A self-focusing method and device based on affine coordinate system BP for high squint SAR

Abstract

The present invention discloses a self-focusing method and device based on an affine coordinate system BP for a high squint SAR, the method comprising: performing range pulse pressure and coarse compensation on the received original echo signal to obtain a coarse compensation signal; establishing an affine coordinate system PX with the beam center P as the origin in the imaging scene based on the coarse compensation signal; ac Y ac Z ac , and in this coordinate system X ac Y ac The imaging scene grid is established within a plane; the imaging scene grid is divided into multiple subgrids, and rapid BP imaging and spectrum tilt correction processing are performed on the coarse compensation signal on a subgrid-by-subgrid basis to obtain multiple coarsely focused subimages; a phase error structure of different coarsely focused subimages is constructed to achieve estimation and inversion of the two-dimensional phase error; the two-dimensional phase errors corresponding to the different coarsely focused subimages are compensated into their respective coarsely focused subimages to obtain multiple finely focused subimages; and the multiple finely focused subimages are spliced ​​to obtain a final finely focused image. This invention can improve SAR imaging quality in high squint modes.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and in particular relates to an autofocusing method and device based on an affine coordinate system BP for a high squint SAR. Background Art

[0002] In early airborne SAR imaging, radars typically operated in high squint mode. High squint generally refers to beam pointing tilts between 50° and 85°. In this case, not only is the Doppler center severely offset, but the Doppler range is folded and blurred. Even the spatial variation of the Doppler center needs to be considered, leading to severe coupling between the range and azimuth dimensions. Therefore, motion correction must be implemented in the imaging algorithm. This correction not only eliminates the shift and blurring of the Doppler spectrum but also minimizes the coupling between the range and azimuth dimensions. Furthermore, airborne SAR inevitably introduces motion errors. In high squint mode, the two-dimensional coupling and spatial variation of motion errors are pronounced, further degrading the two-dimensional coherence of the SAR signal and exacerbating the two-dimensional defocusing of the image. The interpolation and scaling operations involved in frequency-domain imaging algorithms alter the original structure of the motion errors, making accurate correction difficult. Therefore, to achieve high-quality high-squint SAR imaging, motion compensation algorithms require further research. Compared to frequency-domain imaging algorithms, time-domain imaging algorithms have better error tolerance and do not change the original structure of phase errors. To address the huge computational complexity of the original BP algorithm, a fast BP algorithm based on polar or rectangular coordinates was proposed, and based on this, a series of motion compensation algorithms were proposed.

[0003] In existing technologies, most motion compensation algorithms are combined with frequency-domain imaging algorithms. For example, the two-dimensional autofocus algorithm based on RMA further ensures the accuracy of motion compensation by establishing a priori motion error structure. However, the accuracy of this priori structure decreases with increasing squint angles, limiting its accuracy in high squint modes. In contrast, time-domain imaging algorithms use a fast BP algorithm in a ground-based direct coordinate system to perform motion error compensation. By determining the relationship between the BP image spectrum and the system's emission spectrum, the effective emission frequency is obtained using the image's range spectrum range, and a phase error mapping network is constructed. The azimuth-time domain phase error can then be derived from the image-domain phase error. After obtaining a series of sub-aperture phase errors, they need to be spliced ​​into the full-aperture phase error. After estimating the azimuth-time domain error for all local images, N phase errors can be obtained, which are used to estimate the residual trajectory deviation. Finally, the residual trajectory deviation in the ideal trajectory is compensated, and a well-focused image is obtained using the fast BP algorithm in a ground-based rectangular coordinate system. However, the two-dimensional spectrum of high-squint SAR imaging results obtained in the ground rectangular coordinate system is non-orthogonal and has large non-systematic range unit migration and range defocus terms, which limits the accuracy of the motion compensation algorithm.

