Laser warning system and associated method for detecting and characterizing laser radiation

Abstract

This method for detecting and characterizing laser radiation by a laser warning system comprising a laser warning device comprising at least one sensor with logarithmic response under high photonic flux comprises: a step of acquiring an image by said sensor as a function of an exposure; a step of detecting a spot from the acquired image; a step of determining a response of the sensor to the laser radiation by analyzing the detected spot; a step of calculating a diameter of the detected spot; a step of comparing the calculated value of the diameter of the spot and a predetermined maximum theoretical value; and a step of characterizing the laser radiation as a function of the response of the sensor, the result of the comparison and at least one map linking the response of the sensor to characteristics of the laser radiation. Figure for the abstract: Figure 9

Description

Title of the invention: Laser warning system and associated method for detecting and characterizing laser radiation Technical field

[0001] The invention relates to the field of power lasers and directed laser counter-countermeasures. Previous techniques

[0002] Conventionally, the detection of a laser attack is carried out using photosensitive detector systems capable of detecting a laser spot.

[0003] In addition to detecting laser aggression, such systems make it possible to estimate the direction of the incident laser radiation, in particular photodiode systems with matrix technology.

[0004] However, such systems do not allow for fine characterization of the aggressor laser radiation and therefore do not allow for effective adaptation of counter-countermeasures to the characteristics of the aggressor laser radiation. Statement of the invention

[0005] The present invention aims to remedy the aforementioned drawbacks.

[0006] The invention proposes a laser warning system and an associated method allowing the implementation of counter-countermeasures adapted to the characteristics of an aggressor laser radiation.

[0007] The subject of the invention is a method for detecting and characterizing laser radiation by a laser warning system comprising a laser warning device comprising at least one sensor with logarithmic response under high photonic flux. The method comprises: - a step of acquiring an image by the sensor as a function of exposure to laser radiation; - a step of detecting a spot from the image obtained in the acquisition step, the detected spot being representative of the presence of laser aggression; - a step of determining a response of the sensor to the laser radiation by an analysis of the detected spot; - a step of calculating a diameter of the detected spot; - a step of comparing the calculated value of the spot diameter detected and a predetermined maximum theoretical value of the diameter of the detected spot; and - a step of characterization of the laser radiation from the response of the sensor to laser radiation, the result of the comparison and at least one map linking the response of the sensor to characteristics of the laser radiation.

[0008] Such a method makes it possible to determine the characteristics of the laser radiation quickly and efficiently.

[0009] Preferably, the method further comprises a step of implementing counter-countermeasures and / or a step of correcting the image, depending on the characteristics of the laser radiation obtained in the characterization step. The method makes it possible to adapt the counter-countermeasures to the characteristics of the laser radiation. In addition, it allows better detection of the threat by correcting the image depending on the characteristics of the laser radiation, aiming to significantly attenuate the effect of the laser countermeasure and to allow the host system (for example, homing device, sight or camera) to continue to maintain its main detection function.

[0010] For example, the step of implementing counter-countermeasures comprises a step of adjusting a polarization voltage of the sensor making it possible to act on a depolarization of the sensor by the laser radiation.

[0011] Advantageously, the method comprises an image processing step carried out after the acquisition step and before the step of detecting a spot, said processing step comprising a step of detecting the saturated non-atypical pixels of the sensor. Such an image processing step makes it possible to improve the detection of a spot.

[0012] According to one feature, the acquisition of a new image with a reduced exposure is requested if saturated non-atypical pixels are detected and the current exposure is greater than a predetermined minimum exposure. Such a method makes it possible to improve the analysis of a spot.

[0013] According to another characteristic, the position of a barycenter of the detected spot is determined. Such a method makes it possible to determine the angular position of the laser radiation.

[0014] For example, the fluence of the laser radiation is estimated from the area of ​​the detected spot if the calculated value of the diameter of the detected spot is greater than the predetermined maximum theoretical value.

[0015] For example, parameters of the laser radiation are estimated from the maximum energy level of a peak, the average energy level of a plateau and the width of a widening of the flanks of the detected spot if the calculated value of the diameter of the detected spot is greater than the predetermined maximum theoretical value.

[0016] According to another characteristic, the estimated parameters of the laser radiation comprise a peak power and / or a pulse width and / or a duty cycle. emission. Such parameters make it possible to fully characterize pulsed laser radiation.

[0017] Advantageously, at least one mapping depends on the exposure to the laser radiation and / or provides the response of the sensor with respect to the detected spot. Such mapping makes it possible to increase the precision of the characterization of the laser radiation.

