A self-focusing method for arc-track spotlight SAR based on GCBP images

Abstract

The present invention discloses a self-focusing method for GCBP images suitable for arc-track spotlight SAR, comprising: during the flight of a flight platform itself, obtaining an original image signal according to signal transmission parameters of a radar of the flight platform, current flight parameters, and echo signals of received target points; performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system to obtain a first image signal; transforming the first image signal into a target domain to obtain a transformed image signal; performing a second spectrum compression process on the image transformation signal in the ground rectangular coordinate system to obtain a second image signal; determining a full-aperture phase error of the radar according to the second image signal; dividing the full aperture into a preset number of sub-apertures, dividing the phase error into a preset number of sub-errors, and obtaining a sub-error of each sub-aperture; performing coherent synthesis process on the preset number of sub-errors to generate a compensated phase error of the full aperture, and obtaining a focused image signal.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a self-focusing method suitable for arc track spotlight SAR for GCBP images. Background Art

[0002] Most of the traditional frequency domain methods are based on the assumption of azimuth invariance of signals and require relatively ideal radar trajectories, such as range Doppler algorithm and linear variable scaling algorithm. However, due to the particularity of the trajectory of arc trajectory Synthetic Aperture Radar (SAR), the assumption of azimuth invariance of echoes is no longer applicable. Therefore, it becomes very difficult to use frequency domain algorithms to image the arc trajectory SAR.

[0003] Time domain algorithms such as back projection algorithm and decomposed back projection algorithm can be applied to SAR imaging processing under arc trajectory. The back projection (BP) imaging algorithm is considered to be an ideal method for high-precision spotlight SAR imaging, but due to the large amount of computation of the algorithm, it is not suitable for practical use. In order to reduce the computational complexity, some fast BP algorithms have been proposed, such as: the accelerated decomposition back projection algorithm reduces the amount of computation by coherently fusing low-resolution sub-aperture images in the polar coordinate system, but the fusion of sub-aperture images requires image interpolation, which limits the efficiency improvement; the fast decomposition back projection algorithm in the rectangular coordinate system adopts the sub-aperture image spectrum compression method to reduce the Nyquist sampling rate along the azimuth direction, and the sub-aperture images are fused by upsampling and coherent superposition in the Cartesian coordinate system to improve efficiency. However, the fast decomposition back projection algorithm for the rectangular coordinate system (Fast Decomposition Back Projection Algorithm for Cartesian Coordinate System, CFBP) uses many approximations when solving the spectrum compression function, so that CFBP can only perform small-range imaging in the front and side view.

[0004] At present, there are two main types of autofocus methods for BP images: the first type is the estimation method based on fitness function, such as sharpness and contrast. The computational efficiency of these two estimation methods is not high. The second type is the more commonly used autofocus algorithm, such as Phase Gradient Autofocus (PGA) and Map Drift Autofocus Algorithm (MDA). A necessary condition for this type of traditional autofocus algorithm is that there is a Fourier transform relationship between the image domain and the corresponding range compression phase history domain. However, there is no such Fourier transform relationship between the image domain and the corresponding range compression phase history domain in the BP algorithm. In order to establish an approximate Fourier transform relationship between the phase history domain signal and the BP image in the polar coordinate system, some scholars proposed an autofocus algorithm based on CFBP to establish a Fourier transform relationship in the inclined plane rectangular coordinate system. However, since the inclined plane of the airborne arc track SAR does not exist, this method is not applicable to the airborne arc track SAR imaging mode. Summary of the invention

[0005] In order to solve the above problems existing in the related art, the present invention provides a self-focusing method for GCBP images suitable for arc trajectory spotlight SAR. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] The present invention provides a self-focusing method for GCBP images suitable for arc trajectory spotlight SAR, which is applied to a flight platform and includes:

[0007] During the flight of the flight platform itself, an original image signal is obtained according to the signal transmission parameters of the radar of the flight platform, the current flight parameters, and the received echo signal of the target point; the original image signal represents the back projection image of the target point;

[0008] By performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system, the frequency centers of the azimuth beam of the original image signal and the range beam of the original image signal are both zero, thereby obtaining a first image signal; the first image signal is used to represent a first processed image corresponding to the back-projected image;

[0009] transforming the first image signal into a target domain to obtain a transformed image signal;