[0004] In other words, existing high-squint SAR imaging motion compensation techniques, such as those combined with frequency-domain algorithms, involve interpolation and scaling, which alter the original motion error structure and make accurate estimation difficult. Furthermore, when combining motion compensation with time-domain BP imaging algorithms, the two-dimensional spectrum is non-orthogonal when imaging in a terrestrial rectangular coordinate system, resulting in significant non-systematic range cell migration and range defocus, which affects accuracy. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides an autofocusing method and device based on an affine coordinate system BP for a high squint SAR.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The present invention provides a self-focusing method based on an affine coordinate system BP for a high squint SAR, comprising:

[0008] Perform range pulse pressure and coarse compensation on the received original echo signal to obtain a coarse compensation signal;

[0009] Based on the coarse compensation signal, an affine coordinate system PX is established in the imaging scene with the position of the beam center point P as the origin. ac Y ac Z ac , and in the affine coordinate system X ac Y ac Divide the imaging scene into grids within the plane;

[0010] Dividing the imaging scene grid into a plurality of subgrids, performing fast BP imaging and spectrum tilt correction processing on the coarse compensation signal subgrid by subgrid to obtain a coarse focus sub-image of each subgrid;

[0011] Constructing a phase error structure of the coarsely focused sub-images of different sub-grids to achieve estimation and inversion of the two-dimensional phase error;

[0012] Using the two-dimensional phase error of each coarsely focused sub-image, each coarsely focused sub-image is compensated to obtain multiple finely focused sub-images;

[0013] The multiple finely focused sub-images corresponding to the multiple sub-grids are stitched together to obtain a finely focused image.

[0014] The present invention also provides an autofocusing device based on an affine coordinate system BP for a high squint SAR, comprising a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other via the communication bus; the memory is used to store a computer program; and the processor is used to implement the steps of the above-mentioned autofocusing method based on the affine coordinate system BP for a high squint SAR when executing the program stored in the memory.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention constructs an affine coordinate system and uses the coordinate system to perform BP imaging, which can fully reduce the influence of non-systematic range unit migration and range defocus, and improve the SAR imaging quality in the large squint mode. The present invention completes rapid BP imaging and spectral tilt correction of the coarse compensation signal on a sub-grid basis, which can solve the problem that the azimuth phase error caused by spectral aliasing in the BP image is difficult to accurately estimate, so that the spectral aliasing phenomenon is effectively corrected. The present invention determines the two-dimensional phase error of each coarsely focused sub-image, and simultaneously compensates for the azimuth phase error, non-systematic range unit migration and range defocus terms, so the accuracy and efficiency of the motion error compensation of the present invention are greatly improved.

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a flow chart of an autofocusing method based on an affine coordinate system BP for a high squint SAR provided by an embodiment of the present invention;

[0019] Figure 2 An affine coordinate system PX is established according to an embodiment of the present invention. ac Y ac Z ac Schematic diagram of;

[0020] Figure 3 1 is an exemplary high-squint airborne SAR imaging geometry diagram provided by an embodiment of the present invention;

[0021] Figure 4 1 is a schematic diagram of an exemplary process of autofocusing based on an affine coordinate system BP for a high squint SAR provided by an embodiment of the present invention;

[0022] Figure 5 Schematic diagram of the distribution of simulation point targets provided by an embodiment of the present invention;

[0023] Figure 6 The three point targets in the simulation experiment provided by the embodiment of the present invention are acResults in the axial frequency domain;

[0024] Figure 7 The imaging result map of the simulated point target provided by the embodiment of the present invention obtained by using the method of the present invention and the contour map of three point targets;

[0025] FIG8( a ) is a spectrum diagram before spectrum tilt correction provided by an embodiment of the present invention;

[0026] FIG8( b ) is a spectrum diagram after spectrum tilt correction provided by an embodiment of the present invention;

[0027] Figure 9 is the final measured data imaging result provided by the embodiment of the present invention;

[0028] FIG10( a ) is a diagram of an embodiment of the present invention. Figure 9 The effect of enlarging the field in the figure;

[0029] FIG10( b ) is a diagram of an embodiment of the present invention. Figure 9 A magnified rendering of the building in the

[0030] FIG10( c ) is a diagram of an embodiment of the present invention. Figure 9 A magnified view of the river in the figure. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0032] Figure 1 FIG. 1 is a flow chart of a self-focusing method based on an affine coordinate system BP for a high squint SAR according to an embodiment of the present invention. Figure 1 As shown, the method includes:

[0033] S101 , performing range pulse compression and coarse compensation on the received original echo signal to obtain a coarse compensation signal.

