Method and device for rapid reconnaissance and early warning of low-slow small target in air based on correlated imaging

Abstract

The invention provides a method and a device for rapid reconnaissance and early warning of an air low-slow small target based on correlated imaging, and relates to the field of target reconnaissance, early warning and imaging. The method comprises the steps of selecting a light source and irradiating a target object with the light source; performing structured modulation on irradiation light emitted by the light source; aiming at each time of structured modulation, synchronously detecting the intensity of an optical signal returned by the target object; and performing image reconstruction according to the light intensity distribution of the modulated light signal and the intensity of the returned light signal. The method can solve the problems that a traditional aerial target reconnaissance means is low in imaging resolution, the imaging process is uncontrollable, and imaging is difficult in a complex environment.

Description

Technical Field

[0001] The present invention relates to the field of target reconnaissance, early warning and imaging technology, and in particular to a method and device for rapid reconnaissance and early warning of low, slow and small aerial targets based on correlation imaging. Background Art

[0002] Low-altitude safety is an important part of the national security system. Using aerial reconnaissance technology to accurately identify targets such as drones, bird flocks or UFOs is not only related to the daily operation safety of the civil aviation field, but also an effective guarantee for the national airspace security and the non-intrusion of confidential places. Currently, the common reconnaissance technologies are mainly the following:

[0003] (1) Sound wave detection. Sound sensors are used to obtain sound waves from motors, propellers and other devices, and then compared with the audio in the database to detect and classify targets. However, its resolution is low and it is easily affected by environmental noise and overlapping interference between targets. It is basically difficult to use in noisy environments such as airports and cities.

[0004] (2) Radar detection. By sensing the Doppler effect caused by the target's motion, the target information can be captured. However, in low-altitude / ultra-low-altitude conditions, it is seriously affected by low and slow clutter, and the resolution is not high, making it difficult to distinguish between drones and other small targets. In addition, this technical means also has great difficulty in detecting drones with small reflection areas or hovering drones.

[0005] (3) Radio detection. The receiver obtains the external communication signals of drones and other remote-controlled aircraft to achieve target detection and positioning. However, it is only applicable to known drones and cannot detect drones with unknown communication bands or hovering standby, flocks of birds, and other aircraft that do not emit radio signals.

[0006] (4) Visible light detection. This is the most commonly used detection method, which uses CCD, CMOS and other detectors to directly obtain the optical image information of the target. This technology is greatly affected by ambient light. It is difficult to achieve effective imaging in extreme weather conditions such as rain, snow, fog, or low-light environments such as night and cloudy days. At the same time, it is affected by the optical diffraction limit and has an upper limit on the resolution of imaging.

[0007] (5) Infrared detection. It uses the thermal radiation of objects to form images. Compared with visible light detection, this technology has a lower resolution and is also limited by weather factors. The most serious problem is that it is easily disturbed by changes in ambient temperature and has a high false alarm rate. Summary of the invention

[0008] Aiming at the problems of low imaging resolution, uncontrollable imaging process and difficult imaging in complex environments in traditional aerial target reconnaissance means, the present invention proposes a method and device for rapid reconnaissance and early warning of low, slow and small aerial targets based on correlation imaging.

[0009] In a first aspect, the present invention provides a method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging, comprising:

[0010] Step 1: Select a light source and use it to illuminate the target object;

[0011] Step 2: structurally modulating the illumination light emitted by the light source;

[0012] Step 3: For each structured modulation, synchronously detect the intensity of the optical signal returned by the target object;

[0013] Step 4: Reconstruct the image based on the intensity distribution of the modulated optical signal and the intensity of the returned optical signal.

[0014] Furthermore, it is characterized in that step 2 specifically comprises:

[0015] A mask pattern is generated, and the mask pattern is loaded in a preset modulation mode to modulate the irradiation light; the preset modulation mode is any one of an etching mask, a liquid crystal spatial light modulator and a digital micromirror device.

[0016] Furthermore, a Hadamard matrix is ​​used to generate a mask pattern.

[0017] Furthermore, the number of structured modulation times N≥M, wherein M represents the number of image pixels of the object to be imaged.

