EP2140289A2

EP2140289A2 - Method and dual laser device for detecting magnifying optical systems

Info

Publication number: EP2140289A2
Application number: EP08787923A
Authority: EP
Inventors: Jean-Louis Duvent; Jean-Yves Thomas; Pierre Morin
Original assignee: Compagnie Industriel des Lasers CILAS SA
Current assignee: Compagnie Industriel des Lasers CILAS SA
Priority date: 2007-04-11
Filing date: 2008-04-07
Publication date: 2010-01-06
Also published as: FR2915001B1; WO2008142270A3; US20100128992A1; FR2915001A1; RU2009141608A; WO2008142270A2; IL201265A0; CA2681927A1

Abstract

The invention comprises illuminating a scene where said magnifying optical system (OP) may occur with at least a first and a second pulses respectively generated by first and second laser transmitters (E1, E2). The first laser transmitter (E1) and a detector of the scene thus illuminated (D) are adjacent, while the second laser transmitter (E2) is remote from said detector (D) transversally to the direction (d) of said scene.

Description

Method and device with two lasers for detecting magnifying optical systems

The present invention relates to a method and a device for the detection of magnifying optical systems.

It is known that magnifying optical systems (such as riflescopes and eyes) have the property of retroreflecting the light. Also, to detect such a magnifying optical system in a scene, it is known to illuminate said scene by laser pulses and to take images in synchronism with the corresponding laser illumination. Thus, on said images appears a bright spot corresponding to said magnifying optical system. However, in said scene thus illuminated, there may be other retroreflective objects, such as retro-reflectors of motor vehicles, indicating signs, etc. It follows that the light spots shown by the images do not necessarily correspond to magnifying optical systems and therefore there is ambiguity as to the detection of the latter.

The present invention aims to overcome this disadvantage. To this end, according to the invention, the method for distinguishing at least one magnifying optical system among other objects, capable of retroreflecting the light, being in a scene, the method according to which: said scene is illuminated by at least one first laser pulse emitted by a first laser emitter and taking a first image of said scene illuminated by said first pulse by means of a detector observing said scene, said detector and said first laser emitter being at least approximately adjacent transversely to the direction of said scene; said scene is illuminated by at least a second laser pulse emitted by a second laser emitter spaced from said detector transversely to the direction of said scene, said detector being responsive to said second pulse; and - by means of said detector, taking at least a second image of said scene illuminated by said second pulse, is remarkable in that, after comparison of said first and second images, we consider:

that said objects, whose images are in said first and second images of said scene, are not magnifying optical systems; and

said objects, whose images are in the first image of said scene, but are absent from said second image of the latter, are magnifying optical systems. Indeed, the applicant has observed that the retroreflective cone of a magnifying optical system is very narrow (of the order of 0.1 mrad), whereas that of the usual reflex reflectors is much wider (at least equal to 50 mrad). ). Thus, by discarding said second emitter from the detector, it can receive the light emitted by the second emitter and retroreflected by the usual retro-reflectors, but will not see this light retroreflected by a magnifying optical system.

Of course, the transverse difference between the second laser emitter and said detector to benefit from the invention depends on the distance separating the detector and said magnifying optical system, as well as the angle of the retroreflective cone thereof. However, experience has shown that a fixed transversal difference of at least 200 mm, preferably of the order of 400 mm, makes it possible to discriminate an optical system from a conventional retro-reflector for distances of between a few meters and several meters. kilometers. Said first and second pulses may have the same emission wavelength; they are then shifted temporally from one another. In this case, the time offset between said first and second laser pulses is chosen small enough so that the scene is at least approximately identical in said first and second images. It is advantageous to illuminate said scene by means of a series of first and second laser pulses entangled so that a first (or a second) pulse is interposed between two seconds (or two first) pulses, proceed to taking first and second images successive and entangled in correspondence with said first sequence and comparing each time a first and a second images temporally close to each other.