[0010] Based on the quadratic phase function corresponding to the target point, performing a second spectrum compression process on the image transformation signal in the ground rectangular coordinate system to obtain a second image signal; the second image signal is used to represent a second processed image of the back-projected image;

[0011] Determine a phase error of the second image signal according to the second image signal to obtain a full-aperture phase error of the radar;

[0012] Dividing the full aperture into a preset number of sub-apertures, and dividing the phase error into a preset number of sub-errors, to obtain a sub-error corresponding to each sub-aperture;

[0013] The preset number of sub-errors are subjected to coherent synthesis processing to generate the full-aperture compensated phase error, and obtain a focused image signal; the focused image signal is used to represent a focused image of the backward projection image.

[0014] The present invention has the following beneficial technical effects:

[0015] On the one hand, since the backward projection image of the target point represented by the original image signal is subjected to a two-step spectrum compression process in the ground rectangular coordinate system, the spectrum support areas of different target points can be aligned and the phase errors of the aligned positions can be consistent, thereby improving the focusing effect of the image of the target point; on the other hand, since the phase error of the image signal is further estimated after the backward projection image is subjected to the two-step spectrum compression process, the sub-error of the sub-aperture is obtained according to the estimated full-aperture phase error, and the phase error of the image signal is compensated by coherently synthesizing the sub-errors of the sub-aperture in the ground rectangular coordinate system, the focusing effect of the image of the target point is further improved. In addition, since interpolation is not required when coherently synthesizing the sub-errors of the sub-aperture in the ground rectangular coordinate system, the present case not only has high compensation accuracy in the focusing calculation, but more importantly, the amount of calculation is small, thereby improving the efficiency of SAR imaging processing under the arc trajectory.

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 An optional flow chart of a self-focusing method for arc-track spotlight SAR for GCBP images provided in an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of an exemplary arc trajectory spotlight SAR signal model provided by an embodiment of the present invention;

[0019] Figure 3A A schematic diagram of spectrum support areas of three different target points corresponding to an exemplary original image signal provided in an embodiment of the present invention;

[0020] Figure 3BA schematic diagram of beam domain support areas of three different target points corresponding to a first image signal obtained after performing a first spectrum compression process on an original image signal provided by an exemplary embodiment of the present invention;

[0021] Figure 3C A schematic diagram of spectrum support areas of three different target points corresponding to a second image signal obtained after performing a second spectrum compression process on a transformed image signal provided by an exemplary embodiment of the present invention;

[0022] Figure 4A An exemplary image provided in an embodiment of the present invention is obtained by direct GCBP imaging without using the method provided by the present invention;

[0023] Figure 4B An exemplary image after self-focusing processing using the method of the present invention provided in an embodiment of the present invention;

[0024] Figure 5A A schematic diagram of a two-dimensional spectrum of a BP image when the spectrum compression processing is not performed on the BP image according to an exemplary embodiment of the present invention;

[0025] Figure 5B The schematic diagram of the two-dimensional spectrum of the BP image obtained after performing two spectrum compression processes on the BP image is provided as an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0027] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials 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, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0029] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0030] The self-focusing method for the ground Cartesian BackProjection (GCBP) image applicable to the arc track spotlight SAR provided by the present invention can be applied to, for example, a fighter jet, a satellite or other flying platform in the air. The present invention will be described in detail below using the flying platform as the execution subject of the self-focusing method for the GCBP image applicable to the arc track spotlight SAR provided by the present invention.

[0031] Figure 1 FIG. 1 is an optional flow chart of a self-focusing method for arc-track spotlight SAR for GCBP images provided by an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0032] S101. During the flight of the flight platform, an original image signal is obtained according to the signal transmission parameters of the radar of the flight platform, the current flight parameters, and the received echo signal of the target point; the original image signal represents a backward projection image of the target point.

[0033] In the embodiment of the present invention, the signal transmission parameters of the radar include: azimuth slow time t a , the vertical coordinate Y(t a ), the horizontal coordinate X(t a ), frequency f in the distance direction r The current flight parameters include: the radar's flight altitude H and flight speed v, the frequency center f in the range direction c .

[0034] In the embodiment of the present invention, the target point (ie, point target) may be any object or any position point on the ground.

