A laser reflection tomography three-dimensional imaging method and system

Abstract

This invention discloses a laser reflection tomography three-dimensional imaging method and system, relating to the field of three-dimensional imaging technology. The method is used to achieve high-resolution imaging and accurate identification and description of the three-dimensional contour structure of space targets; it includes: acquiring multi-angle echo information of the target, completing the reconstruction of a two-dimensional image of the orbital plane, and efficiently and accurately calculating the target's orbital axial reflectivity distribution based on multiple sets of orbital plane two-dimensional images, thereby completing the accurate reconstruction of the target's three-dimensional image and solving the problem of high-resolution three-dimensional reconstruction of the external structure of space targets. In this method, three-dimensional laser reflection tomography provides an additional dimension of information for reconstructing the three-dimensional image; thus more comprehensively reflecting the target's shape, size, and structural details, which is more conducive to further processing of the target image at the cognitive end.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional imaging technology, and in particular to a laser reflection tomography three-dimensional imaging method and system. Background Technology

[0002] Laser Reflective Tomography (LRT) is a novel laser imaging technology developed from Computed Tomography (CT) in the medical field. It accurately acquires modulated laser echo pulse signals from multiple angles when there is relative angular motion between the detection system and the target. After reconstruction processing using a dedicated algorithm, it can achieve target projection imaging along the laser's vertical axis. Essentially, it's a method of recovering image contours in scenarios where distance is distinguishable but angle is not. The imaging mechanism of RTL dictates that, under sufficient laser echo signal-to-noise ratio, its imaging resolution is independent of detection distance and system aperture, and mainly depends on the laser pulse width, detection circuit bandwidth, and acquisition system sampling rate. It holds great potential for long-distance space target laser detection and space-based laser imaging.

[0003] As early as 1988, Parker, Marino, and others at MIT Lincoln Laboratory began research on the combination of tomographic techniques and lidar, building incoherent / coherent lidar systems to verify the feasibility of range-resolved and Doppler-resolved RTL imaging (FK Knight, SR Kulkarni, RM Marino. Tomographic techniques applied to laserradar reflective measurements[J]. Lincoln Laboratory Journal, 1989(No.2):143-160.). From 1998 to 2001, Matson et al. at the U.S. Air Force Research Laboratory designed the HI-CLASS coherent lidar for long-range detection, tracking, and imaging for the MSSS space monitoring station. Subsequently, scholars both domestically and internationally, such as Henriksson (Henriksson Markus, Olofsson Tomas, ... Christina, et al. Optical reflectance tomography using TCSPC laser radar [C] / / Kamerman GW, Steinvall O, Bishop GJ, et al. SPIE Security+Defence. Edinburgh, United Kingdom, 2012:85420E. doi:10.1117 / 12.974493.), Hu Yihua's team (Hu Yihua, Zhang Xinyuan, Han Fei, et al. Super-resolution imaging of small distant targets using reflectance tomography lidar [J]. Chinese Journal of Lasers, 2023 (No. 3):214-215.), and others have all conducted research on RTL imaging. However, current research is limited to two-dimensional tomography of targets, only obtaining two-dimensional contour images of targets, and has not explored three-dimensional tomography of targets.

[0004] The closest prior art to this invention is the laser reflection tomography method and apparatus based on sparse regularized iteration proposed by Northwestern Polytechnical University (Guo Rui, Jiang Zheyi, Zhang Zhao, Zhang Shuangxi, Guo Liang. A laser reflection tomography method and apparatus for non-cooperative targets [P]. Chinese Patent: CN114820846A, 2022.07.29). This scheme provides a two-dimensional laser reflection tomography iterative algorithm that is superior to traditional filtered back projection (FBP) and algebra reconstruction techniques (ART), and can achieve better two-dimensional reconstruction results for incomplete projection data.

[0005] like Figure 1 As shown, this technology acquires the reflection projection data of non-cooperative targets through lidar, then transforms the reflection projection data into transmission data, obtains the first image through the ART algorithm, and obtains the second image, which is the final result, through sparse regularization iteration.

