A method and system for aliasing suppression of a DBF-combined aperture microwave radiometer

Abstract

The application belongs to the technical field of microwave remote sensing and passive microwave imaging, and particularly relates to an aliasing suppression method and system of a DBF-combined aperture microwave radiometer, which comprises the following steps: receiving microwave radiation signals by using multiple DBF sub-antennas and converting the signals into digital baseband signals; weighting the digital baseband signals of the multiple DBF sub-antennas in the same DBF combined antenna to generate DBF combined antenna output signals; performing cross-correlation and time averaging on the output signals of different DBF combined antennas to generate an actual observation visibility function, and performing image inversion to obtain an uncorrected initial image; obtaining a prior antenna apparent brightness temperature and inputting the same into a system response function as the actual observation to obtain a prior initial response image; and obtaining an antenna apparent brightness temperature estimation after aliasing weakening according to the uncorrected initial image, the prior initial response image and the prior antenna apparent brightness temperature. The application effectively weakens the spatial aliasing in large-interval combined aperture imaging.

Description

Technical Field

[0001] This invention belongs to the field of microwave remote sensing and passive microwave imaging technology, specifically relating to a method and system for suppressing aliasing in a DBF-integrated aperture microwave radiometer. Background Technology

[0002] The resolution of traditional real aperture radiometers depends on the physical size of the antenna. Large antennas are complex to manufacture, difficult to transport, and hard to fit into rocket fairings. Based on this, a synthetic aperture microwave radiometer is proposed. It uses multiple small-aperture receiving units to synthesize an equivalent large aperture. The visibility function is obtained through cross-correlation measurements between multiple receiving units. The brightness temperature distribution of the observed scene is then obtained by inversion based on the visibility function. This is more suitable for passive microwave detection and remote sensing imaging tasks that require higher spatial resolution.

[0003] However, in synthetic aperture microwave radiometers, the spatial baseline between receiving units determines the sampling position of the visibility function in the spatial frequency domain. Regular or quasi-regular arrays, such as the Y-type synthetic aperture array commonly used in engineering, have periodic extension characteristics in the cosine coordinate system for spatial frequency sampling. When the spacing between synthetic aperture units increases, the maximum baseline of the array also increases, which is beneficial for improving angular resolution or reducing the number of equivalent receiving units involved in cross-correlation processing. However, the expansion of the spacing between synthetic aperture units will cause the replicated area in the cosine coordinate system to move closer to the basic extension period, which can easily lead to the overlap between the replicated area and the target imaging area. This can cause background radiation outside the field of view or unknown high brightness temperature targets outside the field of view to fold into the target imaging area, resulting in spatial aliasing.

[0004] In existing technologies, the introduction of digital beamforming technology can alleviate aliasing problems. By weighting the digital baseband signals from multiple receiving channels, an equivalent receiving radiation pattern with spatial selectivity is formed. This allows for spatial filtering of the incident radiation before generating the visibility function, maintaining a high response in the target imaging area and reducing the effective energy of radiation entering the cross-correlation processing in the out-of-field or replicated areas. However, this type of spatial filtering cannot change the coordinates of the center of the replicated circle determined by the synthetic aperture array sampling structure, nor can it eliminate the aliasing components formed by the background brightness temperature after the system response.

[0005] After generating the visibility function, such as with the synthetic aperture radiometer on the SMOS satellite, pattern correction is typically performed directly. This method is suitable for pixels in the uncorrected initial image whose energy originates solely from the central physically visible region. However, in large-pitch synthetic aperture arrays, the same pixel in the uncorrected initial image also contains aliasing contributions from other replicated regions. Since these aliasing contributions correspond to different pattern weights and direction cosine projection factors, direct pattern correction struggles to distinguish between contributions from the physically visible region and aliasing contributions from replicated regions, easily leading to miscorrection. Therefore, this application is proposed. Summary of the Invention

[0006] This application overcomes the above-mentioned defects and provides a method and system for suppressing aliasing in a DBF-synthetic aperture microwave radiometer, which solves the spatial aliasing problem caused by the overlap between the replicated area and the target imaging area in the large-spacing synthetic aperture microwave radiometer of the prior art.

