Method for locating and measuring size of moving target based on sum and difference beams

Abstract

The application discloses a kind of motion target positioning and size measurement method based on sum and difference beam, belong to target positioning field, according to radar original echo data, construct azimuth and, difference beam signal and pitch and, difference beam signal;Sum and difference beam signal is carried out SAR imaging processing, and the SAR image of target is obtained;According to SAR imaging result, the target pixel coordinates of target in SAR image are obtained;According to the SAR image data corresponding to target pixel coordinates, sum and difference beam angle measurement processing is carried out, and the pitch angle and azimuth information of target are obtained;The distance information of target is obtained by the distance gate position where target is located, and the three-dimensional coordinates of target are calculated through geometric relation, realize absolute positioning;The size of target is measured by positioning multiple positions of same target further.The SAR imaging technology and sum and difference beam angle measurement technology are combined, the absolute positioning of motion target is realized, the size of target is measured simultaneously, with the characteristics of wide application range and high positioning precision.

Description

Technical Field

[0001] This invention relates to the field of target positioning technology, and in particular to a method for positioning and measuring the size of moving targets based on sum and difference beams. Background Technology

[0002] Synthetic Aperture Radar (SAR) plays a vital role in various fields due to its advantages of all-weather, all-day, and long-range high-resolution imaging of targets. SAR imaging and positioning technology is an important development direction for SAR technology. Depending on the availability of ground control points, this technology can be divided into relative positioning and absolute positioning. Relative positioning relies on ground reference points for location assistance, but when ground reference points are difficult to obtain, absolute positioning technology is needed to achieve target localization.

[0003] Currently, SAR absolute target localization technology is mainly based on the range Doppler model. This method locates the target by the intersection of equidistant lines and equidoppler lines. Since this method requires the Doppler frequency of the target echo for target localization, the radar velocity error has a significant impact on the localization accuracy. In addition, target movement causes changes in the echo Doppler frequency, making this method unable to accurately locate moving targets. Summary of the Invention

[0004] This invention provides a method for locating and measuring the size of moving targets based on sum-difference beamforming. By combining SAR imaging technology with sum-difference beamforming angle measurement technology, it achieves absolute positioning of moving targets and measures their size. It has the characteristics of wide application range and high positioning accuracy.

[0005] An embodiment of the present invention provides a method for locating and measuring the size of a moving target based on sum and difference beams, comprising the following steps: constructing azimuth and beam signals, azimuth difference beam signals, elevation and beam signals, and elevation difference beam signals based on radar echo data;

[0006] Synthetic Aperture Radar (SAR) imaging processing is performed on the azimuth and beam signals, the azimuth difference beam signals, the elevation and beam signals, and the elevation difference beam signals, respectively, to obtain multiple SAR images containing the target. The target pixel coordinates in any one of the SAR images are selected, and sum-difference beam angle measurement is performed on the multiple SAR images corresponding to the target pixel coordinates to obtain the target's elevation and azimuth angles. The slant distance between the target and the radar aperture center is calculated to obtain the target distance information. Based on the target distance information and the target's elevation and azimuth angles, the target's three-dimensional coordinates are calculated for absolute target positioning. The absolute positioning of multiple pixel coordinates of the same target in the SAR images is then performed to obtain the target's size.

[0007] Optionally, in one embodiment of the present invention, the azimuth and beam signal constructed based on the radar echo data is:

[0008] ∑ θ =E1+E2

[0009] The constructed azimuth difference beam signal is:

[0010] Δ θ =E1-E2

[0011] The constructed pitch and beam signals are as follows:

[0012]

[0013] The constructed elevation difference beam signal is:

[0014]

[0015] E1 and E2 are the echo signals received by the first and second azimuth array elements, respectively, and E3 and E4 are the echo signals received by the third and fourth elevation array elements, respectively.

[0016] Optionally, in one embodiment of the present invention, the process of performing synthetic aperture radar imaging processing on the azimuth and beam signal, the azimuth difference beam signal, the elevation and beam signal, and the elevation difference beam signal is the same. Performing synthetic aperture radar imaging processing on the azimuth and beam signal to obtain a synthetic aperture radar imaging image containing the target includes:

[0017] For the azimuth and beam signals ∑ θ After performing a Fast Fourier Transform operation on the range, multiply by the matched filter and motion compensation reference function S. ref (f τ The signal S obtained after the distance processing is completed is obtained. R (t,f τ ):

[0018] S R (t,f τ ) = FFT(∑ θ )·S ref (f τ )

[0019]

[0020] Where c is the speed of radio wave propagation, τ and t are the distance-fast time and the azimuth-slow time, respectively, and f τ Here, k is the frequency variable, and f is the frequency modulation slope. c R is the carrier frequency for transmitting signals.a This represents the instantaneous distance from the antenna phase center to the scene center.

