A Radar Space Target Echo Processing Method Based on Interferometric Imaging and Beamforming

Abstract

This application provides a radar space target echo processing method based on interferometric imaging and beamforming, comprising: performing interferometric imaging on the space target to obtain the position of the space target in the radar field of view; adjusting the digital beamforming direction to obtain narrow-beam high signal-to-noise ratio echo data; using a range-Doppler algorithm to obtain an image map of a partial area of ​​the space target surface at this time; adjusting the beam direction according to the interferometric imaging map to complete the next interferometric imaging and direction adjustment to obtain image maps of the space target surface in other areas; obtaining multiple range-Doppler imaging maps by adjusting the beam direction multiple times; and obtaining a complete high signal-to-noise ratio radar image map of the space target through scattering point fusion. The advantages of this application are: single-detection imaging, low complexity, high reliability, and high signal-to-noise ratio, while also having the advantage of low system operating cost. It can be widely applied to radar detection and imaging where the beamwidth is too narrow to cover large-sized targets.

Description

Technical Field

[0001] This application belongs to the field of ground-based radar detection, specifically relating to a radar space target echo processing method based on interferometric imaging and beamforming. Background Technology

[0002] 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 the target and receive the target echo, and then processes the echo. Compared with optical imaging systems, it has advantages such as strong penetration, all-weather operation, all-time operation, and low cost.

[0003] When applying ground-based radar to image large space targets such as the Moon, two traditional detection modes are often employed: The first is using a single-aperture antenna radar system. Limited by physical size, this system typically has a wide beam, capable of covering the entire lunar surface, thus acquiring all information about the lunar surface. Data processing yields a lunar radar image, but it suffers from low signal-to-noise ratio (SNR) and high construction and operating costs. The second mode utilizes a multi-antenna array system. Beamforming produces a narrow beam, significantly improving the SNR. However, the beamwidth may not completely cover the lunar surface, only obtaining high SNR images of localized areas. A common solution is to perform multiple scans of the target and then stitch the images together to obtain a complete image. This method is complex and sacrifices real-time detection capabilities. Therefore, if a method could obtain high SNR echo data without requiring multiple scans, it would reduce system operating costs, time costs, and detection complexity, while simultaneously improving radar detection real-time performance. Summary of the Invention

[0004] The purpose of this application is to differentiate itself from traditional ground-based radar methods for detecting space targets by proposing a range-Doppler imaging processing method for space targets that combines interferometric imaging with beamforming pointing adjustment technology, aiming to solve the following problems:

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

[0006] This solves the problem of traditional imaging systems requiring multiple scans for detection;

[0007] This addresses the issue of missing areas in radar imaging caused by the narrow synthetic beamwidth of array radar systems failing to cover the surface of the target.

[0008] To achieve the above objectives, this application proposes a radar space target echo processing method based on interferometric imaging and beamforming, comprising:

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

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

[0011] Step 3: Use the range-Doppler algorithm to obtain an image of a portion of the space target surface at this point. Adjust the beam direction based on the interferometric imaging image to complete the next interferometric imaging and direction adjustment to obtain image images of other areas of the space target surface. By adjusting the beam direction multiple times, obtain multiple range-Doppler imaging images.

[0012] Step 4: By scattering point fusion processing, a complete high signal-to-noise ratio space target radar image is obtained.

[0013] As an improvement to the above-mentioned method, step 1 includes:

[0014] The brightness temperature distribution TB(ξ,η) of the target to be observed is obtained by inversion using the following formula:

[0015]

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

[0017] An interferometric imaging pattern is plotted using the brightness temperature distribution of the target under test; the position of the space target in the radar field of view is obtained from the interferometric imaging pattern.

[0018] As an improvement to the above-mentioned method, step 2 includes:

[0019] The phase offset (phase_offset) of the space target echo data from the center of the radar synthetic beam is calculated based on the position of the space target in the radar field of view.

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

[0021] Where u and v represent the spatial frequency domain baseline; dRA represents the right ascension offset; and dDEC represents the declination offset.

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

[0023] As an improvement to the above-mentioned method, step 4 includes:

[0024] By comparing all pixels in multiple distance-Doppler images with different beam directions, the pixel with the largest scattering point at the same location in the beam is retained, and the pixel with weak or no scattering point is replaced, thus achieving scattering point fusion.

