Moving target positioning method and apparatus, storage medium, and program product

Abstract

The application discloses a moving target positioning method and device, a storage medium and a program product. In the method, a focused moving target SAR image, a Doppler frequency, a distance index of an aperture initial moment and an aperture end moment of each moving target are determined according to original echo signals of the moving target, and a distance position and a Doppler position of each moving target in the focused moving target SAR image are extracted; a nonlinear equation group containing five equations is established according to the distance index of the aperture initial moment and the aperture end moment of each moving target, the Doppler frequency, the distance position and the Doppler position of the moving target in the focused moving target SAR image; the nonlinear equation group is solved to obtain three-dimensional position information of the moving target at a synthetic aperture center moment and a moving target azimuth velocity and a range velocity. The method can determine the position and the velocity of the moving target simultaneously.

Description

Technical Field

[0001] This invention relates to the field of distributed radar imaging detection technology, specifically to a moving target localization method, device, storage medium, and program product. Background Technology

[0002] Bistatic SAR (Synthetic Aperture Radar) systems are SAR systems where the transmitting and receiving stations are located on separate platforms. Compared to monostatic SAR, bistatic SAR, due to its separate transmitting and receiving stations, can acquire richer information about ground features through dual-view observation of the target area. It also boasts advantages such as better concealment, stronger anti-jamming capabilities, and better anti-interception performance, enabling ground reconnaissance, surveillance, and precision strikes in complex electromagnetic environments. After decades of development, bistatic SAR has achieved relatively mature technology for imaging stationary ground features. However, research on imaging and locating moving targets using bistatic SAR is still in its early stages. The challenge lies in the defocusing of moving targets in the range and azimuth directions; to achieve accurate focusing and imaging of moving targets, precise estimation of the moving target parameters is essential.

[0003] When a bistatic SAR system locates a moving target, the target's range velocity causes it to shift along the azimuth direction in the image, and the magnitude of this shift is related to the magnitude of its range velocity. To obtain the accurate position of the moving target, estimating its range velocity is a necessary step in the localization calculation.

[0004] The above analysis shows that the imaging and localization of moving targets by bistatic SAR systems both rely on the estimation of moving target parameters. Traditional monostatic bistatic SAR systems, due to channel limitations, cannot obtain additional information to aid parameter estimation and must rely on multistatic bistatic SAR systems. However, the separate nature of the bistatic transceiver platforms means that the impact on parameters is distributed across two independently moving platforms, complicating the parameter estimation process. Monostatic multi-channel SAR-GMTI parameter estimation methods are not applicable to bistatic SAR-GMTI systems. Therefore, there are still many gaps in the research on bistatic multi-channel SAR-GMTI parameter estimation methods.

[0005] Chinese patent application CN106597436A, entitled "A Method for Estimating Forward Velocity of UAV Spotlight SAR Based on Doppler Parameter Analysis", proposes to establish a set of equations for the forward velocity and acceleration along the flight path versus time. Through polynomial fitting, the estimated forward velocity and acceleration along the flight path of the beam are finally obtained.

[0006] Chinese patent application CN106772378A, entitled "A Synthetic Aperture Radar Method for Estimating the Velocity of Moving Ship Targets at Sea", proposes to perform ATI processing on the front and rear view images to obtain the corresponding ATI phase; by solving a system of equations, the azimuth velocity, range velocity, and acceleration of the moving ship target are estimated. Summary of the Invention

[0007] This invention provides a method, apparatus, storage medium, and program product for locating moving targets.

[0008] This invention adopts the following technical solution: a moving target localization method, comprising: The focused bistatic scene SAR image of the corresponding channel is determined based on the baseband echo signals of the first channel and the second channel, respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. There is a distance difference between the first receiving antenna and the second receiving antenna along the heading of the receiving station. A defocused moving target SAR image is obtained by canceling clutter in the focused bistatic SAR images of the static scene from the first and second channels. The inverse transform of the defocused moving target SAR image is performed to obtain the original echo signal of the moving target; Based on the original echo signal of the moving target, determine the focused moving target SAR image, Doppler modulation frequency, the range index of the aperture initial time and aperture ending time for each moving target, and extract the range position and Doppler position of each moving target in the focused moving target SAR image; Based on the range index of the aperture initial and final times of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image, a nonlinear equation system containing 5 equations is established, with the independent variables being the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target. Solving the nonlinear equations yields the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

[0009] The present invention adopts the following technical solution: a moving target positioning device, comprising: The first image processing module is used to determine the focused bistatic SAR image of the corresponding channel based on the baseband echo signals of the first channel and the second channel, respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. The first receiving antenna and the second receiving antenna have a distance difference along the heading of the receiving station. The second image processing module is used to obtain a defocused moving target SAR image after clutter cancellation of the focused bistatic SAR images of a static scene from the first channel and the second channel. The third image processing module is used to perform inverse transformation on the defocused moving target SAR image to obtain the original echo signal of the moving target. The parameter extraction module is used to determine the range index, Doppler modulation frequency, and focused SAR image of each moving target at the initial and final aperture times based on the original echo signal of the moving target, and to extract the range position and Doppler position of each moving target in the focused SAR image of the moving target. The equation establishment module is used to establish a nonlinear equation system containing 5 equations based on the distance index of the aperture initial time and the end time of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image. The independent variables are the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target. The equation solving module is used to solve the nonlinear equation system to obtain the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

[0010] The present invention adopts the following technical solution: a moving target positioning device, comprising: a memory and a processor, wherein the memory stores a program, and the processor runs the program to execute the aforementioned method.

