Terahertz radar-based focused imaging method, apparatus, device, and medium

Abstract

The application relates to a terahertz radar-based focusing imaging method, device, equipment and medium. The method comprises the following steps: obtaining echo signals of a uniformly rotating large-size target based on a terahertz radar, performing distance-direction pulse compression and azimuth-direction FFT on the echo signals to obtain a two-dimensional RD imaging result, estimating the rotation speed and longitudinal distance center offset of the target according to the spatial distribution law of the PSF inclination of each defocused point in the two-dimensional RD imaging result, constructing a final phase compensation function according to the finally estimated rotation speed and longitudinal distance center offset, performing second-order spatially-varying phase compensation and azimuth-direction FFT on a one-dimensional distance image after Keystone transformation according to the final phase compensation function, and obtaining a finally focused RD image. The method can reduce the calculation search amount of terahertz radar RD focusing imaging and improve the focusing accuracy.

Description

Technical Field

[0001] This application relates to the field of terahertz radar imaging technology, and in particular to a focusing imaging method, apparatus, device and medium based on terahertz radar. Background Technology

[0002] Terahertz radar, characterized by its large bandwidth and short wavelength, offers higher range and azimuth resolution compared to traditional microwave bands when imaging targets using Inverse Synthetic Aperture Radar (ISAR). Due to this higher resolution, when terahertz radar performs range Doppler (RD) imaging on large, uniformly rotating targets, even with a small accumulation angle (3°–5°), significant range cell migration (RCM) can easily occur, leading to range and azimuth defocusing in the imaging results. Existing methods for addressing first-order RCM in RD imaging typically employ Keystone transform for parametric ground correction of range migration, followed by two-dimensional imaging of the Keystone-transformed data. However, when the target's longitudinal dimension is large, traditional Keystone transform alone is insufficient. The second-order phase cannot be ignored, and the influence of the second-order Taylor expansion phase term on azimuth imaging must be considered. The key to second-order phase compensation is obtaining the target's rotational speed and longitudinal range center offset information.

[0003] Currently, existing rotational velocity estimation methods can be broadly categorized into three types. The first type estimates parameters based on the correlation coefficient of the signal phase, including demodulation estimation, Radon-Wigner transform, and discrete polynomial phase transform. The accuracy of this type of algorithm largely depends on the quality of the extracted scattering points; when the signal-to-noise ratio is low or there are many signal components, the estimation accuracy will decrease significantly. The second type estimates the rotational velocity based on the correlation between adjacent frames of the target during rotation, including correlation methods, affine projection matrix methods, and image feature registration methods. This type of algorithm requires a long observation time and involves a large computational burden in image processing. The third type of algorithm takes the overall image quality as the criterion and proposes methods based on minimum image entropy and maximum image contrast. This type of method makes full use of the overall image information and is suitable for target rotational velocity estimation under low signal-to-noise ratio conditions, with high estimation accuracy. However, by using minimum image entropy or maximum contrast, it is necessary to solve for two variables, which not only involves a large search computation but is also affected by individual strong scattering points of the target, making it difficult to accurately focus scattering points that are farther from the rotation center, have weaker scattering, and are more defocused. Summary of the Invention

[0004] Therefore, it is necessary to provide a terahertz radar-based focusing imaging method, apparatus, equipment, and medium that can reduce the computational search volume of terahertz radar RD focusing imaging and improve the focusing accuracy, in order to address the above-mentioned technical problems.

[0005] A focusing imaging method based on terahertz radar, the method comprising:

[0006] Acquiring echo signals from uniformly rotating large targets using terahertz radar;

[0007] Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT (Fast Fourier Transform) on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotational speed and longitudinal range center offset are set according to the spatial distribution law of the PSF (Point Spread Function) tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0008] The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by combining image preprocessing with Hough transform. A tilt threshold is set, and the estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0009] The final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance center offset. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on the final phase compensation function to obtain the final focused RD image. The Keystone-transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0010] In one embodiment, acquiring the echo signal of a large, uniformly rotating target based on terahertz radar includes:

[0011] The original echo data of a large target rotating at a constant speed is obtained by acquiring the original echo data using terahertz radar. The original echo data is then processed by demodulation and second-order Taylor expansion to obtain the echo signal.

[0012] In one embodiment, the spatial distribution pattern of the PSF tilt of the defocus in the two-dimensional RD imaging result is as follows:

[0013] When the longitudinal distance center offset of the target estimation is zero, the PSF tilt of each focal point in the two-dimensional RD imaging results has a distribution characteristic that is symmetric about the x-axis and symmetric about the y-axis at the same time.

[0014] When the estimated rotational velocity of the target is the actual rotational velocity of the target, the PSF tilt of each focal point in the two-dimensional RD imaging result has a distribution characteristic symmetrical about the y-axis, and for points with the same abscissa in the two-dimensional RD imaging result, the PSF tilt of their imaging results is the same.

