonization errors. Finally, in the case where the cube corner is not placed in the center of the pupil of the detector, the effect of aberrations degrades the image and may induce a positional error of his barycentre.

La présente invention propose un dispositif d'harmonisation très précis ne présentant pas les inconvénients de l'art antérieur. Elle consiste à visualiser à l'aide du même détecteur d'imagerie utilisé pour imager la scène, l'image de l'impulsion laser rétroréfléchie par la scène elle-même et non plus par un coin de cube. Pour ce faire, l'invention met en oeuvre un détecteur spécifique pouvant fonctionner selon deux modes, un mode imagerie classique et un mode harmonisation dans lequel le flux provenant de l'impulsion laser rétroréfléchie peut être détecté dans le flux continu diffusé par la scène.The present invention proposes a very harmonizing device precise does not have the disadvantages of the prior art. It consists of visualize using the same imaging detector used to image the scene, the image of the laser pulse retroreflected by the scene itself and no longer by a cube corner. To do this, the invention uses a detector specific that can operate in two modes, an imaging mode classic and a harmonization mode in which the flow from the retroreflected laser pulse can be detected in the streaming stream by the scene.

Plus précisément, l'invention concerne un dispositif pour l'harmonisation entre une voie d'émission d'une impulsion laser vers une scène et une voie passive d'observation de la scène, la voie d'observation comprenant notamment un objectif de focalisation pour former l'image de la scène sur au moins un détecteur d'imagerie, le dispositif étant caractérisé en ce qu'il comprend

  • un détecteur rapide d'impulsion laser permettant de déterminer l'instant d'arrivée de l'impulsion laser rétroréfléchie par la scène sur le ou les détecteur(s) d'imagerie,
  • un détecteur d'harmonisation formant l'un desdits détecteurs d'imagerie et comprenant notamment un ensemble de zones photosensibles dans la bande spectrale du laser d'émission,
  • des moyens de commande du détecteur d'harmonisation en mode imagerie ou en mode harmonisation, recevant le signal délivré par le détecteur rapide, et permettant, en mode harmonisation, le fonctionnement du détecteur d'harmonisation selon deux phases,
  • une première phase d'attente, pendant laquelle les charges électriques issues de la conversion des photons reçus par les zones photosensibles sont intégrées de façon quasi-continue avec un temps d'intégration suffisamment court pour permettre la détection du flux provenant d'une impulsion laser rétroréfléchie par la scène dans le flux continu diffusé par la scène,
  • une deuxième phase de lecture, déclenchée par le signal reçu du détecteur rapide au moment de la détection d'une impulsion laser rétroréfléchie par la scène, entraínant la mise en séquence des charges intégrées au moment de la détection de ladite impulsion afin de détecter dans l'image ainsi obtenue la position de la tache laser correspondante,
  • des moyens de calcul permettant de calculer, à partir de la position de la tache laser dans l'image, les défauts d'harmonisation correspondant aux écarts angulaires entre l'axe de la voie d'observation et celui de la voie d'émission laser.
More specifically, the invention relates to a device for the harmonization between a transmission channel of a laser pulse towards a scene and a passive stage of observation of the scene, the observation channel notably comprising a focusing objective for forming the image of the scene on at least one imaging detector, the device being characterized in that it comprises
  • a fast laser pulse detector for determining the moment of arrival of the retroreflected laser pulse by the scene on the imaging detector (s),
  • a harmonization detector forming one of said imaging detectors and comprising in particular a set of photosensitive zones in the spectral band of the emission laser,
  • control means of the harmonization detector in imaging mode or in harmonization mode, receiving the signal delivered by the fast detector, and allowing, in harmonization mode, the operation of the harmonization detector according to two phases,
  • a first waiting phase, during which the electrical charges resulting from the conversion of the photons received by the photosensitive zones are integrated almost continuously with an integration time sufficiently short to allow the detection of the flux coming from a laser pulse retroreflected by the scene in the continuous flow diffused by the scene,
  • a second reading phase, triggered by the signal received from the fast detector at the time of detection of a retroreflected laser pulse by the scene, causing the sequencing of the integrated charges at the moment of the detection of said pulse in order to detect in the image thus obtained the position of the corresponding laser spot,
  • calculating means making it possible to calculate, from the position of the laser spot in the image, the harmonization defects corresponding to the angular differences between the axis of the observation channel and that of the laser emission pathway .

Outre le fait qu'il apporte une très grande précision, le dispositif selon l'invention permet de faire l'harmonisation en situation réelle, puisque la tache laser imagée sur le détecteur est la même que celle que devra suivre, par exemple, une arme guidée par laser. Il permet en outre de s'affranchir de l'utilisation d'un mélangeur dont les spécifications sont contraignantes, entre la voie laser et la voie d'observation.Besides the fact that it brings a very high precision, the device according to the invention makes it possible to harmonize in a real situation, since the laser spot imaged on the detector is the same as that which will follow, for example, a laser guided weapon. It also allows to avoid the use of a mixer whose specifications are between the laser path and the observation path.

D'autres avantages et caractéristiques de l'invention apparaítront à la lecture de la description qui suit, illustrée par les figures qui représentent :

  • la figure 1 (déjà décrite), un dispositif d'harmonisation entre une voie laser et une voie d'imagerie, selon l'art antérieur ;
  • la figure 2, le schéma de l'architecture d'un système optique mettant en oeuvre un dispositif d'harmonisation selon l'invention ;
  • les figures 3A et 3B, des exemples illustrant la position de la tache laser dans l'image avant et après rectification des défauts d'harmonisation ;
  • la figure 4, un exemple précis de détecteur d'harmonisation ;
  • la figure 5, l'allure du signal délivré par le détecteur d'impulsion en fonction du temps, selon un exemple.
Other advantages and characteristics of the invention will appear on reading the description which follows, illustrated by the figures which represent:
  • FIG. 1 (already described), a device for harmonization between a laser path and an imaging path, according to the prior art;
  • FIG. 2, the diagram of the architecture of an optical system implementing a harmonization device according to the invention;
  • FIGS. 3A and 3B, examples illustrating the position of the laser spot in the image before and after rectification of harmonization defects;
  • FIG. 4, a specific example of a harmonization detector;
  • FIG. 5 shows the shape of the signal delivered by the pulse detector as a function of time, according to an example.

Sur ces figures, les éléments homologues sont repérés par les mêmes indices.In these figures, the homologous elements are identified by the same clues.