[0011] The present invention adopts the following technical solution: a storage medium storing a program, wherein the program is executed to perform the aforementioned method when it is run.

[0012] The present invention adopts the following technical solution: a computer program product, wherein the computer program product is executed to perform the aforementioned method when it is run.

[0013] This method can simultaneously determine the position and velocity of the deployed target. Attached Figure Description

[0014] Figure 1 This is a dual-channel bistatic SAR imaging detection geometric model according to an embodiment of the present invention.

[0015] Figure 2 This is a flowchart of a moving target localization method according to an embodiment of the present invention.

[0016] Figure 3 This is a simplified flowchart of the process for extracting the migration trajectory and distance parameters of a moving target according to an embodiment of the present invention.

[0017] Figure 4 This is a simplified flowchart of the one-dimensional frequency modulation search for a moving target according to an embodiment of the present invention.

[0018] Figure 5 This is a bistatic SAR imaging detection geometric model according to an embodiment of the present invention.

[0019] Figure 6 This is a block diagram of a moving target positioning device according to an embodiment of the present invention.

[0020] Figure 7 This is a block diagram of a moving target positioning device according to another embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] From a programming perspective, the executing entity of the moving target localization method provided in this embodiment of the invention can be a computer program. From a device perspective, the executing entity of the moving target localization method provided in this embodiment of the invention can be an electronic device carrying these computer programs. (Reference) Figure 2 This section describes the detailed steps of the method.

[0023] Step S1: Determine the focused bistatic SAR image of the corresponding channel based on the baseband echo signals of the first channel and the second channel respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. There is a distance difference between the first receiving antenna and the second receiving antenna along the heading of the receiving station.

[0024] Figure 1 This is a dual-channel bistatic SAR imaging detection geometric model according to an embodiment of the present invention.

[0025] refer to Figure 1 One transmitting antenna is installed at the transmitting station, and a first receiving antenna (i.e., ...) is installed at the receiving station. Figure 1 The receiving antenna 1) and the second receiving antenna (i.e. Figure 1 (Receiving antenna 2). During the imaging process, the baseband echo signals of the first receiving antenna and the second receiving antenna are recorded respectively. The baseband echo signal of the first channel is processed by static scene bistatic SAR image processing to obtain a focused static scene bistatic SAR image of the first channel, and the baseband echo signal of the second channel is processed by static scene bistatic SAR image processing to obtain a focused static scene bistatic SAR image of the second channel.

[0026] exist Figure 1In this system, a coordinate system is established with the receiving station's activation point. The OX axis points towards the target area, the OY axis points vertically towards the sky, and the OZ axis, together with the OX and OY axes, forms a right-handed coordinate system. In this coordinate system, the receiving station flies along the OX axis, and the positive direction of the OX axis is also the receiving station's heading. The receiving station has two antennas arranged along its heading, namely the first receiving antenna and the second receiving antenna (represented by s1 and s2 in the following formulas, respectively).

[0027] Note: Figure 5 and Figure 1 The origin and direction of the coordinate system are the same.

[0028] The first and second receiving antennas are directly facing the target area, with the first receiving antenna serving as the receiving reference antenna. The distance between the two antennas is d. The transmitting station and the receiving station form a bistatic configuration, with the transmitting station looking sideways at the target area. The transmitting station adopts a single-channel design. Figure 1 Point P, as shown in the diagram, is the center point of the imaging scene, which is also the pointing point of the antenna beams of the transmitting and receiving stations.

[0029] Assuming the bistatic SAR transmit frequency is If the linear frequency modulated signal is given, then the baseband echo signal of target P at the first receiving antenna can be expressed as: , in, , (abbreviated in the formula as) ), These are the window functions and azimuth window functions for the radar linear frequency modulated signal, respectively, where t is the fast time. m where c is slow time and c is the speed of light. R is the wavelength. T (t) m ) for t m The distance R from the transmitting antenna to point P at any given time r1 (t) m ) for t m The distance from the first receiving antenna to point P at time t is j, where j is the imaginary unit.

[0030] The baseband echo signal of target P at the second receiving antenna can be expressed as: , in, ,in (abbreviated as) w r ), These are the window functions and azimuth window functions for the radar linear frequency modulated signal, respectively, where t is the fast time. m where c is slow time and c is the speed of light. R is the wavelength. T (t)m ) for t m The distance R from the transmitting antenna to point P at any given time r2 (t) m ) for t m The distance from the second receiving antenna to point P at time t.

