High-precision squint InISAR three-dimensional imaging method suitable for small array antenna

Abstract

The invention discloses a high-precision squint InISAR three-dimensional imaging method suitable for a small-sized array antenna, and the method comprises the steps: building a geometric structure and an echo signal model of a squint InISAR imaging system of the small-sized array antenna, carrying out the subarray division and echo signal synthesis of the array antenna, carrying out the imaging processing of the synthesized echo signal, and obtaining a high-precision squint InISAR imaging system. Obtaining an ISAR two-dimensional imaging result of each sub-array signal; extracting strong scattering points from the ISAR two-dimensional imaging result by using a peak value extraction technology; the method comprises the following steps: acquiring height dimension information and azimuth dimension information of a strong scattering point, and carrying out squint distortion correction on distance dimension information in an ISAR two-dimensional imaging result and the height dimension information and the azimuth dimension information of the strong scattering point by utilizing a nonlinear least square squint correction method and combining coordinate transformation, so as to realize reconstruction of a three-dimensional coordinate of an observed target. According to the method, the precision of target three-dimensional imaging can be improved under the conditions that a baseline is short and noise interference exists.

Description

Technical Field

[0001] The present invention relates to the technical field of radar imaging, and particularly to a high-precision squint InISAR three-dimensional imaging method applicable to a small array antenna. Background Art

[0002] High-resolution radar imaging technology has important applications in fields such as environmental situation awareness and target recognition. The traditional ISAR (Inverse Synthetic Aperture Radar) imaging technology can obtain high-resolution two-dimensional images of observed targets. However, its two-dimensional imaging method has many limitations. On the one hand, it can only provide two-dimensional projection images of the target and cannot directly reflect the true three-dimensional structure of the target. On the other hand, the imaging result depends on the image projection plane, resulting in significant changes in the imaging result of the same target at different observation angles, increasing the complexity and uncertainty of target recognition.

[0003] To address the above problems, in recent years, InISAR (Interferometric Inverse Synthetic Aperture Radar) technology has received extensive attention. This technology can obtain the three-dimensional structure information of the target without complex signal processing means and long-term continuous observation, and is insensitive to target attitude changes, thus being able to provide more comprehensive and stable shape and structure information for target recognition. Currently, the research on InISAR technology mainly focuses on key issues such as image registration, phase reconstruction, and squint correction.

[0004] In practical applications, since the RLOS (Radar Line of Sight) may not always be perpendicular to the antenna baseline, there is a certain squint angle, that is, the squint mode, which introduces additional squint distortion into the three-dimensional imaging of the target and affects the three-dimensional reconstruction accuracy. To overcome this problem, some scholars have proposed a squint InISAR imaging method based on NLS-CT (Nonlinear Least Square-Coordinates Transform) to achieve squint distortion correction through iterative optimization. Another study has proposed a squint InISAR imaging algorithm based on prominent points, but this method uses the same reference distance for different antenna echoes, which easily leads to the problem of image mismatch, and the phase unwrapping algorithm borrowed from the InSAR field has poor adaptability to the application scenarios of InISAR.

[0005] At present, antenna arrays have been widely used in many fields due to their multi-channel structure, and InISAR technology can also be applied to such radar systems. However, in application scenarios such as missile-borne and airborne, due to the limitation of the size of the carrier platform, the antenna baseline length is usually short, resulting in a decrease in the accuracy of interferometric measurement, which in turn affects the imaging quality. Existing InISAR methods mainly rely on interferometric measurement to obtain the height and azimuth information of the target, and the interferometric phase is easily affected by noise. Especially under the condition of short baselines, it is difficult to guarantee the imaging accuracy. Summary of the Invention

[0006] The object of the present invention is to provide a high-precision squint InISAR three-dimensional imaging method applicable to small array antennas, which improves the signal-to-noise ratio of the received signal through sub-array division and signal synthesis technology, and optimizes the traditional non-linear least squares squint correction method, which can effectively solve the challenges faced by squint InISAR imaging in the environment of short baselines and affected by noise, and improve the accuracy and reliability of the reconstruction of the observed target.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A high-precision squint InISAR three-dimensional imaging method applicable to small array antennas, comprising the following steps:

[0009] S1. Based on the squint InISAR imaging system of a small array antenna, establish a corresponding geometric structure and echo signal model, perform sub-array division and echo signal synthesis on the array antenna, regard the obtained synthesized echo signal as the echo signal obtained by a self-illuminating and self-receiving equivalent antenna located at the center of the sub-array, and perform imaging processing on the synthesized echo signal to obtain the ISAR two-dimensional imaging results of each sub-array signal.

[0010] S2. Use peak extraction technology to extract the strong scattering points of the observed target from the ISAR two-dimensional imaging results.

[0011] S3. Use interferometric technology to obtain the interferometric phase information of the strong scattering points to obtain the height dimension information of the strong scattering points.

[0012] S4. Use the azimuth calibration algorithm based on ICPF (Integrated Cubic Phase Function) to perform azimuth calibration on the ISAR two-dimensional imaging results to obtain the azimuth dimension information of the strong scattering points.

[0013] S5. Use the non-linear least squares squint correction method combined with coordinate transformation to perform squint distortion correction on the range dimension information, the height dimension information of the strong scattering points, and the azimuth dimension information in the ISAR two-dimensional imaging results, and realize the reconstruction of the three-dimensional coordinates of the observed target.

[0014] Furthermore, in step S1, obtaining the ISAR two-dimensional imaging result includes the following:

[0015] S101. In the geometric structure, the geometric center O of the array antenna is used as the origin, the radar coordinate system is OXYZ, all array antennas are distributed in the XOZ plane, the element spacing is d, and the radar coordinate system is used as the global coordinate system.

[0016] Under far-field conditions, with the geometric center o of the observed target as the origin, an observed target body coordinate system oxyz parallel to the radar coordinate system is established. The position of the observed target center o in the radar coordinate system is (X 0 , Y 0 , Z 0 ), and the distance between the observed target center o and the origin O of the radar coordinate system is denoted as R 0 , Define as the pitch angle, θ as the azimuth angle, θ = arctan(Y 0 / Z 0 ); the observed target rotates uniformly around the z-axis at an angular velocity ω.

