A SAR ship focusing method and device based on aperture segmentation and image quality evaluation

Abstract

This invention discloses a SAR ship focusing method and apparatus based on aperture segmentation and image quality assessment. The method includes: acquiring a ship complex image matrix from a single-view complex image of the ship; processing the ship complex image matrix to obtain a two-dimensional frequency domain matrix; processing the two-dimensional frequency domain matrix to obtain a second sub-aperture complex image matrix set; and processing the second sub-aperture complex image matrix set to obtain a SAR ship image. This invention simplifies the ship imaging processing flow and reduces imaging difficulty by using sub-aperture segmentation and setting an iterative phase error range, and by coupling the iterative compensation process with ship image quality assessment.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, specifically to a SAR ship focusing method and apparatus based on aperture segmentation and image quality evaluation. Background Technology

[0002] With the increasing demand for marine monitoring and continuous technological advancements, Synthetic Aperture Radar (SAR) imaging technology has emerged and gradually become one of the key technologies in the field of marine monitoring. Compared with traditional optical remote sensing technology, SAR imaging technology has many significant advantages. First, SAR imaging technology has all-weather, all-time operating capabilities. Second, SAR imaging technology has high resolution. Third, SAR imaging technology has large-area observation capabilities. Therefore, for monitoring ships at sea, high-resolution SAR images can accurately identify the type, size, and navigation trajectory of ships.

[0003] Currently, the improved resolution of SAR satellites has led to a significant increase in synthetic aperture time. For ship focusing imaging, the direct consequence is that the synthetic aperture time is very close to the ship's swaying period, or even includes several swaying periods. As the motion parameters of ships on the sea surface are unknown, and the Doppler values ​​of the echoes from the ship's scattering points change very complexly over time, most algorithms excessively pursue fine focusing effects under high-resolution conditions, greatly increasing the difficulty of imaging moving ships.

[0004] Furthermore, the high complexity of these algorithms leads to complicated processing, a high barrier to entry for operators, and long processing times, which greatly limits the effectiveness of SAR satellite data in marine monitoring. Therefore, there is an urgent need for a SAR ship focusing method that can shorten imaging time and simplify ship imaging processing to solve the many problems existing in current technologies. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a SAR ship focusing method and apparatus based on aperture segmentation and image quality evaluation, which overcomes the problem that the ship motion under long synthetic aperture time brings more complex distance migration and phase change effects, thus increasing the complexity of imaging.

[0006] To address the aforementioned technical problems, this invention discloses a SAR ship focusing method based on aperture segmentation and image quality assessment, the method comprising:

[0007] S1, obtain the ship complex image matrix of the single-view complex image of the ship;

[0008] S2, process the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix;

[0009] S3, process the two-dimensional frequency domain matrix to obtain a set of second sub-aperture complex image matrices; the set of second sub-aperture complex image matrices includes subNum second sub-aperture complex image matrices; subNum is the number of sub-aperture segments;

[0010] S4, process the second sub-aperture complex image matrix set to obtain SAR ship images.

[0011] As an optional implementation, in the first aspect of the present invention, processing the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix includes:

[0012] S21, Perform a two-dimensional discrete Fourier transform on the complex image matrix to obtain the transform matrix;

[0013] S22, the transformation matrix is ​​frequency shifted to obtain the two-dimensional frequency domain matrix.

[0014] As an optional implementation, in the first aspect of the present invention, processing the two-dimensional frequency domain matrix to obtain a second sub-aperture complex image matrix set includes:

[0015] S31, preset the start number AzfStart and the end number AzfEnd, and initialize the value of the sub-aperture number nn to 1;

[0016] S32, using the spectrum index calculation model, the start index AzfStart, the end index AzfEnd, the number of sub-aperture segments subNum, and the sub-aperture index nn are processed to obtain the spectrum start index and the spectrum end index;

[0017] The expression for the spectrum index calculation model is as follows:

[0018]

[0019]

[0020] Here, round() is the rounding function;