[0007] To achieve the above objectives, the present invention provides a method for aliasing suppression of a DBF-synthetic aperture microwave radiometer, comprising a pre-link and a post-link for visibility function generation; In the preceding link of the visibility function generation process S1. Multiple DBF sub-antennas are used to receive microwave radiated signals and convert them into digital baseband signals; S2. Weighted summation of the digital baseband signals of multiple DBF sub-antennas within the same DBF synthesized antenna to generate the DBF synthesized antenna output signal; S3. Perform cross-correlation and time averaging on the output signals of different DBF synthetic antennas to generate the actual observation visibility function; In the link after the visibility function is generated S4. Perform image inversion based on the actual observed visibility function to obtain the uncorrected initial image in the direction cosine coordinate system; S5. Obtain the prior apparent brightness temperature of the antenna and input the prior apparent brightness temperature of the antenna into the same system response function as the actual observation to obtain the prior initial response image; The system response function represents the imaging response process from the actual observed antenna apparent brightness temperature to the uncorrected initial image. This imaging response process includes at least DBF-synthesized antenna equivalent received radiation pattern weighting, direction cosine projection, normalized baseline and corresponding visibility spatial frequency sampling, and visibility function image inversion. Therefore, it satisfies: , in, Represents the system response function. This indicates the actual apparent brightness temperature of the observed antenna. This indicates that the initial image was not corrected. By considering the prior antenna as a brightness temperature input into the system response function, the prior initial response image is obtained: , in, This indicates the apparent brightness temperature of the prior antenna. Represents the prior initial response image; S6. Based on the uncorrected initial image, the prior initial response image, and the prior antenna apparent brightness temperature, obtain the antenna apparent brightness temperature estimate after aliasing reduction.

[0008] Furthermore, the DBF composite antenna is composed of several DBF sub-antennas arranged in a triangular grid pattern, and the overall outline after the arrangement is a regular hexagon; several DBF composite antennas are arranged in a Y-shaped synthetic aperture array, and the positional difference between different DBF composite antennas forms a synthetic aperture baseline, which is then normalized to obtain a normalized baseline after the observation wavelength is normalized.

[0009] Further, in step S2, the digital baseband signals of multiple DBF sub-antennas within the same DBF synthesized antenna are weighted and accumulated. This weighted accumulation process and the equivalent receiving radiation pattern in the directional domain represent the same spatial filtering process. Through this weighted accumulation process, the apparent brightness temperature of the actual observation antenna is directionally weighted by the equivalent power radiation pattern of the DBF synthesized antenna to increase the radiation receiving weight in the target imaging area, while attenuating the radiation in the replication area, thereby achieving spatial aliasing suppression before the visibility function is generated.

[0010] Furthermore, the equivalent receiving pattern is jointly determined by the DBF sub-antenna array and its digital beamforming processing, satisfying: , in, This represents the normalized voltage pattern of the DBF synthesized antenna. This represents the normalized voltage pattern of a single DBF sub-antenna. Represents the DBF weight vector. Represents a discrete sampling vector in the direction cosine coordinate system. Represents the DBF subarray steering vector. Indicates conjugate transpose; The actual antenna apparent brightness temperature, after DBF spatial filtering, receives weights determined by the equivalent power pattern of the DBF synthesized antenna, and the directional weighting relationship is as follows: Among them, direction cosine coordinates Indicates the corresponding incident direction. This indicates the apparent brightness temperature of the actual observed antenna.

[0011] Further, in step S3, the generation of the visibility function is as follows: a direction cosine grid is constructed within the physically visible unit circle, and the continuous incident direction is discretized into several direction grid points; for each direction grid point, the apparent brightness temperature of the antenna at that grid point is obtained, and after weighting by the equivalent voltage pattern of the two DBF synthesized antennas participating in cross-correlation and correcting by the direction cosine projection factor, the contribution of the direction grid point to the visibility sampling point is obtained by combining the spatial phase relationship between the direction grid point and the normalized baseline; the contributions of all direction grid points are accumulated to obtain the visibility sample corresponding to the normalized baseline, and all visibility samples together constitute the actual observed visibility function.

[0012] Furthermore, the uncorrected initial image is obtained by inverting the actual visibility function through a two-dimensional inverse discrete Fourier transform, as follows: , in, For the uncorrected initial image, Represents direction cosine coordinates, Represents the two-dimensional inverse discrete Fourier transform. Represents the actual observed visibility function. This indicates the spatial frequency sampling position corresponding to the normalized baseline.

[0013] Furthermore, the specific process for constructing the system response function is as follows: a. For each input direction in the apparent brightness temperature direction cosine grid of the antenna, calculate the complex response of that direction to the visibility sampling point corresponding to each normalized baseline after weighted summation and direction cosine projection of the DBF pattern. b. By using IDFT image inversion, the response generated at each visibility sampling point in the input direction is back-projected onto the uncorrected initial image grid to obtain the response distribution formed in the initial image by the unit brightness temperature component in the input direction after passing through the complete imaging link; c. Traverse all input direction grid points to obtain the contribution relationship of each input direction to each pixel of the uncorrected initial image, and construct the system response function accordingly. .