In a variant, said first and second laser pulses are simultaneous and have different emission wavelengths and said detector (comprising, for example, two CCD matrices or two parts of a CCD matrix dedicated respectively to said first and second laser pulses. ) is chosen to deliver two different images respectively corresponding to these two wavelengths. Preferably, these wavelengths are sufficiently close to each other that the backscattering of sunlight by said scene is at least approximately similar in said first and second simultaneous images. It is then advantageous to illuminate said scene by means of a sequence of pairs of laser pulses each comprising a first and a second simultaneous laser pulse, to take successive pairs of images corresponding to said pairs of laser pulses and to successively compare the first image and the second image of each pair of images. The present invention further relates to a device for detecting a magnifying optical system in a scene with other objects capable of retroreflecting light, said device comprising a first laser transmitter for illuminating said scene and a detector capable of detecting the light retroreflected by said objects illuminated by said first emitter, said detector and said first laser emitter being at least approximately adjacent transversely to the direction of said scene, and a second laser emitter spaced from said detector transversely to the direction of said scene, said detector being responsive to the emission wavelength of said second emitter.

The figures of the appended drawing will make it clear how the invention can be realized. In these figures, identical references designate similar elements.

Figure 1 schematically illustrates the present invention in the case of a magnifying optical system.

Figure 2 schematically illustrates the present invention in the case of a conventional retro-reflector.

In these figures, there is shown a device according to the present invention comprising a first and a second impulse laser emitters E1 and E2 and a detector D, for example of the matrix type (s) CCD.

The first laser emitter E1 and the detector D are very close to each other and can even form a single physical unit. They are oriented in a direction towards a scene which is distant from the distance L and in which there is an object OP or OR able to retroreflect the light.

On the other hand, the second laser emitter E2 is located, transversely to the direction d, of a distance x with respect to the detector D. In FIGS. 1 and 2, the angles of the emission cones of the laser emitters E1 and E2 have been designated by e1 and e2, respectively.

The retroreflective object OP, shown in FIG. 1, is a magnifying optical system, such as an eye, a telescope, etc. Consequently, its retroreflection cone is narrow, with an angle r, for example order of 0.1 mrad. As a result, as shown in FIG. 1, the light emitted by the emitter E1 adjacent to the detector D and retroreflected by the magnifying optical system OP into such a narrow retroreflection cone can be received by said detector D. However, the light emitted by the second emitter E2 spaced from the detector D and retroreflected by the magnifying optical system OP in a similar narrow retroreflection cone can not be received by said detector D.

Thus, when the retroreflective object is a magnifying optical system OP, the detector D can receive only the light emitted by the first emitter E1 adjacent and retroreflected by the magnifying optical system OP.

When, as shown in FIG. 2, the retroreflective object is a conventional retro-reflector OR, the retroreflective cone of the latter is wide, with an angle R, for example at least equal to 50 mrad. As a result, the light emitted by the first emitter E1 adjacent to the detector D, as well as that emitted by the second emitter E2 spaced apart from said detector D, are received by the latter.

The laser emission of the first emitter E1 may consist of a train of first pulses. Similarly, the laser emission of the second emitter E2 may be constituted by a train of second pulses. As for him, the detector D is able to form first and second images of the scene in which the retroreflective objects OP and OR are located in synchronism with said first and second pulses, respectively. From the above, we deduce that:

- in the case where the retroreflecting object is a standard reflector OR both said raw ^"images formed by said second image detector D comprises image Tobjet OR illuminated by said first and second laser pulses, respectively; and

in the case where the retroreflective object is a magnifying optical system OP, only said first images comprise the image of the object OP illuminated by said first laser pulses, said second images not being able to comprise the image of the object OP. illuminated by said second laser pulses.

Said first and second laser pulses may have the same emission wavelength. In this case, they are temporally offset and said first and second pulses can form a sequence in which they are entangled, a first laser pulse being interposed between two second pulses and vice versa.