La figure 2 représente pour illustrer l'invention, l'architecture d'ensemble d'un équipement optronique d'imagerie et de poursuite de cible en configuration Air/Sol, équipé avec un dispositif d'harmonisation selon un exemple de réalisation. Les différents sous-ensembles représentés sur la figure sont montés dans une structure porteuse rigide (banc optique équipé non représenté) qui est elle-même installée à l'intérieur d'une enveloppe portée par un aéronef. L'équipement comprend une voie d'émission (d'axe optique Δℓ) d'une impulsion laser émise par un émetteur laser LAS dont la longueur d'onde est compatible avec la fonction d'illumination de cible à réaliser, avec son optique de collimation COL permettant d'obtenir un faisceau de faible divergence dans la direction Δℓ. Il s'agit par exemple dans le cas d'un équipement de poursuite de cible d'un laser Nd :YAG émettant des impulsions de quelques dizaines de nanosecondes, à 1,06 µm. Il comprend par ailleurs une voie d'observation (d'axe optique Δi) formée dans cet exemple d'un imageur multispectral, avantageusement équipé d'une optique de focalisation OPT catadioptrique à plusieurs miroirs dont l'achromatisme limite l'introduction de défauts d'harmonisation supplémentaire. Dans l'exemple de la figure 2, la voie d'émission laser est distincte de la voie d'imagerie, ce qui permet de limiter le flux laser rétrodiffusé dans la voie imagerie. Mais il est possible de concevoir un système dans lequel les impulsions laser à l'émission sont injectées dans la voie d'imagerie, au niveau de la partie afocale de l'optique de la voie d'imagerie. Cela permet, en utilisant une optique catadioptrique, de limiter l'introduction de défauts d'harmonisation liés au chromatisme. Dans l'exemple de la figure 2, il s'agit d'une optique de type 'Cassegrain', réalisée au moyen de deux miroirs M1, M2. Un miroir dichroïque M3 sépare la voie d'observation en une voie infrarouge, d'axe ΔiIR et une voie visible/proche infrarouge d'axe ΔiVIS. Ces deux voies sont équipées respectivement d'un détecteur d'imagerie DETIR sensible dans l'infrarouge et d'un détecteur d'imagerie DETVIS sensible dans le visible et le proche infrarouge, sur lesquels l'optique de focalisation OPT forme l'image de la scène dans chacune des bandes spectrales. L'ensemble opto-mécanique est monté et réglé en usine de façon à ce que les axes Δℓ et Δi soient parallèles. Cependant, malgré toutes les précautions prises lors de la conception, de la fabrication, et du réglage, ce parallélisme ne reste généralement pas valable avec une précision suffisante en utilisation opérationnelle, compte tenu des contraintes d'environnement supportées par l'équipement, qui induisent des déplacements d'axe, surtout au niveau du laser. II est donc nécessaire de procéder à une harmonisation en vol.FIG. 2 represents, to illustrate the invention, the overall architecture of an optronic imaging and target tracking equipment in the Air / Ground configuration, equipped with a harmonization device according to an exemplary embodiment. The different subsystems shown in the figure are mounted in a rigid support structure (optical bench equipped not shown) which is itself installed inside an envelope carried by an aircraft. The equipment comprises a transmission channel (of optical axis Δℓ) of a laser pulse emitted by a laser transmitter LAS whose wavelength is compatible with the target illumination function to be performed, with its optical COL collimation to obtain a low divergence beam in the Δℓ direction. This is for example in the case of a target tracking equipment of a Nd: YAG laser emitting pulses of a few tens of nanoseconds, at 1.06 microns. It also comprises an observation channel (of optical axis Δi) formed in this example of a multispectral imager, advantageously equipped with a reflex optic optic reflector with several mirrors whose achromatism limits the introduction of defects in additional harmonization. In the example of FIG. 2, the laser emission path is distinct from the imaging path, which makes it possible to limit the backscattered laser flux in the imaging path. But it is possible to design a system in which the emission laser pulses are injected into the imaging path, at the afocal portion of the optics of the imaging path. This makes it possible, by using catadioptric optics, to limit the introduction of harmonization defects related to chromaticism. In the example of Figure 2, it is a 'Cassegrain' type optical, made by means of two mirrors M1, M2. A dichroic mirror M3 separates the observation path into an infrared path, of axis Δi IR and a visible / near infrared path of axis Δi VIS . These two paths are respectively equipped with a DET IR sensitive imaging detector in the infrared and a DET VIS sensitive imaging detector in the visible and near infrared range, in which the optical focusing OPT form the image of the scene in each of the spectral bands. The opto-mechanical assembly is mounted and adjusted at the factory so that the axes Δℓ and Δi are parallel. However, despite all the precautions taken during the design, manufacture, and adjustment, this parallelism does not generally remain valid with sufficient accuracy in operational use, given the environmental constraints borne by the equipment, which induce axis movements, especially at the laser level. It is therefore necessary to harmonize in flight.

Selon l'invention, le dispositif pour l'harmonisation entre la voie laser d'axe Δℓ et la voie d'observation d'axe Δi comprend un détecteur rapide d'impulsion laser DETIMP, permettant de déterminer l'instant d'arrivée de l'impulsion laser rétroréfléchie par la scène sur le ou les détecteur(s) de la voie d'observation et délivrant un signal S. Dans l'exemple de la figure 2, le détecteur rapide DETIMP est positionné dans un plan focal de l'optique multispectrale OPT grâce à un miroir M4 prélevant sur la voie visible-proche infrarouge une partie du flux. Il comprend en outre un détecteur d'harmonisation formant l'un des détecteurs d'imagerie (dans l'exemple de la figure 2, il s'agit du détecteur DETVIS), et des moyens de commande MCD du détecteur d'harmonisation, recevant le signal S délivré par le détecteur rapide DETIMP. Selon l'invention, le détecteur d'harmonisation, commandé par les moyens de commande MCD, peut fonctionner selon deux modes, un mode imagerie classique et un mode harmonisation dans lequel le flux provenant de l'impulsion laser rétroréfléchie par la scène peut être détecté dans le flux continu diffusé par la scène, permettant ainsi de détecter les défauts d'harmonisation.According to the invention, the device for the harmonization between the Δℓ axis laser pathway and the Δi axis observation pathway comprises a rapid laser pulse detector DET IMP , which makes it possible to determine the instant of arrival of the laser pulse retroreflected by the scene on the detector (s) of the observation channel and delivering a signal S. In the example of FIG. 2, the fast detector DET IMP is positioned in a focal plane of the OPT multispectral optics through a mirror M 4 taking part of the flow on the visible-near-infrared path. It further comprises a harmonization detector forming one of the imaging detectors (in the example of FIG. 2, this is the DET VIS detector), and the MCD control means of the harmonization detector, receiving the signal S delivered by the fast detector DET IMP . According to the invention, the harmonization detector, controlled by the control means MCD, can operate in two modes, a conventional imaging mode and a harmonization mode in which the flow from the laser pulse retroreflected by the scene can be detected. in the continuous stream diffused by the scene, thus making it possible to detect harmonization defects.

