A SAR imaging method, system, apparatus and storage medium

Abstract

The application discloses a SAR imaging method, system, device and storage medium, and the method comprises the following steps: acquiring original echo data; the original echo data is a random step linear frequency modulation waveform; performing decoupling processing on the original echo data to obtain a target signal; the decoupling processing comprises inclination processing and azimuth resampling; performing frequency synthesis processing on the target signal based on a full grid correction matrix to obtain a focused signal; the frequency synthesis processing comprises coarse Doppler extraction and positioning, full grid Doppler correction, sampling rearrangement and series connection and polar coordinate radial compression; performing angle fine focusing processing on the focused signal to obtain a SAR focused image; the angle fine focusing comprises angle signal recovery, phase compensation, angle wave number interpolation and polar coordinate angle compression. The application can effectively improve the problem that the distance focusing performance of the existing processing method decreases with the increase of the azimuth angle, greatly improves the distance focusing performance, and can be widely applied to the technical field of SAR imaging.

Description

Technical Field

[0001] This invention relates to the field of SAR imaging technology, and in particular to a SAR imaging method, system, device and storage medium. Background Technology

[0002] Sampling stepped linear frequency modulated (LFM) waveforms in synthetic aperture radar (SAR) imaging allows for high resolution through subband stitching. Frequency agility techniques reduce carrier frequency predictability, effectively countering deception and jamming. Random stepped LFM waveforms, due to their multi-subband waveform structure and subband frequency agility, possess both of these advantages, enabling not only high resolution but also a degree of electronic countermeasures capability.

[0003] Subband frequency synthesis is crucial for stochastic step linear frequency modulated (SFM) SAR imaging. When subbands are arranged according to their center frequencies, the coherence between them is essential for successful frequency synthesis. Due to Doppler modulation generated by the high-speed motion of the SAR platform, the additional Doppler phase on the subbands is continuous in time and proportional to the target's azimuth. However, before performing stochastic step linear frequency modulated SAR frequency synthesis and subband stitching, the subbands need to be rearranged according to their center frequencies. This frequency rearrangement disrupts the continuity of the Doppler phase between subbands, leading to Doppler-dependent incoherence. This Doppler-dependent incoherence causes range focusing performance to decrease with increasing azimuth.

[0004] For frequency synthesis of stepped-frequency waveforms, traditional methods focus on range offset correction. However, traditional algorithms disrupt the continuity of Doppler phase between subbands due to frequency rearrangement, leading to Doppler-dependent incoherence. Current techniques for applying stochastic stepped linear frequency modulated waveforms to SAR imaging cannot resolve the issue of range focusing performance decreasing with increasing azimuth angle caused by this Doppler-dependent incoherence.

[0005] Therefore, solving the incoherence problem of Doppler dependence in stochastic step linear frequency modulated SAR is an urgent problem to be solved, which is the key to improving the imaging quality of stochastic step linear frequency modulated SAR. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a SAR imaging method, system, device, and storage medium, which can effectively improve the imaging quality of stochastic step linear frequency modulated SAR.

[0007] On one hand, embodiments of the present invention provide a SAR imaging method, including:

[0008] Acquire raw echo data; the raw echo data is a random step linear frequency modulated waveform.

[0009] The original echo data is decoupled to obtain the target signal; the decoupling process includes deskewing and azimuth resampling.

[0010] Based on the full-grid correction matrix, the target signal is subjected to frequency synthesis processing to obtain the focused signal; the frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sampling rearrangement and concatenation, and polar coordinate radial compression;

[0011] The focusing signal is subjected to angle fine focusing processing to obtain a SAR focused image; angle fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation and polar coordinate angle compression.

[0012] Optionally, the original echo data is decoupled to obtain the target signal, including:

[0013] By describing the random step linear frequency modulated waveform and combining it with deskewing processing, a signal model is obtained;

[0014] Based on the signal model, the target signal is obtained by performing range migration correction through azimuth resampling.

[0015] Optionally, based on the full-grid correction matrix, the target signal is subjected to frequency synthesis processing to obtain the focusing signal, including:

[0016] By extracting and locating coarse Doppler signals, the Doppler frequency of the imaging region of the target signal is corrected.