[0021] S33, using the sub-aperture frequency domain matrix calculation model, process the spectrum start number, the spectrum end number, and the two-dimensional frequency domain matrix to obtain the sub-aperture frequency domain matrix;

[0022] The expression for the sub-aperture frequency domain matrix calculation model is as follows:

[0023]

[0024] Wherein, sig_fft2 is the two-dimensional frequency domain matrix;

[0025] S34, process the sub-aperture frequency domain matrix to obtain the first sub-aperture complex image matrix;

[0026] S35, process the first sub-aperture complex image matrix to obtain the nth second sub-aperture complex image matrix;

[0027] S36, Increment the value of the sub-aperture number nn by 1;

[0028] S37, repeat S32~S36, until nn is greater than subNum;

[0029] S38, combine the n second sub-aperture complex image matrices to obtain the second sub-aperture complex image matrix set.

[0030] As an optional implementation, in the first aspect of the present invention, processing the sub-aperture frequency domain matrix to obtain a first sub-aperture complex image matrix includes:

[0031] S341, Perform inverse frequency shift processing on the sub-aperture frequency domain matrix to obtain the sub-aperture frequency shift matrix;

[0032] S342, perform a two-dimensional discrete Fourier inverse transform on the sub-aperture frequency shift matrix to obtain the first sub-aperture complex image matrix.

[0033] As an optional implementation, in the first aspect of the present invention, processing the first sub-aperture complex image matrix to obtain the nth second sub-aperture complex image matrix includes:

[0034] S351, Initialize the current sub-aperture complex image matrix to the first sub-aperture complex image matrix; initialize the loop count to 1;

[0035] S352, based on the preset error iteration interval sequence and the number of sub-intervals M, perform error compensation on the current sub-aperture complex image matrix to obtain M+1 compensated image matrices;

[0036] The error iteration interval sequence includes N error iteration intervals;

[0037] M and N are both integers greater than 1;

[0038] S353, perform image quality evaluation on the M+1 compensated image matrices to obtain the intermediate sub-aperture complex image matrix;

[0039] S354, Update the current sub-aperture complex image matrix to the intermediate sub-aperture complex image matrix; Increment the value of the loop count by 1;

[0040] S355, repeat S352 to S354 until the number of cycles is greater than N;

[0041] S356, the intermediate sub-aperture complex image matrix is ​​determined as the second sub-aperture complex image matrix.

[0042] As an optional implementation, in the first aspect of the present invention, the step of performing error compensation on the current sub-aperture complex image matrix based on a preset error iteration interval sequence and the number of sub-intervals M to obtain M+1 compensated image matrices includes:

[0043] S3521, initialize the iteration count mm to 1;

[0044] S3522, Based on the number of sub-intervals, the mm-th error iteration interval is divided to obtain M+1 phase error points;

[0045] S3523, Perform a one-dimensional discrete Fourier transform on the first sub-aperture complex image matrix to obtain the first sub-aperture frequency domain matrix;

[0046] S3524, using the intermediate matrix calculation model, the phase error points and the first sub-aperture frequency domain matrix are processed to obtain M+1 intermediate matrices;

[0047] The expression for the intermediate matrix calculation model is as follows:

[0048]

[0049]

[0050] In the formula, j is the imaginary unit; phaseComp(ll) is the value of the ll-th phase error point; 1 ≤ ll ≤ M+1, and ll is an integer; 1 ≤ i ≤ And i is an integer; The row number of the frequency domain matrix of the first sub-aperture; For the ll-th intermediate matrix The i-th element;

[0051] S3525, using the compensation matrix calculation model, the M+1 intermediate matrices and the first sub-aperture frequency domain matrix are processed to obtain the M+1 compensation matrix.

[0052] The expression for the compensation matrix calculation model is as follows:

[0053]

[0054] In the formula, For the ll-th compensation matrix, ones(l, ) is the identity matrix. is the column number of the frequency domain matrix of the first sub-aperture;

[0055] S3526, Perform one-dimensional discrete Fourier inverse transform on the M+1 compensation matrices respectively to obtain M+1 compensation image matrices.

