Radar space target echo processing method based on interference imaging and beam forming

Abstract

The invention provides a radar space target echo processing method based on interference imaging and beam forming, and the method comprises the steps: carrying out the interference imaging of a space target, and obtaining the position of the space target in a radar view field; adjusting the digital beam forming direction to obtain narrow-beam high-signal-to-noise-ratio echo data; a distance Doppler algorithm is adopted to obtain a space target surface partial region imaging graph at the moment, beam pointing is adjusted according to an interference imaging graph, and next interference imaging and pointing adjustment are completed to obtain space target surface imaging graphs of other regions; a plurality of distance-Doppler imaging pictures are obtained by adjusting the beam direction for multiple times; and through scattering point fusion, a complete high-signal-to-noise-ratio space target radar imaging picture is obtained. The method has the advantages that the method has the characteristics of one-time detection imaging, low complexity, high reliability and high signal-to-noise ratio, has the advantage of low system use cost, and can be universally applied to radar detection imaging which is narrow in beam width and cannot cover a large-size target.

Description

Technical Field

[0001] This application belongs to the field of ground-based radar detection, and specifically relates to a method for processing radar spatial target echoes based on interferometric imaging and beam synthesis. Background Art

[0002] A ground-based synthetic aperture radar is a radar system that uses a large-aperture array antenna deployed on the ground to transmit electromagnetic waves to a target, receive the target echo, and process the echo. Compared with an optical imaging system, it has the advantages of strong penetration, all-weather, all-day, and low cost.

[0003] When applying a ground-based radar to image large-size spatial targets such as the moon, two traditional detection modes are often used: the first is to use a single-aperture antenna radar system, which is generally limited by physical size and has a relatively wide beam that can cover the entire lunar surface. Therefore, all information on the lunar surface can be obtained, and a lunar radar image can be obtained through data processing. However, it has problems such as low signal-to-noise ratio, high construction cost, and high usage cost; the second is to use a multi-antenna array system. After beam synthesis, a narrow beam can be obtained, and the signal-to-noise ratio can be greatly improved. However, the beam width may not be able to completely cover the lunar surface, and only high-signal-to-noise images of local areas can be obtained. The general solution is to perform multiple detection scans on the target and then perform stitching processing to obtain a complete image. This method has a high complexity and loses the real-time detection performance. Therefore, if there is a method that can obtain high-signal-to-noise echo data without multiple scanning detections, it can reduce the system usage cost, time cost, and detection complexity, and at the same time improve the real-time performance of radar detection. Summary of the Invention

[0004] The purpose of this application is to propose a method for processing radar range-Doppler imaging of spatial targets that combines interferometric imaging and beam synthesis pointing adjustment technology, different from traditional ground-based radar spatial target detection methods, aiming to solve the following problems:

[0005] Solve the problem of low signal-to-noise ratio of echo data;

[0006] Solve the problem that traditional imaging systems require multiple scanning detections;

[0007] Solve the problem that when the synthesized beam width of an array radar system is too narrow to cover the surface of the detection target, resulting in missing parts of the radar imaging map.

[0008] To achieve the above purpose, this application proposes a method for processing radar spatial target echoes based on interferometric imaging and beam synthesis, including:

[0009] Step 1: Perform interferometric imaging on the spatial target to obtain the position of the spatial target in the radar field of view;

[0010] Step 2: Adjust the digital beamforming direction to obtain narrow-beam high signal-to-noise ratio echo data;

[0011] Step 3: Use the range-Doppler algorithm to obtain an imaging map of a partial area of the spatial target surface at this time. Adjust the beam direction according to the interferometric imaging map, complete the next interferometric imaging and direction adjustment to obtain the imaging map of other areas of the spatial target surface; By adjusting the beam direction multiple times, multiple range-Doppler imaging maps are obtained;

[0012] Step 4: Through scatter point fusion processing, obtain a complete high signal-to-noise ratio spatial target radar imaging map.

[0013] As an improvement of the above method, step 1 includes:

[0014] Invert the following formula to obtain the brightness temperature distribution TB(ξ,η) of the target to be observed:

[0015]

[0016] where (ξ,η) represents the direction coordinates of the brightness temperature image distribution; AP(ξ,η) represents the normalized average antenna pattern; (u,v) represents the baseline coverage in the spatial frequency domain; V(u,v) represents the visibility function;

[0017] Use the brightness temperature distribution of the target to be measured to draw an interferometric imaging map; Obtain the position of the spatial target in the radar field of view from the interferometric imaging map.