[0018] Furthermore, step 4 specifically includes:

[0019] The imaging process is expressed as:

[0020]

[0021] Among them, represents the intensity distribution of the modulated optical signal corresponding to the nth structured modulation, P n represents the intensity of the returned optical signal corresponding to the nth structured modulation, n = 1, 2, ..., N; An image matrix representing the object to be imaged;

[0022] The image reconstruction process is: Solve T = O -1 P.

[0023] Furthermore, the solution of T=O -1 P, specifically includes: using the total variation TV algorithm to solve and obtain an initial reconstructed image; selecting an image optimization algorithm to optimize the initial reconstructed image and obtain a final reconstructed image.

[0024] Furthermore, a bucket detector without spatial resolution capability is used to detect the intensity of the optical signal returned from the monitoring area.

[0025] The present invention utilizes a method for imaging a target based on high-order correlation of the light field, overcomes the dependence on external lighting conditions, lens imaging, and array detectors, and realizes wide-spectrum high-resolution imaging. At the same time, the imaging process has a strong resistance to the scattering and distortion of the light field, and can still achieve observation and imaging of the target in a complex environment and through strong scattering media such as smoke and fog. Moreover, in specific applications, computational imaging methods and compressed sensing algorithms can be introduced to optimize the optical path and imaging process, and ultimately achieve the purpose of rapid and accurate target recognition with a simple imaging optical path structure.

[0026] In a second aspect, the present invention provides a device for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging, comprising:

[0027] A light source, used to illuminate the target object;

[0028] A modulation module, used for performing structured modulation on the illumination light emitted by the light source;

[0029] A detection module, for synchronously detecting the intensity of the optical signal returned by the target object for each structured modulation;

[0030] The image reconstruction module is used to reconstruct the image according to the light intensity distribution of the modulated optical signal and the intensity of the returned optical signal.

[0031] In a third aspect, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method described in the first aspect when executing the program.

[0032] In a fourth aspect, the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the method described in the first aspect.

[0033] Beneficial effects of the present invention:

[0034] The present invention provides a new technical solution for aerial "low, slow and small" target reconnaissance, which has application and promotion value in different demand scenarios, mainly reflected in: (1) the correlation imaging method based on active light illumination does not rely on external lighting conditions and can be applied and promoted in low-light environments such as night and cloudy days; (2) signal capture only requires intensity information, which can avoid the influence of light field scattering and distortion on imaging quality, and can be applied and promoted in rain, snow, smoke and other environments. Compared with the array detector required for traditional optical imaging, the intensity detector has a lower manufacturing cost, is easy to operate and maintain, and has high practical value; (3) the light source band has a wide selectivity and can effectively realize the imaging of "stealth" targets; (4) the imaging process is controllable, and the imaging time and quality can be further optimized by introducing algorithms such as compressed sensing and local threshold processing, which can meet the needs of different scenarios; (5) the imaging resolution is high, and the correlation imaging is not limited by the diffraction limit of traditional imaging. Theoretically, there is no upper limit to the resolution, which can be used to achieve high-resolution imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flowchart of a method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging provided by an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of using a Hadamard matrix to generate a mask pattern provided by an embodiment of the present invention;

[0037] Figure 3 A schematic diagram of the structure of a device for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging provided by an embodiment of the present invention;

[0038] Figure 4 An image of a "cross" shaped hollow square plate provided by an embodiment of the present invention;

[0039] Figure 5 A structural block diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The invention belongs to the field of target reconnaissance, early warning and imaging, and is particularly directed to a fast imaging method for low-altitude, slow-moving and small targets in complex real-world environments with poor visibility such as fog, rain and snow, cloudy days and nights.

[0042] like Figure 1 As shown, the embodiment of the present invention aims to provide a reconnaissance method for "low, slow and small" targets in the air, and realizes rapid early warning imaging of the target by adjusting the optical path structure, controlling the imaging process and selecting the algorithm according to different application scenario requirements. Specifically, the following steps are included:

[0043] S101: Select a light source and illuminate the target object using the light source;

[0044] Specifically, this embodiment adopts the mode of active light illumination, and selects the illumination light source to actively illuminate or cover the target according to the actual scene requirements. Coherent / incoherent light source or visible light band / infrared ultraviolet band are all acceptable, but they must match the detector response band. At the same time, if imaging is performed for a long time, the light intensity must be stable.