[0031] The processing procedure for a stationary bistatic SAR image may include: range compression, range migration correction and Doppler center correction, range curvature correction, range secondary pulse compression and residual migration correction, azimuth spatial variation correction, azimuth higher-order filtering, and azimuth compression processing. Those skilled in the art can design such a process based on existing technology.

[0032] Step S2: Obtain a defocused moving target SAR image by canceling clutter in the focused bistatic SAR images of the static scene from the first channel and the second channel.

[0033] Analyzing the two formulas in step S1, a subtle difference exists between the baseband echo signals of the first and second channels. This difference arises from the difference in bistatic slant range between the moving target and the first and second channels. In actual flight, the bistatic slant range is very large, while the spacing between the first and second receiving antennas is a very small amount compared to the bistatic slant range.

[0034] Therefore, using the focused bistatic SAR image of the first channel as a reference, the focused bistatic SAR image of the second channel is registered. The registered bistatic SAR image of the second channel is then subtracted from the focused bistatic SAR image of the first channel to obtain the canceled moving target SAR image. The canceled moving target SAR image is defocused.

[0035] It should be noted that a focused, static bistatic SAR image from the second channel can also be used as a reference.

[0036] Traditional DPCA (Phase Center Offset Antenna) utilizes the different phase centers of two antennas to detect moving targets by suppressing ground clutter. Specifically, when the platform velocity and baseline length satisfy a certain relationship, the coordinates of the images of the same stationary ground target from the two channels overlap, while the coordinates of the images of the same moving target deviate. Therefore, after imaging by the two channels, ground clutter can be eliminated by subtracting the two focused bistatic SAR images of the stationary scene; the remaining target with stronger amplitude is the moving target. The image-domain DPCA method does not directly cancel stationary scene clutter in the echo domain, but achieves clutter cancellation by image registration of the imaged bistatic SAR images from the two channels. The effectiveness of clutter cancellation depends on the accuracy of image registration. Here, complex images are registered. This invention uses coherence measures as the standard for precise matching, combining the use of amplitude and phase information to achieve sub-pixel image registration.

[0037] The formula for calculating the coherence coefficient is: ; Where u1(n,m) and u2(n,m) are focused bistatic SAR images of a static scene obtained from the first and second receiving channels (hereinafter referred to as Image 1 and Image 2), respectively, n is the pixel x-coordinate, and m is the pixel y-coordinate. The coherence coefficient, The phase of the corresponding pixel after interference is given, and N and M represent the image size.

[0038] After image registration, subtract the registered image 2 from image 1 to obtain the canceled moving target SAR image: ; in, This is a bistatic SAR image of a stationary scene focused by the second channel after registration. The defocused SAR image of the moving target obtained after cancellation is defined as above.

[0039] Because the matching parameters for static scene imaging processing are not properly matched, the echo of the moving target is in a defocused state.

[0040] Step S3: Perform an inverse transform on the defocused SAR image of the moving target to obtain the original echo signal of the moving target.

[0041] The range history deviation of moving targets in both channels differs from that of stationary clutter, and the process of compensating for the range history deviation of stationary clutter in both channels also affects the range history of moving targets. Therefore, in order to reduce the impact of stationary imaging processing and clutter cancellation processing on the moving target echo, an inverse transform process is performed on the clutter-cancelled SAR image of the moving target to restore the most original echo form of the moving target.

[0042] This invention does not limit the specific method of inverse transformation; it can be designed according to conventional techniques in the field.

[0043] Note: The SAR images in steps S1 to S3 are all complex images.

[0044] Step S4: Determine the focused moving target SAR image, Doppler modulation frequency, and distance index of the aperture initial time and aperture ending time for each moving target based on the original echo signal of the moving target, and extract the distance position and Doppler position of each moving target in the focused moving target SAR image.

[0045] Range compression is performed on the raw echo signal of the moving target obtained in step S3 to obtain range-compressed echo data. Then, the migration curve of each moving target is extracted from the range-compressed echo data, and the range index of the aperture initial and final times for each moving target is extracted from the migration curve. , .

[0046] Furthermore, after obtaining the original echo signal of the moving target in step S3, imaging and focusing processing of the moving target can be performed. Since the moving target is a non-cooperative target, its motion parameters need to be estimated to image it. To address the problem of focusing and imaging moving targets without parameter estimation, this invention performs a keystone transform on the range-compressed echo data to obtain transformed echo data. The keystone transform can blindly correct the target's range travel, avoiding range-velocity estimation of the moving target; after keystone transform correction, the moving target energy is basically corrected to the same range gate, achieving range alignment of the moving target energy, resulting in a range-aligned echo signal of the moving target.

[0047] A one-dimensional frequency modulation search is performed on the echo signal after distance alignment of the moving target. The optimal image contrast is used as the termination condition in the azimuth direction to obtain the Doppler frequency modulation with the best image contrast. Based on the determined echo data after Doppler frequency modulation transformation, azimuth compression is performed to obtain the SAR image of the moving target after focusing.

[0048] Perform CFAR (Constant False Alarm Rate) detection on the focused SAR image of the moving target to extract the range and position of the moving target in the focused SAR image. and Doppler position .