Pour ce faire, le détecteur d'harmonisation comprend notamment un ensemble de zones photosensibles dans la bande spectrale du laser d'émission. Les moyens MCD commandent le détecteur d'harmonisation en mode imagerie ou en mode harmonisation. Ils reçoivent le signal S délivré par le détecteur rapide, et permettent, en mode harmonisation, le fonctionnement du détecteur d'harmonisation selon deux phases. Dans une première phase d'attente, les charges électriques issues de la conversion des photons reçus par les zones photosensibles sont intégrées de façon quasi-continue avec un temps d'intégration suffisamment court pour permettre la détection du flux provenant d'une impulsion laser rétroréfléchie par la scène dans le flux continu diffusé par la scène. Dans une deuxième phase de lecture, déclenchée par le signal S reçu du détecteur rapide au moment de la détection d'une impulsion laser rétroréfléchie par la scène, les charges intégrées au moment de la détection de ladite impulsion sont mises en séquence afin de détecter dans l'image ainsi obtenue la position de la tache laser correspondante. Des exemples de détecteurs applicables au dispositif d'harmonisation selon l'invention seront décrits plus en détails dans la suite.To do this, the harmonization detector includes a set of photosensitive zones in the spectral band of the laser resignation. The MCD means control the harmonization detector in imaging mode or in harmonization mode. They receive the S signal issued by the rapid detector, and allow, in harmonization mode, the operation of the harmonization detector according to two phases. In first phase of waiting, the electrical charges resulting from the conversion photons received by the photosensitive zones are integrated so almost continuous with a sufficiently short integration time for enable detection of the flux from a retroreflected laser pulse by the scene in the continuous stream broadcast by the scene. In a second reading phase, triggered by the signal S received from the fast detector at moment of detection of a retroreflected laser pulse by the scene, the integrated charges at the moment of detection of said pulse are set in sequence in order to detect in the image thus obtained the position of the corresponding laser spot. Examples of detectors applicable to harmonization device according to the invention will be described in more detail in the following.

Avantageusement, des moyens de filtrage optique FLTIMP et FLTHAR, dont les transmissions sont centrées sur la bande spectrale du laser d'émission, sont positionnés respectivement devant le détecteur d'impulsion DETIMP et, pendant la phase d'harmonisation, devant le détecteur d'harmonisation (DETVIS dans l'exemple de la figure 2), afin d'améliorer la détectivité de ces détecteurs à la longueur d'onde du laser. Les moyens de filtrage FLTIMP sont fixes, tandis que les moyens de filtrage FLTHAR sont avantageusement amovibles afin de pouvoir être retirés en mode imagerie classique, en dehors des périodes de fonctionnement en mode harmonisation.Advantageously, optical filtering means FLT IMP and FLT HAR , whose transmissions are centered on the spectral band of the emission laser, are respectively positioned in front of the pulse detector DET IMP and, during the harmonization phase, in front of the Harmonization detector (DET VIS in the example of Figure 2), to improve the detectivity of these detectors at the wavelength of the laser. The filtering means FLT IMP are fixed, while the filtering means FLT HAR are advantageously removable in order to be removed in conventional imaging mode, outside the periods of operation in harmonization mode.

Le dispositif d'harmonisation selon l'invention comprend en outre des moyens de calcul MCL permettant de calculer, à partir de la position de la tache laser dans l'image, les défauts d'harmonisation entre l'axe Δi de la voie d'observation et celui Δℓ de la voie d'émission laser, ces défauts correspondant aux écarts angulaires δx, δy entre le centre de l'image et la position de la tache laser, image de l'impulsion laser rétroréfléchie par la scène à travers l'optique de focalisation OPT. La figure 3A illustre ainsi par un exemple la position de la tache laser IML dans l'image, et les écarts δx, δy entre la tache laser IML et le centre de l'image IMC correspondant à l'axe Δi de la ligne de visée du détecteur d'harmonisation. Dans le cas par exemple d'un équipement de poursuite automatique de cible, le centre de l'image IMC correspond au centre de poursuite et la correction de l'erreur d'harmonisation consiste alors par exemple à déplacer électroniquement le centre de poursuite automatique de la valeur opposé de l'écart mesuré. Ainsi, pendant la phase de fonctionnement normal, c'est-à-dire en mode imagerie, les moyens de filtrage FLTHAR sont retirés et le point de la cible sur lequel est accroché le détecteur d'imagerie se trouve alors confondu, comme cela apparaít sur la figure 3B, avec le point d'impact IML de l'impulsion laser.The harmonization device according to the invention further comprises calculating means MCL making it possible to calculate, from the position of the laser spot in the image, the harmonization defects between the axis Δi of the channel of FIG. observation and that Δℓ of the laser emission path, these defects corresponding to angular deviations δx, δy between the center of the image and the position of the laser spot, image of the laser pulse retroreflected by the scene through the OPT optical focusing. FIG. 3A thus illustrates, by an example, the position of the IML laser spot in the image, and the deviations δx, δy between the IML laser spot and the center of the IMC image corresponding to the Δi axis of the line of sight of the harmonization detector. In the case, for example, of automatic target tracking equipment, the center of the IMC image corresponds to the tracking center and the correction of the harmonization error then consists, for example, in electronically moving the automatic tracking center of the opposite value of the measured difference. Thus, during the normal operation phase, that is to say in imaging mode, the filtering means FLT HAR are removed and the point of the target on which the imaging detector is hung is then merged, as shown in FIG. 3B, with the IML impact point of the laser pulse.

Le dispositif d'harmonisation selon l'invention permet ainsi une harmonisation très précise entre l'axe de la ligne de visée du laser et le centre de référence du détecteur d'imagerie de la voie d'observation car elle utilise directement l'image de la tache laser formée sur la scène observée, ce qui permet d'avoir la meilleure résolution possible. Elle permet d'obtenir une harmonisation très précise entre le laser d'illumination et la position du point poursuivi automatiquement sur la scène, ce qui permet une très grande précision d'impact de la munition en cas de tir d'armement à guidage laser, ou une très grande précision de localisation pour les équipements d'observation ou de surveillance.The harmonization device according to the invention thus makes it possible very precise alignment between the line of sight of the laser and the reference center of the imaging detector of the observation channel because it directly uses the image of the laser spot formed on the observed scene, this which allows to have the best possible resolution. It allows to obtain a very precise harmonization between the illumination laser and the position of the point pursued automatically on the scene, allowing for a very large impact accuracy of the ammunition in case of laser guided weapon fire, or a very high accuracy of location for equipment observation or surveillance.

