Single-channel moving target refocusing method and device based on bunching mode

Abstract

The invention relates to a single-channel moving target refocusing method and device based on a bunching mode, and the method comprises the steps: detecting a ground moving scene through a terahertz video radar, obtaining a single-channel echo signal, generating a two-dimensional image of the ground moving scene, and extracting a target image of a moving target from the two-dimensional image; the method comprises the following steps of: performing azimuth inverse Fourier transform on a target image to obtain a one-dimensional range image, performing secondary phase compensation by using an image displacement algorithm, and performing range envelope alignment on a compensated signal by using an adjacent cross-correlation algorithm of linear interpolation to correct a nonlinear error term so as to obtain a moving target refocusing image after the nonlinear error term is corrected. And the two-dimensional image is filled with the image to obtain a complete image. By adopting the method, the problem of image defocusing caused by micro-distance migration can be effectively solved.

Description

Technical Field

[0001] The present application relates to the technical field of radar signal processing, and particularly to a method and device for refocusing moving targets based on a single channel in spotlight mode. Background Art

[0002] The working task of a terahertz video synthetic aperture radar (THz-ViSAR) is to continuously obtain high-resolution images of a scene, detect and monitor moving targets in the scene, and, if possible, image or refocus the moving targets. Through the identification of moving targets, it is more conducive to the monitoring of moving targets. For THz-ViSAR, moving targets are non-cooperative targets relative to radar processing, that is, the motion parameters of moving targets are unknown. For non-cooperative moving targets, the refocusing algorithm of moving targets generally performs a keystone transform after parameter estimation to eliminate the cross-interference in the range and azimuth directions, and performs secondary imaging of the moving targets through two-dimensional Fourier transform.

[0003] However, the THz-ViSAR system has a high working frequency and a short wavelength. During the refocusing process, there is non-linear range migration. This range migration can be ignored for low-frequency video synthetic aperture radars (SARs), such as X-band and Ka-band SARs. However, for high-frequency terahertz video SARs, a small amount of range migration will cause image defocusing. However, existing methods for refocusing moving targets in THz-ViSAR ignore the problem of small range migration. Summary of the Invention

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

[0005] A method for refocusing moving targets based on a single channel in spotlight mode, the method includes: Construct a geometric model for imaging moving targets of a terahertz video SAR in spotlight mode, and obtain the echo mathematical model of the moving targets from the geometric model; Obtain a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and represent the single-channel echo signal in the form of the echo mathematical model; Obtain a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extract the target image of the moving target in the two-dimensional image; Perform an inverse azimuth Fourier transform on the target image to obtain the one-dimensional range image of the moving target, and use the image displacement algorithm to perform quadratic phase compensation on the target image to obtain the compensated target signal; Use the adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated target signal to correct the non-linear error term, and obtain the corrected target signal; Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain the processed target signal; Perform an azimuth Fourier transform on the processed target signal to obtain the 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 moving scene to obtain a complete image.

[0006] In one embodiment, the adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated target signal includes: Determine a prominent point in the compensated target signal, use the frame data where the prominent point is located as the reference frame, use the frame data of the previous frame or the next frame of the reference frame as the 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, and perform equal-proportion interpolation on the other data positions of the test frame with a proportionality coefficient k, and calculate the maximum cross-correlation value between the interpolated test frame data and the reference frame data; Change the equal-proportion coefficient k, obtain the maximum cross-correlation values between the interpolated test frame data and the reference frame data under different k values, form a set of maximum cross-correlation values, and determine the proportionality coefficient Kmax value corresponding to the maximum value in the set of maximum cross-correlation values; Perform energy normalization processing on the other frame data and perform interpolation with the proportionality coefficient Kmax value to form a new data set; In the new data set, using the first frame data as a benchmark, starting from the second frame data, using the maximum cross-correlation function as a criterion, align the previous frame data and the next frame data respectively to complete the envelope alignment of the entire data.

[0007] In one embodiment, the product value of the azimuth imaging time and the range of the azimuth velocity is used as the change range of the proportionality coefficient k.

