A cooperative target ISAR envelope alignment method and system

Abstract

Embodiments of the present specification provide a cooperative target ISAR envelope alignment method and system, the method comprising obtaining a baseband echo of a target to be measured by a radar, compressing the echo to obtain a one-dimensional range image; using prior information of the cooperative target to perform coarse envelope alignment on the obtained one-dimensional range image to obtain a one-dimensional range image sequence after coarse envelope alignment; selecting an arbitrary one-dimensional range image after coarse alignment, determining the envelope shift amount of the previous one-dimensional range image, and determining the reference shift amount; performing a shift in the vicinity of the reference shift amount by a search method, performing cross-correlation calculation with the previous one-dimensional range image, and calculating a correlation coefficient; based on the setting of the shift range, performing traversal of the one-dimensional range image shift until the end of the traversal, determining the shift amount corresponding to the maximum correlation coefficient as the shift amount of the one-dimensional range image, and realizing envelope alignment of the one-dimensional range image. The problem of large amount of calculation and easy jumping of the alignment result in the prior art is solved.

Description

Technical Field

[0001] This document relates to the field of radar imaging system optimization technology, and in particular to a cooperative target ISAR envelope alignment imaging method and system. Background Technology

[0002] Inverse Synthetic Aperture Radar (ISAR) is an important branch of radar imaging. In ISAR imaging, the radar continuously observes moving targets and processes the signals to obtain two-dimensional or even three-dimensional image information of the target, providing support for subsequent target identification. In principle, ISAR achieves high range resolution by compressing each echo pulse and high azimuth resolution by using a virtual aperture formed by the target's motion.

[0003] Envelope alignment is a crucial step in ISAR imaging. Currently, ISAR envelope alignment generally employs the maximum cross-correlation method. This method involves first shifting the pulse compression result (i.e., the one-dimensional range image) of the m-th echo (where m is an integer greater than 1) by -L ("-" indicates left shift) range cells in the range direction, and then correlating it with the pulse compression result of the (m-1)-th echo. Next, the pulse compression result (i.e., the one-dimensional range image) of the m-th echo is shifted by -L+1 range cells in the range direction, and then correlating it with the pulse compression result of the (m-1)-th echo. This process is repeated until 2L+1 range cells have been traversed, where L is determined based on the actual number of echo sampling points. During these 2L+1 traversals, the number of range cells l corresponding to the maximum correlation between two one-dimensional range images is found; the value of l is the number of range cells shifted for the one-dimensional range image of the n-th echo during envelope alignment. Examples before and after envelope alignment are shown below. Figure 1 (a) Figure 1 As shown in (b), this method of envelope alignment has two problems:

[0004] (1) The cross-correlation processing between two echo one-dimensional range images requires shifting and then correlation, which involves a large number of traversals, 2L+1, and a large amount of computation.

[0005] (2) A large number of traversals can easily lead to abrupt changes in the alignment results, such as Figure 1 As shown in (c), image quality cannot be guaranteed.

[0006] Therefore, there is an urgent need to provide an ISAR envelope alignment method that requires less computation and has higher accuracy. Summary of the Invention

[0007] This specification provides one or more embodiments of a cooperative target ISAR envelope alignment method, including the following steps:

[0008] By compressing the fundamental frequency echo of the target obtained by radar, a one-dimensional range profile is obtained.

[0009] By using prior information about the cooperative target, the envelope of the obtained one-dimensional range image is coarsely aligned to obtain a sequence of one-dimensional range images with coarsely aligned envelope.

[0010] Select any coarsely aligned one-dimensional range image and determine the envelope shift of its previous one-dimensional range image, which is then used as the reference shift.

[0011] By searching, the displacement is performed near the reference displacement and cross-correlated with the previous one-dimensional distance image, and the correlation coefficient is calculated.

[0012] Based on the set displacement range, the displacement of the one-dimensional range image of the echo is traversed until the traversal is completed. Then, the displacement corresponding to the maximum correlation coefficient is determined as the displacement of the one-dimensional range image of the echo, thereby achieving envelope alignment of the one-dimensional range image of the echo.