L'utilisation d'une optique multispectrale commune aux deux voies proche infrarouge et infrarouge, comme c'est le cas dans l'exemple de la figure 2, permet à l'équipement de posséder cette capacité d'harmonisation très précise aussi bien en fonctionnement de jour qu'en fonctionnement de nuit. En effet, le dispositif d'harmonisation peut fonctionner de jour, même par très fort éclairement, grâce à l'utilisation du détecteur d'harmonisation spécifique, et il peut également fonctionner de nuit. Dans ce cas, le détecteur d'harmonisation (détecteur d'imagerie proche infrarouge dans l'exemple de la figure 2), est utilisé pendant la phase d'harmonisation pour localiser la tache laser sur la scène, comme cela a été décrit précédemment, tandis que le détecteur infrarouge effectue par exemple la poursuite de la cible de façon continue, sans être perturbé par la phase d'harmonisation. A la fin de chaque cycle d'harmonisation, la correction est appliquée automatiquement sur la position du centre de poursuite du détecteur infrarouge DETIR, permettant d'effectuer l'harmonisation en permanence, à chaque tir. De jour, afin de ne pas perturber la poursuite de la cible, il est également possible d'effectuer la poursuite en infrarouge, avec peut-être une résolution un peu moins bonne, pendant que le détecteur proche infrarouge est utilisé pour effectuer l'harmonisation. Après la phase d'harmonisation, on peut revenir en poursuite proche infrarouge en faisant fonctionner le détecteur d'harmonisation en mode imagerie classique, afin de profiter éventuellement de la meilleure résolution inhérente à cette bande spectrale.The use of multispectral optics common to the two near-infrared and infrared channels, as is the case in the example of FIG. 2, allows the equipment to have this very precise harmonization capability both in operation. by day in night operation. Indeed, the harmonization device can operate by day, even very brightly, thanks to the use of the specific harmonization detector, and it can also operate at night. In this case, the harmonization detector (near infrared imaging detector in the example of FIG. 2) is used during the harmonization phase to locate the laser spot on the stage, as described previously, while the infrared detector performs for example the pursuit of the target continuously, without being disturbed by the harmonization phase. At the end of each harmonization cycle, the correction is applied automatically to the position of the tracking center of the infrared detector DET IR , making it possible to carry out the harmonization permanently, at each shot. By day, in order not to disturb the pursuit of the target, it is also possible to carry out the infrared tracking, with perhaps a slightly less good resolution, while the near infrared detector is used to perform the harmonization . After the harmonization phase, it is possible to return to near-infrared tracking by operating the harmonization detector in conventional imaging mode, in order to possibly benefit from the best resolution inherent to this spectral band.

Notons que dans cet exemple de mise en oeuvre du dispositif d'harmonisation, il est nécessaire que les deux voies infrarouge et proche infrarouge soient parfaitement harmonisées, pour pouvoir transférer sur la voir infrarouge l'écart d'harmonisation mesuré sur la voie proche infrarouge. Cela est relativement aisé dans la mesure où ces deux voies utilisent la même optique multispectrale et que la structure commune portant l'optique et les détecteurs d'imagerie peut être assez compacte et donc très rigide. Si néanmoins, en présence de gradients thermiques an niveau de cette structure, des désalignements entre ces deux voies peuvent se produire, on peut mesurer ces gradients à l'aide de capteurs de température placés sur certaines parties de la structure, et appliquer des corrections d'harmonisation issues d'une table de valeurs préalablement établies par des simulations comportementales en thermique de la structure. En tout état de cause, ces corrections, lorsqu'elles sont nécessaires, restent du second ordre par rapport aux corrections mesurées grâce au détecteur d'harmonisation du dispositif d'harmonisation selon l'invention.Note that in this example of implementation of the device of harmonization, it is necessary that both infrared and near are perfectly harmonized, so that they can be transferred to the see infrared harmonization difference measured on the near infrared path. This is relatively easy in that both routes use the same multispectral optics and that the common structure bearing optics and Imaging detectors can be quite compact and therefore very rigid. Yes nevertheless, in the presence of thermal gradients at this level structure, misalignments between these two paths can occur, can measure these gradients using temperature sensors placed on parts of the structure, and apply harmonization corrections from a table of values previously established by simulations behavioral in thermal structure. In any case, these corrections, where necessary, remain second-order compared to the corrections measured with the harmonization detector of the harmonizing device according to the invention.

Nous décrivons maintenant plus en détails des exemples de détecteurs d'harmonisation, qui, associés au détecteur d'impulsion, permettent le fonctionnement du dispositif selon l'invention.We now describe in more detail examples of harmonization detectors, which, together with the pulse detector, allow the operation of the device according to the invention.

Un premier exemple privilégié consiste à utiliser comme détecteur d'harmonisation un détecteur d'imagerie à intégration et transfert de type CCD (initiales de « Charge Coupled Device » en terminologie anglo-saxonne), situé précisément dans le plan focal de l'objectif de focalisation de la voie d'observation, et comportant un ensemble de zones photosensibles en silicium (ou « pixels » selon la terminiologie anglo-saxonne), organisées en matrice généralement carrée, typiquement 100x100 pixels. L'utilisation d'un matériau photosensible dans le spectre visible et proche infrarouge, par exemple le Silicium, convient particulièrement à la détection d'un laser émettant dans le proche infrarouge, comme le laser Nd:YAG, à 1,06 µm. Selon l'invention, le détecteur CCD est commandé par les moyens de commande MCD de telle sorte à fonctionner selon un mode de fonctionnement CCD classique lorsque le détecteur d'harmonisation est en mode imagerie et selon un mode dit « tapis roulant » lorsque le détecteur est en mode harmonisation. Dans le mode de fonctionnement classique (mode imagerie), le détecteur CCD fait l'acquisition de la scène (conversion des photons reçus en charges puis intégration dans des puits de potentiel des charges libérées proportionnellement à l'éclairement reçu pendant un temps d'intégration prédéterminé, typiquement de l'ordre de 20 msec), puis les charges sont transférées en colonne et échantillonnées par multiplexage ligne à ligne afin de former des signaux séquentiels qui forment le signal de visualisation (phase de lecture de l'image), et ce, pendant l'acquisition de l'image suivante. Un calcul de sensibilité montre que, en absence de bruit dû au fond de scène, le système détecte des impulsions laser avec de bonnes performances. Par contre, de jour, la contribution de l'éclairement solaire perturbe de façon importante le signal, même après filtrage autour de la longueur d'onde du laser, car le temps d'intégration de l'image est long devant la durée de l'impulsion. Le mode « tapis roulant », décrit dans le brevet FR 2 740 558 au nom de la déposante, permet la détection du flux provenant de l'impulsion laser rétroréfléchie par la scène dans le flux continu diffusé par la scène.A prime example is to use as a detector of harmonization an imaging detector with integration and transfer type CCD (initials of "Charge Coupled Device" in English terminology), precisely located in the focal plane of the focus lens of the observation path, and comprising a set of photosensitive zones in silicon (or "pixels" according to Anglo-Saxon terminology), organized in a generally square matrix, typically 100x100 pixels. Use of a photosensitive material in the visible and near infrared spectrum, by example Silicon, is particularly suitable for the detection of a laser emitting in the near infrared, like the Nd: YAG laser, at 1.06 μm. According to the invention, the CCD detector is controlled by the means of MCD command so as to operate in a mode of conventional CCD operation when the harmonization detector is in imaging mode and according to a mode called "treadmill" when the detector is in harmonization mode. In the classic operating mode (mode imaging), the CCD detector acquires the scene (conversion of photons received in charge then integration into potential wells of charges released proportionally to the illumination received for a period of time predetermined integration, typically of the order of 20 msec), then the loads are transferred in column and sampled by multiplexing line to line to form sequential signals that form the signal of visualization (reading phase of the image), and this, during the acquisition of the next image. A sensitivity calculation shows that in the absence of noise due at the back of the stage, the system detects laser pulses with good performance. On the other hand, by day, the contribution of solar irradiance significantly disrupts the signal, even after filtering around the wavelength of the laser, because the time of integration of the image is long before the duration of the pulse. The "treadmill" mode, described in patent FR 2 740 558 in the name of the applicant, allows the detection of the flow from the laser pulse retroreflected by the scene into the continuous flow broadcast by the scene.