[0008] In one embodiment, when using the image displacement algorithm to perform quadratic phase compensation on the target image: Obtain the azimuth Doppler modulation frequency through the quadratic phase term of the one-dimensional range image of the moving target; Adopt an image displacement algorithm to estimate the actual value of the azimuth Doppler modulation frequency according to the azimuth Doppler modulation frequency, and construct an azimuth quadratic phase compensation function; Use the azimuth quadratic phase compensation function to perform quadratic phase compensation on the target image.

[0009] In one embodiment, the azimuth quadratic phase compensation function is expressed as: ; In the above formula, represents the range frequency, represents the slow time, represents the actual value of the estimated azimuth Doppler modulation frequency.

[0010] In one embodiment, the compensated target signal is expressed as: ; Wherein, ; In the above formula, represents the range direction position of the moving target imaging, represents the non - linear term of range migration, is an error term independent of the imaging position, represents the modulation frequency, represents the speed of light, represents the pulse width, represents the center frequency of the chirp signal, represents the flight center coordinates of the radar - carrying platform, represents the coordinates of the moving target, represents the distance from the radar - carrying platform to the center of the moving scene.

[0011] This application also provides a moving target refocusing device based on a single - channel in spotlight mode. The device includes: An echo mathematical model construction module, configured to construct a geometric model of moving target imaging in terahertz video SAR in spotlight mode, and obtain an echo mathematical model of the moving target from the geometric model; An echo signal acquisition module, configured to acquire a single - channel echo signal obtained by a terahertz video radar detecting a ground moving scene, 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 the ground moving scene according to the single - channel echo signal, and extract a target image of the moving target from the two - dimensional image; The quadratic phase compensation module is used to perform inverse azimuth Fourier transform on the target image to obtain the one-dimensional range image of the moving target, and adopt the image displacement algorithm to perform quadratic phase compensation on the target image to obtain the compensated target signal; The non-linear error term correction module is used to correct the non-linear error term by performing range envelope alignment on the compensated target signal by using the adjacent cross-correlation algorithm with linear interpolation to obtain the corrected target signal; The signal processing module is used to perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation to obtain the processed target signal; The complete image obtaining module is used to perform azimuth Fourier transform on the processed target signal to obtain the refocused image of the moving target, and after performing image scaling correction on the refocused image of the moving target, fill it back into the two-dimensional image of the ground moving scene to obtain the complete image.

[0012] A computer device includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the following steps are implemented: Construct a geometric model for imaging moving targets in a spotlight-mode terahertz video SAR, and obtain the echo mathematical model of the moving target from the geometric model; Obtain a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and the single-channel echo signal is represented in the form of the echo mathematical model; Obtain a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extract the target image of the moving target in the two-dimensional image; Perform inverse azimuth Fourier transform on the target image to obtain the one-dimensional range image of the moving target, and adopt the image displacement algorithm to perform quadratic phase compensation on the target image to obtain the compensated target signal; Perform range envelope alignment on the compensated target signal by using the adjacent cross-correlation algorithm with linear interpolation to correct the non-linear error term to obtain the corrected target signal; Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation to obtain the processed target signal; Perform azimuth Fourier transform on the processed target signal to obtain the refocused image of the moving target, and after performing image scaling correction on the refocused image of the moving target, fill it back into the two-dimensional image of the ground moving scene to obtain the complete image.

[0013] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the following steps are implemented: Construct a geometric model for terahertz video SAR moving target imaging in spotlight mode, and obtain the echo mathematical model of the moving target from the geometric model; Obtain a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and represent the single-channel echo signal in the form of the echo mathematical model; Obtain a two-dimensional image of the ground moving scene based on the single-channel echo signal, and extract the target image of the moving target from the two-dimensional image; Perform an inverse Fourier transform in the azimuth direction on the target image to obtain a one-dimensional range image of the moving target, and use an image migration algorithm to perform quadratic phase compensation on the target image to obtain a compensated target signal; Use the adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated target signal to correct the non-linear error term, and obtain a corrected target signal; Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain a processed target signal; Perform a Fourier transform in the azimuth direction 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 moving scene to obtain a complete image.