[0017] Taking RLOS (Radar Line of Sight) as the range direction v-axis, an imaging observation coordinate system ouvw is established. uov is the IPP (Image Projection Plane), and the w-axis is perpendicular to the image projection plane.

[0018] S102. Set the transmitting antenna of the array antenna to transmit LFM (Linear Frequency Modulation) signals, and then establish an echo signal model. The specific expression is:

[0019]

[0020] Among them, represents the echo signal transmitted by the transmitting antenna; j represents the imaginary unit; represents the fast time; t m represents the slow time, t m = m·PRT, PRT represents the pulse repetition interval, m represents the pulse number, 0 ≤ m < M, M represents the total number of pulses; rect() represents the rectangular envelope of the echo signal; T p represents the pulse width; f c represents the carrier frequency of the transmitted signal; t represents the total time, γ represents the frequency modulation slope of the LFM signal.

[0021] The received signal by the receiving antenna from the coordinate (xp , y p , z p ) The expression of the echo signal of the p-th strong scattering point is:

[0022]

[0023] Where, represents the echo signal received by the receiving antenna, and R t (t m ) represents the instantaneous distance from the p-th strong scattering point to the transmitting antenna at time t m , and R r (t m ) represents the instantaneous distance from the p-th strong scattering point to the receiving antenna at time t m , σ p represents the scattering coefficient of the p-th strong scattering point, and c represents the propagation speed of electromagnetic waves.

[0024] Based on the angle selected by the reference distance, using the principle of phase correction to perform image registration, motion compensation, and pulse compression on the echo signal received by the receiving antenna, then the echo signal received by the receiving antenna from the p-th strong scattering point in the range-frequency domain - azimuth-time domain is expressed as:

[0025]

[0026] Where, S r (f, t m ) represents the echo signal of the receiving antenna in the range-frequency domain - azimuth-time domain; f represents the fast-time frequency; R Δt (t m ) represents the difference between the instantaneous distance from the p-th strong scattering point to the transmitting antenna at time t m and the reference distance of the transmitting antenna, and R Δt (t m ) = R t (t m ) - R t_ref , and R t_ref represents the reference distance of the transmitting antenna; R Δr (t m ) represents the difference between the instantaneous distance from the p-th strong scattering point to the receiving antenna at time t m and the reference distance of the receiving antenna, and R Δr (t m ) = R r (t m ) - R r_ref , and R r_ref represents the reference distance of the receiving antenna; λ represents the signal wavelength.

[0027] S103. Divide the array antenna into a set number of non - overlapping sub - arrays. After synthesizing the echo signals, obtain the synthesized echo signal of the nth sub - array. The specific expression is:

[0028]

[0029] where S rn (f,t m ) represents the synthesized echo signal in the range - frequency domain - azimuth - time domain of the nth sub - array; R Δn (t m ) represents the instantaneous distance of the pth strong scatterer relative to the observation target center o at time t m . R Δn (t m ) = R np (t m ) - R no (t m ). R np (t m ) represents the instantaneous distance from the equivalent antenna of the nth sub - array to the pth strong scatterer at time t m . R no (t m ) represents the instantaneous distance from the equivalent antenna of the nth sub - array to the observation target center o at time t m .

[0030] S104. During the set imaging accumulation time, the changes of R np (t m ) and R no (t m ) are approximately linear. The specific expressions are:

[0031] R np (t m ) ≈ R np (0) + V np ·t m

[0032] R no (t m ) ≈ R no (0) + V no ·t m

[0033] where R np (0) represents the distance from the equivalent antenna to the pth strong scatterer at the initial time, V np represents the radial velocity of the pth strong scatterer relative to the equivalent antenna, R no (0) represents the distance from the equivalent antenna to the observation target center o at the initial time, V no represents the radial velocity of the observation target center o relative to the equivalent antenna.

[0034] Perform imaging processing on the synthetic echo signal to obtain the ISAR two-dimensional imaging result of the nth subarray. The specific expression is as follows:

[0035]

[0036] where f m represents the Doppler frequency; T obs represents the imaging accumulation time; R' npo represents the distance of the pth strong scatterer relative to the center o of the observed target at the initial moment. R' npo =R np (0)-R no (0); V′ npo represents the radial velocity of the pth strong scatterer relative to the center o of the observed target. V′ npo =V np -V no .

[0037] Furthermore, in step S2, the multi-channel CLEAN (Coherent Locus and Extraction of Non-coherent Noise) technology is used to extract the strong scatterers in the ISAR two-dimensional imaging result.

[0038] Furthermore, in step S3, the height dimension information of the strong scatterers includes the following:

[0039] Perform interference processing on the ISAR two-dimensional imaging results of the echo signals received by the first equivalent antenna EA1 and the second equivalent antenna EA2 to obtain the interference phase information of the pth strong scatterer. The specific expression is as follows:

[0040]

[0041] where represents the interference phase; Angle() represents the phase extraction operation; S r1 (f,f m ) represents the ISAR two-dimensional imaging result of the first equivalent antenna EA1; S r2 (f,f m ) represents the ISAR two-dimensional imaging result of the second equivalent antenna EA2; R' 2po represents the distance of the pth strong scatterer relative to the center o of the observed target under the imaging geometry of the second equivalent antenna EA2 at the initial moment; R′ 1po represents the distance of the pth strong scatterer relative to the center o of the observed target under the imaging geometry of the first equivalent antenna EA1 at the initial moment.

[0042] According to the imaging geometry, calculate the distances between the p-th strong scattering point and the first equivalent antenna EA1 and the second equivalent antenna EA2, and approximately process R through the far-field condition 1o (0)≈R 2o (0)≈R 1p (0)≈R 2p (0)≈R 0 , and obtain the relationship between the interference phase and the height dimension information at the p-th strong scattering point. The specific expression is:

[0043]

[0044] where L represents the baseline length, that is, the distance difference between the first equivalent antenna EA1 and the second equivalent antenna EA2; z p represents the height dimension information of the p-th strong scattering point; Z' 0 =Z 0 +L / 2; ΔR 12 =R 2o (0)+R 1o (0)-R 2p (0)-R 1p (0), R 2o (0) represents the distance from the center o of the observed target to the second equivalent antenna EA2 at the initial moment, and R 1o (0) represents the distance from the center o of the observed target to the first equivalent antenna EA1 at the initial moment, and R 2p (0) represents the distance from the p-th strong scattering point to the second equivalent antenna EA2 at the initial moment, and R 1p (0) represents the distance from the p-th strong scattering point to the first equivalent antenna EA1 at the initial moment.