La figure 4 montre un schéma d'un mode de fonctionnement d'un détecteur CCD en mode tapis roulant. Il s'agit dans cet exemple d'une matrice de détection dite à transfert de trames, comprenant de manière classique une zone image 40 et une zone mémoire 41. Pour simplifier la figure, la zone image est constituée de 4x4 zones photosensibles (ou pixels) Pi et la zone mémoire forme un circuit de multiplexage CCD, composée de mémoires élémentaires Mi, réalisées en circuiterie CMOS intégrée. Le détecteur comporte en outre un registre de sortie R et un étage d'amplification A. Il est commandé par les moyens de commande MCD du dispositif selon l'invention, reliés au détecteur rapide d'impulsion DETIMP.Figure 4 shows a diagram of a mode of operation of a CCD detector in treadmill mode. In this example, it is a so-called frame transfer detection array, which conventionally comprises an image zone 40 and a memory zone 41. To simplify the figure, the image zone consists of 4x4 photosensitive zones (or pixels ) Pi and the memory area forms a CCD multiplexing circuit, composed of elementary memories Mi, realized in integrated CMOS circuitry. The detector further comprises an output register R and an amplification stage A. It is controlled by the control means MCD of the device according to the invention, connected to the rapid pulse detector DET IMP .

Le fonctionnement en mode tapis roulant appliqué à une matrice CCD à transfert de trames se sépare en deux phases : une phase d'attente de détection et une phase de lecture après détection. Dans la première phase d'attente, le signal S délivré par le détecteur rapide DETIMP est nul, traduisant l'absence d'impulsion. Pendant ce temps, le CCD est en transfert permanent à haute cadence, ce qui se traduit par un temps d'intégration très réduit (typiquement 250 µsec) par rapport au temps d'intégration en mode imagerie. Grâce à la haute cadence de transfert vertical, l'acquisition du signal de fond est donc réduite à un temps minimum, d'où le bruit associé minimale, permettant la détection d'impulsion de très faible niveau. Dans la deuxième phase, lorsque l'impulsion laser rétroréfléchie par la scène est détectée par le détecteur rapide, le transfert des lignes à haute cadence est alors poursuivi jusqu'à amener la zone image dans la zone mémoire, puis la zone mémoire est lue à une cadence normale, la phase de lecture comprenant le transfert des charges vers le circuit de multiplexage intégré au détecteur et vers le registre de sortie R pour former, après amplification par l'étage d'amplification A une image, correspondant à un signal de visualisation SV au standard video désiré.The treadmill mode operation applied to a frame transfer CCD matrix is divided into two phases: a detection waiting phase and a reading phase after detection. In the first waiting phase, the signal S delivered by the fast detector DET IMP is zero, reflecting the absence of pulse. Meanwhile, the CCD is in continuous transfer at high speed, which results in a very short integration time (typically 250 μsec) compared to the integration time in imaging mode. Thanks to the high rate of vertical transfer, the acquisition of the background signal is reduced to a minimum time, hence the minimum associated noise, allowing the detection of very low level pulse. In the second phase, when the laser pulse retroreflected by the scene is detected by the fast detector, the transfer of lines at high speed is then continued until the image zone is brought into the memory zone, then the memory zone is read at a normal cadence, the reading phase comprising the transfer of charges to the multiplexing circuit integrated in the detector and to the output register R to form, after amplification by the amplification stage A, corresponding to a visualization signal SV to the desired video standard.

Les moyens de calcul MCL du dispositif selon l'invention, pouvant être réalisés par un processeur commun aux moyens de commande MCD, permettent alors de calculer, à partir de la position du ou des pixels illuminé(s) dans l'image par l'impulsion laser, les défauts d'harmonisation correspondant aux écarts angulaires entre l'axe de la ligne de visée du détecteur d'harmonisation et l'axe de la voie d'émission laser.The calculation means MCL of the device according to the invention, which can be made by a processor common to the MCD control means, allow to calculate, from the position of the pixel (s) illuminated in the image by the laser pulse, harmonization defects corresponding to the angular differences between the axis of the line of sight of the Harmonization detector and the axis of the laser emission path.

D'autres modes de fonctionnement d'un détecteur CCD en mode tapis roulant sont possibles. On peut par exemple substituer au détecteur à transfert de trames, comme illustré sur la figure 4, un détecteur dit pleine image (« full frame array » en terminologie anglosaxonne) où les pixels occupent quasiment toute la surface de la matrice et dans lequel le transfert est dit par ligne, les charges d'une même ligne étant simultanément transférées ligne à ligne. Comme précédemment, le fonctionnement en mode tapis roulant comprend une première phase d'attente pendant laquelle le transfert se fait à haute cadence, puis une phase de lecture après qu'une impulsion a été détectée par le détecteur rapide DETIMP.Other modes of operation of a CCD detector in treadmill mode are possible. For example, the frame transfer detector can be substituted, as illustrated in FIG. 4, with a so-called "full frame array" detector, in which the pixels occupy almost the entire surface of the array and in which the transfer takes place. is said per line, the charges of the same line being simultaneously transferred line by line. As before, the operation in treadmill mode comprises a first waiting phase during which the transfer is at a high rate, then a reading phase after a pulse has been detected by the fast detector DET IMP .

