Method, system, device and medium for separating weather radar antenna far-field multipath interference

Abstract

The present application relates to radar test and signal processing technical field, especially to a kind of weather radar antenna far field multipath interference separation method, system, equipment and medium, its method includes: obtaining measurement geometry parameter, radar operating parameter and antenna directional diagram parameter;Establish the multipath geometric relationship of weather radar antenna and calibration target, determine the path difference of direct path and ground reflection path;Determine the ground multipath effect area and equivalent multipath radar cross section, determine multipath interference index in combination with the reference radar cross section of calibration target;Based on multipath interference index, pitch angle scanning is carried out, and target pitch angle is determined;According to path difference, frequency diversity parameter is determined, echo power under different frequency is collected and power statistical value is obtained;Based on power statistical value, correct coherent multipath interference, the radar cross section of calibration target is inverted, and interference separation result is obtained.The present application can reduce the influence of incoherent and coherent multipath interference on calibration result, improve calibration accuracy and engineering applicability.

Description

Technical Field

[0001] This invention relates to the field of radar testing and signal processing technology, and in particular to a method, system, device and medium for separating far-field multipath interference of a weather radar antenna. Background Technology

[0002] High-precision weather radar antennas, such as dual-polarization Doppler weather radar antennas, typically require far-field calibration in open areas. During antenna far-field testing and radar target radar cross-section calibration, the electromagnetic waves emitted by the radar, in addition to propagating along the direct path, may also be reflected by the ground before reaching the calibration target or weather radar antenna, resulting in multipath propagation of both direct and reflected waves. Due to factors such as terrain undulations, surface reflection characteristics, and the installation height of the weather radar antenna and calibration target, the lower region or sidelobes of the antenna's main beam may illuminate the ground, creating multipath reflection interference. Multipath interference causes amplitude fluctuations and phase changes in the received echo, thereby reducing the accuracy of far-field echo measurements and calibration results.

[0003] When the test distance is long and the height of the weather radar antenna and the calibration target is limited, the path difference between the direct path and the ground reflection path is usually small, and the corresponding propagation delay may be much smaller than the radar pulse width. Therefore, the direct echo and the multipath echo reflected from the ground are prone to overlap in the time dimension, making it difficult to separate them using only range gating.

[0004] Existing methods for handling multipath interference mainly include improving test site conditions, adjusting the installation height of weather radar antennas or calibration targets, laying absorbing materials, adjusting test pulse widths, and smoothing received data. These methods can reduce the impact of multipath interference on far-field test results to some extent. However, simply improving test conditions by raising the tower or laying absorbing materials is usually costly and subject to limitations imposed by site altitude, terrain, and safety conditions, making implementation difficult. Simple smoothing of received data may simultaneously process power fluctuations caused by target echoes and multipath interference, easily affecting the true echo characteristics and failing to meet measurement accuracy requirements in high-precision calibration scenarios. Furthermore, under test conditions with low grazing angles or strong ground reflections, multipath interference can still significantly affect received echoes and calibration results. Therefore, reducing the impact of ground-reflected multipath interference on received echoes and calibration results during far-field testing and calibration of weather radar antennas is a technical problem that needs to be solved. Summary of the Invention

[0005] (a) Technical problems to be solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method, system, device and medium for separating multipath interference in the far field of weather radar antennas, which solves the technical problem that ground reflection multipath interference is difficult to separate effectively in the far field calibration of weather radar antennas, resulting in a decrease in the accuracy of received echoes and calibration results.

[0006] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by the present invention include: In a first aspect, the present invention provides a method for separating far-field multipath interference from a weather radar antenna, comprising: Acquire the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna; The multipath geometric relationship between the weather radar antenna and the calibration target is established based on the measured geometric parameters in order to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground. The ground multipath effect zone is determined based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is determined based on the ground multipath effect zone and the corresponding ground scattering characteristics. The multipath interference index is determined by combining the reference radar cross-section of the calibration target. Based on the multipath interference index, the elevation angle of the weather radar antenna is scanned, the echo power of the calibration target at different elevation angles is collected, the target elevation angle for suppressing incoherent multipath interference is determined according to the echo power characteristics, and the weather radar antenna is adjusted to the target elevation angle. Based on the frequency diversity parameters determined by the path difference, the echo power of the calibration target at different frequencies is collected, and the power statistics are obtained through statistical processing. Based on the power statistics, coherent multipath interference correction is performed, and the radar cross-section of the calibration target is retrieved to obtain the interference separation result.

[0007] Optionally, the measurement geometric parameters, radar operating parameters, and antenna pattern parameters obtained during the far-field calibration of the weather radar antenna include: The measurement geometric parameters are obtained by acquiring the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target. The radar's transmission power, operating frequency, range resolution, and system loss are obtained to acquire the radar's operating parameters. The antenna pattern parameters are obtained by acquiring the azimuth beamwidth, sidelobe level, and antenna gain at different elevation angles of the weather radar antenna.

[0008] Optionally, the multipath geometric relationship between the weather radar antenna and the calibration target is established based on the measured geometric parameters to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground, including: Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, the direct propagation relationship from the weather radar antenna to the calibration target and the reflection propagation relationship from the weather radar antenna to the calibration target via the ground reflection point are established, and the multipath geometric relationship is obtained. Based on the multipath geometry, the propagation path between the weather radar antenna and the calibration target that does not pass through the ground reflection point is determined as the direct path. The propagation segment from the weather radar antenna to the ground reflection point and the propagation segment from the ground reflection point to the calibration target are combined in the propagation order to obtain the multipath path that passes through the ground reflection. Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, the increased propagation distance of the multipath path relative to the direct path is calculated under far-field conditions according to the two-path propagation path difference relationship. The two-path propagation path difference relationship indicates that the increased propagation distance is directly proportional to the product of the ground clearance of the weather radar antenna feed center and the ground clearance of the calibration target, and inversely proportional to the slant distance. The increased propagation distance of a multipath path relative to a direct path is defined as the path difference between the direct path and the multipath path.

[0009] Optionally, the ground multipath effect zone is determined based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is determined based on the ground multipath effect zone and its corresponding ground scattering characteristics. Furthermore, the multipath interference index is determined by combining this index with the reference radar cross-section of the calibration target, including: The projection angle parameters are determined based on the ground height of the weather radar antenna feed center and the slant distance between the weather radar antenna and the calibration target. The slant distance and range resolution are then projected onto the ground according to the projection angle parameters to obtain the projected distance and range resolution range on the ground. The ground multipath effect area of ​​the main beam is determined based on the projection distance, range resolution range, and azimuth beamwidth; the ground multipath effect area of ​​the sidelobe is determined based on the projection distance and range resolution range. The effective area of ​​the main beam is determined based on the coverage of the ground multipath effect region of the main beam in the azimuth and range directions, and the effective area of ​​the sidelobe is determined based on the coverage of the ground multipath effect region of the sidelobe in the circumferential and range directions. The radar cross-section of the main beam multipath is determined based on the effective area of ​​the main beam, the ground scattering coefficient in the ground multipath effect area of ​​the main beam, and the antenna gain at the corresponding elevation angle. The sidelobe multipath radar cross-section is determined based on the sidelobe effective area, the ground scattering coefficient within the sidelobe ground multipath effect region, and the sidelobe level. The radar cross-sections of the main beam multipath and the sidelobe multipath are combined to obtain the equivalent multipath radar cross-section, and the signal-to-clutter ratio is determined by combining it with the reference radar cross-section, which serves as a multipath interference indicator.

[0010] Optionally, the weather radar antenna is scanned at elevation angles based on multipath interference indices to collect the echo power of the calibration target at different elevation angles. The target elevation angle for suppressing incoherent multipath interference is determined based on the echo power characteristics, and the weather radar antenna is adjusted to the target elevation angle, including: When the multipath interference index meets the preset scanning conditions, the elevation angle of the weather radar antenna is scanned, and the reference elevation angle of the weather radar antenna pointing to the calibration target is determined based on the height difference between the feed center of the weather radar antenna and the calibration target and the slant distance between the weather radar antenna and the calibration target. Multiple candidate elevation angles are determined within a preset range centered on the reference elevation angle. The weather radar antenna is then adjusted to each candidate elevation angle in sequence, and a test pulse sequence is transmitted to the calibration target and the corresponding echo signal is collected. Based on the frequency domain power of the echo signal at each candidate pitch angle, the pitch power distribution is determined, and the frequency domain power variance of the echo signal at each candidate pitch angle is calculated to obtain the pitch variance distribution. The candidate pitch angle corresponding to the minimum echo power is determined based on the pitch power distribution, or the candidate pitch angle corresponding to the minimum frequency domain variance is determined based on the pitch variance distribution, and the determined candidate pitch angle is used as the target pitch angle. Adjust the weather radar antenna to the target elevation angle so that the elevation angle corresponding to the ground reflection point is located at or close to the position of minimum sidelobe gain or null position in the antenna gain corresponding to different elevation angles, thereby minimizing the spatial gain of the ground reflected wave.