[0045] For example, in foggy or rainy or snowy weather, microwave bands or laser light sources can be used, which have strong penetrating power and can effectively reduce the impact of bad weather factors on imaging. For "stealth" targets coated with absorbent materials, non-radar bands can be used to image them. Infrared bands can also be used at night, on cloudy days, etc. to further improve the sensitivity of measurement.

[0046] S102: performing structured modulation on the illumination light emitted by the light source;

[0047] Specifically, the idea of ​​computational imaging is introduced to perform structured modulation of the light source. The appropriate structured illumination pattern and number are selected in combination with the resolution requirements and imaging speed requirements.

[0048] S103: for each structured modulation, synchronously detecting the intensity of the optical signal returned by the target object;

[0049] Specifically, the collection optical path is designed to collect the light signals transmitted or reflected after the object and accurately measure their intensity. It is understandable that the photosensitive surface of the general intensity detector is not large. For large-scale illumination of real scenes, it is generally necessary to design a lens or lens group to collect the required light signals on the photosensitive surface of the detector. In addition, it should be noted that the synchronization of light modulation and light detection should be achieved between step S102 and step S103 to ensure that the structured illumination information corresponds to the collected light intensity signal one by one, thereby preparing for subsequent image reconstruction.

[0050] S104: Reconstruct an image according to the light intensity distribution of the modulated optical signal and the intensity of the returned optical signal.

[0051] Specifically, a suitable image reconstruction algorithm is selected to perform correlation operation on the light modulation information recorded in step S102 and the light intensity information detected in step S103 to demodulate the image information of the object. This step can also introduce image processing algorithms such as filtering, noise reduction, and image enhancement in combination with the characteristics of the imaging object and the requirements of the application scenario to further improve the efficiency and quality of image reconstruction.

[0052] The method for rapid reconnaissance and early warning of low, slow and small targets provided by the embodiment of the present invention has the following advantages: (1) The correlation imaging method based on active light illumination does not rely on external lighting conditions and can be applied and promoted in low-light environments such as night and cloudy days; (2) Signal capture only requires the intensity information of the light signal, which can avoid the influence of light field scattering and distortion on imaging quality, and can be applied and promoted in rain, snow, smoke and other environments. Compared with the array detector required for traditional optical imaging, the intensity detector has a lower manufacturing cost, is easy to operate and maintain, and has high practical value; (3) The light source band has a wide selectivity and can effectively realize the imaging of "stealth" targets; (4) The imaging process is controllable, and the imaging time and quality can be further optimized by introducing algorithms such as compressed sensing and local threshold processing, which can meet the needs of different scenarios; (5) The imaging resolution is high, and the correlation imaging is not limited by the diffraction limit of traditional imaging. Theoretically, there is no upper limit to the resolution, which can be used to achieve high-resolution imaging.

[0053] On the basis of the above embodiment, in this embodiment, vectors and matrices are used to describe the imaging process. The two-dimensional image information of the object is represented by a matrix. The number of matrix elements is M. For the convenience of calculation description, the matrix elements are arranged into a vector T. The purpose of the associated imaging is to solve each element T in the vector. i , where i = 1, 2, 3, ..., M. In order to successfully reconstruct the two-dimensional image of the object, it is necessary to use a series of mask patterns to spatially modulate the illumination light. Suppose the light intensity distribution of the nth illumination pattern is Where j = 1, 2, 3, ..., M; for each illumination pattern, the corresponding detection light intensity is recorded as P n , n=1,2,...,N; then the imaging process can be expressed as:

[0054]

[0055] make

[0056]

[0057] Correspondingly, image reconstruction is to solve T = O -1 P process. To make this equation have a solution, we need I j (n) They are mutually orthogonal, and N ≥ M. In the specific operation process, the appropriate number of mask patterns N can be selected according to the resolution requirements and imaging time requirements of the actual application scenario.

[0058] The mask pattern can be generated using a random matrix or a determined matrix. In order to better combine with the image reconstruction and optimization algorithm, this embodiment uses the Hadamard matrix as the mask pattern. The Hadamard matrix is ​​a square matrix composed of two elements of +1 and -1, and its order is equal to the sum of the squares of all elements in any row or column in the square matrix. The simplest Hadamard matrix is ​​the second-order Hadamard matrix:

[0059]

[0060] Higher-order Hadamard matrices can be further generated through second-order Hadamard matrices as follows:

[0061]

[0062] The Hadamard matrix satisfies orthogonality. In operation, the Hadamard matrix is ​​extracted row by row and reorganized into a square matrix to form a Hadamard derivative pattern that can be directly used for lighting. Figure 2 shown.