Un autre exemple de détecteur peut être adapté au dispositif selon l'invention. Il s'agit d'une matrice de photo-détecteurs, chaque photo-détecteur étant relié à un circuit de lecture des moyens de commande MCD de la matrice par un circuit d'entrée qui assure pour le photo-détecteur qui lui est couplé, les fonctions de polarisation et d'intégration du signal photo-électrique, le circuit de lecture permettant le multiplexage des signaux délivrés pour la formation d'un signal vidéo. Dans un mode de fonctionnement particulier de cette matrice, décrit dans le brevet FR 2 762 082 au nom de la déposante, il est possible de détecter une impulsion laser courte dans le flux continu diffusé par la scène. La matrice de photo-détecteurs est adaptée pour former le détecteur d'harmonisation du dispositif selon l'invention pouvant fonctionner selon un mode imagerie classique et selon un mode harmonisation.Another example of a detector can be adapted to the device according to the invention. It is a matrix of photo-detectors, each photo-detector being connected to a read circuit of the MCD control means of the matrix by an input circuit which ensures for the photodetector that him is coupled, the functions of polarization and integration of the photoelectric signal, the reading circuit allowing the multiplexing of the signals issued for forming a video signal. In a mode of particular functioning of this matrix, described in patent FR 2 762 082 in the name of the applicant, it is possible to detect a laser pulse short in the continuous stream broadcast by the scene. The matrix of photo-detectors is adapted to form the device harmonization detector according to the invention can operate in a conventional imaging mode and according to a harmonization mode.

En mode harmonisation, le fonctionnement de la matrice de photo-détecteurs comprend comme précédemment deux phases, une phase d'attente de détection, pendant laquelle le signal photo-électrique généré par chaque photo-détecteur est intégré de manière continue, et une phase de lecture de l'image, après détection par le détecteur rapide DETIMP de l'impulsion laser rétroréfléchie par la scène. La phase d'attente comprend pour chaque photodétecteur une succession de cycles d'intégration très courts (de l'ordre de la microseconde). Durant chaque cycle d'intégration, le photodétecteur n'intègre qu'une quantité de charges infinitésimale qui est transférée dans une mémoire tampon et conservée jusqu'à l'approche de la fin du cycle suivant puis rejeté sans lecture préalable si aucun signal provenant du détecteur rapide n'est détecté. Lorsqu'une impulsion laser est détectée par le détecteur rapide, les moyens de commande MCD déclenchent dans chaque photodétecteur la sommation du signal en cours d'intégration avec le contenu de la cellule mémoire associée, permettant d'éviter ainsi toute perte d'information. Chaque cellule mémoire contient alors un signal négligeable issu du fond de scène, à l'exception de celle associée au photodétecteur ayant reçu l'impulsion laser et pour lequel le signal de fond est dominé par le signal détecté provenant de l'impulsion. Les moyens de commande MCD déclenchent alors la seconde phase correspondant à la lecture, à cadence normale (typiquement quelques millisecondes) du contenu des mémoires, délivrant une image à partir de laquelle on peut connaítre la position de la tache laser sur le détecteur d'harmonisation formé de la matrice de photo-détecteurs. Les moyens de calcul MCL permettent alors l'évaluation des défauts d'harmonisation.In harmonization mode, the operation of the photodetector array comprises, as previously, two phases, a detection waiting phase, during which the photoelectric signal generated by each photodetector is continuously integrated, and a phase of detection. reading of the image, after detection by the rapid detector DET IMP of the laser pulse retroreflected by the scene. The waiting phase comprises for each photodetector a succession of very short integration cycles (of the order of one microsecond). During each integration cycle, the photodetector integrates only an infinitesimal amount of charge that is transferred to a buffer memory and held until the end of the next cycle and then discarded without prior reading if no signal from the fast detector is not detected. When a laser pulse is detected by the fast detector, the DCM control means trigger in each photodetector the summation of the signal being integrated with the contents of the associated memory cell, thereby preventing any loss of information. Each memory cell then contains a negligible signal from the back of the scene, with the exception of that associated with the photodetector having received the laser pulse and for which the background signal is dominated by the detected signal coming from the pulse. The MCD control means then trigger the second phase corresponding to the reading, at a normal rate (typically a few milliseconds) of the contents of the memories, delivering an image from which the position of the laser spot on the harmonization detector can be known. formed of the matrix of photo-detectors. The calculation means MCL then make it possible to evaluate the harmonization defects.

En mode imagerie, les moyens de commande MCD génèrent un temps d'intégration beaucoup plus long pour chaque photodétecteur (de l'ordre de la milliseconde par exemple), puis déclenchent la phase de lecture, permettant ainsi d'obtenir une image normale de la scène.In imaging mode, the MCD control means generate a much longer integration time for each photodetector (from the order of the millisecond, for example), then trigger the reading phase, thus allowing to obtain a normal image of the scene.

La matrice de détecteurs est plus complexe, et plus coûteuse, à mettre en oeuvre que le détecteur à « tapis roulant » du fait que chaque photo-détecteur a son propre circuit d'intégration des charges (circuit d'entrée). Elle présente cependant par rapport au détecteur CCD plusieurs avantages. Notamment, le choix des photo-détecteurs, de préférence de type photo-voltaïque, permet de s'adapter à d'autres longueurs d'onde du laser d'émission. Ainsi, pour la longueur d'onde usuelle de 1,06 µm ou de 1,56 µm pour l'application télémétrie par exemple, les détecteurs réalisés sur InGaAs, InSb ou encore HgCdTe seront privilégiés et pourront, selon leur nature et selon les performances recherchées, fonctionner fortement, peu ou non refroidis. Pour les longueurs d'onde situées dans l'infrarouge lointain, des détecteurs de type HgCdTe ou AsGa multipuits quantiques, fortement refroidis, seront préférés. Dans le cas où le matériau choisi pour le détecteur est compatible d'une imagerie dans la bande infrarouge, il n'est pas nécessaire de rajouter un second détecteur d'imagerie infrarouge, comme c'est le cas dans l'exemple de la figure 2, sauf si l'on veut une totale simultanéité entre les modes harmonisation et imagerie. L'utilisation d'une matrice de photo-détecteurs comme détecteur d'harmonisation permet également, en mode harmonisation, de limiter les photo-détecteurs utilisés à ceux situés à proximité du centre du champ du détecteur (fenêtrage de la matrice centré sur l'axe de visée de la voie d'observation). En effet, comme il s'agit d'harmonisation, les écarts entre les lignes de visée de la voie d'observation et de la voie laser sont a priori faibles et l'impulsion laser que l'on cherche à détecter ne peut pas apparaítre dans la partie centrale du champ. Cela permet de diminuer un peu la complexité de traitement du détecteur en mode harmonisation.The matrix of detectors is more complex, and more expensive, at implement that the "treadmill" detector because each photo-detector has its own circuit for integrating loads (circuit input). However, it has several different CCD detector advantages. In particular, the choice of photo-detectors, preferably of the type photo-voltaic, allows to adapt to other laser wavelengths resignation. Thus, for the usual wavelength of 1.06 μm or 1.56 μm for the telemetry application for example, the sensors made on InGaAs, InSb or HgCdTe will be privileged and may, depending on their nature and depending on the desired performance, work strongly, little or no cooled. For far infrared wavelengths, HgCdTe or AsGa multiwell quantum well detectors, strongly cooled, will be preferred. In the case where the material chosen for the detector is compatible with imaging in the infrared band, it is not necessary to add a second infrared imaging detector, as this is the case in the example of Figure 2, unless we want a total simultaneity between harmonization and imaging modes. The use of a photodetector matrix as harmonization detector allows also, in harmonization mode, to limit the photodetectors used to those located near the center of the detector field (windowing of the matrix centered on the line of sight of the observation channel). Indeed, as he This is harmonization, the differences between the lines of sight of the track of observation and the laser path are a priori weak and the laser pulse that one seeks to detect can not appear in the central part of field. This makes it possible to reduce somewhat the complexity of processing the detector in harmonization mode.