[0006] This method only provides two-dimensional cross-sectional imaging of an object's contour. Three-dimensional laser reflection tomography, by providing an additional dimension of information, reconstructs the image in three dimensions. It can more comprehensively reflect the target's shape, size, and structural details, making it more conducive to further processing of the target image at the cognitive end. Furthermore, existing technologies lack signal deconvolution and projection registration processes. When the laser pulse width is greater than the sampling period (after laser beam broadening) and the object undergoes random rigid motion, the projection angle deviates from the projection center, resulting in imaging distortion and a decrease in imaging resolution. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention proposes a laser reflection tomography three-dimensional imaging scheme (method and system).

[0008] The first aspect of this invention provides a laser reflection tomography three-dimensional imaging method, the method comprising:

[0009] Step S1: A narrow-pulse picosecond laser emits a laser to acquire a spatial distribution signal suitable for reflection tomography from an ultra-sensitive high-speed detection module;

[0010] Step S2: Perform axial-dimensional overlapping scanning of a distant spatial target using a high-precision scanning pointing system, and repeat step S1 to obtain the spatial distribution signal of the entire axis under the current orbital angle.

[0011] Step S3: Fly around the predetermined route and repeat step S2 within a certain angle range to obtain a spatial distribution signal suitable for reflection tomography at a certain axial angle.

[0012] Step S4: Reconstruct the spatial distribution signals of tomographic imaging at different axial scanning angles and various orbital angles into multiple sets of two-dimensional tomographic images;

[0013] Step S5: Combine multiple sets of two-dimensional tomographic images into a three-dimensional tomographic image according to the order of axial scanning.

[0014] In the method: after obtaining the laser echo information of the target at a fixed position along the flight axis, the two-dimensional image of the flight plane at the corresponding axial position is reconstructed according to a predetermined route; the laser echo information of the target at multiple positions along the flight axis is repeatedly processed to obtain the two-dimensional image of the target at the flight plane along the axial position.

[0015] In the method described above: based on the field of view and scanning range, the reflectivity distribution along the target's flight axis is calculated, thereby correcting the two-dimensional images of the flight plane at different axial positions, and completing the calculation of the reflectivity distribution along the flight axis and the reconstruction of the two-dimensional images of the flight plane.

[0016] In the method described above: the signal intensity in the laser echo signal is represented by the integral of the echo signal at each point along a specific path. The laser echo intensity signal at that moment is projected onto each point of the integration path through back projection transformation. Multiple sets of laser detection data are obtained from different observation angles. The echo signal intensity at each point inside the target is represented by the target grayscale. It is regarded as the superposition of the signal intensity on the integration path corresponding to each angle, thereby realizing the image reconstruction of each point inside the target and obtaining a high-resolution planar image of the target.

[0017] In the method: by spatial scanning and signal reconstruction in the axial dimension orthogonal to the flight trajectory, the target's layered signals in this direction are extracted, and by multi-layer signal image reconstruction, three-dimensional high-resolution imaging of the target is achieved.

[0018] A second aspect of this invention provides a laser reflection tomography three-dimensional imaging system, the system comprising: a narrow-pulse picosecond laser, an ultra-sensitive high-speed detection module, a high-precision scanning pointing system, and a processing unit; the system performs the following steps in operation:

[0019] Step S1: A narrow-pulse picosecond laser emits a laser to acquire a spatial distribution signal suitable for reflection tomography from an ultra-sensitive high-speed detection module;

[0020] Step S2: Perform axial-dimensional overlapping scanning of a distant spatial target using a high-precision scanning pointing system, and repeat step S1 to obtain the spatial distribution signal of the entire axis under the current orbital angle.

[0021] Step S3: Fly around the predetermined route and repeat step S2 within a certain angle range to obtain a spatial distribution signal suitable for reflection tomography at a certain axial angle.

