High resolution wide swath imaging method, apparatus, and storage medium

Abstract

The application provides a high-resolution wide-surveying-band imaging method, device and storage medium, and belongs to the technical field of data processing. The method is applied to a synthetic aperture radar, and comprises the following steps: the synthetic aperture radar randomly selects a current pulse repetition frequency in a predetermined pulse repetition frequency value range every preset interval, and adjacent two current pulse repetition frequencies are different and discontinuous; according to the current pulse repetition frequency, the synthetic aperture radar transmits a pulse signal and receives a target-reflected echo signal; and the fast iterative soft threshold algorithm is used to process the target-reflected echo signal, so that a sparse reconstructed target imaging result is obtained. The application aims to solve the problem of high-resolution wide-surveying-band of a single-channel SAR system.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of data processing, and in particular to a high-resolution wide-swath imaging method, device, and storage medium. Background Art

[0002] Synthetic Aperture Radar (SAR) is a high-resolution imaging radar that can obtain high-resolution radar images similar to optical photography under extremely low visibility weather conditions. It can be installed on carrier platforms such as satellites and aircraft. While the platform moves, the radar transmits electromagnetic wave pulses and receives echo signals reflected from the target area, and obtains an image of the scene through data processing.

[0003] With the rapid development of science and technology, the requirements for spaceborne SAR imaging performance are constantly increasing. In many applications, high-resolution, wide-swath SAR imaging is required. However, in single-channel SAR systems, the two key performance indicators of azimuth resolution and range bandwidth conflict with each other. Specifically, improving azimuth resolution requires increasing the pulse repetition frequency (PRF), while increasing range bandwidth requires decreasing the PRF.

[0004] Therefore, how to achieve high-resolution wide swath mapping of the widely used single-channel SAR system is an urgent problem to be solved. Summary of the Invention

[0005] The embodiments of the present application provide a high-resolution wide-swath imaging method, apparatus, and storage medium, which aim to solve the problem of high-resolution wide-swath imaging in a single-channel SAR system.

[0006] In a first aspect, an embodiment of the present application provides a radar high-resolution wide swath imaging method based on azimuthally randomly variable PRF sampling, which is applied to a synthetic aperture radar. The method includes:

[0007] The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range at every preset interval, and two adjacent current pulse repetition frequencies are different and discontinuous;

[0008] According to the current pulse repetition frequency, the synthetic aperture radar transmits a pulse signal and receives an echo signal reflected by a target;

[0009] The echo signal reflected by the target is processed by a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

[0010] Optionally, the method further includes:

[0011] Drawing a zebra diagram according to the constraints on pulse repetition frequency of the synthetic aperture radar's transmitted pulse and the sub-satellite point echo;

[0012] According to the zebra diagram obtained by drawing, a value range of the pulse repetition frequency of the synthetic aperture radar is determined.

[0013] Optionally, the constraint of the transmit pulse on the pulse repetition frequency is expressed as:

[0014]

[0015]

[0016]

[0017] The constraint of the sub-satellite echo on the pulse repetition frequency is expressed as:

[0018] 2H / c+k / f r >2R f / c,k=0,±1,…,±n

[0019] 2H / c+2τ+k / f r <2R n / c,k=0,±1,…,±n

[0020] Where, f r is the pulse repetition frequency PRF, Frac(·) represents the fractional part, Int(·) represents the integer part, R n is the minimum slant distance to the observation area, R f is the farthest slant distance of the observation area, τ p is the pulse width, τ g is the protection time band, c is the speed of light, n is the number of transmitted pulses, H is the orbital height of the satellite, and τ is the pulse width τ p With the protection time band τ g The sum of , k is the sequence number of the pulse repetition period.

[0021] Optionally, the synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range at every preset interval, including:

[0022] The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range every M pulse signals, wherein M is a positive integer greater than 1.

[0023] Optionally, the pulse signal transmitted by the synthetic aperture radar includes a linear frequency modulation pulse signal, and the linear frequency modulation pulse signal is in the form of:

[0024]

[0025] Where τ represents the distance to the fast time, T p represents the duration of the linear frequency modulation pulse, f0 represents the carrier frequency of the transmitted signal, K r represents the linear modulation frequency, rect(·) represents the rectangular window function, and j is the imaginary unit.