Bien que les détecteurs d'harmonisation décrits ci-dessus soient des exemples préférés pour la mise en oeuvre du dispositif d'harmonisation selon l'invention, celui-ci n'est pas limité à ces exemples. D'autres détecteurs d'imagerie sont envisageables si, en plus de leur fonction d'imageur, ils peuvent, dans un mode de fonctionnement particulier, et associés à un détecteur rapide d'impulsion, détecter une impulsion laser dans un flux de fond continu, afin de procéder à l'harmonisation entre la voie laser d'émission et la voie d'observation en conditions réelles, c'est à dire grâce à l'impulsion laser rétroréfléchie par la scène elle-même.Although the harmonization detectors described above are preferred examples for the implementation of the harmonization system according to the invention, it is not limited to these examples. Other detectors imagery are possible if, in addition to their imaging function, they can, in a particular mode of operation, and associated with a fast pulse detector, detect a laser pulse in a flow of continuous background, in order to proceed with the harmonization between the emission laser and the way of observation in real conditions, ie thanks to the impulse laser retroreflected by the scene itself.

Avantageusement, pour la même raison que celle invoquée plus haut, la surface de détection du détecteur rapide DETIMP peut être réduite par rapport au champ total de l'image, en la centrant sur l'axe de la ligne de visée de la voie d'observation. En effet, la probabilité de détection de l'impulsion rétroréfléchie par la scène lors de la procédure d'harmonisation est maximale dans la partie centrale du champ. En réduisant la zone sensible du détecteur, on augmente sa détectivité, ce qui améliore encore les performances du dispositif d'harmonisation. En améliorant ainsi la détectivité du détecteur rapide, on peut en outre utiliser ce même détecteur, le cas échéant, comme détecteur de télémétrie.Advantageously, for the same reason as that mentioned above, the detection surface of the fast detector DET IMP can be reduced with respect to the total field of the image, by centering it on the axis of the line of sight of the signal path. 'observation. Indeed, the probability of detection of the retroreflected impulse by the scene during the harmonization procedure is maximum in the central part of the field. By reducing the sensitive area of the detector, its detectivity is increased, which further improves the performance of the harmonization device. By thus improving the detectivity of the fast detector, it is also possible to use the same detector, if necessary, as a telemetry detector.

Avantageusement, le dispositif d'harmonisation selon l'invention comprend en outre des moyens électroniques de filtrage passe-haut du signal délivré par le détecteur d'impulsion DETIMP, permettant de couper le signal correspondant au flux lumineux généré par la rétrodiffusion sur l'atmosphère de l'impulsion laser émise. En effet, lors d'une procédure d'harmonisation, une impulsion laser est émise vers la scène puis le flux rétroréfléchi par la scène est détecté comme cela a été décrit précédemment, afin de calculer les éventuels erreurs d'harmonisation. Nous avons vu que la fonction du détecteur d'impulsion est de détecter l'instant d'arrivée de l'impulsion rétroréfléchie sur le détecteur d'harmonisation afin de déclencher la phase de lecture de l'image sur laquelle apparaít l'impact laser. Or suivant les conditions météorologiques, il est possible qu'il y ait un effet de rétrodiffusion de l'impulsion laser par l'atmosphère à sa sortie de l'équipement, entraínant une détection intempestive de flux lumineux à la longueur d'onde du laser d'émission par le détecteur rapide DETIMP. Cependant, le flux détecté par le détecteur rapide DETIMP et correspondant à la rétrodiffusion sur l'atmosphère s'étend pendant un temps beaucoup plus long que la durée de l'impulsion. La figure 5 représente ainsi, selon un exemple, l'allure du signal délivré par le détecteur rapide en fonction du temps. L'origine des temps correspond à l'instant d'émission de l'impulsion laser. Le signal S1 correspondant au flux rétrodiffusé par l'atmosphère s'étend pendant un temps T1 prédéterminé, dont la durée est corrélée à la distance sur laquelle l'impulsion laser peut être rétrodiffusée vers l'équipement. Ce temps, qui peut être de quelques dizaines de microsecondes, est nettement supérieur au temps T2 du signal S2 correspondant à la durée de l'impulsion rétroréfléchie par la scène. Les moyens de filtrage électroniques du dispositif selon l'invention permettent ainsi de couper le signal parasite basse fréquence S1 et de ne garder que le signal utile S2 correspondant à l'impulsion rétroréfléchie par la scène. Un autre moyen de s'en affranchir consiste à prévoir en sortie du détecteur rapide DETIMP des moyens électroniques d'inhibition du signal délivré par le détecteur d'impulsion pendant un temps prédéterminé après l'émission d'une impulsion laser, et correspondant au flux lumineux généré par la rétrodiffusion sur l'atmosphère de l'impulsion laser émise. Ce temps d'inhibition, pendant lequel le signal délivré ne sera pas pris en compte par les moyens de commande MCD, pourra être de quelques dizaines de microsecondes par exemple.Advantageously, the harmonization device according to the invention further comprises electronic means for high-pass filtering of the signal delivered by the pulse detector DET IMP , making it possible to cut off the signal corresponding to the luminous flux generated by the backscattering on the atmosphere of the emitted laser pulse. Indeed, during a harmonization procedure, a laser pulse is emitted to the scene and the stream retroreflected by the scene is detected as described above, in order to calculate possible harmonization errors. We have seen that the function of the pulse detector is to detect the moment of arrival of the retroreflected pulse on the harmonization detector in order to trigger the reading phase of the image on which the laser impact appears. Depending on the weather conditions, it is possible that there is a backscattering effect of the laser pulse by the atmosphere at its output from the equipment, resulting in an inadvertent detection of luminous flux at the wavelength of the laser. of emission by the fast detector DET IMP . However, the flux detected by the fast detector DET IMP and corresponding to the backscattering on the atmosphere extends for a much longer time than the duration of the pulse. FIG. 5 thus represents, in one example, the shape of the signal delivered by the fast detector as a function of time. The origin of the times corresponds to the moment of emission of the laser pulse. The signal S 1 corresponding to the flux backscattered by the atmosphere extends for a predetermined time T 1 , the duration of which is correlated with the distance over which the laser pulse can be backscattered towards the equipment. This time, which may be a few tens of microseconds, is significantly greater than the time T 2 of the signal S 2 corresponding to the duration of the pulse retroreflected by the scene. The electronic filtering means of the device according to the invention thus make it possible to cut the low frequency spurious signal S 1 and to keep only the useful signal S 2 corresponding to the pulse retroreflected by the scene. Another way to overcome this is to provide at the output of the rapid detector DET IMP electronic means for inhibiting the signal delivered by the pulse detector for a predetermined time after the emission of a laser pulse, and corresponding to the luminous flux generated by the backscattering on the atmosphere of the emitted laser pulse. This inhibition time, during which the delivered signal will not be taken into account by the MCD control means, may be a few tens of microseconds for example.