[0015] When there are errors in the longitudinal distance center offset and rotation speed of the target estimation, the PSF tilt of each focal point in the two-dimensional RD imaging result has a distribution characteristic that is symmetric about the y-axis but asymmetrical about the x-axis, and for points with the same abscissa in the two-dimensional RD imaging result, the PSF tilt of the imaging result is different.

[0016] In one embodiment, the phase compensation function is constructed from the target's estimated rotational velocity and longitudinal distance center offset, denoted as:

[0017]

[0018] Where Δy represents the longitudinal distance center offset of the target estimate, The target's estimated rotational speed is represented by exp, which represents an exponential function with base e, j represents the imaginary unit, c is the speed of light, and t is the speed of light. m The azimuth time is the slowest time, y is the vertical axis, and f is the horizontal axis. c This is the radar carrier frequency.

[0019] In one embodiment, the PSF tilt of each divergence point in the spatially phase-compensated 2D RD image is estimated using image preprocessing combined with Hough transform, including:

[0020] Image preprocessing is performed on the two-dimensional RD image after spatial phase compensation to extract the parallelogram contours of each divergence point PSF in the two-dimensional RD image.

[0021] The extracted parallelogram contour is subjected to Hough transform to detect the longitudinal straight lines in the parallelogram contour, and the angle between the longitudinal straight lines and the vertical axis is used as the PSF tilt of each divergence point.

[0022] In one embodiment, the image preprocessing method includes sub-image segmentation, image grayscale conversion, binarization, edge smoothing, contour extraction, and noise removal.

[0023] In one embodiment, a final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance-center offset distance. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on this final phase compensation function to obtain the final focused RD image, represented as:

[0024]

[0025] Among them, f r For the range frequency, f a Indicates the azimuth Doppler frequency. For the final phase compensation function, Δy final For the final estimated longitudinal distance center offset, For the final estimated rotational speed, For echo signal, Indicates the distance and time. Perform a Fast Fourier Transform (FFT), where KT() represents a Keystone Transform on the echo signal. Indicates the time t for the direction. m Perform a Fast Fourier Transform.

[0026] A focusing imaging device based on terahertz radar, the device comprising:

[0027] The signal acquisition module is used to acquire the echo signal of a large target rotating at a constant speed based on terahertz radar.

[0028] The phase compensation module is used to perform range pulse compression on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. Then, a phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. Finally, azimuth FFT is performed on the phase-compensated one-dimensional range image to obtain a spatially variable phase-compensated two-dimensional RD image.

[0029] The tilt estimation module is used to estimate the PSF tilt of each divergence point in the spatially phase-compensated 2D RD image by combining image preprocessing with Hough transform, and to set a tilt threshold. It then iterates through the estimated rotation speed and longitudinal distance from the center until the estimated PSF tilt is less than the set tilt threshold, and uses the rotation speed and longitudinal distance from the center obtained from the current traversal search as the final estimated rotation speed and longitudinal distance from the center.

[0030] The focusing imaging module is used to construct the final phase compensation function based on the final estimated rotational speed and longitudinal distance center offset distance. Based on the final phase compensation function, second-order spatially variable phase compensation and azimuth FFT are performed on the Keystone transformed one-dimensional range image to obtain the final focused RD image. The Keystone transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0031] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program performing the following steps:

[0032] Acquiring echo signals from uniformly rotating large targets using terahertz radar;

[0033] Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0034] The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by combining image preprocessing with Hough transform. A tilt threshold is set, and the estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0035] The final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance center offset. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on the final phase compensation function to obtain the final focused RD image. The Keystone-transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0036] A computer-readable storage medium having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0037] Acquiring echo signals from uniformly rotating large targets using terahertz radar;

[0038] Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0039] The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by combining image preprocessing with Hough transform. A tilt threshold is set, and the estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0040] The final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance center offset. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on the final phase compensation function to obtain the final focused RD image. The Keystone-transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0041] Compared with existing technologies, the above-mentioned focusing imaging method, device, equipment, and medium based on terahertz radar have the following advantages:

[0042] 1. This application is based on a focusing imaging method of terahertz radar. Compared with traditional microwave frequency radar, it can give full play to the high resolution advantage of terahertz radar, and is especially effective for large-size targets.

[0043] 2. This application estimates the longitudinal distance to the center of the target and the rotational speed based on the tilt of the PSF of the defocus point. Compared with the traditional method of parameter estimation based on minimum entropy or maximum contrast, this application can avoid calculating the scattering intensity of each scattering point, thus avoiding the risk of interference from strong scattering points during the traversal solution process based on minimum entropy. Especially when the strong scattering point is close to the rotation center and the defocus is not obvious, its large amplitude value will make the minimum entropy method insensitive to parameter solution, resulting in a large estimation error. However, this application can avoid the influence of strong scattering points by analyzing the tilt of the PSF shape of the defocus point, and can solve for points with more severe defocus multiple times, thereby improving the estimation accuracy and focusing precision.