[0056] As an optional implementation, in the first aspect of the present invention, the step of performing image quality evaluation on the M+1 compensated image matrices to obtain an intermediate sub-aperture complex image matrix includes:

[0057] S3531, The evaluation index is calculated and processed on the M+1 compensated image matrices to obtain M+1 evaluation index values;

[0058] S3532, the intermediate sub-aperture complex image matrix is ​​set as the compensation image matrix corresponding to the largest evaluation index value among the M+1 evaluation index values.

[0059] As an optional implementation, in the first aspect of the present invention, processing the second sub-aperture complex image matrix set to obtain a SAR ship image includes:

[0060] S41, perform evaluation index calculation on the subNum second sub-aperture complex image matrices to obtain subNum evaluation index values;

[0061] S42, set the SAR ship image as the grayscale image corresponding to the second sub-aperture complex image matrix corresponding to the largest evaluation index value among the subNum evaluation index values.

[0062] A second aspect of the present invention discloses a SAR ship focusing device based on aperture segmentation and image quality assessment, the device comprising:

[0063] Memory containing executable program code;

[0064] A processor coupled to the memory;

[0065] The processor calls the executable program code stored in the memory to execute some or all of the steps in the SAR ship focusing method based on aperture segmentation and image quality evaluation disclosed in the first aspect of the present invention.

[0066] The third aspect of the present invention discloses a computer-storable medium storing computer instructions, which, when invoked, are used to execute some or all of the steps in the SAR ship focusing method based on aperture segmentation and image quality evaluation disclosed in the first aspect of the present invention.

[0067] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0068] This invention discloses a SAR ship focusing method and apparatus based on aperture segmentation and image quality evaluation. By using azimuth sub-aperture segmentation and setting an iterative phase error range, and by highly coupling the iterative compensation process with the ship image quality evaluation, the method aims to reduce the difficulty of SAR ship image focusing, simplify the focusing process, and meet the requirements of ship identification. Attached Figure Description

[0069] 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.

[0070] Figure 1 This is a flowchart illustrating a SAR ship focusing method based on aperture segmentation and image quality evaluation disclosed in an embodiment of the present invention.

[0071] Figure 2 This is a schematic diagram of the structure of a SAR ship focusing device based on aperture segmentation and image quality evaluation disclosed in an embodiment of the present invention. Detailed Implementation

[0072] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0073] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0074] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0075] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0076] This invention discloses a SAR ship focusing method and apparatus based on aperture segmentation and image quality assessment. The method includes: acquiring a ship complex image matrix from a single-view complex image of the ship; processing the ship complex image matrix to obtain a two-dimensional frequency domain matrix; processing the two-dimensional frequency domain matrix to obtain a second sub-aperture complex image matrix set; and processing the second sub-aperture complex image matrix set to obtain a SAR ship image. This invention simplifies the ship imaging process and reduces imaging difficulty by using sub-aperture segmentation and setting an iterative phase error range, and by coupling the iterative compensation process with ship image quality assessment. Detailed descriptions follow.

[0077] Example 1

[0078] Please see Figure 1 , Figure 1 This is a schematic flowchart of a SAR ship focusing method based on aperture segmentation and image quality evaluation disclosed in an embodiment of the present invention. Figure 1 The SAR ship focusing method based on aperture segmentation and image quality assessment described herein is applied in the field of signal processing technology, and the embodiments of this invention are not limited thereto. Figure 1 As shown, this SAR ship focusing method based on aperture segmentation and image quality assessment can include the following operations:

[0079] S1, obtain the ship complex image matrix of the single-view complex image of the ship;

[0080] It should be noted that the ship complex image matrix sig of the single-view complex image of the ship is a Na×Nr matrix, where Na is the number of rows in the ship complex image matrix and Nr is the number of columns in the ship complex image matrix. sig(a,r) represents the complex value of the backscattering at pixel (a,r) in the ship complex image matrix, where 1≤a≤Na and 1≤r≤Nr.