[0022] Step S4: The processing unit reconstructs the spatial distribution signals of tomographic imaging at different axial scanning angles and various orbital angles into multiple sets of two-dimensional tomographic images;

[0023] Step S5: The processing unit combines multiple sets of two-dimensional tomographic images into a three-dimensional tomographic image according to the axial scanning order.

[0024] When the system is in operation, it is configured to perform the following: after acquiring the laser echo information of a fixed position along the target's flight axis, reconstruct the two-dimensional image of the flight plane at the corresponding axial position according to a predetermined route; and repeatedly process the laser echo information of the target's flight axis at multiple positions to obtain the two-dimensional image of the target's flight plane at the target's axial position.

[0025] When the system is in operation, it is configured to perform the following: based on the field of view and scanning range, calculate the target's axial reflectivity distribution around the flight path, thereby correcting the two-dimensional images of the flight path plane at different axial positions, and completing the calculation of the axial reflectivity distribution around the flight path and the reconstruction of the two-dimensional images of the flight path plane.

[0026] The system is configured to perform the following operations when in operation: the signal intensity in the laser echo signal is represented as the integral of the echo signal at each point along a specific path, and the laser echo intensity signal at that moment is projected onto each point of the integration path through back projection transformation; multiple sets of laser detection data are obtained from different observation angles, and the echo signal intensity at each point inside the target is represented as the target grayscale, which is regarded as the superposition of the signal intensity on the integration path corresponding to each angle, thereby realizing the image reconstruction of each point inside the target and obtaining a high-resolution planar image of the target.

[0027] Therefore, the system is configured to perform the following when in operation: extract the target's layered signals in the axial dimension orthogonal to the flight trajectory through spatial scanning and signal reconstruction, and achieve three-dimensional high-resolution imaging of the target through multi-layer signal image reconstruction.

[0028] A third aspect of this invention provides an electronic device. The electronic device includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements a laser reflection tomography three-dimensional imaging method according to the first aspect of this disclosure.

[0029] A fourth aspect of this invention provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, which, when executed by a processor, implements a laser reflection tomography three-dimensional imaging method according to the first aspect of this disclosure.

[0030] In summary, this invention achieves high-resolution imaging and accurate identification and description of the three-dimensional contour structure of space targets. The proposed solution involves: acquiring multi-angle echo information of the target, reconstructing a two-dimensional image of the orbital plane, and efficiently and accurately calculating the target's orbital axial reflectivity distribution based on multiple sets of two-dimensional orbital plane images, thereby achieving accurate reconstruction of the target's three-dimensional image and solving the problem of high-resolution three-dimensional reconstruction of the external structure of space targets. Three-dimensional laser reflection tomography provides an additional dimension of information, reconstructing the image in three dimensions. This allows for a more comprehensive reflection of the target's shape, size, and structural details, facilitating further processing of the target image at the cognitive end. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 Flowchart for implementing existing technologies.

[0033] Figure 2 This is a schematic diagram of a laser reflection tomography three-dimensional imaging scene according to an embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of the laser reflection tomography three-dimensional imaging process according to an embodiment of the present invention.

[0035] Figure 4 (Including (a)-(d)) are schematic diagrams of imaging results according to embodiments of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Definitions of abbreviations and key terms (the full English names and Chinese translations of the English abbreviations appearing below, or detailed explanations of the Chinese technical terms, are provided here):

[0038] LRT: Laser Reflective Tomography;

[0039] APD: Avalanche photodiode;

[0040] CT: Computer Tomography;

[0041] RTL: Reflective Tomography LiDAR.