[0021] For signal S R (t,f τ The azimuth direction is transformed using Keystone transformation to obtain the azimuth-processed signal S. KT (t',f τ ):

[0022]

[0023] in, t' is the azimuth-time variable after Keystone transformation;

[0024] Signal S KT (t',f τ Perform a two-dimensional Fourier transform to obtain a synthetic aperture radar image containing the target.

[0025] Optionally, in one embodiment of the present invention, sum-difference beamforming is performed on multiple synthetic aperture radar imaging image data corresponding to the target pixel coordinates to obtain the target's elevation and azimuth angles as follows:

[0026]

[0027] Where, θ p and Let λ be the azimuth and elevation angles of the target point from the beam center, respectively; λ be the signal wavelength; d be the spacing between echo receiver elements; (m,n) be the pixel coordinates of the target point in the synthetic aperture radar image; m and n are the range and azimuth coordinates of the target, respectively; Im(·) is the imaginary part operation; ∑ θ (m,n), Δ θ (m,n) and These are multiple synthetic aperture radar imaging image data corresponding to pixel coordinates (m,n).

[0028] Optionally, in one embodiment of the present invention, the target range information is obtained by calculating the slant range between the target and the radar aperture center, and the target's three-dimensional coordinates are calculated based on the target range information and the target's elevation and azimuth information, including:

[0029] The slant distance between the target and the center of the radar aperture is:

[0030]

[0031] Where R0 is the radar range, m is the target range-axis pixel coordinate, Nr is the number of range-axis sampling points, and f s This refers to the echo sampling frequency;

[0032] The target's three-dimensional coordinates are:

[0033]

[0034] Where (x0,y0,z0) are the time coordinates of the radar antenna phase center at the aperture center.

[0035] The moving target localization and size measurement method based on sum-difference beams in this invention combines SAR imaging technology with sum-difference beam angle measurement technology to achieve absolute localization of moving targets and measure their size. Compared with traditional range-Doppler localization methods, which cannot measure the three-dimensional coordinates of moving targets and whose positioning accuracy is greatly affected by radar velocity errors, this method has the characteristics of wide application range and high positioning accuracy.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0038] Figure 1 A flowchart illustrating a method for locating and measuring the size of a moving target based on sum and difference beams according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram illustrating the execution process of a moving target localization and size measurement method based on sum and difference beams according to an embodiment of the present invention;

[0040] Figure 3 The imaging positioning geometric model provided according to an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of a set of antennas for transmitting and receiving according to an embodiment of the present invention;

[0042] Figure 5 This is an example of a sum-difference beam equivalent antenna pattern provided according to an embodiment of the present invention.

[0043] Figure 6 A simulated motion ship geometric model provided according to an embodiment of the present invention;

[0044] Figure 7(a) shows an azimuth and beam SAR image provided according to an embodiment of the present invention;

[0045] Figure 7(b) is an azimuth difference beam SAR image provided according to an embodiment of the present invention;

[0046] Figure 7(c) shows elevation and beam SAR images provided according to an embodiment of the present invention;

[0047] Figure 7(d) is an elevation difference beam SAR image provided according to an embodiment of the present invention;

[0048] Figure 8 This is a schematic diagram of the contour points of a moving ship target selected based on azimuth and beam SAR images according to an embodiment of the present invention. Detailed Implementation

[0049] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0050] Sum-and-difference beamforming utilizes the amplitude or phase comparison of multi-channel signals to obtain the elevation and azimuth angles of a target. Its positioning error is almost unaffected by radar velocity errors and target motion, offering advantages such as high accuracy and strong anti-interference capabilities, and is widely used in target positioning. This invention, based on the advantages of SAR imaging and the characteristics of sum-and-difference beamforming technology, proposes a method for locating and measuring the size of moving targets using sum-and-difference beamforming.

[0051] Figure 1 This is a flowchart illustrating a method for locating and measuring the size of a moving target based on sum and difference beams, according to an embodiment of the present invention.

[0052] like Figure 1 As shown, the method for locating and measuring the size of a moving target based on sum and difference beams includes the following steps:

[0053] In step S101, azimuth and beam signals, azimuth difference beam signals, elevation and beam signals, and elevation difference beam signals are constructed based on radar echo data.