[0017] The target signal after Doppler frequency correction in the imaging area is subjected to full-grid Doppler correction to obtain the target matrix;

[0018] Based on the target matrix, the sampling points of the sub-pulses are sampled, rearranged, and concatenated to obtain the output matrix;

[0019] Based on the output matrix, the focused signal is obtained by polar coordinate radial compression through inverse Fourier transform.

[0020] Optionally, full-grid Doppler correction is performed on the target signal after Doppler frequency correction in the imaging region to obtain the target matrix, including:

[0021] In fast-time sampling, the target signal after Doppler frequency correction in the imaging region is divided into matrices to obtain several two-dimensional matrices;

[0022] Based on the two-dimensional matrix, a discrete Fourier transform is performed in slow time, and full-grid Doppler correction is performed through the full-grid correction matrix to obtain the target matrix.

[0023] Optionally, full-grid Doppler correction is performed using a full-grid correction matrix, including:

[0024] Doppler-dependent phase incoherence is eliminated by using a full-grid correction matrix, thus completing full-grid Doppler correction.

[0025] The expression for the full-grid correction matrix is:

[0026]

[0027] in, Let n denote the full-grid correction matrix, e denote the natural constant, j denote the imaginary unit, and n represent the full-grid correction matrix. a The nth step of the random step linear frequency modulation waveform a The nth pulse group, where n represents the nth pulse group. a The nth sub-pulse of the nth pulse group, N represents the nth sub-pulse. a The number of sub-pulses in each pulse group, N a This indicates the number of pulse groups in a random-step linear frequency modulated waveform. It represents N×N a A set of matrices of dimension 1.

[0028] Optionally, the focusing signal is subjected to angle fine focusing processing to obtain a SAR focused image, including:

[0029] The angle information of the focusing signal is recovered by inverse Fourier transform to obtain the recovered signal;

[0030] Based on the recovered signal, phase compensation and radial gate-based angular wavenumber interpolation are performed to obtain the polar coordinate angular wavenumber interval;

[0031] Based on the polar coordinate angular wavenumber interval, a SAR focused image is obtained by performing a discrete Fourier transform in the angular wavenumber domain.

[0032] Optionally, based on the polar coordinate angular wavenumber interval, a SAR focused image is obtained by performing a discrete Fourier transform in the angular wavenumber domain, including:

[0033] Based on the polar coordinate angular wavenumber interval, the azimuth angle is compressed by performing discrete Fourier transform in the angular wavenumber domain, and the focused target is obtained in the polar coordinate system to obtain the SAR focused image.

[0034] The expression for the focused target is:

[0035]

[0036] Among them, S ra (r t ,θ t ) represents the focused target, DFT represents the Discrete Fourier Transform, S ra (t na ;r t ,θ t ) represents the recovery signal, Sref (r t ) represents the polar coordinate angular wavenumber interval, sinc(r) t -r c ) represents the distance dimension function of the focused target, sinc(θ) t ) represents the angular dimension function of the focused target.

[0037] On the other hand, embodiments of the present invention provide a SAR imaging system, comprising:

[0038] The first module is used to acquire raw echo data; the raw echo data is a random step linear frequency modulated waveform.

[0039] The second module is used to decouple the raw echo data to obtain the target signal; the decoupling process includes deskewing and azimuth resampling.

[0040] The third module is used to perform frequency synthesis processing on the target signal based on the full-grid correction matrix to obtain the focused signal; the frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sampling rearrangement and concatenation, and polar coordinate radial compression;

[0041] The fourth module is used to perform angle fine focusing processing on the focusing signal to obtain a SAR focused image; angle fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation, and polar coordinate angle compression.

[0042] On the other hand, embodiments of the present invention provide a SAR imaging device, including a processor and a memory;

[0043] Memory is used to store programs;

[0044] The processor executes the program as described above.

[0045] On the other hand, embodiments of the present invention provide a computer-readable storage medium storing a program that is executed by a processor to implement the method described above.

[0046] This invention also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform the aforementioned method.