[0042] This invention proposes a laser reflection tomography three-dimensional imaging method and system. For example... Figure 2 As shown, laser reflection tomography 3D imaging acquires multi-angle echo information of the target to reconstruct a 2D image of the flight plane, and then combines this with 1D scanning information along the flight axis to achieve 3D image reconstruction of the spatial target. The system acquires 1D laser echo information along the target's flight axis to reconstruct multiple sets of 2D images of the flight plane at different axial positions. Based on the field of view and scanning range, the system calculates the reflectivity distribution along the target's flight axis, thereby correcting the 2D images of the flight plane at different axial positions. Combining these corrected 2D images, a high-resolution 3D image reconstruction of the target is achieved using a spatial target 3D image reconstruction method. The system generates a probe laser signal using a high-repetition-rate picosecond laser, obtains a spatial distribution signal suitable for reflection tomography through beam spatial shaping and control, and then performs axial overlapping scanning of distant spatial targets using a high-precision scanning pointing system. The weak echo signal of the target is received by an ultra-sensitive high-speed detection module, and the target echo signal preprocessing module obtains the target echo waveform distribution information. This information is combined with the pointing information provided by the high-precision scanning pointing module, and then processed by the axial dimension echo signal calculation module to obtain super-resolution reconstructed data of the axial dimension target echo information. By observing the target from a certain angle, and processing the information from multiple angles, a three-dimensional super-resolution imaging result of the space target is finally obtained.

[0043] Laser reflection tomography (LCT) reconstructs a 3D image of a target by acquiring multi-angle echo information from the target, thus reconstructing a 2D image of the target around the flight plane. This image is then combined with 1D scanning information along the flight axis to achieve a 3D image reconstruction of the target in space. After reconstructing multiple sets of 2D images around the flight plane at different axial positions, the reflectivity distribution along the flight axis of the target needs to be calculated based on the field of view and scanning range. This allows for the correction of the 2D images around the flight plane at different axial positions. The effectiveness of the 2D image correction directly affects the quality of the 3D image reconstruction.

[0044] The process of running the system and obtaining 3D super-resolution imaging results can be summarized in 5 steps:

[0045] Step 1: A narrow-pulse picosecond laser emits a laser beam to acquire spatial distribution signals suitable for reflection tomography from an ultra-sensitive high-speed detection module.

[0046] Step 2: Using a high-precision scanning pointing system, perform axial overlapping scanning of the distant spatial target. Repeat Step 1 to obtain the spatial distribution signal of the entire axis under this orbital angle.

[0047] Step 3: Fly around the route and repeat Step 2 at a certain angle to finally obtain a spatial distribution signal suitable for reflection tomography at a certain axial angle.

[0048] Step 4: Reconstruct the spatial distribution signals of tomographic imaging at different scanning angles and various flight angles along the axis into multiple sets of two-dimensional tomographic images.

[0049] Step 5: Combine multiple sets of two-dimensional tomographic images into a three-dimensional tomographic image according to the axial scanning order.

[0050] In some embodiments, after acquiring the laser echo information of a fixed position along the target's flight axis, a two-dimensional image reconstruction of the flight plane at the corresponding axial position is completed according to the above-described route. The laser echo information along the target's flight axis at multiple positions is processed repeatedly to obtain two-dimensional images of the target's flight plane at the target's axial position. Then, based on the field of view and scanning range, the reflectivity distribution along the target's flight axis is calculated using the same method, thereby correcting the two-dimensional images of the flight plane at different axial positions, completing the calculation of the reflectivity distribution along the flight axis and the reconstruction of the two-dimensional images of the flight plane.

[0051] In some embodiments, the basic principle of achieving three-dimensional imaging of space targets using laser reflection tomography is as follows: Figure 2As shown, the signal intensity of a laser echo signal at a certain moment is represented by the integral of the echo signals at each point along a specific path. A back-projection transformation projects the laser echo intensity signal at that moment onto each point along this integration path. By obtaining multiple sets of laser detection data from different observation angles, the echo signal intensity at each point within the target (represented by the target's grayscale) can be considered as the superposition of signal intensities along the corresponding integration path at each angle. This allows for image reconstruction of each point within the target, resulting in a high-resolution planar image of the target. In the axial dimension orthogonal to the orbital trajectory, through spatial scanning and signal reconstruction, the layered signals of the target in this direction are extracted. Through multi-layer signal image reconstruction, a three-dimensional high-resolution image of the target is ultimately achieved.