[0025] Compared with existing technologies, the advantages of this application are:

[0026] The radar space target echo processing method based on interferometric imaging and beamforming provided in this application is applicable to distributed antenna array radar systems. This method first utilizes interferometric imaging technology to obtain a brightness temperature map of the space target, which not only confirms the effectiveness of the radar system's echo detection but also accurately observes the position of ultra-long-range targets within the array radar's field of view. Secondly, it uses pointing adjustment technology to obtain high signal-to-noise ratio (SNR) data at different locations on the target surface. Finally, it proposes a range-Doppler scattering point fusion processing method, successfully obtaining a complete range-Doppler image of the space target with high SNR. Experiments demonstrate that the radar space target echo processing method based on interferometric imaging and beamforming technology provided in this application, compared to traditional wide-beam radar systems and scanning radar systems, features single-detection imaging, low complexity, high reliability, and high SNR. It also boasts the advantage of low system operating costs and can be universally applied to radar detection and imaging systems with narrow beamwidths that cannot cover large-sized targets. Attached Figure Description

[0027] Figure 1 The diagram shows a flowchart of a radar space target echo processing method based on interferometric imaging and beamforming.

[0028] Figure 2 The image shown is an interferometric image of the moon (radar position).

[0029] Figure 3 The image shows a comparison of the echoes before and after correction (left: before correction, right: after correction).

[0030] Figure 4 The image shown is a narrow-beam RD lunar image.

[0031] Figure 5 The image shown is an interferometric imaging pattern of the lunar duration.

[0032] Figure 6 The image shown is an illustration of repeated beam pointing adjustments and imaging.

[0033] Figure 7 The image shown is a comparison of the scattering points before and after fusion. Detailed Implementation

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

[0035] The radar space target echo processing method based on interferometric imaging and beamforming provided by this invention is applicable to array antenna radar equipment. It utilizes the characteristic that each antenna element in the array can receive space target echo data, and achieves high signal-to-noise ratio space target surface imaging processing through data post-processing. In this application, "space target" refers to a quasar in space, including celestial bodies such as the Moon and asteroids.

[0036] Specifically, this application first uses interferometric imaging to confirm the validity of the space target echo and obtain the position of the space target in the radar field of view; then, it uses digital beamforming pointing adjustment technology to obtain narrow-beam high signal-to-noise ratio echo data; next, it uses the range Doppler algorithm to obtain an image of a partial area of ​​the space target surface at this time; then, it performs fine adjustment of the beam pointing based on the interferometric imaging image to complete the next interferometric imaging and pointing adjustment to obtain an image of the space target surface in another area; through multiple beam pointing adjustments, multiple range Doppler imaging images are obtained, so that the pixels in each image present an approximately complementary relationship; finally, after scattering point fusion processing, a complete high signal-to-noise ratio space target radar imaging image is obtained. The main process is as follows: Figure 1 As shown.

[0037] In this embodiment, the interferometric imaging method for space targets is described using the moon as an example.

[0038] Radar space target echo processing methods based on interferometric imaging and beamforming include:

[0039] Procedure 1: Interferometric Imaging

[0040] A multi-antenna array radar receiving device, where each pair of antenna elements forms an interferometric baseline, enables instantaneous sampling in the frequency domain (UV), thereby achieving high-quality interferometric imaging of the target. The method of this invention employs a circular array interferometric system in the experiment, where the detection antenna elements are distributed on the circumference, forming a dense circular UV coverage. The relationship between the target brightness temperature and the spatial frequency domain measurement results (visibility function) can be expressed by the following formula:

[0041]

[0042] Where (ξ,η) are the directional 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 the frequency domain data of the target is obtained by the observation system, the brightness temperature distribution of the target can be obtained by inversion using the following formula:

[0044]

[0045] Interferometric imaging is plotted using the brightness temperature distribution of the target object.

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

[0047] Figure 2 The horizontal axis RA represents the apparent right ascension, the vertical axis DEC represents the apparent declination, and the origin (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 in the center of the synthetic beam of the radar's field of view, and high signal-to-noise ratio radar echo data cannot be obtained at this time.

[0048] The validity of the lunar echo can be confirmed by the interferometric imaging, and the position of the moon off the beam center can also be obtained. The offset shown in the figure is approximately (0.43°, -0.34°).

[0049] Step 2: Synthetic Beam Pointing Adjustment

[0050] Once the position of the moon deviating from the center of the radar detection beam is known, the phase offset of the lunar echo data from the center of the radar composite beam can be calculated, which can be expressed by the following formula:

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

[0052] Where u and v are the spatial frequency domain baselines, calculated from the baseline projection in the interferometric imaging step; dRA is the right ascension offset, and dDEC is the declination offset. After solving for the phase offset, correction processing can be performed to obtain high signal-to-noise ratio echo data, such as... Figure 3 As shown.

[0053] The comparison shows 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 high signal-to-noise ratio lunar radar echo data, the moon can be imaged using traditional range-Doppler algorithms, such as... Figure 4 As shown.

[0056] Depend on Figure 4 The image is incomplete, with blank stripes appearing. This is because the beamwidth of the array antenna radar system is too narrow to cover the lunar surface, resulting in nulls between the main lobe and side lobes of the beam.

