Sea surface moving target positioning method and device, storage medium and equipment

Abstract

The invention provides a sea surface moving target positioning method and device, a storage medium and equipment, and the method comprises the steps: dividing a full aperture into a plurality of sub-apertures, carrying out the imaging of a sea surface moving target through the plurality of sub-apertures, estimating the rotation center of the sea surface moving target based on the images of the plurality of sub-apertures, and carrying out the positioning of the sea surface moving target. And extracting echoes of scattering points near the rotation center, and estimating a Doppler center of the sea surface moving target based on the echoes of the scattering points near the rotation center so as to obtain positioning information of the sea surface moving target. As Doppler spectrum broadening and distortion caused by rotation of the scattering points near the target rotation center are small, Doppler center estimation is carried out by extracting the scattering point echoes near the target rotation center, the influence of three-dimensional rotation of the target on Doppler center estimation can be effectively reduced, the estimation precision of the Doppler center is effectively improved, and the estimation accuracy of the Doppler center is improved. And accurate repositioning of the sea surface moving target is realized.

Description

Technical Field

[0001] This application relates to the field of synthetic aperture radar technology, and more specifically, to a method, apparatus, storage medium, and device for locating moving targets on the sea surface. Background Technology

[0002] Synthetic Aperture Radar (SAR) is an active microwave remote sensing device mounted on mobile platforms such as aircraft or satellites. With the continuous development of spaceborne SAR technology, the detection, localization, and motion parameter estimation of moving ships have become a hot topic and have received widespread attention. Compared to stationary targets, imaging and localizing moving targets on the sea surface is much more difficult. In complex sea conditions, moving targets on the sea surface move violently; their self-driven translational motion and wave-driven three-dimensional rotation are not negligible. These non-cooperative motions introduce radial velocity components into the target, causing a shift in the Doppler center frequency, which in turn leads to a shift in the target's imaging position. Therefore, repositioning techniques are needed to correct the shift in the imaging position of moving targets.

[0003] Currently, when relocating moving targets with three-dimensional rotation, the relocation algorithms in related technologies suffer from significant Doppler differences at different scattering points due to the target's three-dimensional rotation. This leads to additional Doppler spectral broadening, resulting in Doppler spectral aliasing, which affects the accuracy of Doppler center estimation and ultimately leads to poor positioning accuracy of moving targets on the sea surface. Summary of the Invention

[0004] The purpose of this application is to provide a method, apparatus, storage medium and device for locating moving targets on the sea surface, aiming to solve the problem of poor positioning accuracy in the relevant art for locating moving targets on the sea surface.

[0005] In a first aspect, this application provides a method for locating a moving target on the sea surface, comprising: imaging the moving target on the sea surface using multiple sub-apertures based on echo signals from a spaceborne SAR, thereby obtaining multiple sub-aperture images; estimating the rotation center of the moving target based on the multiple sub-aperture images; extracting echoes from scattering points near the rotation center, estimating the Doppler center of the moving target based on the echoes from the scattering points near the scattering points, and obtaining the location information of the moving target based on the Doppler center.

[0006] In the above implementation process, multi-aperture technology is used to image moving targets on the sea surface. The rotation center of the moving target is estimated based on multiple sub-aperture images. Then, the echoes from scattered points near the rotation center are extracted, and the Doppler center of the moving target is estimated based on these echoes, thereby obtaining the target's positioning information. Since the Doppler spectral broadening and distortion caused by the rotation of scattered points near the target's rotation center are relatively small, extracting the echoes from these scattered points for Doppler center estimation can effectively reduce the impact of the target's three-dimensional rotation on the Doppler center estimation. This effectively improves the accuracy of the Doppler center estimation and achieves precise repositioning of moving targets on the sea surface.

[0007] Furthermore, in some examples, the step of imaging moving targets on the sea surface using multiple sub-apertures based on the echo signals from the spaceborne SAR includes: selecting the sub-aperture length based on a minimum detectable signal-to-noise ratio criterion according to an objective function; the objective function is used to describe the functional relationship between the target signal-to-noise ratio of the sub-aperture imaging and the sub-aperture length; dividing the echo signals from the spaceborne SAR into multiple sub-aperture echoes using the sub-aperture lengths, and imaging moving targets on the sea surface based on each sub-aperture echo.

[0008] In the above implementation process, an objective function is established to describe the functional relationship between the target signal-to-noise ratio and the sub-aperture length in sub-aperture imaging. Combined with the minimum detectable signal-to-noise ratio criterion, an appropriate sub-aperture length is selected to divide the full aperture into multiple sub-apertures. The moving target is then imaged using the sub-apertures respectively, thereby improving the accuracy of the target's rotation center estimation.

