Three-dimensional rapid imaging method, device and equipment for terahertz-band space target

Abstract

The invention relates to a terahertz frequency band space target three-dimensional rapid imaging method, device and equipment. The method comprises the following steps: acquiring a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, constructing a projection relation from a three-dimensional space to a two-dimensional imaging plane; randomly selecting an initial candidate point of the space target, taking the initial candidate point as a starting point, performing first expansion according to a mode of diverging from inside to outside, and generating a plurality of first candidate points; based on the projection relation from the three-dimensional space to the two-dimensional imaging plane, the maximum energy projection criterion is adopted to calculate the projection energy of each first candidate point, a second candidate point with the maximum projection energy is screened out, and the second candidate point is reserved as a real three-dimensional point of the space target; and taking the second candidate point as a starting point, carrying out second expansion according to a mode of diverging from inside to outside until a termination condition is reached, and obtaining a final space target three-dimensional imaging result. According to the invention, three-dimensional imaging can be realized quickly, and the body characteristics of a real target can be reflected better.

Description

Technical Field

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

[0002] At present, the algorithms for 3D imaging based on 2D ISAR image sequences can be mainly divided into two categories, namely, the 3D imaging algorithms with factorization and its improved algorithms as the core, and the 3D imaging algorithms with energy projection as the core idea. Both types of 3D imaging algorithms have their own advantages and disadvantages. The former mainly forms the observation matrix of the target through the coordinates of multiple feature points tracked and matched in the 2D ISAR image sequence, and then uses the factorization method to solve the 3D motion matrix and 3D point coordinate information of the target. The reconstructed 3D point coordinates are the final 3D imaging results. Its advantage is that it does not require the known relative line of sight angle information between the radar and the target, but the difficulty of its algorithm lies in the accurate tracking and matching of feature points, and it is easy to produce the problem of matrix non-positive definiteness in the process of factorization; the latter is based on the premise of the known relative line of sight angle between the radar and the target, and the imaging area of ​​each 2D image sequence containing the target is projected from the 3D space to the energy area of ​​the 2D plane as several 3D points. The 3D points with energy projection greater than the set threshold are considered to be the real location of the target. These 3D points constitute the 3D imaging results of the target. Its advantage is that the imaging principle is relatively simple, but the relative line of sight angle between the radar and the target needs to be known.

[0003] When the rotation angle between the two-dimensional image sequences is large, the target posture 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 the occlusion problem in the image and obtaining more precise three-dimensional imaging results. However, the existing three-dimensional imaging algorithms based on energy projection need to use the maximum energy projection function as a criterion to search for scattering points in the three-dimensional space that meet the maximum energy criterion. Basically, PSO and its improved algorithms are used. 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 present sparse features. Summary of the invention

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

[0005] A method for rapid three-dimensional imaging of space targets in the terahertz frequency band, the method comprising: 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.

[0006] A terahertz frequency band space target three-dimensional rapid imaging device, the device comprising: 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 to perform a first expansion from the initial candidate point as a starting point in a manner of diverging from the inside to the outside to 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.

[0007] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the method for three-dimensional rapid imaging of space targets in the terahertz frequency band when executing the computer program.

[0008] The above-mentioned terahertz frequency band space target three-dimensional rapid imaging method, device and equipment obtain a two-dimensional ISAR image sequence; based on the two-dimensional ISAR image sequence, construct a projection relationship from three-dimensional space to two-dimensional imaging plane; randomly select the initial candidate point of the space target, take the initial candidate point as the starting point, perform the 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, use the maximum energy projection criterion to calculate the projection energy of each first candidate point, screen out the second candidate point with the largest projection energy, and retain the second candidate point as the real three-dimensional point of the space target; take the second candidate point as the starting point, perform the second expansion in a manner of diverging from the inside to the outside, until the termination condition is reached, and obtain the final three-dimensional imaging result of the space target.