[0014] Further, in step S6, the uncorrected initial image and the prior initial response image are subjected to image domain difference operation to cancel the aliasing components of the copy region introduced by the stable background. At the same time, the prior antenna apparent brightness temperature is superimposed on the difference operation result as the background substrate to obtain the antenna apparent brightness temperature estimate after aliasing reduction, expressed as: , in, This is an estimate of the apparent brightness temperature of the antenna after aliasing reduction.

[0015] The present invention also includes a system for implementing the above-described DBF-synthetic aperture microwave radiometer aliasing suppression method, comprising: a visibility function generation front link and a visibility function generation back link; The visibility function generation frontlink includes multiple DBF sub-antennas, multiple DBF synthesized antennas, a receiving channel, an analog-to-digital conversion unit, a digital beamforming processing unit, and a cross-correlation processing unit. Multiple DBF sub-antennas are used to receive passive microwave radiation signals and output digital baseband signals through corresponding receiving channels and analog-to-digital conversion units. Multiple sub-antennas are combined to form a DBF synthesized antenna. Multiple DBF composite antennas serve as the equivalent receiving unit of a synthetic aperture microwave radiometer. The multiple DBF composite antennas are arranged in a Y-shaped synthetic aperture array. The multiple DBF sub-antennas inside each DBF composite antenna are arranged in a triangular grid, and the overall outline of the DBF composite antenna is a regular hexagon. The digital beamforming processing unit is used to weight and accumulate the digital baseband signals output by multiple DBF sub-antennas within the same DBF synthesized antenna to form the DBF synthesized antenna output signal. The cross-correlation processing unit is used to perform cross-correlation processing on the output signals of different DBF synthesized antennas to generate a visibility function. The visibility function generation post-processing link includes an image inversion processing unit, a priori scene input unit, a system response calculation unit, and a system response compensation unit. The image inversion processing unit generates an uncorrected initial image based on the visibility function obtained from actual observations. The prior scene input unit is used to input the prior antenna apparent brightness temperature; The system response calculation unit is used to input the a priori antenna apparent brightness temperature into the same system response function as the actual observation for processing, so as to obtain the a priori initial response image; The system response compensation unit is used to obtain the brightness temperature estimate after aliasing reduction based on the actual observed uncorrected initial image and the prior initial response image.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: First, the present invention uses a DBF synthesized antenna for spatial filtering in the link before the visibility function is generated, which can reduce the effective energy of radiation in the copy region entering the cross-correlation processing before the visibility function is generated, thereby weakening the influence of the brightness temperature component in the copy region on the uncorrected initial image of the target imaging region. Second, the present invention employs system response compensation dealiasing processing based on prior scene in the link after the visibility function is generated. The prior antenna apparent brightness temperature input is the same as the actual observation system response function to generate a prior initial response image, and the prior initial response image is used to weaken the influence of background components in the actual observation uncorrected initial image. Third, this invention enables DBF spatial filtering to reduce the effective energy of radiation entering the cross-correlation processing in the copied region by working in concert with the visibility function generation front link and the visibility function generation back link, and enables system response compensation to weaken the uncorrected initial image components corresponding to the prior background, thereby reducing the impact of spatial aliasing on the brightness temperature inversion of the target imaging region. Fourth, this invention is applicable to target detection applications, and is particularly beneficial in scenarios where the background brightness temperature can be approximately described by prior information and the target to be detected appears in the form of scattered small targets. It improves the availability of brightness temperature images in the target imaging area and reduces the interference of scattered small targets in the copy area on the judgment of the target imaging area. Fifth, this invention uses DBF synthetic antenna as synthetic aperture unit and adopts a DBF synthetic antenna structure with triangular grid points and regular hexagonal contour, which is beneficial to form an equivalent receiving pattern with spatial selectivity in Y-type synthetic aperture array, thereby reducing spatial aliasing in large-spacing synthetic aperture imaging. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the DBF-integrated aperture microwave radiometer system of the present invention; Figure 2 This is a diagram showing the antenna layout of the DBF-synthetic aperture microwave radiometer of the present invention. Figure 3 This is a schematic diagram illustrating the relationship between the copied region and the target imaging region in the cosine coordinate system in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the process after the visibility function is generated, according to an embodiment of the present invention. Figure 5 The following is a comparison diagram of simulation results of the embodiments of the present invention, wherein (a) is the simulation input scene, (b) is the brightness temperature estimation result after system response compensation and dealiasing, and (c) is the residual diagram between the brightness temperature estimation result after system response compensation and dealiasing and the ideal imaging result; In the above figures, 1-physically visible unit circle region, 2-replicated unit circle region, 3-basic traverse periodic region, 4-replicated traverse periodic region. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: This invention provides a method for suppressing aliasing in a DBF-integrated aperture microwave radiometer, such as... Figure 1 As shown, specifically, it includes the link before visibility function generation and the link after visibility function generation; In the link before the visibility function is generated, S1. Multiple DBF sub-antennas are used to receive microwave radiated signals and convert them into digital baseband signals; Specifically, each DBF sub-antenna is connected to an independent receiver and ADC analog-to-digital converter. Multiple DBF sub-antennas receive passive microwave radiation signals and generate digital baseband signals through corresponding receiving channels and analog-to-digital conversion units. S2. Weighted summation of the digital baseband signals of multiple DBF sub-antennas within the same DBF composite antenna to form the DBF composite antenna output signal; Digital beamforming (DBF) enhances signal reception in a specific direction by precisely processing signals from an array of antennas to enable directional transmission or reception, while suppressing interference from other directions. The geometry of the array, the spacing between elements, and the type of antenna elements all affect the performance of beamforming.