[0026] Optionally, after receiving the echo signal reflected by the target, the method further includes:

[0027] The echo signal reflected by the target is represented as the first echo signal. The first echo signal is the result of the two-dimensional convolution of the impulse response of the synthetic aperture radar system and the scene scattering coefficient, and is in the form of:

[0028]

[0029] Where τ represents the fast time in range, t represents the slow time in azimuth, x represents the azimuth coordinate, y represents the range coordinate, σ(x,y) represents the scattering coefficient of the target at the position (x,y) in space, and w a (·) represents the envelope function of the azimuth beam pattern, p(τ) is the linear frequency modulation pulse signal, R(x, y, t) is the slant range function between the radar and the target, which is related to the target's position and azimuth slow time, λ is the central wavelength of the synthetic aperture radar, c represents the speed of light, N(τ, t) represents the additive noise at the receiving end of the synthetic aperture radar, and V is the equivalent velocity of the synthetic aperture radar platform;

[0030] The echo signal of synthetic aperture radar is discretely sampled and expressed as the second echo signal s(τ nr ,t na ):

[0031]

[0032]

[0033] Where, the second echo signal is the first echo signal s(τ,t)nth a The nth pulse r Sample values, M r Indicates the number of discrete scattering points in the scene in the distance direction, M a They represent the number of discrete scattering points in the scene, It is located in the mth direction a coordinates, distance to the mth r The scattering intensity coefficient of the scattering point with coordinates, is the discretized additive noise;

[0034] The second echo signal in the form of two-dimensional discrete data and scattering intensity coefficient Expressed in matrix form:

[0035] The matrix representation of the second echo signal is:

[0036] The matrix expression of the scattering intensity coefficient is:

[0037] Then the matrix representation of the echo signal is y=Ax+n;

[0038] Where N a Indicates the number of pulses transmitted in azimuth, N r Represent the number of sampling points of each pulse in the range direction, y and x represent the vectorized results of matrices Y and X respectively, n is the additive noise vector, and the matrix A is in the following form:

[0039]

[0040] Optionally, the echo signal reflected by the target is processed by a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result, including:

[0041] Build a sparse optimization model:

[0042]

[0043] Where, is the reconstructed scene image, ρ is the regularization parameter, ||·|| F represents the Frobenius norm of the matrix, and ||·||1 represents the L1 norm of the matrix;

[0044] The sparsely reconstructed target imaging result is obtained by solving the problem through a fast iterative soft threshold algorithm.

[0045] Optionally, a fast iterative soft threshold algorithm is used to solve the problem, thereby obtaining a sparsely reconstructed target imaging result, including:

[0046] A1: Initialize parameters and variables: Initialize iterative result estimation Residual vector r (0) =y, iteration number k=1, vector Variable t1=1, maximum number of iterations I max , constant threshold

[0047] A2: Calculate current estimate in, is the soft threshold operator, A Hrepresents the conjugate transpose of matrix A;

[0048] A3: Calculate the residual vector:

[0049] A4: Calculation

[0050] A5: Update vector:

[0051] A6: Calculate: and Δf=|f k -f k-1 | / f k-1 ;

[0052] If Δf≤δ or k>I max , then the iteration ends and the sparsely reconstructed target imaging result is obtained. Otherwise, let k = k + 1 and return to step A2.

[0053] In a second aspect, an embodiment of the present application provides a radar high-resolution wide-swath imaging device based on azimuthally randomly variable PRF sampling, the device comprising:

[0054] A random selection module is used for randomly selecting a current pulse repetition frequency from a predetermined pulse repetition frequency range at a preset interval for the synthetic aperture radar, wherein two adjacent current pulse repetition frequencies are different and discontinuous;

[0055] a transmitting and receiving module, configured to transmit a pulse signal from the synthetic aperture radar and receive an echo signal reflected by a target according to the current pulse repetition frequency;

[0056] The imaging processing module is used to process the echo signal reflected by the target through a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

[0057] In a third aspect, an embodiment of the present application provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the radar high-resolution wide-swath imaging method based on azimuthally randomly variable PRF sampling as described in the first aspect of the embodiment.