[0049] Figure 3 This is a simplified flowchart of the process for extracting the migration trajectory and distance parameters of a moving target according to an embodiment of the present invention. The following is combined with... Figure 3 The process will be explained.

[0050] The first step is to perform range compression on the original echo signal of the moving target to obtain range-compressed echo data (i.e., range-compressed composite image).

[0051] The second step is to take the modulus of the distance-compressed echo data to obtain the amplitude diagram, and then perform 8-bit quantization.

[0052] The third step is to set the initial detection interval T=10, with mT=255-T as the detection threshold. That is, pixels with gray levels from 246 to 255 in the amplitude image are grouped together. The detection interval can also be other values ​​such as 8, 9, 11, 12, 13, etc.

[0053] Step 4: Extract the coordinates of all target points with amplitude values ​​greater than mT from the amplitude map.

[0054] Step 5: Use the distance from the target point as the ordinate (i.e., ...) Figure 3 The row coordinates in the equation are used as the independent variable, and the azimuth x-coordinate (i.e., the x-coordinate) is used as the independent variable. Figure 3 Using the column coordinates in the graph as the dependent variable, the least squares method is used to fit the curve.

[0055] Step 6: Using the distance ordinate of pixels with amplitude values ​​greater than the threshold point as the independent variable, calculate the theoretical azimuth abscissa based on the fitted curve. Remove clutter points in the current amplitude map whose difference from the theoretical azimuth abscissa is greater than three points, obtaining the amplitude map after clutter removal. The amplitude value of the removed clutter points can be set to 0, for example.

[0056] Step 7: Extract the azimuth abscissa indices of the two endpoints of the current point's trajectory from the amplitude diagram after clutter removal. This yields the distance indices of the moving target at the initial and final moments of the aperture, labeled nrn_start and nrn_end, respectively. Note: In this amplitude diagram, the horizontal axis represents the azimuth coordinate axis, and the vertical axis represents the range coordinate axis.

[0057] Step 8: Clear the amplitude of the pixels on the current point trajectory to zero in the amplitude image of the distance-compressed echo data.

[0058] Step 9: Increase the detection interval T by 10, i.e., T = T * 2, thereby decreasing the detection threshold mT by 10. Return to Step 4: Extract the coordinates of all target points with amplitude values ​​greater than mT (235 to 255) from the current amplitude map. Since the pixels of the detected trajectories with amplitude values ​​between 245 and 255 have been cleared, the extraction is actually performed within the range of amplitude values ​​between 235 and 244.

[0059] The cycle ends when mT is less than or equal to 125. In other words, this method assumes that the amplitude value of the moving target in the amplitude diagram will not be less than or equal to 125.

[0060] The above steps can be summarized as follows: The original echo signal of the moving target is sequentially quantized using range compression, modulus extraction, and a set number of bits to obtain the quantized amplitude map; In the distance index extraction step, the coordinates of target points with amplitude values ​​greater than the amplitude threshold are extracted. The distance ordinate of the target point is used as the independent variable, and the azimuth abscissa is used as the dependent variable. Least squares fitting is performed to obtain the fitted curve. Clutter points whose theoretical and actual azimuth abscissas differ from the fitted curve by a greater than a set threshold are removed. The azimuth abscissa indices at the two endpoints of the current point's trajectory are extracted from the amplitude map after clutter removal to obtain the distance indices of the moving target at the initial and final moments of the aperture; The amplitude values ​​of pixels on the current point's trajectory are cleared to zero, the amplitude threshold is lowered, and the distance index extraction step is returned when the amplitude threshold is greater than the set value. The process ends when the amplitude threshold is less than the set value.

[0061] In the above steps, based on the scattering characteristics of different moving targets, the amplitude domain is segmented, and moving targets are detected in different amplitude intervals. Least squares fitting is used to eliminate the influence of nearby amplitude targets on the migration curve.

[0062] Combination Figure 4 The following describes the method for obtaining SAR images of moving targets using Doppler frequency modulation and focusing.

[0063] The first step is to perform a keystone transformation on the range-compressed echo data to obtain the range-aligned echo data of the moving target.

[0064] The second step is to set the initial value of the distance gate as n=1.

[0065] The third step is to perform azimuth compression based on the echo data after the range gate is aligned with the moving target. In this process, the Doppler modulation frequency during azimuth compression is continuously updated, and the azimuth one-dimensional contrast of the SAR image obtained after azimuth compression is calculated. When the optimal one-dimensional contrast is obtained, the SAR image and Doppler modulation frequency at this time are determined to be the focused SAR image and Doppler modulation frequency corresponding to the current range gate.

[0066] Fourth step: Increment the range gate by 1, and execute the third step again to obtain the focused SAR image and Doppler modulation frequency corresponding to the current range gate.

[0067] Step 5: After traversing all range gates, complete the precise focusing and Doppler frequency modulation search of all moving targets in the entire SAR image.

[0068] Subsequently, CFAR (constant false alarm rate) detection was performed on the focused SAR image of the moving target to extract the range and Doppler position of the moving target in the focused SAR image.