[0013] This specification provides one or more embodiments of a cooperative target ISAR envelope alignment system, wherein the data acquisition unit is the fundamental frequency echo of the target to be measured acquired by radar;

[0014] Signal processing unit: compresses the echo to obtain a one-dimensional range image;

[0015] Envelope coarse alignment unit: The envelope of the obtained one-dimensional range image is coarsely aligned using the prior information of the cooperative target to obtain the one-dimensional range image sequence after coarse envelope alignment;

[0016] Envelope fine alignment unit: For any coarsely aligned one-dimensional range image, determine the envelope shift of the previous one-dimensional range image, and set it as the reference shift; by searching, shift the image near the reference shift and cross-correlate it with the previous one-dimensional range image, and calculate the correlation coefficient; then traverse the displacement of the echo one-dimensional range image. After the traversal, determine the shift corresponding to the maximum correlation coefficient, which is the shift of the current echo one-dimensional range image, thus achieving envelope alignment of the echo one-dimensional range image.

[0017] This specification provides one or more embodiments of a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the cooperative target ISAR envelope alignment method described above.

[0018] This specification provides one or more embodiments of a computer-readable storage medium storing a computer program that, when executed by a processor, implements the cooperative target ISAR envelope alignment method described above.

[0019] The method of this invention performs coarse-fine alignment operations on all echoes, completing the envelope alignment of all echo one-dimensional range images. This method completes the coarse envelope alignment using prior information of the cooperative target, and then performs shifting and correlation on the one-dimensional range image, which greatly reduces the number of traversals and thus reduces the amount of computation. In addition, the small-scale traversal operation increases the accuracy of the envelope alignment, providing a one-dimensional range image basis for ensuring the quality of two-dimensional imaging, and solving the problems of large computational load and easy jump in alignment results in the prior art. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in one or more embodiments of this specification or in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A comparison of one-dimensional range image sequences before and after ISAR envelope alignment provided for one or more embodiments of this specification;

[0022] Figure 2 A schematic diagram of the first module composition of a cooperative target ISAR envelope alignment method provided in one or more embodiments of this specification;

[0023] Figure 3 A detailed flowchart of ISAR envelope alignment provided for one or more embodiments of this specification;

[0024] Figure 4 A schematic diagram of a first unit composition of a cooperative target ISAR envelope alignment system provided for one or more embodiments of this specification;

[0025] Figure 5 This is a schematic diagram of the structure of a computer device provided for one or more embodiments of this specification. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the technical solutions in one or more embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, and not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of this document.

[0027] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0028] Method Implementation Examples

[0029] According to embodiments of the present invention, a cooperative target ISAR envelope alignment method is provided, such as... Figure 2 The diagram shown is a flowchart of the cooperative target ISAR envelope alignment imaging method provided by the present invention. The cooperative target ISAR envelope alignment imaging method according to an embodiment of the present invention includes the following steps:

[0030] S1. The fundamental frequency echo of the target to be measured is obtained by radar, and the echo is compressed to obtain a one-dimensional range image;

[0031] S2. Use the prior information of the cooperative target to coarsely align the envelope of the obtained one-dimensional range image to obtain the one-dimensional range image sequence after coarsely aligning the envelope.

[0032] S3. Select a coarsely aligned one-dimensional range image from step S2, determine the envelope shift of its previous one-dimensional range image, and set it as the reference shift.

[0033] S4. By searching, shift the image near the reference shift amount and cross-correlate it with the previous one-dimensional distance image, and calculate the correlation coefficient.

[0034] S5. Based on the setting of the displacement range, the displacement of the one-dimensional range image of the echo is traversed through steps S3-S4 until the traversal is completed. The displacement corresponding to the maximum correlation coefficient is determined to be the displacement of the one-dimensional range image of the echo, thereby realizing the envelope alignment of the one-dimensional range image of the echo.

[0035] S6. Through steps S3-S5, the envelope alignment of the one-dimensional distance image of all pulses is completed sequentially.