[0011] Optionally, according to the frequency diversity parameters determined by the path difference, the echo power of the calibration target at different frequencies is collected, and statistical power statistics are obtained through statistical processing, including: The multipath fading frequency period between the direct echo and the multipath echo reflected from the ground is determined based on the path difference between the direct path and the multipath path reflected from the ground. The frequency step and frequency diversity bandwidth are determined based on the multipath fading frequency period. The frequency step is no more than one-third of the multipath fading frequency period, and the frequency diversity bandwidth covers at least three multipath fading frequency periods. The number of frequency sampling points is determined based on the frequency diversity bandwidth and frequency step, and the frequency diversity pulse sequence is configured according to the frequency step and the number of frequency sampling points to configure the weather radar into inter-pulse frequency diversity mode. Keep the weather radar antenna at the target elevation angle, change the operating frequency of the weather radar between adjacent pulses in the frequency diversity pulse sequence according to the frequency step, collect the linear echo power of the target at each operating frequency, and obtain the echo power sequence arranged according to the operating frequency. The echo power sequence is statistically processed to obtain power statistics.

[0012] Optionally, coherent multipath interference correction is performed based on power statistics, and the radar cross-section of the calibration target is retrieved to obtain the interference separation results, including: Obtain the surface type of the location of the ground reflection point, and determine the ground reflection coefficient according to the preset correspondence between surface type and ground reflection coefficient; Based on the coherent superposition relationship between direct echo and multipath echo reflected from the ground, the coherent multipath gain term in the echo power at each operating frequency is determined. The coherent multipath gain term is characterized by the ground reflection coefficient and the path phase difference, and the path phase difference is determined by the path difference and the corresponding operating frequency. Based on the coherent cross term in the coherent multipath gain term that varies with the operating frequency, the power bias relationship between the power statistics and the direct echo power corresponding to the calibration target is determined under the frequency diversity bandwidth and frequency step. Based on the power offset relationship, the sum of the square of the modulus of the ground reflection coefficient and 1 is determined as the multipath power offset factor, and the ratio of the power statistics value to the multipath power offset factor is determined as the direct echo power corresponding to the calibration target. Based on the transmit power, the antenna gain corresponding to the direction of the calibration target, the operating wavelength corresponding to the center frequency determined by the operating frequency, the slant range between the weather radar antenna and the calibration target, and the system loss, the inversion relationship between the direct echo power and the radar cross-section of the calibration target is determined. The radar cross-section of the calibration target is determined based on the inversion relationship and the direct echo power, and the radar cross-section of the calibration target is used as the result of interference separation.

[0013] Secondly, the present invention provides a far-field multipath interference separation system for a weather radar antenna, comprising: The parameter acquisition module is used to acquire the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna. The multipath geometry establishment module is used to establish the multipath geometric relationship between the weather radar antenna and the calibration target based on the measured geometric parameters, so as to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground. The multipath interference evaluation module is used to determine the ground multipath effect zone based on the measured geometric parameters, radar operating parameters and antenna pattern parameters, determine the equivalent multipath radar cross-section based on the ground multipath effect zone and the corresponding ground scattering characteristics, and determine the multipath interference index in combination with the reference radar cross-section of the calibration target. The elevation angle adjustment module is used to scan the elevation angle of the weather radar antenna based on the multipath interference index, collect the echo power of the calibration target at different elevation angles, determine the target elevation angle to suppress incoherent multipath interference based on the echo power characteristics, and adjust the weather radar antenna to the target elevation angle. The frequency diversity processing module is used to collect the echo power of the calibration target at different frequencies according to the frequency diversity parameters determined by the path difference, and obtain the power statistics value through statistical processing. The interference correction and inversion module is used to perform coherent multipath interference correction based on power statistics and invert the radar cross-section of the calibration target to obtain the interference separation result.

[0014] Thirdly, the present invention provides a weather radar antenna far-field multipath interference separation device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and when the instructions are executed by the at least one processor, the at least one processor performs the weather radar antenna far-field multipath interference separation method as described above.

[0015] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the far-field multipath interference separation method for weather radar antennas as described above.

[0016] (III) Beneficial Effects The beneficial effects of this invention are: First, by acquiring the measurement geometric parameters, radar operating parameters, and antenna pattern parameters of the weather radar antenna far-field measurement, this invention reduces reliance on empirical judgment or single test conditions, which is beneficial to improving the controllability and consistency of the far-field calibration process.

[0017] Next, the present invention establishes the multipath geometric relationship between the weather radar antenna and the calibration target, and determines the path difference between the direct path and the multipath path reflected from the ground, thereby characterizing the spatial propagation relationship and propagation difference between the direct echo and the multipath echo reflected from the ground.

[0018] Furthermore, the ground multipath effect zone is determined based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is calculated using ground scattering characteristics, and the multipath interference index is determined by combining this with the reference radar cross-section of the calibration target. This allows for the quantification of the multipath interference level caused by the main beam and sidelobes illuminating the ground. Based on this, the weather radar antenna is scanned at elevation angles according to the multipath interference index. The target elevation angle is determined based on the echo power characteristics of the calibration target at different elevation angles, thereby avoiding or reducing elevation directions with strong incoherent multipath interference and minimizing the impact of ground-scattered echoes on the calibration target echo.

[0019] Subsequently, frequency diversity parameters are determined based on the path difference, and echo power of the calibration target at different frequencies is collected. Power statistics are obtained through statistical processing, which weakens the fluctuations in coherent multipath power that vary with the operating frequency and path phase difference.

[0020] Finally, coherent multipath interference correction is performed based on power statistics, and the radar cross-section of the calibration target is retrieved, thereby achieving effective separation of the calibration target echo from ground reflection multipath interference and improving the accuracy of the received echo and radar cross-section calibration results in the far-field calibration of weather radar antennas.

[0021] Therefore, this invention can effectively reduce the impact of incoherent and coherent multipath interference on calibration results without relying on large-scale site modifications or additional absorbing facilities, thereby improving the accuracy, reliability, and engineering applicability of the far-field calibration results of weather radar antennas. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall process of the method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the specific process of step S1 of the method provided in this embodiment of the invention; Figure 3 This is a detailed flowchart illustrating step S2 of the method provided in this embodiment of the invention; Figure 4 This is a schematic diagram illustrating the geometric relationship between the direct path and the ground reflection path in a far-field calibration scenario provided by an embodiment of the present invention. Figure 5 This is a detailed flowchart illustrating step S3 of the method provided in this embodiment of the invention; Figure 6 This is a simplified diagram illustrating the calculation parameters of the ground scattering region and the equivalent multipath radar cross-section provided in an embodiment of the present invention. Figure 7 This is a detailed flowchart illustrating step S4 of the method provided in this embodiment of the invention; Figure 8 This is a detailed flowchart illustrating step S5 of the method provided in this embodiment of the invention; Figure 9 A schematic diagram illustrating the specific process of step S6 of the method provided in this embodiment of the invention. Detailed Implementation

[0023] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown in the embodiment of the present invention, a method for separating far-field multipath interference of a weather radar antenna includes: acquiring measurement geometric parameters, radar operating parameters, and antenna pattern parameters during the far-field calibration of the weather radar antenna; establishing the multipath geometric relationship between the weather radar antenna and the calibration target based on the measurement geometric parameters to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground; determining the ground multipath effect zone based on the measurement geometric parameters, radar operating parameters, and antenna pattern parameters; and determining the equivalent multipath radar cross-section based on the ground multipath effect zone and the corresponding ground scattering characteristics. The multipath interference index is determined by combining the reference radar cross-section of the calibration target; the weather radar antenna is scanned at elevation angles based on the multipath interference index, and the echo power of the calibration target at different elevation angles is collected. The target elevation angle used to suppress incoherent multipath interference is determined according to the echo power characteristics, and the weather radar antenna is adjusted to the target elevation angle; the echo power of the calibration target at different frequencies is collected according to the frequency diversity parameters determined by the path difference, and the power statistics are obtained through statistical processing; coherent multipath interference correction is performed based on the power statistics, and the radar cross-section of the calibration target is retrieved to obtain the interference separation result.

[0025] First, by acquiring the measurement geometric parameters, radar operating parameters, and antenna pattern parameters of the weather radar antenna far-field measurement, this invention reduces reliance on empirical judgment or single test conditions, which is beneficial to improving the controllability and consistency of the far-field calibration process.

[0026] Next, the present invention establishes the multipath geometric relationship between the weather radar antenna and the calibration target, and determines the path difference between the direct path and the multipath path reflected from the ground, thereby characterizing the spatial propagation relationship and propagation difference between the direct echo and the multipath echo reflected from the ground.