[0044] 3. The method of this application analyzes the spatial distribution law of the PSF tilt of the divergence point, which can quickly determine the estimation accuracy and approximate search range of the two estimated parameters, rotation speed and longitudinal distance center offset. Compared with the traditional large-scale traversal search, it can greatly reduce the amount of computation and improve the parameter estimation efficiency. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating a focusing imaging method based on terahertz radar in one embodiment;

[0046] Figure 2 This is a schematic diagram of a simulated point target in one embodiment;

[0047] Figure 3 This is a schematic diagram of a one-dimensional range profile and RD imaging result of the echo signal in one embodiment, wherein, Figure 3 (a) is a schematic diagram of the one-dimensional range profile of the echo signal. Figure 3 (b) is a schematic diagram of the RD imaging results of the echo signal;

[0048] Figure 4 This is a schematic diagram of a one-dimensional range image and RD imaging result after Keystone transformation in one embodiment, wherein, Figure 4 (a) is a schematic diagram of the one-dimensional range image after Keystone transformation. Figure 4 (b) is a schematic diagram of the RD imaging results after Keystone transformation;

[0049] Figure 5 This is a schematic diagram of the RD imaging results after second-order spatially variable phase compensation when the estimated rotational speed and longitudinal distance center offset are the true values ​​in one embodiment.

[0050] Figure 6 This is a schematic diagram of the RD imaging results after second-order spatially variable phase compensation when there are errors in the estimated rotational velocity and longitudinal distance center offset in one embodiment; wherein, Figure 6 (a) Schematic diagram of RD imaging results after second-order spatially variable phase compensation when the estimated rotational speed is 1.2 times the true value. Figure 6 (b) is a schematic diagram of the RD imaging results after second-order spatially variable phase compensation when the estimated longitudinal distance center offset differs from the true value by 0.8m. Figure 6 (c) Schematic diagram of RD imaging results after second-order spatially variable phase compensation when both the estimated rotational speed and longitudinal distance center offset have errors.

[0051] Figure 7 This is a schematic diagram of the outer contour of the defocusing PSF in one embodiment;

[0052] Figure 8This is a schematic diagram of the Hough transform result of the outer contour of the divergence point PSF in one embodiment;

[0053] Figure 9 This is a schematic diagram of the RD imaging result obtained by directly performing RD imaging after performing second-order spatially variable phase compensation and inverse fast Fourier transform of the one-dimensional range image according to the final phase compensation function.

[0054] Figure 10 This is a schematic diagram of the finally focused RD image in one embodiment;

[0055] Figure 11 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0057] In one embodiment, such as Figure 1 As shown, a focusing imaging method based on terahertz radar is provided, including the following steps:

[0058] Step S1: Acquire the echo signal of a large target rotating at a constant speed based on terahertz radar.

[0059] Step S2: Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0060] Step S3: The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by image preprocessing combined with Hough transform, and a tilt threshold is set. The estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0061] Step S4: Construct the final phase compensation function based on the final estimated rotation speed and longitudinal distance center offset distance. Perform second-order spatially variable phase compensation and azimuth FFT on the one-dimensional range image after Keystone transformation based on the final phase compensation function to obtain the final focused RD image. The one-dimensional range image after Keystone transformation is obtained by performing Keystone transformation and range FFT on the echo signal.

[0062] In one embodiment, step S1 includes: acquiring raw echo data of a large target rotating at a constant speed based on terahertz radar, performing demodulation and second-order Taylor expansion on the raw echo data to obtain the echo signal.

[0063] Specifically, step S1 includes:

[0064] First, the raw echo data of a large target rotating at a constant speed is acquired based on the terahertz broadband radar system. The transmitted signal of the terahertz broadband radar system is shown in equation (1).

[0065]

[0066] in, For the distance of fast time, t m For azimuth slow time, rect() represents the azimuth pulse, T p f is the pulse width of a pulse radar or the frequency sweep period of a frequency-modulated continuous wave radar. c γ is the radar carrier frequency, exp represents an exponential function with base e, j represents the imaginary unit, and t is time.

[0067] Assume the distance from the terahertz broadband radar to the center of the turntable is R. ref The reference echo can then be written as:

[0068]

[0069] Where c is the speed of light and σ is the target scattering coefficient.

[0070] ISAR imaging in the far field can be simplified to turntable imaging. Assuming the distance between the rotating target and the radar is R, a rectangular coordinate system xoy is established with the center of the turntable as the origin. In turntable mode, the distance from the target point (x, y) to the radar can be expressed as R = R0 + (xsinθ + ycosθ), where R0 is the initial distance of the radar to the center of the turntable, and θ is the target rotation accumulation angle. The received echo signal can be written as:

[0071]

[0072] Among them, T aLet R be the total signal observation time. Assume the reference distance and the initial distance from the radar to the turntable center are equal, i.e., R. ref =R0, after demodulating the line frequency and compensating for the residual video phase (RVP), the received baseband target echo signal can also be expressed as:

[0073]

[0074] Based on the turntable model, equation (4) above can also be expressed as:

[0075]

[0076] Furthermore, in traditional RD imaging, the accumulation angle is generally small (3°–5°), and in approximation, only the first order of the Taylor expansion is often retained, i.e.