[0069] Step S5: Based on the distance index of the aperture initial time and the end time of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image, establish a nonlinear equation system containing 5 equations. The independent variables are the three-dimensional position information of the moving target at the center time of the synthetic aperture, as well as the azimuth velocity and range velocity of the moving target.

[0070] Preferably, the transmitting and receiving stations move at a constant speed in the horizontal direction, which makes it easier to suppress clutter.

[0071] The following section focuses on the motion characteristics and echo points of bistatic moving target imaging geometry. The quantitative relationships involved in the moving target imaging process are precisely analyzed to obtain strict equality constraints. Finally, a set of nonlinear equations concerning the three-dimensional position information and movement speed of the moving target is established, enabling the simultaneous localization of the moving target and calculation of the target velocity parameters.

[0072] The geometric relationship for bistatic SAR moving target imaging detection is as follows: Figure 5 As shown.

[0073] exist Figure 5 middle, For the receiving station speed, Let P be the velocity of the transmitting station, and let P be an arbitrary moving target within the bistatic SAR beam illumination area, with the target's velocity being... The direction can be in any direction. , These are the trajectory velocity and lateral velocity components of the moving target along the receiving station, respectively. , These are the historical distances from the receiving station and the transmitting station to the moving target, respectively, t. m Here, h represents the azimuth time variable, and h represents the horizontal height of the receiving station.

[0074] Assuming the beam center time, the coordinates of the transmitting station and the receiving station are respectively and The position coordinates of the moving target are Then the distance history from the launching station and the receiving station to the moving target can be expressed as follows: ; in, , v x It is the velocity of the moving target along the x-axis (i.e., the direction of the receiver's trajectory), v z This is the velocity of the moving target along the z-axis (i.e., the side of the receiver). Of the four variables mentioned above, only two are free unknowns. , , , respectively the launch station speed The velocity components in the heading and lateral directions, , The receiving station speed V is respectively R The velocity components in the heading and lateral directions, these parameters, can be accurately measured using inertial measurement equipment on the platform. , The time for synthesizing the aperture is denoted as .

[0075] The bibase distance history of a moving target can then be represented as: .

[0076] Where, x T y T z T x R y R z R The x, y, z coordinates of the transmitting station at the beam center time and the x, y, z coordinates of the receiving station at the beam center time are shown in that order.

[0077] The transmission signal format of the bistatic system is as follows: ; in, In the formula, k r f0 represents the center frequency, and τ represents the fast time.

[0078] The delay of the echo signal from the transmitted signal reflected back to the receiving station after passing through a moving target can be expressed as: ; Represents the slant range function of the launch station. Represents the slant distance function of the receiving station. This represents the slope distance function of the two base cases.

[0079] The received two-dimensional time-domain echo signal, after down-conversion processing, can be expressed as: .

[0080] In the above formula, Indicates the target reflectance coefficient. This represents the antenna pattern modulation function. The time delay function representing the transmitted waveform. Represents fast-time variables. f0 represents the target echo delay, f0 represents the radar system center frequency, and the other symbols are defined as above.

[0081] The first phase term is the intra-pulse range-direction linear frequency modulated signal, which determines the range resolution and range migration pattern.

[0082] The second phase term is the inter-pulse azimuth Doppler phase signal, which determines the azimuth modulation information of the moving target. This is also the key process analyzed in this invention, which requires calculating the Doppler center frequency and Doppler modulation frequency of the moving target. Differentiating the phase information yields the frequency, and taking the second derivative of the phase information yields the rate of change of the frequency, i.e., the modulation frequency. Therefore, this analysis of the Doppler phase yields the Doppler frequency and the Doppler modulation frequency.

[0083] The bistatic slant range history in (That is, at the moment of the synthesis aperture center) a second expansion is performed, in the form of: ; in: .

[0084] The Doppler phase function of the moving target is: .

[0085] Differentiate the Doppler phase function and let The expression for the Doppler center frequency of the moving target is obtained as follows: .

[0086] Taking the second derivative of the Doppler phase, the Doppler modulation frequency of the moving target is obtained as follows: ; λ is the wavelength corresponding to the radar's operating center frequency.

[0087] The extracted moving target parameter information will then be mapped to the parameter information corresponding to the nonlinear solution system of equations. The specific mapping relationship is as follows: ; in, These are the system's preset initial parameters. denoted as the echo baseband sampling rate, PRF as the system pulse repetition frequency, Na as a constant, denoted as the number of azimuth pulses accumulated during imaging, m' as the Doppler blur factor, and c as the speed of light. and Here, `range_x` represents the target distance and position index at the initial and final moments of the aperture focusing process, `doppler_y` represents the target detection distance and position after the moving target is focused, and `doppler_y` represents the Doppler position of the target detection after the moving target is focused. Since target focusing generally occurs at the center moment of the synthetic aperture, these are the target distance and Doppler position at the center moment. All of the above parameters are known or can be estimated.

