Moving target refocusing method and device based on single channel in beamforming mode

Abstract

This application relates to a moving target refocusing method and device based on a single channel in a spotlight mode. This method generates a two-dimensional image of the ground motion scene based on a single-channel echo signal obtained by detecting the ground motion scene using a terahertz video radar. The target image of the moving target is extracted from this image. An inverse Fourier transform of the target image is performed in azimuth to obtain a one-dimensional range image. Quadratic phase compensation is performed using an image shift algorithm. The compensated signal is then aligned in range using a linear interpolation cross-correlation algorithm to correct for nonlinear error terms. This results in a refocused image of the moving target after the nonlinear error terms have been corrected, and this image is then patched back into the two-dimensional image to obtain a complete image. This method can effectively address the problem of image defocus caused by small range migrations.

Description

Technical Field

[0001] The present application relates to the field of radar signal processing technology, and in particular to a method and device for refocusing a moving target based on a single channel in a beamforming mode. Background Art

[0002] The mission of Terahertz Video Synthetic Aperture Radar (THz-ViSAR) is to continuously acquire high-resolution images of a scene, detect and monitor moving targets within it, and, when possible, image or refocus moving targets. This identification facilitates monitoring of moving targets. For THz-ViSAR, moving targets are considered non-cooperative compared to radar processing, meaning their motion parameters are unknown. For non-cooperative moving targets, the refocusing algorithm typically performs a keystone transform after parameter estimation to eliminate cross-interference in range and azimuth. A two-dimensional Fourier transform is then used to re-image the moving target.

[0003] However, the high frequency and short wavelength of THz-ViSAR systems introduce nonlinear range migration during the refocusing process. While this range migration is negligible for low-frequency video synthetic aperture radars (SARs), such as those operating in the X-band and Ka-band, for high-frequency terahertz video SARs, minute range migration can cause image defocus. Existing methods for refocusing moving targets in THz-ViSAR ignore this issue. Summary of the Invention

[0004] Based on this, it is necessary to provide a moving target refocusing method and device based on a single channel in a beamforming mode, which can obtain high-quality refocused images in a THz-ViSAR system for non-cooperative moving targets with unknown range migration.

[0005] A moving target refocusing method based on a single channel in a spotlight mode, the method comprising:

[0006] Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model;

[0007] Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0008] Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image;

[0009] Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0010] Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal;

[0011] The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0012] The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0013] In one embodiment, the performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm includes:

[0014] Determine a prominent point in the compensated target signal, use the frame data where the prominent point is located as a reference frame, use the frame data before or after the reference frame as a test frame, and perform energy normalization processing on the reference frame and the test frame data;

[0015] Using the reference frame as a reference, align the first data position of the test frame with the first data position of the reference frame, perform proportional interpolation on the other data positions of the test frame using the proportional coefficient k, and calculate the maximum cross-correlation between the interpolated test frame data and the reference frame data.

[0016] Changing the proportional coefficient k, obtaining the maximum cross-correlation values between the interpolated test frame data and the reference frame data under different k values, forming a cross-correlation maximum value set with these cross-correlation maximum values, and determining the proportional coefficient Kmax value corresponding to the maximum value of the cross-correlation maximum value set;

[0017] After performing energy normalization processing on other frame data, interpolation is performed using the proportional coefficient Kmax value to form a new data set;

[0018] In the new data set, the first frame of data is used as the benchmark, starting from the second frame of data, and taking the maximum cross-correlation function as the criterion, the previous frame of data and the next frame of data are aligned respectively to complete the envelope alignment of the entire data.

[0019] In one embodiment, the product of the azimuth imaging time and the range of the azimuth velocity is used as the change range of the proportional coefficient k.

[0020] In one embodiment, when performing secondary phase compensation on the target image using an image shift algorithm:

[0021] Obtaining the azimuth Doppler modulation rate through the quadratic phase term of the one-dimensional range image of the moving target;

[0022] An image shift algorithm is used to estimate the actual value of the azimuth Doppler modulation frequency according to the azimuth Doppler modulation frequency, and an azimuth quadratic phase compensation function is constructed;

[0023] The target image is subjected to secondary phase compensation using the directional secondary phase compensation function.