[0027] Furthermore, the ground multipath effect zone is determined based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is calculated using ground scattering characteristics, and the multipath interference index is determined by combining this with the reference radar cross-section of the calibration target. This allows for the quantification of the multipath interference level caused by the main beam and sidelobes illuminating the ground. Based on this, the weather radar antenna is scanned at elevation angles according to the multipath interference index. The target elevation angle is determined based on the echo power characteristics of the calibration target at different elevation angles, thereby avoiding or reducing elevation directions with strong incoherent multipath interference and minimizing the impact of ground-scattered echoes on the calibration target echo.

[0028] Subsequently, frequency diversity parameters are determined based on the path difference, and echo power of the calibration target at different frequencies is collected. Power statistics are obtained through statistical processing, which weakens the fluctuations in coherent multipath power that vary with the operating frequency and path phase difference.

[0029] Finally, coherent multipath interference correction is performed based on power statistics, and the radar cross-section of the calibration target is retrieved, thereby achieving effective separation of the calibration target echo from ground reflection multipath interference and improving the accuracy of the received echo and radar cross-section calibration results in the far-field calibration of weather radar antennas.

[0030] Therefore, this invention can effectively reduce the impact of incoherent and coherent multipath interference on calibration results without relying on large-scale site modifications or additional absorbing facilities, thereby improving the accuracy, reliability, and engineering applicability of the far-field calibration results of weather radar antennas.

[0031] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0032] Specifically, embodiments of the present invention provide a method for separating far-field multipath interference of a weather radar antenna, comprising: S1. Obtain the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna.

[0033] Furthermore, such as Figure 2 As shown, step S1 includes: S11. Obtain the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target to obtain the measurement geometric parameters.

[0034] In practice, the altitude h above the ground of the weather radar antenna feed center can be obtained through surveying data of the calibration site, distance measuring equipment, and height measuring equipment. r The ground clearance h of the calibration target t And the slant distance R between the weather radar antenna and the calibration target. The ground clearance of both the weather radar antenna feed center and the calibration target is based on the ground of the calibration site, and the slant distance R is the spatial distance between the weather radar antenna feed center and the calibration target.

[0035] S12. Obtain the transmit power, operating frequency, range resolution, and system loss of the weather radar to obtain the radar operating parameters.

[0036] In practice, the transmit power P can be obtained from the weather radar's system configuration file, calibration parameter file, operating status data, system calibration results, on-site technical test results, or technical reports. t Operating frequency f, range resolution ΔR, and system loss L. Transmit power P t The peak transmit power of the weather radar is used. The range resolution ΔR represents the range range corresponding to a single range cell. The range cell is the echo sampling interval divided along the detection range direction of the weather radar according to the range resolution ΔR. The system loss L is used to characterize the power loss introduced by the weather radar's transmit link, receive link, and signal processing link.

[0037] S13. Obtain the azimuth beamwidth, sidelobe level, and antenna gain corresponding to different elevation angles of the weather radar antenna to obtain the antenna pattern parameters.

[0038] In this step, the azimuth beamwidth, sidelobe level, and antenna gain corresponding to different elevation angles can be obtained from the design parameters, factory test data, or pre-measured antenna pattern data of the weather radar antenna. In this embodiment, the azimuth beamwidth is the 3dB azimuth beamwidth of the weather radar antenna, denoted as θ. A θ A The parameters are known and determined by the factory specifications of the weather radar antenna itself; the sidelobe level can be determined based on the antenna pattern parameters, and the root mean square level (RMS) of the sidelobe (SL) is used. rms The overall illumination level of the sidelobes is characterized; the antenna gain corresponding to different elevation angles is determined by the antenna elevation pattern, which is used to characterize the gain distribution of the weather radar antenna in different elevation directions.

[0039] S2. Establish the multipath geometric relationship between the weather radar antenna and the calibration target based on the measured geometric parameters, so as to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground.

[0040] Furthermore, such as Figure 3 As shown, step S2 includes: S21. Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, establish the direct propagation relationship from the weather radar antenna to the calibration target, and the reflection propagation relationship from the weather radar antenna to the calibration target via the ground reflection point, and obtain the multipath geometric relationship.

[0041] In this embodiment, the calibration target is a target object with a known radar cross-section deployed in the far-field region of the weather radar antenna, such as... Figure 4 As shown in the figure, the solid line connecting the center of the weather radar antenna feed and the calibration target represents the direct propagation relationship; the solid line that turns back to the calibration target after passing through the ground reflection point represents the reflection propagation relationship, that is, the electromagnetic wave emitted by the weather radar antenna first propagates to the ground reflection point, and then propagates to the calibration target after being reflected by the ground.

[0042] To facilitate the characterization of the propagation process after ground reflection, the symmetrical position of the calibration target with respect to the ground is taken as the target's mirror image point. A representative reflection propagation path is equivalently represented by a line connecting the weather radar antenna feed center to the target's mirror image point. The intersection of this line with the ground corresponds to the ground reflection point of this propagation path. Based on the positional relationships between the weather radar antenna feed center, the ground reflection point, the calibration target, and the target's mirror image point, a multipath geometry is established.

[0043] S22. Based on the multipath geometry, the propagation path between the weather radar antenna and the calibration target that does not pass through the ground reflection point is determined as the direct path. The propagation segment from the weather radar antenna to the ground reflection point and the propagation segment from the ground reflection point to the calibration target are combined in the propagation order to obtain the multipath path that passes through the ground reflection point.

[0044] The direct propagation path between the weather radar antenna feed center and the calibration target does not pass through the ground reflection point, and its propagation distance corresponds to the slant range R. Therefore, this propagation path is determined as the direct path.

[0045] The multipath path after ground reflection consists of two sequentially connected propagation segments. The first segment is from the center of the weather radar antenna feed to the ground reflection point, and the second segment is from the ground reflection point to the calibration target. Combining the two segments according to the propagation order of electromagnetic waves yields the multipath path from the weather radar antenna to the calibration target after ground reflection. Compared to a direct path, the multipath path, by passing through the ground reflection point, has a correspondingly increased propagation distance.

[0046] S23. Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, calculate the increased propagation distance of the multipath path relative to the direct path under far-field conditions according to the two-path propagation path difference relationship; wherein, the two-path propagation path difference relationship indicates that the increased propagation distance is directly proportional to the product of the ground clearance of the weather radar antenna feed center and the ground clearance of the calibration target, and inversely proportional to the slant distance.

[0047] The increased propagation distance of a multipath path relative to a direct path is denoted as ΔL. According to the relationship between the two-path propagation differences, the increased propagation distance is expressed as: ΔL = 2h r sinθ, where the target is located in the far field of the weather radar antenna, and the slant distance R between the center of the weather radar antenna feed and the target is much greater than the target's height h above the ground. t Under the condition of sinθ and h t The approximate relationship between / R determines the increased propagation distance ΔL as: 2h r h t / R, where θ is the equivalent propagation elevation angle corresponding to the height of the calibration target in the two-path propagation path difference relationship.

[0048] S24. The increased propagation distance of the multipath path relative to the direct path is defined as the path difference between the direct path and the multipath path.

[0049] S3. Determine the ground multipath effect zone based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. Determine the equivalent multipath radar cross-section based on the ground multipath effect zone and the corresponding ground scattering characteristics. Combine the multipath interference index with the reference radar cross-section of the calibration target.

[0050] Furthermore, such as Figure 5 As shown, step S3 includes: S31. Determine the projection angle parameters based on the ground height of the weather radar antenna feed center and the slant distance between the weather radar antenna and the calibration target. Perform ground projection on the slant distance and range resolution according to the projection angle parameters to obtain the projected distance and range resolution range on the ground.

[0051] In this step, the altitude h of the weather radar antenna feed center above the ground is used as a reference. r And the spatial geometric relationship characterized by the slant range R between the weather radar antenna and the calibration target, to determine the projection angle parameter θ r =arcsin(h r / R). According to the projection angle parameter θ r By projecting the slant distance R onto the ground, we obtain the projected distance R on the ground. g ; and according to the projection angle parameter θ rBy projecting the distance resolution ΔR onto the ground, we obtain the distance resolution range ΔR on the ground. g , respectively represented as R g =Rcosθ r ;ΔR g =ΔRcosθ r .

[0052] S32. Determine the ground multipath effect area of ​​the main beam based on the projection distance, range resolution range and azimuth beamwidth, and determine the ground multipath effect area of ​​the sidelobe based on the projection distance and range resolution range.

[0053] Based on the azimuth and range illumination ranges of the weather radar antenna's main beam on the ground, the ground multipath effect zone of the main beam is determined. This is based on the projected distance R. g and 3dB azimuth beamwidth θ A Determine the main beam at the projection distance R g The azimuth illumination range at a location is determined by the distance resolution range ΔR. g Determine the range of the main beam in the range direction, and define the area formed by the azimuth and range directions on the ground as the ground multipath effect zone of the main beam.

[0054] Based on the sidelobe at the projection distance R g The circumferential illumination range and distance resolution range ΔR formed at the location g The sidelobe ground multipath effect region was determined. Since the sidelobe may illuminate the ground from multiple directions, the sidelobe was positioned within the distance resolution range ΔR. g The circumferential region formed within the lobe serves as the sidelobe ground multipath effect zone.