[0034] Specifically, the radar transmits a radar signal and receives an echo signal reflected by the target (i.e., the original echo signal). Afterwards, the original echo signal is first subjected to range pulse compression processing to obtain a range pulse compressed signal. The range pulse compressed signal is then subjected to coarse compensation by the inertial navigation system to obtain a coarse compensated signal.

[0035] S102: Based on the coarse compensation signal, an affine coordinate system PX is established in the imaging scene with the position of the beam center point P as the origin. ac Y ac Z ac , and in the affine coordinate system X ac Y ac Divide the imaging scene into a grid in the plane.

[0036] For example, Figure 2 An affine coordinate system PX is established ac Y ac Z ac Schematic diagram of . Figure 2 As shown, Figure 2 The blue horizontal line in the figure is the radar trajectory, and the affine coordinate system PX ac Y ac Z ac The origin of the coordinate system is the beam center O, X ac The Y axis is the projection of the vector perpendicular to the beam centerline on the ground. ac The Z axis direction is the direction of the target side lobe, ac The axis is perpendicular to the ground plane, X ac Axis and Y ac There is an angle θ in the middle of the axis ra , in the affine coordinate system X ac -Y ac The plane is divided into imaging scene grids, and the coordinates of each grid point in the affine coordinate system PXacYacZac can be expressed as (x ac ,y ac ,z ac ). The size of the imaging scene grid is consistent with the size of the imaging scene.

[0037] S103 , dividing the imaging scene grid into a plurality of sub-grids, and performing fast BP imaging and spectrum tilt correction processing on the coarse compensation signal on a sub-grid basis to obtain a plurality of coarse focus sub-images.

[0038] Here, when performing subgrid division, the division can be performed according to actual needs, and the space-variant error of each subgrid is as small as possible or zero.

[0039] S104 , constructing a phase error structure of coarsely focused sub-images of different sub-grids to achieve estimation and inversion of the two-dimensional phase error.

[0040] S105 , using the two-dimensional phase error of each coarsely focused sub-image to compensate for the coarsely focused sub-image, to obtain a plurality of finely focused sub-images.

[0041] S106 , stitching the multiple precisely focused sub-images corresponding to the multiple sub-grids to obtain a precisely focused image.

[0042] In some embodiments, the above S102 is implemented by the following steps:

[0043] S1021. Determine the beam centerline vector CP according to the radar phase center position and the beam center point P in the ground rectangular coordinate system.

[0044] S1022. Determine vector A according to the beam centerline vector CP and the unit normal vector n of the imaging plane.

[0045] S1023. Determine, based on the beam centerline vector CP and the unit matrix I, a vector m that is perpendicular to the beam centerline vector CP in the slant range plane.

[0046] S1024. Determine vector R based on vector m and the unit vector v in the velocity direction of the radar at the central moment.

[0047] S1025, the position of the target P is used as the affine coordinate system PX ac Y ac Z ac The origin of the unit normal vector n is used as the direction of the affine coordinate system PX ac Y ac Z ac Z ac Axis, the direction pointed by vector A is used as the affine coordinate system PX ac Y ac Z ac X ac Axis, the direction pointed by vector R is used as the affine coordinate system PX ac Y ac Z ac Y ac Axis, get the affine coordinate system PX ac Y ac Z ac .

[0048] Specifically, the expressions of vector m, vector A, and vector R are: T is the transpose symbol.

[0049] For example, Figure 3 Figure 1 is an exemplary high squint airborne SAR imaging geometry diagram. Figure 3 As shown, OXYZ is the ground direct coordinate system, the blue horizontal line is the ideal motion trajectory of the radar, and the red curve is the actual motion trajectory of the radar. Figure 3 Gray area in the figure) to establish the affine coordinate system PX ac Y ac Z ac , divide the imaging scene into grids, the origin of the affine coordinate system is P, and the vector A corresponds to X ac The unit vector of the axis, vector R corresponds to Y ac The unit vector of the axis. The vector m is perpendicular to the beam centerline vector CP in the slant range plane, θ0 is the slant angle, R s is the center slope distance, R y is the projection of the center slant distance on the ground onto the Y axis in the ground rectangular coordinate system OXYZ, n is the unit normal vector of the imaging plane, θac is the affine coordinate system PX ac Y ac Z ac X ac Axis and Y ac The angle between the axes.