[0014] Beneficial effects: The above-mentioned method and device for refocusing moving targets based on a single channel in spotlight mode generate a two-dimensional image of the ground moving scene according to the single-channel echo signal detected by the terahertz video radar, extract the target image of the moving target from it, perform an inverse Fourier transform in the azimuth direction on the target image to obtain a one-dimensional range image, perform quadratic phase compensation using an image migration algorithm, and then use the adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated signal to correct the non-linear error term, thereby obtaining a refocused image of the moving target with the non-linear error term corrected, and filling it back into the two-dimensional image to obtain a complete image. Using this method can effectively solve the problem of image defocus caused by small range migration. Description of the drawings

[0015] Figure 1 It is a schematic flow chart of a method for refocusing moving targets based on a single channel in spotlight mode in an embodiment; Figure 2 It is a schematic diagram of the imaging geometric model of a squinted spotlight mode THz-ViSAR moving target in an embodiment; Figure 3 It is a schematic diagram of the moving target image extracted from a certain moving scene in an experiment; Figure 4 It is a schematic diagram of an unaligned one-dimensional range image in an experiment; Figure 5 Schematic diagram of one-dimensional range profile with envelope alignment in an experiment; Figure 6 Schematic diagram of the target image with moving target refocusing in an experiment; Figure 7 Schematic diagram of the imaging result after compensating the moving target in an experiment; Figure 8 Schematic diagram of the target image formed by envelope alignment of the cross-correlation algorithm in an experiment; Figure 9 Block diagram of the structure of a moving target refocusing device based on a single-channel in spotlight mode in an embodiment; Figure 10 Internal structure diagram of a computer device in an embodiment. Specific implementation manners

[0016] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0017] Aiming at the problem in the prior art that there is a non-linear range migration amount in the range envelope of a moving target in a terahertz video SAR, and this migration amount is of the same order of magnitude as the wavelength of the terahertz band, and the effect of envelope alignment is poor, a method for obtaining a high-quality refocused image in a THz-ViSAR system of a non-cooperative moving target with unknown range migration amount is proposed. As Figure 1 shown, specifically, a moving target refocusing method based on a single-channel in spotlight mode includes the following steps: Step S100, constructing a geometric model for imaging a moving target in a terahertz video SAR in spotlight mode, and obtaining a mathematical echo model of the moving target from the geometric model.

[0018] Step S110, obtaining a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and representing the single-channel echo signal in the form of the mathematical echo model.

[0019] Step S120, obtaining a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extracting the target image of the moving target in the two-dimensional image.

[0020] Step S130, performing an inverse azimuth Fourier transform on the target image to obtain a one-dimensional range profile of the moving target, and performing quadratic phase compensation on the target image by using an image displacement algorithm to obtain a compensated target signal.

[0021] Step S140: Perform range envelope alignment on the compensated target signal using the adjacent cross-correlation algorithm with linear interpolation to correct the non-linear error term, and obtain the corrected target signal.

[0022] Step S150: Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain the processed target signal.

[0023] Step S160: Perform azimuth Fourier transform on the processed target signal to obtain the refocused image of the moving target. After performing image scaling correction on the refocused image of the moving target, it is filled back into the two-dimensional image of the ground moving scene to obtain the complete image.

[0024] In this application, a spotlight-mode single-channel THz-ViSAR moving target refocusing algorithm is proposed. This algorithm uses the adjacent cross-correlation algorithm with linear interpolation to perform envelope alignment on the range data under refocusing, improve the similarity between adjacent frame data, and improve the quality of the refocused image of the moving target.

[0025] In this article, first, the inference process of the theoretical part of this method is presented. Assume that the radar emits a linear frequency modulation signal with a pulse width of which is expressed as: (1) In formula (1), , is the center frequency of the linear frequency modulation signal, is the frequency modulation rate, is the fast time, is the slow time, is the range pulse width.

[0026] Then the signal received by the radar structure from the moving target P is expressed as: (2) In formula (2), is the speed of light, is the distance from the radar to the moving target.

[0027] Considering the spotlight mode with the distance from the radar to the illumination center as the reference distance, the reference signal can be expressed as: (3) In formula (3), the distance from the radar to the center of the ground moving scene.

[0028] If , the signal after Dechirp processing is: (4) In formula (4): (5) After compensating the residual video phase term and the range term, the echo signal can be expressed as: (6) Next, perform a range Fourier transform on formula (6) to obtain: (7) In formula (7), 、 respectively represent the azimuth pulse width and the difference frequency.