[0009] Furthermore, in some examples, the objective function is expressed as the following formula:

[0010] in, The target signal-to-noise ratio; The unit backscattering coefficient of the moving target on the sea surface; The backscattering coefficient is the noise equivalent unit. This is the azimuth time corresponding to the sub-aperture echo; The time for synthesizing the aperture; This is the signal-to-noise ratio loss caused by defocusing.

[0011] In the above implementation process, a method for calculating the target signal-to-noise ratio of sub-aperture coarse imaging is provided. Based on this formula, an appropriate sub-aperture length can be selected, thereby effectively reducing the risk of decreased target rotation center estimation accuracy due to the decrease in the signal-to-noise ratio of moving targets.

[0012] Furthermore, in some examples, before estimating the rotation center of the moving sea surface target based on the plurality of sub-aperture images, the method includes: correcting the offset of the imaging position of the moving sea surface target in each sub-aperture image.

[0013] In the above implementation process, before estimating the rotation center of the moving target, the target position offset correction is first performed on each sub-aperture image to eliminate the influence of the translational component of the relative motion between the target and the radar on the imaging position, which facilitates subsequent multi-aperture joint processing.

[0014] Furthermore, in some examples, the offset of the imaging position of the moving target on the sea surface is expressed based on the following formula:

[0015] in, For the first Individual aperture images and the first The offset of the slant range corresponding to the imaging position of the moving target on the sea surface in the sub-aperture image; For the first Individual aperture images and the first The azimuth time offset corresponding to the imaging position of the sea surface moving target in the sub-aperture image; The radar wavelength of the spaceborne SAR; and They are the first The and the first The azimuth center time of the individual aperture echo; for Corresponding Doppler center; for Corresponding Doppler center; and These are the first-order and second-order component coefficients of the slant range history, respectively.

[0016] In the above implementation process, a specific method is provided that can accurately calculate the target position offset of each sub-aperture image, thereby enabling efficient target position offset correction.

[0017] Furthermore, in some examples, estimating the rotation center of the sea surface moving target based on the plurality of sub-aperture images includes: binarizing each sub-aperture image; superimposing the binarized sub-aperture images and determining the peak center of the superimposed region as the estimated value of the rotation center of the sea surface moving target; updating the target parameters used to correct the offset according to the estimated value, and re-estimating the rotation center based on the updated target parameters; the target parameters include the first-order component coefficients and the second-order component coefficients.

[0018] In the above implementation process, after correcting the offset, each sub-aperture image can be binarized and then superimposed. The peak region of the superimposed image is the overlapping region of the sub-aperture images, and the center of this region can be used as the rotation center of the target. Then, the first-order and second-order component coefficients of the slant range history are updated based on the estimated rotation center, and the steps of target position offset correction, binarization, and sub-aperture image superposition are repeated to iteratively estimate the rotation center. In this way, the accurate estimation of the rotation center of the moving target is achieved.

[0019] Furthermore, in some examples, the nearby scattering points include scattering points contained within the superimposed region.

[0020] In the above implementation process, the images of each sub-aperture are superimposed, and strong scattering points in the peak region of the superimposed image are detected. These scattering points are identified as scattering points near the target rotation center. Then, Doppler center estimation is performed based on the echo data of these scattering points, thereby improving the accuracy of Doppler center estimation.

[0021] Furthermore, in some examples, extracting the echo of the scattering point near the center of rotation includes: extracting an image of the scattering point near the center of rotation; and obtaining the echo of the scattering point near the center of rotation based on the image through the reverse process of imaging.

[0022] In the above implementation process, a specific method is provided for extracting the echo from the scattering point near the rotation center of the target.

[0023] Furthermore, in some examples, estimating the Doppler center of the moving target on the sea surface based on the echoes from the nearby scattering points includes: performing deskewing and fast Fourier transform on the echoes from the nearby scattering points to obtain the spectrum of the nearby scattering points, and estimating the Doppler center of the moving target on the sea surface based on the spectrum.

[0024] In the above implementation process, a specific method for Doppler center estimation based on the echo of the scattering point near the target rotation center is provided.

[0025] Secondly, this application provides a sea surface moving target positioning device, comprising: an imaging module, used to image the sea surface moving target using multiple sub-apertures based on the echo signal of a spaceborne SAR, to obtain multiple sub-aperture images; an estimation module, used to estimate the rotation center of the sea surface moving target based on the multiple sub-aperture images; and a positioning module, used to extract the echoes of scattering points near the rotation center, estimate the Doppler center of the sea surface moving target based on the echoes of the scattering points, and obtain the positioning information of the sea surface moving target based on the Doppler center.