[0035] In the embodiment of the present invention, the original image signal may be expressed as formulas (1) to (4):

[0036] I(K x ,K y )=exp(-jK x x-j y y); (1)

[0037]

[0038]

[0039]

[0040] Among them, I(K x ,K y ) represents the original image signal, x represents the horizontal coordinate of the target point in the ground rectangular coordinate system, y represents the vertical coordinate of the target point in the ground rectangular coordinate system, K x represents the azimuth beam of the original image signal, K y Represents the range beam of the original image signal, K r Indicates the distance wave number, f r The frequency in the distance direction, f c represents the frequency center in the distance direction, c represents the speed of light, π represents the circumference of a circle, j represents the imaginary unit, and t a Indicates the azimuth slow time, X(t a ) represents the horizontal coordinate of the radar antenna phase center in the ground rectangular coordinate system, Y(t a ) represents the ordinate of the radar antenna phase center in the ground rectangular coordinate system, R(t a ; x, y) represents the distance between the radar and the target point.

[0041] Here, the above formulas (1) to (4) can be obtained through the following derivation process:

[0042] First, in the ground rectangular coordinate system (X, Y, Z), the arc trajectory spotlight SAR signal model can be as follows: Figure 2 As shown, among which, Figure 1 As shown, the flight platform F moves in an arc, and the motion trajectory is S. In the ground rectangular coordinate system, the instantaneous slant distance from the antenna phase center of the radar of the flight platform F to the target point Q is R (t a ), the instantaneous slant range from the antenna phase center of the radar of the flight platform F to the target point P is R s The instantaneous slant range from the antenna phase center of the radar of the flight platform F to any target point can be calculated by the following formula (5):

[0043]

[0044] Among them, R(t a; x, y) represents the instantaneous slope distance, t a represents the azimuth slow time, x is the horizontal coordinate of the target point, y is the vertical coordinate of the target point, H is the radar flight altitude, X(t a ) is the horizontal coordinate of the antenna phase center, Y(t a ) is the ordinate of the antenna phase center.

[0045] Assuming that the radar transmits a linear frequency modulation signal, the echo signal of any target point can be expressed as the following formula (6) after demodulation and range pulse compression:

[0046]

[0047] Among them, ss(t r ,t a ) represents the signal of the target point echo signal after demodulation and range pulse compression, t r represents fast time, rect(.) represents window function, R(t a ; x, y) is the distance between the target and the radar (the instantaneous slant range mentioned above), c is the speed of light, v is the movement speed of the flight platform, B is the signal bandwidth, λ is the wavelength, exp(.) is the exponential function, L is the pulse width, and j is the imaginary unit.

[0048] Then, using the stationary phase point principle, ss(t r ,t a ) is transformed along the distance direction to obtain Ss(K r ,t a ), Ss(K r ,t a ) is expressed as follows (7) to (8):

[0049]

[0050]

[0051] Among them, K r Indicates the distance wave number, f r represents the frequency in the distance direction, f c represents the center frequency, t a Indicates slow time in azimuth.

[0052] Then, according to the principle of BP algorithm, Ss(K r ,t a ) is processed, and the back projection image of the target point can be expressed as I(x, y). The expression of I(x, y) is as follows:

[0053]

[0054] Among them, t s represents the aperture start time, t e Indicates the end time of the aperture.

[0055] Next, transform I(x, y) to the beam domain, and we can get the frequency domain expression I′(K x ,K y ), I′(K x ,K y ) is expressed as follows (10):

[0056]

[0057] Among them, K x Indicates the size of the BP image azimuth wave number, K y Indicates the size of the BP image distance wave number, W r represents the distance range of the imaging grid, W a represents the azimuth range of the imaging grid, (x, y) represents the horizontal and vertical coordinates of a target point in the ground rectangular coordinate system, and n represents any target point.

[0058] Next, ignoring the amplitude and the constant phase π / 4, the stationary phase point principle is used to calculate I′(K x ,K y ) are integrated to obtain the above formulas (1) to (4).

[0059] S102, performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system so that the frequency centers of the azimuth beam and the range beam of the original image signal are both zero, thereby obtaining a first image signal; the first image signal is used to represent a first processed image corresponding to the backward projection image.