[0055] S33. Determine the effective area of ​​the main beam based on the coverage range of the ground multipath effect region of the main beam in the azimuth and range directions, and determine the effective area of ​​the sidelobe based on the coverage range of the ground multipath effect region of the sidelobe in the circumferential and range directions.

[0056] Let the effective area of ​​the main beam be denoted as A. MBc For a given main beam ground multipath effect area, its azimuth coverage range is R. g θ A The distance coverage range is ΔR g The effective area of ​​the main beam is determined based on the coverage range in the azimuth and range directions: A MBc =ΔR g R g θ A .

[0057] Next, let A be the area of ​​the sidelobe's effect. SLc For a defined sidelobe ground multipath effect region, its circumferential coverage area is taken as πR. gThe distance coverage area is taken as ΔR. g The sidelobe effective area is determined based on the circumferential coverage area and the distance-oriented coverage area: A SLc =ΔR g πR g Main beam area A MBc The area used to characterize the ground multipath effect region of the main beam, and the sidelobe effect area A. SLc Used to characterize the area of ​​the sidelobe ground multipath effect region.

[0058] S34. Determine the radar cross-section of the main beam multipath based on the effective area of ​​the main beam, the ground scattering coefficient in the ground multipath effect area of ​​the main beam, and the antenna gain at the corresponding elevation angle.

[0059] Let the cross-sectional area of ​​the main beam multipath radar be denoted as σ. MBc And obtain the ground scattering coefficient σ corresponding to the ground multipath effect area of ​​the main beam. 0 Ground scattering coefficient σ 0 The scattering intensity per unit ground area is used to characterize the scattering intensity, and its value is predetermined based on the ground scattering characteristics of the main beam's ground multipath effect zone. The ground scattering coefficient can be obtained from preset ground scattering parameters or from measurements of the corresponding ground area. When the ground scattering characteristics differ in different ground multipath effect zones, σ... 0 The values ​​corresponding to the ground multipath effect zone of the main beam are adopted.

[0060] To determine the antenna gain corresponding to the ground reflection direction in the weather radar antenna pattern, the theoretical pointing elevation angle of the weather radar antenna when pointing at the calibration target is determined, and this theoretical pointing elevation angle is denoted as θ. el Theoretically, it points to an elevation angle θ. el When the center line of the main lobe of a weather radar antenna is theoretically pointed towards the calibration target, the angle between the center line of the antenna's main lobe and the horizontal line is denoted as θ. el =arcsin((h t h r ) / R).

[0061] Based on the main beam's effective area, ground scattering coefficient, and antenna gain at the corresponding elevation angle, the main beam multipath radar cross-section is expressed as: σ MBc =σ 0 A MBc G²(θ) el +θ r ) = σ 0 ΔR g R g θ A G²(θ) el +θ r In the formula, G(θ) el +θ r) represents the angle θ el +θ r The antenna gain corresponding to the antenna pattern of the weather radar. The radar cross-section of the main beam multipath radar varies with the main beam's effective area, the ground scattering coefficient, and the antenna gain at the corresponding elevation angle.

[0062] S35. Determine the radar cross-section of the sidelobe multipath based on the sidelobe effective area, the ground scattering coefficient in the sidelobe ground multipath effect region, and the sidelobe level.

[0063] Let the sidelobe multipath radar cross-section be denoted as σ. SLc The ground scattering coefficient corresponding to the sidelobe ground multipath effect region is denoted as σ. 0 When the ground scattering characteristics differ in different ground multipath effect zones, σ 0 The values ​​corresponding to the sidelobe ground multipath effect region are used. The root mean square level (RMS) of the sidelobe is used. rms Characterizes the overall illumination level of the sidelobe within the corresponding ground multipath effect region. The sidelobe multipath radar cross-section is expressed as: σ SLc =σ 0 A SLc (SL) rms ) 2 =σ 0 ΔR g πR g (SL rms ) 2 In the formula, σ 0 A is the ground scattering coefficient corresponding to the sidelobe ground multipath effect region. SLc SL is the area of ​​the sidelobe. rms This represents the root-mean-square level of the sidelobes. During calculation, the ground scattering coefficient σ... 0 and the root mean square level of the sidelobe SL rms Use a linear value that is compatible with the above formula.

[0064] S36. The radar cross-sections of the main beam multipath and the sidelobe multipath are combined to obtain the equivalent multipath radar cross-section, and the signal-to-clutter ratio is determined by combining it with the reference radar cross-section as a multipath interference index.

[0065] For the main beam multipath radar cross-section σ MBc and sidelobe multipath radar cross-section σ SLc By performing synthesis, the equivalent multipath radar cross-section σ is obtained. c Equivalent multipath radar cross-section σ c Used to characterize the combined multipath scattering intensity formed by the main beam and side lobes illuminating the ground.

[0066] Combined with the reference radar cross-section σ of the calibration target t and equivalent multipath radar cross-section σ cThe signal-to-noise ratio (SCR) is determined and used as an indicator of multipath interference. A higher SCR indicates stronger multipath interference relative to the ground, while a lower SCR indicates a more significant impact of ground multipath interference on the target echo.

[0067] As another implementation of step S3, without separately calculating the main beam multipath radar cross-section and the sidelobe multipath radar cross-section, it can also be done according to... Figure 6 The ground multipath effect area shown provides a simplified estimate of multipath interference. When using this simplified estimation method, the pulse width τ of the weather radar can also be obtained from the weather radar's system configuration file, calibration parameter file, or operational status data.

[0068] Based on the ground elevation h of the weather radar antenna feed center r and projection distance R g Determine the ground glancing angle φ g , represented as: φ g =arctan(h r / R g ), where the ground glancing angle φ g Used to characterize the angle between the direction of propagation of weather radar beams and the ground.

[0069] like Figure 6 As shown, the weather radar beam sweeps across the ground at an angle φ. g Illuminate the ground. Figure 6 The upper part shows the range-oriented illumination range (cτ / 2)secφ formed by projecting the range scale cτ / 2 corresponding to the pulse width τ along the beam propagation direction onto the ground. g Where c is the speed of electromagnetic wave propagation; Figure 6 The lower part shows the planar projection of the weather radar beam on the ground. The azimuth illumination range defined by the 3dB azimuth beamwidth intersects with the range illumination range, forming the ground multipath effect area shown in the shaded area in the figure. Figure 6 θ (marked in the middle) 3dB The 3dB azimuth beamwidth of the weather radar antenna, obtained from on-site measurements, is related to θ. A The physical meanings are the same, the difference lies in θ. 3dB θ is the value measured on-site. A R represents the known parameters determined by the factory specifications of the weather radar antenna itself, and R is the slant distance between the feed center of the weather radar antenna and the calibration target.

[0070] Will Figure 6 The area of ​​the ground multipath effect zone shown is denoted as A. c , represented as: A c =Rθ 3dB (cτ / 2)secφ g .

[0071] Next, based on the area A of the ground multipath effect zone... c and the corresponding ground scattering coefficient σ in this region 0 The simplified estimate yields the equivalent multipath radar cross-section, expressed as: σc = σ 0 A c When the ground scattering characteristics of this region differ from those of the main beam ground multipath effect region and the sidelobe ground multipath effect region, σ 0 Use the value corresponding to this region.

[0072] When using the simplified estimation method described above, the reference radar cross-section σ of the calibration target should be considered. t The signal-to-noise ratio (SCR) is determined as follows: SCR = 2σ t cosφ g / (σ 0 θ 3dB The larger the SCR, the stronger the target echo is relative to ground multipath interference; the smaller the SCR, the more significant the impact of ground multipath interference on the target echo.

[0073] S4. Based on the multipath interference index, perform elevation angle scanning on the weather radar antenna, collect the echo power of the calibration target at different elevation angles, determine the target elevation angle to suppress incoherent multipath interference based on the echo power characteristics, and adjust the weather radar antenna to the target elevation angle.

[0074] In this embodiment, incoherent multipath interference mainly includes scattered echoes generated by the sidelobes or main lobe edges of the weather radar antenna illuminating the ground. The reflection intensity of incoherent multipath interference is related to the gain of the weather radar antenna in the direction of the ground reflection point. By finely adjusting the elevation angle of the weather radar antenna near the elevation direction corresponding to the calibration target, the direction of the ground reflection point is made closer to the sidelobe gain trough or null region in the antenna gain corresponding to different elevation angles. This reduces the spatial gain of the ground reflected wave and achieves spatial filtering of incoherent multipath interference.

[0075] Furthermore, such as Figure 7 As shown, step S4 includes: S41. When the multipath interference index meets the preset scanning conditions, perform an elevation angle scan on the weather radar antenna, and determine the reference elevation angle of the weather radar antenna pointing towards the calibration target based on the height difference between the feed center of the weather radar antenna and the calibration target and the slant distance between the weather radar antenna and the calibration target.