[0077] sinθ≈θ=wt m ,cosθ≈1 (6)

[0078] Where w is the rotational speed, this is because the resolution of traditional radar is not high enough to ignore the influence of second-order and higher-order expansion on imaging. However, in the terahertz band, especially for large targets, the influence of second-order phase is difficult to ignore. If the second-order Taylor expansion is retained, the above equation (6) can be expressed as:

[0079]

[0080] Therefore, a more accurate representation of the echo signal is:

[0081]

[0082] If RD imaging is performed directly on the received echo signal, that is, a fast time-range imaging is performed... and direction slow time t m The two-dimensional Fourier transform yields the imaging expression as follows:

[0083]

[0084] Among them, f r For the range frequency, f a This indicates the azimuth Doppler frequency.

[0085] At this point, since the (x, y) coordinates of the large target are relatively large, the first sinc function is affected by xwt. mDue to the influence of slow time, significant cross-cell migration occurs, and the amount of migration varies for points with different lateral distributions. Migration correction is typically performed using the Keystone transform. This invention considers first-order migration, while second-order expansion does not result in cross-cell migration but only generates Doppler modulation in the phase, affecting azimuth imaging. Therefore, the y-coordinate range of the imaging target in the longitudinal direction is constrained as follows:

[0086]

[0087] That is, the maximum second-order migration term does not exceed one range resolution cell, where θ max =wT a That is, the maximum accumulation angle, therefore the longitudinal distribution range of the target is Under this constraint, only the target's lateral dimension x and the maximum accumulation angle θ are considered. max The resulting problem of cross-distance cell migration.

[0088] The second term, sinc, in equation (9) corresponds to azimuth imaging, where... The first term corresponds to the horizontal coordinate x of the target, while the second term is the modulation of the Doppler frequency and includes parameters y and t. m It is evident that the signal is spatially and temporally variable; that is, with the accumulation of slow time, the position of the azimuth coordinate x will shift more and more, and the amount of shift is also related to the parameter y of the longitudinal distribution. For scattering points with the same lateral position, the farther the longitudinal distribution is from the rotation center, i.e., the larger the coordinate y, the greater its lateral shift. Furthermore, when the longitudinal distribution y is symmetrically distributed about the rotation center 0, its lateral shift is also symmetrically shifted left and right. If this modulation term is fully phase-compensated in the range-slow time domain, then there will be no different lateral shifts along the longitudinal direction, i.e., the influence of this modulation term on the lateral shift is eliminated. This invention is essentially based on this characteristic, using the elimination of lateral shift as the criterion, to estimate the target's longitudinal range center deviation (RCD) and the magnitude of the accumulation angle. Since the signal slow time is known and the target rotates at a uniform speed, the target's rotational speed information can be obtained.

[0089] Ignoring the effect of the second-order migration term on the range direction and the constant phase, the echo signal can be simplified to:

[0090]

[0091] Under normal circumstances, the PSF of an ideal scattering point should be a point. When a first-order cross-range cell migration occurs in the range direction, it directly leads to radial broadening of the PSF distribution in two-dimensional imaging. Simultaneously, because the cross-range cell migration shortens the azimuth accumulation time, it results in a decrease in azimuth resolution, corresponding to the broadening of the azimuth PSF. The reasons for the broadening in the two directions are different. Therefore, if we disregard the influence of the second-order unfolded phase on the azimuth shift, the ideal PSF of a point target should be a rectangle broadened simultaneously in both the range and azimuth directions, rather than an ideal point.

[0092] Based on this, in one embodiment, step S2 includes: firstly, performing range pulse compression on the echo signal to obtain a one-dimensional range image of the target; then, performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result; and finally, based on the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result, setting initial values ​​for the estimated rotational speed and longitudinal range center offset of the target, and constructing a phase compensation function as follows. Where Δy represents the longitudinal distance center offset of the target estimate, The rotational velocity of the target is represented; finally, after performing second-order spatially variable phase compensation on the one-dimensional range image according to the phase compensation function, the azimuth-directed fast Fourier transform is performed on the phase-compensated one-dimensional range image to obtain the spatially variable phase-compensated two-dimensional RD image.

[0093] Specifically, in another embodiment, step S2 includes: when Δy = 0 and When the true value is used, a phase compensation function is constructed to perform second-order spatially variable phase compensation on the echo signal. The echo signal obtained after compensation can be expressed as:

[0094]

[0095] in, Indicates the distance and time. Perform FFT, Indicates the distance and time. Perform inverse FFT;

[0096] Then, performing a two-dimensional Fourier transform on the compensated echo signal yields the two-dimensional RD image expression:

[0097]

[0098] The RD imaging result obtained at this time is a two-dimensional broadened rectangular shape without the influence of the second-order spatial phase variation. This is also the standard for subsequent evaluation of whether the estimated parameters of the compensation function are accurate.

