Ground Synthetic Aperture Radar Moving Target Imaging Method and Device

Abstract

The present invention discloses a method and device for ground-based synthetic aperture radar moving target imaging. The method includes: obtaining the velocity information and position information of a ground-based synthetic aperture radar moving target; determining an echo signal based on the relative velocity according to the velocity information, position information, and a pre-established moving target signal model; performing range migration correction on the echo signal based on the relative velocity; performing range-direction Fourier transform on the corrected echo signal; and performing re-focusing processing on the transformed echo signal to obtain a ground-based synthetic aperture radar moving target image. The present invention can perform ground-based synthetic aperture radar moving target imaging and effectively re-focus and image defocused moving targets.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic aperture radar imaging, and particularly to a method and device for imaging moving targets by a ground-based synthetic aperture radar. Background Art

[0002] This section aims to provide background or context for the embodiments of the present invention described in the claims. The descriptions herein are not admitted to be prior art merely because they are included in this section.

[0003] The ground-based synthetic aperture radar GBSAR, that is, the ground-based SAR, is a SAR system capable of continuously monitoring regional deformation in real time for a long time, and has the ability of all-weather and high-resolution imaging. However, when vehicles in a mining area are running continuously, moving targets will have different speeds in the azimuth and range directions, resulting in defocusing of the moving target images.

[0004] In order to be able to remove the influence of moving target vehicles on ground-based SAR images and deformation monitoring, it is necessary to perform refocusing processing on the moving targets. Compared with traditional airborne and spaceborne SAR platforms, the significant difference in imaging of the GBSAR system is that the synthetic aperture is limited by the orbit length and cannot form a complete aperture. Existing methods are for airborne and spaceborne platforms and meet the conditions of a complete synthetic aperture, so they cannot be directly applied to the GBSAR system.

[0005] Therefore, there is an urgent need for a ground-based synthetic aperture radar moving target imaging scheme that can overcome the above problems. Summary of the Invention

[0006] The embodiments of the present invention provide a method for imaging moving targets by a ground-based synthetic aperture radar, which is used for imaging moving targets by a ground-based synthetic aperture radar and effectively refocusing and imaging defocused moving targets. The method includes:

[0007] Obtaining the speed information and position information of the moving targets of the ground-based synthetic aperture radar;

[0008] Determining the echo signal based on the relative speed according to the speed information, position information, and a pre-established moving target signal model;

[0009] Performing range migration correction on the echo signal based on the relative speed;

[0010] Performing range-direction Fourier transform on the corrected echo signal;

[0011] Performing refocusing processing on the transformed echo signal to obtain the moving target image of the ground-based synthetic aperture radar.

[0012] An embodiment of the present invention provides a ground synthetic aperture radar moving target imaging device for performing ground synthetic aperture radar moving target imaging and effectively refocusing defocused moving targets. The device includes:

[0013] A moving target information acquisition module for acquiring the speed information and position information of a ground synthetic aperture radar moving target;

[0014] An echo signal determination module for determining an echo signal based on the relative speed according to the speed information, position information, and a pre-established moving target signal model;

[0015] A range migration correction module for performing range migration correction on the echo signal based on the relative speed;

[0016] A Fourier transform module for performing range-direction Fourier transform on the corrected echo signal;

[0017] A refocusing processing module for performing refocusing processing on the transformed echo signal to obtain a ground synthetic aperture radar moving target image.

[0018] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned ground synthetic aperture radar moving target imaging method is implemented.

[0019] An embodiment of the present invention also provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the above-mentioned ground synthetic aperture radar moving target imaging method is implemented.

[0020] An embodiment of the present invention also provides a computer program product including a computer program, and when the computer program is executed by a processor, the above-mentioned ground synthetic aperture radar moving target imaging method is implemented.