[0045] Obtain the height dimension information of the p-th strong scattering point according to the interference phase. The specific formula is:

[0046]

[0047] Furthermore, in step S4, obtaining the azimuth dimension information of the strong scattering point includes the following:

[0048] Estimate the effective rotational speed of the observed target through the ICPF method Calculate the azimuth calibration scale factor according to the estimated effective rotational angular velocity Furthermore, obtain the azimuth dimension information u of each strong scattering point in the imaging observation coordinate system p =(m-M / 2)·η a .

[0049] Furthermore, in step S5, completing the reconstruction of the three-dimensional coordinates of the observed target includes the following:

[0050] S501. There is a non - linear relationship between the function \(g(z)\) of the interference phase and the height - dimension information \(z_p\) of the \(p\) - th strong scattering point. The specific expression is: p ) and the height - dimension information \(z_p\) of the \(p\) - th strong scattering point has a non - linear relationship. The specific expression is:

[0051]

[0052] h(z p ,x p ,y p ) = R 2o (0)+R 1o (0)-R 2p (0)-R 1p (0)

[0053] where \(h()\) represents a function related to \(x\) p , y p , z p .

[0054] S502. Use the non - linear least - squares method to calculate \(z\) through an iterative optimization process. The specific expression is: p ), and the specific expression is:

[0055]

[0056] where represents the calculated value of the height - dimension information of the \(p\) - th strong scattering point.

[0057] When the squint angle is less than \(5^{\circ}\), the azimuth - dimension information \(u\) p of the strong scattering point obtained in step S4 and the range - dimension information \(v\) p in the ISAR two - dimensional imaging result in step S1 are used as the azimuth - dimension information \(x\) p and range - dimension information \(y\) p of the observation target in the observation - target body coordinate system.

[0058] When the squint angle is greater than or equal to \(5^{\circ}\), convert the range - dimension information and azimuth - dimension information between the imaging observation coordinate system and the observation - target body coordinate system. The specific expression is:

[0059]

[0060] where \(u\) p , \(v\) p and \(w\) p represent the three - dimensional coordinates of the \(p\) - th strong scattering point in the imaging observation coordinate system.

[0061] Obtain the range - dimension information \(y\) p and azimuth - dimension information \(x\) p of the observation target in the observation - target body coordinate system. The specific expression is:

[0062]

[0063]

[0064] S503. Based on the distance dimension information y of the observed target in the observed target body coordinate system obtained in step S502 p and the azimuth dimension information x p , through the process of circularly iteratively solving the non - linear least - squares problem, the height dimension information z of the non - squint distorted observed target in the observed target body coordinate system is obtained p , realizing the three - dimensional reconstruction of the observed target.

[0065] Furthermore, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the high - precision squint InISAR three - dimensional imaging method applicable to small - scale array antennas are implemented.

[0066] Furthermore, the present invention also proposes a computer - readable storage medium. The computer - readable storage medium stores a computer program, and when the computer program is run by a processor, the high - precision squint InISAR three - dimensional imaging method applicable to small - scale array antennas is executed.

[0067] Compared with the prior art, the present invention adopts the above - mentioned technical solutions and has the following technical effects:

[0068] (1) The present invention is applicable to small - scale array antennas. By means of sub - array division and signal synthesis technology, the signal - to - noise ratio of the received signal is improved, and in the case of short baselines, the accuracy of three - dimensional reconstruction of the observed target is improved.

[0069] (2) The present invention combines azimuth calibration technology to improve the original non - linear least - squares squint correction method, and obtains the azimuth dimension information of the observed target from the two - dimensional ISAR imaging results with noise robustness, improving the accuracy of three - dimensional imaging of the observed target in the presence of noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 is the overall implementation flowchart of the present invention.

[0071] Figure 2 is the geometric structure diagram of the present invention.

[0072] Figure 3 is the schematic diagram of sub - array division and signal synthesis of the present invention.

[0073] Figure 4 is the observed target model diagram in the embodiment of the present invention.

[0074] Figure 5 It is a schematic diagram of the array antenna and its equivalent processing in the embodiments of the present invention.

[0075] Figure 6 It is a diagram of the ISAR two-dimensional imaging results in the frontal view mode and the squint mode in the embodiments of the present invention.

[0076] Figure 7 It is a diagram of the InISAR three-dimensional imaging results of the observed target in the frontal view mode in the embodiments of the present invention.

[0077] Figure 8 It is a diagram of the InISAR three-dimensional imaging of the ship model in the squint mode in the embodiments of the present invention. Specific embodiments

[0078] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0079] To achieve the above object, the present invention proposes a high-precision squint InISAR three-dimensional imaging method applicable to a small array antenna. First, the azimuth dimension information of the observed target is extracted from the ISAR two-dimensional imaging results with strong noise robustness; subsequently, the azimuth dimension information and the range dimension information are accurately corrected by using coordinate transformation; finally, the corrected data is substituted into the iterative optimization process, and the three-dimensional coordinate estimation value of the observed target is finally obtained. As Figure 1 shown, the specific steps are as follows:

[0080] S1. Based on the squint InISAR imaging system of the small array antenna, establish the corresponding geometric structure and echo signal model, divide the array antenna into sub-arrays and synthesize the echo signals, regard the obtained synthesized echo signal as the echo signal obtained by the equivalent antenna located at the center of the sub-array through self-transmitting and self-receiving, and perform imaging processing on the synthesized echo signal to obtain the ISAR two-dimensional imaging results of each sub-array signal; the specific content is:

[0081] S101. As Figure 2 shown, in the geometric structure, the geometric center O of the array antenna is the origin, the radar coordinate system is OXYZ, all the array antennas are distributed in the XOZ plane, the element spacing is d, and the radar coordinate system is used as the global coordinate system.

[0082] Under the far-field condition, with the geometric center o of the observed target as the origin, establish an observed target body coordinate system oxyz parallel to the radar coordinate system, and the position of the observed target center o in the radar coordinate system is (X 0 , Y 0 , Z 0), the distance between the center o of the observation target and the origin O of the radar coordinate system is denoted as R 0 , Define as the elevation angle, θ is the azimuth angle, θ = arctan(Y 0 / Z 0 ); The observation target rotates uniformly around the z-axis with an angular velocity ω.