[0088] The physical meaning of the first equation is: the nearest sampling distance of the bistatic SAR image obtained in step S4. The target distance index nrn_start at the initial aperture moment, the speed of light c, and the echo complex baseband sampling rate F. s The distances from the moving target to the transmitting and receiving stations at the initial moment of the determined aperture, and R1.

[0089] The physical meaning of the second equation is: the nearest sampling distance of the bistatic SAR image obtained in step S4. The target distance index nrn_end at the end of the aperture, the speed of light c, and the echo complex baseband sampling rate F. s The distance from the moving target to the transmitting and receiving stations and R2 at the end of the determined aperture.

[0090] The physical meaning of the third equation is: the nearest sampling distance of the bistatic SAR image obtained in step S4. The target distance range_x at the aperture center time, the speed of light c, and the echo complex baseband sampling rate F. s The distance from the moving target to the transmitting and receiving stations and R3 at a given aperture center time.

[0091] The physical meaning of the fourth equation is: the Doppler center frequency of the moving target, determined by the Doppler position (doppler_y) of the moving target at the aperture center moment, the azimuth pulse accumulation number (Na), and the system pulse repetition frequency (PRF). .

[0092] Assume the receiving station's position information at the initial, center, and final moments of the synthetic aperture is as follows: The location information of the launch station is as follows: .

[0093] Synthesis pore size time is Assuming the motion of the moving target remains constant during the small aperture time interval, the positions of the moving target at the initial, center, and final aperture times are: .

[0094] Based on the above information, the mathematical expression of the nonlinear positioning equation system containing the position and motion information of the moving target is as follows: ; in, The above system of equations is to As obtained by substituting the input, as described above... , The launch station velocity V at the center of the synthetic aperture is respectively T The velocity components in the heading and lateral directions, , The receiving station velocity at the center of the synthetic aperture is respectively The velocity components in the heading and lateral directions are both known parameters.

[0095] The expression on the left side of the first equation means: Based on the velocity of the transmitter at the initial moment of the synthetic aperture (known quantity), the velocity of the receiver at the initial moment of the synthetic aperture (known quantity), the position of the moving target at the center moment of the synthetic aperture (unknown quantity), and the velocity of the moving target at the center moment of the synthetic aperture (unknown quantity), calculate the distance R1 from the moving target to the transmitter and receiver at the initial moment of the aperture.

[0096] The expression on the left side of the second equation means: Based on the velocity of the transmitter at the center of the synthetic aperture (known quantity), the velocity of the receiver at the center of the synthetic aperture (known quantity), the position of the moving target at the center of the synthetic aperture (unknown quantity), and the velocity of the moving target at the center of the synthetic aperture (unknown quantity), calculate the distance R2 from the moving target to the transmitter and receiver at the center of the aperture at the time of the synthetic aperture.

[0097] The expression on the left side of the third equation means: Based on the velocity of the transmitter at the end of the synthetic aperture (known quantity), the velocity of the receiver at the end of the synthetic aperture (known quantity), the position of the moving target at the center of the synthetic aperture (unknown quantity), and the velocity of the moving target at the center of the synthetic aperture (unknown quantity), calculate the distance R3 from the moving target to the transmitter and receiver at the end of the aperture.

[0098] The expression on the left side of the fourth equation means: Calculate the Doppler center frequency based on the known velocity and position of the transmitter at the time of the synthetic aperture center, the known velocity and position of the transmitter at the time of the synthetic aperture center, and the unknown velocity of the moving target at the time of the synthetic aperture center. .

[0099] The expression on the left side of the fifth equation means: Determine the Doppler modulation frequency based on the known velocity and position of the transmitting station at the center time of the synthetic aperture, the known velocity and position of the receiving station at the center time of the synthetic aperture, and the unknown position and velocity of the moving target at the center time of the synthetic space. (Obtained from step S4).

[0100] Step S6: Solve the nonlinear equations to obtain the three-dimensional coordinates of the moving target, as well as the velocity and lateral velocity of the moving target along the track of the receiving station.

[0101] As can be seen from the nonlinear equations established in step S5, solving these equations allows direct determination of the position and velocity parameters of the moving target, thus avoiding the complex parameter estimation problems required in traditional moving target detection and imaging. Many methods exist for solving nonlinear equations, but the most efficient is Newton's iteration method, the steps of which are given below.

[0102] First, let the system of equations take the form: .

[0103] Solving the partial derivatives of the five equations above, we obtain the Jacobian matrix form as follows: .

[0104] Given an initial value, set to ,in Let be the center point of the aperture beam. The initial Jacobian matrix is ​​then solved as follows: .

[0105] Based on the initial Jacobian matrix, the iterative solution system of equations is established as follows: ; in Solve the above system of linear equations to obtain the solution, which is denoted as . Further solve the Jacobian matrix Iterate continuously until the solution to the system of equations is found. This makes the following equation true: .

[0106] The solution at this point is an approximate solution to the nonlinear system of equations, denoted as . .

[0107] Furthermore, the method also includes: step S7, relocating the moving target in one of the static scene bistatic SAR images based on the three-dimensional position information of the moving target at the synthetic aperture center time and the moving target's velocity and lateral velocity along the receiving station track during the synthetic aperture period.