[0057] To address this issue, this application employs a data post-processing method that involves multiple adjustments to the synthetic beam pointing:

[0058] First, the direction of the pointing adjustment needs to be confirmed through interferometric imaging. Due to the Moon's unique characteristics, its diameter is approximately 1738 km, and the echo duration is approximately 1738 × 10⁻⁶. 3 / 3×10 8 ×2≈11.6ms, interferometric imaging of the duration in the southern hemisphere of the moon (time resolution 1ms) is shown below. Figure 5 As shown.

[0059] Depend on Figure 5 As can be seen, the echo spreads towards the southwest corner, indicating that the southwest direction in the view corresponds to the southern hemisphere of the moon. Therefore, moving the radar to the opposite northeast direction is equivalent to moving the beam towards the southern hemisphere of the moon.

[0060] Then, by adjusting the synthesized beamwidth by half a beam each time, and imaging again, the desired result can be obtained. Figure 6 The image shown.

[0061] As can be seen, after repeated synthetic beam pointing adjustments, the range-Doppler diagrams are approximately complementary.

[0062] Step 4: Scattering point fusion

[0063] Finally, since the pixel brightness of the range-Doppler image represents the scattering intensity of electromagnetic waves at that location, and since the repeated adjustment of the synthesized beam pointing step primarily relies on beam sidelobes to obtain data lost at null points, scattering point fusion can be achieved by comparing all pixels of range-Doppler images with different beam pointing, retaining the pixel with the largest scattering point at the same location within the beam, and replacing pixels with weak or no scattering points. Experiments show that this method is effective and highly feasible, as demonstrated by the results. Figure 7 As shown.

[0064] Depend on Figure 7 As can be seen, the image signal-to-noise ratio is significantly improved, and the image loss caused by beam null is compensated for.

[0065] The method described in this application enables a narrow-beam array antenna radar system to obtain high signal-to-noise ratio radar echo data and a complete and clear image through a single detection.

[0066] This invention provides a radar space target echo processing method based on interferometric imaging and beamforming. Firstly, it innovatively applies interferometric imaging technology to ground-based radar space target detection. This helps confirm the validity of radar echo data and allows for centroid localization using interferometric imaging, thus obtaining the accurate position of ultra-long-range targets within the radar beam. Secondly, it proposes a method for precisely adjusting the beam direction based on interferometric imaging and digital beamforming technology. This method enables the acquisition of radar images of different target areas in a single detection through data post-processing. Finally, it proposes a range-Doppler scattering point fusion processing method to obtain high signal-to-noise ratio radar images. Compared to traditional ground-based space target detection methods, this method overcomes the shortcomings of traditional methods. The data post-processing-based radar detection method allows the system to obtain high signal-to-noise ratio echo data without requiring multiple scans.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application do not depart from the spirit and scope of the technical solutions of this application, and should all be covered within the scope of the claims of this application.

Claims

1. A radar space target echo processing method based on interferometric imaging and beamforming, comprising: Step 1: Perform interferometric imaging on the space target to obtain its position in the radar field of view; Step 2: Adjust the direction of digital beamforming to obtain narrow-beam, high signal-to-noise ratio echo data; Step 3: Use the range-Doppler algorithm to obtain an image of a portion of the space target surface at this point. Adjust the beam direction based on the interferometric imaging image to complete the next interferometric imaging and direction adjustment to obtain image images of other areas of the space target surface. By adjusting the beam direction multiple times, obtain multiple range-Doppler imaging images. Step 4: Obtain a complete high signal-to-noise ratio space target radar image by scattering point fusion processing; Step 1 includes: The brightness temperature distribution of the target to be observed is obtained by inversion using the following formula. : ； in, Indicates the directional coordinates of the brightness temperature image distribution; This represents the normalized average antenna radiation pattern. Indicates baseline coverage in the spatial frequency domain; Represents the visibility function; An interferometric imaging pattern is plotted using the brightness temperature distribution of the target under test; the position of the space target in the radar field of view is obtained from the interferometric imaging pattern. Step 2 includes: The phase offset of the space target echo data from the center of the radar synthetic beam is calculated from the position of the space target in the radar field of view. : ； in, u and v Represents the spatial frequency domain baseline; dRA Indicates the right ascension offset; dDEC Indicates the declination offset; The phase offset is used to correct the interferometric image to obtain narrow-beam, high signal-to-noise ratio echo data.

2. The radar space target echo processing method based on interferometric imaging and beamforming according to claim 1, characterized in that, Step 4 includes: By comparing all pixels in multiple distance-Doppler images with different beam directions, the pixel with the largest scattering point at the same location in the beam is retained, and the pixel with weak or no scattering point is replaced, thus achieving scattering point fusion.

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