[0020] In this embodiment of the invention, the equivalent receiving unit of the synthetic aperture microwave radiometer adopts a DBF synthesized antenna, each DBF synthesized antenna consisting of multiple DBF sub-antennas; the multiple DBF synthesized antennas serve as synthetic aperture units and are arranged in a Y-shaped synthetic aperture array; the Y-shaped synthetic aperture array includes three antenna arms with an included angle between adjacent antenna arms; the multiple DBF sub-antennas inside the DBF synthesized antenna are arranged in a triangular grid pattern, and the overall outline is a regular hexagon, which enables it to maintain good geometric adaptability in the Y-shaped synthetic aperture array and facilitates the formation of an equivalent receiving pattern with spatial selectivity; The digital baseband signals of multiple DBF sub-antennas within the same DBF synthesized antenna are weighted and accumulated to obtain the DBF synthesized antenna output signal, such as... Figure 1 As shown, the DBF synthesized antenna P outputs the weighted output signals of the DBF sub-antennas P1~PN, and the DBF synthesized antenna Q outputs the weighted output signals of the DBF sub-antennas Q1~QN. The weighted output process is represented as follows: , in, For DBF synthesized antenna output signal, It is the k-th digital baseband signal output from the i-th ADC analog-to-digital converter. It is the window function weight of the i-th antenna. The beam center of the DBF synthesized antenna points to... The steering vector of the i-th antenna in the direction, where N represents the number of DBF sub-antennas.

[0021] By weighted accumulation of digital baseband signals, the signal reception capability in a specific direction can be enhanced while suppressing interference from other directions. Therefore, an equivalent reception pattern with spatial selectivity is formed in the directional domain. Let... The equivalent power pattern of a DBF synthesized antenna, representing the direction cosine vector, is as follows: , , , , in, This represents the normalized voltage pattern of the DBF synthesized antenna. This represents the normalized voltage pattern of a single DBF sub-antenna. Represents a discrete sampling vector in the direction cosine coordinate system. Represents the DBF weight vector. Represents the DBF subarray steering vector. This represents the conjugate transpose. The DBF weight vector is jointly determined by the window function weights and the main beam phase compensation. Therefore, changing the main beam pointing or the window function will change the equivalent receive pattern of the DBF synthesized antenna.

[0022] DBF digital signal weighted and equivalent receiver radiation pattern describes two representations of the same spatial filtering process in the signal domain and the directional domain. For direction cosine coordinates... The corresponding incident direction, the actual antenna apparent brightness temperature in that direction, after being spatially filtered by DBF, receives weights determined by the equivalent power pattern of the DBF synthesized antenna, and their directional weighting relationship is as follows: ; Thus, radiation within the target imaging area maintains a high reception weight in the high-response region of the main beam, while radiation in the copy region or other low-response directions is attenuated before entering subsequent cross-correlation processing, achieving spatial aliasing suppression in the pre-link of visibility generation.