[0099] If there are large errors in the estimated longitudinal distance center offset and rotation speed, a certain offset will occur in the azimuth direction, causing the rectangular PSF to become a parallelogram, as expressed below:

[0100]

[0101] Theoretically, PSF tilt is defined as the horizontal offset of a two-dimensional image divided by the tangent angle corresponding to the vertical offset, expressed as:

[0102]

[0103] in Related to radar parameters, it can be considered a constant term. It is known that when the estimated longitudinal range center deviation Δy is 0 and the rotational speed... When w is the true value, the tilt of the PSF of the divergence point A slope of 0° means the parallelogram transforms into a rectangle. Analyzing the above expression, we can see that the angle of inclination... It is spatially variable about (x, y), and its magnitude is related to the position of the scattering point. Therefore, the spatial distribution law of the PSF tilt of each astigmatism in the two-dimensional RD imaging results is as follows: when the center offset of the estimated longitudinal distance of the target is zero, the PSF tilt of each astigmatism in the two-dimensional RD imaging results has a distribution characteristic that is symmetric about both the x-axis and the y-axis; when the estimated rotational speed of the target is the actual rotational speed of the target, y in the numerator of the expression is eliminated, and it no longer has the spatially variable characteristic, while It can be considered a constant. In this case, only x in the denominator retains the spatial variation characteristic. At this time, the PSF tilt of each astigmatism in the two-dimensional RD imaging result has a distribution characteristic that is symmetrical about the y-axis. For points with the same x-coordinate in the two-dimensional RD imaging result, the PSF tilt of their imaging results is the same. When there are errors in the longitudinal distance center offset and rotation speed of the target estimation, the distribution law of the PSF tilt of each astigmatism in the two-dimensional RD imaging result conforms to the intersection of the above two characteristics. It has a distribution characteristic that is symmetrical about the y-axis but asymmetrical about the x-axis. For points with the same x-coordinate in the two-dimensional RD imaging result, the PSF tilt of their imaging results is different.

[0104] Based on the above distribution pattern, a preliminary judgment can be made on the estimation accuracy of the two parameters. However, since ISAR images cannot be laterally calibrated before rotational speed estimation, the actual calculation method in the subsequent PSF tilt estimation based on the dot matrix is ​​to solve for the tangent angle corresponding to the number of lateral offset units in the two-dimensional image divided by the number of longitudinal offset units.

[0105] In one embodiment, step S3 includes:

[0106] Image preprocessing is performed on the two-dimensional RD image after spatial phase compensation, including sub-image segmentation, image grayscale conversion, binarization, edge smoothing, contour extraction and noise removal, etc., to extract the parallelogram contour of each divergence point PSF in the two-dimensional RD image.

[0107] A Hough transform is performed on the extracted parallelogram contour to detect the longitudinal lines within the contour. The angle between the longitudinal lines and the vertical axis is then used as the PSF tilt K of each divergence point. psf ;

[0108] Then, the estimated rotational velocity and longitudinal distance-center offset of the target are traversed separately. The rotational velocity and longitudinal distance-center offset of each traversal are substituted into the phase compensation function and second-order spatially variable phase compensation is performed on the one-dimensional range image. Then, an azimuth FFT is performed to obtain a new two-dimensional RD image. The PSF tilt of several defocused scattering points is solved until the tilt of all PSFs in the image is less than the set tilt threshold. The traversal is stopped. At this time, the rotational velocity and longitudinal distance-center offset obtained by the search are the final estimated results. In one embodiment, step S4 includes:

[0109] The final estimated rotational speed and longitudinal distance from the center offset are used to construct the final phase compensation function. The final focused RD image is obtained by performing second-order spatially variable phase compensation and azimuth FFT on the one-dimensional range image after Keystone transform based on the final phase compensation function; the one-dimensional range image after Keystone transform is obtained by performing Keystone transform and range FFT on the echo signal. The final focused RD image is represented as follows.

[0110]

[0111] Among them, f r For the range frequency, f a Indicates the azimuth Doppler frequency. For the final phase compensation function, Δy final For the final estimated longitudinal distance center offset, For the final estimated rotational speed, For echo signal, Indicates the distance and time. Perform a Fast Fourier Transform (FFT), where KT() represents a Keystone Transform on the echo signal. Indicates the time t for the direction. m Perform a Fast Fourier Transform.

[0112] Furthermore, the focusing imaging method based on terahertz radar provided in this application has been verified through simulation experiments. Taking a terahertz broadband radar system with a carrier frequency of 220 GHz and a bandwidth of 10 GHz as an example, and using 16 ideal points rotated by 4° as targets, with the target distribution range being [-6m, 6m], the correctness and effectiveness of the method are demonstrated by implementing the above steps step by step and finally estimating the longitudinal distance center offset and rotation speed. In the simulation experiment, the radar system carrier frequency was 220 GHz, bandwidth was 10 GHz, pulse repetition period was 0.11 ms, the number of sampling points in each pulse was 1212, the observation time was about 0.222 s, the point targets were uniformly distributed in a 4*4 two-dimensional pattern, and the uniform rotation speed was 18° / s. The simulated point targets are as follows. Figure 2 As shown.