[0029] Furthermore, construct a geometric model for imaging moving targets in terahertz video SAR in the spotlight mode, as Figure 2 shown, so as to obtain in formula (6).

[0030] Refer to Figure 2 , on the flight trajectory of the radar-carrying platform, point B with coordinates is the flight center of the airborne platform, and the flight speed is . The coordinates of the corresponding moving target p are , its azimuth speed is , the acceleration is , the range speed is , and the acceleration is . Then, 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: (8) And the distance from the radar to the moving target is expressed as: (9) Furthermore: (10) Further organize formula (10) to obtain the motion change amount, which is expressed as: (11) Substitute formula (11) into formula (6) to obtain that the first-order phase term is expressed as: (12) And the second-order phase term is expressed as: (13) Furthermore, the imaging position of the moving target, where the range frequency domain position is: (14) The azimuth frequency domain position is: (15) Converting the above-mentioned range to frequency-domain position and azimuth frequency-domain position into time-domain position gives: (16) Since , the main factor affecting the offset of the moving target is the range velocity. Then formula (15) can be simplified to: (17) In formula (17), represents the wavelength.

[0031] Then according to formula (17), the range velocity can be obtained and expressed as: (18) Furthermore, the chirp rate in the quadratic phase term of formula (13) is expressed as: (19) And according to formula (16), it can be known that the imaging position and the true position have the following relationship in the azimuth direction: (20) In formula (20), . Since the imaging position in the azimuth direction is offset and there is image stretching, the stretching coefficient is expressed as: (21) The stretching coefficient is related to the azimuth velocity of the moving target. The stretching coefficient is proportional to the broadening of the moving target in the azimuth direction. That is, given the true broadening (shadow) of the moving target and the broadening of the target image in the azimuth direction, the azimuth velocity of the moving target can be estimated.

[0032] Since , the azimuth acceleration has little effect on the defocusing of the target. The azimuth velocity, range velocity, and range acceleration can all have a greater impact on the imaging of the moving target. For slow-moving targets, formula (19) can be simplified to: (22) Then the range acceleration can be obtained using the following formula: (23) Since the azimuth chirp rate is related to the azimuth velocity and range acceleration, by using the image displacement algorithm, the azimuth chirp rate , given the azimuth velocity of a moving target, the range acceleration can be estimated.

[0033] The above is the derivation process of the method theory in this paper. Next, the specific steps of this method will be introduced.

[0034] In step S100, first construct a geometric model of moving target imaging of terahertz video SAR in spotlight mode as shown in Figure 2 . This geometric model has been introduced above, and based on this geometric model, the distances from the radar to the center of the ground moving scene and from the radar to the moving target shown in formulas (8) and (9) are obtained, which will not be elaborated here.

[0035] In step S110, a single-channel video SAR in the terahertz band carried on an aircraft detects the ground moving scene to obtain a single-channel echo signal. And this echo signal is represented in the form of an echo mathematical model, namely formulas (4), (5) and (11).

[0036] In step S120, generating a two-dimensional image of the ground moving scene from the echo signal includes: after compensating the residual video phase term and range term for the echo data, obtaining the echo signal in range time domain - azimuth time domain, and performing range and azimuth Fourier transforms on the echo signal in range time domain - azimuth time domain to obtain a two-dimensional image of the ground moving scene.

[0037] Specifically, the echo signal in range time domain - azimuth time domain is obtained as shown in formula (6).

[0038] Furthermore, in the two-dimensional image of the ground moving scene, extract the target image of the moving target and perform inverse azimuth Fourier transform to obtain the one-dimensional range image of the moving target, and its expression is as shown in formula (7).

[0039] In step S130, when using the image migration algorithm to perform quadratic phase compensation on the target image: obtain the azimuth Doppler modulation rate through the quadratic phase term of the one-dimensional range image of the moving target, namely formula (13), then use the image migration algorithm to estimate the actual value of the azimuth Doppler modulation rate according to the azimuth Doppler modulation rate, and construct an azimuth quadratic phase compensation function. Finally, use the azimuth quadratic phase compensation function to perform quadratic phase compensation on the target image.