[0058] Beneficial effects:

[0059] The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency range at preset intervals, and two adjacent current pulse repetition frequencies are different and discontinuous; based on the current pulse repetition frequency, the synthetic aperture radar transmits a pulse signal and receives an echo signal reflected by the target; and the echo signal reflected by the target is processed using a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

[0060] In this method, the synthetic aperture radar randomly selects a pulse repetition frequency to transmit a pulse signal at every preset interval, which makes the sampler design easy and the imaging quality high. At the same time, the sparse reconstruction method and the fast iterative soft threshold algorithm adopted have low computational complexity and high operating efficiency. Compared with the traditional linear frequency modulation scaling (CSA) imaging method, this method has a larger range mapping bandwidth and a smaller echo data size. It improves the real-time processing capability with almost no loss of imaging quality, reduces the complexity of hardware design, and significantly improves the high resolution and wide mapping swath mapping capabilities of the single-channel SAR system. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0062] Figure 1 This is a flowchart of the steps of a radar high-resolution wide swath imaging method based on azimuthally randomly variable PRF sampling proposed in one embodiment of the present application;

[0063] Figure 2 This is a zebra diagram proposed in one embodiment of the present application;

[0064] Figure 3 is a schematic diagram of a pulse train and pulse repetition frequency proposed in one embodiment of the present application;

[0065] Figure 4 This is a schematic diagram of the imaging results obtained using the traditional linear frequency modulation scaling CSA algorithm;

[0066] Figure 5 This is a schematic diagram of the high-resolution wide-swath imaging results obtained using the azimuthal Poisson disk undersampling method;

[0067] Figure 6 is a schematic diagram of the imaging results obtained using the imaging method of the present application;

[0068] Figure 7 This is a functional module diagram of a radar high-resolution wide-swath imaging device based on azimuthally randomly variable PRF sampling proposed in one embodiment of the present application. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0070] In a single-channel synthetic aperture radar (SAR) system, there is an inherent contradiction between the two important indicators: azimuth resolution and range mapping bandwidth. Improving azimuth resolution requires increasing the pulse repetition frequency (PRF), while increasing the range mapping bandwidth requires reducing the PRF. This contradiction is reflected in various operating modes, such as strip, beam, and scanning. Strip mode SAR cannot achieve both high azimuth resolution and a wide range mapping swath. Beam mode increases the synthetic aperture time to improve azimuth resolution, but since increasing the Doppler bandwidth requires a larger PRF, this will reduce the range mapping bandwidth. Scanning mode increases the range mapping bandwidth through range scanning, but at the same time reduces the synthetic aperture time, resulting in a loss of azimuth resolution.

[0071] To address the contradiction between azimuth resolution and range mapping bandwidth, some existing solutions mainly use a multi-channel perspective to achieve high-resolution wide-swath imaging. For example, by using technologies such as shifted phase center antenna (DPCA) and digital beamforming (DBF), or by adopting small satellite formations, the imaging results of multiple channels are stitched together to achieve the goal of simultaneously achieving high resolution and wide-swath imaging.

[0072] However, multi-channel imaging systems require the deployment of multiple antennas and even multiple satellite platforms, and system parameter design is more complex. This requires high system complexity and hardware design, making it difficult to implement on currently deployed single-channel spaceborne SAR systems or on low-cost spaceborne SAR systems planned for future launches. Therefore, achieving high resolution and wide swath coverage for widely used single-channel SAR systems is an urgent issue that needs to be addressed.

[0073] In order to solve the problem of high resolution and wide swath of a single-channel SAR system, this application proposes a radar high-resolution wide swath imaging method based on azimuthally randomly variable PRF sampling.

[0074] Reference Figure 1 , shows a flowchart of a radar high-resolution wide swath imaging method based on azimuthally randomly variable PRF sampling in an embodiment of the present invention, which is applied to synthetic aperture radar. The method includes the following steps:

[0075] S101: The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range at every preset interval, and two adjacent current pulse repetition frequencies are different and discontinuous.

[0076] In spaceborne SAR systems, two main issues need to be considered when determining the value range of the pulse repetition frequency (PRF) of the synthetic aperture radar: avoiding aliasing of the return signal and avoiding interference from the sub-satellite point echo. Therefore, the PRF needs to be restricted so that the transmitted pulse and the sub-satellite point echo do not fall within the target's echo receiving window.

[0077] In a feasible implementation, when determining the value range of the pulse repetition frequency (PRF) of a synthetic aperture radar, a zebra diagram can be drawn based on the constraints on the pulse repetition frequency imposed by the synthetic aperture radar's transmitted pulse and the sub-satellite point echo; and then, based on the drawn zebra diagram, the value range of the pulse repetition frequency of the synthetic aperture radar can be determined.