[0113] The one-dimensional range image and RD image obtained by performing range FFT and two-dimensional FFT on the echo signal of the simulated point target are as follows: Figure 3 (a) and Figure 3 As shown in (b), from Figure 3 (a) It can be seen that the target underwent severe cross-range cell migration during the rotation process, which needs to be corrected by using the Keystone transformation method.

[0114] After performing Keystone transform on the echo signal, the resulting one-dimensional range image and RD imaging results are as follows: Figure 4 (a) and Figure 4 As shown in (b), the Keystone transformation greatly improves the migration of distance cells in the one-dimensional range image. The two-dimensional RD imaging results after the Keystone transformation are also significantly improved compared to the previous RD imaging. However, defocusing still exists in the azimuth direction, and the larger the longitudinal coordinate, the more severe the defocusing. This is consistent with the influence of spatially variable secondary phase on imaging mentioned earlier. Therefore, spatially variable phase compensation is still required. The key parameters for secondary spatially variable phase compensation are the rotation speed and the longitudinal distance center offset. Therefore, the defocusing PSF tilt method is used to estimate and extract relevant parameters.

[0115] Based on the method described above, second-order spatially variable phase compensation is performed on the echo signal. When the input rotational speed and longitudinal distance center offset are taken as true values, the imaging result obtained by directly performing a two-dimensional FFT after compensation is as follows. Figure 5 As shown.

[0116] When there is a certain error in two parameters of the compensated spatially variable second phase, the obtained RD imaging result is as follows: Figure 5 As shown. Among them, Figure 6 (a) Schematic diagram of RD imaging results after second-order spatially variable phase compensation when the estimated rotational speed is 1.2 times the true value. Figure 6(b) is a schematic diagram of the RD imaging results after second-order spatially variable phase compensation when the estimated longitudinal distance center offset differs from the true value by 0.8m. Figure 6 (c) Schematic diagram of RD imaging results after second-order spatially variable phase compensation when both the estimated rotational velocity and longitudinal distance center offset have errors. Figure 6 It can be seen that the distribution law of PSF tilt change with parameter error is consistent with the theoretical analysis above.

[0117] After precise second-order spatially variable phase compensation, the target's RD imaging result is a standard rectangle. By extracting the tilt of the PSF at the point of significant defocusing, a search threshold can be roughly defined. When the extracted PSF tilt is below this threshold, the phase is considered to be sufficiently accurate. Furthermore, based on the distribution law of the PSF tilt of the defocusing point changing with the error of the parameter to be estimated, the search value can be adaptively adjusted. The PSF tilt is estimated using the method proposed in step S3 above to verify the parameter estimation accuracy of the proposed method.

[0118] First, taking the compensated RD imaging result after substituting the true rotational velocity and longitudinal distance center offset as an example, we extract and segment a scattering point with obvious defocus, namely... Figure 4 The first point target in the upper left corner undergoes image grayscale conversion, binarization, edge smoothing, contour extraction, and noise removal to obtain the outer contour of the PSF, as shown below. Figure 7 As shown in the figure. After the above series of image processing steps, a clear PSF contour was obtained. Applying a Hough transform to it yielded the line detection result as shown in the figure. Figure 8 As shown, the detected straight lines are classified into horizontal and vertical categories. Horizontal line segments are represented by dashed lines with endpoints marked with "×", while vertical line segments are represented by solid lines with endpoints marked with "○". The tilt of the vertical line segments is calculated, which is the tangent angle corresponding to the number of horizontal offset units in the 2D image divided by the number of vertical offset units. Due to the sidelobe effect of the PSF of the scattering points, redundant corner points inevitably appear at the four corners of the rectangle after contour extraction. Therefore, three vertical line segments are extracted: one on the left and two on the right. Their tilts are calculated to be 0, 1, and 2, respectively. The redundant line segment on the right can be discarded, or the tilts of the two line segments can be averaged as the standard for subsequent tilt judgment. Furthermore, when estimating the tilt of the scattering points, the horizontal and vertical aspect ratio of the scattering point image can be appropriately adjusted to make the vertical line segments shorter, thus making their tilt more obvious. This can improve the estimation accuracy of the proposed method to a certain extent. Increasing the interpolation factor during imaging can also improve the estimation accuracy.

[0119] Based on the tilt angle extracted by the Hough transform, the tilt angle threshold for the two longitudinal line segments was set to 2. According to this threshold and the distribution law mentioned above, the two parameters were searched and estimated. The search estimated rotation speed that finally reached the tilt angle threshold was 17.9° / s, which differed from the true value of 18° / s by 0.1° / s. The center offset of the search estimated longitudinal distance was -0.025m, with an error of 2.5cm, which proved the accuracy and effectiveness of the proposed method. The reason for the certain error is that the side lobes of the focal spot have a significant impact on the extraction of the PSF tilt angle.

