Three-dimensional fast imaging method, device and equipment for space targets in terahertz band

Abstract

The present invention relates to a three-dimensional fast imaging method, device and equipment for space targets in the terahertz band. The method includes: obtaining a two-dimensional ISAR image sequence; constructing a projection relationship from a three-dimensional space to a two-dimensional imaging plane based on the two-dimensional ISAR image sequence; randomly selecting an initial candidate point of the space target, and starting from the initial candidate point, performing a first expansion in a divergent manner from the inside out to generate a number of first candidate points; calculating the projection energy of each first candidate point using the maximum energy projection criterion based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, screening out the second candidate point with the maximum projection energy, and retaining the second candidate point as the true three-dimensional point of the space target; starting from the second candidate point, performing a second expansion in a divergent manner from the inside out until a termination condition is reached to obtain the final three-dimensional imaging result of the space target. The present invention can quickly achieve three-dimensional imaging and better reflect the volume characteristics of the real target.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing, and in particular, to a three-dimensional fast imaging method, device and equipment for space targets in the terahertz band. Background Art

[0002] Currently, the algorithms for three-dimensional imaging based on two-dimensional ISAR image sequences can be mainly divided into two categories: three-dimensional imaging algorithms centered on factorization and its improved algorithms, and three-dimensional imaging algorithms centered on energy projection. Each of the two types of three-dimensional imaging algorithms has its own advantages and disadvantages. The former mainly constructs an observation matrix of the target through the coordinates of multiple feature points tracked and matched in the two-dimensional ISAR image sequence, and then uses the factorization method to calculate the three-dimensional motion matrix and three-dimensional point coordinate information of the target. The reconstructed three-dimensional point coordinates are the final three-dimensional imaging result. Its advantage is that it does not require the known relative line-of-sight angle information between the radar and the target. However, the difficulty of its algorithm lies in the accurate tracking and matching of feature points, and it is easy to have the problem of non-positive definite matrix in the factorization process; the latter is based on the premise of knowing the relative line-of-sight angle between the radar and the target. The imaging regions of each two-dimensional image sequence containing the target are regarded as the energy regions where several three-dimensional points are projected from three-dimensional space to a two-dimensional plane. The three-dimensional points with energy projection greater than the set threshold are considered as the positions where the target truly exists. These three-dimensional points constitute the three-dimensional imaging result of the target. Its advantage is that the imaging principle is relatively simple, but it requires the known relative line-of-sight angle between the radar and the target.

[0003] When the rotation angle between two-dimensional image sequences is large, the target attitude changes greatly, and there are occlusion problems, the three-dimensional imaging algorithm based on the factorization method will fail. Compared with the three-dimensional imaging based on the factorization method, the three-dimensional imaging algorithm based on energy projection has the advantages of better handling occlusion problems in images and obtaining finer three-dimensional imaging results. However, the existing three-dimensional imaging algorithms based on energy projection need to search for scatter points in three-dimensional space that meet the energy maximum criterion with the energy projection maximum function as the criterion, and basically all use PSO and its improved algorithms, etc. Optimizing the energy function usually involves a large number of iterative processes, resulting in a very high computational cost of the energy projection method, and the three-dimensional imaging results often show relatively sparse features. Summary of the Invention

[0004] Based on this, it is necessary to provide a three-dimensional fast imaging method, device and equipment for space targets in the terahertz band that can improve the search speed and the imaging result is more realistic for the above technical problems.

[0005] A three-dimensional fast imaging method for space targets in the terahertz band, the method includes:

[0006] Obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct a projection relationship from three-dimensional space to a two-dimensional imaging plane;

[0007] Randomly select the initial candidate points of the spatial target. Starting from the initial candidate points, perform the first expansion in a divergent manner from the inside out to generate a number of first candidate points;

[0008] Based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, calculate the projection energy of each first candidate point using the maximum energy projection criterion, screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the true three-dimensional point of the spatial target;

[0009] Starting from the second candidate point, perform the second expansion in a divergent manner from the inside out until the termination condition is reached to obtain the final three-dimensional imaging result of the spatial target.