[0047] This invention first acquires raw echo data, which is a random-step linear frequency modulated waveform. The raw echo data is then decoupled to obtain the target signal. The decoupling process includes deskewing and azimuth resampling. Based on a full-grid correction matrix, the target signal undergoes frequency synthesis to obtain a focused signal. This frequency synthesis process includes coarse Doppler extraction and localization, full-grid Doppler correction, sample rearrangement and concatenation, and polar coordinate radial compression. Finally, the focused signal undergoes fine-angle focusing to obtain a SAR focused image. Fine-angle focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation, and polar coordinate angle compression. This invention first prepares for frequency synthesis by decoupling the echo data. Then, in frequency synthesis, full-grid Doppler correction is used to achieve Doppler correction for the entire scene, successfully eliminating incoherent phase between subbands before frequency synthesis. Finally, fine-angle focusing completes SAR imaging. This invention effectively improves the problem of decreased range focusing performance with increasing azimuth angle in existing processing methods, significantly improving range focusing performance. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a schematic flowchart of a SAR imaging method provided in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the overall process of a SAR imaging method provided in an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram illustrating an application scenario of the signal model provided in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the time-frequency characteristics of a pulse group provided in an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of the structure of a SAR imaging system provided in an embodiment of the present invention;

[0054] Figure 6 This is a schematic diagram of the structure of a SAR imaging device provided in an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] First, it's important to clarify that subband frequency synthesis is crucial for random-step linear frequency modulated (RFFM) SAR imaging. When subbands are arranged according to their center frequencies, the coherence between them is essential for successful frequency synthesis. Due to the high-speed motion of the SAR platform generating Doppler modulation, the additional Doppler phase on the subbands is continuous in time and proportional to the target's azimuth. However, before stitching together RFFM SAR subbands, the subbands need to be rearranged according to their center frequencies. This rearrangement disrupts the continuity of the Doppler phase between subbands, leading to Doppler-dependent incoherence. This Doppler-dependent incoherence causes range-focusing performance to decrease with increasing azimuth. Solving this Doppler-dependent incoherence problem for RFFM SAR is key to improving its imaging quality. However, current technologies for applying RFFM waveforms to SAR imaging cannot resolve this issue of range-focusing performance decreasing with increasing azimuth caused by Doppler-dependent incoherence.

[0057] In view of this, the present invention proposes a SAR imaging method to solve the above problems. Considering that the waveform consists of repeating pulse groups, this waveform structure can be used for Doppler separation. Correction processing for different Doppler grid positions can eliminate the Doppler phase in the subband, thereby solving the incoherence problem of Doppler dependence between subbands after frequency rearrangement. Frequency synthesis can be achieved in the Doppler domain, and finally imaging is performed. In the embodiments of the present invention, full-grid Doppler correction is integrated into the polar coordinate imaging algorithm of random step linear frequency modulated SAR. For any random step frequency arrangement, the parameters and process of the algorithm remain unchanged.

[0058] On the one hand, refer to Figure 1 and Figure 2 The present invention provides a SAR imaging method, comprising:

[0059] S100, Obtain raw echo data;

[0060] It should be noted that the original echo data is a random step linear frequency modulated waveform;

[0061] Specifically, the raw echo data based on random step linear frequency modulation waveform received from the SAR radar is first acquired.

[0062] S200. Decouple the raw echo data to obtain the target signal;

[0063] It should be noted that the decoupling process includes deskewing and azimuth resampling; in some embodiments, a signal model is obtained by describing the random step linear frequency modulated waveform and combining it with deskewing; based on the signal model, range migration correction is performed through azimuth resampling to obtain the target signal.

[0064] Specifically, in some specific embodiments, the random step linear frequency modulation waveform is first described, illustrating its signal model. For example... Figure 3 As shown, the radar antenna phase center moves uniformly along the solid line at a speed of v and a height of H. Point A is the center of the synthetic aperture, point B is the scene center, and T represents the target position. The polar coordinate system described in this method is established on the range slant range plane marked by the grid shaded area, with the pole at A and the polar axis at AB. The coordinates of the target T and the scene center B are respectively represented as (r t θ t ) and (r c ,0).