[0021] In an embodiment of the present invention, the velocity information and position information of a moving target of a ground-based synthetic aperture radar are obtained; based on the velocity information, position information, and a pre-established moving target signal model, an echo signal based on the relative velocity is determined; range migration correction is performed on the echo signal based on the relative velocity; range Fourier transform is performed on the corrected echo signal; and re-focusing processing is performed on the transformed echo signal to obtain a ground-based synthetic aperture radar moving target image. In the embodiment of the present invention, a moving target signal model based on relative velocity is introduced, so that an echo signal based on relative velocity is obtained according to the velocity information and position information. The moving target is equivalent to a stationary target signal for further range migration correction. After range Fourier transform is performed on the corrected echo signal, re-focusing processing is performed to achieve quadratic phase compensation in the azimuth time domain, and a ground-based synthetic aperture radar moving target image is obtained, thereby effectively re-focusing and imaging the defocused moving target. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In the drawings:

[0023] Figure 1 Schematic diagram of the method for imaging a moving target of a ground-based synthetic aperture radar in an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of another method for imaging a moving target of a ground-based synthetic aperture radar in an embodiment of the present invention;

[0025] Figures 3a - 3d Schematic diagram of four cases for determining the rotation angle according to geometric relationships in an embodiment of the present invention;

[0026] Figure 4 Schematic diagram of another method for imaging a moving target of a ground-based synthetic aperture radar in an embodiment of the present invention;

[0027] Figure 5 GBSAR moving target defocused image obtained by the prior art;

[0028] Figure 6 GBSAR moving target re-focused image obtained by the method provided in the embodiment of the present invention;

[0029] Figure 7 Structural diagram of the device for imaging a moving target of a ground-based synthetic aperture radar in an embodiment of the present invention. Detailed Embodiments

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear and understandable, the following further elaborates on the embodiments of the present invention in conjunction with the accompanying drawings. Herein, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

[0031] To perform ground-based synthetic aperture radar (SAR) moving target imaging and effectively refocus defocused moving targets, an embodiment of the present invention provides a ground-based SAR moving target imaging method. As Figure 1 shown, the method may include:

[0032] Step 101: Obtain the velocity information and position information of the ground-based SAR moving target;

[0033] Step 102: Determine the echo signal based on the relative velocity according to the velocity information, position information, and a pre-established moving target signal model;

[0034] Step 103: Perform range migration correction on the echo signal based on the relative velocity;

[0035] Step 104: Perform range-direction Fourier transform on the corrected echo signal;

[0036] Step 105: Perform refocusing processing on the transformed echo signal to obtain the ground-based SAR moving target image.

[0037] As can be seen from Figure 1 shown, in the embodiment of the present invention, the velocity information and position information of the ground-based SAR moving target are obtained; the echo signal based on the relative velocity is determined according to the velocity information, position information, and a pre-established moving target signal model; range migration correction is performed on the echo signal based on the relative velocity; range-direction Fourier transform is performed on the corrected echo signal; refocusing processing is performed on the transformed echo signal to obtain the ground-based SAR moving target image. The embodiment of the present invention introduces a moving target signal model based on relative velocity, thereby obtaining the echo signal based on relative velocity according to the velocity information and position information, equivalent the moving target to a stationary target signal for further range migration correction, performing range-direction Fourier transform on the corrected echo signal and then performing refocusing processing, realizing quadratic phase compensation in the azimuth time domain, obtaining the ground-based SAR moving target image, and thus effectively refocusing defocused moving targets.

[0038] The inventor found that moving targets have different speeds in the azimuth and range directions, resulting in defocusing of the moving target image. Compared with traditional SAR, the significant difference in imaging of the GBSAR system is that the synthetic aperture is limited by the track length and cannot form a complete aperture. In contrast, traditional methods are proposed for a full synthetic aperture and thus cannot be directly applied to the GBSAR system. Moreover, due to the slow movement speed of the ground-based radar, the speed of the moving target is often greater than the platform speed, leading to a more complex motion situation and greater difficulty in directly analyzing the moving target model. The inventor studied the above problems and believed that the moving target signal model under the ground-based system is too complex for direct imaging processing. The reason is that the motion parameters of the moving target are unknown, and it is impossible to construct a range migration correction function to correct it. Therefore, it is impossible to directly use the Range Doppler Algorithm (RDA) to image the corrected signal. So it is necessary to introduce a moving target signal model based on relative velocity to perform range migration correction on the moving target echo. Then, the quadratic phase in the azimuth time domain of the corrected signal is compensated to obtain a refocused image. The inventor provided a ground-based SAR moving target imaging method based on relative velocity refocusing in the present invention through further research.

[0039] In steps 101 to 102, obtain the moving target speed information and position information of the ground-based synthetic aperture radar, and determine the echo signal based on relative velocity according to the speed information, position information, and the pre-established moving target signal model.