[0036] This embodiment follows the above method to perform coarse-fine alignment of all pulse echoes, completing the envelope alignment of all echo one-dimensional range images. This method completes the coarse envelope alignment using the prior information of the cooperative target, and then performs shifting and correlation on the one-dimensional range image, greatly reducing the number of traversals and thus reducing the amount of computation. In addition, the small-scale traversal operation increases the accuracy of the envelope alignment, providing a one-dimensional range image basis for ensuring the quality of two-dimensional imaging, and solving the problems of large computational load and easy jump in alignment results in the prior art.

[0037] In this embodiment, step S1 obtains a one-dimensional range image by compressing the acquired fundamental frequency echo of the target under test. The specific implementation steps are as follows:

[0038] Based on the radar transmitting a linear frequency modulated signal, the pulse repetition period is T. PRT The transmitted signal of the m-th pulse is:

[0039]

[0040] In the formula, rect(·) represents a rectangular window function and To save time, t m =mT PRT (m=0,1,2,...) represents the launch time, called the slow time, and t represents the total time. The relationship between the three is as follows: f c T is the carrier frequency. P Where is the pulse width and K is the modulation frequency.

[0041] Assume the scattering coefficient of the scattering point P on the target is fixed at σ. P Then the m-th pulse echo signal received by the radar is:

[0042]

[0043] In the formula, R pm It is the two-way distance from the radar to the target scattering point P.

[0044] Coherent mixing of the echo yields the following baseband echo signal:

[0045]

[0046] In the formula This is the baseband transmitted signal. By using a matched filter to compress the echo signal pulses, a one-dimensional range profile of the ISAR image can be obtained. The time domain representation of the one-dimensional range profile is as follows:

[0047]

[0048] Its spectrum is:

[0049]

[0050] Based on the one-dimensional distance image obtained by the above method, envelope coarse alignment is performed in step S2, specifically as follows:

[0051] For cooperative targets, the radar can obtain the two-way distance measurement R from the target center. ref_m The two-way distance R from the scattering point P on the target to the radar pm for:

[0052] R pm =R ref_m +VR m +2(y P -x P sinθ m (11);

[0053] Among them, (x P ,y P ) represents the coordinates of the scattering point P in the imaging coordinate system; VR m The ranging error of the radar is unknown, but it varies regularly across different echoes; θ m The cumulative rotation angle corresponds to the m-th echo.

[0054] According to formula (11) R pm The first term for constructing the envelope coarse compensation is:

[0055]

[0056] By compensating equation (10) with equation (12), we can obtain the following equation:

[0057]

[0058] In the formula, S b (f) is The fast time-frequency domain representation.

[0059] Transforming equation (13) to the time domain, we obtain the m-th one-dimensional distance image after coarse envelope alignment as follows:

[0060]

[0061] As can be seen from equation (14), the peak of the one-dimensional distance image envelope appears in That is, the envelope movement of the range image scattering point is caused by the radar ranging error VR. m The smaller the ranging error, the smaller the envelope movement.

[0062] In this embodiment, based on the coarse alignment of the envelope of the obtained one-dimensional distance image using the prior information of the cooperative target, the specific traversal steps of steps S3-S6 are as follows:

[0063] Assuming that envelope fine alignment is performed on all M echoes during imaging, the specific steps are as follows:

[0064] A101. Determine the number of distance units shifted when aligning the m-th echo envelope as K. m And denote the shifted one-dimensional distance image as s m ;

[0065] A102, Let k = K m -L, where the magnitude of L is determined by an empirical value of the ranging error;

[0066] A103. For the one-dimensional range image of the (m+1)th echo, cyclically shift it by k range units, and denot the shifted one-dimensional range image as s. m+1；

[0067] Where k is positive, it is a circular right shift; and k is negative, it is a circular left shift.