[0065] The random step linear frequency modulation waveform is composed of N a The system consists of N identical pulse groups, each pulse group containing N randomly arranged step-linear frequency modulated pulses. a Each pulse group has the same frequency sequence. For example... Figure 4 The figure shows the time-frequency characteristics of a pulse group. All linearly modulated pulses have the same pulse width T. p T r This represents the sub-pulse repetition interval. The total bandwidth of the N sub-pulses in the pulse group is B. Δf is the bandwidth of each sub-pulse.

[0066] After removing the slant, the nth... a The received baseband signal (i.e., signal model) of the nth linear frequency modulated pulse group is:

[0067]

[0068] In the formula, Represents fast time; rect(·) represents a rectangular function; Represents discrete slow time. j represents the imaginary unit, c represents the speed of light, and γ represents the linear frequency modulation. Let T represent the instantaneous distance from the radar phase center (APC) to the target T, where:

[0069]

[0070] Similarly, the reference distance for declination This represents the instantaneous distance between the APC and the center of the scene. n It is the center frequency of the nth linear frequency modulated pulse, where:

[0071]

[0072] In the formula, δ n f is a random integer in the range [1, N]. c It is the carrier frequency.

[0073] Further slow-time azimuth resampling is performed, firstly... about Perform a Taylor expansion; the plane wave assumption is not required here. exist The first-order expansion at point can be expressed as:

[0074]

[0075] Slow-time azimuth resampling can decouple the polar radius and azimuth angle, and at the same time, this operation can also correct for distance migration between sub-band pulses.

[0076] Kt p =K c t p ′

[0077] In the formula, K represents the radial wavenumber corresponding to the instantaneous frequency. K c Indicates the carrier frequency f c The relevant radial wavenumber. When the carrier frequency is much higher than the bandwidth, t p ′ approximates t p , After resampling, K becomes K c , and t p ′ approximate Right now Therefore, the resampled signal (i.e., the target signal) can be expressed as:

[0078]

[0079] Azimuth resampling has completed range migration correction, and historical slant ranges are all concentrated in the range synthesis center, providing a basis for frequency synthesis.

[0080] S300: Based on the full-grid correction matrix, the target signal is processed by frequency synthesis to obtain the focusing signal;

[0081] It should be noted that frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sample rearrangement and concatenation, and polar coordinate radial compression. In some embodiments, the Doppler frequency of the target signal in the imaging region is corrected through coarse Doppler extraction and localization. The target signal after Doppler frequency correction in the imaging region is then subjected to full-grid Doppler correction to obtain the target matrix. Based on the target matrix, the sampling points of the sub-pulses are sampled, rearranged, and concatenated to obtain the output matrix. Based on the output matrix, polar coordinate radial compression is performed through inverse Fourier transform to obtain the focused signal.

[0082] In some embodiments, full-grid Doppler correction is performed on the target signal after Doppler frequency correction in the imaging region to obtain a target matrix. This includes: dividing the target signal after Doppler frequency correction in the imaging region into a matrix in fast-time sampling to obtain several two-dimensional matrices; performing a discrete Fourier transform in slow time based on the two-dimensional matrices, and performing full-grid Doppler correction through the full-grid correction matrix to obtain the target matrix.

[0083] In some embodiments, full-grid Doppler correction is performed using a full-grid correction matrix, including: eliminating Doppler-dependent phase incoherence using the full-grid correction matrix to complete full-grid Doppler correction; wherein the expression for the full-grid correction matrix is:

[0084]

[0085] in, Let n denote the full-grid correction matrix, e denote the natural constant, j denote the imaginary unit, and n represent the full-grid correction matrix. a The nth step of the random step linear frequency modulation waveform a The nth pulse group, where n represents the nth pulse group. a The nth sub-pulse of the nth pulse group, N represents the nth sub-pulse. a The number of sub-pulses in each pulse group, N a This indicates the number of pulse groups in a random-step linear frequency modulated waveform. It represents N×N a A set of matrices of dimension 1, that is, a set of matrices of dimension 2, representing It is an N×N a A 3D matrix.