[0040] In this embodiment, after obtaining the quadratic phase term of the one-dimensional range image of the moving target, since , the defocusing effect of the azimuth acceleration on the target is very small. For slow moving targets, the azimuth Doppler modulation rate in the above formula can be simplified to obtain formula (22), and the obtained from this formulaAs the initial azimuth Doppler frequency modulation rate, the image displacement algorithm is adopted to estimate the actual value of the azimuth Doppler frequency modulation rate , and construct the azimuth quadratic phase compensation function, expressed as: (24) In formula (24), represents the range frequency, represents the slow time, represents the actual value of the estimated azimuth Doppler frequency modulation rate.

[0041] Furthermore, multiply formula (24) by the one-dimensional range image of the target image expressed by formula (7) to obtain the compensated target signal.

[0042] Specifically, the compensated target signal is expressed as: (25) Among them, ; In formula (25), represents the range direction position of the moving target imaging, represents the non-linear term of range migration, is the error term independent of the imaging position, represents the frequency modulation rate, represents the speed of light, represents the pulse width, represents the center frequency of the chirp signal, represents the flight center coordinates of the radar carrying platform, represents the coordinates of the moving target, represents the distance from the radar carrying platform to the center of the moving scene.

[0043] Specifically, is the non-linear error term caused by range migration that needs to be corrected, and this is also the part ignored in other existing technologies.

[0044] Then, aiming at the non-linear migration amount existing in range migration, which affects the similarity of inter-frame data and thus affects the alignment of inter-frame data in the cross-correlation algorithm, the adjacent cross-correlation algorithm with linear interpolation is adopted, a scaling factor is introduced, the one-dimensional range image data is interpolated, and then the range envelope alignment is performed through the adjacent cross-correlation algorithm to improve the imaging quality of the image.

[0045] In step S140, the range envelope alignment of the compensated target signal using the adjacent cross-correlation algorithm with linear interpolation includes: determining a special display point in the compensated target signal, using the data of the frame where the special display point is located as the reference frame, using the data of the frame before or after the reference frame as the 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 the reference, and performing equal-proportion interpolation on the other data positions of the test frame with a proportionality coefficient k. Calculate the maximum cross-correlation value between the interpolated test frame data and the reference frame data, change the equal-proportion coefficient k, obtain the maximum cross-correlation values between the interpolated test frame data and the reference frame data under different k values, form a set of maximum cross-correlation values from these maximum cross-correlation values, determine the value of the proportionality coefficient Kmax corresponding to the maximum value in the set of maximum cross-correlation values, perform energy normalization processing on the data of other frames and then perform interpolation with the proportionality coefficient Kmax value to form a new data set. In the new data set, using the first frame data as the benchmark, starting from the second frame data, using the maximum cross-correlation function as the criterion, align the previous frame data and the next frame data respectively to complete the envelope alignment of the entire data.

[0046] Further, take the product value of the azimuth imaging time and the range of the azimuth velocity as the change range of the proportionality coefficient k.

[0047] In step S160, when compensating the refocused image of the moving target back to the two-dimensional image of the ground moving scene after image scaling correction, estimate the azimuth velocity of the moving target through the displacement of the shadow in the azimuth direction in different data frames, calculate the azimuth stretching coefficient of the moving target using formula (21), stretch the moving target image in the azimuth direction, and compensate the target image back to the moving scene.

[0048] In this article, the effectiveness of the method in this article is also demonstrated through experiments. In the experiment, the imaging of measured data is carried out, and the technical parameters used are shown in Table 1.

[0049]

[0050] Figure 3 It is the target image extracted from the image formed by the 333rd frame data of a certain flight test of a terahertz video SAR, and the moving target is a model car. The imaging scene parameters of the terahertz video SAR are shown in Table 1.

[0051] Figures 4 - 8 For Figure 3 It is the schematic diagram of the results obtained after each step in the processing of the experimental data shown.