[0076] The decision to perform an elevation scan is based on the determined signal-to-noise ratio (SCR). When the SCR is low, the calibration target is easily submerged in multipath interference due to statistical fluctuations. Therefore, a detection threshold is set using the calculated SCR to determine the appropriate operating mode.

[0077] When SCR < 1, the calibration target is easily completely submerged in multipath interference; when SCR > 3, the calibration target begins to appear. Based on the above SCR threshold, it is determined whether to initiate elevation angle scanning and spatial filtering processing against incoherent multipath interference. To further improve the separability of the calibration target from multipath interference, the equivalent multipath radar cross-section σ can be reduced. c To improve the SCR, it is usually necessary to increase the SCR to 5 or higher and use it as the target threshold for non-coherent multipath interference separation processing.

[0078] Furthermore, the impact of incoherent multipath interference on the calibration target echo can be reduced by decreasing the beamwidth of the weather radar or by using a calibration target with a large reference radar cross-section. The theoretical pointing elevation angle θ when the weather radar antenna is pointed at the calibration target is... el The pitch angle serves as the reference pitch angle for pitch angle scanning.

[0079] S42. Within a preset range centered on the reference elevation angle, determine multiple candidate elevation angles, adjust the weather radar antenna to each candidate elevation angle in sequence, transmit test pulse sequences to the calibration target, and collect the corresponding echo signals.

[0080] Using the reference pitch angle θ el Centered on the target, multiple candidate pitch angles θ are determined within a preset pitch scan range. i The preset pitch scan range is expressed as: [θ el -Δθscan, θ el +Δθscan]. Where Δθscan represents the single-sided scanning range relative to the reference elevation angle. Candidate elevation angles θ are sequentially selected within the elevation scanning range according to a preset scanning step size. i The weather radar antenna was then adjusted sequentially to each candidate elevation angle.

[0081] At each candidate pitch angle θ i The system transmits a test pulse sequence towards the calibration target and collects the corresponding echo signal. By conducting multi-angle tests near the reference elevation angle, the correlation between changes in the elevation direction of the weather radar antenna and changes in the echo power of the calibration target is obtained.

[0082] S43. Based on the frequency domain power of the echo signal at each candidate pitch angle, determine the pitch power distribution, and calculate the frequency domain power variance of the echo signal at each candidate pitch angle to obtain the pitch variance distribution.

[0083] For each candidate pitch angle θ i The acquired echo signal is processed in the frequency domain to obtain the corresponding frequency domain power data, and the candidate pitch angle θ is determined based on the frequency domain power data. i The echo power P iAccording to the order of the candidate elevation angles, the echo power P of each echo is... i The data is organized to form an elevation power distribution. The elevation power distribution is used to characterize the change in the received power of the calibration target as the elevation angle of the weather radar antenna changes.

[0084] Calculate the pitch angle θ for each candidate. i The frequency domain power variance of the lower echo signal, denoted as: Var(P|θ) i According to the order of candidate elevation angles, the power variance Var(P|θ) in each frequency domain is calculated. i The data is organized to form an elevation variance distribution. The frequency domain power variance is used to characterize the degree of fluctuation of the echo power in the frequency domain at the corresponding candidate elevation angle.

[0085] S44. Determine the candidate pitch angle corresponding to the minimum echo power based on the pitch power distribution, or determine the candidate pitch angle corresponding to the minimum frequency domain variance based on the pitch variance distribution, and use the determined candidate pitch angle as the target pitch angle.

[0086] In one determination method, the candidate pitch angles θ are compared. i Corresponding echo power Pi The candidate pitch angle corresponding to the minimum echo power is determined as the target pitch angle θ. opt At this candidate elevation angle, the gain of the weather radar antenna in the direction of the ground reflection point is lower than that of other candidate elevation angles, and the power of the ground reflected wave is correspondingly reduced.

[0087] In another method of determination, the candidate pitch angles θ are compared. i The corresponding frequency domain power variance Var(P|θ) i The candidate pitch angle corresponding to the minimum frequency domain power variance is determined as the target pitch angle θ. opt The small frequency domain power variance indicates that the echo power fluctuates weakly with frequency at the corresponding pitch angle, and the impact of ground multipath reflection on the echo power is relatively small.

[0088] The target pitch angle is determined by the minimum echo power or the minimum frequency domain power variance, which is used to select the pitch position with weaker ground multipath reflection from multiple candidate pitch angles.

[0089] S45. Adjust the weather radar antenna to the target elevation angle so that the elevation angle corresponding to the ground reflection point is located at or close to the position of minimum sidelobe gain or null position in the antenna gain corresponding to different elevation angles, thereby minimizing the spatial gain of the ground reflected wave.

[0090] Adjust and fix the weather radar antenna to the target elevation angle θ. opt Let θ be the equivalent elevation angle of the ground reflection point. ref θref =-arctan((h t +h r ) / R g If ), then G can be used. norm (θ) ref -θ opt The normalized antenna gain represents the direction of the ground reflection point relative to the target elevation angle.

[0091] By adjusting the target pitch angle θ opt This makes the elevation direction corresponding to the ground reflection point approach the sidelobe gain trough or null region in the antenna gain corresponding to different elevation angles, thereby reducing G. norm (θ) ref -θ opt This reduces the spatial gain of ground-reflected waves.

[0092] After the weather radar antenna is fixed at the target elevation angle, the gain attenuation characteristics at the edge of the antenna pattern and the low gain or null characteristics of the sidelobes are used to further reduce the power of the ground reflected wave, and subsequent measurements are performed at the target elevation angle.

[0093] S5. According to the frequency diversity parameters determined by the path difference, collect the echo power of the calibration target at different frequencies, and obtain the power statistics value through statistical processing.

[0094] The path difference between the direct echo and the multipath echo formed by ground reflection is small, and the difference in their propagation delay is much smaller than the pulse width of the weather radar. Therefore, they overlap in time and are difficult to separate using time gating. The radar cross-section of the calibration target remains relatively stable within the frequency diversity bandwidth, while the interference terms formed by coherent multipath change with the operating frequency, causing the received power to fluctuate periodically in the frequency domain.

[0095] When a change in operating frequency causes a 2π change in the phase difference between the direct echo and the multipath echo, the received power completes one multipath fading cycle, undergoing a complete process of decreasing from a larger value to a smaller value and then recovering to a larger value. If measurements are performed only at a single operating frequency, the selected operating frequency may happen to correspond to an interference trough or peak, resulting in a significantly lower or higher measured echo power, with calibration deviations potentially exceeding 10 dB.

[0096] Weather radar typically has a narrow single-pulse spectral bandwidth, for example, less than 0.6 MHz, making it difficult to cover one or more multipath fading frequency cycles within a single pulse. Therefore, an inter-pulse frequency diversity approach is employed, changing the operating frequency between adjacent pulses to acquire the linear echo power of the calibration target at multiple operating frequencies, and statistical processing is used to reduce power fluctuations caused by coherent interference.

[0097] Furthermore, such as Figure 8As shown, step S5 includes: S51. Determine the multipath fading frequency period between the direct echo and the multipath echo reflected from the ground based on the path difference between the direct path and the multipath path reflected from the ground.

[0098] Based on the path difference ΔL between the direct path and the multipath path reflected from the ground, the phase difference Δφ between the direct echo and the multipath echo is expressed as: Δφ=2πΔL / λ=2πΔLf / c. Where λ is the wavelength corresponding to the weather radar's operating frequency, f is the weather radar's operating frequency, and c is the electromagnetic wave propagation speed.

[0099] As the operating frequency f changes, the phase difference between the direct echo and the multipath echo changes accordingly. When the change in operating frequency causes a phase difference change of 2π, the received power completes one multipath fading cycle. This multipath fading frequency cycle is denoted as Δf. c Then: Δf c = c / ΔL. The larger the path difference ΔL, the longer the multipath fading frequency period Δf. c The smaller the path difference ΔL, the smaller the multipath fading frequency period Δf. c The larger the value, the better. The multipath fading frequency period is used to determine the interval and coverage of subsequent frequency sampling to avoid measurements being taken only near the interference peaks or troughs.

[0100] S52. Determine the frequency step and frequency diversity bandwidth based on the multipath fading frequency period, wherein the frequency step is no greater than one-third of the multipath fading frequency period, and the frequency diversity bandwidth covers at least three multipath fading frequency periods.

[0101] Let the frequency step be denoted as δ f Let the frequency diversity bandwidth be denoted as B. w Frequency step δ f Satisfy: δ f ≤(1 / 3)Δf c By stepping the frequency δ f Set to no greater than the multipath fading frequency period Δf c One-third of the frequency step size allows for multiple frequency sampling points within a single multipath fading frequency period, thus reflecting the periodic changes in echo power with the operating frequency. If the frequency step is too small, the echo power correlation between adjacent pulses is high, and more frequency sampling points are required while maintaining a constant frequency diversity bandwidth; if the frequency step is too large, some power fluctuation characteristics may be missed. When the weather radar operates in the S-band, the frequency step size δ... f It can be set to 2MHz to 5MHz to take into account the correlation between samples of different frequencies and the sampling effect on frequency domain fluctuations.