[0009] The present invention uses each candidate point as a starting point and expands in a divergent manner from the inside out. The number of generated new candidate points increases exponentially, which can speed up 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 select the second candidate point with the largest 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, and the body characteristics of the real target can be better reflected. The scattering points in the three-dimensional imaging result are denser, which can better reflect the structural body characteristics of the real space target, and it has the characteristics of simplicity and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0011] Figure 1 A schematic diagram of the process of the method for three-dimensional rapid imaging of space targets in the terahertz frequency band provided in Example 1; Figure 2 A schematic diagram of the structure of a satellite three-dimensional point cloud model for the simulation experiment provided in Example 1; Figure 3 This is a schematic diagram of a two-dimensional image sequence obtained by using a high-resolution ISAR imaging algorithm provided in Example 1, wherein: 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 2D ISAR image. Figure 3 (c) is a schematic diagram of the third frame of 2D ISAR image; Figure 4 This is a schematic diagram of the three-dimensional imaging results using different algorithms provided in Example 1, wherein: Figure 4 (a) is a schematic diagram of the three-dimensional imaging result of the method proposed in the present invention, Figure 4 (b) is a schematic diagram of the three-dimensional imaging results based on the PSO algorithm; Figure 5 This is a structural block diagram of the terahertz frequency band space target three-dimensional rapid imaging device provided in Example 2; Figure 6 This is a diagram of the internal structure of the computer device provided in Example 3.

[0012] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0013] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of 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.

[0014] 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 ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0015] The implementation modes of the present invention will be described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0016] Example 1 This embodiment discloses a method for fast three-dimensional imaging of space targets in the terahertz frequency band, and proposes a fast three-dimensional imaging algorithm based on "seed growth" under the maximum energy projection criterion, that is, a search is performed in a divergent manner from the inside to the outside, and the number of candidate points in the search process increases exponentially, which greatly improves the search speed. In the iterative update process, the second candidate point with the largest energy is used as the real three-dimensional point, and the second candidate point is used as the starting point for new expansion. While reducing the computational redundancy, the probability of obtaining the real target is greater, and the body characteristics of the real target can be better reflected; and the scattering points in the three-dimensional imaging result are denser, which can better reflect the structural body characteristics of the real space target, and it has the characteristics of simplicity and high efficiency.

[0017] like Figure 1 As shown, the terahertz frequency band space target three-dimensional rapid imaging method provided in this embodiment includes the following steps: Step 201, acquiring a two-dimensional ISAR image sequence; and constructing a projection relationship from a three-dimensional space to a two-dimensional imaging plane based on the two-dimensional ISAR image sequence.

[0018] Step 202, randomly select an initial candidate point of the space target, take the initial candidate point as the starting point, perform the first expansion in a manner of diverging from the inside to the outside, and generate a number of first candidate points.

[0019] Step 203, 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 using the maximum energy projection criterion, the second candidate point with the largest projection energy is screened out, and the second candidate point is retained as the real three-dimensional point of the space target.

[0020] Step 204, starting from the second candidate 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.

[0021] In the specific implementation process of step 201, the space target echo signals under different radar viewing angles are obtained, and a two-dimensional ISAR image sequence is obtained by using a terahertz frequency band high-resolution ISAR imaging algorithm.

[0022] For the terahertz broadband radar system, it is assumed that the relative rotation angle between the space target and the terahertz radar during the observation process is , it can be approximated as a uniform speed at a small turning angle, and the target speed is , corresponding to the observation time , then the relative rotation angle can be expressed as .

[0023] Then the linear frequency modulated (LFM) signal expression emitted by the terahertz radar is: (1) In the formula, Indicates fast time; Indicates slow time; Indicates radar carrier frequency; Indicates the frequency modulation; represents the pulse repetition period; Represents an imaginary unit.

[0024] Let a scattering point on the space target be in the Cartesian coordinate system The coordinates below are , and its scattering intensity is expressed as Indicates that the echo signal expression is: (2) In the formula, The speed of light.

[0025] ISAR imaging can be simplified to turntable imaging under far-field conditions. By demodulating the line frequency and compensating the residual video phase (RVP), the received baseband target echo signal expression is: (3) 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 a space target. Total observation time The relationship between fast time and slow time can be expressed as . is the rectangular window expression.

[0026] Using the terahertz band high-resolution ISAR imaging algorithm, a two-dimensional ISAR image sequence is obtained from the original radar echo signal. The process expression is: (4) 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.