[0063] After the mask pattern is generated, the specific method of implementing structured modulation can be to load the above mask pattern by etching the mask, liquid crystal spatial light modulator (LC-SLM) and digital micromirror device (DMD). The above three modulation methods have their own advantages and disadvantages (as shown in Table 1), and can also be selected according to application requirements.

[0064] Table 1 Advantages and disadvantages of different structured modulation methods

[0065]

[0066] In one embodiment, when selecting a detector, it is also necessary to consider selecting a detector of appropriate accuracy. Structured lighting based on the Hadamard pattern may not cause a large change in signal light intensity in practice. Generally, if you want to obtain a higher imaging resolution, you need to select an intensity detector with higher accuracy. In addition, in some special scenarios, in order to avoid interference from stray light, you can also consider adding a filter in front of the detector to ensure that only light with the frequency of the associated imaging light source can be detected. In this embodiment, a bucket detector (i.e., an intensity detector without spatial resolution) is used to record the light intensity after reflection / transmission of the object.

[0067] In one embodiment, image reconstruction needs to ensure the light intensity distribution of the structured illumination pattern The same optical signal strength P i One-to-one correspondence, therefore, in practical applications, two detection devices are used to measure the light intensity distribution respectively. and the optical signal strength P i To perform detection, it is necessary to ensure that the two detection devices work synchronously. For example, the synchronization control code can be written in combination with the SDK of the hardware device.

[0068] There are many reconstruction algorithms available, but the ideal reconstruction needs to be based on enough sampling (that is, N is much larger than M). In real detection, it is generally necessary to achieve imaging in a short time. Therefore, in one embodiment, a compressed sensing algorithm is introduced as an image reconstruction algorithm. The compressed sensing algorithm can reconstruct the original image signal with high probability from a small number of observations when the sampling rate is much lower than the traditional Nyquist sampling theorem requirement. As long as it is ensured that the object to be imaged is sparse relative to the spatial environment, it can be mathematically represented sparsely by a certain sparse basis. The "low, slow and small" targets in the air meet this requirement. As an implementable method, the total variation TV (Total Variation) algorithm is one of the more commonly used and mature compressed sensing algorithms. It removes noise and restores image details by minimizing the total variation of the image (that is, the integral of the absolute value of the image gradient), while maintaining the edge and contour features of the image.

[0069] Furthermore, after the image is initially reconstructed with the help of the compressed sensing algorithm, the image depth can also be optimized in combination with the characteristics of the target to be measured and the scene requirements. For example, for black and white images, without considering the color distribution, algorithms such as contrast enhancement and noise removal can be used to improve the image quality; for scenes that do not pay attention to the resolution of the image but only pay attention to the contour information of the object, algorithms such as edge detection and contour extraction can be used to highlight the contour of the object in the image. All of these can meet the imaging warning needs of real-world applications while ensuring fast imaging sampling.

[0070] To verify the effectiveness of the above method, the present invention also built a device for rapid reconnaissance and early warning of low and slow small targets in the air based on correlation imaging to implement rapid imaging of static small targets. The basic structure of the device is as follows: Figure 3As shown. From left to right, they are light source, beam expander collimator, aperture, modulator, object to be imaged, lens and optical power meter. The light source is an ordinary semiconductor laser with a wavelength of 632nm. After the beam expander collimator, the light spot is magnified 20 times, and after the aperture, it is parallel to the modulator. The modulator is a TSLM07U-A liquid crystal spatial light modulator produced by Zhongke Microstar Company. The rise time and fall time are 7ms and 20ms respectively, and the maximum refresh frequency is 60Hz. The computer can be used to input a specific modulation pattern (the Hadamard pattern in the embodiment) into the liquid crystal spatial light modulator to achieve spatial structured modulation of the illumination. The modulated light is directed to the object to be imaged (the "cross" hollow square plate), and then is collected by the collection lens into the Thorlab S142C optical power meter to record the optical power. During the imaging process, C# programming is used to realize the synchronous control of spatial light modulation and light intensity detection, and then the TVAL algorithm is used to realize image reconstruction. Since the object to be imaged is a binary object with no obvious color distinction, a local adaptive threshold algorithm is finally written for further optimization.