[0068] A104, s m+1 With s m Perform cross-correlation calculations to obtain the cross-correlation coefficient;

[0069] A105. Let the cyclic shift value of the (m+1)th echo one-dimensional range image be k = k+1;

[0070] A106. Repeat steps A103 to A105 until k = K. m +L;

[0071] A107. Determine the k value corresponding to the maximum cross-correlation coefficient. This k value is the number of range cells that need to be shifted for the one-dimensional range image envelope alignment of the (m+1)th echo.

[0072] A108. Let m = m + 1, and repeat steps A101 to A107 until the envelope alignment of the one-dimensional range images of all echoes is completed.

[0073] like Figure 3 As shown below, the specific implementation process of this method will be explained in detail.

[0074] B101. The fundamental frequency echo of the target to be measured is obtained by radar. Each echo is pulse-compressed to obtain a one-dimensional range profile of each echo.

[0075] B102. Using prior information about the cooperative target, perform envelope coarse alignment on the one-dimensional range image of each echo to obtain a sequence of one-dimensional range images after envelope coarse alignment.

[0076] B103. Determine the number of distance units shifted when aligning the m-th echo envelope as K. m And denote the shifted one-dimensional distance image as s m ;

[0077] B104, Let k = K m -L;

[0078] B105. For the one-dimensional range image of the (m+1)th echo, cyclically shift it by k range units, and denot the shifted one-dimensional range image as s. m+1 ;

[0079] B106, s m+1 With s m Perform cross-correlation calculations to obtain the cross-correlation coefficient;

[0080] B107. Let the cyclic shift value of the (m+1)th echo one-dimensional range image be k = k+1, and determine whether k > K. mIf the sum is not greater than +L, then jump to step B105; if it is greater than +L, then the loop ends and jump to step B108.

[0081] B108. The k value corresponding to the maximum cross-correlation coefficient is the number of range units that need to be shifted for the one-dimensional range image envelope alignment of the (m+1)th echo.

[0082] B109. Let m = m + 1, and determine whether m > M. If it is not greater than M, then jump to step B103; if it is greater than M, then end the loop and complete the envelope alignment of the one-dimensional range images of all echoes.

[0083] System Implementation Examples

[0084] According to embodiments of the present invention, a cooperative target ISAR envelope alignment imaging system is provided, such as... Figure 4 The diagram shown is a schematic block diagram of the cooperative target ISAR envelope alignment imaging system provided in this embodiment. The cooperative target ISAR envelope alignment imaging system according to this embodiment of the invention includes:

[0085] Data acquisition unit: acquires the fundamental frequency echo of the target under test via radar;

[0086] Signal processing unit: compresses the pulses to obtain a one-dimensional range image;

[0087] Envelope coarse alignment unit: The envelope of the obtained one-dimensional range image is coarsely aligned using the prior information of the cooperative target to obtain the one-dimensional range image sequence after coarse envelope alignment;

[0088] Envelope fine alignment unit: Based on the coarsely aligned one-dimensional range image sequence obtained from the envelope coarse alignment unit, for a coarsely aligned one-dimensional range image, the envelope shift of the previous one-dimensional range image is determined and set as the reference shift. A search is performed to shift the image near the reference shift and cross-correlate it with the previous one-dimensional range image, and the correlation coefficient is calculated. The displacement of the echo one-dimensional range image is then iterated. After the iterative process, the shift corresponding to the maximum correlation coefficient is determined as the shift of the current echo one-dimensional range image, thus achieving envelope alignment of the echo one-dimensional range image. This process is repeated for the one-dimensional range image sequence until the iterative process is complete, thus achieving envelope alignment of all echo one-dimensional range images.

[0089] In this preferred embodiment, the specific envelope fine alignment unit includes:

[0090] One-dimensional distance image acquisition module: acquires the one-dimensional distance image after coarse alignment of the envelope coarse alignment unit and its previous one-dimensional distance image.

[0091] Envelope shift confirmation module: Determines the envelope shift of the previous one-dimensional distance image and uses it as the reference shift.

[0092] Cross-correlation calculation module: Performs cross-correlation on the two one-dimensional distance images from the one-dimensional distance image acquisition module, calculates the correlation coefficient, and stores it.