[0052] In the above-mentioned moving target refocusing method based on a single channel in the spotlight mode, there is a non-linear range migration amount in the range envelope of the moving target in the terahertz video SAR. This migration amount is of the same order of magnitude as the wavelength in the terahertz frequency band, and the effect of envelope alignment is poor. A single-channel THz-ViSAR moving target refocusing algorithm in the spotlight mode is proposed. By improving the similarity of inter-frame data, the imaging quality after envelope alignment is improved. Compared with other refocusing algorithms, the radar of the THz-ViSAR system has a high operating frequency and a short wavelength. The small migration in the range direction is of the same order of magnitude as the radar wavelength, and range envelope alignment needs to be considered. However, there is a linear range error in range envelope alignment. In the present invention, the linear interpolation adjacent cross-correlation algorithm is used to correct the range position, improve the similarity of inter-frame data, and facilitate range envelope alignment. At the same time, this method improves the refocused image quality when the moving target has a large range velocity and range acceleration.

[0053] It should be understood that although Figure 1 the steps in the flowchart of Figure 1 are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise clearly stated in this article, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover,

[0054] In one embodiment, as Figure 9 shown, a moving target refocusing device based on a single channel in the spotlight mode is provided, including: 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 non-linear error term correction module 240, a signal processing module 250, and a complete image obtaining module 260, where: The echo mathematical model construction module 200 is used to construct a geometric model for imaging a moving target in terahertz video SAR in the spotlight mode, and obtain an echo mathematical model of the moving target from the geometric model; The echo signal acquisition module 210 is used to acquire a single-channel echo signal obtained by detecting a ground moving 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 220, 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 secondary phase compensation module 230, configured to perform an inverse azimuth Fourier transform on the target image to obtain a one-dimensional range image of the moving target, and perform secondary phase compensation on the target image by using an image displacement algorithm to obtain a compensated target signal; A non-linear error term correction module 240, configured to perform range envelope alignment on the compensated target signal by using a linear interpolation-based adjacent cross-correlation algorithm to correct the non-linear error term, and obtain a corrected target signal; A signal processing module 250, configured to perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain a processed target signal; A complete image obtaining module 260, configured to perform an 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 supplement it back into the two-dimensional image of the ground motion scene to obtain a complete image.

[0055] For the specific limitations on the moving target refocusing device based on the single-channel in the spotlight mode, reference can be made to the limitations on the moving target refocusing method based on the single-channel in the spotlight mode in the foregoing text, which will not be elaborated herein. Each module in the above-mentioned moving target refocusing device based on the single-channel in the spotlight mode can be implemented in whole or in part by software, hardware, and their combination. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or stored in the memory in the computer device in the form of software, so as to facilitate the processor to call and execute the operations corresponding to the above-mentioned modules.

[0056] In one embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as Figure 10As shown in the figure. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected through a system bus. Among them, 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 computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it realizes a method for refocusing moving targets in a single channel based on a spotlight mode. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer covered on the display screen, or a button, a trackball, or a touchpad provided on the outer shell of the computer device, or an external keyboard, a touchpad, or a mouse, etc.

[0057] Those skilled in the art can understand that Figure 10 the structure shown in the figure is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0058] In one embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory. When the processor executes the computer program, the following steps are implemented: Construct a geometric model for imaging moving targets of a terahertz video SAR in a spotlight mode, and obtain an echo mathematical model of the moving targets from the geometric model; Obtain a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and the single-channel echo signal is represented in the form of the echo mathematical model; Obtain a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extract a target image of the moving target in the two-dimensional image; Perform an inverse Fourier transform in the azimuth direction on the target image to obtain a one-dimensional range image of the moving target, and use an image displacement algorithm to perform quadratic phase compensation on the target image to obtain a compensated target signal; Use the adjacent cross-correlation algorithm of linear interpolation to perform range envelope alignment on the compensated target signal to correct the non-linear error term, and obtain a corrected target signal; Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain a processed target signal; Perform azimuth Fourier transform on the processed target signal to obtain a re-focused image of the moving target. After performing image scaling correction on the re-focused image of the moving target, it is filled back into the two-dimensional image of the ground moving scene to obtain a complete image.