[0078] Specifically, the constraint of the transmit pulse on the pulse repetition frequency is expressed as:

[0079]

[0080]

[0081]

[0082] The constraint of the sub-satellite echo on the pulse repetition frequency is expressed as:

[0083] 2H / c+k / f r >2R f / c,k=0,±1,…,±n

[0084] 2H / c+2τ+k / f r <2R n / c,k=0,±1,…,±n

[0085] Where, f r is the pulse repetition frequency PRF, Frac(·) represents the fractional part, Int(·) represents the integer part, R n is the minimum slant distance to the observation area, R f is the farthest slant distance of the observation area, T n is the echo time corresponding to the nearest slant range, T f is the echo time corresponding to the farthest slant range, τ p is the pulse width, τ g is the protection time band, c is the speed of light, n is the number of transmitted pulses, H is the orbital height of the satellite, and τ is the pulse width τ p With the protection time band τ gThe sum of , k is the sequence number of the pulse repetition period.

[0086] Reference Figure 2 , shows a zebra diagram provided by an embodiment of the present application, where the horizontal axis is the pulse repetition frequency PRF, and the vertical axis is the distance between the carrier platform of the synthetic aperture radar and the target. This method is different from the traditional strip mode. In order to avoid echo signal aliasing and interference from the sub-satellite point echo, the relationship curve between the pulse repetition frequency PRF and the incident angle is obtained according to the constraints of the transmitted pulse and the sub-satellite point echo on the pulse repetition frequency, and a zebra diagram is drawn. Then, based on the zebra diagram, the interval for selecting the pulse repetition frequency PRF is obtained. The obtained interval is the value range of the pulse repetition frequency PRF of the synthetic aperture radar.

[0087] Subject to Figure 2 The zebra diagram shown in the figure constrains that the selected pulse repetition frequency PRF value range should not conflict with the transmitted pulse and the sub-satellite point echo. Figure 2 The PRF value range shown includes two areas on the left and right. When selecting the current pulse repetition frequency from the PRF value range, you can alternately select from the left and right areas, that is, first randomly select a PRF value in the left area, then randomly select a PRF value in the right area, then return to the left area to randomly select a PRF value, and so on.

[0088] When transmitting a pulse signal, the SAR randomly selects a pulse repetition frequency (PRF) within a predetermined range at preset intervals. Adjacent pulse repetition frequencies are different and discontinuous. This ensures random sampling in azimuth, improving imaging quality. This ensures that the receiving window for the target's reflected echo signal always falls completely within the diamond-shaped area of ​​the zebra pattern formed by the transmitted pulse and the sub-satellite echo.

[0089] Reference Figure 3 , showing a schematic diagram of the pulse train and pulse repetition frequency provided by an embodiment of the present application. In actual implementation, the synthetic aperture radar can randomly select the current pulse repetition frequency from a predetermined pulse repetition frequency value range every M pulse signals, where M is a positive integer greater than 1, and the pulse repetition frequency corresponding to each group is different and discontinuous. The value of the qth group is PRF q , q = 1, 2, ..., N, where N represents the number of selected PRF groups.

[0090] S102: According to the current pulse repetition frequency, the synthetic aperture radar transmits a pulse signal and receives an echo signal reflected by a target.

[0091] While the carrier platform of the synthetic aperture radar moves relative to the target along the route, a pulse signal is transmitted according to the current pulse transmission frequency. The pulse signal transmitted by the synthetic aperture radar includes a linear frequency modulation pulse signal. The linear frequency modulation pulse signal has the form of:

[0092]

[0093] Where τ represents the fast time in distance, t represents the slow time in azimuth, and T p represents the duration of the linear frequency modulation pulse, f0 represents the carrier frequency of the transmitted signal, K r represents the linear modulation frequency, rect(·) represents the rectangular window function, and j is the imaginary unit.

[0094] In a feasible implementation manner, after receiving the echo signal reflected by the target, the processing process includes:

[0095] S1: The echo signal reflected by the target is expressed as the first echo signal. The first echo signal is the result of the two-dimensional convolution of the impulse response of the synthetic aperture radar system and the scene scattering coefficient, and is in the form of:

[0096]

[0097] Where τ represents the fast time in range, t represents the slow time in azimuth, x represents the azimuth coordinate, y represents the range coordinate, σ(x,y) represents the scattering coefficient of the target at the position (x,y) in space, and w a (·) represents the envelope function of the azimuth beam pattern, p(τ) is the linear frequency modulation pulse signal, R(x, y, t) is the slant range function between the radar and the target, which is related to the target's position and azimuth slow time, λ is the central wavelength of the SAR, c represents the speed of light, N(τ, t) represents the additive noise at the SAR receiver, and V is the equivalent velocity of the SAR platform.