[0026] Thirdly, this application provides an electronic device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the method described in any of the first aspects.

[0027] Fourthly, this application provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the method described in any of the first aspects.

[0028] Fifthly, this application provides a computer program product that, when run on a computer, causes the computer to perform the method described in any of the first aspects.

[0029] Other features and advantages disclosed in this application will be set forth in the following description, or some features and advantages may be inferred from the description or determined without doubt, or may be learned by practicing the above-described technology disclosed in this application.

[0030] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A flowchart illustrating a method for locating a moving target on the sea surface, provided in an embodiment of this application; Figure 2 A schematic diagram illustrating the workflow of a sea surface moving target relocation scheme based on multi-aperture processing provided in this application embodiment; Figure 3 A schematic diagram of a geometric model for imaging moving targets on the sea surface using spaceborne SAR, provided in an embodiment of this application; Figure 4 This is a schematic diagram showing the relationship between moving targets in images of different sub-apertures after offset correction, provided in an embodiment of this application. Figure 5(a) is a statistical histogram of the moving target positioning error after relocation based on the traditional algorithm provided in the embodiment of this application; Figure 5(b) is a statistical histogram of the positioning error of the moving target after the sea surface moving target repositioning scheme based on multi-aperture processing is completed to correct the azimuth offset of the imaging position and realize the repositioning of the moving target according to the embodiment of this application. Figure 6 A block diagram of a sea surface motion target positioning device provided in an embodiment of this application; Figure 7 This is a structural block diagram of an electronic device provided in an embodiment of this application. Detailed Implementation

[0033] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0034] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0035] SAR (Radar SAR) is an active microwave remote sensing device mounted on mobile platforms such as aircraft or satellites. It transmits and receives wide-bandwidth linear frequency modulated signals in the range direction, achieving high range resolution through range-matched filtering. In the azimuth direction, it utilizes the relative motion between the radar and the target to form a large synthetic aperture, effectively obtaining a very narrow azimuth beam and achieving high azimuth resolution. With the continuous development of spaceborne SAR technology, the detection, location, and motion parameter estimation of moving ships have become a hot topic and received widespread attention. Compared to stationary targets, imaging and locating moving targets on the sea surface is more difficult. In complex sea conditions, moving targets on the sea surface move violently; their self-driven translational motion and wave-driven three-dimensional rotation are not negligible. These non-cooperative movements introduce radial velocity components into the target, causing a shift in the Doppler center frequency, resulting in a shift in the target's imaging position. Therefore, repositioning techniques are needed to correct the shift in the imaging position of moving targets.

[0036] Currently, retargeting algorithms in related technologies generally employ imaging methods such as Non-linear Chirp Scaling (NCS) to perform coarse or fine imaging of echo data. After imaging, constant false alarm rate (CFAR) is used to detect moving targets on the sea surface, and echo data of each moving target is acquired. After acquiring the moving target echo data, the moving target echo data is transformed to the Doppler domain through deskewing and Fast Fourier Transform (FFT). The range-Doppler domain echoes are then incoherently superimposed along the range direction. Subsequently, methods such as energy equalization are used to estimate the Doppler center, thereby correcting the imaging position offset of the moving target. Finally, the precise latitude and longitude information of the moving target can be obtained through range-Doppler positioning methods to achieve relocation of the moving target. However, when this method is used to relocate moving targets with three-dimensional rotation, the three-dimensional rotation of the target will cause large Doppler differences at different scattering points, which will introduce additional Doppler spectrum broadening and lead to Doppler domain spectrum aliasing. This will affect the accuracy of Doppler center estimation and ultimately result in poor positioning accuracy of moving targets on the sea surface.

[0037] To address the aforementioned problems, this application provides a sea surface moving target localization scheme. It utilizes multi-aperture imaging technology to image the sea surface moving target, estimates the target's rotation center based on multiple sub-aperture images, extracts echoes from scattered points near the rotation center, and estimates the target's Doppler center based on these echoes, thereby obtaining the target's localization information. By extracting echoes from scattered points near the target's rotation center, the impact of the target's three-dimensional rotation on the Doppler center estimation is minimized, effectively improving the accuracy of the Doppler center estimation and achieving precise relocation of the sea surface moving target.

