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

Abstract

This method for detecting and characterizing laser radiation using a laser warning system comprising a laser warning device including at least one high-flux logarithmic response sensor includes: an image acquisition step with said sensor as a function of exposure; a spot detection step from the acquired image; a determination of the sensor's response to laser radiation by analyzing the detected spot; a calculation of the diameter of the detected spot; a comparison of the calculated spot diameter with a predetermined maximum theoretical value; and a characterization step of the laser radiation based on the sensor's response, the comparison result, and at least one map relating the sensor's response to characteristics of the laser radiation. Figure 9 (for the abstract)

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 high-power lasers and directed laser counter-countermeasures. Previous techniques

[0002] Classically, the detection of a laser attack is carried out using photosensitive detector systems that allow the detection of 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 matrix technology photodiode systems.

[0004] However, such systems do not allow for a fine characterization of the aggressor laser radiation and therefore do not allow for the effective adaptation of counter-countermeasures to the characteristics of the aggressor laser radiation. Description 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 enabling the implementation of counter-countermeasures adapted to the characteristics of an aggressive laser radiation.

[0007] The invention relates to a method for detecting and characterizing laser radiation using a laser warning system comprising a laser warning device including at least one sensor with a logarithmic response under high photon flux. The method comprises: - an image acquisition step 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 a laser attack; - a step of determining a sensor response to laser radiation by analyzing the detected spot; - a step to calculate the diameter of the detected spot; - a step of comparing the calculated value of the spot diameter detected and of a predetermined maximum theoretical value of the diameter of the detected spot; and - a step of characterizing the laser radiation based on the response of the laser radiation sensor, the result of the comparison and at least one map linking the sensor response to characteristics of the laser radiation.

[0008] Such a method makes it possible to determine the characteristics of the laser radiation in a rapid and efficient manner.

[0009] Preferably, the method further includes a step for implementing counter-countermeasures and / or an image correction step, depending on the laser radiation characteristics obtained in the characterization step. The method allows the counter-countermeasures to be adapted to the laser radiation characteristics. Moreover, it enables improved threat detection through image correction based on the laser radiation characteristics, aiming to significantly mitigate the effect of the laser countermeasure and allow the host system (e.g., seeker, sight, or camera) to continue performing its primary detection function.

[0010] For example, the step of setting up counter-countermeasures includes a step of adjusting a bias voltage of the sensor allowing to act on a depolarization of the sensor by laser radiation.

[0011] Advantageously, the method includes an image processing step performed after the acquisition step and before the spot detection step, said processing step comprising a step for detecting saturated non-atypical pixels of the sensor. Such an image processing step improves spot detection.

[0012] According to one feature, a new image is acquired with a lower exposure if saturated non-atypical pixels are detected and the current exposure is higher than a predetermined minimum exposure. Such a method improves the analysis of a spot.

[0013] According to another feature, 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 broadening 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 feature, the estimated parameters of the laser radiation include a peak power and / or a pulse width and / or a duty cycle emission. Such parameters allow for a complete characterization of pulsed laser radiation.

[0017] Advantageously, at least one map depends on the exposure to laser radiation and / or provides the sensor's response to the detected spot. Such a map makes it possible to increase the accuracy of the laser radiation characterization.

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

[0019] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

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

[0021] [Fig.2] schematically illustrates the architecture of a laser warning system comprising the laser warning device of [Fig.1];

[0022] [Fig.3] and [Fig.4] illustrate the response of a sensor of the laser warning device of [Fig.1] respectively at the center and edge of a laser spot formed by an incident laser beam;

[0023] [Fig.5] and [Fig.6] respectively illustrate an image acquired by the sensor of [Fig.1] of a continuous or pseudo-continuous type laser radiation 5 and a cross-sectional variation of the associated captured energy;

[0024] [Fig.7] and [Fig.8] respectively illustrate an image acquired by the sensor of [Fig.1] of a pulsed laser beam 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] Figure 1 shows a detection field 1 of a laser warning device 2 according to an embodiment of the invention.

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

[0028] The sensor 4 is adapted to capture an image of an incident laser beam 5 representative of a laser attack. Here, the sensor 4 is a focal plane array (FPA). The collimation optics 3 allow the image to be reflected. any laser radiation 5 which 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 an X axis of line of sight 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 configuration of the architecture shown. Depending on the required accuracy and sensitivity, the sensor 4 may comprise a photodiode array, a four-quadrant photosensitive structure, or an n-quadrant photosensitive structure. Alternatively, the collimation optics 3 may be replaced by a masking system to ensure encoding of the angle of arrival of the laser beam 5 relative to the X-axis line of sight of the warning device 2.

[0030] The collimation optics 3 are here separate 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 image monitoring system 7 and a low-level image processing module 8 ([Fig. 2]). Preferably, the sensor 4 is controlled by the image monitoring system 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 includes 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. Alternatively, 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 has 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 sensor 4 and / or provides the response of sensor 4 to a light spot formed on sensor 4 in response to laser radiation 5. It should be noted that the light spot can form at any location on sensor 4. For example, Figures 3 and 4 illustrate the response of a sensor 4 at the center and edge, respectively, of a laser spot formed by incident laser radiation 5 in the case of a pulsed laser. This response depends on the power of the laser radiation 5 as well as the exposure time of sensor 4.