[0083] Taking RLOS (Radar Line of Sight) as the range axis v, an imaging observation coordinate system ouvw is established. uov is the IPP (Image Projection Plane), and the w-axis is perpendicular to the image projection plane. The coordinate system ouv'w is an auxiliary coordinate system introduced for subsequent coordinate transformation.

[0084] S102. Set the transmitting antenna of the array antenna to transmit an LFM (Linear Frequency Modulation) signal, and then establish an echo signal model. The specific expression is:

[0085]

[0086] Among them, represents the echo signal transmitted by the transmitting antenna; j represents the imaginary unit; represents the fast time; t m represents the slow time, t m = m·PRT, PRT represents the pulse repetition interval, m represents the pulse number, 0 ≤ m < M, M represents the total number of pulses; rect() represents the rectangular envelope of the echo signal; T p represents the pulse width; f c represents the carrier frequency of the transmitted signal; t represents the total time, γ represents the frequency modulation slope of the LFM signal.

[0087] Assume that the observation target is an ideal scatterer model composed of P scatterers. There is an ideal scatterer p on the target, and its position in the target body coordinate system oxyz is (x p , y p , z p ), and the scattering coefficient is σ p . Ignoring the amplitude change, the expression of the echo signal received by the receiving antenna from the p-th strong scatterer is:

[0088]

[0089] Among them, represents the echo signal received by the receiving antenna, R t (tm ) represents the instantaneous distance from the p-th strong scattering point to the transmitting antenna at time t, R m ; and R r (t m ) represents the instantaneous distance from the p-th strong scattering point to the receiving antenna at time t, c represents the propagation speed of electromagnetic waves. m Image registration plays a fundamental and crucial role in the InISAR three-dimensional imaging process, and its registration accuracy will directly affect the quality of the final three-dimensional imaging. From the perspective of the reference distance, using the principle of phase correction to perform image registration, motion compensation, and pulse compression on the echo signal received by the receiving antenna, the echo signal received by the receiving antenna from the p-th strong scattering point in the range frequency domain - azimuth time domain is expressed as:

[0090] Among them, S

[0091]

[0092] where S r (f, t m ) represents the echo signal of the receiving antenna in the range frequency domain - azimuth time domain, that is, the Fourier transform result along the fast time ; f represents the fast time frequency; R Δt (t m ) represents the difference between the instantaneous distance from the p-th strong scattering point to the transmitting antenna at time t and the reference distance of the transmitting antenna, R m ; R Δt (t m ) = R t (t m ) - R t_ref , R t_ref represents the reference distance of the transmitting antenna; R Δr (t m ) represents the difference between the instantaneous distance from the p-th strong scattering point to the receiving antenna at time t and the reference distance of the receiving antenna, R m ; R Δr (t m ) = R r (t m ) - R r_ref , R r_ref represents the reference distance of the receiving antenna; λ represents the signal wavelength.

[0093] S103. For example, Figure 3As shown in the figure, considering the symmetry of the array antenna structure, signals are superimposed in the complex domain, which can, to a certain extent, alleviate the phase differences caused by different antenna positions. Additionally, since the noise received by each antenna is not the same, while the effective target echo signals have high coherence, the array antenna is divided into multiple non-overlapping sub-arrays. After synthesizing the echo signals, a synthesized echo signal with a higher signal-to-noise ratio is obtained, ignoring the problem of signal separation. The specific expression is as follows:

[0094]

[0095] where S rn (f, t m ) represents the synthesized echo signal in the range-frequency domain - azimuth-time domain of the nth sub-array, where n = 1, 2, 3, 4; R Δn (t m ) represents the instantaneous distance of the pth strong scattering point relative to the center o of the observed target at time t m , and R Δn (t m ) = R np (t m ) - R no (t m ). R np (t m ) represents the instantaneous distance from the equivalent antenna of the nth sub-array to the pth strong scattering point at time t m , and R no (t m ) represents the instantaneous distance from the equivalent antenna of the nth sub-array to the center o of the observed target at time t m .

[0096] S104. Since the target is moving in a uniform rotational motion, within a short imaging accumulation time, the changes of R np (t m ) and R no (t m ) are approximately linear. Ignoring the high-order terms generated by complex motions, we have:

[0097] R np (t m ) ≈ R np (0) + V np ·t m

[0098] R no (t m ) ≈ R no (0) + V no ·t m

[0099] where R np(0) represents the distance from the equivalent antenna to the p-th strong scattering point at the initial moment, V np represents the radial velocity of the p-th strong scattering point relative to the equivalent antenna, R no (0) represents the distance from the equivalent antenna to the center o of the observed target at the initial moment, V no represents the radial velocity of the center o of the observed target relative to the equivalent antenna.

[0100] Then at time t m the distance difference between the p-th strong scattering point and the target center o can be expressed as:

[0101] R Δn (t m ) = R np (0) + V np ·t m - R no (0) - V no ·t m

[0102] = R′ npo + V′ npo ·t m

[0103] where R' npo represents the distance of the p-th strong scattering point relative to the center o of the observed target at the initial moment, R' npo = R np (0) - R no (0); V′ npo represents the radial velocity of the p-th strong scattering point relative to the center o of the observed target, V′ npo = V np - V no .

[0104] Performing Fourier transform on the synthesized echo signal, the ISAR two-dimensional imaging result of the echo signal received by the n-th equivalent antenna is obtained, and the specific expression is:

[0105]

[0106] where f m represents the Doppler frequency; T obs represents the imaging accumulation time.

[0107] S2. Due to the influence of the sidelobes of the LFM signal, in the obtained ISAR two-dimensional imaging result, false scatterers will appear around the actual scatterers on the target, which will have an adverse impact on subsequent three-dimensional imaging and target recognition. Therefore, using multi-channel CLEAN (Coherent Locus and Extraction of Non-coherent Noise) technology to extract the strong scatterers of the observed target from the ISAR two-dimensional imaging result can make the imaging result clearer and improve the quality of three-dimensional imaging.