[0052] The overall system implementation scheme is as follows: Figure 3 As shown, a high-repetition-rate picosecond laser generates a probe laser signal. Through beam spatial shaping and control, a spatial distribution signal suitable for reflection tomography is obtained. Then, a high-precision scanning and pointing system performs axial-dimensional overlapping scanning of a distant spatial target. The target's weak echo signal is received by an ultra-sensitive high-speed detection module. After passing through a target echo signal preprocessing module to obtain the target echo waveform distribution information, this is combined with the pointing information provided by the high-precision scanning and pointing module. The axial-dimensional echo signal calculation module then obtains super-resolution reconstructed data of the target echo information in the axial dimension. Through accompanying fly-around observations at a certain angle with the target, multi-angle information is processed to finally obtain the three-dimensional super-resolution imaging result of the spatial target.

[0053] In some embodiments:

[0054] (1) A narrow-pulse picosecond laser emits a laser and collects spatial distribution signals suitable for reflection tomography from an ultra-sensitive high-speed detection module.

[0055] (2) By using a high-precision scanning pointing system, perform axial overlapping scanning on distant spatial targets, repeat (1) to obtain the entire axial (2) under the flying angle, and finally obtain a spatial distribution signal of a certain axial angle that is suitable for reflection tomography.

[0056] (4) Combine the tomographic spatial distribution signals of different scanning angles and different flight angles along the axis into a tomographic spatial distribution signal of an axial angle.

[0057] (5) Perform deconvolution operation on the tomographic spatial distribution signal at a certain axial angle to recover the waveform of the tomographic spatial distribution signal, thereby recovering the true reflectivity distribution of the target.

[0058] (6) Based on (5), the spatial distribution signal is registered and corrected with the projection center by projection registration.

[0059] (7) Based on the registration in (6), the two-dimensional image of the axial angle is reconstructed using the filtered back projection method.

[0060] (8) Repeat steps (5)-(7) to obtain tomographic images of two-dimensional laser reflection distributions at different axial angles. Extract the two-dimensional image contours and convert them into two-dimensional scatter points based on the axial angles. See also Figure 4 (See details) Figure 4 The images (a)-(d) in the figure combine two-dimensional scattered points at different axial angles into a three-dimensional point cloud image (b), and can also be reconstructed into a continuous three-dimensional curved surface image (d) based on the three-dimensional point cloud image.

[0061] In summary, this invention achieves high-resolution imaging and accurate identification and description of the three-dimensional contour structure of space targets. The proposed solution involves: acquiring multi-angle echo information of the target, reconstructing a two-dimensional image of the orbital plane, and efficiently and accurately calculating the target's orbital axial reflectivity distribution based on multiple sets of two-dimensional orbital plane images, thereby achieving accurate reconstruction of the target's three-dimensional image and solving the problem of high-resolution three-dimensional reconstruction of the external structure of space targets. Three-dimensional laser reflection tomography provides an additional dimension of information, reconstructing the image in three dimensions. This allows for a more comprehensive reflection of the target's shape, size, and structural details, facilitating further processing of the target image at the cognitive end.