[0108] After calculating the three-dimensional position and velocity information of the moving target in step S6, the moving target is relocated. Relocation involves calculating the true coordinates of the moving target in the bistatic SAR image of the static scene. The calculation formula is as follows: ; The definitions of each symbol are the same as above.

[0109] Based on the same inventive concept, continue to refer to Figure 6Embodiments of the present invention also provide a moving target positioning device, comprising: a memory and a processor, wherein the memory stores a program and the processor runs the program to perform the aforementioned method.

[0110] Based on the same inventive concept, continue to refer to Figure 7 Embodiments of the present invention also provide a moving target positioning device, comprising: The first image processing module 10 is used to determine the focused bistatic SAR image of the corresponding channel based on the baseband echo signals of the first channel and the second channel, respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. The first receiving antenna and the second receiving antenna have a distance difference along the heading of the receiving station. The second image processing module 20 is used to obtain a defocused moving target SAR image after clutter cancellation of the focused bistatic SAR images of a static scene from the first channel and the second channel. The third image processing module 30 is used to perform an inverse transformation on the defocused moving target SAR image to obtain the original echo signal of the moving target. The parameter extraction module 40 is used to determine the range index, Doppler modulation frequency and focused SAR image of each moving target at the initial and final aperture times based on the original echo signal of the moving target, and to extract the range position and Doppler position of each moving target in the focused SAR image of the moving target. The equation establishment module 50 is used to establish a nonlinear equation system containing 5 equations based on the distance index of the aperture initial time and the end time of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image, and the independent variables are the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target. The equation solving module 60 is used to solve the nonlinear equation system to obtain the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

[0111] Optionally, it also includes a relocation module 70, used to relocate the moving target in one of the static scene bistatic SAR images based on the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target.

[0112] Specifically, the device can be implemented in hardware such as application-specific integrated circuits (ASICs), microcontroller units (MCUs), programmable logic devices, or in software, or in a combination of software and hardware.

[0113] Based on the same inventive concept, embodiments of the present invention also provide a storage medium on which a program is stored, the program being executed to perform the aforementioned method.

[0114] Based on the same inventive concept, embodiments of the present invention also provide a computer program product that executes the aforementioned method during runtime.

[0115] The various embodiments in this invention are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for the embodiments of apparatus, computer-readable storage media, and computer program products, since they are substantially similar to the method embodiments, their descriptions have been simplified, and relevant parts can be referred to the descriptions of the method embodiments.

[0116] The scope of protection of this invention is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its scope and spirit. If these modifications and variations fall within the scope of the claims of this invention and their equivalents, then the intent of this invention also includes these modifications and variations.

Claims

1. A method for locating a moving target, characterized in that, include: The focused bistatic scene SAR image of the corresponding channel is determined based on the baseband echo signals of the first channel and the second channel, respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. There is a distance difference between the first receiving antenna and the second receiving antenna along the heading of the receiving station. A defocused moving target SAR image is obtained by canceling clutter in the focused bistatic SAR images of the static scene from the first and second channels. The inverse transform of the defocused moving target SAR image is performed to obtain the original echo signal of the moving target; Based on the original echo signal of the moving target, determine the focused moving target SAR image, Doppler modulation frequency, the range index of the aperture initial time and aperture ending time for each moving target, and extract the range position and Doppler position of each moving target in the focused moving target SAR image; Based on the range index of the aperture initial and final times of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image, a nonlinear equation system containing 5 equations is established, with the independent variables being the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target. Solving the nonlinear equations yields the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

2. The method according to claim 1, characterized in that, A defocused moving target SAR image is obtained from the focused bistatic SAR images of the static scene in the first and second channels, including: Using the bistatic SAR image of a stationary scene focused by one of the first and second channels as a reference, the bistatic SAR image of a stationary scene focused by the other channel is registered. The defocused bistatic SAR image of the moving target is obtained by canceling out the reference focused bistatic SAR image of the static scene with the registered focused bistatic SAR image of the static scene.

3. The method according to claim 1, characterized in that, The distance index for the initial and final aperture times of each moving target is determined as follows: The original echo signal of the moving target is sequentially quantized by range compression, modulus extraction, and a set number of bits to obtain the quantized amplitude diagram; The distance index extraction step involves extracting the coordinates of target points with amplitude values ​​greater than an amplitude threshold. The distance ordinate of the target point is used as the independent variable and the azimuth abscissa as the dependent variable. The least squares method is used to fit the curve to obtain the fitting curve. Clutter points whose theoretical azimuth abscissa obtained from the fitting curve differs from the actual azimuth abscissa by a set threshold are removed. The azimuth abscissa index of the two endpoints of the current point's trajectory is extracted from the amplitude map after removing clutter points to obtain the distance index of the moving target at the initial and final moments of the aperture. Clear the amplitude value of the pixel on the current point trajectory to zero, lower the amplitude threshold, return to the distance index extraction step again when the amplitude threshold is greater than the set value, and end when the amplitude threshold is less than the set value.