[0010] A three-dimensional fast imaging device for spatial targets in the terahertz band, the device includes:

[0011] A projection relationship construction module, configured to obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct a projection relationship from the three-dimensional space to the two-dimensional imaging plane;

[0012] A first candidate point generation module, configured to randomly select the initial candidate points of the spatial target, and starting from the initial candidate points, perform the first expansion in a divergent manner from the inside out to generate a number of first candidate points;

[0013] A second candidate point screening module, configured to calculate the projection energy of each first candidate point using the maximum energy projection criterion based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the true three-dimensional point of the spatial target;

[0014] An iterative imaging module, configured to start from the second candidate point and perform the second expansion in a divergent manner from the inside out until the termination condition is reached to obtain the final three-dimensional imaging result of the spatial target.

[0015] A computer device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the steps of the three-dimensional fast imaging method for spatial targets in the terahertz band are implemented.

[0016] The above-mentioned three-dimensional fast imaging method, device and equipment for space targets in the terahertz band obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct the projection relationship from the three-dimensional space to the two-dimensional imaging plane; randomly select the initial candidate points of the space target, and starting from the initial candidate points, perform the first expansion in a divergent manner from the inside out to generate a number of first candidate points; based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, calculate the projection energy of each first candidate point using the maximum energy projection criterion, screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the real three-dimensional point of the space target; starting from the second candidate point, perform the second expansion in a divergent manner from the inside out until the termination condition is reached to obtain the final three-dimensional imaging result of the space target.

[0017] In the present invention, starting from each candidate point, expansion is performed in a divergent manner from the inside out, and the number of newly generated candidate points increases exponentially, which can accelerate the search for real scattering points and greatly improve the search speed. In addition, the expansion method from the inside out combines the maximum energy projection criterion to screen out the second candidate point with the maximum energy as the real three-dimensional point, and uses the second candidate point as the starting point for new expansion. While reducing the computational redundancy, the probability of obtaining the real target is greater, which can better reflect the volume characteristics of the real target, and the scattering points in the three-dimensional imaging result are denser, which can better reflect the structural characteristics of the real space target, and has the characteristics of simplicity and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0019] Figure 1 It is a schematic flowchart of the three-dimensional fast imaging method for space targets in the terahertz band provided in Embodiment 1;

[0020] Figure 2 It is a schematic structural diagram of the satellite three-dimensional point cloud model of the simulation experiment provided in Embodiment 1;

[0021] Figure 3 It is a schematic diagram of the two-dimensional image sequence obtained by using the high-resolution ISAR imaging algorithm provided in Embodiment 1, where Figure 3 (a) is a schematic diagram of the first frame of two-dimensional ISAR image, Figure 3 (b) is a schematic diagram of the second frame of two-dimensional ISAR image, Figure 3 (c) is a schematic diagram of the third frame of two-dimensional ISAR image;

[0022] Figure 4 Schematic diagrams of 3D imaging results using different algorithms provided in Embodiment 1. Among them, Figure 4 (a) is the schematic diagram of the 3D imaging result of the method proposed in the present invention; Figure 4 (b) is the schematic diagram of the 3D imaging result based on the PSO algorithm;

[0023] Figure 5 is the structural block diagram of the 3D fast imaging device for space targets in the terahertz band provided in Embodiment 2;

[0024] Figure 6 is the internal structure diagram of the computer device provided in Embodiment 3.

[0025] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific Embodiments

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0027] It can be understood that the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions conflicts with each other or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0028] Next, the embodiments of the present invention will be described in detail with reference to the accompanying drawings in the embodiments of the present invention.

[0029] Embodiment 1

[0030] This embodiment discloses a 3D fast imaging method for space targets in the terahertz band, and proposes a fast 3D imaging algorithm based on "seed growth" under the maximum energy projection criterion, that is, a search is carried out in a way of diverging from the inside outwards. The number of candidate points in the search process increases exponentially, greatly improving the search speed. During the iterative update process, the second candidate point with the maximum energy is used as the real 3D point, and the second candidate point is used as the starting point for new expansion. While reducing the amount of calculation redundancy, the probability of obtaining the real target is greater, and it can better reflect the volume characteristics of the real target; and the scattering points in the 3D imaging result are denser, and can better reflect the structural characteristics of the real space target, with the characteristics of simplicity and high efficiency.