[0054] Four sets of raw radar echo data are acquired, including the raw radar echo signals received by azimuth array elements 1 and 2, and the raw radar echo signals received by elevation array elements 3 and 4. Based on these four sets of raw radar echo data, azimuth sum and difference beam signals and elevation sum and difference beam signals are constructed. The constructed azimuth and beam signals are as follows:

[0055] ∑ θ =E1+E2

[0056] The constructed azimuth difference beam signal is:

[0057] Δ θ =E1-E2

[0058] The constructed elevation and beam signals are:

[0059]

[0060] The constructed elevation difference beam signal is:

[0061]

[0062] E1 and E2 are the echo signals received by the first and second azimuth array elements, respectively, and E3 and E4 are the echo signals received by the third and fourth elevation array elements, respectively.

[0063] In step S102, synthetic aperture radar imaging processing is performed on the azimuth and beam signal, azimuth difference beam signal, elevation and beam signal, and elevation difference beam signal respectively to obtain multiple synthetic aperture radar imaging images containing the target.

[0064] Synthetic aperture radar (SAR) imaging processing is performed on the azimuth sum and difference beam signals and the elevation sum and difference beam signals constructed above to obtain SAR imaging images corresponding to the azimuth sum and difference beam signals and the elevation sum and difference beam signals. The imaging process of the four signals is the same, and the target pixels on each SAR imaging image are the same.

[0065] In one embodiment of the present invention, the azimuth and beam signal ∑ θ Taking the imaging process as an example, firstly, the orientation and beam signal ∑ θ Perform an FFT operation on the range and multiply by the matched filter and motion compensation reference function S. ref (f τ The signal S obtained after the distance processing is completed is obtained. R (t,f τ ):

[0066] S R (t,f τ ) = FFT(∑ θ )·S ref (f τ )

[0067] Matched filtering and motion compensation reference function S ref (f τ )for:

[0068]

[0069] Where c is the speed of radio wave propagation, τ and t are the distance-fast time and the azimuth-slow time, respectively, and f τ Here, k is the frequency variable, and f is the frequency modulation slope. c R is the carrier frequency for transmitting signals. a This represents the instantaneous distance from the antenna phase center to the scene center.

[0070] Secondly, for signal S R (t,f τ The azimuth direction is transformed using Keystone transformation to obtain the azimuth-processed signal S. KT (t',f τ ):

[0071]

[0072] in, t' is the azimuth-time variable after Keystone transformation.

[0073] Finally, the signal S KT (t',f τ A two-dimensional Fourier transform is performed to obtain a synthetic aperture radar image containing the target.

[0074] In step S103, the target pixel coordinates in any synthetic aperture radar imaging image are selected, and sum-difference beam angle measurement is performed on the multiple synthetic aperture radar imaging image data corresponding to the target pixel coordinates to obtain the target's elevation and azimuth information.

[0075] Since the target pixels are the same in each synthetic aperture radar (SAR) image, the target pixels are selected from the SAR images corresponding to either the azimuth sum and difference beam signal or the elevation sum and difference beam signal.

[0076] When selecting target pixels, taking azimuth and signal as an example, the location of the target is determined based on the SAR imaging results of the azimuth and beam signal. Then, a relatively clear and characteristic target point (target outline position) is selected in the target image to confirm the pixel coordinates of the target point in the image.

[0077] Based on the sum-difference beamforming processing of multiple synthetic aperture radar imaging images corresponding to the target pixel coordinates, the target's elevation and azimuth angles are obtained as follows:

[0078]

[0079] Where, θ p and Let λ be the azimuth and elevation angles of the target point from the beam center, respectively; λ be the signal wavelength; d be the spacing between echo receiver elements; (m,n) be the pixel coordinates of the target point in the synthetic aperture radar image; m and n are the range and azimuth coordinates of the target, respectively; Im(·) is the imaginary part operation; ∑ θ (m,n), Δ θ (m,n) and These are multiple synthetic aperture radar imaging image data corresponding to pixel coordinates (m,n).

[0080] In step S104, the target distance information is obtained by calculating the slant distance between the target and the center of the radar aperture. Based on the target distance information and the target's elevation and azimuth angles, the three-dimensional coordinates of the target are calculated to perform absolute positioning of the target.

[0081] In embodiments of the present invention, the target distance information is obtained by the target location at the distance gate position, and the three-dimensional coordinates of the target are calculated by geometric relationships to achieve absolute positioning.