[0018] According to another aspect, the invention relates to a laser warning system comprising a laser warning device comprising at least one sensor with logarithmic response under high photonic flux. The laser warning system is suitable for implementing a method as described above. Brief description of the drawings

[0019] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0020] [Fig-1] illustrates a detection field of a laser warning device according to an example of carrying out the invention;

[0021] [Fig.2] schematically illustrates the architecture of a laser warning system comprising the laser warning device of [Fig.l];

[0022] [Fig.3] and [Fig.4] illustrate the response of a sensor of the laser warning device of [Fig.l] respectively at the center and at the edge of a laser spot formed by incident laser radiation;

[0023] [Fig.5] and [Fig.6] respectively illustrate an image acquired by the sensor of [Fig.l] of a continuous or pseudo-continuous type laser radiation 5 and a variation in section of the associated captured energy;

[0024] [Fig.7] and [Fig.8] respectively illustrate an image acquired by the sensor of [Fig.l] of a pulsed laser radiation and a cross-sectional variation of the associated captured energy; and

[0025] [Fig.9] is a flowchart of a method for detecting and characterizing laser radiation according to an embodiment of the invention. Detailed description of at least one embodiment

[0026] In [Fig.l] a detection field 1 of a laser warning device 2 according to an embodiment of the invention is shown.

[0027] The laser warning device 2 comprises a collimation optic 3 and at least one sensor 4 with logarithmic response under strong photonic flux. A strong photonic flux is for example a flux which is capable of depolarizing the sensor 4.

[0028] The sensor 4 is adapted to capture an image of incident laser radiation 5 representative of a laser attack. Here, the sensor 4 is a focal plane array called FPA or “Focal Plane Array” in English. The collimation optics 3 makes it possible to return any laser radiation 5 that enters the detection field 1 towards the sensor 4 and concentrates the laser radiation at a point on the sensor 4. The detection field 1 is centered around a line-of-sight axis X of the warning device 2.

[0029] The architecture of the laser warning device 2 is given by way of example and does not limit the invention to the sole configuration of the architecture presented. Depending on the desired precision and sensitivity, the sensor 4 may comprise a matrix of photodiodes, a four-quadrant photosensitive structure or an n-quadrant photosensitive structure. Alternatively, the collimation optics 3 may be replaced by a mask system so as to ensure coding of the angle of arrival of the laser radiation 5 relative to the X axis of the line of sight of the warning device 2.

[0030] The collimation optics 3 are here distinct from the sensor 4. Alternatively, the collimation optics 3 and the sensor 4 could form a single detection module.

[0031] Preferably, the laser warning device 2 is associated within a laser warning system 6 with an imager supervision 7 and a low-level image processing module 8 ([Fig.2]). Preferably, the sensor 4 is controlled by the imager supervision 7. Preferably, the sensor 4 is adapted to transmit the captured images to the low-level processing module 8 which is adapted to analyze the response of the sensor 4.

[0032] In the example illustrated in [Fig.2], the laser warning system 6 further comprises a high-level image analysis module 9 adapted to analyze the images captured by the sensor 4 according to information from the low-level processing module 8. As a variant, it remains possible to integrate the high-level image analysis module 9 and the low-level processing module 8 within a general image processing module.

[0033] The high-level image analysis module 9 is provided with a memory comprising at least one predetermined map linking the response of the sensor 4 to the characteristics of the laser radiation 5.

[0034] Preferably, such mapping depends on the exposure of the sensor 4 and / or provides the response of the sensor 4 with respect to a light spot formed on the sensor 4 in response to laser radiation 5. It should be noted that the light spot can be formed at any location on the sensor 4. For example, FIGS. 3 and 4 illustrate the response of a sensor 4 respectively at the center and at the edge of a laser spot formed by incident laser radiation 5 in the case of a pulsed type laser. This response depends on the power of the laser radiation 5 as well as the exposure time of the sensor 4.

[0035] For example, such maps are obtained by laboratory calibration and make it possible to access the morphological characteristics of the light spot formed on the sensor 4 according to the characteristics or parameters of the laser radiation 5.

[0036] Indeed, the response of the sensor 4 depends on the characteristics of the laser radiation 5. Generally speaking, laser radiation 5 can be of the continuous type or of the pulsed type.

[0037] [Fig. 5] and 6 respectively illustrate an image acquired by the sensor 4 of a continuous or pseudo-continuous type laser radiation 5 and the spatial variation of the energy captured by the sensor 4 according to a section oriented in the Y direction. Figures 5 and 6 highlight a large saturated surface which is typical of a continuous or pseudo-continuous type laser radiation 5.

[0038] Continuous laser radiation is a laser beam having a constant and uninterrupted energy flow. Pseudo-continuous laser radiation is a laser beam having pulses so close together in time that they constitute practically a continuous laser beam. In other words, continuous or pseudo-continuous laser radiation is characterized by a very high emission duty cycle.