[0050] In the present invention, The energy accumulation formula of BP image in affine coordinate system is: Among them, t s , t e is the start and end time of the synthetic aperture time, s(τ,t) is the coarse compensation signal, k rc =4π / λ, R(t) is the distance from the radar phase center to the grid point of the imaging scene grid at time t, where R(t) is expressed as:

[0051]

[0052] h(x ac ,y ac ) and g(x ac ,y ac ) are the x-coordinate and y-coordinate of the grid point in the affine coordinate system in the ground rectangular coordinate system, X(t) is the x-coordinate of the radar phase center in the ground rectangular coordinate system at time t, Y(t) is the y-coordinate of the radar phase center in the ground rectangular coordinate system at time t, and Z(t) is the z-coordinate of the radar phase center in the ground rectangular coordinate system at time t.

[0053] In some embodiments, the above S103 "in the X coordinate system of the affine coordinate system" ac Y ac The in-plane grid division of the imaging scene is achieved by the following steps:

[0054] S1031. Calculate the true resolution of the center point of the imaging scene.

[0055] S1032, in the affine coordinate system X ac Y ac The imaging scene is divided into grids within the plane, wherein the resolution of the divided imaging scene grids is smaller than the actual resolution of the center point of the imaging scene.

[0056] Specifically, the expression of the true resolution of the center point of the imaging scene is as follows:

[0057]

[0058] Among them, ρ x and ρ y is the true resolution of the center point of the imaging scene, t c is the synthetic aperture center time, ts , t e are the start and end time of synthetic aperture time, R0 is the instantaneous ideal slant distance, X(t c ) is the x-coordinate of the radar phase center in the ground rectangular coordinate system at time tc, Y(t c ) is the y coordinate of the radar phase center in the ground rectangular coordinate system at time tc, R0(t s ) is the instantaneous ideal slant distance at time ts, X(t e ) is the x-coordinate of the radar phase center in the ground rectangular coordinate system at time te, Y(t e ) is the y coordinate of the radar phase center in the ground rectangular coordinate system at time te, R0(t e ) is the instantaneous ideal slant distance at time te, X(t s ) is t s The x-coordinate of the radar phase center in the ground rectangular coordinate system at time t s ) is t s The y coordinate of the radar phase center in the ground rectangular coordinate system at the moment, θ0 is the oblique angle, θ bw is the beam width, θ ac is the affine coordinate system PX ac Y ac Z ac X ac Axis and Y ac The angle between the axes, B is the bandwidth, c is the speed of light, R s is the center slope distance, R y k is the projection of the center slope distance on the ground on the Y axis of the ground rectangular coordinate system, rc =4π / λ, λ is the wavelength.

[0059] In some embodiments, the above step S103 of "dividing the imaging scene grid into a plurality of sub-grids, performing fast BP imaging and spectrum tilt correction processing on the coarse compensation signal sub-grid by sub-grid, and obtaining a plurality of coarsely focused sub-images" is implemented by the following steps:

[0060] S1033 , completing rapid BP imaging of the coarse compensation signal in each subgrid to obtain a rapid BP imaging result of the subgrid.

[0061] For example, the fast BP imaging result I(x ac ,y ac ) is as follows:

[0062]

[0063] j is the imaginary unit, Z(t c) is the z coordinate of the radar phase center at time tc in the ground rectangular coordinate system.

[0064] S1034 , performing spectrum tilt correction on the rapid BP imaging result of the sub-grid by compensating the phase of the rapid BP imaging result of the sub-grid, and obtaining a coarse focus sub-image of the sub-grid.

[0065] For example, the phase H(xac, ΔKyac) of the rapid BP imaging result of each sub-grid is expressed as follows:

[0066]

[0067] ; where t a is the azimuth time, ΔK yac Y ac The spectrum support area after removing the spectrum center on the axis, x ac is the coordinate of the grid point of the imaging scene grid on the Xac axis, X(t a ) is the x-coordinate of the radar phase center in the ground rectangular coordinate system at time ta, Y(t c ) is the y coordinate of the radar phase center at time tc in the ground rectangular coordinate system.