[0082] First, the slant range between the target and the center of the radar aperture is calculated as follows:

[0083]

[0084] Where R0 is the radar range, m is the target range-axis pixel coordinate, Nr is the number of range-axis sampling points, and f s This refers to the echo sampling frequency;

[0085] Based on the target distance information and the target's pitch and azimuth angles, the target's three-dimensional coordinates are calculated using geometric relationships:

[0086]

[0087] Where (x0,y0,z0) are the time coordinates of the radar antenna phase center at the aperture center.

[0088] In step S105, the absolute location of multiple pixel coordinates of the same target in the synthetic aperture radar imaging image is performed to obtain the size of the target.

[0089] Absolute target localization can be achieved using a single target pixel in any synthetic aperture radar (SAR) image. By selecting multiple target pixels of the same target within the SAR image and performing multiple absolute localization operations, the target's size can be obtained. Figure 2 As shown, the target size is calculated by selecting a sufficient number of target points. The calculation method can use existing methods and is not specifically limited. It is understandable that when selecting multiple target pixels, a single synthetic aperture radar image can still be used.

[0090] SAR data acquisition geometric model such as Figure 3 As shown, the scene center O is defined as the origin, and the aircraft track is parallel to the X-axis. The start and end positions of the synthetic aperture are A and B, respectively, and the instantaneous coordinates of the radar antenna phase center (APC) are (x... a ,y a ,z aAt the moment the aperture center is reached, point C is located at (x0, y0, z0). The target point P in the scene has coordinates (x...). p ,y p ,z p ), θ p , These represent the azimuth and elevation angles of the target point P from the beam center, respectively. The radar transmits signals through the antenna phase center, and the echo signals are received by array elements 1, 2, 3, and 4, respectively.

[0091] Figure 4 The specific model of the antenna transmitting and receiving signals is shown. The antenna transmits signals from the center O of the aperture, and the signals are received by sub-apertures A and B, which are spaced apart by d. In the far field, the two beams almost overlap, and the target echo can be approximated as a plane wave, meaning that the signals received by the two antennas have equal amplitudes but different phases. If the target deviates from the axis by an angle θ, then the path difference is:

[0092] Δr=d sinθ

[0093] The phase difference caused by the path difference is:

[0094]

[0095] Where λ is the signal wavelength.

[0096] Figure 5 The equivalent antenna patterns of the radar's sum and difference beams are shown, ∑(θ) and Δ(θ), respectively, and their amplitude-phase relationship is as follows:

[0097]

[0098] set up Figure 4 The echo signals received by array elements A and B are E respectively. A E B The beam signal is constructed as E. ∑ =E A +E B The difference beam signal is E Δ =E B -E A Furthermore, the sum and difference beam signals are orthogonal. The relationship between the echo signals is as follows:

[0099]

[0100] This gives the angle by which the target deviates from the axis:

[0101]

[0102] Simulations were performed on point targets at different locations, and the simulation parameters are shown in Table 1. The actual position of the point target is defined as (x... p ,yp ,z p The sum and difference beam localization results are (x p ',y p ',z p '), Positioning error The simulation positioning results are shown in Table 2. As can be seen from the results in Table 2, the positioning error of the method of the present invention is less than 1m, indicating that the positioning method is effective.

[0103] Table 1 Radar Simulation Parameters

[0104]

[0105] Table 2 Simulation and localization results of point targets

[0106]

[0107]

[0108] To demonstrate the effectiveness of sum-difference beamforming for locating and measuring the size of moving targets, Figure 6 A simulation model of a moving ship target is shown, in which the ship moves at a speed of 10 m / s and is accompanied by its own rotation and sway. Figures 7(a), 7(b), 7(c), and 7(d) are azimuth and beam SAR images, azimuth difference beam SAR images, elevation and beam SAR images, and elevation difference beam SAR images, respectively. Figure 8 The target outline points of the ship selected based on the azimuth and beam SAR images are shown in Table 3. The target point localization results are shown in Table 3.

[0109] Table 3 Simulation and localization results of ship targets

[0110]

[0111] The size of the target ship can be deduced from the target location results. Table 4 shows the measured ship dimensions.

[0112] Table 4 Comparison of ship sizes

[0113] Actual dimensions (m) Location result (m) Error (m) Ship length 150 148.4142 1.5858 ship width 30 29.914 0.086 Ship height 60 60.6578 0.6578

[0114] The positioning results show that the positioning method of this invention can accurately locate moving target points, and based on the target point positioning results, the size of the target ship can also be accurately calculated. Therefore, this invention is suitable for locating moving targets and can calculate the target size based on the coordinates of the contour points at different positions of the moving target, exhibiting good positioning accuracy.