[0108] S3. Use the interference technology to obtain the interference phase information of the strong scatterers and obtain the height dimension information of the strong scatterers; the specific content is as follows:

[0109] It can be seen from Figure 3 that the first equivalent antenna EA1 and the second equivalent antenna EA2 are separated in the vertical height direction, and the height dimension information of the observed target can be obtained through interference processing. Similarly, the height dimension information of the observed target can also be obtained by performing interference processing on the third equivalent antenna EA3 and the fourth equivalent antenna EA4. In the actual imaging processing flow, the three-dimensional imaging of the observed target can be realized only by using the echo data of the first equivalent antenna EA1 and the second equivalent antenna EA2. It is also possible to, on the basis of using the first equivalent antenna EA1 and the second equivalent antenna EA2 to perform three-dimensional reconstruction on the observed target, then use the echo data of the third equivalent antenna EA3 and the fourth equivalent antenna EA4 to perform another estimation of the three-dimensional coordinates of the observed target, and average the two three-dimensional imaging results to improve the estimation accuracy.

[0110] Through the ISAR two-dimensional imaging result of the echo signal received by the equivalent antenna, the ISAR imaging results of the echo signals received by the first equivalent antenna EA1 and the second equivalent antenna EA2 can be obtained. The specific expression is:

[0111]

[0112]

[0113] Among them, S r1 (f, f m ) represents the ISAR two-dimensional imaging result of the first equivalent antenna EA1; S r2 (f, f m ) represents the ISAR two-dimensional imaging result of the second equivalent antenna EA2; R′ 1po represents the distance of the p-th strong scatterer from the center o of the observed target in the imaging geometry of the first equivalent antenna EA1 at the initial moment; R' 2poIt represents the distance of the p-th strong scattering point relative to the center o of the observed target under the imaging geometry of the second equivalent antenna EA2 at the initial moment; V′ 1po It represents the radial velocity of the p-th strong scattering point relative to the center o of the observed target under the system geometry of the first equivalent antenna EA1; V′ 2po It represents the radial velocity of the p-th strong scattering point relative to the center o of the observed target under the system geometry of the second equivalent antenna EA2.

[0114] Perform interference processing on the ISAR two-dimensional imaging results of the echo signals received by the first equivalent antenna EA1 and the second equivalent antenna EA2 to obtain the interference phase information of the p-th strong scattering point. The specific expression is:

[0115]

[0116] Among them, It represents the interference phase; Angle() represents the phase extraction operation.

[0117] The distances between the p-th strong scattering point and the first equivalent antenna EA1 and the second equivalent antenna EA2 can be expressed as:

[0118]

[0119]

[0120]

[0121] Among them, z p It represents the height dimension information of the p-th strong scattering point; R 1p (0) represents the distance of the p-th strong scattering point to the first equivalent antenna EA1 at the initial moment; X' 0 =X 0 +L / 2; Z' 0 =Z 0 +L / 2; L represents the baseline length, that is, the distance difference between the first equivalent antenna EA1 and the second equivalent antenna EA2; R 2p (0) represents the distance of the p-th strong scattering point to the second equivalent antenna EA2 at the initial moment; R 1o (0) represents the distance from the center o of the observed target to the first equivalent antenna EA1 at the initial moment; R 2o (0) represents the distance from the center o of the observed target to the second equivalent antenna EA2 at the initial moment; ΔR 12 =R 2o (0)+R 1o (0)-R 2p (0)-R 1p (0).

[0122] According to the imaging geometry, calculate the distances between the p-th strong scattering point and the first equivalent antenna EA1 and the second equivalent antenna EA2, and approximate and process R through the far-field condition 1o (0)≈R 2o (0)≈R 1p (0)≈R 2p (0)≈R 0 , and obtain the relationship between the interference phase and the height dimension information at the p-th strong scattering point. The specific expression is:

[0123]

[0124] Term ① is the main phase, and term ② is the squint additional phase, that is, the source of squint error.

[0125] When the squint angle is small, the height dimension information of the p-th strong scattering point can be directly obtained according to the interference phase. The specific formula is:

[0126]

[0127] S4. Use the azimuth calibration algorithm based on ICPF (Integrated Cubic Phase Function) to perform azimuth calibration on the ISAR two-dimensional imaging result and obtain the azimuth dimension information of the strong scattering point. The specific content is:

[0128] Estimate the effective rotation speed of the observed target through the ICPF method Calculate the azimuth calibration scale factor according to the estimated effective rotation angular velocity Furthermore, obtain the azimuth dimension information u of each strong scattering point in the imaging observation coordinate system p =(m - M / 2)·η a .

[0129] S5. Use the non-linear least squares squint correction method combined with coordinate transformation to perform squint distortion correction on the range dimension information, the height dimension information of the strong scattering point, and the azimuth dimension information in the ISAR two-dimensional imaging result, and achieve the precise reconstruction of the three-dimensional coordinates of the observed target. The specific content is:

[0130] S501. There is a non-linear relationship between the function g(z p ) of the interference phase and the height dimension information zp of the p-th strong scattering point. The specific expression is:

[0131]

[0132] h(z p , x p , y p ) = R 2o (0) + R1o (0)-R 2p (0)-R 1p (0)

[0133] Among them, h() represents a function related to x p , y p , z p related function.

[0134] S502. Estimate z through an iterative optimization process using the non-linear least squares method. The specific expression is: p For:

[0135]

[0136] Among them, represents the estimated value of the height dimension information of the p-th strong scattering point.

[0137] It should be noted that the coordinate information obtained from the ISAR two-dimensional imaging result is the coordinate information of the observed target in the imaging observation coordinate system, that is, u p and v p ; what needs to be obtained in the final 3D reconstruction is the three-dimensional coordinate information of the observed target in the observed target body coordinate system, that is, x p and y p .

[0138] When the oblique viewing angle is less than 5°, the observed target body coordinate system oxyz and the imaging observation coordinate system ouvw almost coincide. The azimuth dimension information u of the strong scattering point obtained in step S4 p and the range dimension information v in the ISAR two-dimensional imaging result p can be directly used as the azimuth dimension information x p and the range dimension information y p of the observed target in the observed target body coordinate system respectively.