[0120] Next, based on the final phase compensation function, second-order spatially variable phase compensation and inverse fast Fourier transform of the range image are performed, followed by direct RD imaging. The results are as follows: Figure 9 As shown, the PSF shape of each divergence point is very close to a rectangle, which is consistent with the theoretical analysis mentioned above, that is, the influence of the second-order spatial phase has been eliminated. It also shows that the rotational speed and longitudinal distance center offset estimated by the method proposed in this application are accurate enough.

[0121] Finally, Keystone transform and range-directed Fast Fourier Transform are performed on the echo signal to eliminate the influence of the first-order RCM, resulting in a one-dimensional range image after Keystone transform. After spatially variable phase compensation is applied to the one-dimensional range image after Keystone transform according to the final phase compensation function, a range-directed Fast Fourier Transform is performed again to obtain the final focused RD image. Figure 10 As shown, the focusing effect of each scattering point has been greatly improved, and the image entropy value has increased from 8.76 in the original RD image to 5.54 after focusing, which proves the correctness and effectiveness of the method proposed in this application.

[0122] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed 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 some of the sub-steps or stages of other steps.

[0123] In one embodiment, a focusing imaging device based on terahertz radar is provided, comprising:

[0124] The signal acquisition module is used to acquire the echo signal of a large target rotating at a constant speed based on terahertz radar.

[0125] The phase compensation module is used to perform range pulse compression on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. Then, a phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. Finally, azimuth FFT is performed on the phase-compensated one-dimensional range image to obtain a spatially variable phase-compensated two-dimensional RD image.

[0126] The tilt estimation module is used to estimate the PSF tilt of each divergence point in the spatially phase-compensated 2D RD image by combining image preprocessing with Hough transform, and to set a tilt threshold. It then iterates through the estimated rotation speed and longitudinal distance from the center until the estimated PSF tilt is less than the set tilt threshold, and uses the rotation speed and longitudinal distance from the center obtained from the current traversal search as the final estimated rotation speed and longitudinal distance from the center.

[0127] The focusing imaging module is used to construct the final phase compensation function based on the final estimated rotational speed and longitudinal distance center offset distance. Based on the final phase compensation function, second-order spatially variable phase compensation and azimuth FFT are performed on the Keystone transformed one-dimensional range image to obtain the final focused RD image. The Keystone transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0128] Specific limitations regarding the terahertz radar-based focusing imaging device can be found in the above description of the limitations of the terahertz radar-based focusing imaging method, and will not be repeated here. Each module in the aforementioned terahertz radar-based focusing imaging device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the computer device's memory as software, so that the processor can call and execute the corresponding operations of each module.

[0129] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 11As shown, the computer device includes a processor, memory, network interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the 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 media. The network interface is used to communicate with external terminals via a network connection. When the computer program is executed by the processor, it implements a focusing imaging method based on terahertz radar. The display screen can be a liquid crystal display (LCD) or an e-ink display. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad mounted on the computer device casing, or an external keyboard, touchpad, or mouse.

[0130] Those skilled in the art will understand that Figure 11 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0131] In one embodiment, a computer device is provided, including a memory and a processor, the memory storing a computer program, the processor executing the computer program to perform the following steps:

[0132] Acquiring echo signals from uniformly rotating large targets using terahertz radar;

[0133] Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0134] The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by combining image preprocessing with Hough transform. A tilt threshold is set, and the estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0135] The final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance center offset. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on the final phase compensation function to obtain the final focused RD image. The Keystone-transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0136] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0137] Acquiring echo signals from uniformly rotating large targets using terahertz radar;

[0138] Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained.

[0139] The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by combining image preprocessing with Hough transform. A tilt threshold is set, and the estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are used as the final estimated rotation speed and longitudinal distance from the center.

[0140] The final phase compensation function is constructed based on the final estimated rotational speed and longitudinal distance center offset. Second-order spatially variable phase compensation and azimuth FFT are then performed on the Keystone-transformed one-dimensional range image based on the final phase compensation function to obtain the final focused RD image. The Keystone-transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

[0141] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0143] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A focusing imaging method based on terahertz radar, characterized in that, The method includes: Acquiring echo signals from uniformly rotating large targets using terahertz radar; Range pulse compression is performed on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the initial values ​​of the target's estimated rotation speed and longitudinal range center offset are set according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. A phase compensation function is constructed to perform second-order spatially variable phase compensation on the one-dimensional range image. After performing azimuth FFT on the phase-compensated one-dimensional range image, a spatially variable phase-compensated two-dimensional RD image is obtained. The PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation is estimated by image preprocessing combined with Hough transform, and a tilt threshold is set. The estimated rotation speed and longitudinal distance from the center are traversed and searched until the estimated PSF tilt is less than the set tilt threshold. The rotation speed and longitudinal distance from the center obtained by the current traversal search are taken as the final estimated rotation speed and longitudinal distance from the center. Based on the final estimated rotational speed and longitudinal distance center offset distance, a final phase compensation function is constructed. Based on the final phase compensation function, second-order spatially variable phase compensation and azimuth FFT are performed on the Keystone transformed one-dimensional range image to obtain the final focused RD image. The Keystone transformed one-dimensional range image is obtained by performing Keystone transformation and range FFT on the echo signal.