[0086] Specifically, in some embodiments, in order to achieve frequency synthesis within a pulse group, the Doppler-dependent incoherence problem must be addressed. The specific steps for coarse Doppler extraction and localization are as follows; here, the coarse Doppler can be calculated as:

[0087] f dc =2vsinθ t f c / c

[0088] Signals with different azimuth angles will carry different Doppler frequencies f. dc By f dc The resulting Doppler phase continuity will be disrupted by frequency rearrangement. Therefore, it is necessary to correct the Doppler frequency f of the entire imaging region before frequency rearrangement. dc .

[0089] The discrete form of the signal in coarse Doppler calculation can be written as:

[0090] S rs (m, n, n) a )=exp{-j(K n +K fm )(r t -r c )}·exp{j2πf dc [(n-1)+(n a -1)N]T r}

[0091] In the formula, S rs (m, n, n) a ) represents the nth a The m-th sampling point of the n-th sub-pulse in a pulse group. The value of m ranges from 1 to M, where M is the value of T. p The total number of sampling points in K. n It is related to the center frequency f n The relevant radial wavenumber, K n =4πf n / c,K fm K is the radial wavenumber corresponding to the modulation frequency within a fast time interval. fm =4πγ(m-1) / f s c, f s This indicates the sampling rate.

[0092] Then, full-grid Doppler correction is performed. The specific steps are as follows: Since the instantaneous distance within a linear frequency modulated pulse is approximately constant, this embodiment of the invention divides the signal into M two-dimensional matrices during fast-time sampling. The m-th two-dimensional matrix can be represented as:

[0093]

[0094] in:

[0095]

[0096]

[0097]

[0098]

[0099] As shown in the expression for a two-dimensional matrix, S rs，m Each item contains a slow-time Doppler exponent. Since the frequency hopping pattern is consistent across all columns, S... rs，m It is a rank-1 matrix. Therefore, performing the DFT (Discrete Fourier Transform) on the slow time of the pulse group (i.e., the pulse set) can compress each target into its corresponding Doppler grid.

[0100]

[0101] In the formula, l v =f dc / T r NN a The Doppler grid index of the target; ζ N (l) is a column vector, where the value of the l-th element is... All other elements are 0; F N Let be the DFT matrix. Where ζ N (l) is a function representation, where in the above formula... Represents ζ N (l) This function in l = l v N = N a In the case of T, T represents the matrix transpose.

[0102]

[0103] Since the target is separated and compressed into its corresponding Doppler grid, Doppler correction within the pulse group is achieved using a complete grid correction matrix (i.e., the full grid correction matrix), as shown below:

[0104]

[0105] matrix The exponential term in the matrix corresponds to the Doppler phase term at each grid location. Element-wise multiplication can eliminate S v，m The Doppler phase of each column eliminates Doppler-dependent phase incoherence.

[0106]

[0107] In the formula, ⊙ represents the Hadamard product. Full-grid Doppler correction eliminates the Doppler phase at the m-th sampling point of all linear frequency modulated pulses in a random-step linear frequency modulated waveform. The same correction operation is performed on all M two-dimensional matrices. Using S... vc，m S represents rs，mThe matrix after full-grid Doppler correction. The performance of full-grid Doppler correction depends not only on the accuracy of the coarse Doppler model based on slow-time Taylor expansion, but also on the size of the discrete Doppler grid.

[0108] After full-grid Doppler correction, the sampling points of all sub-pulses in each pulse group are rearranged and concatenated (i.e., rearrangement and concatenation are used), reconstructing a broadband spectrum in the Doppler domain. denoted as , this represents the output matrix after rearrangement and concatenation. Frequency synthesis is now complete. Range compression (i.e., polar coordinate radial compression) can be achieved using MN-point (i.e., M×N-point) IFT (Inverse Fourier Transform). The focused signal is as follows:

[0109]

[0110] in, S represents the inverse Fourier transform of M×N points; vc_reorder Represents the rearranged and serialized signals; ζ MN (·) Similar to the previous ones That is ζ N (l) The case of the function when N = M × N; r Indicates the distance to the peak index.