[0039] The image acquired by the sensor 4 is representative of the response of the sensor 4 to the laser radiation 5 and generally comprises a spot 10 having a barycenter 10a.

[0040] It is noted that the central part of the spot is saturated, which corresponds to the reaching of a predetermined saturation threshold 11.

[0041] As will be described in more detail below, an analysis of the response of the sensor 4 to the laser radiation 5 makes it possible to determine the direction of the radiation 5 and its characteristics.

[0042] For example, the angular position of the laser radiation 5 is determined from the position of the barycenter 10a of the spot 10 in a local reference frame YZ of the sensor 4 centered on the aiming axis X.

[0043] For example, the fluence of the laser radiation 5 is estimated from the area of ​​the spot 10.

[0044] Figures 7 and 8 respectively illustrate an image acquired by the sensor 4 of a pulsed laser radiation 5 and the energy variation according to a section oriented in the Y direction.

[0045] Pulsed laser radiation is a laser beam whose power varies cyclically over time.

[0046] The response of the sensor 4 to a pulsed type radiation 5 is characterized by energy values ​​corresponding to a maximum energy level of a peak 12 and to an average energy level of a substantially horizontal plateau 13, as well as by the width L of a widening of the sides of the spot extending between two adjacent ends 14 of the plateau 13. In other words, the widening corresponds to the maximum spread of the curve 15 outside the plateau 13.

[0047] It should be noted that when the peak power or the maximum power over time of the laser radiation 5 becomes significant, the energy value of the peak 12 is no longer proportional to the fluence of the laser radiation 5, due to the logarithmic response under high photonic flux of the sensor 4.

[0048] We will now describe with reference to [Fig.9] a method for detecting and characterizing laser radiation 5 by a laser warning system 6 according to the invention.

[0049] The method begins with a preliminary initialization step 20, in which an image capture is carried out in the dark and a background noise level is determined in the absence of any disturbance.

[0050] During the following acquisition step 21, the sensor 4 acquires an image representative of an optronic scene present in the detection field 1 of the laser warning device 2. The acquisition of the image is carried out according to an exposure chosen before carrying out the actual acquisition. For example, to avoid excessive exposure, the integration time can be reduced in order to reduce the risk of saturation of the image or the number of saturated pixels in the image.

[0051] The method continues with a step 22 of processing the image acquired in step 21. Step 22 is carried out by the image processing module 8 and conventionally comprises a step of detecting contrasting points, a step of detecting saturated non-atypical pixels and a step of calculating the minimum and maximum levels of a histogram of the image. It should be noted that the step of detecting saturated non-atypical pixels only concerns the detection of pixels whose saturation is due to an external photonic flux, i.e. a flux coming from the imaged scene, and not the detection of intrinsically saturated pixels.

[0052] When saturated non-atypical pixels are detected and the current exposure is greater than a predetermined minimum exposure, it is possible to request the acquisition of a new image with a reduced exposure. In this case, step 21 is re-executed while reducing the exposure.

[0053] After step 22, the method continues with a step 23 of detecting a spot from the image acquired in step 21, the detected spot being representative of the presence of laser aggression. Step 23 is carried out by the image analysis module 9.

[0054] If no spot is detected in step 23, the laser threat is determined to be low to zero and the method stops. Alternatively, instead of stopping after step 23, the method can resume at step 21 if the imager supervision 7 requests a new image acquisition.

[0055] If a light spot is detected in step 23, it is considered that the laser attack is detected and the method continues with a step 24 of determining the response of the sensor 4 to the laser radiation 5 by an analysis of the detected spot carried out by the image analysis module 9.

[0056] The analysis includes a conventional estimation of the position of the barycenter of the detected spot, representative of an angular position of the laser radiation 5.

[0057] Depending on the results of the step of detecting saturated non-atypical pixels carried out in the processing step 22, the analysis is completed by additional calculations. Alternatively, it remains possible to carry out a new detection of saturated non-atypical pixels.

[0058] For example, if non-atypical saturated pixels are detected, the analysis is completed by a calculation of the area of ​​the spot.

[0059] For example, if no non-atypical saturated pixels are detected, the analysis is completed by a calculation of the energy level of peak 12 and a calculation of the average energy level corresponding to plateau 13.

[0060] After step 24, the method continues with a step 25 of calculating a diameter of the detected spot. Step 25 is carried out by the image analysis module 9.

[0061] In the following comparison step 26, the image analysis module 9 compares the calculated value of the diameter of the detected spot and a maximum theoretical value of the diameter of the detected spot, predetermined and contained in its memory. For example, the maximum theoretical value of the diameter of the detected spot (known calculation of the diameter of the Airy spot) is determined as a function of the characteristics of the collimation optics 3, the sensor 4 and the laser radiation 5.