[0018] As an improvement of the above method, step 2 includes:

[0019] Calculate the phase offset phase_offset of the spatial target echo data deviating from the center of the radar synthesis beam according to the position of the spatial target in the radar field of view:

[0020] phase_offset = exp(j2π*(u*dRA + v*dDEC))

[0021] where u and v represent the baselines in the spatial frequency domain; dRA represents the right ascension offset; dDEC represents the declination offset;

[0022] Use the phase offset to correct the interferometric image to obtain narrow-beam high signal-to-noise ratio echo data.

[0023] As an improvement of the above method, step 4 includes:

[0024] By comparing all pixel points of multiple range-Doppler maps with different beam directions, retain the maximum scatter point pixel at the same position in the beam, and replace the pixel positions with weak or no scatter points to achieve scatter point fusion.

[0025] Compared with the prior art, the advantages of the present application are as follows:

[0026] The radar spatial target echo processing method based on interferometric imaging and beam synthesis provided by the present application is applicable to a distributed antenna array radar system. This method first uses interferometric imaging technology to obtain the bright temperature map of the spatial target, which can not only confirm the effectiveness of the radar system's detected echo but also accurately observe the position of the ultra-long-range target in the field of view of the array radar. Secondly, the pointing adjustment technology is used to obtain high signal-to-noise ratio data at different positions on the target surface. Finally, a distance-Doppler scatter point fusion processing method is proposed to successfully obtain a complete distance-Doppler image of the spatial target with high signal-to-noise ratio. Experiments prove that the radar spatial target echo processing method based on interferometric imaging and beam synthesis technology provided by the present application has the characteristics of one-time detection and imaging, low complexity, high reliability, and high signal-to-noise ratio compared with traditional wide-beam radar systems and scanning radar systems. At the same time, it has the advantage of low system usage cost and can be generally applied to radar detection and imaging systems with narrow beam widths that cannot cover large-sized targets. Description of the Drawings

[0027] Figure 1 Shown is the flow chart of the radar spatial target echo processing method based on interferometric imaging and beam synthesis;

[0028] Figure 2 Shown is the lunar interferometric imaging map (radar sub-point position);

[0029] Figure 3 Shown is the comparison chart of the echo before and after calibration (left: before calibration, right: after calibration);

[0030] Figure 4 Shown is the narrow-beam RD lunar imaging map;

[0031] Figure 5 Shown is the lunar duration interferometric imaging map;

[0032] Figure 6 Shown is the map of repeatedly adjusting the beam pointing and imaging;

[0033] Figure 7 Shown is the comparison chart of the scatter points before and after fusion. Detailed Embodiment

[0034] The technical solution of the present application will be described in detail below with reference to the drawings.

[0035] The method for processing the radar space target echo based on interferometric imaging and beam synthesis provided by the present invention is applicable to array antenna radar equipment. By utilizing the characteristic that each antenna element in the array can receive the space target echo data, high-signal-to-noise ratio spatial target surface imaging processing is achieved through post-data processing. In this application, the space target refers to various celestial bodies in space, including the moon, asteroids, etc.

[0036] Specifically, in this application, the validity of the space target echo is first confirmed by interferometric imaging to obtain the position of the space target in the radar field of view; then, the digital beam synthesis pointing adjustment technology is used to obtain narrow-beam high-signal-to-noise ratio echo data; then, the range-Doppler algorithm is used to obtain the imaging map of a partial area of the space target surface at this time; then, the beam pointing is finely adjusted according to the interferometric imaging map, and the next interferometric imaging and pointing adjustment are completed to obtain the imaging map of another area of the space target surface; by adjusting the beam pointing multiple times, multiple range-Doppler imaging maps are obtained, so that the pixel points between each image show an approximately complementary relationship; finally, through scatter point fusion processing, a complete high-signal-to-noise ratio radar imaging map of the space target is obtained. The main process is as Figure 1 shown.

[0037] In this embodiment, taking the moon as an example, the interferometric imaging method of the space target is described.