[0062] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of laser reflectance tomographic three-dimensional imaging, characterized by, The method includes: Step S1: A narrow-pulse picosecond laser emits a laser to acquire a spatial distribution signal suitable for reflection tomography from an ultra-sensitive high-speed detection module; Step S2: Perform axial-dimensional overlapping scanning of a distant spatial target using a high-precision scanning pointing system, and repeat step S1 to obtain the spatial distribution signal of the entire axis under the current orbital angle. Step S3: Fly around the predetermined route and repeat step S2 within a certain angle range to obtain a spatial distribution signal suitable for reflection tomography at a certain axial angle. Step S4: Reconstruct the spatial distribution signals of tomographic imaging at different axial scanning angles and various orbital angles into multiple sets of two-dimensional tomographic images; Step S5: Combine multiple sets of two-dimensional tomographic images into a three-dimensional tomographic image according to the order of axial scanning; In the method: after obtaining the laser echo information of the target at a fixed position along the flight axis, the two-dimensional image of the flight plane at the corresponding axial position is reconstructed according to a predetermined route; the laser echo information of the target at multiple positions along the flight axis is processed repeatedly to obtain the two-dimensional image of the target at the flight plane along the axial position. In the method: based on the field of view and scanning range, the target's axial reflectivity distribution around the flight path is calculated, thereby correcting the two-dimensional images of the flight path plane at different axial positions, and completing the calculation of the axial reflectivity distribution around the flight path and the reconstruction of the two-dimensional images of the flight path plane; In the method described above: the signal intensity in the laser echo signal is represented by the integral of the echo signal at each point along a specific path. The laser echo intensity signal at that moment is projected onto each point of the integration path through back projection transformation. Multiple sets of laser detection data are obtained from different observation angles. The echo signal intensity at each point inside the target is represented by the target grayscale. It is regarded as the superposition of the signal intensity on the integration path corresponding to each angle, thereby realizing the image reconstruction of each point inside the target and obtaining a high-resolution planar image of the target.

2. The laser reflection tomography three-dimensional imaging method according to claim 1, characterized in that, In the method: by spatial scanning and signal reconstruction in the axial dimension orthogonal to the flight trajectory, the target's layered signals in this direction are extracted, and by multi-layer signal image reconstruction, three-dimensional high-resolution imaging of the target is achieved.

3. A laser reflection tomography three-dimensional imaging system, characterized in that, The system includes: a narrow-pulse picosecond laser, an ultra-sensitive high-speed detection module, a high-precision scanning and pointing system, and a processing unit; the system performs the following steps in operation: Step S1: A narrow-pulse picosecond laser emits a laser to acquire a spatial distribution signal suitable for reflection tomography from an ultra-sensitive high-speed detection module; Step S2: Perform axial-dimensional overlapping scanning of a distant spatial target using a high-precision scanning pointing system, and repeat step S1 to obtain the spatial distribution signal of the entire axis under the current orbital angle. Step S3: Fly around the predetermined route and repeat step S2 within a certain angle range to obtain a spatial distribution signal suitable for reflection tomography at a certain axial angle. Step S4: The processing unit reconstructs the spatial distribution signals of tomographic imaging at different axial scanning angles and various orbital angles into multiple sets of two-dimensional tomographic images; Step S5: The processing unit combines multiple sets of two-dimensional tomographic images into a three-dimensional tomographic image according to the axial scanning order; When the system is in operation, it is configured to perform the following: after acquiring the laser echo information of a fixed position along the target's flight axis, reconstruct the two-dimensional image of the flight plane at the corresponding axial position according to a predetermined route; and repeatedly process the laser echo information of the target's flight axis at multiple positions to obtain the two-dimensional image of the target's axial position flight plane. When the system is in operation, it is configured to perform the following: based on the field of view and scanning range, calculate the target's axial reflectivity distribution around the flight path, thereby correcting the two-dimensional images of the flight path plane at different axial positions, and completing the calculation of the axial reflectivity distribution around the flight path and the reconstruction of the two-dimensional images of the flight path plane. The system is configured to perform the following operations when in operation: the signal intensity in the laser echo signal is represented as the integral of the echo signal at each point along a specific path, and the laser echo intensity signal at that moment is projected onto each point of the integration path through back projection transformation; multiple sets of laser detection data are obtained from different observation angles, and the echo signal intensity at each point inside the target is represented as the target grayscale, which is regarded as the superposition of the signal intensity on the integration path corresponding to each angle, thereby realizing the image reconstruction of each point inside the target and obtaining a high-resolution planar image of the target.

4. The laser reflection tomography three-dimensional imaging system according to claim 3, characterized in that, When in operation, the system is configured to perform the following: extract the target's layered signals in the axial dimension orthogonal to the orbital trajectory through spatial scanning and signal reconstruction, and achieve three-dimensional high-resolution imaging of the target through multi-layer signal image reconstruction.

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