[0102] Frequency diversity bandwidth B w Satisfy: Bw ≥3Δf c The frequency diversity bandwidth should cover at least three multipath fading frequency periods, ensuring that the acquired echo power sequence contains multiple complete strength and weakness fluctuations. The more multipath fading frequency periods the frequency diversity bandwidth covers, the closer the statistical average of the echo power at different operating frequencies will be to the true echo power of the calibration target.

[0103] S53. Determine the number of frequency sampling points based on the frequency diversity bandwidth and frequency step, and configure the frequency diversity pulse sequence according to the frequency step and the number of frequency sampling points to configure the weather radar in inter-pulse frequency diversity mode.

[0104] Let N be the number of frequency sampling points, and then determine the frequency diversity bandwidth B. w and frequency step δ f Determine the number of frequency sampling points: N = [B w / δ f In the formula, [·] represents rounding up. The number of frequency sampling points N is used to determine the working frequency configuration in the frequency diversity pulse sequence, so that each working frequency follows the frequency step δ. f Arrange the frequencies so that the corresponding frequency coverage range meets the frequency diversity bandwidth B. w The setup requirements.

[0105] The initial operating frequency of the weather radar is denoted as f0, and the frequency is incremented by δ. f Configure the frequency diversity pulse sequence with the number of frequency sampling points N. Configure the weather radar in frequency agility mode or step frequency mode, so that the operating frequency changes between adjacent pulses, and samples coherent multipath fading in an inter-pulse frequency diversity manner, without relying on the spectral bandwidth of a single pulse to cover the multipath fading frequency period.

[0106] To improve the stability of statistical processing, 2N to 4N pulses can be emitted for accumulation. When the weather radar operates in the S-band, the operating center frequency f0 can be set to 3 GHz.

[0107] In one configuration example, the frequency step δ f Set to 2MHz, the frequency diversity pulse sequence consists of 64 pulses, with operating frequencies of f0, f0+2MHz, f0+4MHz, up to f0+126MHz. This configuration illustrates changing the operating frequency between adjacent pulses in fixed frequency steps. The number of pulses, frequency steps, and frequency coverage can be set according to the multipath fading frequency period.

[0108] S54. Keep the weather radar antenna at the target elevation angle, change the operating frequency of the weather radar between adjacent pulses in the frequency diversity pulse sequence according to the frequency step, collect the linear echo power of the calibrated target at each operating frequency, and obtain the echo power sequence arranged according to the operating frequency.

[0109] Keep the weather radar antenna at the target elevation angle θ opt This keeps incoherent multipath interference suppressed. Based on this, test pulses are transmitted according to the configured frequency diversity pulse sequence, with frequency steps δ between adjacent pulses. f Change the operating frequency of the weather radar.

[0110] Let f be the operating frequency of the nth pulse in the frequency diversity pulse sequence. n The corresponding wavelength is denoted as λ. n The linear echo power of the distance cell where the target is located at the operating frequency is denoted as P. n Under coherent multipath conditions, the echo power P n It can be characterized as: In the formula, Γ is the ground reflectance coefficient corresponding to the land surface type, and P... c To determine the residual incoherent multipath interference power generated by the main lobe edge or side lobe illuminating the ground after the weather radar antenna is adjusted to the target elevation angle, which is superimposed on the direct echo of the calibration target, multiple range cells that do not contain the echo energy of the calibration target are selected on both sides of the range cell where the calibration target is located. The echo power corresponding to the selected range cells is then averaged or medianized to obtain P. c .

[0111] With operating frequency f n Changes, wavelength λ n The corresponding changes in the phase relationship between direct echo and multipath echo cause the linear echo power P at different operating frequencies to change accordingly. n It exhibits obvious periodic fluctuations. For each pulse in the frequency diversity pulse sequence, the linear echo power of the distance cell where the calibration target is located is measured, and the operating frequency and echo power corresponding to each pulse are recorded, resulting in an echo power sequence arranged according to the operating frequency: {P1, P2, ..., P...} N In the example configuration using 64 pulses, the echo power corresponding to each operating frequency, from f0, f0+2MHz, f0+4MHz, up to f0+126MHz, was recorded. The echo power was recorded as a linear power value for subsequent arithmetic averaging.

[0112] S55. Perform statistical processing on the echo power sequence to obtain power statistics.

[0113] The statistical processing involves either arithmetic averaging or median filtering. Since the received power caused by coherent multipath propagation periodically increases or decreases with the operating frequency, when the frequency diversity bandwidth covers multiple multipath fading frequency periods, arithmetic averaging smooths the power fluctuations at different operating frequencies, while median filtering reduces the impact of extreme power values ​​such as interference peaks and troughs on the statistical results. This reduces measurement errors caused by a single operating frequency being at an interference peak or trough, and yields power statistics less affected by coherent multipath frequency fluctuations.

[0114] When the weather radar employs a dual-polarization operating mode, the linear echo power of the horizontally polarized channel and the vertically polarized channel at each operating frequency is collected separately, forming echo power sequences for the horizontally polarized channel and the vertically polarized channel. The echo power sequences of the two polarization channels are then subjected to the appropriate statistical processing to obtain the power statistics for the horizontally polarized channel and the vertically polarized channel, thus preserving the echo power characteristics of different polarization channels.

[0115] S6. Based on the power statistics, perform coherent multipath interference correction and invert the radar cross-section of the calibration target to obtain the interference separation result.

[0116] In this embodiment, coherent multipath interference refers to the coherent superposition of direct echoes and multipath echoes reflected from the ground at the receiving end, resulting in signal enhancement or cancellation. After frequency diversity acquisition and statistical processing, the coherent cross term in the coherent multipath gain term, which varies periodically with the operating frequency, is smoothed, or the influence of extreme values ​​such as interference peaks and troughs is suppressed. Based on the adopted statistical processing method and the ground reflection coefficient, the corresponding power correction relationship is determined, and the power statistics are corrected to obtain the direct echo power corresponding to the calibration target. Then, the radar cross-section of the calibration target is retrieved by combining the weather radar's operating parameters, measurement geometric parameters, and system loss.

[0117] Furthermore, such as Figure 9 As shown, step S6 includes: S61. Obtain the surface type of the location of the ground reflection point, and determine the ground reflection coefficient according to the preset correspondence between surface type and ground reflection coefficient.

[0118] In this step, the acquired ground reflectance coefficient is denoted as Γ. Γ is the complex ground reflectance coefficient, used to characterize the ground's reflection characteristics of radar waves. Based on the surface type of the ground area between the weather radar and the calibration target, the corresponding ground reflectance coefficient Γ is obtained through a preset correspondence. The preset correspondence includes: for dry surfaces, the modulus of the ground reflectance coefficient Γ can be 0.3–0.5; for water surfaces or wetlands, the modulus of the ground reflectance coefficient Γ can be 0.8–0.9. These value ranges are merely examples; specific values ​​can be determined based on pre-stored empirical data, test data, or calibration data.

[0119] S62. Based on the coherent superposition relationship between the direct echo and the multipath echo reflected from the ground, determine the coherent multipath gain term in the echo power at each operating frequency. The coherent multipath gain term is characterized by the ground reflection coefficient and the path phase difference. The path phase difference is determined by the path difference and the corresponding operating frequency.

[0120] Under the condition that the incoherent multipath interference has been suppressed by the pitch angle adjustment and spatial filtering in the aforementioned step S4, the coherent superposition relationship between the direct echo and the multipath echo reflected from the ground is considered.

[0121] Let P be the direct echo power corresponding to the calibration target. d Subtract the residual incoherent multipath interference power P at the operating frequency f. c The echo power is denoted as P. r (f). The direct echo and the multipath echo reflected from the ground are coherently superimposed at the receiving end, and the corresponding echo power can be expressed as: P r (f) = P d ·|1+Γe [－jφ（f）] | 2 In the formula, Γ is the ground complex reflection coefficient, φ(f) is the path phase difference corresponding to the operating frequency f, and |1+Γe [－jφ（f）] | 2 This is the coherent multipath gain term. As the operating frequency changes, the path phase difference and the coherent multipath gain term change periodically, causing the received power to fluctuate between interference enhancement and interference cancellation states.

[0122] When the power statistics are obtained by arithmetic averaging in step S55, the following steps S63 and S64 are executed: S63. Based on the coherent cross term in the coherent multipath gain term that varies with the operating frequency, determine the power bias relationship between the power statistics and the direct echo power corresponding to the calibration target under the frequency diversity bandwidth and frequency step.

[0123] Coherent multipath gain term |1+Γe [－jφ（f）] | 2This includes the power components corresponding to the direct echo, the power components corresponding to the ground-reflected echo, and coherent cross terms that vary with the path phase difference. The coherent cross terms change periodically with the operating frequency, causing the echo power at different operating frequencies to exhibit peaks and troughs.