[0111] S400: Perform angle fine focusing processing on the focusing signal to obtain a SAR focused image;

[0112] It should be noted that angle-based fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation, and polar coordinate angle compression. In some embodiments, the angle information of the focusing signal is recovered by inverse Fourier transform to obtain the recovered signal; based on the recovered signal, phase compensation and radial gate-based angular wavenumber interpolation are performed to obtain the polar coordinate angular wavenumber interval; based on the polar coordinate angular wavenumber interval, a discrete Fourier transform is performed in the angular wavenumber domain to obtain the SAR focused image.

[0113] In some embodiments, based on the polar coordinate angular wavenumber interval, a SAR focused image is obtained by performing a discrete Fourier transform in the angular wavenumber domain. This includes: compressing the azimuth angle by performing a discrete Fourier transform in the angular wavenumber domain according to the polar coordinate angular wavenumber interval, obtaining the focused target in the polar coordinate system, and thus obtaining the SAR focused image; wherein the expression for the focused target is:

[0114]

[0115] Among them, S ra (r t θ t () represents the focused target, and DFT represents the Discrete Fourier Transform. Indicates the recovery signal, S ref(r t ) represents the polar coordinate angular wavenumber interval, sinc(r) t -r c ) represents the distance dimension function of the focused target, sinc(θ) t ) represents the angular dimension function of the focused target.

[0116] Specifically, in some embodiments, radial focusing and Doppler coarse focusing are achieved through the preceding steps. Since the radial and Doppler domains are not perfectly orthogonal, imaging performance is reduced, especially when the target is far from the scene center. Therefore, angle information recovery is performed, specifically using IFT (Inverse Fourier Transform) to recover the Doppler information between pulse groups in slow time. The recovered signal (i.e., the recovered signal) is represented as follows:

[0117]

[0118] In the formula, The pulse group is slow in time.

[0119] In this case, Applying θ, which is orthogonal to the radial domain t Taylor expansion, at θ t The expanded expression at =0 is:

[0120]

[0121] In the formula, Represents point (r) t The instantaneous slant distance of ,0) Represents point (r) c The instantaneous slant distance of ,0) This represents second-order and higher-order terms. It has been proven that in focus mode, when the target's polar angle is relatively small, the second-order and higher-order phase terms have little impact on imaging performance. Therefore, these terms can be omitted, and the recovered signal can be rewritten as:

[0122]

[0123] In the formula, Defined as the polar coordinate angular wavenumber. After S... ref After phase compensation and radial gate-based angular wavenumber interpolation, equal polar coordinate angular wavenumber intervals were obtained. The phase compensation term is represented by the following expression:

[0124]

[0125] By performing DFT in the angular wavenumber domain, the azimuth angle can be compressed (i.e., polar coordinate angle compression), thereby obtaining the focused target in the polar coordinate system.

[0126]

[0127] In summary, the purpose of this invention is to propose a SAR imaging method that solves the aforementioned problems through random step linear frequency modulated SAR imaging based on full-grid Doppler correction. Considering that the waveform consists of repeating pulse groups, this waveform structure can be used for Doppler separation. Correction processing for different Doppler grid positions eliminates Doppler phase in sub-bands, thereby solving the incoherence problem of Doppler dependence between sub-bands after frequency rearrangement. Frequency synthesis can be achieved in the Doppler domain before final imaging. This invention integrates full-grid Doppler correction into the polar coordinate imaging algorithm of random step linear frequency modulated SAR, maintaining unchanged parameters and procedures for any random step frequency arrangement. The beneficial effects of this invention include: achieving Doppler correction for the entire scene through the imaging processing method, thus successfully eliminating incoherent phase between sub-bands before frequency synthesis. It effectively improves the problem of decreased range focusing performance with increasing azimuth angle in existing processing methods, significantly enhancing range focusing performance.

[0128] On the other hand, such as Figure 5 As shown, an embodiment of the present invention provides a SAR imaging system 500, comprising: a first module 510 for acquiring raw echo data; the raw echo data is a random step linear frequency modulated waveform; a second module 520 for decoupling the raw echo data to obtain a target signal; the decoupling process includes deskewing and azimuth resampling; a third module 530 for performing frequency synthesis processing on the target signal based on a full-grid correction matrix to obtain a focused signal; the frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sample rearrangement and concatenation, and polar coordinate radial compression; and a fourth module 540 for performing angle fine focusing processing on the focused signal to obtain a SAR focused image; the angle fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation, and polar coordinate angle compression.