Claims (11)

  1. Device for harmonizing a channel for emitting a laser pulse towards a scene and a passive channel for observing the scene, the observation channel comprising in particular a focusing objective (OBJ, OBT) for forming the image of the scene on at least one imaging detector (DETVIS, DETIR), the device being characterized in that it comprises
    a laser pulse fast detector (DETIMP) making it possible to determine the instant of arrival of the laser pulse backreflected by the scene onto the imaging detector or detectors,
    a harmonization detector (DETVIS) forming one of the said imaging detectors and comprising in particular a set of zones that are photosensitive in the spectral band of the emission laser,
    means of control (MCD) of the harmonization detector in imaging mode or in harmonization mode, receiving the signal (S) delivered by the fast detector, and allowing, in harmonization mode, the operation of the harmonization detector according to two phases,
    a first standby phase, during which the electric charges arising from the conversion of the photons received by the photosensitive zones are integrated in a quasi-continuous manner with an integration time short enough to allow the detection of the flux originating from a laser pulse backreflected by the scene in the continuous flux scattered by the scene,
    a second reading phase, triggered by the signal received from the fast detector at the moment of the detection of a laser pulse backreflected by the scene, entailing the placing into sequence of the charges integrated at the moment of the detection of the said pulse so as to detect in the image thus obtained the position of the corresponding laser spot,
    means of calculation (MCL) making it possible to calculate, on the basis of the position of the laser spot in the image, the harmonization defects corresponding to the angular deviations (δx, δy) between the axis (δi) of the observation channel and that (δl) of the laser emission channel.
  2. Device according to Claim 1, characterized in that it furthermore comprises optical means of transmission filtering (FLTIMP) centred on the spectral band of the emission laser, positioned in front of the fast detector of pulses (DETIMP).
  3. Device according to one of the preceding claims, characterized in that the fast detector is positioned in proximity to a focal plane of the focusing objective of the observation channel, and exhibits a photosensitive surface of smaller dimension than the total field of the image, centred on the axis (δi) of the observation channel.
  4. Device according to Claim 3, characterized in that the emission channel exhibiting a telemetry function, the fast detector is also the laser receiver for carrying out the telemetry.
  5. Device according to one of the preceding claims, characterized in that the harmonization detector being used either in harmonization mode or in imaging mode, it furthermore comprises removable optical means of transmission filtering (FLTHAR) centred on the spectral band of the emission laser, positioned in front of the matrix detector during the harmonization phase and removed during the imaging phase.
  6. Device according to one of the preceding claims, characterized in that it furthermore comprises electronic means of high-pass filtering of the signal delivered by the pulse detector, making it possible to out the signal corresponding to the light flux generated by the backscattering on the atmosphere of the laser pulse emitted.
  7. Device according to one of the preceding claims, characterized in that it furthermore comprises electronic means of disabling the signal delivered by the pulse detector for a predetermined time after the emission of a laser pulse, and corresponding to the light flux generated by the backscattering on the atmosphere of the laser pulse emitted.
  8. Device according to one of the preceding claims, characterized in that the harmonization detector is a CCD detector operating in conveyor belt mode during the harmonization phase, the means of control (MCD) causing the CCD detector to operate by permanent transfer at high rate during the standby phase.
  9. Device according to one of Claims 1 to 7, characterized in that the harmonization detector is formed of a matrix of photodetectors, each photodetector being linked to a reading circuit belonging to the control means (MCD) by an input circuit which provides, in respect of the photodetector which is coupled to it, for the integration of the charges, the means (MCD) triggering during the standby phase, for each photodetector, a succession of very short integration cycles during which the photodetector integrates a quantity of infinitesimal charges which is rejected without prior reading if no signal originating from the fast detector (DETIMP) is detected.
  10. Optronic system for tracking a target in a scene, comprising in particular a laser (LAS) for illuminating the target through the emission of pulses and a multispectral imager for tracking the scene comprising in particular a detector sensitive in the infrared (DETIR), a detector sensitive in the visible/near infrared (DETVIS) and a multispectral optic (OPT) for forming the image of the scene simultaneously on each of the said detectors, the system being characterized in that it is equipped with a device for harmonizing the laser channel and the channel of the multispectral imager according to one of the preceding claims, the harmonization detector of the device being the detector (DETVIS) sensitive in the visible/near infrared, and characterized in that in harmonization mode, a correction of the harmonization defects is applied to the position of the centre of tracking of the infrared detector (DETIR) after each emission of a laser pulse towards the target.
  11. Optronic system according to Claim 10, characterized in that it comprises a dichotic mirror (M3), in that the multispectral optic is of catadioptric type, made by means of mirrors (M1, M2), which, associated with the said dichotic mirror, make it possible to image the scene on each of the said detectors.
EP01402722A 2000-10-27 2001-10-19 Apparatus for boresighting a laser transmitting channel with a passive observing channel Expired - Lifetime EP1202021B1 (en)

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FR0013849 2000-10-27
FR0013849A FR2816118B1 (en) 2000-10-27 2000-10-27 DEVICE FOR THE HARMONIZATION BETWEEN A LASER TRANSMISSION CHANNEL AND A PASSIVE OBSERVATION CHANNEL

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FR2661518B1 (en) * 1985-12-13 1992-08-07 Thomson Trt Defense METHOD OF HARMONIZATION BETWEEN THE AXIS OF A SIGHT GLASS AND THAT OF A THERMAL CAMERA.
FR2652166B1 (en) * 1989-09-19 1991-10-31 Thomson Csf AUTOMATIC HARMONIZATION DEVICE FOR AN OPTRONIC SYSTEM.
FR2740558B1 (en) * 1995-10-27 1997-11-28 Thomson Csf DETECTION BY LASER DESIGNATION AND MATRIX DETECTOR ECARTOMETRY DEVICE
FR2784185B1 (en) * 1998-10-06 2001-02-02 Thomson Csf DEVICE FOR THE HARMONIZATION BETWEEN A LASER EMISSION CHANNEL AND A PASSIVE OBSERVATION CHANNEL

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FR2816118B1 (en) 2003-01-31
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FR2816118A1 (en) 2002-05-03
DE60108587T2 (en) 2006-03-30

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