4. The method according to claim 1, characterized in that, The Doppler modulation frequency and the focused SAR image of the moving target are determined as follows: The range-compressed echo data is subjected to Keystone transformation to obtain the range-aligned echo data of the moving target; Set the initial value of the distance gate to 1; The steps are defined as follows: azimuth compression is performed on the echo data after aligning the range of the moving target with the range gate. The Doppler modulation frequency during azimuth compression is continuously updated, and the azimuth one-dimensional contrast of the SAR image obtained after azimuth compression is calculated. When the optimal one-dimensional contrast is obtained, the SAR image and Doppler modulation frequency at this time are determined to be the focused SAR image and Doppler modulation frequency corresponding to the current range gate. Increment the range gate by 1, execute the determination step again, and obtain the focused SAR image and Doppler frequency corresponding to the current range gate. After traversing all range gates, complete the precise focusing and Doppler frequency search of all moving targets in the entire SAR image.

5. The method according to claim 1, characterized in that, The nonlinear equation system is as follows: In this coordinate system, the X-axis represents the trajectory of the receiving station, the Y-axis points vertically upwards, and the Z-axis, along with the X and Y axes, forms a right-handed coordinate system. The origin of this coordinate system is located on the ground directly below the receiving station at the moment it is powered on. x0, y0, and z0 are the x-axis, y-axis, and z-axis coordinates of the moving target at the aperture center moment, respectively. x and v z The values ​​are, in order, the velocity of the moving target along the x-axis and the velocity along the z-axis at the moment of aperture center. R1 y R1 ,z R1 ), (x R2 y R2 ,z R2 ), (x R3 y R3 ,z R3 The following are the receiving station's position information for the initial aperture time, center time, and end time, respectively. (x) T1 y T1 ,z T1 ), (x T2 y T2 ,z T2 ), (x T3 y T3 ,z T3 The following are the launch station's position information for the initial, center, and final aperture times, respectively. Rx V Rz (v) represents the velocity information of the receiving station at the aperture center time. Tx V Tz () represents the velocity information of the launching station at the aperture center time; R0 is the nearest sampling distance of the bistatic SAR image, which is also the system distance to the sampling reference point, F s The baseband sampling rate is denoted as , PRF is the system pulse repetition frequency, Na is a constant, is the number of azimuth pulses accumulated during imaging, m' is the Doppler blur factor, c is the speed of light, nrn_start and nrn_end are the target range and position indices at the initial and final aperture times, respectively, range_x and doppler_y are the range and Doppler positions of the moving target in the focused SAR image, respectively, and K... a_opt Doppler modulation frequency, Ts is the synthetic aperture time, λ is the wavelength corresponding to the radar's operating center frequency, and x T x R z T z R The coordinates of the transmitting station, receiving station, transmitting station, and receiving station at the beam center time are, in order: x-axis coordinates, z-axis coordinates, and z-axis coordinates. The sum of the distances from the moving target to the transmitting and receiving stations at the initial aperture time is denoted as R1, R2 at the final aperture time, and R3 at the center aperture time. R0 R T0 It is an intermediate variable used to connect the equations, and the Doppler center frequency is denoted as . .

6. The method according to claim 1, characterized in that, The method further includes: relocating the moving target in one of the static scene bistatic SAR images based on the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

7. A moving target positioning device, characterized in that, include: The first image processing module is used to determine the focused bistatic SAR image of the corresponding channel based on the baseband echo signals of the first channel and the second channel, respectively. The first channel includes a first receiving antenna on the receiving station of the distributed radar system, and the second channel includes a second receiving antenna on the receiving station. The first receiving antenna and the second receiving antenna have a distance difference along the heading of the receiving station. The second image processing module is used to obtain a defocused moving target SAR image after clutter cancellation of the focused bistatic SAR images of a static scene from the first channel and the second channel. The third image processing module is used to perform inverse transformation on the defocused moving target SAR image to obtain the original echo signal of the moving target. The parameter extraction module is used to determine the range index, Doppler modulation frequency, and focused SAR image of each moving target at the initial and final aperture times based on the original echo signal of the moving target, and to extract the range position and Doppler position of each moving target in the focused SAR image of the moving target. The equation establishment module is used to establish a nonlinear equation system containing 5 equations based on the distance index of the aperture initial time and the end time of each moving target, the Doppler modulation frequency, the range position and Doppler position of the moving target in the focused moving target SAR image. The independent variables are the three-dimensional position information of the moving target at the synthetic aperture center time and the azimuth velocity and range velocity of the moving target. The equation solving module is used to solve the nonlinear equation system to obtain the three-dimensional position information of the moving target at the moment of the synthetic aperture center, as well as the azimuth velocity and range velocity of the moving target.

8. A moving target positioning device, characterized in that, include: A memory and a processor, wherein the memory stores a program and the processor runs the program to perform the method according to any one of claims 1 to 6.

9. A storage medium, characterized in that, The storage medium stores a program, which, when run, executes the method according to any one of claims 1 to 6.

10. A computer program product, characterized in that, The computer program product is executed to perform the method according to any one of claims 1 to 6.

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