[0024] In one embodiment, the azimuth quadratic phase compensation function is expressed as:

[0025] ;

[0026] In the above formula, represents the distance frequency, Indicates slow time, Indicates the actual value of the estimated azimuth Doppler modulation frequency.

[0027] In one embodiment, the compensated target signal is expressed as:

[0028] ;

[0029] in, ;

[0030] In the above formula, Indicates the range position of the moving target imaging, represents the nonlinear term of distance migration, is the error term that is independent of the imaging position, Indicates frequency modulation. represents the speed of light, Indicates the pulse width, represents the center frequency of the linear FM signal, Indicates the flight center coordinates of the radar carrying platform, represents the coordinates of the moving target, Indicates the distance from the radar platform to the center of the motion scene.

[0031] The present application also provides a moving target refocusing device based on a single channel in a beamforming mode, the device comprising:

[0032] The echo mathematical model construction module is used to construct the geometric model of terahertz video SAR moving target imaging in the spotlight mode, and the echo mathematical model of the moving target obtained from the geometric model;

[0033] An echo signal acquisition module is used to acquire a single-channel echo signal obtained by detecting a ground motion scene by a terahertz video radar, and the single-channel echo signal is represented in the form of the echo mathematical model;

[0034] a target image extraction module, configured to obtain a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extract a target image of a moving target from the two-dimensional image;

[0035] a quadratic phase compensation module, configured to perform an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and perform a quadratic phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0036] a nonlinear error term correction module, configured to perform range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct the nonlinear error term, thereby obtaining a corrected target signal;

[0037] a signal processing module, configured to perform phase gradient autofocusing processing on the corrected target signal, perform initial phase correction and high-order phase error compensation, and obtain a processed target signal;

[0038] The complete image acquisition module is used to perform azimuth Fourier transform on the processed target signal to obtain a refocused image of the moving target, perform image scaling correction on the refocused image of the moving target, and then fill it back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0039] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0040] Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model;

[0041] Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0042] Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image;

[0043] Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0044] Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal;

[0045] The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0046] The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0047] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the following steps:

[0048] Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model;

[0049] Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0050] Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image;

[0051] Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0052] Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal;

[0053] The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0054] The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0055] Beneficial effects:

[0056] The above-mentioned single-channel moving target refocusing method and device based on spotlight mode generates a two-dimensional image of the ground motion scene based on the single-channel echo signal obtained by detecting the ground motion scene using a terahertz video radar. The target image of the moving target is extracted from this image. The target image is then subjected to an inverse Fourier transform in azimuth to obtain a one-dimensional range image. Quadratic phase compensation is performed using an image shift algorithm. The compensated signal is then aligned in range using a linear interpolation cross-correlation algorithm to correct for nonlinear errors. This results in a refocused image of the moving target after the nonlinear error terms have been corrected, and this image is then infilled back into the two-dimensional image to obtain a complete image. This method effectively addresses the problem of image defocus caused by small range migrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 1. A schematic flow chart of a moving target refocusing method based on a single channel in a spotlight mode according to an embodiment;

[0058] Figure 2 Schematic diagram of a geometric model for THz-ViSAR moving target imaging in a squint spotlight mode according to one embodiment;

[0059] Figure 3 This is a schematic diagram of a moving target image extracted from a certain moving scene in an experiment;

[0060] Figure 4 Schematic diagram of a one-dimensional range image without envelope alignment in an experiment;

[0061] Figure 5 Schematic diagram of the one-dimensional range image of envelope alignment in an experiment;

[0062] Figure 6 A schematic diagram of the target image of a moving target in an experiment;

[0063] Figure 7 This is a schematic diagram of the imaging results after the moving target is restored in an experiment;

[0064] Figure 8 A schematic diagram of a target image formed by envelope alignment using a cross-correlation algorithm in an experiment;

[0065] Figure 9 2. It is a structural block diagram of a moving target refocusing device based on a single channel in a spotlight mode according to an embodiment;