[0031] Such as Figure 1As shown in the figure, the three-dimensional fast imaging method for space targets in the terahertz band provided by this embodiment includes the following steps:

[0032] Step 201, obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct a projection relationship from the three-dimensional space to the two-dimensional imaging plane.

[0033] Step 202, randomly select an initial candidate point of the space target, and starting from the initial candidate point, perform the first expansion in a divergent manner from the inside to the outside to generate a number of first candidate points.

[0034] Step 203, based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, calculate the projection energy of each first candidate point using the maximum energy projection criterion, screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the true three-dimensional point of the space target.

[0035] Step 204, starting from the second candidate point, perform the second expansion in a divergent manner from the inside to the outside until the termination condition is reached to obtain the final three-dimensional imaging result of the space target.

[0036] In the specific implementation process of step 201, obtain the echo signals of the space target under different radar perspectives, and use the high-resolution ISAR imaging algorithm in the terahertz band to obtain a two-dimensional ISAR image sequence.

[0037] For the terahertz broadband radar system, assuming that the relative rotation angle between the space target and the terahertz radar during the observation process is , it can be approximately regarded as uniform under a small rotation angle. Let the target rotation speed be , and the corresponding observation time be , then the relative rotation angle can be expressed as .

[0038] Then the expression of the linear frequency modulated (LFM) signal emitted by the terahertz radar is:

[0039] (1)

[0040] In the formula, represents the fast time; represents the slow time; represents the radar carrier frequency; represents the frequency modulation rate; represents the pulse repetition period; represents the imaginary unit.

[0041] Let the coordinates of a certain scattering point on the space target in the Cartesian coordinate system be , and its scattering intensity is represented by It is shown that the expression of the echo signal is:

[0042] (2)

[0043] In the formula, is the speed of light.

[0044] ISAR imaging can be simplified to turntable imaging under far-field conditions. By solving the linear frequency modulation and compensating the Residual Video Phase (RVP), the expression of the baseband target echo signal received is:

[0045] (3)

[0046] In the formula, represents the fast time; represents the slow time; represents the radar carrier frequency; represents the chirp rate; represents the distance between the radar and the target; represents the initial distance between the radar and the center of rotation of the target; represents the relative rotation angle between the space target and the terahertz radar; represents the coordinates of a scattering point on the space target. The total observation time The relationship with the fast time and the slow time can be expressed as . is the rectangular window expression.

[0047] Using the high-resolution ISAR imaging algorithm in the terahertz band, a two-dimensional ISAR image sequence is obtained from the original echo signal of the radar. The process expression is:

[0048] (4)

[0049] In the formula, represents the high-resolution two-dimensional ISAR image; represents performing a fast Fourier transform in the azimuth direction; represents performing a non-uniform fast Fourier transform in the range direction with as the resampling factor; represents the Keystone transform; represents the compensated spatially variant phase error.

[0050] In the specific implementation process of step 202, taking the centroid of the space target as the origin of the three-dimensional coordinate system, assuming the three-dimensional coordinates of a scattering point on the space target are , where , a total of three-dimensional scattering points, is the index of the extracted feature point number. If the total imaging the frame two-dimensional ISAR image, then the scattering point in the frame two-dimensional ISAR image, the horizontal and vertical coordinates are respectively:

[0051] (5)

[0052] Then, when constructing the projection relationship from the three-dimensional space to the two-dimensional imaging plane based on the two-dimensional ISAR image sequence, for a certain scattering point of the space target the range projection vector and the azimuth projection vector the expressions are:

[0053] (6)

[0054] In the formula, represents the range projection; represents the azimuth projection; represents the pitch angle corresponding to the frame two-dimensional ISAR image; represents the azimuth angle corresponding to the frame two-dimensional ISAR image; represents matrix transpose, where is a replaceable variable.

[0055] In the specific implementation process of step 203, based on the preset extended direction pitch angle and extended direction azimuth angle, starting from the initial candidate point, the first expansion is carried out in a spherical outward divergence manner from the starting point to generate a number of first candidate points.