[0098] S2: The echo signal of the synthetic aperture radar is discretely sampled and represented as the second echo signal

[0099] in

[0100]

[0101] Where, the second echo signal is the first echo signal s(τ,t)nth a The nth pulse r Sample values, M r Indicates the number of discrete scattering points in the scene in the distance direction, M aThey represent the number of discrete scattering points in the scene, It is located in the mth direction a coordinates, distance to the mth r The scattering intensity coefficient of the scattering point with coordinates, is the discretized additive noise;

[0102] S3: The second echo signal in the form of two-dimensional discrete data and scattering intensity coefficient Expressed in matrix form:

[0103] The matrix representation of the second echo signal is:

[0104] The matrix expression of the scattering intensity coefficient is:

[0105] Then the matrix representation of the echo signal is y=Ax+n;

[0106] Where N a Indicates the number of pulses transmitted in azimuth, N r Represent the number of sampling points of each pulse in the range direction, y and x represent the vectorized results of matrices Y and X respectively, n is the additive noise vector, and the matrix A is in the following form:

[0107]

[0108] S103: Processing the echo signal reflected by the target by a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

[0109] Because the received echo signals are undersampled in azimuth, we take advantage of the sparsity of the scene and use the compressed sensing method to accurately reconstruct the observed scene from the undersampled echo data. Specifically, we first build a sparse optimization model:

[0110]

[0111] Where, is the reconstructed scene image, ρ is the regularization parameter, ||·|| F represents the Frobenius norm of the matrix, and ||·||1 represents the L1 norm of the matrix;

[0112] Then, the sparse optimization problem is solved by a fast iterative soft threshold algorithm to obtain the sparse reconstructed target imaging result. The solution process specifically includes the following steps:

[0113] A1: Initialize parameters and variables:

[0114] Initialization iterative result estimation Residual vector r (0) =y, iteration number k=1, vector Variable t1=1, maximum number of iterations I max , constant threshold

[0115] A2: Calculate current estimate in, is the soft threshold operator, A H represents the conjugate transpose of matrix A;

[0116] For any vector Where N is the dimension of vector z, z p is the p-th component of vector z, p = 1, 2, ..., N, and has the following relationship:

[0117]

[0118] in,

[0119]

[0120] Where sgn(·) is the sign function;

[0121] A3: Calculate the residual vector:

[0122] A4: Calculation

[0123] A5: Update vector:

[0124] A6: Calculate: and Δf=|f k -f k-1 | / f k-1 ;

[0125] If Δf≤δ or k>Imax, the iteration ends and the sparsely reconstructed target imaging result is obtained. Otherwise, set k=k+1 and return to step A2.

[0126] This invention addresses the need for high-resolution, wide-swath synthetic aperture radar (SAR) imaging. Leveraging the Fast Iterative Threshold Reconstruction Algorithm (FISTA), this method achieves high-resolution, wide-swath imaging of a scene using an azimuthally variable repetition rate sampling pattern below the Nyquist sampling rate. Compared to traditional line-frequency modulated SAR imaging methods, this method achieves a larger bandwidth. Compared to existing wide-swath SAR imaging methods based on non-uniform sampling patterns, this method significantly reduces computational complexity and improves imaging quality.

[0127] For example, the effect of the imaging method proposed in this method is verified by using the measured spaceborne SAR echo data.

[0128] The raw data parameters of the spaceborne GF-3 radar are as follows: sampling rate fs = 66.66 MHz, signal bandwidth B = 60 MHz, range modulation rate Kr = 2.4 MHz / μs, pulse width Tp = 25 μs, carrier frequency F = 5.4 GHz, pulse repetition frequency prf = 2589.17 Hz, and platform velocity v = 7126 m / s. The raw echo data size selected for this example is 2700 × 4400 (2700 in range and 4400 in azimuth).