[0040] In one embodiment, as Figure 2 shown, the moving target signal model is pre-established in the following manner:

[0041] Step 201: Determine the speed information and position information based on relative velocity according to the geometric relationship;

[0042] Step 202: Determine the instantaneous slant range based on relative velocity according to the speed information and position information based on relative velocity;

[0043] Step 203: Establish a moving target signal model according to the instantaneous slant range based on relative velocity.

[0044] It should be noted that the position and speed of the moving target can be obtained by using existing algorithms or existing information. When the speed and position information are not obtained, imaging can be completed in the form of iterative parameter adjustment.

[0045] During specific implementation, assume that the radar is at the coordinate origin and the moving speed is v s , and its coordinate is (0, v s ×(t r +t a))。The moving target in the scene starts from an arbitrary position (x0, y0), and its velocities in the azimuth and range directions are v a and v r , respectively. Therefore, the coordinates of the moving target can be expressed as (x0 + v r ×(t r + t a ), y0 + v a ×(t r + t a ))。According to the geometric relationship, the velocity information and position information based on the relative velocity are determined as follows: The radar moving speed and the moving target coordinates based on the relative velocity are v' s and (x'0, y'0), and the expressions are: x'0 = x0cosθ - y0sinθ, y'0 = x0sinθ + y0cosθ. Since the rotation angle θ changes according to the different motion relationships between the two, therefore, θ needs to be determined according to the geometric relationship as follows:

[0046] As Figures 3a - 3d shown, assume that the target velocity is positive when it is along the positive direction of the coordinate axis, and negative otherwise. From Figure 3a it can be seen that when the radar velocity v s is greater than the target azimuth velocity v a , and the target range velocity component v r < 0, the resultant velocity v' s is located in the first quadrant of the coordinate system, and the angle with the positive y-axis is θ. Therefore, in order to be consistent with the coordinate system before introducing the relative velocity, it needs to be rotated counterclockwise by θ. From Figure 3b it can be seen that when the radar velocity v s is greater than the target azimuth velocity v a , and the target range velocity component v r > 0, the resultant velocity v' s is located in the second quadrant of the coordinate system, and the angle with the positive y-axis is θ. To be consistent with the coordinate system before introducing the relative velocity, it needs to be rotated clockwise by θ. From Figure 3c it can be seen that when the radar velocity v s is less than the target azimuth velocity v a , and the target range velocity component v r > 0, the resultant velocity v' s is located in the third quadrant of the coordinate system, and the angle with the negative y-axis is θ. To be consistent with the coordinate system before introducing the relative velocity, it needs to be rotated counterclockwise by θ. From Figure 3d it can be seen that when the radar velocity v s is less than the target azimuth velocity v a , and the target range velocity component v r < 0, the resultant velocity v' sLocated in the fourth quadrant of the coordinate system, with an angle of θ with the negative semi-axis of the y-axis. To be consistent with the coordinate system before introducing the relative velocity, it needs to be rotated clockwise by θ.

[0047] Furthermore, the expression for the instantaneous slant range based on the relative velocity is obtained as:

[0048]

[0049] where A = x0cosθ - y0sinθ, B = x0sinθ + y0cosθ,

[0050] Substitute the expression for the instantaneous slant range based on the relative velocity into the following expression:

[0051]

[0052] Thus, the moving target signal model based on the relative velocity is obtained as:

[0053]

[0054] where t r is the fast time in the range direction, t a is the slow time in the azimuth direction, K r is the range modulation frequency, and R ref is the reference slant range.

[0055] In step 103, range migration correction is performed on the echo signal based on the relative velocity.

[0056] In one embodiment, performing range migration correction on the echo signal based on the relative velocity includes:

[0057] Performing range migration correction according to the echo signal based on the relative velocity and a pre-established range migration correction function.

[0058] Specifically in implementation, the inventor considered that the interpolation method has a large amount of computation, so a range migration correction function formula H rcmc is constructed. Multiplying it with the form of the echo signal can complete the range migration correction. The method is simple and has high processing efficiency. The pre-established range migration correction function is:

[0059]

[0060] where is the distance between the target at zero time and the Doppler center (coordinate origin), and θ' is the angle between the line connecting the target at zero time and the Doppler center (coordinate origin) and the positive semi-axis of the x-axis.

[0061] In step 104, range direction Fourier transform is performed on the corrected echo signal.

[0062] In one embodiment, after performing range Fourier transform on the corrected echo signal, residual video phase (RVP) correction is performed on the transformed echo signal.