[0066] Figure 10 FIG. 1 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0068] In view of the problem in the existing technology that there is nonlinear range migration in the range envelope of moving targets in terahertz video SAR, which is of the same order of magnitude as the wavelength of the terahertz frequency band and the envelope alignment effect is poor, a method for obtaining high-quality refocusing images in the THz-ViSAR system for non-cooperative moving targets with unknown range migration is proposed. Figure 1 As shown, a moving target refocusing method based on a single channel in a beamforming mode is specifically provided, comprising the following steps:

[0069] Step S100 : constructing a geometric model for imaging a moving target using terahertz video SAR in a spotlight mode, and a mathematical model for obtaining an echo of the moving target using the geometric model.

[0070] Step S110 , obtaining a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, and representing the single-channel echo signal in the form of an echo mathematical model.

[0071] Step S120 , obtaining a two-dimensional image of the ground motion scene according to the single-channel echo signal, and extracting a target image of the moving target from the two-dimensional image.

[0072] In step S130 , an inverse Fourier transform is performed on the target image in azimuth to obtain a one-dimensional range image of the moving target, and a quadratic phase compensation is performed on the target image using an image shift algorithm to obtain a compensated target signal.

[0073] Step S140 , using a linear interpolation adjacent cross-correlation algorithm to perform range envelope alignment on the compensated target signal to correct the nonlinear error term, thereby obtaining a corrected target signal.

[0074] In step S150 , the corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal.

[0075] In step S160 , the processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0076] In this application, a single-channel THz-ViSAR moving target refocusing algorithm in spotlight mode is proposed. This algorithm uses a linear interpolation adjacent cross-correlation algorithm to align the envelope of the refocused range data, improving the similarity between adjacent frames and enhancing the refocused image quality of the moving target.

[0077] In this paper, we first show the inference process of the theoretical part of this method. Assume that the radar emits a pulse with a width of The linear frequency modulation signal is expressed as:

[0078] (1)

[0079] In formula (1), , is the center frequency of the linear FM signal, To adjust the frequency, For quick time, For slow time, is the distance pulse width.

[0080] Then the signal of the moving target P detected by the radar is Expressed as:

[0081] (2)

[0082] In formula (2), is the speed of light, The distance between the radar and the moving target.

[0083] Considering the beamforming mode with the distance from the radar to the irradiation center as the reference distance, the reference signal can be expressed as:

[0084] (3)

[0085] In formula (3), the distance from the radar to the center of the ground motion scene.

[0086] like , the signal after Dechirp processing is:

[0087] (4)

[0088] In formula (4):

[0089] (5)

[0090] After compensating the residual video phase term and distance term, the echo signal can be expressed as:

[0091] (6)

[0092] Then, perform distance Fourier transform on formula (6) to obtain:

[0093] (7)

[0094] In formula (7), 、 They represent the azimuth pulse width and difference frequency respectively.

[0095] Furthermore, a geometric model of THz video SAR moving target imaging is constructed in the spotlight mode, such as Figure 2 As shown, we can get the formula (6) .

[0096] refer to Figure 2 , on the flight trajectory of the radar-carrying platform, the coordinates are Point B is the flight center of the airborne platform, and the flight speed is , the corresponding coordinates of the moving target p are , and its azimuthal velocity is , the acceleration is , the range velocity is , the acceleration is According to the geometric relationship of the imaging model, the distance from the radar to the center of the moving scene can be expressed as:

[0097] (8)

[0098] The distance between the radar and the moving target is expressed as:

[0099] (9)

[0100] Further:

[0101] (10)

[0102] Further sorting out formula (10) yields the motion variation, which is expressed as:

[0103] (11)

[0104] Substituting formula (11) into formula (6), the first-order phase term is expressed as:

[0105] (12)

[0106] The quadratic phase term is expressed as:

[0107] (13)

[0108] The imaging position of the moving target is further described, where the range frequency domain position is:

[0109] (14)

[0110] The azimuth frequency domain position is:

[0111] (15)

[0112] Convert the above distance frequency domain position and azimuth frequency domain position into time domain position:

[0113] (16)

[0114] because, , the main factor affecting the displacement of the moving target is the range velocity. Then formula (15) can be simplified as:

[0115] (17)

[0116] In formula (17), Indicates wavelength.