On the contrary, said first and second laser pulses can be simultaneous, but they then have different emission wavelengths to which said detector D is also sensitive. Whatever the mode of emission of said first and second laser pulses, it follows from the foregoing that the comparison made by the detector D, a first and a second images respectively corresponding to a first and a second pulse laser, simultaneous or temporally close to each other, allows to consider that: - if the first image and the second image both include the image of the retroreflective object, it is a reflex reflector; and

- If only the first image has the image of the retroreflective object, it is a magnifying optical system. L-experiment has shown that the foregoing was verified when the transverse deviation x between the second emitter E2 and the detector D was at least 200 mm and, preferably, of the order of 400 mm.

Claims

1. Method for distinguishing at least one magnifying optical system (OP) from among other objects (OR), capable of retroreflecting light, being in a scene, according to which method: - illuminating said scene by at least a first laser pulse emitted by a first laser emitter (E1) and taking a first image of said scene illuminated by said first pulse by means of a detector (D) observing said scene, said detector (D) and said first laser emitter (E1) being at least approximately adjacent transverse to the direction (d) of said scene;

said scene is illuminated by at least a second laser pulse emitted by a second laser emitter (E2) spaced from said detector (D) transversely to the direction (d) of said scene, said detector (D) being responsive to said second pulse; and - by means of said detector (D), taking at least a second image of said scene illuminated by said second pulse, characterized in that, after comparison of said first and second images, we consider:

that said objects (OR), whose images are in said first and second images of said scene, are not magnifying optical systems (OP); and

- That said objects (OP), whose images are in the first image of said scene, but are absent from said second image of the latter, are magnifying optical systems (OP).

2. Method according to claim 1, characterized in that the transverse distance (x) between said second laser emitter (E2) and said detector (D) is at least 200 mm.

3. Method according to claim 2, characterized in that said cross ecrert (x) is of the order of 400 mm.

4. Method according to any one of claims 1 to 3, characterized in that said first and second laser pulses are simultaneous and have different emission wavelengths and in that said detector (D) is chosen to deliver two different images respectively corresponding to these two wavelengths.

5. Method according to claim 4, characterized in that said wavelengths are sufficiently close to each other so that the backscattering of sunlight by said scene is at least approximately similar in said first and second simultaneous images. .

6. Method according to one of claims 4 or 5, characterized in that illuminates said scene by means of a series of laser pulse pairs each having a first and a second laser pulse simultaneous, in that proceeds to take successive pairs of images corresponding to said pairs of laser pulses and in that successively comparing the first image and the second image of each pair of images.

7. Method according to any one of claims 1 to 3, characterized in that said first and second laser pulses have the same wavelength and are temporally offset from each other.

The method of claim 7, characterized in that the time offset between said first and second laser pulses is sufficiently small that the scene is at least approximately identical in said first and second images.

9. Method according to one of claims 7 or 8, characterized in that illuminates said scene by means of a sequence of first and second laser pulses entangled so that a first (or a second) pulse is found sandwiched between two elbows (or two first) pulses, in that takes the first and second successive images and entangled in correspondence with said first sequence and in that one compares each time a first and a second temporally close images one from the other.

10. A device for detecting a magnifying optical system (OP) in a scene with other objects (OR) capable of retroreflecting light, said device comprising:

a first laser transmitter (E1) for illuminating said scene and a detector (D) able to detect the light retroreflected by said objects illuminated by said first emitter (E1), said detector (D) and said first laser emitter (E1) being at least approximately adjacent transversely to the direction (d) of said scene; and

a second laser emitter (E2) spaced from said detector (D) transversely to the direction (d) of said scene, said detector (D) being sensitive to the emission wavelength of said second emitter, characterized in that that the transverse difference (x) between said second laser emitter and said detector is at least equal to 200 mm.

1 1. Device according to claim 10, characterized in that said transverse deviation (x) is of the order of 400 mm.