[0063] In this embodiment, the transformed echo signal is multiplied by a pre-established residual video phase correction function. The residual video phase correction function is:

[0064]

[0065] where K r is the range chirp rate.

[0066] In step 105, the transformed echo signal is refocused to obtain a ground-based synthetic aperture radar moving target image.

[0067] In one embodiment, as Figure 4 shown, refocusing the transformed echo signal to obtain a ground-based synthetic aperture radar moving target image includes:

[0068] Step 401: Multiply the transformed echo signal by a pre-established refocusing compensation function;

[0069] Step 402: Perform azimuth Fourier transform on the multiplication result to obtain a ground-based synthetic aperture radar moving target image.

[0070] Specifically, when implemented, range pulse compression is completed by performing range Fourier transform on the corrected echo signal. The echo signal is multiplied by the refocusing compensation function and azimuth Fourier transform is performed, thereby obtaining a refocused SAR image. The inventor found that in the moving target signal model based on relative velocity, the first exponential term is the azimuth phase history, which determines the azimuth focusing effect. Through analysis, it can be obtained that if imaging processing is performed with the parameters of a stationary scene, due to the existence of the azimuth velocity of the moving target, azimuth defocusing of the moving target imaging will occur. The reason is that this quadratic phase will cause the main lobe of the target signal to extend to both sides, resulting in defocusing of the image in the azimuth direction. Therefore, it is necessary to compensate for this quadratic phase. Considering that the GBSAR system performs imaging in the azimuth frequency domain, it is necessary to compensate for this quadratic phase in the azimuth time domain, that is, multiply the transformed echo signal by a pre-established refocusing compensation function and perform azimuth Fourier transform on the multiplication result to obtain a ground-based synthetic aperture radar moving target image.

[0071] In one embodiment, the refocusing compensation function is:

[0072]

[0073] Figure 5 The defocused image of the moving target obtained by the existing technology for GBSAR Figure 6 The refocused image of the moving target obtained by the method provided in the embodiment of the present invention for GBSAR. From Figure 5 It can be seen that the images obtained by the existing technology are defocused to varying degrees in both the azimuth and range directions, and there is Figure 6 It can be seen that the focusing effects of the images obtained by the method provided in the embodiment of the present invention in the azimuth and range directions are significantly improved.

[0074] Based on the same inventive concept, the embodiment of the present invention also provides a ground-based synthetic aperture radar moving target imaging device as described in the following embodiments. Since the principles for solving the problems are similar to those of the ground-based synthetic aperture radar moving target imaging method, the implementation of the ground-based synthetic aperture radar moving target imaging device can refer to the implementation of the method, and the repeated parts will not be described again.

[0075] Figure 7 The structure diagram of the ground-based synthetic aperture radar moving target imaging device in the embodiment of the present invention is as follows Figure 7 As shown, the ground-based synthetic aperture radar moving target imaging device includes:

[0076] A moving target information acquisition module 701, configured to acquire the velocity information and position information of the ground-based synthetic aperture radar moving target;

[0077] An echo signal determination module 702, configured to determine an echo signal based on the relative velocity according to the velocity information and position information, and a pre-established moving target signal model;

[0078] A range migration correction module 703, configured to perform range migration correction on the echo signal based on the relative velocity;

[0079] A Fourier transform module 704, configured to perform range-direction Fourier transform on the corrected echo signal;

[0080] A refocusing processing module 705, configured to perform refocusing processing on the transformed echo signal to obtain a ground-based synthetic aperture radar moving target image.

[0081] In one embodiment, the moving target signal model is pre-established in the following manner:

[0082] According to the geometric relationship, determine the velocity information and position information based on the relative velocity;

[0083] According to the velocity information and position information based on the relative velocity, determine the instantaneous slant range based on the relative velocity;

[0084] According to the instantaneous slant range based on the relative velocity, establish a moving target signal model.

[0085] In one embodiment, the refocusing processing module 705 is further configured to:

[0086] Multiply the transformed echo signal by a pre-established refocusing compensation function;

[0087] Perform azimuth Fourier transform on the result of the multiplication to obtain a ground-based synthetic aperture radar moving target image.

[0088] Based on the foregoing inventive concept, an embodiment of the present invention further provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned ground-based synthetic aperture radar moving target imaging method is implemented.

[0089] Based on the foregoing inventive concept, an embodiment of the present invention further provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned ground-based synthetic aperture radar moving target imaging method is implemented.