[0038] The method for processing the radar space target echo based on interferometric imaging and beam synthesis includes:

[0039] Process 1: Interferometric imaging

[0040] The array radar receiving device with multiple antenna elements can form an interferometric measurement baseline between its antenna elements in pairs, and perform instantaneous sampling in the frequency domain (u-v), so as to achieve high-quality interferometric imaging of the target. In the experiment, the interferometric measurement system in the form of a circular array is adopted in the method of the present invention. Its detection antenna elements are distributed on the circumference, and a circular dense u-v coverage can be formed. The relationship between the target brightness temperature and the measurement result in the spatial frequency domain (visibility function) can be expressed by the following formula:

[0041]

[0042] Among them, (ξ, η) are the direction coordinates of the brightness temperature image distribution, TB(ξ, η) is the target brightness temperature distribution, AP(ξ, η) is the normalized average antenna pattern, (u, v) is the spatial frequency domain baseline coverage, and V(u, v) is the visibility function.

[0043] After V(u, v) obtains the frequency domain data of the target observed by the observation system, the brightness temperature distribution of the target to be observed can be inversely obtained through the following formula:

[0044]

[0045] Use the brightness temperature distribution of the target to be measured to draw an interferometric imaging map.

[0046] After performing interferometric imaging processing on the radar echo data of the southern hemisphere of the moon, an interferometric imaging map of the moon can be obtained, as Figure 2 shown.

[0047] Figure 2 In it, the abscissa RA is the right ascension, the ordinate DEC is the declination, and the origin of coordinates (0, 0) is the center of the synthetic beam of the array radar; due to system errors, it can be seen that the moon is not at the center position of the synthetic beam of the radar's field of view, and at this time, radar echo data with a high signal-to-noise ratio cannot be obtained.

[0048] Through the interferometric imaging map, the validity of the lunar echo can be confirmed, and at the same time, the position where the moon deviates from the beam center is obtained. The deviation shown in this map is approximately (0.43°, -0.34°).

[0049] Procedure 2: Adjustment of the synthetic beam pointing

[0050] After knowing the position where the moon deviates from the center of the radar detection beam, the phase offset of the lunar echo data deviating from the center of the radar synthetic beam can be calculated, and its calculation can be expressed by the following formula:

[0051] phase_offset = exp(j2π*(u*dRA + v*dDEC))

[0052] where u and v are the baselines in the spatial frequency domain, obtained by calculating the baseline projection in the interferometric imaging step; dRA is the right ascension offset, and dDEC is the declination offset. After solving the phase offset, correction processing can be performed to obtain radar echo data with a high signal-to-noise ratio, as Figure 3 shown.

[0053] It can be seen by comparison that the method proposed in this paper for correcting the synthetic beam using interferometric imaging can obtain radar echo data with a higher signal-to-noise ratio.

[0054] Procedure 3: Imaging and repeated pointing adjustment

[0055] After obtaining the lunar radar echo data with a high signal-to-noise ratio, the moon can be imaged by the traditional range-Doppler algorithm, as Figure 4 shown.

[0056] It can be seen from Figure 4 that the imaging is incomplete and there are blank stripes; this is due to the narrow beam width of the array antenna radar system being unable to cover the lunar surface, resulting in nulls formed between the main lobe and the side lobes of the beam.

[0057] To solve this problem, the present application adopts a data post - processing method of adjusting the synthetic beam pointing multiple times:

[0058] First, it is necessary to confirm the direction of pointing adjustment through the interference imaging map. Due to the particularity of the moon, its diameter is about 1738 km, and the echo duration is about 1738×10 3 / 3×10 8 ×2≈11.6 ms. The interference imaging map of the southern hemisphere of the moon with a duration (time resolution 1 ms) is as Figure 5 shown.

[0059] As can be seen from Figure 5 , if the echo spreads to the southwest corner, it indicates that the southwest direction in the view is the direction of the southern hemisphere of the moon. Then, moving the radar in the opposite northeast direction is equivalent to pointing the beam towards the southern hemisphere of the moon.

[0060] Then, each time the synthetic beam is adjusted by half of the beam width, and imaging again can obtain Figure 6 the image shown.

[0061] It can be seen that after repeatedly adjusting the synthetic beam pointing, there is an approximately complementary relationship between the range - Doppler maps.