[0027] In the specific implementation process of step 202, the center of mass of the space target is taken as the origin of the three-dimensional coordinate system, and the three-dimensional coordinates of a scattering point on the space target are assumed to be ,in ,common Three-dimensional scattering points, is the index of the extracted feature points. Frame 2D ISAR image, then the scattering points In the The horizontal and vertical coordinates in the frame two-dimensional ISAR image are: (5) Based on the two-dimensional ISAR image sequence, when constructing the projection relationship from three-dimensional space to two-dimensional imaging plane, a scattering point of the space target The distance to the projection vector and the azimuth projection vector The expression is: (6) In the formula, Represents the distance projection; represents 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.

[0028] In the specific implementation process of step 203, based on the preset pitch angle and azimuth angle of the expansion direction, the initial candidate point is used 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.

[0029] It can be understood that, unlike the traditional random search for candidate points such as group optimization, the inside-out search process proposed in the present invention draws on the law of "seed growth" in nature. Plants grow from seeds to mature vegetation through continuous cell division. If the candidate points are regarded as cells that can continuously divide, 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 characteristics of regional connectivity, which also provides a growable area for the generation of candidate points. Even if there are individual non-connected areas in the image, they can be overcome by adjusting the step size of the candidate points.

[0030] Assume that the initial candidate point is , the coordinates of the first candidate point obtained by the first expansion The expression is: (7) 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 of candidate points, which is generally a multiple of the ISAR image resolution; Indicates the pitch angle in the expansion direction. The expansion method is ,in, Indicates the number of first candidate points in the pitch angle direction; Indicates the azimuth of the expansion direction. The expansion method is ,in, Indicates the number of first candidate points in the azimuth direction.

[0031] The expansion is carried out in a spherical outward divergent manner. During each expansion process, each candidate point can generate A new candidate point.

[0032] When expanding, the step factor is used to adjust the compensation for each expansion. The step factor is a random number. The expansion step length of the candidate points The product of .

[0033] After obtaining the new first candidate points, the maximum energy projection criterion is used to calculate the projection energy of each first candidate point. The expression is: (8) 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.

[0034] Then filter out the one with the largest energy accumulation The second candidate point can be considered as the real scattering point on the space target. The second candidate point is used as the "seed point" for the next expansion. When there is no real scattering point that can reach the maximum energy projection among the new candidate points obtained in a certain expansion, the "seed point" selected for the next expansion remains unchanged. Take each candidate point as the origin, expand the new candidate point in a spherical shape, and so on, continuously iterate and update until the termination condition is reached. The termination conditions include: the ratio of the residual energy value to the total energy of the two-dimensional ISAR image is less than the preset threshold; and / or the maximum number of iterations is reached.

[0035] In addition, in order to prevent falling into local search when expanding candidate points, during the second and subsequent expansion processes, some real three-dimensional points that have been solved are randomly added as candidate points to participate in the calculation, so as to enhance the globality and robustness of the search for valid candidate points.

[0036] The three-dimensional rapid imaging method of space targets in the terahertz frequency band proposed by the present invention has a detailed process of three-dimensional imaging as follows: Preparation: Initialize candidate points. Since the targets are all in the center of the ISAR image after processing, the origin of the three-dimensional coordinate system is generally selected. As the initial candidate point coordinates. According to the projection relationship from the constructed three-dimensional space to the two-dimensional imaging plane, the high-resolution imaging algorithm is used to obtain Frame 2D ISAR images, calculate the total energy of all ISAR image sequences At the same time, the initial value of the residual energy of the two-dimensional ISAR image is , 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 , the ratio of the residual energy value to the total energy of the two-dimensional ISAR image is 1 at the time of initialization; in addition, the threshold for the termination of the iteration is set to , the total number of iterations is set to .

[0037] Start the first iteration: Perform the first expansion according to formula (7) and get New candidate points are projected into the two-dimensional ISAR image, and the accumulated energy of each candidate point after projection is calculated. Then, the second candidate points are screened out based on formula (8) and retained as the real three-dimensional points of the space target, which are recorded as the first point set , and the initial three-dimensional imaging point set Update to the first 3D imaging point set .

[0038] Based on the idea of ​​CLEAN algorithm, the first point set is gradually removed The energy projected onto the two-dimensional ISAR image, and the residual energy value of the two-dimensional ISAR image is updated as , and the ratio of the residual energy value to the total energy of the updated two-dimensional ISAR image is .