[0038] The embodiments of this application will be described below: like Figure 1 As shown, Figure 1 This is a flowchart illustrating a method for locating a moving target on the sea surface, as provided in an embodiment of this application. The method includes: Step 101: Based on the echo signal from the spaceborne SAR, image the moving target on the sea surface using multiple sub-apertures to obtain multiple sub-aperture images. The echo signal mentioned in this step refers to the electromagnetic wave pulse emitted by the spaceborne SAR, which, after illuminating the sea surface, is reflected back by various scattering bodies on the sea surface and captured by the satellite radar receiver. This electromagnetic signal contains information about the geometric and physical characteristics of the target scene. The moving target on the sea surface mentioned in this step refers to a moving object that needs to be detected, identified, and tracked from the sea surface echo, such as ships, ice floes, periscopes, etc. For simplicity, the moving target on the sea surface will be referred to as the target or moving target. In this embodiment, to achieve accurate repositioning of the moving target, the full aperture is first divided into multiple sub-apertures, and the moving target is imaged using each sub-aperture.

[0039] In some embodiments, the step of imaging a moving target on the sea surface using multiple sub-apertures based on the echo signal from a spaceborne SAR can include: selecting a sub-aperture length based on a minimum detectable signal-to-noise ratio (SNR) criterion using an objective function; the objective function describing the functional relationship between the target SNR of the sub-aperture imaging and the sub-aperture length; dividing the spaceborne SAR echo signal into multiple sub-aperture echoes using the sub-aperture length, and imaging the moving target on the sea surface based on each sub-aperture echo. In other words, a minimum detectable SNR can be calculated based on the specific requirements of the scenario, such as the system detection probability and false alarm probability requirements. This refers to the minimum signal-to-noise ratio threshold required for target detection. Simultaneously, an objective function is established to describe the target signal-to-noise ratio in sub-aperture imaging. The functional relationship between the aperture length and the sub-aperture length is determined, and then optimization is performed to find a solution that satisfies... The maximum sub-aperture length is used to divide the echo signal of the spaceborne SAR into multiple sub-aperture echoes in the azimuth and time domain. This improves the accuracy of target rotation center estimation.

[0040] Alternatively, the objective function mentioned above can be expressed as the following formula:

[0041] in, The target signal-to-noise ratio; The unit backscattering coefficient of the moving target on the sea surface; The backscattering coefficient is the noise equivalent unit. This is the azimuth time corresponding to the sub-aperture echo; The time for synthesizing the aperture; This refers to the signal-to-noise ratio loss caused by defocusing. Here... This can be considered as the sub-aperture length. As shown in the formula above, the shorter the azimuth time corresponding to the sub-aperture echo, the lower the target signal-to-noise ratio (SNR). Based on this formula, a suitable sub-aperture length can be selected, thereby effectively reducing the risk of decreased target rotation center estimation accuracy due to the decrease in the moving target SNR.

[0042] Step 102: Based on the multiple sub-aperture images, estimate the rotation center of the moving target on the sea surface; The rotation center mentioned in this step can refer to the "pivot point" of the moving target on the sea surface. Taking a ship as an example, its rotation center can be the fixed point in the ship's coordinate system around which all its translational, rotational, and oscillating motions revolve. For the target's rotation center, the radial velocity introduced by rotation is always zero. Therefore, the imaging position of the rotation center is the same in different sub-aperture images. Thus, based on multiple sub-aperture images, the rotation center of the moving target can be accurately estimated.

[0043] In some embodiments, prior to this step, the offset of the imaging position of the moving target on the sea surface in each sub-aperture image may be corrected. That is, since the imaging position of the moving target is different in each sub-aperture image, the target position offset can be corrected in each sub-aperture image before estimating the rotation center of the moving target, so as to eliminate the influence of the translational component of the relative motion between the target and the radar on the imaging position, which facilitates subsequent multi-sub-aperture joint processing.

[0044] Optionally, the offset of the imaging position of the aforementioned moving target on the sea surface can be expressed based on the following formula:

[0045] in, For the first Individual aperture images and the first The offset of the slant range corresponding to the imaging position of the moving target on the sea surface in the sub-aperture image; For the first Individual aperture images and the first The azimuth time offset corresponding to the imaging position of the sea surface moving target in the sub-aperture image; The radar wavelength of the spaceborne SAR; and They are the first The and the first The azimuth center time of the sub-aperture echo; for Corresponding Doppler center; for Corresponding Doppler center; and These are the first-order and second-order component coefficients of the slant range history, respectively. Using the above formulas, the target position offset of each sub-aperture image can be accurately calculated, thus enabling efficient target position offset correction.