[0081] S2, process the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix;

[0082] S3, process the two-dimensional frequency domain matrix to obtain a set of second sub-aperture complex image matrices; the set of second sub-aperture complex image matrices includes subNum second sub-aperture complex image matrices; subNum is the number of sub-aperture segments;

[0083] It should be noted that the setting of subNum is determined by the resolution of the original image and the minimum resolution required for ship identification. For example, if the minimum resolution threshold of the SAR image required to identify and classify ships with a length of 100 meters is 2 meters, and the resolution of the original image is 0.5 meters, then subNum can be set to 2 / 0.5 = 4.

[0084] S4, process the second sub-aperture complex image matrix set to obtain SAR ship images.

[0085] Optionally, processing the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix includes:

[0086] S21, Perform a two-dimensional discrete Fourier transform on the complex image matrix to obtain the transform matrix;

[0087] It should be noted that performing a two-dimensional discrete Fourier transform on the rows and columns of the ship complex image matrix sig involves first performing a one-dimensional discrete Fourier transform on each row, and then performing a one-dimensional discrete Fourier transform on each column, ultimately obtaining the transform matrix.

[0088] S22, the transformation matrix is ​​frequency shifted to obtain the two-dimensional frequency domain matrix.

[0089] It should be noted that shifting the zero frequency of the above transformation matrix to the center of the spectrum yields the two-dimensional frequency domain data matrix sig_fft2.

[0090] Optionally, the processing of the two-dimensional frequency domain matrix to obtain the second sub-aperture complex image matrix set includes:

[0091] S31, preset the start number AzfStart and the end number AzfEnd, and initialize the value of the sub-aperture number nn to 1;

[0092] S32, using the spectrum index calculation model, the start index AzfStart, the end index AzfEnd, the number of sub-aperture segments subNum, and the sub-aperture index nn are processed to obtain the spectrum start index and the spectrum end index;

[0093] The expression for the spectrum index calculation model is as follows:

[0094]

[0095]

[0096] Here, round() is the rounding function;

[0097] S33, using the sub-aperture frequency domain matrix calculation model, process the spectrum start number, the spectrum end number, and the two-dimensional frequency domain matrix to obtain the sub-aperture frequency domain matrix;

[0098] The expression for the sub-aperture frequency domain matrix calculation model is as follows:

[0099]

[0100] Wherein, sig_fft2 is the two-dimensional frequency domain matrix;

[0101] S34, process the sub-aperture frequency domain matrix to obtain the first sub-aperture complex image matrix;

[0102] S35, process the first sub-aperture complex image matrix to obtain the nth second sub-aperture complex image matrix;

[0103] S36, Increment the value of the sub-aperture number nn by 1;

[0104] S37, repeat S32~S36, until nn is greater than subNum;

[0105] S38, combine the n second sub-aperture complex image matrices to obtain the second sub-aperture complex image matrix set.

[0106] Optionally, processing the sub-aperture frequency domain matrix to obtain the first sub-aperture complex image matrix includes:

[0107] S341, Perform inverse frequency shift processing on the sub-aperture frequency domain matrix to obtain the sub-aperture frequency shift matrix;

[0108] It should be noted that shifting the zero frequency of the above sub-aperture frequency domain matrix to the center of the spectrum yields the sub-aperture frequency shift matrix.

[0109] S342, perform a two-dimensional discrete Fourier inverse transform on the sub-aperture frequency shift matrix to obtain the first sub-aperture complex image matrix.

[0110] It should be noted that a two-dimensional discrete Fourier inverse transform is performed on the rows and columns of the sub-aperture frequency shift matrix. That is, a one-dimensional discrete Fourier pseudo-transform is first performed on each row, and then a one-dimensional discrete Fourier pseudo-transform is performed on each column to finally obtain the first aperture complex image matrix.