[0117] According to formula (17), the range velocity can be obtained as:

[0118] (18)

[0119] Furthermore, the modulation frequency in the quadratic phase term of formula (13) is Expressed as:

[0120] (19)

[0121] According to formula (16), the imaging position With real location The relationship in azimuth is:

[0122] (20)

[0123] In formula (20), Since the imaging position in the azimuth direction is offset and there is image expansion and contraction, the expansion coefficient Expressed as:

[0124] (twenty one)

[0125] Stretch factor The expansion factor is proportional to the azimuth spread of the moving target. That is, if the true spread (shadow) of the moving target and the azimuth spread of the target image are known, the azimuth spread of the moving target can be estimated.

[0126] because , the azimuth acceleration has little effect on the defocus of the target. The azimuth velocity, range velocity and range acceleration can all have a significant impact on the imaging of the moving target. For slow-moving targets, formula (19) can be simplified to:

[0127] (twenty two)

[0128] The distance acceleration can be obtained using the following formula:

[0129] (twenty three)

[0130] Because the azimuth frequency modulation It is related to the azimuth velocity and range acceleration. The azimuth frequency modulation is estimated through the image displacement algorithm. , if the azimuth velocity of the moving target is known, the range acceleration can be estimated.

[0131] The above is the derivation process of the theoretical method of this article. Next, the specific steps of this method are introduced.

[0132] In step S100, first construct Figure 2 The geometric model of terahertz video SAR imaging of moving targets in spotlight mode is shown in Figure 1. This geometric model has been introduced above, and based on this geometric model, the distance from the radar to the center of the ground moving scene and the distance from the radar to the moving target are obtained as shown in formulas (8) and (9), which will not be repeated here.

[0133] In step S110, a single-channel video SAR in the terahertz frequency band carried by the aircraft detects the ground motion scene and obtains a single-channel echo signal. The echo signal is represented in the form of an echo mathematical model, namely, formula (4), formula (5), and formula (11).

[0134] In step S120, generating a two-dimensional image of the ground motion scene based on the echo signal includes: compensating the echo data for the residual video phase term and the distance term to obtain an echo signal in the range time domain-azimuth time domain, performing a range and azimuth Fourier transform on the echo signal in the range time domain-azimuth time domain to obtain a two-dimensional image of the ground motion scene.

[0135] Specifically, the echo signal of the range time domain-azimuth time domain is obtained as shown in formula (6).

[0136] Furthermore, in the two-dimensional image of the ground motion scene, the target image of the moving target is extracted and the azimuth inverse Fourier transform is performed to obtain the one-dimensional range image of the moving target, which is expressed as shown in formula (7).

[0137] In step S130, when the image shift algorithm is used to perform quadratic phase compensation on the target image, the azimuth Doppler modulation frequency is obtained by the quadratic phase term of the one-dimensional range image of the moving target, that is, formula (13). Then, the image shift algorithm is used to estimate the actual value of the azimuth Doppler modulation frequency based on the azimuth Doppler modulation frequency, and the azimuth quadratic phase compensation function is constructed. Finally, the azimuth quadratic phase compensation function is used to perform quadratic phase compensation on the target image.

[0138] In this embodiment, after obtaining the quadratic phase term of the one-dimensional range image of the moving target, due to The azimuth acceleration has little effect on the defocus of the target. For slow-moving targets, the azimuth Doppler modulation frequency of the above formula can be simplified to obtain formula (22). As the initial azimuth Doppler modulation frequency, the image shift algorithm is used to estimate the actual value of the azimuth Doppler modulation frequency. , and construct the azimuth quadratic phase compensation function, which is expressed as:

[0139] (twenty four)

[0140] In formula (24), represents the distance frequency, Indicates slow time, Indicates the actual value of the estimated azimuth Doppler modulation frequency.

[0141] Furthermore, formula (24) is multiplied with the one-dimensional range image of the target image represented by formula (7) to obtain the compensated target signal.