[0046] Further, in some embodiments, this step may include: binarizing each sub-aperture image; superimposing the binarized sub-aperture images, and determining the peak center of the superimposed region as an estimated value of the rotation center of the sea surface moving target; updating the target parameters used to correct the offset based on the estimated value, and re-estimating the rotation center based on the updated target parameters; the target parameters include the first-order component coefficients and the second-order component coefficients. That is, since the target rotation center is at the same imaging position in different sub-aperture images, while the target edge points are at different imaging positions in different sub-aperture images, after correcting the offset, each sub-aperture image can be binarized, and then the sub-aperture images can be superimposed. The peak region after superposition is the overlapping region of the sub-aperture images, and the center of this region can be used as the rotation center of the target. and The initial values ​​may deviate from the motion parameters of the actual rotation center, leading to errors in the rotation center estimation based on multi-aperture joint processing. Therefore, the values ​​are updated according to the estimated rotation center. and The value of the rotation center is determined, and the above steps are repeated iteratively to estimate the rotation center of the moving target. In this way, an accurate estimation of the rotation center of the moving target is achieved.

[0047] Step 103: Extract the echoes from the scattering points near the rotation center, estimate the Doppler center of the moving target on the sea surface based on the echoes from the scattering points, and obtain the positioning information of the moving target on the sea surface based on the Doppler center.

[0048] In this embodiment, since the Doppler spectral broadening and distortion caused by the rotation of scattering points near the target's rotation center are relatively small, extracting the echoes from these scattering points minimizes the impact of the target's three-dimensional rotation on the Doppler center estimation, improving the accuracy of the Doppler center estimation and thus achieving precise repositioning of the moving target. Optionally, the nearby scattering points mentioned in this step can include the scattering points contained in the previously mentioned superimposed region. That is, by superimposing the images of each sub-aperture, detecting the strong scattering points in the peak region of the superimposed image, identifying these scattering points as the scattering points near the target's rotation center, and then performing Doppler center estimation based on the echo data of these scattering points, thereby improving the accuracy of the Doppler center estimation.

[0049] In some embodiments, extracting the echoes of scattering points near the center of rotation mentioned in this step may include: extracting images of the scattering points near the center of rotation; and obtaining the echoes of the scattering points near the center of rotation based on the images through the reverse process of imaging. That is, from the SAR imaging results, images of the scattering points near the center of rotation are extracted, and the scattering point information in the images is used to infer the echoes of these scattering points using a SAR signal model of a moving target. In this way, the echoes of scattering points near the center of rotation of a moving target are extracted.

[0050] Furthermore, in some embodiments, estimating the Doppler center of the moving sea surface target based on the echoes from the nearby scattering points mentioned in this step may include: performing deskewing processing and Fast Fourier Transform on the echoes from the nearby scattering points to obtain the spectrum of the nearby scattering points, and estimating the Doppler center of the moving sea surface target based on the spectrum. That is, after extracting the echoes from the scattering points near the rotation center, deskewing processing can be used to remove the differences in Doppler centers of different scattering points introduced by the beam rotation of the sliding convergence mode, and an azimuth FFT can be performed to obtain the spectrum of the scattering points near the rotation center. Then, based on the Doppler center estimation method, the Doppler center of the moving target can be obtained. In implementation, the Doppler center estimation method used can be the energy equalization method, the clutter locking method, etc. Additionally, after obtaining the Doppler center of the moving target, the precise latitude and longitude information of the moving target can be obtained through the range-Doppler positioning method.

[0051] In this embodiment, multi-aperture imaging is used to image a moving target on the sea surface. The rotation center of the moving target is estimated based on multiple sub-aperture images. Then, the echoes from scattered points near the rotation center are extracted, and the Doppler center of the moving target is estimated based on these echoes, thereby obtaining the target's positioning information. Since the Doppler spectral broadening and distortion caused by the rotation of scattered points near the target's rotation center are relatively small, extracting the echoes from these scattered points effectively reduces the impact of the target's three-dimensional rotation on the Doppler center estimation. This effectively improves the accuracy of the Doppler center estimation and achieves precise repositioning of the moving target on the sea surface.