[0059] 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: Construct a geometric model for terahertz video SAR moving target imaging in spotlight mode, and obtain an echo mathematical model of the moving target from the geometric model; Obtain a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and the single-channel echo signal is represented in the form of the echo mathematical model; Obtain a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extract the target image of the moving target in the two-dimensional image; Perform inverse azimuth Fourier transform on the target image to obtain a one-dimensional range image of the moving target, and use an image displacement algorithm to perform quadratic phase compensation on the target image to obtain a compensated target signal; Use the adjacent cross-correlation algorithm of linear interpolation to perform range envelope alignment on the compensated target signal to correct the non-linear error term, and obtain a corrected target signal; Perform phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtain a processed target signal; Perform azimuth Fourier transform on the processed target signal to obtain a re-focused image of the moving target. After performing image scaling correction on the re-focused image of the moving target, it is filled back into the two-dimensional image of the ground moving scene to obtain a complete image.

[0060] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memories. Non-volatile memories can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memories can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0061] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0062] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A moving target refocusing method based on a single channel in spotlight mode, characterized in that The method includes: Constructing a geometric model for terahertz video SAR moving target imaging in spotlight mode, and obtaining an echo mathematical model of the moving target from the geometric model; Obtaining a single-channel echo signal detected by a terahertz video radar for a ground moving scene, and representing the single-channel echo signal in the form of the echo mathematical model; Obtaining a two-dimensional image of the ground moving scene according to the single-channel echo signal, and extracting a target image of the moving target in the two-dimensional image; Performing an inverse Fourier transform in the azimuth direction on the target image to obtain a one-dimensional range image of the moving target, and using an image displacement algorithm to perform quadratic phase compensation on the target image to obtain a compensated target signal; Using an adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated target signal to correct the non-linear error term, and obtaining a corrected target signal; Performing phase gradient autofocus processing on the corrected target signal to perform initial phase correction and high-order phase error compensation, and obtaining a processed target signal; Performing a Fourier transform in the azimuth direction on the processed target signal to obtain a refocused image of the moving target, and performing image scaling correction on the refocused image of the moving target and then filling it back into the two-dimensional image of the ground moving scene to obtain a complete image.

2. The method for refocusing a moving target based on a single channel in a spotlight mode according to claim 1, wherein The using an adjacent cross-correlation algorithm with linear interpolation to perform range envelope alignment on the compensated target signal includes: 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 of the previous frame or the next frame of the reference frame as a test frame, and performing energy normalization processing on the reference frame and the test frame data; Using the reference frame as a reference, aligning the first data position of the test frame with the first data position of the reference frame, and equally interpolating the other data positions of the test frame with a proportionality coefficient k, and calculating the maximum cross-correlation value between the interpolated test frame data and the reference frame data; Changing the proportionality 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 set of maximum cross-correlation values from these maximum cross-correlation values, and determining the proportionality coefficient Kmax value corresponding to the maximum value in the set of maximum cross-correlation values; Performing energy normalization processing on the other frame data and then interpolating with the proportionality coefficient Kmax value to form a new data set; In the new data set, using the first frame data as a benchmark, starting from the second frame data, using the maximum cross-correlation function as a criterion, aligning the previous frame data and the next frame data respectively to complete the envelope alignment of the entire data.

3. The method for refocusing a moving target based on a single-channel in a spotlight mode according to claim 2, wherein Taking the product value of the azimuth imaging time and the range of the azimuth velocity as the changing range of the proportionality coefficient k.

4. The method for refocusing a moving target based on a single-channel in a spotlight mode according to claim 3, wherein When using an image displacement algorithm to perform quadratic phase compensation on the target image: Obtaining the azimuth Doppler modulation rate through the quadratic term phase term of the one-dimensional range image of the moving target; Using an image displacement algorithm to estimate the actual value of the azimuth Doppler modulation rate according to the azimuth Doppler modulation rate, and constructing an azimuth quadratic phase compensation function; Using the azimuth quadratic phase compensation function to perform quadratic phase compensation on the target image.

5. The method for refocusing a moving target 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 range frequency, represents the slow time, represents the actual value of the estimated azimuth Doppler modulation frequency.

6. The method for refocusing a moving target based on a single-channel in a spotlight mode according to claim 5, wherein The compensated target signal is expressed as: ； Among them, ; In the above formula, represents the range position of the moving target imaging, represents the non - linear term of range migration, is the error term independent of the imaging position, represents the chirp rate, represents the speed of light, represents the pulse width, represents the center frequency of the chirp signal, represents the flight center coordinates of the radar - carrying platform, represents the coordinates of the moving target, represents the distance from the radar - carrying platform to the center of the moving scene.

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

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