[0060] In the embodiment of the present invention, performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system includes: performing a first spectrum compression process on the original image signal using an f(x, y) function;

[0061]

[0062] K rc =4πf c / c (12)

[0063] Among them, x represents the horizontal coordinate of the target point in the ground rectangular coordinate system, y represents the vertical coordinate of the target point in the ground rectangular coordinate system, K rc Indicates the distance beam size to the center of the scene (the center point of the radar), t M represents the aperture center moment, X(t M) represents the horizontal coordinate of the aperture center in the ground rectangular coordinate system at that moment, Y(t M ) represents the ordinate of the aperture center in the ground rectangular coordinate system at that moment.

[0064] In the embodiment of the present invention, by performing the first spectrum compression processing on the original image signal in the ground rectangular coordinate system, the two-dimensional wave number domain support area (spectrum support area) can be reduced.

[0065] S103: transform the first image signal into a target domain to obtain a transformed image signal.

[0066] In the embodiment of the present invention, the target domain is (x,ΔK y )domain.

[0067] S104 , based on the quadratic phase function corresponding to the target point, perform a second spectrum compression process on the image transformation signal in a ground rectangular coordinate system to obtain a second image signal; the second image signal is used to represent a second processed image of the back-projected image.

[0068] In the embodiment of the present invention, the image transformation signal may be multiplied by a quadratic phase function to obtain a second image signal; the quadratic phase function may be expressed as the following formulas (13) to (14):

[0069]

[0070] ΔK y =K y -K yc (14)

[0071] Among them, K r Indicates the distance wave number, K yc Indicates the beam size of the radar center point in the ordinate direction of the ground rectangular coordinate system, y c represents the distance to the center point of the scene, x represents the horizontal coordinate of the target point in the ground rectangular coordinate system, and y represents the vertical coordinate of the target point in the ground rectangular coordinate system.

[0072] In the embodiment of the present invention, the expression of the second image signal may be the following formulas (15) to (16):

[0073] ΔK x =K x -K xc (16)

[0074] Among them, I com (ΔK x ,ΔK y ) represents the second image signal, exp(.) represents the exponential function, Kx represents the azimuth beam of the original image signal, K xc Indicates the beam size in the horizontal direction of the scene center in the ground rectangular coordinate system.

[0075] In the embodiment of the present invention, in the ground rectangular coordinate system, the back-projected image of the target point represented by the original image signal is subjected to two-step spectrum compression processing, so that the spectrum support areas of different target points can be aligned and the phase errors of the aligned positions can be consistent, thereby improving the focusing effect of the image of the target point. For example, Figure 3A is the spectrum support area of ​​3 different target points corresponding to the original image signal, Figure 3B is the beam domain support area of ​​three different target points corresponding to the first image signal obtained after performing the first spectrum compression processing on the original image signal, Figure 3C is the spectrum support area of ​​three different target points corresponding to the second image signal obtained after performing the second spectrum compression processing on the transformed image signal; Figure 3A , 3B As shown in FIG3B , after two consecutive spectrum compression processes, the spectrum support areas of different target points are gradually aligned, so that the back projection images corresponding to the different target points can be focused.

[0076] S105. Determine a phase error of the second image signal according to the second image signal to obtain a full-aperture phase error of the radar.

[0077] Here, I com (ΔK x ,ΔK y ) is the disturbance phase, which will cause the distance distortion of the image. In the embodiment of the present invention, the influence of the disturbance phase on the error estimation accuracy can be ignored. com (ΔK x ,ΔK y ) And the third term exp(-jΔK y y) is the compressed spectrum.

[0078] In the embodiment of the present invention, it is assumed that the phase error is non-space-varying. com (ΔK x ,ΔK y ) can obtain the phase error of the second image signal, and the phase error of the second image signal can be expressed by the following formula (17):

[0079]

[0080] Among them, I′ com (ΔK x, y) represents the phase error of the second image signal, Represented by the motion error ΔR(t a ) determines the phase error.

[0081] Here, according to I com (ΔK x ,ΔK y The principle of obtaining the phase error of the second image signal from the second and third terms in ) is as follows:

[0082] During the actual flight of the flight platform, there are three-dimensional directional errors, which lead to distance errors and azimuth errors of the target in the rectangular coordinate system. It is assumed that the measurement error is corrected in advance by high-precision measurement of the navigation equipment. The residual motion error is very small and will not cause the range unit to migrate, but only manifests as a phase error. In fact, the phase error is retained in the phase history domain. Assuming that the phase error is non-space-varying, the phase error contained in the range compression phase history can be expressed as the above formula (17).