[0062] Process 4: Scatter point fusion

[0063] Finally, since the brightness of the pixel points in the range - Doppler map represents the scattering intensity of electromagnetic waves at that position, and at the same time, in the process of repeatedly adjusting the synthetic beam pointing, more data lost at the null points are obtained by the sidelobes of the beam. Therefore, by comparing all pixel points of multiple range - Doppler maps with different beam pointings, retaining the pixel with the maximum scattering point at the same position in the beam, and replacing the pixel positions with weak or no scattering points, scatter point fusion can be achieved. Through experiments, it can be known that this method has the characteristics of good effect and high feasibility, and its result is as Figure 7 shown.

[0064] As can be seen from Figure 7 , the signal - to - noise ratio of the image is significantly improved, and at the same time, the image missing caused by the beam null is complemented.

[0065] Through the method described in the present application, through a single detection, a radar echo data with high signal - to - noise ratio and a complete and clear imaging map can be obtained for an array antenna radar system with a narrow beam.

[0066] The radar space target echo processing method based on interferometric imaging and beam synthesis provided by the present invention first innovatively applies the interferometric imaging technology to the detection of space targets by ground-based radars. It can help confirm the validity of radar echo data and, at the same time, perform centroid positioning through the interferometric imaging map to obtain the accurate position of ultra-long-range targets in the radar beam. Secondly, a method for accurately adjusting the beam direction based on interferometric imaging and digital beam synthesis technology is proposed, which can obtain radar images of different target areas through data post-processing in a single detection. Finally, a distance-Doppler scatter point fusion processing method is proposed to obtain a high signal-to-noise ratio radar imaging map. Compared with the traditional ground-based space target detection method, the deficiencies are made up. This radar detection method through data post-processing enables the system to obtain high signal-to-noise ratio echo data without the need for multiple scanning detections.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present application does not depart from the spirit and scope of the technical solutions of the present application, and they should all be covered within the scope of the claims of the present application.

Claims

1. A radar spatial target echo processing method based on interferometric imaging and beam synthesis, comprising: Step 1: Perform interferometric imaging on the spatial target to obtain the position of the spatial target in the radar field of view; Step 2: Adjust the digital beam synthesis direction to obtain narrow beam high signal-to-noise ratio echo data; Step 3: Use the range-Doppler algorithm to obtain an imaging map of a partial area on the surface of the spatial target at this time. Adjust the beam direction according to the interferometric imaging map, complete the next interferometric imaging and direction adjustment to obtain the imaging map of the surface of the spatial target in other areas; by adjusting the beam direction multiple times, obtain multiple range-Doppler imaging maps; Step 4: Through scatter point fusion processing, obtain a complete high signal-to-noise ratio radar imaging map of the spatial target.

2. The method for processing radar spatial target echo based on interference imaging and beam synthesis according to claim 1, wherein The said Step 1 includes: Invert to obtain the brightness temperature distribution TB(ξ,η) of the target to be observed through the following formula: where, (ξ,η) represents the direction coordinates of the brightness temperature image distribution; AP(ξ,η) represents the normalized average antenna pattern; (u,v) represents the baseline coverage in the spatial frequency domain; V(u,v) represents the visibility function; Use the brightness temperature distribution of the target to be measured to draw an interferometric imaging map; obtain the position of the spatial target in the radar field of view from the interferometric imaging map.

3. The method for processing radar spatial target echo based on interference imaging and beam synthesis according to claim 1, wherein The said Step 2 includes: Calculate the phase offset phase_offset of the spatial target echo data deviating from the center of the radar synthesized beam according to the position of the spatial target in the radar field of view: phase_offset = exp(j2π*(u*dRA + v*dDEC)) where, u and v represent the baselines in the spatial frequency domain; dRA represents the right ascension offset; dDEC represents the declination offset; Use the phase offset to correct the interferometric image to obtain narrow beam high signal-to-noise ratio echo data.

4. The method for processing radar spatial target echo based on interference imaging and beam synthesis according to claim 1, wherein The said Step 4 includes: By comparing all pixel points of multiple range-Doppler maps with different beam directions, retain the maximum scatter point pixel at the same position in the beam, replace the pixel positions with weak or no scatter points, and achieve scatter point fusion.

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