[0124] When the determined frequency diversity bandwidth covers at least three multipath fading frequency cycles, and each frequency sampling point is distributed in frequency step within the frequency diversity bandwidth, the path phase difference corresponding to each frequency sampling point covers multiple complete change cycles. The coherent cross terms that change with the operating frequency tend to cancel each other out after arithmetic averaging, and the average value of the coherent multipath gain term approaches: 1 + |Γ|².

[0125] Therefore, the power statistics obtained by arithmetic averaging still retain the average power increment corresponding to the ground reflected echo, and a power bias relationship is formed between the power statistics and the direct echo power corresponding to the calibration target, characterized by 1 + |Γ|².

[0126] S64. Based on the power offset relationship, the sum of the square of the modulus of the ground reflection coefficient and 1 is determined as the multipath power offset factor, and the ratio of the power statistics value to the multipath power offset factor is determined as the direct echo power corresponding to the calibration target.

[0127] The multipath power bias factor is denoted as K, and determined based on the ground complex reflection coefficient Γ: K = 1 + |Γ|². The power statistical value obtained by arithmetic averaging is denoted as P. avg The direct echo power P corresponding to the calibration target d Represented as: P d =P avg / K.

[0128] The multipath power bias factor K is used to correct the ground reflection power increment retained after frequency averaging. When the magnitude of the ground complex reflection coefficient Γ is 0.3 to 0.5, the multipath power bias factor K is approximately 1.1 to 1.25; when the magnitude of the ground complex reflection coefficient Γ is 0.8 to 0.9, the multipath power bias factor K is approximately 1.6 to 1.8.

[0129] When the weather radar adopts a dual-polarization operating mode, the bias correction is performed by using the power statistics corresponding to the horizontal polarization channel and the vertical polarization channel respectively, so as to obtain the direct echo power corresponding to each polarization channel.

[0130] S65. Based on the transmit power, the antenna gain corresponding to the direction of the calibration target, the operating wavelength corresponding to the center frequency determined by the operating frequency, the slant range between the weather radar antenna and the calibration target, and the system loss, determine the inversion relationship between the direct echo power and the radar cross-section of the calibration target.

[0131] According to the transmission power P of the weather radart The antenna gain G corresponding to the calibration target direction, the operating wavelength λ corresponding to the weather radar center frequency f, the slant range R, and the system loss L, and the direct echo power P corresponding to the calibration target. d With the radar cross-section σ of the calibration target t The relationship between them is represented as: P d =P t G 2 λ 2 σ t / [(4π) 3 R 4 L]. This yields the radar cross-section σ of the calibration target. t Inversion relation: σ t =P d (4π) 3 R 4 L / (P) t G 2 λ 2 ).

[0132] When the weather radar adopts a dual-polarization operating mode, the radar cross-section inversion relationship of the corresponding polarization channel is determined based on the antenna gain, system loss and direct echo power of the horizontal polarization channel and the vertical polarization channel, respectively.

[0133] S66. Determine the radar cross-section of the calibration target based on the inversion relationship and the direct echo power, and use the radar cross-section of the calibration target as the interference separation result.

[0134] The determined direct echo power P d Substituting the established inversion relationship, the radar cross-section of the calibration target is obtained. This radar cross-section is the target parameter obtained by inversion after adjusting the target elevation angle to suppress incoherent multipath interference, reducing the influence of coherent multipath frequency fluctuations through frequency diversity and the adopted statistical processing, and obtaining the direct echo power according to the corresponding power correction relationship.

[0135] The radar cross-section σ of the calibration target obtained after multipath interference suppression and correction is... t The results are determined as interference separation results. When the weather radar adopts a dual-polarization operating mode, the radar cross-section of the calibration target under each polarization channel is determined based on the direct echo power corresponding to the horizontal polarization channel and the vertical polarization channel, as well as the antenna gain and system loss of the corresponding polarization channel. The radar cross-section corresponding to each polarization channel is then determined as the corresponding interference separation result.

[0136] In another embodiment, when median filtering is used, the power correction method corresponding to median filtering is used instead of the arithmetic mean power bias correction method in steps S63 and S64 to determine the direct echo power corresponding to the calibration target.

[0137] Specifically, the linear echo power collected at each operating frequency is arranged in ascending order, and the power value corresponding to the median of the echo power sequence is determined as the median power, denoted as P. m .

[0138] Under coherent multipath conditions, the coherent multipath gain term is expressed as: |1+Γe [－jφ（f）] | 2 ; The coherent multipath gain term varies periodically with the operating frequency, ranging from approximately 0 to (1 + |Γ|). 2 The signal fluctuates drastically within a certain range, causing the received power to vary between interference peaks and troughs. When the modulus of the ground complex reflection coefficient Γ approaches 1, the coherent multipath gain term can vary between a trough close to 0 and a peak close to 4. Therefore, the coherent echo power corresponding to the calibration target can range from close to 0 to 4P. d It fluctuates between.

[0139] Incoherent multipath interference power P c The power is relatively stable or changes slowly with the operating frequency. When using arithmetic averaging, the power statistics may still be affected by extreme power values ​​such as interference peaks and troughs; when using median filtering, the impact of extreme power values ​​close to interference troughs and peaks on the statistical results can be reduced, and power values ​​close to the middle level of the echo power sequence can be retained.

[0140] When the magnitude of the ground complex reflection coefficient Γ is close to 1, and the incoherent multipath interference power P is temporarily neglected... c Alternatively, if the median power is subtracted, the median power obtained by median filtering is usually closer to 2P. d The power level is approximately [value missing], and the specific value depends on the distribution of echo power at each operating frequency. Consider the incoherent multipath interference power P. c After that, the median power P m It can be approximated as: P m ≈P d (1+∣Γ∣ 2 )+P c .

[0141] The ground complex reflection coefficient Γ can be determined based on the surface type and the center frequency of the weather radar, or it can be inferred from the variation of average echo power at different calibration target heights. Based on the median power P... m Ground complex reflection coefficient Γ and incoherent multipath interference power P c Determine the direct echo power P corresponding to the calibration target. d .

[0142] The determined direct echo power P dSubstituting the given radar cross-section inversion relationship, we obtain the radar cross-section σ of the calibration target. t and the radar cross-section σ t The result was determined to be interference separation.

[0143] When the weather radar adopts a dual-polarization working mode, the echo power sequences corresponding to the horizontal polarization channel and the vertical polarization channel are subjected to median filtering to obtain the median power corresponding to each polarization channel. Based on the median power corresponding to each polarization channel, the ground complex reflection coefficient and the incoherent multipath interference power, the direct echo power corresponding to each polarization channel is determined. Based on the radar cross-section inversion relationship of the corresponding polarization channel determined in step S65, the radar cross-section of the calibration target under each polarization channel is obtained.

[0144] In addition, after step S6, the interference separation effect can be further evaluated by multipath suppression ratio and relative error of radar cross-section.

[0145] In one embodiment, the fluctuation levels of the echo power sequences before and after multipath interference separation processing are compared, and the multipath suppression ratio is denoted as: MSR = 10lg(ΔP) raw / ΔP res In the formula, ΔP raw To process the echo power sequence fluctuation index obtained under a single operating frequency and a fixed theoretical pointing elevation angle, ΔP res ΔP is the residual fluctuation index of the echo power sample sequence after target elevation angle adjustment and frequency diversity processing. raw With ΔP res The same calculation method is used, and the echo power values ​​included in the statistics are all linear power values, which can be in W or mW. dB values ​​are not used directly for calculation.

[0146] Residual fluctuation index ΔP res The standard deviation method can be used to calculate. In the formula, P n P represents the linear echo power value after processing the nth pulse. When the arithmetic mean is used, P cen The median power is the arithmetic mean of the echo power sequence. When median filtering is used, the median power can be used as the center value to calculate the residual dispersion. N is the total number of frequency diversity pulses.

[0147] The residual fluctuation index ΔPres can also be calculated using the peak-to-peak method: ΔP res =max(P1, ..., P N ) - min(P1, ..., P N ).

[0148] Accordingly, in the same multipath suppression ratio calculation, the unprocessed fluctuation index ΔP rawCalculate using the same method. ΔP res This is used to characterize the combined fluctuations caused by residual system noise, incompletely eliminated weak multipath components, and radar amplitude and phase instability after target elevation angle adjustment and frequency diversity processing. When MSR = 20dB, it means that the power fluctuation index after processing is approximately 1 / 100 of that before processing.

[0149] Further, the radar cross-section of the calibrated target obtained in step S66 is compared with the reference radar cross-section of the calibrated target to obtain the relative error ε of the radar cross-section. When ε < 5% and MSR ≥ 15dB, the target signal after interference separation, the radar cross-section of the calibrated target, and the calibration result are output; when ε ≥ 5% or MSR < 15dB, the processing parameters are adjusted, and the multipath interference separation process is re-executed. The adjusted processing parameters may include increasing the frequency diversity bandwidth B. w Alternatively, the target elevation angle scanning range Δθscan can be adjusted to further reduce the impact of coherent multipath interference and incoherent multipath interference on the calibration results.