[0142] Specifically, the target signal after compensation is expressed as:

[0143] (25)

[0144] in, ;

[0145] In formula (25), Indicates the range position of the moving target imaging, represents the nonlinear term of distance migration, is the error term that is independent of the imaging position, Indicates frequency modulation. represents the speed of light, Indicates the pulse width, represents the center frequency of the linear FM signal, Indicates the flight center coordinates of the radar carrying platform, represents the coordinates of the moving target, Indicates the distance from the radar platform to the center of the motion scene.

[0146] Specifically, This is the nonlinear error term caused by distance migration that needs to be corrected, and is also the part that is ignored in other existing technologies.

[0147] Next, in view of the nonlinear migration in the range migration, which affects the similarity of the inter-frame data and thus affects the alignment of the inter-frame data in the cross-correlation algorithm, the adjacent cross-correlation algorithm with linear interpolation is adopted, and a proportional factor is introduced to interpolate the one-dimensional range image data. The distance envelope is then aligned through the adjacent cross-correlation algorithm to improve the imaging quality of the image.

[0148] In step S140, the range envelope alignment of the compensated target signal is performed using a linear interpolation adjacent cross-correlation algorithm, including: determining a prominent point in the compensated target signal, using the frame data where the prominent point is located as a reference frame, using the frame data before or after the reference frame as a test frame, performing energy normalization processing on the reference frame and the test frame data, aligning the first data position of the test frame with the first data position of the reference frame with the reference frame as a reference, performing proportional interpolation on other data positions of the test frame using a proportional coefficient k, and calculating the maximum cross-correlation value between the interpolated test frame data and the reference frame data. , change the proportional coefficient k, obtain the maximum cross-correlation value between the interpolated test frame data and the reference frame data under different k values, form these cross-correlation maximum values into a cross-correlation maximum value set, determine the proportional coefficient Kmax value corresponding to the maximum value of the cross-correlation maximum value set, perform energy normalization on the other frame data and interpolate with the proportional coefficient Kmax value to form a new data set. In the new data set, take the first frame data as the benchmark, start from the second frame data, use the maximum cross-correlation function as the criterion, align the previous frame data with the next frame data respectively, and complete the envelope alignment of the entire data.

[0149] Furthermore, the product of the azimuth imaging time and the range of the azimuth velocity is used as the range of change of the proportional coefficient k.

[0150] In step S160, when the refocused image of the moving target is corrected for image expansion and then restored to the two-dimensional image of the ground motion scene, the azimuth velocity of the moving target is estimated by the azimuth displacement of the shadow in different data frames, and the azimuth stretch coefficient of the moving target is calculated using formula (21). The moving target image is stretched in the azimuth and the target image is restored to the motion scene.

[0151] In this paper, the effectiveness of the proposed method is also demonstrated through experiments. In the experiments, the imaging of measured data is carried out, and the technical parameters used are shown in Table 1.

[0152]

[0153] Figure 3 This is a target image extracted from the 333rd frame of data from a terahertz video SAR flight test. The moving target is a model car. The terahertz video SAR imaging scene parameters are shown in Table 1.

[0154] Figure 4-Figure 8 For Figure 3 Schematic diagram of the results obtained after each step of the experimental data processing process.

[0155] The aforementioned single-channel moving target refocusing method based on spotlight mode addresses the nonlinear range migration present in the range envelope of moving targets in terahertz video SAR (THz-ViSAR), which is of the same order of magnitude as the wavelength in the terahertz band, resulting in poor envelope alignment. Therefore, a single-channel THz-ViSAR moving target refocusing algorithm in spotlight mode is proposed. This algorithm improves the image quality after envelope alignment by enhancing the similarity of inter-frame data. Compared with other refocusing algorithms, the THz-ViSAR radar system operates at a high frequency and short wavelength, and the tiny range migration is of the same order of magnitude as the radar wavelength, necessitating range envelope alignment. However, range envelope alignment can contain linear range errors. The present invention uses a linear interpolation adjacent cross-correlation algorithm to correct the range position, improve inter-frame data similarity, and facilitate range envelope alignment. Furthermore, this method improves the refocused image quality for moving targets with large range velocity and range acceleration.