[0093] The first traversal module: Based on the set shift distance range, it traverses the pulse one-dimensional range image until the traversal is completed. Then, it determines the shift amount corresponding to the maximum correlation coefficient, which is the shift amount of the pulse one-dimensional range image, thus realizing the envelope alignment of the pulse one-dimensional range image.

[0094] The second traversal module: Based on the loop end information fed back by the first traversal module, and based on the number of echoes M, it sequentially completes the envelope alignment of the one-dimensional range image of all echoes through the envelope shift confirmation module, the cross-correlation calculation module, and the first traversal module.

[0095] In this embodiment, the signal processing unit specifically performs the following calculations:

[0096] Based on the radar transmitting a linear frequency modulated signal, the pulse repetition period is T. PRT The transmitted signal of the m-th pulse is:

[0097]

[0098] In the formula, rect(·) represents a rectangular window function and To save time, t m =mT PRT (m=0,1,2,...) represents the launch time, called the slow time, and t represents the total time. The relationship between the three is as follows: f c T is the carrier frequency. p Where is the pulse width and K is the modulation frequency.

[0099] Assume the scattering coefficient of the scattering point P on the target is fixed at σ. P Then the transmitted signal of the m-th pulse received by the radar is:

[0100]

[0101] In the formula, R pm It is the two-way distance from the radar to the target scattering point P.

[0102] Coherent mixing of the echo yields the following baseband echo signal:

[0103]

[0104] By using a matched filter to compress the echo signal pulses, a one-dimensional range profile of ISAR imaging can be obtained. The time domain representation of the one-dimensional range profile can be expressed as:

[0105]

[0106] Its spectrum is:

[0107]

[0108] In this embodiment, the specific processing steps of the envelope coarse alignment unit are as follows:

[0109] For cooperative targets, the radar can obtain the two-way distance measurement R from the target center. ref_m The two-way distance R from the scattering point P on the target to the radar pm for:

[0110] R pm =R ref_m +VR m +2(y P -x P sinθ m (15);

[0111] Among them, (x P ,y P ) represents the coordinates of the scattering point P in the imaging coordinate system; VR m The ranging error of the radar is unknown, but it varies regularly with each pulse echo; θ m The cumulative rotation angle corresponds to the m-th echo.

[0112] According to formula (15) R pm The first term for constructing the envelope coarse compensation is:

[0113]

[0114] By compensating equation (14) with equation (16), we can obtain the following equation:

[0115]

[0116] Transforming equation (17) to the time domain, we obtain the m-th one-dimensional distance image after coarse envelope alignment as follows:

[0117]

[0118] Equation (18), the peak of the one-dimensional distance image envelope appears That is, the envelope movement of the range image scattering point is caused by the radar ranging error VR. m The smaller the ranging error, the smaller the envelope movement.

[0119] like Figure 5As shown, the present invention also provides a computer-readable storage medium storing a computer program thereon. When the computer program is executed by a processor, it implements the cooperative target ISAR envelope alignment imaging method in the above embodiments, or when the computer program is executed by a processor, it implements the cooperative target ISAR envelope alignment imaging method in the above embodiments. When the computer program is executed by the processor, it implements the following method steps:

[0120] S1. The fundamental frequency echo of the target to be measured is obtained by radar, and the echo is compressed to obtain a one-dimensional range image;

[0121] S2. Use the prior information of the cooperative target to coarsely align the envelope of the obtained one-dimensional range image to obtain the one-dimensional range image sequence after coarsely aligning the envelope.

[0122] S3. Select any one of the coarsely aligned one-dimensional range images from step S2, determine the envelope shift of the previous one-dimensional range image, and set it as the reference shift.

[0123] S4. By searching, shift the image near the reference shift amount and cross-correlate it with the previous one-dimensional distance image, and calculate the correlation coefficient.

[0124] S5. Based on steps S3-S4, traverse the displacement of the one-dimensional range image of the echo until the traversal is completed. Then, determine the displacement corresponding to the maximum correlation coefficient, which is the displacement of the one-dimensional range image of the echo, and realize the envelope alignment of the one-dimensional range image of the echo.