[0083] In the embodiment of the present invention, the phase error of the second image signal is a full-aperture phase error of the radar.

[0084] S106 , dividing the full aperture into a preset number of sub-apertures, and dividing the phase error into a preset number of sub-errors, to obtain a sub-error corresponding to each sub-aperture.

[0085] Here, the full aperture can be equally divided into m sub-apertures, and the phase error of the full aperture can also be equally divided into m sub-errors, so as to obtain the sub-error of each sub-aperture. m is an integer greater than 1, and m can be set according to actual needs, which is not limited in the embodiment of the present invention.

[0086] S107 , performing coherent synthesis processing on a preset number of sub-errors to generate a full-aperture compensated phase error to obtain a focused image signal; the focused image signal is used to represent a focused image of the backward projection image.

[0087] In the embodiment of the present invention, the focused image is the final processed image of the back-projected image corresponding to the original image signal.

[0088] In the embodiment of the present invention, on the one hand, since the backward projection image of the target point represented by the original image signal is subjected to a two-step spectrum compression process in the ground rectangular coordinate system, the spectrum support areas of different target points can be aligned and the phase errors of the aligned positions can be consistent, thereby improving the focusing effect of the image of the target point; on the other hand, since the phase error of the image signal is continuously estimated after the backward projection image is subjected to the two-step spectrum compression process, the sub-error of the sub-aperture is obtained according to the estimated full-aperture phase error, and the phase error of the image signal is compensated by coherently synthesizing the sub-errors of the sub-aperture in the ground rectangular coordinate system, the focusing effect of the image of the target point is further improved. In addition, since interpolation is not required when coherently synthesizing the sub-errors of the sub-aperture in the ground rectangular coordinate system, the present case has not only high compensation accuracy in the focusing calculation, but more importantly, less calculation amount, thereby improving the efficiency of SAR imaging processing under the arc trajectory.

[0089] In the embodiment of the present invention, since the above method can perform SAR imaging processing under an arc trajectory, even if the motion trajectory of the flying platform is a straight line, the above method is still applicable. Therefore, the above method is not limited by the radar motion trajectory of the flying platform and has the advantage of a wide range of applications.

[0090] The focusing effect of the embodiment of the present invention is further described below through simulation result diagrams.

[0091] Simulation 1:

[0092] Figure 4A It is an image obtained by direct GCBP imaging without using the method provided by the embodiment of the present invention; Figure 4B This is the image after the self-focusing process is performed using the method of the present invention. Figure 4A and Figure 4B It can be seen that in the image obtained by direct GCBP imaging, the target point A is completely defocused, while the target point A in the image after the self-focusing process using the method of the present invention is clearer and has a good focusing effect.

[0093] Simulation 2:

[0094] Figure 5A is a schematic diagram of the two-dimensional spectrum of the BP image when the BP image is not subjected to spectrum compression processing; Figure 5B This is a schematic diagram of the two-dimensional spectrum of the BP image obtained after performing two spectrum compression processes on the BP image. Figure 5A and Figure 5B It can be seen that the two-step spectrum compression process can align the spectrum support areas of the target points.

[0095] It can be seen from the above simulations 1 and 2 that the method of the present invention can remove the phase error.

[0096] An embodiment of the present invention further provides a flight device, comprising: a memory for storing a computer program; and a processor for implementing, when executing the computer program stored in the memory, some or all of the steps in the above-mentioned self-focusing method for GCBP images applicable to arc trajectory spotlight SAR.

[0097] The embodiment of the present invention further provides a computer-readable storage medium, wherein a computer program is stored in the computer-readable storage medium, and the computer program is used to execute some or all of the steps in the above-mentioned self-focusing method for GCBP images applicable to arc-track spotlight SAR. The computer-readable storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program codes.