[0052] To provide a more detailed explanation of the solution in this application, a specific embodiment is described below: This embodiment provides a sea surface moving target relocation scheme based on multi-aperture processing. The workflow of this scheme is as follows: Figure 2 As shown, it includes: S201. Obtain spaceborne SAR echo; S202, Multiple Aperture Imaging; Specifically, the geometric model for imaging moving targets on the sea surface using spaceborne SAR is as follows: Figure 3As shown, a rectangular coordinate system OXYZ is established with the centroid of the moving target 31 on the sea surface at the imaging center time as the origin O. The X-axis represents the target's travel direction, the Z-axis is perpendicular to the ground plane and away from the Earth's center, and the Y-axis is determined according to the right-hand rule. Assuming... The location coordinates of the spaceborne SAR (number 32 in the figure) at that time are: Any scattering point on a moving target The coordinates are Then the slant range of each scattering point of the moving target It can be represented as:

[0053] Since the moving target on the sea surface is a non-cooperative moving target, its three-dimensional structure, translational velocity, and three-dimensional rotation angle are all unknown. Therefore, slant range modeling is required through parameter estimation. Equation (1) contains too many unknown parameters and is difficult to apply directly to SAR imaging. Therefore, the scheme in this embodiment expands it as follows: Taylor series form

[0054] in, The scattering point of the spaceborne SAR and the moving target at the imaging center time The slope distance, Let be the th-th Taylor expansion coefficients of the slant range history. Finally, based on this slant range history, the echo signal model can be obtained as follows:

[0055] in, The number of target scattering points, For scattering points The backscattering coefficient, To adjust the frequency of the Chirp signal, For distance and time, At the speed of light, For wavelength, The imaginary unit is represented. For simplicity, the range and azimuth envelope terms of the echo are omitted in equation (3). Furthermore, after range pulse compression, the echo signal can be expressed as:

[0056] in, This refers to the gain of the distance pulse voltage signal; In this embodiment, the full aperture is divided into multiple sub-apertures, and the target is imaged using each sub-aperture. In implementation, the sub-aperture length is selected based on the minimum detectable signal-to-noise ratio criterion. The sub-aperture coarse imaging target signal-to-noise ratio... for:

[0057] in, The unit backscattering coefficient of the target; The backscattering coefficient is the noise equivalent unit. This is the azimuth time corresponding to the sub-aperture echo; The time for synthesizing the aperture; This refers to the signal-to-noise ratio loss caused by defocusing. The sub-aperture length is selected based on the minimum detectable signal-to-noise ratio criterion, i.e.:

[0058] in, This represents the minimum signal-to-noise ratio threshold required for target detection. After the sub-aperture echo is drawn, coarse sub-aperture imaging can be performed using the motion parameters corresponding to each sub-aperture.

[0059] S203. Based on multi-aperture images, estimate the rotation center of a moving target; Specifically, since the target's imaging position is different in each sub-aperture image, target position offset correction is first performed on each sub-aperture image to facilitate multi-aperture joint processing. Since target position offset correction aims to eliminate the influence of the translational component of the target's relative motion with the radar on the imaging position, the rotational component can be ignored during derivation. Furthermore, since the higher-order components in the slant range history shown in equation (2) have minimal influence on the imaging position, these higher-order components can be ignored during derivation. Considering that the NCS-based imaging algorithm can achieve range travel correction, the slant range history of the target center in the first sub-aperture echo after travel correction can be expressed as:

[0060] in, For the first The azimuth center time of the sub-aperture echo for The Doppler center corresponding to the azimuth time. and These are the first-order and second-order component coefficients of the slant range history, respectively. After evading and after coarse NCS imaging, the moving target will be focused to the range and azimuth position corresponding to the zero Doppler time. Therefore, based on the following formula, the first... Slant range corresponding to the imaging position of moving target in sub-aperture image and direction and time :

[0061] Furthermore, the first Individual aperture images and the first The offset of the imaging position of a moving target in a sub-aperture image can be expressed as:

[0062] The moving target relationship in images with different sub-apertures after offset correction is as follows: Figure 4 As shown, the three ellipses represent different sub-apertures 41, and the center point of the overlapping region of the sub-aperture images is the target rotation center 42. Specifically, for the target rotation center, the radial velocity introduced by rotation is always zero, so the imaging position of the rotation center is the same in different sub-aperture images; for the edge points of the target, the radial velocity introduced by rotation is different at different sub-aperture centers, resulting in different Doppler centers and thus different imaging positions. The images of each sub-aperture can be binarized and superimposed. The peak region of the superimposed image is the overlapping region of the sub-aperture images, and the center of this region can be used as the target rotation center. Furthermore, due to the position offset correction method used... and The initial values ​​may deviate from the motion parameters of the actual rotation center, leading to errors in the rotation center estimation based on multi-aperture joint processing. Therefore, the values ​​are updated according to the estimated rotation center. and The value of is determined, and the above steps are repeated iteratively to estimate the center of rotation.