[0056] It can be understood that different from the traditional group optimization and other random search candidate points, the in - out search process proposed by the present invention draws on the law of "seed growth" in nature. Plants grow from seeds into mature vegetation through continuous cell division. If the candidate points are regarded as cells that can divide continuously, then the final three - dimensional image of the space target can be regarded as mature vegetation. During the three - dimensional imaging process of the space target, the number of its scattering points will increase exponentially, greatly accelerating the generation speed of candidate points. In addition, the ISAR image of the space target generally has the characteristic of regional connectivity, which also provides a growth area for the generation of candidate points. Even if there are individual non - connected areas in the image, it can be overcome by adjusting the step size of the candidate points.

[0057] Assume the initial candidate point is and the coordinates of the first candidate points obtained by its first expansion are expressed as:

[0058] (7)

[0059] In the formula, represents the initial candidate point coordinates; represents the first candidate point coordinates; represents a random number between 0 and 1; represents the expansion step size of the candidate point, generally a multiple of the ISAR image resolution; represents the elevation angle of the expansion direction, and the expansion method is , where represents the number of the first candidate points in the elevation angle direction; represents the azimuth angle of the expansion direction, and the expansion method is , where represents the number of the first candidate points in the azimuth angle direction.

[0060] Expand in a spherical outward divergence manner. During each expansion process, each candidate point can generate new candidate points.

[0061] When expanding, adjust the compensation of each expansion through the step factor. The step factor is the product of the random number and the expansion step size of the candidate point.

[0062] After obtaining the new first candidate points, calculate the projection energy of each first candidate point using the maximum energy projection criterion. The expression is:

[0063] (8)

[0064] In the formula, represents the set of the first candidate points calculated using the maximum energy projection criterion; represents the total number of frames of the two-dimensional ISAR image; represents the th frame of the two-dimensional ISAR image, represents the cost function; represents the three-dimensional scatter points of the space target; represents the th characteristic point index of the three-dimensional scatter point; represents the range-direction projection vector; represents the range-direction resolution; represents the number of range-direction points of the ISAR image; represents the azimuth-direction projection vector; represents the azimuth-direction resolution; represents the number of azimuth-direction points of the ISAR image.

[0065] Then screen out the second candidate points with the maximum energy accumulation. The second candidate points can be considered as the real scatter points on the space target. Based on this, A second candidate point is used as the "seed point" for the next expansion. When there is no true scattering point that can achieve the maximum energy projection among the newly obtained candidate points in a certain expansion, the "seed point" selected for the next expansion remains unchanged. Taking each candidate point as the origin, new candidate points are expanded in a spherical shape, and so on, continuously iterating and updating until the termination condition is reached. The termination conditions include: the ratio of the remaining energy value of the two-dimensional ISAR image to the total energy is less than a pre-set threshold; and / or the maximum number of iterations is reached.

[0066] In addition, to prevent getting stuck in local search when expanding candidate points, during the second expansion and subsequent expansion processes, some of the already solved true three-dimensional points are randomly added as candidate points to participate in the calculation, so as to enhance the globality and robustness of the search for effective candidate points.

[0067] The three-dimensional fast imaging method for space targets in the terahertz band proposed by the present invention has the following detailed three-dimensional imaging process:

[0068] Preparation: Initialize candidate points. Since the target is processed to be at the center position of the ISAR image, generally the origin of the three-dimensional coordinate system is used as the initial candidate point coordinates. According to the established projection relationship from the three-dimensional space to the two-dimensional imaging plane, the frame of two-dimensional ISAR images processed by the high-resolution imaging algorithm is obtained, and the total energy of all ISAR image sequences is calculated . At the same time, the initial value of the remaining energy of the two-dimensional ISAR image is , the initial three-dimensional imaging point set is set as , the ratio of the remaining energy value of the two-dimensional ISAR image to the total energy is , and the ratio of the remaining energy value of the two-dimensional ISAR image to the total energy is 1 during initialization; in addition, the threshold for terminating iteration is set as , and the total number of iterations is set as .

[0069] Start the first iteration: According to formula (7), the first expansion is performed to obtain new candidate points. The new candidate points are projected onto the two-dimensional ISAR image, and the accumulated energy after projection of each candidate point is calculated. Then, based on formula (8), the second candidate points are screened out and retained as the true three-dimensional points of the space target, denoted as the first point set , and the initial three-dimensional imaging point set is updated to the first three-dimensional imaging point set .