[0115] The proposed method for locating and measuring the size of moving targets based on sum-difference beams combines SAR imaging technology with sum-difference beam angle measurement technology to achieve absolute positioning of moving targets and measure their size. Compared with traditional range-Doppler positioning methods, which cannot measure the three-dimensional coordinates of moving targets and whose positioning accuracy is greatly affected by radar velocity errors, this method has the advantages of wide application range and high positioning accuracy.

[0116] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0117] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0118] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

Claims

1. A method for locating and measuring the size of a moving target based on sum and difference beams, characterized in that, Includes the following steps: Construct azimuth and beam signals, azimuth difference beam signals, elevation and beam signals, and elevation difference beam signals based on radar echo data; Synthetic aperture radar imaging processing is performed on the azimuth and beam signal, the azimuth difference beam signal, the elevation and beam signal, and the elevation difference beam signal respectively to obtain multiple synthetic aperture radar imaging images containing the target. Select the target pixel coordinates in any synthetic aperture radar imaging image, and perform sum-difference beam angle measurement processing based on the synthetic aperture radar imaging image data corresponding to the target pixel coordinates to obtain the target's elevation angle and azimuth angle information. The target distance information is obtained by calculating the slant distance between the target and the center of the radar aperture. Based on the target distance information and the target's elevation and azimuth angles, the three-dimensional coordinates of the target are calculated to perform absolute positioning of the target. The size of the target is obtained by absolutely locating the pixel coordinates of the same target in the synthetic aperture radar image. The azimuth and beam signals constructed based on the radar echo data are as follows: ∑ θ =E1+E2 The constructed azimuth difference beam signal is: D θ =E1-E2 The constructed pitch and beam signals are as follows: The constructed elevation difference beam signal is: E1 and E2 are the echo signals received by the first and second azimuth array elements, respectively, and E3 and E4 are the echo signals received by the third and fourth elevation array elements, respectively.

2. The method according to claim 1, characterized in that, The process of performing synthetic aperture radar (SAR) imaging processing on the azimuth and beam signals, the azimuth difference beam signals, the elevation and beam signals, and the elevation difference beam signals is the same. Performing SAR imaging processing on the azimuth and beam signals yields a SAR image containing the target, including: For the azimuth and beam signals ∑ θ After performing a Fast Fourier Transform operation on the range, multiply by the matched filter and motion compensation reference function S. ref (f τ The signal S obtained after the distance processing is completed is obtained. R (t,f τ ): S R (t,f τ )=FFT(∑ θ )·S ref (f τ ) Where c is the speed of radio wave propagation, τ and t are the distance-fast time and the azimuth-slow time, respectively, and f τ Here, k is the frequency variable, and f is the frequency modulation slope. c R is the carrier frequency for transmitting signals. a This represents the instantaneous distance from the antenna phase center to the scene center. For signal S R (t,f τ The azimuth direction is transformed using Keystone transformation to obtain the azimuth-processed signal S. KT (t',f τ ): in, t' is the azimuth-time variable after Keystone transformation; Signal S KT (t',f τ Perform a two-dimensional Fourier transform to obtain a synthetic aperture radar image containing the target.

3. The method according to claim 1, characterized in that, Based on the target pixel coordinates, sum-difference beam angle measurement is performed on multiple synthetic aperture radar imaging image data to obtain the target's elevation and azimuth angles: Where, θ p and Let λ be the azimuth and elevation angles of the target point from the beam center, respectively; λ be the signal wavelength; d be the spacing between echo receiver elements; (m,n) be the pixel coordinates of the target point in the synthetic aperture radar image; m and n are the range and azimuth coordinates of the target, respectively; Im(·) is the imaginary part operation; ∑ θ (m,n), Δ θ (m,n) and These are multiple synthetic aperture radar imaging image data corresponding to pixel coordinates (m,n).

4. The method according to claim 1, characterized in that, The target range information is obtained by calculating the slant range between the target and the center of the radar aperture. Based on the target range information and the target's elevation and azimuth angles, the target's three-dimensional coordinates are calculated, including: The slant distance between the target and the center of the radar aperture is: Where R0 is the radar range, m is the target range-axis pixel coordinate, Nr is the number of range-axis sampling points, and f s This refers to the echo sampling frequency; The target's three-dimensional coordinates are: Where (x0,y0,z0) are the time coordinates of the radar antenna phase center at the aperture center.

Images