[0156] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these 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 these steps, and these steps can be executed in other orders. In addition, Figure 1 At 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.

[0157] In one embodiment, Figure 9 As shown, a moving target refocusing device based on a single channel in a spotlight mode is provided, comprising: an echo mathematical model construction module 200, an echo signal acquisition module 210, a target image extraction module 220, a quadratic phase compensation module 230, a nonlinear error term correction module 240, a signal processing module 250, and a complete image acquisition module 260, wherein:

[0158] The echo mathematical model construction module 200 is used to construct a geometric model for imaging a moving target using terahertz video SAR in a spotlight mode, and to obtain an echo mathematical model of the moving target using the geometric model;

[0159] An echo signal acquisition module 210 is configured to acquire a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0160] a target image extraction module 220 for obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal and extracting a target image of a moving target from the two-dimensional image;

[0161] The secondary phase compensation module 230 is configured to perform an inverse Fourier transform on the target image in azimuth direction to obtain a one-dimensional range image of the moving target, and perform secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal.

[0162] a nonlinear error term correction module 240 for performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct the nonlinear error term and obtain a corrected target signal;

[0163] A signal processing module 250 is configured to process the corrected target signal using phase gradient autofocusing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0164] The complete image acquisition module 260 is used to perform azimuth Fourier transform on the processed target signal to obtain a refocused image of the moving target, perform image scaling correction on the refocused image of the moving target, and then fill it back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0165] Regarding the specific definition of the moving target refocusing device based on a single channel in a spotlight mode, please refer to the definition of the moving target refocusing method based on a single channel in a spotlight mode above, and will not be repeated here. Each module in the above-mentioned moving target refocusing device based on a single channel in a spotlight mode can be implemented in whole or in part by software, hardware, or a combination thereof. Each of the above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0166] In one embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as follows: Figure 10As shown. The computer device includes a processor, a memory, a network interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, a method for refocusing a moving target based on a single channel in a beamforming mode is implemented. The display screen of the computer device can be a liquid crystal display or an electronic ink display screen, and the input device of the computer device can be a touch layer covering the display screen, or a button, trackball or touchpad provided on the computer device housing, or an external keyboard, touchpad or mouse.

[0167] Those skilled in the art will understand that Figure 10 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0168] In one embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the computer program, the following steps are implemented:

[0169] Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model;

[0170] Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0171] Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image;

[0172] Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing a secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0173] Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal;

[0174] The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0175] The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0176] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0177] Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model;

[0178] Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model;

[0179] Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image;

[0180] Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal;

[0181] Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal;

[0182] The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal;

[0183] The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0184] Those skilled in the art will understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the 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-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 DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0185] The technical features of the above embodiments can 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.

[0186] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A moving target refocusing method based on a single channel in a spotlight mode, characterized in that: The method comprises: Construct a geometric model for imaging moving targets using terahertz video SAR in spotlight mode, and a mathematical model for obtaining the echo of moving targets from the geometric model; Acquiring a single-channel echo signal obtained by detecting a ground motion scene using a terahertz video radar, wherein the single-channel echo signal is represented in the form of the echo mathematical model; Obtaining a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extracting a target image of a moving target from the two-dimensional image; Performing an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and performing secondary phase compensation on the target image using an image shift algorithm to obtain a compensated target signal; Performing range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct a nonlinear error term, thereby obtaining a corrected target signal; The corrected target signal is subjected to phase gradient autofocusing processing to perform initial phase correction and high-order phase error compensation to obtain a processed target signal; The processed target signal is subjected to azimuth Fourier transform to obtain a refocused image of the moving target. The refocused image of the moving target is subjected to image scaling correction and then inserted back into the two-dimensional image of the ground motion scene to obtain a complete image.