[0070] Based on the CLEAN algorithm idea, the energy projected by the first point set onto the two-dimensional ISAR image is gradually removed, and the remaining energy value of the two-dimensional ISAR image is updated to , and updating the ratio of the remaining energy value to the total energy of the two-dimensional ISAR image to .

[0071] Randomly extract from the initial three-dimensional imaging point set scattering points, and merge them into the first point set as the second candidate point to participate in the calculation. It can be understood that by extracting some scattering points from the initial three-dimensional imaging point set to participate in the calculation, on the one hand, because the growth mode of candidate points in the method of the present invention is exponential growth. If all the points in the initial three-dimensional imaging point set obtained in the previous iteration are used as candidate points for the next iteration, it will increase a very large amount of calculation. On the other hand, the initial three-dimensional imaging point set obtained in the previous iteration has already participated in the search for candidate points. Searching all of them again will cause computational redundancy. Randomly selecting a small number of three-dimensional points among them can ensure a certain global search ability.

[0072] Repeat the above steps, and continuously update the point set and the three-dimensional imaging point set during the iteration process. When the ratio of the image remaining energy value to the image total energy calculated in the th iteration and / or , the iteration terminates, and the final three-dimensional imaging result is obtained. Among them, the point set and the three-dimensional imaging point set respectively contain the new target true scattering point set and the total true scattering point set obtained in the th iteration.

[0073] In one embodiment, based on the terahertz-band space target three-dimensional fast imaging method proposed by the present invention, a simulation experiment is carried out to verify the effectiveness of its three-dimensional imaging. In the simulation, the radar carrier frequency is set to 220 GHz, the bandwidth is 20 GHz, the sampling rate is 5.12 MHz, the pulse repetition time is 800 us, the pulse width is 200 us, and the observed target is the three-dimensional point cloud model of a satellite. The three-dimensional size of the satellite model is, as Figure 2 shown.

[0074] Set multiple groups of radar line-of-sight angles to observe the target model, and use the terahertz-band high-resolution ISAR imaging algorithm to obtain a two-dimensional ISAR image sequence. The two-dimensional ISAR image sequence includes several two-dimensional ISAR images arranged in chronological order. Three of the two-dimensional ISAR images are as Figure 3 shown.

[0075] After obtaining the two-dimensional ISAR image sequence, it is expanded in a manner that diverges from the inside outwards, and the projection energy of candidate points is calculated based on the maximum energy projection criterion. Through iterative update, the final three-dimensional imaging result of the spatial target as shown in Figure 4 Figure (a) is obtained. Comparing with Figure 4 the three-dimensional imaging result obtained by using the common PSO algorithm in Figure (b), the scatter points in the three-dimensional imaging result of the method proposed by the present invention are denser and can better reflect the structural characteristics of the real spatial target.

[0076] For the method proposed by the present invention, by fully considering the three-dimensional volume characteristics of the target and adopting the expansion method from the inside to the outside, several candidate points can be expanded from each real three-dimensional point. It can not only achieve exponential growth, but also the probability that the candidate points are real target points is greater. Compared with the traditional inefficient random search based on the PSO algorithm, the present invention starts searching near the real target points, so the probability of obtaining real target points is greater, the search efficiency is higher, and since there are more scatter points searched, the points of the three-dimensional image of the spatial target obtained are denser and the structural characteristics are more obvious.

[0077] Although the steps in this embodiment Figure 1 are sequentially shown according to the indication of the arrows, these steps do not necessarily need to be executed sequentially according to the order indicated by the arrows. Unless there is a clear description in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, Figure 1 at least a part of the steps in it may include multiple sub-steps or multiple stages. These sub-steps or stages do not necessarily need to be executed at the same moment, but can be executed at different moments. The execution order of these sub-steps or stages does not necessarily need to be sequential, but can be executed alternately or in turn with at least a part of other steps or sub-steps or stages of other steps.

[0078] Embodiment 2

[0079] Based on the three-dimensional fast imaging method for spatial targets in the terahertz band in Embodiment 1, this embodiment discloses a three-dimensional fast imaging device for spatial targets in the terahertz band. As shown in Figure 5 Figure, the three-dimensional fast imaging device for spatial targets in the terahertz band includes: a projection relationship construction module 401, a first candidate point generation module 402, a second candidate point screening module 403, and an iterative imaging module 404, where:

[0080] The projection relationship construction module 401 is used to obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct the projection relationship from the three-dimensional space to the two-dimensional imaging plane.