[0023] S3. Perform cross-correlation processing and time averaging on the output signals of different DBF synthetic antennas to generate the actual observation visibility function; Multiple DBF synthesized antennas are arranged as synthetic aperture receiving units in a Y-shaped synthetic aperture array, such as... Figure 2 As shown. After determining the position of each DBF synthesized antenna in the synthetic aperture array, the 1st... The DBF synthetic antenna and the first The positional differences between the DBF synthetic antennas form a synthetic aperture baseline, which is based on the observation wavelength. After normalization, the corresponding spatial frequency sampling positions are: , in, and They represent the first The and the first The position coordinates of each DBF synthesized antenna. Each normalized baseline. The corresponding sampling position of the visibility function in the spatial frequency domain is determined by the geometry of the overall aperture baseline, which in turn determines the set of spatial frequency sampling points for the visibility function.

[0024] Using the DBF synthesized antenna output signal obtained in step S2 as input, cross-correlation and time averaging are performed on any two DBF synthesized antenna output signals to generate the actual observation visibility function, the calculation expression of which is: , in, Indicates the first The output of the first DBF synthesized antenna A digital baseband signal Indicates the first The output of the first DBF synthesized antenna The complex conjugate of a digital baseband signal This represents the average number of digital baseband sampling points over the participation time.

[0025] To describe the relationship between the above cross-correlation results and the apparent brightness temperature of the directional cosine domain antenna, a directional cosine grid is constructed within the physically visible unit circle, and the _i ... Each direction grid point is Its direction cosine coordinates are The projection factor introduced by the direction cosine coordinate transformation is: , Then the first The and the first The visibility sample formed by a DBF synthetic antenna can be represented as: , in, For discrete space sampling points Coordinates in a cosine coordinate system Indicates the actual scenario in the first... The apparent brightness temperature of the antenna at each grid point in each direction. This indicates the number of directional grid points within the physically visible unit circle that participate in the calculation. Indicates the area of ​​the direction cosine mesh cell; and They represent the first The and the first The equivalent voltage pattern response of each DBF synthesized antenna in the incident direction, when each DBF synthesized antenna adopts the same array structure, DBF weight and main beam pointing, the product of the two corresponds to the directional weighting effect of the DBF equivalent power pattern of step S2 on the apparent brightness temperature of the antenna. The visibility samples formed by all DBF synthesized antennas together constitute the actual observed visibility function.

[0026] Therefore, in step S2, the equivalent receiving pattern formed by the DBF synthesized antenna determines the receiving weights for different incident directions entering the cross-correlation processing, and in step S3, the normalized baseline of the synthetic aperture array determines the sampling positions of these weighted radiation components in the spatial frequency domain. The cross-correlation results simultaneously retain the real and imaginary parts of the correlation, thus forming the actual observed visibility function required for subsequent synthetic aperture image inversion. From a statistical perspective, it characterizes the second-order spatial statistical properties of the received signal. Integration processing can suppress uncorrelated noise and improve stability. At the same time, compared to transmitting and storing the original data from multiple DBF antennas, only the integrated negative correlation results are output, which can significantly reduce the data rate and the pressure of subsequent processing, storage, and transmission.

[0027] After the visibility function is generated, in the link: S4. Perform image inversion on the actual observed visibility function to obtain the uncorrected initial image; In actual observation processing, the actual observed visibility function obtained from S3 is data that can be directly obtained and used for subsequent image processing. This invention, based on the spatial frequency sampling positions corresponding to each normalized baseline, inputs the visibility samples into a two-dimensional inverse discrete Fourier transform (IDFT) to obtain an uncorrected initial image in cosine coordinates: , in, This indicates that the initial image was not corrected. Represents the visibility function. This indicates the spatial frequency sampling location determined by the normalized baseline. Represents the direction cosine coordinate.

[0028] Since the actual observed visibility function already includes the direction weighting of the DBF equivalent radiation pattern, the direction cosine projection, and the influence of finite spatial frequency sampling of the combined aperture, the uncorrected initial image obtained by IDFT simultaneously contains the aforementioned system response as well as periodic folding and spatial aliasing caused by large-spacing regular sampling, such as... Figure 3 As shown, the energy of all replicated unit circle regions 2 is a copy of the energy of physically visible unit cell region 1, resulting in all replicated along-topography periodic regions 4 being copies of the basic along-topography periodic regions. Therefore, the same pixel in the uncorrected initial image also includes aliasing contributions from other replicated regions, which cannot be directly used as the final brightness temperature inversion result, but rather as the input for dealiasing processing based on prior scene system response compensation.