2. The moving target refocusing method based on a single channel in a spotlight mode according to claim 1, characterized in that: The performing range envelope alignment on the compensated target signal using the adjacent cross-correlation algorithm of linear interpolation includes: Determine a prominent point in the compensated target signal, use the frame data where the prominent point is located as a reference frame, use the frame data before or after the reference frame as a test frame, and perform energy normalization processing on the reference frame and the test frame data; Using the reference frame as a reference, align the first data position of the test frame with the first data position of the reference frame, perform proportional interpolation on the other data positions of the test frame using the proportional coefficient k, and calculate the maximum cross-correlation between the interpolated test frame data and the reference frame data. Changing the proportional coefficient k, obtaining the maximum cross-correlation values between the interpolated test frame data and the reference frame data under different k values, forming a cross-correlation maximum value set with these cross-correlation maximum values, and determining the proportional coefficient Kmax value corresponding to the maximum value of the cross-correlation maximum value set; After performing energy normalization processing on other frame data, interpolation is performed using the proportional coefficient Kmax value to form a new data set; In the new data set, the first frame of data is used as the benchmark, starting from the second frame of data, and taking the maximum cross-correlation function as the criterion, the previous frame of data and the next frame of data are aligned respectively to complete the envelope alignment of the entire data.

3. The moving target refocusing method based on a single channel in a spotlight mode according to claim 2, characterized in that: The product of the azimuth imaging time and the range of the azimuth velocity is used as the range of change of the proportional coefficient k.

4. The moving target refocusing method based on a single channel in a spotlight mode according to claim 3, characterized in that: When the image shift algorithm is used to perform secondary phase compensation on the target image: Obtaining the azimuth Doppler modulation rate through the quadratic phase term of the one-dimensional range image of the moving target; An image shift algorithm is used to estimate the actual value of the azimuth Doppler modulation frequency according to the azimuth Doppler modulation frequency, and an azimuth quadratic phase compensation function is constructed; The quadratic phase compensation function is used to perform quadratic phase compensation on the target image.

5. The moving target refocusing method based on a single channel in a spotlight mode according to claim 4, characterized in that: The azimuth quadratic phase compensation function is expressed as: ； In the above formula, represents the distance frequency, Indicates slow time, Indicates the actual value of the estimated azimuth Doppler modulation frequency.

6. The moving target refocusing method based on a single channel in a spotlight mode according to claim 5, characterized in that: The compensated target signal is expressed as: ； in, ; In the above formula, Indicates the range position of the moving target imaging, represents the nonlinear term of distance migration, is the error term that is independent of the imaging position, Indicates frequency modulation. represents the speed of light, Indicates the pulse width, represents the center frequency of the linear FM signal, Indicates the flight center coordinates of the radar carrying platform, represents the coordinates of the moving target, Indicates the distance from the radar platform to the center of the motion scene.

7. A moving target refocusing device based on a single channel in a beamforming mode, characterized in that: The device comprises: The echo mathematical model construction module is used to construct the geometric model of terahertz video SAR moving target imaging in the spotlight mode, and the echo mathematical model of the moving target obtained from the geometric model; An echo signal acquisition module is used to acquire a single-channel echo signal obtained by detecting a ground motion scene by a terahertz video radar, and the single-channel echo signal is represented in the form of the echo mathematical model; a target image extraction module, configured to obtain a two-dimensional image of a ground motion scene according to the single-channel echo signal, and extract a target image of a moving target from the two-dimensional image; a quadratic phase compensation module, configured to perform an inverse Fourier transform on the target image in azimuth to obtain a one-dimensional range image of the moving target, and perform a quadratic phase compensation on the target image using an image shift algorithm to obtain a compensated target signal; a nonlinear error term correction module, configured to perform range envelope alignment on the compensated target signal using a linear interpolation adjacent cross-correlation algorithm to correct the nonlinear error term, thereby obtaining a corrected target signal; a signal processing module, configured to perform phase gradient autofocusing processing on the corrected target signal, perform initial phase correction and high-order phase error compensation, and obtain a processed target signal; The complete image acquisition module is used to perform azimuth Fourier transform on the processed target signal to obtain a refocused image of the moving target, perform image scaling correction on the refocused image of the moving target, and then fill it back into the two-dimensional image of the ground motion scene to obtain a complete image.

Images