[0081] The first candidate point generation module 402 is used to randomly select an initial candidate point of the spatial target, and starting from the initial candidate point, perform the first expansion in a divergent manner from the inside outwards to generate a number of first candidate points.

[0082] The second candidate point screening module 403 is used to calculate the projection energy of each first candidate point based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, and adopt the maximum energy projection criterion to screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the true three-dimensional point of the spatial target.

[0083] The iterative imaging module 404 is used to perform the second expansion in a divergent manner from the inside outwards starting from the second candidate point until the termination condition is reached, to obtain the final three-dimensional imaging result of the spatial target.

[0084] In this embodiment, the specific working processes and working principles of the projection relationship construction module 401, the first candidate point generation module 402, the second candidate point screening module 403, and the iterative imaging module 404 are the same as those of the method in Embodiment 1, so they will not be elaborated herein. Each of these unit modules can be implemented in whole or in part by software, hardware, and their combination. Each unit module can be embedded in the processor in the computer device in hardware form or be independent of it, or can be stored in the memory in the computer device in software form, so that the processor can call and execute the operations corresponding to each of these unit modules.

[0085] Embodiment 3

[0086] As Figure 6 shown, a terminal device disclosed in this embodiment includes a transmitter, a receiver, a memory, and a processor. Among them, the transmitter is used to send instructions and data, the receiver is used to receive instructions and data, the memory is used to store computer execution instructions, and the processor is used to execute the computer execution instructions stored in the memory to implement the method in Embodiment 1 above.

[0087] It should be noted that the above-mentioned memory can be either independent or integrated with the processor. When the memory is independently set, the terminal device further includes a bus for connecting the memory and the processor.

[0088] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memories. Non-volatile memories can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memories can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0089] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0090] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it cannot be construed as a limitation on the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A method for rapid three-dimensional imaging of space targets in the terahertz frequency band, characterized in that: The method comprises: Acquire a two-dimensional ISAR image sequence; and construct a projection relationship from a three-dimensional space to a two-dimensional imaging plane based on the two-dimensional ISAR image sequence; Randomly select an initial candidate point of the space target, take the initial candidate point as the starting point, perform a first expansion in a manner of diverging from the inside to the outside, and generate a number of first candidate points; Based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane, the projection energy of each first candidate point is calculated by using the maximum energy projection criterion, the second candidate point with the maximum projection energy is screened out, and the second candidate point is retained as the real three-dimensional point of the space target; Taking the second candidate point as the starting point, a second expansion is performed in a manner of diverging from the inside to the outside until the termination condition is reached, thereby obtaining the final three-dimensional imaging result of the space target.

2. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 1, characterized in that: Acquire 2D ISAR image sequences, including: The echo signals of space targets under different radar viewing angles are acquired, and a two-dimensional ISAR image sequence is obtained using a high-resolution ISAR imaging algorithm in the terahertz frequency band.

3. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 2, characterized in that: The expression of the echo signal is: ； In the formula, Indicates fast time; Indicates slow time; Indicates radar carrier frequency; Indicates the frequency modulation; Indicates the distance between the radar and the target; Indicates the initial distance between the radar and the target's rotation center; Indicates the relative rotation angle between the space target and the terahertz radar; Indicates the coordinates of a scattering point on the space target; The speed of light.

4. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 3, characterized in that: The terahertz band high-resolution ISAR imaging algorithm is used to obtain a two-dimensional ISAR image sequence. The process expression is: ； In the formula, Represents a high-resolution two-dimensional ISAR image; Indicates the direction of the fast Fourier transform; Indicates the distance to Do non-uniform fast Fourier transform for the resampling factor; Represents Keystone transformation; Represents the compensated space-variant phase error.

5. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to any one of claims 1 to 4, characterized in that: Based on the two-dimensional ISAR image sequence, a projection relationship from three-dimensional space to two-dimensional imaging plane is constructed, and a scattering point of a space target The distance to the projection vector and the azimuth projection vector The expression is: ； In the formula, Represents the distance projection; Indicates azimuthal projection; Indicates The pitch angle corresponding to the frame 2D ISAR image; Indicates The azimuth angle corresponding to the frame 2D ISAR image; represents the matrix transpose, where A replaceable variable.

6. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 5, characterized in that: After constructing the projection relationship from the three-dimensional space to the two-dimensional imaging plane based on the two-dimensional ISAR image sequence, the method further includes: According to the projection relationship from the constructed three-dimensional space to the two-dimensional imaging plane, we can get Frame 2D ISAR image, calculation Total energy of a two-dimensional ISAR image frame ; Let the initial residual energy of the two-dimensional ISAR image be , set the initial 3D imaging point set to The ratio of the residual energy value to the total energy of the two-dimensional ISAR image is .

7. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 6, characterized in that: Taking the initial candidate point as the starting point, the first expansion is performed in a manner of diverging from the inside to the outside to generate several first candidate points, including: Based on the preset pitch angle and azimuth angle of the expansion direction, the initial candidate point is taken as the starting point, and the first expansion is performed in a spherical outward divergent manner from the starting point to generate a plurality of first candidate points.

8. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 7, characterized in that: The coordinate expression of the first candidate point is: ； In the formula, Represents the coordinates of the initial candidate points; Represents the coordinates of the first candidate point; Represents a random number between 0 and 1; Indicates the expansion step length of the candidate point; Indicates the pitch angle in the expansion direction; Indicates the azimuth of the expansion direction.

9. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 8, characterized in that: When expanding, the compensation for each expansion is adjusted by the step factor.

10. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 9, characterized in that: The step factor is a random number The expansion step length of the candidate points The product of .

11. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 7, characterized in that: The origin of the three-dimensional coordinate system As the initial candidate point coordinates.

12. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to any one of claims 7 to 11, characterized in that: The maximum energy projection criterion is used to calculate the projection energy of each first candidate point, and the expression is: ； In the formula, represents the first candidate point set calculated using the maximum energy projection criterion; Indicates the total number of frames of the 2D ISAR image; Indicates Frame 2D ISAR image, represents the cost function; Represents three-dimensional scattering points of space targets; Indicates The feature point index of three-dimensional scattering points; represents the distance projection vector; Indicates the range resolution; Indicates the number of range points of ISAR image; represents the azimuth projection vector; Indicates the azimuth resolution; Indicates the number of azimuth points of the ISAR image.

13. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 12, characterized in that: After retaining the second candidate point as the real three-dimensional point of the space target, the method further includes: Record all second candidate points as the first point set , and the initial three-dimensional imaging point set Update to the first 3D imaging point set ; Remove the first point set The energy projected onto the two-dimensional ISAR image, and the residual energy value of the two-dimensional ISAR image is updated as , and updating the ratio of the residual energy value to the total energy of the two-dimensional ISAR image to .

14. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 13, characterized in that: During the second and subsequent expansion processes, some real 3D points are randomly added as candidate points to participate in the calculation.

15. The method for rapid three-dimensional imaging of space targets in the terahertz frequency band according to claim 14, characterized in that: Termination conditions include: The ratio of the residual energy value to the total energy of the two-dimensional ISAR image is less than a preset threshold; and / or a maximum number of iterations is reached.

16. A terahertz frequency band space target three-dimensional rapid imaging device, characterized in that: The device comprises: A projection relationship building module is used to acquire a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, a projection relationship from a three-dimensional space to a two-dimensional imaging plane is built; A first candidate point generation module is used to randomly select an initial candidate point of the space target, and take the initial candidate point as the starting point, perform a first expansion in a manner of diverging from the inside to the outside, and generate a number of first candidate points; A second candidate point screening module is used to calculate the projection energy of each first candidate point based on the projection relationship from the three-dimensional space to the two-dimensional imaging plane by using the maximum energy projection criterion, screen out the second candidate point with the maximum projection energy, and retain the second candidate point as the real three-dimensional point of the space target; The iterative imaging module is used to take the second candidate point as the starting point and perform a second expansion in a manner of diverging from the inside to the outside until the termination condition is reached to obtain the final three-dimensional imaging result of the space target.

17. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for three-dimensional rapid imaging of space targets in the terahertz frequency band described in any one of claims 1 to 15 are implemented.

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