[0029] S5. Obtain the prior apparent brightness temperature of the antenna and input it into the same system response function as the actual observation to obtain the prior initial response image; In real-world scenarios, the apparent brightness temperature of an antenna is an objectively existing brightness temperature distribution in a cosine coordinate system, but the receiving hardware cannot directly measure this distribution. The prior apparent brightness temperature of the antenna represents the prior scene itself, derived from historical observation data, background brightness temperature models, auxiliary sensors, environmental models, or preset background brightness temperature information. It is at least used to describe the background brightness temperature distribution and does not require the inclusion of scattered small targets for detection. To map the prior apparent brightness temperature of the antenna to the same image response domain as the actual observed uncorrected initial image, and to directly perform differential operations between the image domain and the actual uncorrected initial image to cancel the aliasing components of the duplicated region introduced by the stable background, this invention constructs a system response function to represent the complete imaging process from the apparent brightness temperature of the antenna to the uncorrected initial image. in, The system response function, which includes weighted DBF synthetic antenna equivalent radiation pattern, direction cosine projection, normalized baseline and its corresponding visibility spatial frequency sampling, and IDFT image inversion, is constructed as follows: ① For each input direction in the apparent brightness temperature direction cosine grid of the antenna, calculate the complex response of that direction to the visibility sampling point corresponding to each normalized baseline after weighted summation and direction cosine projection of the DBF pattern. ② By using IDFT image inversion, the response generated at each visibility sampling point in the input direction is back-projected onto the uncorrected initial image grid to obtain the response distribution formed in the initial image by the unit brightness temperature component in the input direction after passing through the complete imaging link; ③ Traverse all input direction grid points to obtain the contribution relationship of each input direction to each pixel of the uncorrected initial image, and construct the system response function accordingly. .

[0030] By inputting the a priori apparent brightness temperature of the antenna into the same system response function as the actual observation, the a priori initial response image is obtained: , in, This represents the prior initial response image. This indicates the apparent brightness temperature of the prior antenna.

[0031] S6, according to , and Calculate the apparent brightness temperature estimate of the antenna after aliasing reduction. ; The prior initial response image obtained by applying the same system response function to the apparent brightness temperature of the prior antenna is used to reduce the influence of background components in the uncorrected initial image obtained from actual observation. The expression is as follows: , in, This represents the apparent brightness temperature estimate of the antenna after dealiasing processing based on prior scenario system response compensation.

[0032] When scattered small targets or high brightness temperature targets not included in the prior antenna apparent brightness temperature exist in the copied region, these targets will not appear in the prior antenna apparent brightness temperature. Therefore, the uncorrected initial image components generated by these targets will not appear in the prior initial response image. This invention uses DBF synthesized antenna spatial filtering in the pre-link of visibility function generation to first reduce the effective energy of radiation entering the cross-correlation processing in the copied region. Then, it uses system response compensation in the post-link of visibility function generation to weaken the influence of background components on the uncorrected initial image, thereby achieving coordinated aliasing suppression before and after visibility function generation.

[0033] To further verify the effectiveness of the present invention, the embodiments of the present invention are verified through simulation modeling, wherein, Figure 5 In Figure (a), the input simulation scenario is used. Using the method of this invention, the apparent brightness temperature estimate distribution of the antenna after dealiasing processing based on prior scenario system response compensation is obtained, as shown below. Figure 5 As shown in (b); finally, through Figure 5 (b) minus Figure 5 (a) Imaging results under ideal, alias-free conditions, while preserving... Figure 5 The regular hexagonal region in (b) is obtained Figure 5 (c) serves as a comparison between the inversion result and the true scenario.

[0034] Figure 5 The target in the lower left corner of (a) is not in the prior background, but in Figure 5 In image (c), the aliasing energy of the target was successfully suppressed, and the aliasing energy of the target in the inverted image was only about 2% to 3% of the original energy; apart from the aliasing energy of the target, the aliasing caused by the background was almost invisible. Figure 5 (c) Most regions are close to 0, indicating that the inversion result is very close to the ground truth scene. In summary, the aliasing of the background and other targets was successfully suppressed by this method.

[0035] Example 2: This invention provides an aliasing suppression system for a DBF-synthetic aperture microwave radiometer, comprising a visibility function generation front link and a visibility function generation back link; The visibility function generation frontlink includes multiple DBF sub-antennas, multiple DBF synthesized antennas, a receiving channel, an analog-to-digital conversion unit, a digital beamforming processing unit, and a cross-correlation processing unit. Multiple DBF sub-antennas are used to receive passive microwave radiation signals and output digital baseband signals through corresponding receiving channels and analog-to-digital conversion units. Multiple sub-antennas are combined to form a DBF synthesized antenna. Multiple DBF composite antennas serve as the equivalent receiving unit of a synthetic aperture microwave radiometer. The multiple DBF composite antennas are arranged in a Y-shaped synthetic aperture array. The multiple DBF sub-antennas inside each DBF composite antenna are arranged in a triangular grid, and the overall outline of the DBF composite antenna is a regular hexagon. The digital beamforming processing unit is used to weight and accumulate the digital baseband signals output by multiple DBF sub-antennas within the same DBF synthesized antenna to form the DBF synthesized antenna output signal. The cross-correlation processing unit is used to perform cross-correlation processing on the output signals of different DBF synthesized antennas to generate a visibility function.