[0071] In this embodiment, two imagings were performed, and the imaging results are shown in FIG. Figure 4 The sampling rates are 30% and 40% respectively, and the imaging sampling time is 3.2s and 4.0s respectively. Figure 4 (a) and Figure 4 (b) Figure 4 (c) is the reconstruction result after further introducing the binarization algorithm based on the sampling rate of 40%, and the reconstruction error is less than 1%.

[0072] Figure 5 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 5 As shown, the electronic device may include: a processor 501, a communication interface 502, a memory 503 and a communication bus 504, wherein the processor 501, the communication interface 502 and the memory 503 communicate with each other through the communication bus 504. The processor 501 may call the logic instructions in the memory 503 to execute a method for rapid reconnaissance and early warning of low, slow and small targets in the air based on associated imaging, the method comprising: performing structured modulation on the illumination light emitted by the light source; for each structured modulation, synchronously detecting the intensity of the light signal returned by the target object; and reconstructing the image according to the light intensity distribution of the modulated light signal and the intensity of the returned light signal.

[0073] In addition, when the logic instructions in the above-mentioned memory 503 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0074] An embodiment of the present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided by the above-mentioned method embodiments, for example, including: performing structured modulation on the illumination light emitted by the light source; for each structured modulation, synchronously detecting the intensity of the light signal returned by the target object; and reconstructing the image based on the light intensity distribution of the modulated light signal and the intensity of the returned light signal.

[0075] An embodiment of the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the methods provided by the above-mentioned method embodiments are implemented, for example, including: performing structured modulation on the illumination light emitted by the light source; for each structured modulation, synchronously detecting the intensity of the light signal returned by the target object; and reconstructing the image based on the light intensity distribution of the modulated light signal and the intensity of the returned light signal.

[0076] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging, characterized in that: include: Step 1: Select a light source and use it to illuminate the target object; Step 2: structurally modulating the illumination light emitted by the light source; Step 3: For each structured modulation, synchronously detect the intensity of the optical signal returned by the target object; Step 4: Reconstruct the image based on the intensity distribution of the modulated optical signal and the intensity of the returned optical signal.

2. According to claim 1, a method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging is characterized in that: Step 2 specifically includes: A mask pattern is generated, and the mask pattern is loaded in a preset modulation mode to modulate the irradiation light; the preset modulation mode is any one of an etching mask, a liquid crystal spatial light modulator and a digital micromirror device.

3. The method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging according to claim 2 is characterized in that: The Hadamard matrix is ​​used to generate the mask pattern.

4. The method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging according to claim 1 is characterized in that: The number of structured modulations N≥M, wherein M represents the number of image pixels of the object to be imaged.

5. The method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging according to claim 4 is characterized in that: Step 4 specifically includes: The imaging process is expressed as: Among them, represents the intensity distribution of the modulated optical signal corresponding to the nth structured modulation, P n represents the intensity of the returned optical signal corresponding to the nth structured modulation, n = 1, 2, ..., N; An image matrix representing the object to be imaged; The image reconstruction process is: Solve T = O -1 P.

6. The method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging according to claim 5 is characterized in that: The solution of T=O -1 P, specifically includes: using the total variation TV algorithm to solve and obtain an initial reconstructed image; selecting an image optimization algorithm to optimize the initial reconstructed image and obtain a final reconstructed image.

7. A method for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging according to any one of claims 1 to 6, characterized in that: A bucket detector without spatial resolution is used to detect the intensity of the optical signal returned from the monitoring area.

8. A device for rapid reconnaissance and early warning of low, slow and small targets in the air based on correlation imaging, characterized in that: include: A light source, used to illuminate the target object; A modulation module, used for performing structured modulation on the illumination light emitted by the light source; A detection module, for synchronously detecting the intensity of the optical signal returned by the target object for each structured modulation; The image reconstruction module is used to reconstruct the image according to the light intensity distribution of the modulated optical signal and the intensity of the returned optical signal.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the method according to any one of claims 1 to 7 is implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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