[0068] In some embodiments, the above S104 is implemented by the following steps:

[0069] S1041 , using a phase gradient autofocus algorithm, to estimate the one-dimensional azimuth phase error of each coarsely focused sub-image to obtain the one-dimensional azimuth phase error of the coarsely focused sub-image.

[0070] S1042: Calculate the two-dimensional phase error of the coarsely focused sub-image according to the one-dimensional azimuth phase error of the coarsely focused sub-image and the analytical relationship between the one-dimensional azimuth phase error and the two-dimensional phase error.

[0071] For example, the expression of the two-dimensional phase error is as follows:

[0072]

[0073] By applying the above formula to Y ac The center point of the spectrum of the axis ΔK yacc Performing Taylor expansion, we can get the two-dimensional phase error as:

[0074]

[0075] Among them, φ A (ΔKx′ac, ΔKyac) represents the two-dimensional phase error, ΔR is the motion error, is a composite function, ΔK xac is the affine coordinate system PXac Y ac Z ac X ac The spectrum support area after removing the spectrum center on the axis, ΔK yac is the affine coordinate system PX ac Y ac Z ac Y ac The spectrum support area after removing the spectrum center on the axis, x ac The grid points of the imaging scene grid are in X ac The coordinates on the axis, γ is the lower viewing angle, t c is the synthetic aperture center time, X(t c ) is t c The x-coordinate of the radar phase center in the ground rectangular coordinate system at time t c ) is the y coordinate of the radar phase center in the ground rectangular coordinate system at time tc, Rs is the center slant distance, R y is the projection of the center slope distance on the ground on the Y axis in the ground rectangular coordinate system, θ ac is the affine coordinate system PX ac Y ac Z ac X ac Axis and Y ac The angle between the axes, n is

[0076] For example, Figure 4 FIG. 1 is another flow chart of the self-focusing method based on the affine coordinate system BP for high squint SAR of the present invention. Figure 4 As shown, the radar acquires the echo signal of the target and uses the echo signal as the raw data. Then, the raw data is coarsely compensated for the range pulse compression inertial navigation. After obtaining the coarse compensation signal, the resolution of the center point of the imaging scene is calculated, an affine coordinate system is established, and an imaging scene grid is established according to the actual resolution. The imaging scene grid is divided into multiple sub-grids. Fast BP imaging and spectrum tilt correction processing are independently completed for each sub-grid to obtain multiple coarsely focused sub-images. The azimuth phase error of each coarsely focused sub-image is estimated, and the two-dimensional phase error of the coarsely focused sub-image is calculated based on the estimated one-dimensional azimuth phase error of the coarsely focused sub-image. The coarsely focused sub-image is compensated using the two-dimensional phase error of the coarsely focused sub-image to obtain an accurately focused sub-image. When all the coarsely focused sub-images are compensated, all the accurately focused sub-images are spliced ​​to obtain a finely focused imaging result.

[0077] The present invention has the following advantages:

[0078] 1) The present invention proposes an affine coordinate system and uses the coordinate system for BP imaging, which can fully reduce the influence of non-systematic range unit migration and range defocus. Therefore, the imaging quality of the method of the present invention is higher.

[0079] 2) The present invention introduces a new spectrum correction method to solve the problem that the azimuth phase error caused by spectrum aliasing in BP images is difficult to accurately estimate. Therefore, the method of the present invention can effectively correct the spectrum aliasing phenomenon.

[0080] 3) The present invention constructs a phase error prior structure of the BP image in an affine coordinate system, and uses this prior structure and the estimated azimuth phase error of the image to derive the two-dimensional phase error, while compensating for the azimuth phase error, non-systematic range unit migration and range defocus terms. Therefore, the accuracy and efficiency of the motion error compensation of the present invention are greatly improved.

[0081] The effectiveness of the present invention can be further illustrated by the following simulation and measured data imaging.