[0036] The visibility function generation process includes an image inversion processing unit, a priori scene input unit, a system response calculation unit, and a system response compensation unit, such as... Figure 4 As shown; The image inversion processing unit generates an uncorrected initial image based on the visibility function obtained from actual observations. The prior scene input unit is used to input the prior antenna apparent brightness temperature; The system response calculation unit is used to input the a priori antenna apparent brightness temperature into the same system response function as the actual observation for processing, so as to obtain the a priori initial response image; The system response compensation unit is used to obtain the brightness temperature estimate after aliasing reduction based on the actual observed uncorrected initial image and the prior initial response image.

[0037] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for suppressing aliasing in a DBF-synthetic aperture microwave radiometer, characterized in that, This includes the pre-visibility function generation link and the post-visibility function generation link; In the preceding link of the visibility function generation process S1. Multiple DBF sub-antennas are used to receive microwave radiated signals and convert them into digital baseband signals; S2. Weighted summation of the digital baseband signals of multiple DBF sub-antennas within the same DBF synthesized antenna to generate the DBF synthesized antenna output signal; S3. Perform cross-correlation and time averaging on the output signals of different DBF synthetic antennas to generate the actual observation visibility function; In the link after the visibility function is generated S4. Perform image inversion based on the actual observed visibility function to obtain the uncorrected initial image in the direction cosine coordinate system; S5. Obtain the prior apparent brightness temperature of the antenna and input the prior apparent brightness temperature of the antenna into the same system response function as the actual observation to obtain the prior initial response image; The system response function represents the imaging response process from the actual observed antenna apparent brightness temperature to the uncorrected initial image. This imaging response process includes at least DBF-synthesized antenna equivalent received radiation pattern weighting, direction cosine projection, normalized baseline and corresponding visibility spatial frequency sampling, and visibility function image inversion. Therefore, it satisfies: ， in, Represents the system response function. This indicates the actual apparent brightness temperature of the observed antenna. This indicates that the initial image was not corrected. By considering the prior antenna as a brightness temperature input into the system response function, the prior initial response image is obtained: ， in, This indicates the apparent brightness temperature of the prior antenna. Represents the prior initial response image; S6. Based on the uncorrected initial image, the prior initial response image, and the prior antenna apparent brightness temperature, obtain the antenna apparent brightness temperature estimate after aliasing reduction.

2. The aliasing suppression method for a DBF-synthetic aperture microwave radiometer according to claim 1, characterized in that, The DBF synthesized antenna is composed of several DBF sub-antennas arranged in a triangular grid pattern, and the overall outline after the arrangement is a regular hexagon. The several DBF synthesized antennas are arranged in a Y-shaped synthetic aperture array, and the positional difference between different DBF synthesized antennas forms a synthetic aperture baseline, which is then normalized to obtain a normalized baseline after the observation wavelength is normalized.

3. The aliasing suppression method for a DBF-integrated aperture microwave radiometer according to claim 2, characterized in that, In step S2, the digital baseband signals of multiple DBF sub-antennas within the same DBF synthesized antenna are weighted and accumulated. This weighted accumulation process and the equivalent receiving radiation pattern in the directional domain represent the same spatial filtering process. Through this weighted accumulation process, the apparent brightness temperature of the actual observation antenna is directionally weighted by the equivalent power radiation pattern of the DBF synthesized antenna to increase the radiation receiving weight in the target imaging area, while attenuating the radiation in the replication area, thereby achieving spatial aliasing suppression before the visibility function is generated.

4. The aliasing suppression method for a DBF-integrated aperture microwave radiometer according to claim 3, characterized in that, The equivalent receiver pattern is jointly determined by the DBF sub-antenna array and its digital beamforming processing, satisfying the following: ， in, This represents the normalized voltage pattern of the DBF synthesized antenna. This represents the normalized voltage pattern of a single DBF sub-antenna. Represents the DBF weight vector. Represents a discrete sampling vector in the direction cosine coordinate system. Represents the DBF subarray steering vector. Indicates conjugate transpose; The actual antenna apparent brightness temperature, after DBF spatial filtering, receives weights determined by the equivalent power pattern of the DBF synthesized antenna, and the directional weighting relationship is as follows: Among them, direction cosine coordinates Indicates the corresponding incident direction. This indicates the apparent brightness temperature of the actual observed antenna.