[0139] When the oblique viewing angle is greater than or equal to 5°, the difference between the observed target body coordinate system oxyz and the imaging observation coordinate system ouvw is relatively large. An additional coordinate transformation process needs to be introduced to correct the range dimension and azimuth dimension information. First, rotate xoy around the z-axis clockwise by (π / 2 - θ) to become uov'. The rotation matrix M 1 is expressed as:

[0140]

[0141] Then, rotate uov' around the u-axis counterclockwise by to become vow. The rotation matrix M 2 is expressed as:

[0142]

[0143] Multiply the rotation matrix M 1 and M 2 , then we have:

[0144]

[0145] where u p , v p and w p represent the three-dimensional coordinates of the p-th strong scattering point in the imaging observation coordinate system.

[0146] Obtain the range dimension information y p and azimuth dimension information x p of the observed target in the observed target body coordinate system. The specific expressions are:

[0147]

[0148]

[0149] S503. Based on the range dimension information y p and azimuth dimension information x p of the observed target obtained in step S502, iterate the process of solving the non-linear least squares problem to obtain the height dimension information z p of the non-squint distorted observed target in the observed target body coordinate system, and achieve the accurate three-dimensional reconstruction of the observed target.

[0150] Embodiment:

[0151] To verify the effectiveness of the above algorithm, the following simulation experiments will be carried out in combination with the attached drawings and specific embodiments to verify the theory of the method proposed by the present invention:

[0152] Simulation conditions: The observed target model used is as Figure 4 shown. This model is a ship model composed of 38 ideal scattering points, with a length of 50 m and a width of 10 m. At the initial moment, the position of the center of the observed target in the global coordinate system is (X 0 , Y 0 , Z 0 ), where Y 0 = 10 km, and X 0 and Z 0 are variable parameters under different squint angles. According to different azimuth angles and pitch angles, two different modes are set in the experiment, namely: the frontal view mode (X 0 = 0 km, Z 0 = 0 km) and the squint mode (X 0 = 5 km, Z 0= 5 km). During the simulation process, it is assumed that the relative motion between the radar and the observed target is compensated, and the observed target only has rotation around the z-axis with an angular velocity of ω. The transmitted signal is an LFM signal with a carrier frequency of 10 GHz, and the other system simulation parameters are shown in Table 1.

[0153] Table 1 InISAR System Simulation Parameters

[0154]

[0155]

[0156] The array structure used during the simulation process is as shown in Figure 5 (a) of. This array antenna is divided into 4 non-overlapping sub-arrays. After synthesizing the sub-array signals, an equivalent antenna array composed of 4 self-transmitting and self-receiving antennas as shown in Figure 5 (b) of can be obtained.

[0157] To quantitatively evaluate the image quality of 3D imaging, assume that the coordinates of the p-th strong scattering point are (x p , y p , z p ), and the reconstructed coordinates are In this embodiment, the RMSE (Root Mean Square Error) between the reconstructed coordinates and the true coordinates of the p-th strong scattering point, and the 3D reconstruction error calculated from the average value of the Euler distances between the true coordinates and the reconstructed coordinates of all strong scattering points are selected to evaluate the quality of the imaging result, denoted as E x , E y , E z , E 3d respectively. The specific expressions are as follows:

[0158]

[0159]

[0160]

[0161]

[0162] Among them, P represents the total number of strong scattering points.

[0163] Taking the front view mode and the squint mode as examples, the effectiveness of the method proposed by the present invention is verified. Figure 6 are the ISAR 2D imaging results in two modes. Among them, Figure 6 (a) of is the ISAR 2D imaging result in the front view mode, Figure 6 (b) of is the ISAR 2D imaging result in the squint mode. CompareFigure 6 in (a) and Figure 6 in (b), it is not difficult to find that, compared with the frontal view mode, the two-dimensional ISAR imaging result of the target will be distorted in the case of squint. Figure 7 and Figure 8 are respectively the InISAR three-dimensional imaging results of the target obtained by the method proposed in the present invention in the frontal view mode and the squint mode. The blue hollow circles in the figure represent the strong scattering points of the real target, and the orange solid points represent the strong scattering points reconstructed by the simulation experiment. During the simulation experiment, the signal-to-noise ratio was set to 15 dB. Figure 7 In (a) of is the InISAR three-dimensional imaging result diagram of the observed target in the frontal view mode. It can be found from the figure that the estimated strong scattering points are in good agreement with the real strong scattering points. Figure 7 In (b) of is the xoy plane view of the three-dimensional imaging result of the observed target in the frontal view mode. From this view, it can be more intuitively explained that the estimation accuracy of the x coordinate and y coordinate of the observed target is very high. Figure 7 In (c) of and Figure 7 In (d) of are respectively the xoz plane and yoz plane views of the three-dimensional imaging result of the observed target in the frontal view mode. It can be found from them that the estimation accuracy of the z coordinate is relatively high, slightly lower than the estimation accuracy of the x coordinate and y coordinate. Figure 8 In (a) of is the InISAR three-dimensional imaging result diagram of the observed target in the squint mode, Figure 8 In (b) of is the xoy plane view of the three-dimensional imaging result of the observed target in the squint mode, Figure 8 In (c) of is the xoz plane view of the three-dimensional imaging result of the observed target in the squint mode, Figure 8 In (d) of is the yoz plane view of the three-dimensional imaging result of the observed target in the squint mode. It is not difficult to find from the InISAR three-dimensional imaging result of the target shown in Figure 8 in the squint mode that the proposed method can still achieve the three-dimensional reconstruction of the coordinates of the observed target in the squint mode. Comparing the three-dimensional imaging results of Figure 7 and Figure 8 , it can be found that the reconstruction accuracy of the three-dimensional coordinates of the observed target in the squint mode is slightly lower than that in the frontal view mode.

[0164] To verify the anti-noise performance of the proposed method, simulation experiments were carried out under different signal-to-noise ratio conditions. The InISAR three-dimensional imaging result of the original NLS-CT based on the multi-antenna structure was recorded as Case 1, and the InISAR three-dimensional imaging result of the original NLS-CT based on the three-antenna structure (baseline length is 4d / 3) was recorded as Case 2, which were used as control groups. Table 2 records the average three-dimensional reconstruction error results after 100 Monte Carlo experiments under different signal-to-noise ratio conditions.