[0082] Simulation experiment: The simulated radar parameters are shown in Table 1, and the point target parameters are shown in Table 1. Figure 5 As shown, the distance between point target 1 and point targets 2 and 3 is 150m:

[0083] Table 1

[0084] speed bandwidth Squint angle Pulse repetition frequency carrier frequency Center slope distance 85m / s 600MHz 60° 1000Hz 11.5GHz 16km

[0085] Use the present invention to process simulation data:

[0086] Figure 6 For three point targets in X ac The results in the axial frequency domain, Figure 6 The right part of the figure is an enlarged view of the three envelopes. Figure 6 As shown, the envelope energy is concentrated, and the non-systematic range cell migration and range defocus terms have been compensated. Figure 7 The imaging results of a simulated point target using the method of the present invention, as well as contour plots of three point targets, show good imaging quality. Table 2 provides a quantitative evaluation of the simulation results. By calculating the pulse response width (IRW), peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR) in the range and azimuth directions, it can be seen that the method of the present invention has good imaging effects for high-squint SAR imaging.

[0087] Table 2

[0088]

[0089] Measured data imaging and result analysis:

[0090] Measured data experiment: The measured radar imaging parameters are shown in Table 3. The radar operates in the X-band:

[0091] Table 3

[0092] speed bandwidth Squint angle Pulse repetition frequency carrier frequency Center slope distance 112m / s 600MHz 42° 2000Hz 9.8GHz 15.14km

[0093] FIG8( a ) is a spectrum diagram before spectrum tilt correction, and FIG8( b ) is a spectrum diagram after spectrum tilt correction. It can be seen that the spectrum tilt correction process effectively solves the spectrum aliasing problem.

[0094] Figure 9 The final measured data imaging result shows that the imaging quality is good. Figure 9 Three rectangular imaging areas were selected: a field, a building, and a river. These were magnified to reveal their details. Figure 10(a) shows the magnified image of the field, Figure 10(b) shows the magnified image of the building, and Figure 10(c) shows the magnified image of the river. It can be seen that even after magnification, the image quality remains relatively clear, further demonstrating the high imaging quality of the method of the present invention.

[0095] Table 4 shows the quantization quality evaluation results of point A in FIG10( a ), which are analyzed from the perspectives of IRW, PSLR, and ISLR, further illustrating the effectiveness and accuracy of the present invention.

[0096] Table 4

[0097]

[0098] In summary, the simulation experiments and the measured data imaging experiments have verified the correctness, effectiveness and reliability of the present invention.

[0099] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0100] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0101] In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple situations. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0102] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A self-focusing method based on affine coordinate system BP for high squint SAR, characterized in that: include: Perform range pulse pressure and coarse compensation on the received original echo signal to obtain a coarse compensation signal; Based on the coarse compensation signal, a beam center point is established in the imaging scene. An affine coordinate system with the origin at , and in the affine coordinate system Divide the imaging scene into grids within the plane; The imaging scene grid is divided into a plurality of subgrids, and the rapid BP imaging and spectrum tilt correction processing of the coarse compensation signal are performed on each of the plurality of subgrids one by one to obtain a coarse focus sub-image of each subgrid, wherein the rapid BP imaging result of each subgrid is expressed as follows: ,in, The fast BP imaging results for each subgrid are: is the synthetic aperture center time, 、 are the start and end time of synthetic aperture time, is the coarse compensation signal, for The distance from the radar phase center to the grid point of the sub-grid at the moment, is the distance from the radar phase center to the grid point at the synthetic aperture center moment, is the imaginary unit, , is the wavelength; Constructing a phase error structure of the coarsely focused sub-images of different sub-grids to achieve estimation and inversion of the two-dimensional phase error; Using the two-dimensional phase error of each coarsely focused sub-image, each coarsely focused sub-image is compensated to obtain multiple finely focused sub-images; splicing the multiple finely focused sub-images corresponding one-to-one to the multiple sub-grids to obtain a finely focused image; Wherein, based on the coarse compensation signal, a beam center point is established in the imaging scene. Affine coordinate system with origin , including: according to the ground rectangular coordinate system, the radar phase center position and beam center point The position of the beam centerline vector is determined ; According to the beam centerline vector and the unit normal vector of the imaging plane , determine the vector ; According to the beam centerline vector and the identity matrix , determine the vector in the slant range plane with the beam centerline Perpendicular vector ; According to the vector and the unit vector of the radar's center moment velocity direction , determine the vector ;Will The position as the affine coordinate system The origin of the unit normal vector The direction of the affine coordinate system of axis, the vector The direction of the affine coordinate system of axis, the vector The direction of the affine coordinate system of Axis, get the affine coordinate system ; Wherein, in the affine coordinate system Dividing the imaging scene grid in the plane includes: calculating the true resolution of the center point of the imaging scene; The imaging scene is divided into grids within the plane, wherein the resolution of the divided imaging scene grids is smaller than the actual resolution of the center point of the imaging scene.