[0129] Reference Figure 4 , shows a schematic diagram of the imaging results obtained using the traditional linear frequency modulation scaling CSA algorithm; refer to Figure 5 , shows a schematic diagram of high-resolution wide-swath imaging results obtained using the azimuth Poisson disk undersampling method. The scale of the undersampled echo data is 2700×2200 (2700 in range and 2200 in azimuth).

[0130] To simulate the generation of echo data using a random PRF sampling pattern in azimuth, the original radar echo data is first upsampled 30 times in azimuth. The upsampled echo data is then resampled using the random PRF sampling pattern in this method. The random PRF value is determined based on the value range within the zebra pattern, with the PRF changing every 100 pulses. (In this embodiment, 22 random PRFs are selected; in practice, more PRFs can be selected, with the number of transmitted pulses for each PRF ranging from 50 to 150.) In this random PRF sampling pattern, the minimum interval between azimuth sampling moments is no less than 1.5 times that of the traditional CSA method. This reduces the size of the echo data while providing 1.5 times the range mapping bandwidth.

[0131] Reference Figure 6 , shows a schematic diagram of the imaging results obtained by using this method in this embodiment. The scale of the undersampled echo data is 2700×2200 (2700 in range and 2200 in azimuth). Obviously, the scene imaging result obtained by using this method is clear, without obvious azimuth aliasing phenomenon. The same number of undersampled points in azimuth is obtained. Figure 5 The proposed method has similar imaging performance to the Poisson disk sampling method in

[15] , but with simpler sampler implementation and lower computational complexity. At the same time, the proposed method increases the mapping bandwidth to 1.5 times the original one, achieving high-resolution wide-band imaging and reducing the data size.

[0132] Reference Figure 7 , shows a functional module diagram of a radar high-resolution wide-swath imaging device based on azimuthally randomly variable PRF sampling provided by an embodiment of the present application, the device comprising:

[0133] A random selection module 100 is configured to randomly select a current pulse repetition frequency from a predetermined pulse repetition frequency range at a preset interval for the synthetic aperture radar, wherein two adjacent current pulse repetition frequencies are different and discontinuous;

[0134] The transmitting and receiving module 200 is configured to transmit a pulse signal from the synthetic aperture radar and receive an echo signal reflected by a target according to the current pulse repetition frequency;

[0135] The imaging processing module 300 is used to process the echo signal reflected by the target by using a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

[0136] An embodiment of the present application further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the radar high-resolution wide-swath imaging method based on azimuthally randomly variable PRF sampling described in the embodiment is implemented.

[0137] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0138] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, devices, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0139] The embodiments of the present application are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0140] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0141] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device so that a series of operating steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable terminal device to implement the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0142] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0143] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

[0144] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A radar high-resolution wide swath imaging method based on azimuthally randomized PRF sampling, characterized in that: Applied to synthetic aperture radar, the method includes: The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range at every preset interval, and two adjacent current pulse repetition frequencies are different and discontinuous; According to the current pulse repetition frequency, the synthetic aperture radar transmits a pulse signal and receives an echo signal reflected by a target; The target reflected echo signal is processed by a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result; The synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range at every preset interval, comprising: the synthetic aperture radar randomly selects a current pulse repetition frequency from a predetermined pulse repetition frequency value range every M pulse signals, wherein M is a positive integer greater than 1; The pulse signal transmitted by the synthetic aperture radar includes a linear frequency modulation pulse signal, and the linear frequency modulation pulse signal is in the form of: Where τ represents the distance to the fast time, T p represents the duration of the linear frequency modulation pulse, Indicates the carrier frequency of the transmitted signal, K r represents the linear modulation frequency, Represents the rectangular window function, j is the imaginary unit.

2. The method according to claim 1, characterized in that The method further comprises: Drawing a zebra diagram according to the constraints on pulse repetition frequency of the synthetic aperture radar's transmitted pulse and the sub-satellite point echo; According to the zebra diagram obtained by drawing, a value range of the pulse repetition frequency of the synthetic aperture radar is determined.

3. The method according to claim 2, characterized in that The constraint of the transmit pulse on the pulse repetition frequency is expressed as: The constraint of the sub-satellite echo on the pulse repetition frequency is expressed as: Where, f r is the pulse repetition frequency PRF, Indicates taking the decimal part. Indicates taking the integer part, R n is the minimum slant distance to the observation area, R f is the farthest slant distance of the observation area, τ p is the pulse width, τ g is the protection time band, c is the speed of light, n is the number of transmitted pulses, H is the orbital height of the satellite, and τ is the pulse width τ p With the protection time band τ g The sum of , k is the sequence number of the pulse repetition period.