[0165] Table 2 Reconstruction Error

[0166]

[0167]

[0168] As can be seen from Table 2, under short baseline conditions, noise has a greater impact on the three-dimensional reconstruction results of the observed target. When the SNR is 0 dB, using the traditional three-antenna structure, the error reaches 5 m, which is quite large. However, the reconstruction error of the target three-dimensional coordinates obtained by using the method proposed in the present invention is about 1 m, which is acceptable for the reconstruction of large targets. Comparing the simulation results of Case 1 and Case 2 shows that signal synthesis can effectively improve the reconstruction accuracy of the target position.

[0169] An embodiment of the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. It should be noted that when the processor executes the computer program, it corresponds to the specific steps of the method provided by the embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method. For technical details not described in detail in this embodiment, reference can be made to the method provided by the embodiment of the present invention.

[0170] An embodiment of the present invention also provides a computer-readable storage medium storing a computer program. It should be noted that when the computer program is run by the processor, it corresponds to the specific steps of the method provided by the embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method. For technical details not described in detail in this embodiment, reference can be made to the method provided by the embodiment of the present invention.

[0171] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A high-precision squint InISAR three-dimensional imaging method suitable for small array antennas, characterized in that: include: S1. Based on the squint InISAR imaging system of small array antenna, the corresponding geometric structure and echo signal model are established, the array antenna is divided into sub-arrays and the echo signal is synthesized. The synthesized echo signal is regarded as the echo signal obtained by the equivalent antenna located at the center of the sub-array through self-transmission and self-reception, and the synthesized echo signal is imaged and processed to obtain the ISAR two-dimensional imaging results of each sub-array signal; S2, using peak extraction technology to extract strong scattering points of the observed target from the ISAR two-dimensional imaging results; S3, using interference technology to obtain interference phase information of strong scattering points, and obtain height dimensional information of strong scattering points; S4. Use the ICPF-based azimuth calibration algorithm to calibrate the ISAR two-dimensional imaging results in azimuth to obtain the azimuth information of strong scattering points; S5. Using the nonlinear least squares squint correction method combined with coordinate transformation, the distance dimension information, the height dimension information and the azimuth dimension information of the strong scattering points in the ISAR two-dimensional imaging results are corrected for squint distortion to achieve reconstruction of the three-dimensional coordinates of the observed target.

2. The high-precision squint InISAR three-dimensional imaging method suitable for small array antennas according to claim 1, characterized in that: In step S1, obtaining the ISAR two-dimensional imaging results includes the following: S101, in the geometric structure, the geometric center O of the array antenna is the origin, the radar coordinate system is OXYZ, all array antennas are distributed in the XOZ plane, the array element spacing is d, and the radar coordinate system is the global coordinate system; Under far-field conditions, the geometric center o of the observed target is taken as the origin to establish the observed target body coordinate system oxyz parallel to the radar coordinate system. The position of the observed target center o in the radar coordinate system is (X0, Y0, Z0), and the distance between the observed target center o and the origin O of the radar coordinate system is recorded as R0. definition is the pitch angle, θ is the azimuth angle, θ = arctan (Y0 / Z0); the observed target rotates uniformly around the z axis at an angular velocity ω; The imaging observation coordinate system ouvw is established with the radar line of sight as the distance v-axis, uov is the image projection plane, and the w-axis is perpendicular to the image projection plane; S102, setting the transmitting antenna of the array antenna to transmit a linear frequency modulation signal, and then establishing an echo signal model, the specific expression is: in, represents the echo signal emitted by the transmitting antenna; j represents the imaginary unit; Indicates fast time; t m represents slow time, t m =m·PRT, PRT represents the pulse repetition interval, m represents the pulse number, 0≤m<M, M represents the total number of pulses; rect() represents the rectangular envelope of the echo signal; T p Indicates pulse width; f c represents the carrier frequency of the transmitted signal; t represents the full time, γ represents the frequency modulation slope of the LFM signal; The receiving antenna receives the signal from the coordinate (x p ,y p ,z p The expression of the echo signal of the pth strong scattering point is: in, Represents the echo signal received by the receiving antenna, R t (t m ) indicates that at t m The instantaneous distance from the pth strong scattering point to the transmitting antenna at time, R r (t m ) indicates that at t m The instantaneous distance from the pth strong scattering point to the receiving antenna at time σ p represents the scattering coefficient of the pth strong scattering point, and c represents the propagation speed of electromagnetic waves; Based on the angle selected by the reference distance, the echo signal received by the receiving antenna is image registered, motion compensated and pulse compressed using the principle of phase correction. The echo signal received by the receiving antenna from the pth strong scattering point is expressed in the range frequency domain-azimuth time domain as follows: Among them, S r (f,t m ) represents the receiving antenna echo signal in the range frequency domain-azimuth time domain; f represents the fast time frequency; R Δt (t m ) indicates that at t m The difference between the instantaneous distance from the pth strong scattering point to the transmitting antenna and the reference distance of the transmitting antenna, R Δt (t m )=R t (t m )-R t_ref , R t_ref Indicates the reference distance of the transmitting antenna; R Δr (t m ) indicates that at t m The difference between the instantaneous distance from the pth strong scattering point to the receiving antenna and the reference distance of the receiving antenna, R Δr (t m )=R r (t m )-R r_ref , R r_ref represents the reference distance of the receiving antenna; λ represents the signal wavelength; S103, dividing the array antenna into a set number of non-overlapping sub-arrays, and synthesizing the echo signals to obtain a synthesized echo signal of the nth sub-array, the specific expression of which is: Among them, S rn (f,t m ) represents the synthetic echo signal of the range frequency domain and azimuth time domain of the nth subarray; R Δn (t m ) indicates that at t m The instantaneous distance of the pth strong scattering point relative to the observation target center o at time, R Δn (t m )=R np (t m )-R no (t m ), R np (t m ) indicates that at t m The instantaneous distance from the equivalent antenna of the nth subarray to the pth strong scattering point at time R no (t m ) indicates that at t m The instantaneous distance from the equivalent antenna of the nth subarray to the center o of the observed target at time; S104, within the set imaging accumulation time, R np (t m ) and R no (t m ) changes approximately linearly, and the specific expression is: R np (t m )≈R np (0)+V np ·t m R no (t m )≈R no (0)+V no ·t m Among them, R np (0) represents the distance from the equivalent antenna to the pth strong scattering point at the initial moment, V np represents the radial velocity of the pth strong scattering point relative to the equivalent antenna, R no (0) represents the distance from the equivalent antenna to the center o of the observed target at the initial moment, V no It represents the radial velocity of the observation target center o relative to the equivalent antenna; The synthetic echo signal is imaged and processed to obtain the ISAR two-dimensional imaging result of the nth subarray. The specific expression is: Among them, f m represents the Doppler frequency; T obs Represents the imaging accumulation time; R' npo Indicates the distance of the pth strong scattering point relative to the center o of the observed target at the initial moment, R' npo =R np (0)-R no (0); V′ npo represents the radial velocity of the pth strong scattering point relative to the center o of the observed target, V n ' po =V np -V no .