[0129] The content of the method embodiments of the present invention is applicable to the system embodiments. The specific functions implemented in the system embodiments are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0130] like Figure 6 As shown, another aspect of the present invention provides a SAR imaging device 600, including a processor 610 and a memory 620;

[0131] Memory 620 is used to store programs;

[0132] The processor 610 executes the program as described above.

[0133] The content of the method embodiments of the present invention is applicable to the device embodiments. The specific functions implemented by the device embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0134] Another aspect of this invention provides a computer-readable storage medium storing a program that is executed by a processor to implement the method described above.

[0135] The content of the method embodiments of the present invention is applicable to the computer-readable storage medium embodiments. The specific functions implemented by the computer-readable storage medium embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0136] This invention also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform the aforementioned method.

[0137] In some alternative embodiments, the functions / operations mentioned in the block diagrams may not occur in the order shown in the operation diagrams. For example, depending on the functions / operations involved, two consecutively shown blocks may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order. Furthermore, the embodiments presented and described in the flowcharts of this invention are provided by way of example to provide a more comprehensive understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed and sub-operations described as part of a larger operation are executed independently.

[0138] Furthermore, although the invention has been described in the context of functional modules, it should be understood that, unless otherwise stated, one or more of the functions and / or features may be integrated into a single physical device and / or software module, or one or more functions and / or features may be implemented in a separate physical device or software module. It is also understood that a detailed discussion of the actual implementation of each module is unnecessary for understanding the invention. Rather, given the properties, functions, and internal relationships of the various functional modules in the apparatus disclosed herein, the actual implementation of the module will be understood within the scope of conventional skill of an engineer. Therefore, those skilled in the art can implement the invention as set forth in the claims using ordinary techniques without excessive experimentation. It is also understood that the specific concepts disclosed are merely illustrative and not intended to limit the scope of the invention, which is determined by the full scope of the appended claims and their equivalents.

[0139] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0140] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution means, apparatus, or device (such as a computer-based device, a processor-including device, or other means that can fetch and execute instructions from, or in conjunction with, an instruction execution means, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution means, apparatus, or device.

[0141] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which programs can be printed, because programs can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0142] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution device. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0143] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0144] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0145] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A SAR imaging method, characterized in that, include: Acquire raw echo data; the raw echo data is a random step linear frequency modulated waveform; The original echo data is decoupled to obtain the target signal; The decoupling process includes deskewing and azimuth resampling; Based on the full-grid correction matrix, the target signal is subjected to frequency synthesis processing to obtain the focusing signal; The frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sample rearrangement and concatenation, and polar coordinate radial compression. The focusing signal is subjected to angle fine focusing processing to obtain a SAR focused image; the angle fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation and polar coordinate angle compression. The step of performing frequency synthesis processing on the target signal based on a full-grid correction matrix to obtain a focusing signal includes: The Doppler frequency of the imaging region of the target signal is corrected by coarse Doppler extraction and localization. The target signal after Doppler frequency correction in the imaging region is subjected to full-grid Doppler correction to obtain the target matrix; Based on the target matrix, the sampling points of the sub-pulses are sampled, rearranged, and concatenated to obtain the output matrix; Based on the output matrix, a focused signal is obtained by polar coordinate radial compression through inverse Fourier transform; The process of performing angle fine-focusing processing on the focusing signal to obtain a SAR focused image includes: The angle information of the focusing signal is recovered by inverse Fourier transform to obtain the recovered signal; Based on the recovered signal, phase compensation and radial gate-based angular wavenumber interpolation are performed to obtain the polar coordinate angular wavenumber interval. Based on the polar coordinate angular wavenumber interval, a SAR focused image is obtained by performing a discrete Fourier transform in the angular wavenumber domain.