[0063] S204. Extract the echo from the scattering point near the rotation center; Specifically, the image of the scattering point near the center of rotation is extracted, and the echo of the scattering point near the center of rotation is obtained through the reverse process of imaging; S205, estimated Doppler center; Specifically, by deskewing, the Doppler center differences between different scattering points introduced by beam rotation in the sliding convergence mode are removed, and azimuth FFT is performed to obtain the spectrum of scattering points near the rotation center. The Doppler center of the moving target can then be obtained based on traditional Doppler center estimation methods such as the energy equalization method. Therefore, the estimated value of the imaging position azimuth offset can be obtained as shown by the following formula:

[0064] S206. Obtain the latitude and longitude information of moving targets using the range-Doppler positioning method.

[0065] To verify the adaptability of the proposed scheme for 3D rotating target positioning, the positioning accuracy of the moving target was evaluated through 120 repeated simulations, all under high sea states. To increase the credibility of the Monte Carlo simulation, complex Gaussian white noise was added to the echo to make its noise level close to that of the real system, with the simulated echo signal-to-noise ratio set to -49dB. After repositioning the moving target based on the traditional algorithm, the statistical histogram of the moving target positioning error is shown in Figure 5(a), with a mean of 1727.9m and a standard deviation of 1010.0m. After completing the imaging position azimuth offset correction based on the proposed scheme and achieving moving target repositioning, the statistical histogram of the moving target positioning error is shown in Figure 5(b), with a mean of 416.7m and a standard deviation of 315.3m. The simulation results show that the proposed scheme effectively improves the positioning accuracy of 3D rotating targets.

[0066] Corresponding to the embodiments of the aforementioned methods, this application also provides embodiments of a sea surface motion target positioning device and a terminal for its application: like Figure 6 As shown, Figure 6 This is a block diagram of a sea surface motion target positioning device provided in an embodiment of this application. The device includes: Imaging module 61 is used to image moving targets on the sea surface using multiple sub-apertures based on the echo signals of the spaceborne SAR, and obtain multiple sub-aperture images. Estimation module 62 is used to estimate the rotation center of the sea surface moving target based on the plurality of sub-aperture images; The positioning module 63 is used to extract the echoes of the scattering points near the rotation center, estimate the Doppler center of the moving target on the sea surface based on the echoes of the scattering points, and obtain the positioning information of the moving target on the sea surface based on the Doppler center.

[0067] The specific implementation process of the functions and roles of each module in the above device can be found in the implementation process of the corresponding steps in the above method, and will not be repeated here.

[0068] This application also provides an electronic device, please refer to [link to application]. Figure 7 , Figure 7 This is a structural block diagram of an electronic device provided in an embodiment of this application. The electronic device may include a processor 710, a communication interface 720, a memory 730, and at least one communication bus 740. The communication bus 740 is used to enable direct communication between these components. In this embodiment, the communication interface 720 of the electronic device is used for signaling or data communication with other node devices. The processor 710 may be an integrated circuit chip with signal processing capabilities.

[0069] The processor 710 described above can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an off-the-shelf programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor, or the processor 710 can be any conventional processor.

[0070] The memory 730 may be, but is not limited to, random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc. The memory 730 stores computer-readable instructions, and when these computer-readable instructions are executed by the processor 710, the electronic device can perform the aforementioned operations. Figure 1 The various steps involved in the method implementation examples.

[0071] Alternatively, the electronic device may also include a storage controller and an input / output unit.

[0072] The memory 730, storage controller, processor 710, peripheral interface, and input / output unit are electrically connected directly or indirectly to achieve data transmission or interaction. For example, these components can be electrically connected to each other through one or more communication buses 740. The processor 710 is used to execute executable modules stored in the memory 730, such as software function modules or computer programs included in electronic devices.

[0073] The input / output unit is used to provide users with the ability to create tasks and to set optional start periods or preset execution times for those tasks, thereby enabling user-server interaction. The input / output unit may be, but is not limited to, a mouse and keyboard.

[0074] Understandable. Figure 7 The structure shown is for illustrative purposes only; the electronic device may also include components that are more advanced than those shown. Figure 7 The more or fewer components shown, or having the same Figure 7 The different configurations shown. Figure 7 The components shown can be implemented using hardware, software, or a combination thereof.

[0075] This application also provides a storage medium storing instructions. When the instructions are run on a computer, the computer program is executed by a processor to implement the method described in the method embodiment. To avoid repetition, the method will not be described again here.

[0076] This application also provides a computer program product that, when run on a computer, causes the computer to perform the method described in the method embodiment.