[0111] Optionally, processing the first sub-aperture complex image matrix to obtain the nth second sub-aperture complex image matrix includes:

[0112] S351, Initialize the current sub-aperture complex image matrix to the first sub-aperture complex image matrix; initialize the loop count to 1;

[0113] S352, based on the preset error iteration interval sequence and the number of sub-intervals M, perform error compensation on the current sub-aperture complex image matrix to obtain M+1 compensated image matrices;

[0114] The error iteration interval sequence includes N error iteration intervals;

[0115] M and N are both integers greater than 1;

[0116] S353, perform image quality evaluation on the M+1 compensated image matrices to obtain the intermediate sub-aperture complex image matrix;

[0117] S354, Update the current sub-aperture complex image matrix to the intermediate sub-aperture complex image matrix; Increment the value of the loop count by 1;

[0118] S355, repeat S352 to S354 until the number of cycles is greater than N;

[0119] S356, the intermediate sub-aperture complex image matrix is ​​determined as the second sub-aperture complex image matrix.

[0120] Optionally, the step of performing error compensation on the current sub-aperture complex image matrix based on a preset error iteration interval sequence and the number of sub-intervals M, to obtain M+1 compensated image matrices, includes:

[0121] S3521, initialize the iteration count mm to 1;

[0122] S3522, Based on the number of sub-intervals, the mm-th error iteration interval is divided to obtain M+1 phase error points;

[0123] S3523, Perform a one-dimensional discrete Fourier transform on the first sub-aperture complex image matrix to obtain the first sub-aperture frequency domain matrix;

[0124] S3524, using the intermediate matrix calculation model, the phase error points and the first sub-aperture frequency domain matrix are processed to obtain M+1 intermediate matrices;

[0125] The expression for the intermediate matrix calculation model is as follows:

[0126]

[0127]

[0128] In the formula, j is the imaginary unit; phaseComp(ll) is the value of the ll-th phase error point; 1 ≤ ll ≤ M+1, and ll is an integer; 1 ≤ i ≤ And i is an integer; The row number of the frequency domain matrix of the first sub-aperture; For the ll-th intermediate matrix The i-th element;

[0129] S3525, using the compensation matrix calculation model, the M+1 intermediate matrices and the first sub-aperture frequency domain matrix are processed to obtain the M+1 compensation matrix.

[0130] The expression for the compensation matrix calculation model is as follows:

[0131]

[0132] In the formula, For the ll-th compensation matrix, ones(l, ) is the identity matrix. is the column number of the frequency domain matrix of the first sub-aperture;

[0133] S3526, Perform one-dimensional discrete Fourier inverse transform on the M+1 compensation matrices respectively to obtain M+1 compensation image matrices.

[0134] Optionally, the step of evaluating the image quality of the M+1 compensated image matrices to obtain the intermediate sub-aperture complex image matrix includes:

[0135] S3531, The evaluation index is calculated and processed on the M+1 compensated image matrices to obtain M+1 evaluation index values;

[0136] It should be noted that image quality evaluation metrics include one or more of image contrast, image entropy, and image peak value.

[0137] The method for calculating the evaluation index of the above-mentioned compensated image matrix is ​​as follows:

[0138] The expression for image contrast is:

[0139]

[0140] The expression for image entropy is:

[0141]

[0142] The expression for the peak value in the image is:

[0143]

[0144] Where g(a,r) is the pixel amplitude at coordinate (a,r), a=1,2,...,Na, r=1,1,...,Nr.

[0145] S3532, the intermediate sub-aperture complex image matrix is ​​set as the compensation image matrix corresponding to the largest evaluation index value among the M+1 evaluation index values.

[0146] Optionally, the processing of the second sub-aperture complex image matrix set to obtain SAR ship images includes:

[0147] S41, perform evaluation index calculation on the subNum second sub-aperture complex image matrices to obtain subNum evaluation index values;

[0148] It should be noted that image quality evaluation metrics include one or more of image contrast, image entropy, and image peak value.

[0149] The method for calculating the evaluation index of the above-mentioned compensated image matrix is ​​as follows:

[0150] The expression for image contrast is:

[0151]

[0152] The expression for image entropy is:

[0153]

[0154] The expression for the peak value in the image is:

[0155]

[0156] Where g(a,r) is the pixel amplitude at coordinate (a,r), a=1,2,...,Na, r=1,1,...,Nr.