4. The method according to claim 1, wherein After receiving the echo signal reflected by the target, it also includes: The echo signal reflected by the target is represented as the first echo signal. The first echo signal is the result of the two-dimensional convolution of the impulse response of the synthetic aperture radar system and the scene scattering coefficient, and is in the form of: In the formula, τ represents the fast time in range, t represents the slow time in azimuth, x represents the coordinate in azimuth, and y represents the coordinate in range. Indicates that the space is located The target scattering coefficient at position, represents the envelope function of the azimuth beam pattern, is a linear frequency modulated pulse signal, is the slant range function between the radar and the target, which is related to the position and azimuth slow time of the target, λ is the central wavelength of the synthetic aperture radar, c represents the speed of light, represents the additive noise at the receiving end of the synthetic aperture radar, and V is the equivalent velocity of the synthetic aperture radar platform; The echo signal of the synthetic aperture radar is discretely sampled and expressed as the second echo signal : Where, the second echo signal Is the first echo signal nth a The nth pulse r Sample values, M r Indicates the number of discrete scattering points in the scene in the distance direction, M a They represent the number of discrete scattering points in the scene, It is located in the mth direction a coordinates, distance to the mth r The scattering intensity coefficient of the scattering point with coordinates, is the discretized additive noise; The second echo signal in the form of two-dimensional discrete data and scattering intensity coefficient Expressed in matrix form: The matrix representation of the second echo signal is: ; The matrix expression of the scattering intensity coefficient is: ; Then the matrix representation of the echo signal is ; Where N a Indicates the number of pulses transmitted in azimuth, N r Represent the number of sampling points of each pulse in the range direction, y and x represent the vectorized results of matrices Y and X respectively, n is the additive noise vector, and the matrix A is in the following form: 。 5. The method according to claim 4, characterized in that The echo signal reflected by the target is processed by a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result, including: Build a sparse optimization model: Where, is the reconstructed scene image, is the regularization parameter, represents the Frobenius norm of the matrix, represents the L1 norm of the matrix; The sparsely reconstructed target imaging result is obtained by solving the problem through a fast iterative soft threshold algorithm.

6. The method according to claim 5, characterized in that Through the rapid iterative soft threshold algorithm, the sparsely reconstructed target imaging results are obtained, including: A1: Initialize parameters and variables: Initialize iterative result estimation , the residual vector , iteration number k = 1, vector ,variable , the maximum number of iterations I max , constant threshold ; A2: Calculate current estimate ,in, is the soft threshold operator, Representation matrix The conjugate transpose of A3: Calculate the residual vector: ; A4: Calculation ; A5: Update vector: ; A6: Calculate: as well as ; if or k>I max , then the iteration ends and the sparsely reconstructed target imaging result is obtained. Otherwise, let k = k + 1 and return to step A2.

7. A radar high-resolution wide-swath imaging device based on azimuthally randomized PRF sampling, characterized in that: The device comprises: The random selection module is used for randomly selecting a current pulse repetition frequency from a predetermined pulse repetition frequency range at every preset interval of the synthetic aperture radar, where two adjacent current pulse repetition frequencies are different and discontinuous. Specifically, the module is used for randomly selecting a current pulse repetition frequency from a predetermined pulse repetition frequency range every M pulse signals of the synthetic aperture radar, where M is a positive integer greater than 1. The pulse signal transmitted by the synthetic aperture radar includes a linear frequency modulation pulse signal, and the linear frequency modulation pulse signal is in the form of: Where τ represents the distance to the fast time, T p represents the duration of the linear frequency modulation pulse, Indicates the carrier frequency of the transmitted signal, K r represents the linear modulation frequency, represents the rectangular window function, j is the imaginary unit; a transmitting and receiving module, configured to transmit a pulse signal from the synthetic aperture radar and receive an echo signal reflected by a target according to the current pulse repetition frequency; The imaging processing module is used to process the echo signal reflected by the target through a fast iterative soft threshold algorithm to obtain a sparsely reconstructed target imaging result.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the radar high-resolution wide-swath imaging method based on azimuthally randomly variable PRF sampling is implemented as claimed in any one of claims 1 to 6.

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