2. The autofocusing method based on affine coordinate system BP for high squint SAR according to claim 1, characterized in that: The vector , the vector and the vector The expressions are: , is the transpose symbol.

3. The autofocusing method based on affine coordinate system BP for high squint SAR according to claim 1, characterized in that: The expression of the true resolution of the center point of the imaging scene is as follows: ； ； in, and is the true resolution of the center point of the imaging scene, is the instantaneous ideal slant distance, for The x-coordinate of the radar phase center in the ground rectangular coordinate system at this moment, for The y coordinate of the radar phase center at the moment in the ground rectangular coordinate system, for The instantaneous ideal slant distance at time , for The x-coordinate of the radar phase center at the moment in the ground rectangular coordinate system, for The y coordinate of the radar phase center at the moment in the ground rectangular coordinate system, for The instantaneous ideal slant distance at time , for The x-coordinate of the radar phase center at the moment in the ground rectangular coordinate system, for The y coordinate of the radar phase center at the moment in the ground rectangular coordinate system, For oblique viewing angle, is the beam width, For the affine coordinate system of Axis and The angle between the axes, is the bandwidth, is the speed of light, is the center slope distance, is the projection of the center slope distance on the ground in the ground rectangular coordinate system Projection on the axis.

4. The autofocusing method based on affine coordinate system BP for high squint SAR according to claim 1, characterized in that: The method of performing fast BP imaging and spectrum tilt correction processing on the coarse compensation signal for each of the plurality of subgrids to obtain a coarse focus sub-image of each subgrid includes: Performing fast BP imaging of the coarse compensation signal in each subgrid to obtain a fast BP imaging result of the subgrid; By compensating the phase of the rapid BP imaging result of the subgrid, the spectrum tilt correction of the rapid BP imaging result of the subgrid is achieved, and a coarse focus sub-image of the subgrid is obtained.

5. The autofocusing method based on affine coordinate system BP for high squint SAR according to claim 1, characterized in that: The phase error structure of the coarsely focused sub-images of different sub-grids is constructed to achieve estimation and inversion of the two-dimensional phase error, including: The phase gradient autofocus algorithm is used to estimate the one-dimensional azimuth phase error of each coarsely focused sub-image, thereby obtaining the one-dimensional azimuth phase error of the coarsely focused sub-image. The two-dimensional phase error of the coarsely focused sub-image is calculated according to the one-dimensional azimuth phase error of the coarsely focused sub-image and the analytical relationship between the one-dimensional azimuth phase error and the two-dimensional phase error.

6. The autofocusing method based on affine coordinate system BP for high squint SAR according to claim 5, characterized in that: The expression of the two-dimensional phase error is as follows: ； ； ； in, represents the two-dimensional phase error, is the motion error, is a composite function, For the affine coordinate system of The spectrum support area after removing the spectrum center on the axis, For the affine coordinate system of The spectrum support area after removing the spectrum center on the axis, The grid points of the imaging scene grid are The coordinates on the axis, For the lower perspective, for The x-coordinate of the radar phase center in the ground rectangular coordinate system at this moment, for The y coordinate of the radar phase center at the moment in the ground rectangular coordinate system, is the center slope distance, is the projection of the center slope distance on the ground in the ground rectangular coordinate system The projection on the axis, is the beam width, For the affine coordinate system of Axis and The angle between the axes, for .

7. A self-focusing device based on an affine coordinate system (BP) for a high squint SAR, comprising a processor, a communication interface, a memory, and a communication bus, characterized in that: The processor, the communication interface and the memory communicate with each other via the communication bus; The memory is used to store computer programs; The processor is configured to implement the method steps described in any one of claims 1 to 6 when executing a program stored in the memory.

Images