5. The aliasing suppression method for a DBF-integrated aperture microwave radiometer according to claim 4, characterized in that, In step S3, the generation of the visibility function is as follows: a direction cosine grid is constructed within the physically visible unit circle, and the continuous incident direction is discretized into several direction grid points; for each direction grid point, the apparent brightness temperature of the antenna at that grid point is obtained, and after weighting by the equivalent voltage pattern of the two DBF synthesized antennas participating in cross-correlation and correcting by the direction cosine projection factor, the contribution of the direction grid point to the visibility sampling point is obtained by combining the spatial phase relationship between the direction grid point and the normalized baseline; The contributions of all grid points in all directions are summed to obtain the visibility sample corresponding to the normalized baseline. All visibility samples together constitute the actual observed visibility function.

6. The aliasing suppression method for a DBF-synthetic aperture microwave radiometer according to claim 1, characterized in that, The uncorrected initial image is obtained by inverting the actual visibility function through a two-dimensional inverse discrete Fourier transform, and is expressed as follows: ， in, For the uncorrected initial image, Represents direction cosine coordinates, Represents the two-dimensional inverse discrete Fourier transform. Represents the actual observed visibility function. This indicates the spatial frequency sampling position corresponding to the normalized baseline.

7. The aliasing suppression method for a DBF-synthetic aperture microwave radiometer according to claim 1, characterized in that, The specific process for constructing the system response function is as follows: a. For each input direction in the apparent brightness temperature direction cosine grid of the antenna, calculate the complex response of that direction to the visibility sampling point corresponding to each normalized baseline after weighted summation and direction cosine projection of the DBF pattern. b. By using IDFT image inversion, the response generated at each visibility sampling point in the input direction is back-projected onto the uncorrected initial image grid to obtain the response distribution formed in the initial image by the unit brightness temperature component in the input direction after passing through the complete imaging link; c. Traverse all input direction grid points to obtain the contribution relationship of each input direction to each pixel of the uncorrected initial image, and construct the system response function accordingly. .

8. The aliasing suppression method for a DBF-integrated aperture microwave radiometer according to claim 1, characterized in that, In step S6, the uncorrected initial image and the prior initial response image are subjected to image domain difference operation to cancel the aliasing components of the duplicate region introduced by the stable background. At the same time, the prior antenna apparent brightness temperature is superimposed on the difference operation result as the background substrate to obtain the antenna apparent brightness temperature estimate after aliasing reduction, expressed as: ， in, This is an estimate of the apparent brightness temperature of the antenna after aliasing reduction.

9. A system for suppressing aliasing in a DBF-synthetic aperture microwave radiometer according to any one of claims 1-8, characterized in that, This includes the pre-visibility function generation link and the post-visibility function generation link; The visibility function generation frontlink includes multiple DBF sub-antennas, multiple DBF synthesized antennas, a receiving channel, an analog-to-digital conversion unit, a digital beamforming processing unit, and a cross-correlation processing unit. Multiple DBF sub-antennas are used to receive passive microwave radiation signals and output digital baseband signals through corresponding receiving channels and analog-to-digital conversion units. Multiple sub-antennas are combined to form a DBF synthesized antenna. Multiple DBF composite antennas serve as the equivalent receiving unit of a synthetic aperture microwave radiometer. The multiple DBF composite antennas are arranged in a Y-shaped synthetic aperture array. The multiple DBF sub-antennas inside each DBF composite antenna are arranged in a triangular grid, and the overall outline of the DBF composite antenna is a regular hexagon. The digital beamforming processing unit is used to weight and accumulate the digital baseband signals output by multiple DBF sub-antennas within the same DBF synthesized antenna to form the DBF synthesized antenna output signal. The cross-correlation processing unit is used to perform cross-correlation processing on the output signals of different DBF synthesized antennas to generate a visibility function. The visibility function generation post-processing link includes an image inversion processing unit, a priori scene input unit, a system response calculation unit, and a system response compensation unit. The image inversion processing unit generates an uncorrected initial image based on the visibility function obtained from actual observations. The prior scene input unit is used to input the prior antenna apparent brightness temperature; The system response calculation unit is used to input the a priori antenna apparent brightness temperature into the same system response function as the actual observation for processing, so as to obtain the a priori initial response image; The system response compensation unit is used to obtain the brightness temperature estimate after aliasing reduction based on the actual observed uncorrected initial image and the prior initial response image.

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