2. The method according to claim 1, characterized in that, Based on terahertz radar, the echo signal of a large target rotating at a constant speed is acquired, including: The original echo data of a large target rotating at a constant speed is obtained by acquiring the original echo data using terahertz radar. The original echo data is then subjected to demodulation and second-order Taylor expansion to obtain the echo signal.

3. The method according to claim 1, characterized in that, The spatial distribution pattern of the PSF tilt of the astigmatism in the two-dimensional RD imaging results is as follows: When the longitudinal distance center offset of the target estimation is zero, the PSF tilt of each focal point in the two-dimensional RD imaging results has a distribution characteristic that is symmetric about the x-axis and symmetric about the y-axis at the same time. When the estimated rotational velocity of the target is the actual rotational velocity of the target, the PSF tilt of each focal point in the two-dimensional RD imaging result has a distribution characteristic symmetrical about the y-axis, and for points with the same abscissa in the two-dimensional RD imaging result, the PSF tilt of their imaging results is the same. When there are errors in the longitudinal distance center offset and rotation speed of the target estimation, the PSF tilt of each focal point in the two-dimensional RD imaging result has a distribution characteristic that is symmetric about the y-axis but asymmetrical about the x-axis, and for points with the same abscissa in the two-dimensional RD imaging result, the PSF tilt of the imaging result is different.

4. The method according to claim 1, characterized in that, The phase compensation function is constructed from the target's estimated rotational velocity and longitudinal distance from the center offset, and is expressed as follows: Where Δy represents the longitudinal distance center offset of the target estimate, The target's estimated rotational speed is represented by exp, which represents an exponential function with base e, j represents the imaginary unit, c is the speed of light, and t is the speed of light. m The azimuth time is the slowest time, y is the vertical axis, and f is the horizontal axis. c This is the radar carrier frequency.

5. The method according to claim 1, characterized in that, The PSF tilt of each divergence point in the spatially variable phase-compensated 2D RD image is estimated using image preprocessing combined with Hough transform, including: The two-dimensional RD image after spatial phase compensation is preprocessed to extract the parallelogram contour of each divergence point PSF in the two-dimensional RD image. The extracted parallelogram contour is subjected to Hough transform to detect the longitudinal straight lines in the parallelogram contour, and the angle between the longitudinal straight lines and the longitudinal axis is used as the PSF tilt of each divergence point.

6. The method according to claim 1 or 5, characterized in that, The image preprocessing methods include sub-image segmentation, image grayscale conversion, binarization, edge smoothing, contour extraction, and noise removal.

7. The method according to claim 1, characterized in that, Based on the final estimated rotational speed and longitudinal distance-center offset distance, a final phase compensation function is constructed. Then, second-order spatially variable phase compensation and azimuth FFT are performed on the Keystone-transformed one-dimensional range image using this final phase compensation function to obtain the final focused RD image, represented as: Among them, f r For the range frequency, f a Indicates the azimuth Doppler frequency. For the final phase compensation function, Δy final For the final estimated longitudinal distance center offset, For the final estimated rotational speed, For echo signal, Indicates the distance and time. Perform a Fast Fourier Transform (FFT), where KT() represents a Keystone Transform on the echo signal. Indicates the time t for the direction. m Perform a Fast Fourier Transform.

8. A focusing imaging device based on terahertz radar, characterized in that, The device includes: The signal acquisition module is used to acquire the echo signal of a large target rotating at a constant speed based on terahertz radar. The phase compensation module is used to perform range pulse compression on the echo signal to obtain a one-dimensional range image of the target. After performing azimuth FFT on the one-dimensional range image to obtain a two-dimensional RD imaging result, the module sets the initial values ​​of the target's estimated rotation speed and longitudinal range center offset according to the spatial distribution law of the PSF tilt of the focal point in the two-dimensional RD imaging result. After constructing a phase compensation function to perform second-order spatially variable phase compensation on the one-dimensional range image, the module performs azimuth FFT on the phase-compensated one-dimensional range image to obtain a spatially variable phase-compensated two-dimensional RD image. The tilt estimation module is used to estimate the PSF tilt of each divergence point in the two-dimensional RD image after spatial phase compensation by combining image preprocessing with Hough transform, and to set a tilt threshold. It then performs a traversal search on the estimated rotation speed and longitudinal distance from the center until the estimated PSF tilt is less than the set tilt threshold, and uses the rotation speed and longitudinal distance from the center obtained from the current traversal search as the final estimated rotation speed and longitudinal distance from the center. The focusing imaging module is used to construct a final phase compensation function based on the final estimated rotation speed and longitudinal distance center offset distance, and to perform second-order spatially variable phase compensation and azimuth FFT on the one-dimensional range image after Keystone transformation based on the final phase compensation function to obtain the final focused RD image; wherein, the one-dimensional range image after Keystone transformation is obtained by performing Keystone transformation and range FFT on the echo signal.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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