3. The high-precision squint InISAR three-dimensional imaging method suitable for small array antennas according to claim 1, characterized in that: In step S2, multi-channel coherent localization and incoherent noise extraction technology are used to extract strong scattering points in the ISAR two-dimensional imaging results.

4. The high-precision squint InISAR three-dimensional imaging method suitable for small array antennas according to claim 1, characterized in that: In step S3, the height dimension information of the strong scattering point is obtained, including the following contents: The ISAR two-dimensional imaging results of the echo signals received by the first equivalent antenna EA1 and the second equivalent antenna EA2 are subjected to interference processing to obtain the interference phase information of the pth strong scattering point. The specific expression is: in, represents the interference phase; R' 2po R1' represents the distance of the pth strong scattering point relative to the center o of the observed target under the imaging geometry of the second equivalent antenna EA2 at the initial moment; po represents the distance of the pth strong scattering point relative to the center o of the observed target under the imaging geometry of the first equivalent antenna EA1 at the initial moment; λ represents the signal wavelength; According to the imaging geometry, the distance between the pth strong scattering point and the first equivalent antenna EA1 and the second equivalent antenna EA2 is calculated, and R is approximated by the far-field condition. 1o (0)≈R 2o (0)≈R 1p (0)≈R 2p (0)≈R0, and the relationship between the interference phase and the height dimension information at the pth strong scattering point is obtained. The specific expression is: Where L is the baseline length; R0 is the distance between the center of the observed target o and the origin of the radar coordinate system O; z p represents the height dimension information of the pth strong scattering point; Z'0 = Z0 + L / 2, Z0 represents the Z-axis coordinate of the observation target center o in the radar coordinate system; ΔR 12 =R 2o (0)+R 1o (0)-R 2p (0)-R 1p (0), R 2o (0) represents the distance from the center o of the observed target to the second equivalent antenna EA2 at the initial moment, R 1o (0) represents the distance from the center o of the observed target to the first equivalent antenna EA1 at the initial moment, R 2p (0) represents the distance from the pth strong scattering point to the second equivalent antenna EA2 at the initial moment, R 1p (0) represents the distance of the first equivalent antenna EA1 of the p-th strong scattering point at the initial moment; The height dimension information of the pth strong scattering point is obtained according to the interference phase. The specific formula is:

5. The high-precision squint InISAR three-dimensional imaging method suitable for small array antennas according to claim 1, characterized in that: In step S4, obtaining the azimuth dimension information of the strong scattering point includes the following contents: Estimation of the effective rotation speed of the observed target by ICPF method Calculate the azimuth calibration factor based on the estimated effective rotation angular velocity Where λ represents the signal wavelength, T obs Represents the imaging accumulation time, and then obtains the azimuth information u of each strong scattering point in the imaging observation coordinate system p =(mM / 2)·η a , where m represents the pulse number, 0≤m<M, and M represents the total number of pulses.

6. The high-precision squint InISAR three-dimensional imaging method suitable for small array antennas according to claim 1, characterized in that: In step S5, completing the reconstruction of the three-dimensional coordinates of the observed target includes the following: S501, interference phase function g(z p ) and the height dimension information z of the pth strong scattering point p There is a nonlinear relationship between them, and the specific expression is: h(z p ,x p ,y p )=R 2o (0)+R 1o (0)-R 2p (0)-R 1p (0) Where L is the baseline length; λ is the signal wavelength; R0 is the distance between the center o of the observed target and the origin O of the radar coordinate system; Z'0 = Z0 + L / 2, Z0 is the Z-axis coordinate of the center o of the observed target in the radar coordinate system; (x p ,y p ,z p ) represents the three-dimensional coordinates of the pth strong scattering point; R 2o (0) represents the distance from the center o of the observed target to the second equivalent antenna EA2 at the initial moment, R 1o (0) represents the distance from the center o of the observed target to the first equivalent antenna EA1 at the initial moment, R 2p (0) represents the distance from the pth strong scattering point to the second equivalent antenna EA2 at the initial moment, R 1p (0) represents the distance from the first equivalent antenna EA1 to the pth strong scattering point at the initial moment; h() represents the distance from x p ,y p 、z p Related functions; S502, using nonlinear least squares method through iterative optimization process to optimize z p Calculate, the specific expression is: in, represents the calculated value of the height dimension information of the p-th strong scattering point, represents the interference phase; When the oblique angle is less than 5°, the azimuth information u of the strong scattering point obtained in step S4 is p and the distance dimension information v in the ISAR two-dimensional imaging result in step S1 p As the orientation dimension information x of the observed object in the observed object's coordinate system p and distance dimension information y p ; When the oblique angle is greater than or equal to 5°, the distance dimension information and the azimuth dimension information between the imaging observation coordinate system and the observed target body coordinate system are converted. The specific expression is: Among them, u p 、v p and w p represents the three-dimensional coordinates of the pth strong scattering point in the imaging observation coordinate system, θ represents the azimuth angle, Indicates the pitch angle; Get the distance dimension information y of the observed target in the observed target body coordinate system p and azimuth information x p , the specific expression is: S503: Based on the distance dimension information y of the observed object in the observed object body coordinate system obtained in step S502, p and azimuth information x p , the process of iteratively solving the nonlinear least squares problem, and obtaining the height dimension information z of the observed target without squint distortion in the observed target body coordinate system p , realizing three-dimensional reconstruction of the observed target.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the high-precision squint InISAR three-dimensional imaging method suitable for a small array antenna as described in any one of claims 1 to 6 are implemented.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the high-precision squint InISAR three-dimensional imaging method suitable for a small array antenna is executed as described in any one of claims 1 to 6.

Images