[0090] An embodiment of the present invention further provides a computer program product. The computer program product includes a computer program, and when the computer program is executed by a processor, the above-mentioned ground-based synthetic aperture radar moving target imaging method is implemented.

[0091] In the embodiment of the present invention, the speed information and position information of the ground-based synthetic aperture radar moving target are obtained; based on the speed information and position information, and a pre-established moving target signal model, an echo signal based on the relative speed is determined; range migration correction is performed on the echo signal based on the relative speed; range Fourier transform is performed on the corrected echo signal; refocusing processing is performed on the transformed echo signal to obtain a ground-based synthetic aperture radar moving target image. In the embodiment of the present invention, a moving target signal model based on relative speed is introduced, so that an echo signal based on relative speed is obtained according to the speed information and position information. The moving target is equivalent to a stationary target signal for further range migration correction. After range Fourier transform is performed on the corrected echo signal, refocusing processing is performed to achieve quadratic phase compensation in the azimuth time domain, and a ground-based synthetic aperture radar moving target image is obtained, thereby effectively refocusing the defocused moving target for imaging.

[0092] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) that contain computer-usable program code.

[0093] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0094] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0095] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0096] The specific embodiments described above further elaborate on the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A ground synthetic aperture radar moving target imaging method, characterized in that Including: Obtaining the velocity information and position information of the ground-based synthetic aperture radar and the moving target; Determining the echo signal based on the relative velocity according to the velocity information, position information, and the pre-established moving target signal model; Performing range migration correction on the echo signal based on the relative velocity; Performing range-direction Fourier transform on the corrected echo signal; Performing re-focusing processing on the transformed echo signal to obtain the moving target image of the ground-based synthetic aperture radar.

2. The ground synthetic aperture radar moving target imaging method according to claim 1, characterized in that, The moving target signal model is pre-established in the following manner: Determining the moving speed of the radar based on the relative velocity and the moving target coordinates according to the geometric relationship; Determining the instantaneous slant range based on the relative velocity according to the moving speed of the radar based on the relative velocity and the moving target coordinates; Establishing the moving target signal model according to the instantaneous slant range based on the relative velocity.

3. The ground synthetic aperture radar moving target imaging method according to claim 1, characterized in that, Performing range migration correction on the echo signal based on the relative velocity, including: Performing range migration correction according to the echo signal based on the relative velocity and the pre-established range migration correction function.

4. The ground synthetic aperture radar moving target imaging method according to claim 1, characterized in that, Performing re-focusing processing on the transformed echo signal to obtain the moving target image of the ground-based synthetic aperture radar, including: Multiplying the transformed echo signal by the pre-established re-focusing compensation function; Performing azimuth-direction Fourier transform on the multiplication result to obtain the moving target image of the ground-based synthetic aperture radar.

5. A ground synthetic aperture radar moving target imaging device, characterized in that, Including: A moving target information acquisition module for obtaining the velocity information and position information of the ground-based synthetic aperture radar and the moving target; An echo signal determination module for determining the echo signal based on the relative velocity according to the velocity information, position information, and the pre-established moving target signal model; A range migration correction module for performing range migration correction on the echo signal based on the relative velocity; A Fourier transform module for performing range-direction Fourier transform on the corrected echo signal; A re-focusing processing module for performing re-focusing processing on the transformed echo signal to obtain the moving target image of the ground-based synthetic aperture radar.

6. The ground synthetic aperture radar moving target imaging device according to claim 5, wherein, The moving target signal model is pre-established in the following manner: Determining the velocity information and position information based on the relative velocity according to the geometric relationship; Determining the instantaneous slant range based on the relative velocity according to the velocity information and position information based on the relative velocity; Establishing the moving target signal model according to the instantaneous slant range based on the relative velocity.

7. The ground synthetic aperture radar moving target imaging device according to claim 5, characterized in that, The re-focusing processing module is further configured to: Multiply the transformed echo signal by the pre-established re-focusing compensation function; Perform azimuth-direction Fourier transform on the multiplication result to obtain the moving target image of the ground-based synthetic aperture radar.

8. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method according to any one of claims 1 to 4.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, and when the computer program is executed by the processor, it implements the method according to any one of claims 1 to 4.

10. A computer program product, characterized in that, The computer program product includes a computer program, and when the computer program is executed by the processor, it implements the method according to any one of claims 1 to 4.

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