[0157] S42, set the SAR ship image as the grayscale image corresponding to the second sub-aperture complex image matrix corresponding to the largest evaluation index value among the subNum evaluation index values.

[0158] As can be seen, the SAR ship focusing method based on aperture segmentation and image quality evaluation provided in this embodiment, by sub-aperture segmentation and setting the iterative phase error range, and by highly coupling the iterative compensation process with the ship image quality evaluation, achieves the purpose of reducing the difficulty of SAR ship image focusing, simplifying the focusing process, and meeting the needs of ship identification at the same time. It solves the problems that ship motion under long synthetic aperture time brings more complex range migration and phase change effects, which increases the complexity of imaging and makes it difficult for various high-resolution refocusing methods to be effective.

[0159] Example 2

[0160] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of a SAR ship focusing device based on aperture segmentation and image quality evaluation, as disclosed in an embodiment of the present invention. Figure 2 The SAR ship focusing device based on aperture segmentation and image quality assessment described herein is applied in the field of signal processing technology, and the embodiments of this invention are not limited thereto. Figure 2 As shown, the device may include:

[0161] Memory containing executable program code;

[0162] A processor coupled to memory;

[0163] The processor calls the executable program code stored in memory to execute the steps in the SAR ship focusing method described in Embodiment 1.

[0164] Example 3

[0165] This invention discloses a computer read storage medium that stores a computer program for electronic data exchange, wherein the computer program causes a computer to execute the steps in the SAR ship focusing method described in Embodiment 1.

[0166] The device embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0167] Through the detailed description of the above embodiments, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, including read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), one-time programmable read-only memory (OTPROM), electrically-erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium that can be used to carry or store data.

[0168] Finally, it should be noted that the SAR ship focusing method and apparatus based on aperture segmentation and image quality evaluation disclosed in the embodiments of the present invention are merely preferred embodiments of the present invention and are only used to illustrate the technical solutions of the present invention, not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SAR ship focusing method based on aperture segmentation and image quality assessment, characterized in that, include: S1, obtain the ship complex image matrix of the single-view complex image of the ship; S2, process the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix; S3, process the two-dimensional frequency domain matrix to obtain a set of second sub-aperture complex image matrices; the set of second sub-aperture complex image matrices includes subNum second sub-aperture complex image matrices; subNum is the number of sub-aperture segments; wherein processing the two-dimensional frequency domain matrix to obtain the set of second sub-aperture complex image matrices includes: S31, preset the start number AzfStart and the end number AzfEnd, and initialize the value of the sub-aperture number nn to 1; S32, using the spectrum index calculation model, the start index AzfStart, the end index AzfEnd, the number of sub-aperture segments subNum, and the sub-aperture index nn are processed to obtain the spectrum start index and the spectrum end index; S33, using the sub-aperture frequency domain matrix calculation model, process the spectrum start number, the spectrum end number, and the two-dimensional frequency domain matrix to obtain the sub-aperture frequency domain matrix; S34, process the sub-aperture frequency domain matrix to obtain the first sub-aperture complex image matrix; S35, process the first sub-aperture complex image matrix to obtain the nth second sub-aperture complex image matrix; including: S351, Initialize the current sub-aperture complex image matrix to the first sub-aperture complex image matrix; initialize the loop count to 1; S352, based on the preset error iteration interval sequence and the number of sub-intervals M, perform error compensation on the current sub-aperture complex image matrix to obtain M+1 compensated image matrices; The error iteration interval sequence includes N error iteration intervals; M and N are both integers greater than 1; S353, perform image quality evaluation on the M+1 compensated image matrices to obtain the intermediate sub-aperture complex image matrix; S354, Update the current sub-aperture complex image matrix to the intermediate sub-aperture complex image matrix; Increment the value of the loop count by 1; S355, repeat S352 to S354 until the number of cycles is greater than N; S356, the intermediate sub-aperture complex image matrix is ​​determined as the second sub-aperture complex image matrix; S36, Increment the value of the sub-aperture number nn by 1; S37, repeat S32~S36, until nn is greater than subNum; S38, combine the n second sub-aperture complex image matrices to obtain the set of second sub-aperture complex image matrices; S4, process the second sub-aperture complex image matrix set to obtain SAR ship images.

2. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The process of processing the complex image matrix of the ship to obtain a two-dimensional frequency domain matrix includes: S21, Perform a two-dimensional discrete Fourier transform on the complex image matrix to obtain the transform matrix; S22, the transformation matrix is ​​frequency shifted to obtain the two-dimensional frequency domain matrix.

3. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The expression for the spectrum index calculation model is as follows: Here, round() is the rounding function; The expression for the sub-aperture frequency domain matrix calculation model is as follows: Wherein, sig_fft2 is the two-dimensional frequency domain matrix.

4. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The process of processing the sub-aperture frequency domain matrix to obtain the first sub-aperture complex image matrix includes: S341, Perform inverse frequency shift processing on the sub-aperture frequency domain matrix to obtain the sub-aperture frequency shift matrix; S342, perform a two-dimensional discrete Fourier inverse transform on the sub-aperture frequency shift matrix to obtain the first sub-aperture complex image matrix.

5. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The error compensation is performed on the current sub-aperture complex image matrix based on a preset error iteration interval sequence and the number of sub-intervals M, resulting in M+1 compensated image matrices, including: S3521, initialize the iteration count mm to 1; S3522, Based on the number of sub-intervals, the mm-th error iteration interval is divided to obtain M+1 phase error points; S3523, Perform a one-dimensional discrete Fourier transform on the first sub-aperture complex image matrix to obtain the first sub-aperture frequency domain matrix; S3524, using the intermediate matrix calculation model, the phase error points and the first sub-aperture frequency domain matrix are processed to obtain M+1 intermediate matrices; The expression for the intermediate matrix calculation model is as follows: In the formula, j is the imaginary unit; phaseComp(ll) is the value of the ll-th phase error point; 1 ≤ ll ≤ M+1, and ll is an integer; 1 ≤ i ≤ And i is an integer; The row number of the frequency domain matrix of the first sub-aperture; For the ll-th intermediate matrix The i-th element; S3525, using the compensation matrix calculation model, the M+1 intermediate matrices and the first sub-aperture frequency domain matrix are processed to obtain the M+1 compensation matrix. The expression for the compensation matrix calculation model is as follows: In the formula, For the ll-th compensation matrix, ones(l, ) is the identity matrix. is the column number of the frequency domain matrix of the first sub-aperture; S3526, Perform one-dimensional discrete Fourier inverse transform on the M+1 compensation matrices respectively to obtain M+1 compensation image matrices.

6. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The step of evaluating the image quality of the M+1 compensated image matrices to obtain the intermediate sub-aperture complex image matrix includes: S3531, The evaluation index is calculated and processed on the M+1 compensated image matrices to obtain M+1 evaluation index values; S3532, the intermediate sub-aperture complex image matrix is ​​set as the compensation image matrix corresponding to the largest evaluation index value among the M+1 evaluation index values.

7. The SAR ship focusing method based on aperture segmentation and image quality evaluation according to claim 1, characterized in that, The process of processing the second sub-aperture complex image matrix set to obtain SAR ship images includes: S41, perform evaluation index calculation on the subNum second sub-aperture complex image matrices to obtain subNum evaluation index values; S42, set the SAR ship image as the grayscale image corresponding to the second sub-aperture complex image matrix corresponding to the largest evaluation index value among the subNum evaluation index values.

8. A SAR ship focusing device based on aperture segmentation and image quality assessment, characterized in that, The device includes: Memory containing executable program code; A processor coupled to the memory; The processor calls the executable program code stored in the memory to execute the SAR ship focusing method based on aperture segmentation and image quality evaluation as described in any one of claims 1-7.

9. A computer-storable medium, characterized in that, The computer storage medium stores computer instructions, which, when invoked, are used to execute the SAR ship focusing method based on aperture segmentation and image quality assessment as described in any one of claims 1-7.

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