[0039] From the initial 3D imaging point set Randomly select Scattering points are merged into the first point set As the second candidate point, it participates in the calculation. It can be understood that by Some scattered points are extracted to participate in the calculation. On the one hand, the growth mode of candidate points in the method of the present invention is exponential increase. If the initial three-dimensional imaging point set obtained in the last iteration is All points are used as candidate points for the next iteration, which will increase the amount of calculation. On the other hand, the initial 3D imaging point set obtained in the previous iteration If all the candidate points that have already participated in the search are searched again, it will cause computational redundancy. It is sufficient to randomly select a small number of 3D points to ensure a certain global search capability.

[0040] Repeat the above steps and continuously update the point set during the iteration process and 3D imaging point set , when The ratio of the image residual energy value calculated by the iteration to the total image energy and\or When , the iteration is terminated and the final three-dimensional imaging result is obtained. Among them, the point set and 3D imaging point set Contains the The new target real scattering point set and the total real scattering point set obtained in the iteration.

[0041] In one embodiment, based on the terahertz frequency band space target three-dimensional rapid imaging method proposed in 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 a three-dimensional point cloud model of a satellite. The three-dimensional size of the satellite model is, as shown in FIG. Figure 2 shown.

[0042] Multiple radar sight angles are set to observe the target model, and a 2D ISAR image sequence is obtained using a terahertz band high-resolution ISAR imaging algorithm. The 2D ISAR image sequence includes several 2D ISAR images arranged in time sequence, of which three frames of 2D ISAR images are as follows: Figure 3 shown.

[0043] After obtaining the two-dimensional ISAR image sequence, it is expanded in a divergent manner from the inside to the outside, and the projection energy of the candidate points is calculated based on the maximum energy projection criterion. Through iterative updating, the following is obtained: Figure 4 (a) shows the final three-dimensional imaging result of the space target. Figure 4 (b) The three-dimensional imaging results obtained by the commonly used PSO algorithm. The scattering points in the three-dimensional imaging results of the method proposed in the present invention are denser and can better reflect the structural characteristics of the real space target.

[0044] The method proposed in the present invention fully considers the three-dimensional features of the target and adopts an expansion method from the inside to the outside. Each real three-dimensional point can expand to a number of candidate points, which can not only achieve exponential growth, but also has a higher probability that the candidate point is the real point of the target. Compared with the traditional inefficient random search based on the PSO algorithm, the present invention starts searching from the vicinity of the real target point, has a higher probability of obtaining the real target point, and has a higher search efficiency. In addition, due to the large number of scattered points searched, the points of the obtained three-dimensional image of the spatial target are denser and the structural features are more obvious.

[0045] Although this embodiment Figure 1 The steps in the process are shown in sequence as indicated by the arrows, but the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of the steps, and the steps can be executed in other orders. Figure 1At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0046] Example 2 Based on the method for rapid three-dimensional imaging of space targets in the terahertz frequency band in Example 1, this embodiment discloses a device for rapid three-dimensional imaging of space targets in the terahertz frequency band, such as Figure 5 As shown, the terahertz frequency band space target three-dimensional rapid imaging device 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, wherein: The projection relationship building module 401 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.

[0047] The first candidate point generation module 402 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.

[0048] 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 using the maximum energy projection criterion, screen out the second candidate point with the largest projection energy, and retain the second candidate point as the real three-dimensional point of the space target.

[0049] The iterative imaging module 404 is used to perform a second expansion from the second candidate point as the starting point in a divergent manner from the inside to the outside until the termination condition is reached, thereby obtaining the final three-dimensional imaging result of the space target.

[0050] In this embodiment, the specific working process and working principle 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 in the method of Embodiment 1, so they are not described in detail in this embodiment. Each unit module can be implemented in whole or in part by software, hardware and a combination thereof, and each unit module can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above unit modules.

[0051] Example 3 like Figure 6The terminal device disclosed in this embodiment includes a transmitter, a receiver, a memory, and a processor. 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-executable instructions, and the processor is used to execute the computer-executable instructions stored in the memory to implement the method in the above-mentioned embodiment 1.

[0052] It should be noted that the above memory can be independent or integrated with the processor. When the memory is independently provided, the terminal device further includes a bus for connecting the memory and the processor.

[0053] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and 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-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may 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 (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0054] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0055] The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached 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; represents 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 frame 2D ISAR image ; 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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