[0077] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can also be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0078] In addition, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0079] If the aforementioned functions are implemented as software functional modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0080] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0081] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0082] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A method for locating a surface moving target, characterized in that, The method comprises: imaging the sea surface moving target by using multiple sub-apertures based on echo signals of the space-borne SAR, to obtain multiple sub-aperture images; estimating a rotation center of the sea surface moving target based on the multiple sub-aperture images; extracting echoes of scattering points near the rotation center, estimating a Doppler center of the sea surface moving target based on the echoes of the scattering points near the rotation center, and obtaining positioning information of the sea surface moving target according to the Doppler center.

2. The method of claim 1, wherein, The imaging the sea surface moving target by using multiple sub-apertures based on echo signals of the space-borne SAR comprises: selecting a sub-aperture length according to a minimum detectable signal-to-noise ratio criterion based on a target function; the target function is used to describe a functional relationship between a target signal-to-noise ratio of sub-aperture imaging and the sub-aperture length; dividing the echo signals of the space-borne SAR into multiple sub-aperture echoes by using the sub-aperture length, and imaging the sea surface moving target according to each sub-aperture echo.

3. The method of claim 2, wherein, The target function is expressed as the following formula: wherein, is the target signal-to-noise ratio; is the unit backscattering coefficient of the sea surface movement target; is the noise equivalent unit backscattering coefficient; is the azimuth time corresponding to the sub-aperture echo; is the synthetic aperture time; is the signal-to-noise ratio loss caused by defocusing.

4. The method of claim 1, wherein, Before the estimating the rotation center of the sea surface moving target based on the multiple sub-aperture images, the method comprises: correcting an offset of an imaging position of the sea surface moving target in each sub-aperture image.

5. The method of claim 4, wherein, The offset of the imaging position of the sea surface moving target is expressed based on the following formula: wherein, is the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the offset of the slant range corresponding to the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the offset of the azimuth time corresponding to the imaging position of the sea surface moving target in the first sub-aperture image and the second sub-aperture image; is the radar wavelength of the space-borne SAR; and are the azimuth center time of the first and the second sub-aperture echo respectively; are the azimuth center time of the first and the second sub-aperture echo respectively; are the azimuth center time of the first and the second sub-aperture echo respectively; are the corresponding Doppler centers; are the corresponding Doppler centers; are the corresponding Doppler centers; are the corresponding Doppler centers; and are the first and second order component coefficients of the slant range history respectively.

6. The method of claim 5, wherein, The estimating the rotation center of the sea surface moving target based on the multiple sub-aperture images comprises: performing binaryzation processing on each sub-aperture image; stacking each sub-aperture image after the binaryzation processing, and determining a peak center of a stacking region as an estimated value of the rotation center of the sea surface moving target; updating a target parameter used for correcting the offset according to the estimated value, and re-estimating the rotation center based on the updated target parameter; the target parameter comprises the first-order component coefficient and the second-order component coefficient.

7. The method of claim 6, wherein, The scattering points near the rotation center comprise scattering points contained in the stacking region.

8. The method of claim 1, wherein, The extracting the echoes of the scattering points near the rotation center comprises: extracting images of the scattering points near the rotation center; obtaining the echoes of the scattering points near the rotation center through an inverse process of imaging based on the images.

9. The method of claim 1, wherein, The estimating the Doppler center of the sea surface moving target based on the echoes of the scattering points near the rotation center comprises: performing desquaring processing and fast Fourier transform on the echoes of the scattering points near the rotation center, to obtain a spectrum of the scattering points near the rotation center, and estimating the Doppler center of the sea surface moving target based on the spectrum.

10. A device for locating a target on the sea surface, characterized in that The method comprises: an imaging module, configured to image the sea surface moving target by using multiple sub-apertures based on echo signals of the space-borne SAR, to obtain multiple sub-aperture images; an estimating module, configured to estimate a rotation center of the sea surface moving target based on the multiple sub-aperture images; a positioning module, configured to extract echoes of scattering points near the rotation center, estimate a Doppler center of the sea surface moving target based on the echoes of the scattering points near the rotation center, and obtain positioning information of the sea surface moving target according to the Doppler center.

11. A computer readable storage medium, characterized in that, A computer program is stored on the computer readable storage medium, and the computer program is executed by a processor to implement the method according to any one of claims 1 to 9.

12. An electronic device, comprising: A computer program product comprising a computer readable medium having stored thereon instructions that, when executed by a computer, cause the computer to execute a method according to any one of claims 1 to 9. A computer program comprising instructions which, when executed by a computer, cause the computer to execute a method according to any one of claims 1 to 9. A computer program comprising instructions which, when executed by a computer, cause the computer to execute a method according to any one of claims 1 to 9. A computer program comprising instructions which,

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