[0035] For example, such maps are obtained by laboratory calibration and allow access to 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. In general, a laser radiation 5 can be of the continuous type or of the pulsed type.

[0037] Figures 5 and 6 respectively illustrate an image acquired by sensor 4 of a continuous or pseudo-continuous type laser radiation 5 and the spatial variation of the energy captured by sensor 4 according to a section oriented along the Y direction. Figures 5 and 6 highlight a large saturated area 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 flux. Pseudo-continuous laser radiation is a laser beam having pulses so close together in time that they practically constitute 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 includes a spot 10 having a barycenter 10a.

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

[0041] As will be described in more detail later, 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 beam 5 is determined from the position of the barycenter 10a of the spot 10 in a local YZ frame of the sensor 4 centered on the X axis of aiming.

[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 type laser radiation 5 and the energy variation according to a section oriented along the Y direction.

[0045] A pulsed laser beam 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 broadening of the sides of the spot extending between two adjacent ends 14 of the plateau 13. In other words, the broadening corresponds to the maximum spreading of the curve 15 outside the plateau 13.

[0047] It should be noted that when the peak power or 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, because of the logarithmic response under high photon 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 process begins with a preliminary initialization step 20, in which an image capture is performed in the dark and a background noise level is determined in the absence of any disturbance.

[0050] During the next acquisition step 21, the sensor 4 acquires a representative image of an optronic scene present in the detection field 1 of the laser warning device 2. The image acquisition is performed according to an exposure chosen before the actual acquisition takes place. For example, to avoid overexposure, the integration time can be reduced to decrease the risk of image saturation or the number of saturated pixels in the image.

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

[0052] When non-atypical saturated 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 lower exposure. In this case, step 21 is repeated, reducing the exposure.

[0053] After step 22, the process continues with step 23, which involves detecting a spot from the image acquired in step 21. The detected spot is representative of the presence of a laser injury. Step 23 is performed 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 process stops. Alternatively, instead of stopping after step 23, the process can resume at step 21 if the imager supervisor 7 requests a new image acquisition.

[0055] If a light spot is detected in step 23, the laser aggression is considered to be detected and the process 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 classical 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 saturated non-atypical pixel detection step performed in processing step 22, the analysis is completed by additional calculations. Alternatively, it remains possible to perform a new detection of saturated non-atypical pixels.

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

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

[0060] After step 24, the process continues with step 25, which calculates the diameter of the detected spot. Step 25 is performed by the image analysis module 9.

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

[0062] The process continues with a laser radiation characterization step 5 carried out by the image analysis module 9. The characterization is carried out based on the response of the sensor 4 to the laser radiation 5, the result of the comparison and 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 continuous or pseudo-continuous laser radiation is present. In this case, the fluence of the laser radiation 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 a pulsed laser 5 is present, and the width L of a broadening of the flanks of the detected spot is calculated. In this case, the parameters of the laser 5 are estimated from the maps specific to pulsed laser 5 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 broadening of the flanks of the detected spot. For example, the estimated parameters of the laser 5 include a peak power and / or a pulse width and / or emission duty cycle.

[0065] After step 27 of characterizing the laser radiation 5, the process continues with a step 28 of implementing counter-countermeasures and / or a step 29 of correcting the image acquired in step 21, based on the characteristics of the laser radiation 5 determined in the characterization step 27. This makes it possible to effectively adapt the counter-countermeasures to the characteristics of the intrusive laser radiation. For example, the detector exposure can be reduced if it is not already at its minimum. For example, if the sensor's bias voltage is used for detection, this voltage can be adjusted to control the sensor's depolarization by the laser radiation. For example, an offset and / or a low frequency in the acquired image can be removed through high-level image processing.

Claims

Demands

1. A method for detecting and characterizing laser radiation (5) by a laser warning system (6) comprising a laser warning device (2) including at least one sensor (4) with logarithmic response under high photon flux, said method being characterized in that it comprises: - a step of acquiring an image by said sensor (4) as a function of 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 mapping linking the response of the sensor (4) to characteristics of the laser radiation.;

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

3. A method according to claim 2, wherein the step of setting up counter-countermeasures includes a step of adjusting a bias voltage of the sensor (4) allowing to act on a depolarization of the sensor (4) by the laser radiation (5).

4. A 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 spot detection step, said processing step comprising a step for detecting saturated non-atypical pixels of the sensor (4).

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

6. A method according to any one of claims 1 to 5, wherein 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. A method according to any one of claims 1 to 6, wherein 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 an expansion 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) include a peak power and / or pulse width and / or emission duty cycle.

10. A method according to any one of claims 1 to 9, wherein at least one mapping depends on exposure to 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 high photon flux logarithmic response sensor (4), said system being adapted for implementation of a method according to any one of claims 1 to 10.

Images