[0062] The method continues with a step of characterizing the laser radiation 5 carried out by the image analysis module 9. The characterization is carried out as a function of the response of the sensor 4 to the laser radiation 5, of the result of the comparison and of at least one map available in a memory of the module 9.

[0063] For example, if the calculated value of the diameter of the detected spot is greater than the predetermined maximum theoretical value available in a memory of the analysis module, it is considered that there is continuous or pseudo-continuous laser radiation 5. In this case, the fluence of the laser radiation 5 is estimated from maps specific to continuous or pseudo-continuous laser radiation as a function of the area of ​​the detected spot.

[0064] For example, if the calculated value of the diameter of the detected spot is less than or equal to the predetermined maximum theoretical value available in a memory of the analysis module, it is considered that there is pulsed laser radiation 5 and the width L of a widening of the flanks of the detected spot is calculated. In this case, the parameters of the laser radiation 5 are estimated from the maps specific to pulsed laser radiation as a function of the maximum energy level of the peak 12, the average energy level of the plateau 13 and the width L of the widening of the flanks of the detected spot. For example, the estimated parameters of the laser radiation 5 include a peak power and / or a pulse width and / or a transmission duty cycle.

[0065] After step 27 of characterizing the laser radiation 5, the method continues with a step 28 of setting up counter-countermeasures and / or a step 29 of correcting the image acquired in step 21, as a function of the characteristics of the laser radiation 5 determined in the characterization step 27. Thus, it becomes possible to effectively adapt the counter-countermeasures to the characteristics of the aggressor laser radiation. For example, it is possible to reduce the exposure of the detector if it is not already at its minimum. For example, if the polarization voltage of the sensor is used for detection, it is possible to adjust this voltage to act on the depolarization of the sensor by the laser radiation. For example, it is possible to remove an offset and / or a low frequency from the image acquired by high-level image processing.

Claims

Claims

1. Method for detecting and characterizing laser radiation (5) by a laser warning system (6) comprising a laser warning device (2) comprising at least one sensor (4) with logarithmic response under high photonic flux, said method being characterized in that it comprises: - a step of acquiring an image by said sensor (4) as a function of an exposure to said laser radiation (5); - a step of detecting a spot from the image obtained in the acquisition step, the detected spot being representative of the presence of a laser attack; - a step of determining a response of the sensor (4) to the laser radiation by an analysis of the detected spot; - a step of calculating a diameter of the detected spot; - a step of comparing the calculated value of the diameter of the detected spot and a predetermined maximum theoretical value of the diameter of the detected spot;and - a step of characterizing the laser radiation from the response of the sensor (4) to the laser radiation, the result of the comparison and at least one map linking the response of the sensor (4) to characteristics of the laser radiation.;

2. Method according to claim 1 further comprising a step of implementing counter-countermeasures and / or a step of correcting the image, depending on the characteristics of the laser radiation obtained in the characterization step.

3. Method according to claim 2, in which the step of implementing counter-countermeasures comprises a step of adjusting a bias voltage of the sensor (4) making it possible to act on a depolarization of the sensor (4) by the laser radiation (5).

4. Method according to any one of claims 1 to 3 further comprising an image processing step carried out after the acquisition step and before the step of detecting a spot, said processing step comprising a step of detecting the saturated non-atypical pixels of the sensor (4).

5. A method according to claim 4, wherein the acquisition is requested of a new image with a reduced exposure if saturated non-atypical pixels are detected and the current exposure is higher than a predetermined minimum exposure.

6. Method according to any one of claims 1 to 5, in which the position of a barycenter of the detected spot is determined.

7. A method according to any one of claims 1 to 6, wherein the fluence of the laser radiation is estimated from the area of ​​the detected spot if the calculated value of the diameter of the detected spot is greater than the predetermined maximum theoretical value.

8. Method according to any one of claims 1 to 6, in which parameters of the laser radiation are estimated, from the maximum energy level of a peak (12), the average energy level of a plateau (13) and the width (L) of a widening of the flanks of the detected spot if the calculated value of the diameter of the detected spot is greater than the predetermined maximum theoretical value.

9. A method according to claim 8, wherein the estimated parameters of the laser radiation (5) comprise a peak power and / or a pulse width and / or an emission duty cycle.

10. A method according to any one of claims 1 to 9, wherein at least one mapping depends on the exposure to the laser radiation (5) and / or provides the response of the sensor (4) with respect to the detected spot.

11. Laser warning system (6) comprising a laser warning device (2) comprising at least one sensor (4) with logarithmic response under high photonic flux, said system being suitable for implementing a method according to any one of claims 1 to 10.

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