[0125] S6. Based on steps S1-S5, sequentially complete the envelope alignment of the one-dimensional range images of all echoes.

[0126] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0127] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cooperative target ISAR envelope alignment method, characterized in that, Includes the following steps: The fundamental frequency echo of the target acquired by radar is compressed to obtain a one-dimensional range profile. The time domain of the one-dimensional range profile can be expressed as: （1）； Its spectrum is: （2）； Using prior information about the cooperative target, the envelope of the obtained one-dimensional range image is coarsely aligned to obtain a sequence of one-dimensional range images with coarsely aligned envelopes. The specific steps include: For cooperative targets, the radar can obtain the two-way distance measurement from the target center. scattering point on the target Two-way distance to radar for: R pm ＝R ref_m +VR m +2 ( y P -x P sinθ m )（3）； in, For scattering points Coordinate values ​​within the imaging coordinate system; VR m This represents the ranging error of the radar; the value is unknown, but it varies regularly across different echoes. For the first m The cumulative rotation angle corresponding to the next echo; According to formula (3) The first term for constructing the envelope coarse compensation is: （4）； By compensating equation (2) with equation (4), we can obtain the following equation: （5）； In the formula, for Fast time-frequency domain representation; Transforming equation (5) to the time domain, we obtain the first coarsely aligned envelope. m The next one-dimensional distance image is: （6）； In the formula, For the scattering point on the target The scattering coefficient, To save time; , m =0,1,2,…, representing the launch time. For the entire time period, the relationship between the three is as follows: ; For carrier frequency, The pulse width. To adjust the frequency; Select any coarsely aligned one-dimensional range image and determine the envelope shift of its previous one-dimensional range image, which is then used as the reference shift. By searching, the displacement is performed near the reference displacement and cross-correlated with the previous one-dimensional distance image, and the correlation coefficient is calculated. Based on the set displacement range, the displacement of the one-dimensional range image of the echo is traversed until the traversal is completed. The displacement corresponding to the maximum correlation coefficient is determined as the displacement of the one-dimensional range image of the echo, thereby achieving envelope alignment of the one-dimensional range image of the echo. Complete the envelope alignment of all echo one-dimensional range images in sequence.

2. The cooperative target ISAR envelope alignment method as described in claim 1, characterized in that, Envelope-aligned imaging of M echoes includes the following steps: B1. By acquiring the fundamental frequency echo of the target under test through radar, pulse compression is performed on each echo to obtain a one-dimensional range profile of each echo; B2. Using prior information about the cooperative target, perform envelope coarse alignment on the one-dimensional range image of each echo to obtain a sequence of one-dimensional range images after envelope coarse alignment. B3. Determine the number of distance units shifted when aligning the m-th echo envelope. And the shifted one-dimensional distance image is denoted as s m ; B4, Order k = K m -L; where the value of L is determined by an empirical value of the ranging error; B5. For the one-dimensional range image of the (m+1)th echo, perform cyclic shifting. A distance unit is defined, and the shifted one-dimensional distance image is denoted as . s m+1 ; B6, will s m+1 and s m Perform cross-correlation calculations to obtain the cross-correlation coefficient; B7. Let the cyclic shift value of the (m+1)th echo one-dimensional range image be... k=k +1, check if k > K m If the sum is not greater than +L, then jump to step B5; if it is greater than +L, then the loop ends and jump to step B8. B8. The value corresponding to the maximum cross-correlation coefficient. The value is the first one. m The number of distance cells required to align the one-dimensional range image envelope of +1 echo; B9, Order m=m +1, check if m > M. If not, jump to step B3; if greater, end the loop and complete the envelope alignment of the one-dimensional range images of all echoes.