[0098] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A self-focusing method for GCBP images suitable for arc-track spotlight SAR, characterized in that: Applied to flight platforms, including: During the flight of the flight platform itself, an original image signal is obtained according to the signal transmission parameters of the radar of the flight platform, the current flight parameters, and the received echo signal of the target point; the original image signal represents the back projection image of the target point; By performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system, the frequency centers of the azimuth beam of the original image signal and the range beam of the original image signal are both zero, thereby obtaining a first image signal; the first image signal is used to represent a first processed image corresponding to the back-projected image; transforming the first image signal into a target domain to obtain a transformed image signal; Based on the quadratic phase function corresponding to the target point, performing a second spectrum compression process on the image transformation signal in the ground rectangular coordinate system to obtain a second image signal; the second image signal is used to represent a second processed image of the back-projected image; Determine a phase error of the second image signal according to the second image signal to obtain a full-aperture phase error of the radar; Dividing the full aperture into a preset number of sub-apertures, and dividing the phase error into a preset number of sub-errors, to obtain a sub-error corresponding to each sub-aperture; The preset number of sub-errors are subjected to coherent synthesis processing to generate the full-aperture compensated phase error to obtain a focused image signal; the focused image signal is used to represent a focused image of the backward projection image.

2. The self-focusing method for GCBP images suitable for arc-track spotlight SAR according to claim 1, characterized in that: Performing a first spectrum compression process on the original image signal in a ground rectangular coordinate system includes: The first spectrum compression process is performed on the original image signal using the f(x, y) function; the expression of the f(x, y) function is: K rc =4πf c / c; Wherein, x represents the abscissa of the target point in the ground rectangular coordinate system, y represents the ordinate of the target point in the ground rectangular coordinate system, K rc represents the distance beam size of the radar center point, f c represents the frequency center in the distance direction, c represents the speed of light, π represents the circumference, and t M represents the aperture center moment, X(t M ) represents the horizontal coordinate of the aperture center in the ground rectangular coordinate system at the moment, Y(t M ) represents the ordinate of the aperture center in the ground rectangular coordinate system at any moment, and H represents the flight altitude of the radar.

3. The self-focusing method for GCBP images suitable for arc-track spotlight SAR according to claim 1 or 2, characterized in that: The target domain is (x,ΔK y ) domain; the second spectrum compression processing is performed on the image transformation signal in the ground rectangular coordinate system based on the quadratic phase function corresponding to the target point to obtain a second image signal, including: multiplying the image transformation signal by the quadratic phase function to obtain the second image signal; The expression of the quadratic phase function is: ΔK y =K y -K yc ; Among them, K r Indicates the distance wave number, f r The frequency in the distance direction, f c represents the frequency center in the distance direction, c represents the speed of light, π represents the circumference, K y represents the range beam size of the original image signal, K yc represents the beam size of the center point of the radar in the ordinate direction in the ground rectangular coordinate system, y c represents the distance to the center point of the scene, x represents the horizontal coordinate of the target point in the ground rectangular coordinate system, y represents the vertical coordinate of the target point in the ground rectangular coordinate system, and t M represents the aperture center moment, X(t M ) represents the horizontal coordinate of the aperture center in the ground rectangular coordinate system at the moment, Y(t M ) represents the ordinate of the aperture center in the ground rectangular coordinate system at the moment, t a Indicates the azimuth slow time, Y(t a ) represents the ordinate of the antenna phase center of the radar in the ground rectangular coordinate system, R(t a ; x, y) represents the distance between the radar and the target point.

4. The self-focusing method for GCBP images suitable for arc-track spotlight SAR according to claim 2, characterized in that: The expression of the original image signal is: I(K x ,K y )=exp(-jK x x-jK y y); Among them, K x represents the azimuth beam of the original image signal, K y represents the range beam of the original image signal, j represents an imaginary unit, and f r represents the frequency in the distance direction, t a Indicates the azimuth slow time, X(t a ) represents the abscissa of the antenna phase center of the radar in the ground rectangular coordinate system, Y(t a ) represents the ordinate of the antenna phase center of the radar in the ground rectangular coordinate system, R(t a ; x, y) represents the distance between the radar and the target point.

5. The self-focusing method for GCBP images suitable for arc-track spotlight SAR according to claim 3, characterized in that: The expression of the second image signal is: ΔK x =K x -K xc ; Among them, exp(.) represents the exponential function, K x represents the azimuth beam of the original image signal, K xc represents the beam size of the scene center in the horizontal coordinate direction in the ground rectangular coordinate system, j represents an imaginary unit, X(t a ) represents the horizontal coordinate of the antenna phase center of the radar in the ground rectangular coordinate system.

6. The self-focusing method for GCBP images suitable for arc-track spotlight SAR according to claim 5, characterized in that: The expression of the phase error of the second image signal is: in, Represented by the motion error ΔR(t a ) determines the phase error.

Images