2. The SAR imaging method according to claim 1, characterized in that, The process of decoupling the original echo data to obtain the target signal includes: By describing the random step linear frequency modulated waveform and combining it with the deskewing process, a signal model is obtained; Based on the aforementioned signal model, the target signal is obtained by performing range migration correction through azimuth resampling.

3. The SAR imaging method according to claim 1, characterized in that, The target signal, after being corrected for the Doppler frequency of the imaging region, undergoes full-grid Doppler correction to obtain a target matrix, including: In fast-time sampling, the target signal after Doppler frequency correction in the imaging region is matrix-divided to obtain several two-dimensional matrices; Based on the two-dimensional matrix, a discrete Fourier transform is performed in slow time, and full-grid Doppler correction is performed through the full-grid correction matrix to obtain the target matrix.

4. A SAR imaging method according to claim 3, characterized in that, The full-grid Doppler correction using a full-grid correction matrix includes: Doppler-dependent phase incoherence is eliminated by using a full-grid correction matrix, thus completing full-grid Doppler correction. The expression for the full-grid correction matrix is ​​as follows: in, Represents the full-grid correction matrix. Represents the natural constant. Represents the imaginary unit. The first step of the random step linear frequency modulation waveform represents the first step of the random step linear frequency modulation waveform. A pulse group, Indicates the first The first sub-pulse of a pulse group Indicates the first Number of sub-pulses in each pulse group This indicates the number of pulse groups in a random-step linear frequency modulated waveform. Indicates by A set of matrices of dimension 1.

5. A SAR imaging method according to claim 1, characterized in that, The process of obtaining a SAR focused image based on the polar coordinate angular wavenumber interval by performing a discrete Fourier transform in the angular wavenumber domain includes: Based on the polar coordinate angular wavenumber interval, the azimuth angle is compressed by performing discrete Fourier transform in the angular wavenumber domain, and the focused target is obtained in the polar coordinate system to obtain the SAR focused image. The expression for the focusing target is: in, This indicates a focus on the objective. Represents the Discrete Fourier Transform. Indicates a recovery signal. Represents the polar coordinate angular wavenumber interval. This represents the distance dimension function of the focused target. This represents the angular dimension function of the focused target.

6. A SAR imaging system, characterized in that, include: The first module is used to acquire raw echo data; the raw echo data is a random step linear frequency modulated waveform. The second module is used to decouple the original echo data to obtain the target signal; the decoupling process includes deskewing and azimuth resampling. The third module is used to perform frequency synthesis processing on the target signal based on the full-grid correction matrix to obtain the focusing signal; The frequency synthesis processing includes coarse Doppler extraction and localization, full-grid Doppler correction, sample rearrangement and concatenation, and polar coordinate radial compression. The fourth module is used to perform angle fine focusing processing on the focusing signal to obtain a SAR focused image; the angle fine focusing includes angle signal recovery, phase compensation, angular wavenumber interpolation, and polar coordinate angle compression. The step of performing frequency synthesis processing on the target signal based on a full-grid correction matrix to obtain a focusing signal includes: The Doppler frequency of the imaging region of the target signal is corrected by coarse Doppler extraction and localization. The target signal after Doppler frequency correction in the imaging region is subjected to full-grid Doppler correction to obtain the target matrix; Based on the target matrix, the sampling points of the sub-pulses are sampled, rearranged, and concatenated to obtain the output matrix; Based on the output matrix, a focused signal is obtained by polar coordinate radial compression through inverse Fourier transform; The process of performing angle fine-focusing processing on the focusing signal to obtain a SAR focused image includes: The angle information of the focusing signal is recovered by inverse Fourier transform to obtain the recovered signal; Based on the recovered signal, phase compensation and radial gate-based angular wavenumber interpolation are performed to obtain the polar coordinate angular wavenumber interval. Based on the polar coordinate angular wavenumber interval, a SAR focused image is obtained by performing a discrete Fourier transform in the angular wavenumber domain.

7. A SAR imaging device, comprising a processor and a memory; The memory is used to store programs; The processor executes the program to implement the method as described in any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that, The storage medium stores a program that is executed by a processor to implement the method as described in any one of claims 1 to 5.

Images