3. The cooperative target ISAR envelope alignment method as described in claim 1, characterized in that, The process of compressing the echo to obtain a one-dimensional range image specifically includes the following steps: Based on the radar transmitting a linear frequency modulated signal, the pulse repetition period is... , No. m The transmitted signal of each pulse is: （7）； In the formula, Represents a rectangular window function and , To save time; , m =0,1,2,…, representing the launch time. t For the entire time period, the relationship between the three is as follows: ; f c For carrier frequency, T P Where K is the pulse width and K is the frequency modulation frequency; Assume the scattering coefficient of scattering point P on the target is fixed. Then the radar receives the first m The echo signals are: （8）； In the formula, The radar reaches the target scattering point The round trip distance; Coherent mixing of the echo yields the following baseband echo signal: （9）； By using a matched filter to compress the echo signal pulses, a one-dimensional range profile of ISAR imaging can be obtained. The time domain representation of the one-dimensional range profile can be expressed as: （10）； Its spectrum is: （11）。 4. A cooperative target ISAR envelope alignment system, characterized in that, include Data acquisition unit: The fundamental frequency echo of the target under test acquired by radar; Signal processing unit: Compresses the echo to obtain a one-dimensional range image. The time domain representation of the one-dimensional range image can be expressed as: （1）； Its spectrum is: （2）； Envelope coarse alignment unit: Utilizing prior information about the cooperative target, the envelope of the obtained one-dimensional range image is coarsely aligned to obtain a sequence of coarsely aligned one-dimensional range images, specifically: For cooperative targets, the radar can obtain the two-way distance measurement from the target center. scattering point on the target Two-way distance to radar for: R pm ＝R ref_m +VR m +2 ( y P -x P sinθ m )（3）； in, For scattering points Coordinate values ​​within the imaging coordinate system; VR m This represents the ranging error of the radar; the value is unknown, but it varies regularly across different echoes. For the first m The cumulative rotation angle corresponding to the next echo; According to formula (3) The first term for constructing the envelope coarse compensation is: （4）； By compensating equation (2) with equation (4), we can obtain the following equation: （5）； In the formula, for Fast time-frequency domain representation; Transforming equation (5) to the time domain, we obtain the first coarsely aligned envelope. m The next one-dimensional distance image is: （6）； In the formula, For the scattering point on the target The scattering coefficient, To save time; , m =0,1,2,…, representing the launch time. For the entire time period, the relationship between the three is as follows: ; For carrier frequency, The pulse width. For frequency tuning; envelope fine alignment unit: For any coarsely aligned one-dimensional range image, determine the envelope shift of the previous one-dimensional range image, and set it as the reference shift; by searching, shift near the reference shift and cross-correlate with the previous one-dimensional range image, and calculate the correlation coefficient; and traverse the echo displacement. After the traversal, determine the shift corresponding to the maximum correlation coefficient as the shift of the current echo one-dimensional range image, thus achieving envelope alignment of the echo one-dimensional range image.

5. The cooperative target ISAR envelope alignment system as described in claim 4, characterized in that, The envelope fine alignment unit includes: One-dimensional distance image acquisition module: acquires any one-dimensional distance image after coarse alignment of the envelope coarse alignment unit and its previous one-dimensional distance image; Envelope shift confirmation module: Determines the envelope shift of the previous one-dimensional range image and uses it as the reference shift. Cross-correlation calculation module: Performs cross-correlation on the two one-dimensional distance images from the one-dimensional distance image acquisition module, calculates the correlation coefficient, and stores it; The first traversal module: Based on the set displacement range, it traverses the displacement of the one-dimensional range image of the echo until the traversal is completed. Then, it determines the displacement corresponding to the maximum correlation coefficient, which is the displacement of the one-dimensional range image of the echo in this case, thus realizing the envelope alignment of the one-dimensional range image of the echo.

6. The cooperative target ISAR envelope alignment system as described in claim 5, characterized in that, It also includes a second traversal module, which, based on the loop end information fed back by the first traversal module, and according to the number of echoes, completes the envelope alignment of the one-dimensional range image of all echoes through the envelope shift confirmation module, the cross-correlation calculation module, and the first traversal module.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the cooperative target ISAR envelope alignment method as described in any one of claims 1 to 3.

8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the cooperative target ISAR envelope alignment method as described in any one of claims 1 to 3.

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