[0150] Furthermore, embodiments of the present invention provide a far-field multipath interference separation system for a weather radar antenna, comprising: a parameter acquisition module for acquiring measurement geometric parameters, radar operating parameters, and antenna pattern parameters during far-field calibration of the weather radar antenna; a multipath geometry establishment module for establishing the multipath geometric relationship between the weather radar antenna and the calibration target based on the measurement geometric parameters, thereby determining the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground; and a multipath interference evaluation module for determining the ground multipath effect zone based on the measurement geometric parameters, radar operating parameters, and antenna pattern parameters, and determining the equivalent multipath radar cross-section based on the ground multipath effect zone and the corresponding ground scattering characteristics. The system includes a multipath interference index determination module, a pitch angle adjustment module, and an interference correction inversion module. The former is used to scan the weather radar antenna for pitch angle based on the multipath interference index, collect the echo power of the target at different pitch angles, determine the target pitch angle for suppressing incoherent multipath interference based on the echo power characteristics, and adjust the weather radar antenna to the target pitch angle. The latter is used to collect the echo power of the target at different frequencies according to the frequency diversity parameters determined by the path difference, and obtain power statistics after statistical processing.

[0151] Then, an embodiment of the present invention provides a weather radar antenna far-field multipath interference separation device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed by the at least one processor, and when the instructions are executed by the at least one processor, the at least one processor performs the weather radar antenna far-field multipath interference separation method as described above.

[0152] Furthermore, embodiments of the present invention provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the far-field multipath interference separation method for weather radar antennas as described above.

[0153] In summary, the embodiments of the present invention provide a method, system, device, and medium for separating far-field multipath interference from a weather radar antenna. By acquiring measurement geometric parameters, radar operating parameters, and antenna pattern parameters, the multipath geometric relationship between the weather radar antenna and the calibration target is established, and the path difference between the direct path and the multipath path reflected from the ground is determined. Furthermore, the ground multipath effect zone and the equivalent multipath radar cross-section are determined, and the multipath interference index is determined in combination with the reference radar cross-section of the calibration target. Thus, the multipath interference intensity in far-field calibration is quantitatively predicted using radar cross-section theory, avoiding blind testing under unknown multipath conditions, and providing a basis for the selection of elevation angle scanning and frequency diversity parameters.

[0154] This invention employs a multipath interference index to perform elevation angle scanning on a weather radar antenna. The target elevation angle is determined based on the echo power characteristics of the calibration target at different elevation angles, thereby reducing incoherent multipath interference from ground-reflected clutter in the spatial domain. Simultaneously, the frequency step, frequency diversity bandwidth, and number of frequency sampling points are determined based on the path difference between the direct path and the multipath path. Inter-pulse frequency diversity is used to collect echo power at different frequencies, and statistical processing is used to smooth periodic interference fluctuations caused by coherent multipath. Spatial filtering primarily utilizes the difference in elevation direction between the calibration target and the ground-reflected multipath components to suppress reflected echoes, while frequency diversity primarily utilizes the characteristic of path phase difference changing with the operating frequency. Statistical processing smooths interference peaks and troughs. The two processing mechanisms are different but work together. After joint processing by spatial filtering and frequency diversity, the multipath suppression ratio can reach 15dB to 20dB.

[0155] After frequency diversity processing, the multipath power bias factor is determined based on the ground reflection coefficient. The average ground reflection power increment retained in the power statistics is corrected to obtain the direct echo power corresponding to the calibration target. Combined with the weather radar's transmit power, antenna gain, operating wavelength, target slant range, and system loss, the radar cross-section of the calibration target is retrieved, thus achieving joint separation of incoherent and coherent multipath interference. Using this method, the relative error of the calibration target's radar cross-section measurement can be stably controlled within 3%, the amplitude error after separation can be less than 0.05 dB, the phase error can be less than 0.5°, and the phase information of the target echo can be retained when the corresponding phase measurement function is enabled.

[0156] This method is highly adaptable to changes in ground dielectric constant and humidity fluctuations. It does not require the laying of absorbing materials in the test field, nor does it require hardware modifications to existing weather radars. It can be applied to existing open test fields and reduce far-field calibration costs by upgrading the software of existing meteorological radars or telemetry radars and adjusting parameters in conjunction with their existing frequency agility functions, test instruments, and antenna servo systems.

[0157] When a weather radar adopts a dual-polarization operating mode, the horizontal polarization channel and the vertical polarization channel can be processed independently to reflect the influence of ground reflection on different polarization channels and cross-polarization components, thereby improving the reliability of polarization isolation calibration results.

[0158] Furthermore, when using 64 pulses for frequency diversity acquisition and combined with statistical averaging, the processing time can be less than 50ms. This method can be embedded into weather radar calibration software to achieve automatic closed-loop processing of parameter adjustment, echo acquisition, interference separation, effect evaluation, and result output, demonstrating good real-time performance and engineering application capabilities.

[0159] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0160] Furthermore, it should be noted that in the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0161] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims should be interpreted to include both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0162] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, then this invention should also include these modifications and variations.

Claims

1. A method for separating far-field multipath interference from a weather radar antenna, characterized in that, include: Acquire the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna; The multipath geometric relationship between the weather radar antenna and the calibration target is established based on the measured geometric parameters in order to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground. The ground multipath effect zone is determined based on the measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is determined based on the ground multipath effect zone and the corresponding ground scattering characteristics. The multipath interference index is determined by combining the reference radar cross-section of the calibration target. Based on the multipath interference index, the elevation angle of the weather radar antenna is scanned, the echo power of the calibration target at different elevation angles is collected, the target elevation angle for suppressing incoherent multipath interference is determined according to the echo power characteristics, and the weather radar antenna is adjusted to the target elevation angle. Based on the frequency diversity parameters determined by the path difference, the echo power of the calibration target at different frequencies is collected, and the power statistics are obtained through statistical processing. Based on the power statistics, coherent multipath interference correction is performed, and the radar cross-section of the calibration target is retrieved to obtain the interference separation result.

2. The method for separating far-field multipath interference from a weather radar antenna as described in claim 1, characterized in that, Obtain the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna, including: The measurement geometric parameters are obtained by acquiring the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target. The radar's transmission power, operating frequency, range resolution, and system loss are obtained to acquire the radar's operating parameters. The antenna radiation pattern parameters are obtained by acquiring the azimuth beamwidth, sidelobe level, and antenna gain at different elevation angles of the weather radar antenna.

3. The method for separating far-field multipath interference from a weather radar antenna as described in claim 2, characterized in that, Based on the measured geometric parameters, the multipath geometric relationship between the weather radar antenna and the calibration target is established to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground, including: Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, the direct propagation relationship from the weather radar antenna to the calibration target and the reflection propagation relationship from the weather radar antenna to the calibration target via the ground reflection point are established, and the multipath geometric relationship is obtained. Based on the multipath geometry, the propagation path between the weather radar antenna and the calibration target that does not pass through the ground reflection point is determined as the direct path. The propagation segment from the weather radar antenna to the ground reflection point and the propagation segment from the ground reflection point to the calibration target are combined in the propagation order to obtain the multipath path that passes through the ground reflection. Based on the ground clearance of the weather radar antenna feed center, the ground clearance of the calibration target, and the slant distance between the weather radar antenna and the calibration target, the increased propagation distance of the multipath path relative to the direct path is calculated under far-field conditions according to the two-path propagation path difference relationship. The two-path propagation path difference relationship indicates that the increased propagation distance is directly proportional to the product of the ground clearance of the weather radar antenna feed center and the ground clearance of the calibration target, and inversely proportional to the slant distance. The increased propagation distance of a multipath path relative to a direct path is defined as the path difference between the direct path and the multipath path.

4. The method for separating far-field multipath interference from a weather radar antenna as described in claim 2, characterized in that, The ground multipath effect zone is determined based on measured geometric parameters, radar operating parameters, and antenna pattern parameters. The equivalent multipath radar cross-section is determined based on the ground multipath effect zone and corresponding ground scattering characteristics. Finally, multipath interference indicators are determined by combining these indicators with the reference radar cross-section of the calibrated target, including: The projection angle parameters are determined based on the ground height of the weather radar antenna feed center and the slant distance between the weather radar antenna and the calibration target. The slant distance and range resolution are then projected onto the ground according to the projection angle parameters to obtain the projected distance and range resolution range on the ground. The ground multipath effect area of ​​the main beam is determined based on the projection distance, range resolution range, and azimuth beamwidth; the ground multipath effect area of ​​the sidelobe is determined based on the projection distance and range resolution range. The effective area of ​​the main beam is determined based on the coverage of the ground multipath effect region of the main beam in the azimuth and range directions, and the effective area of ​​the sidelobe is determined based on the coverage of the ground multipath effect region of the sidelobe in the circumferential and range directions. The radar cross-section of the main beam multipath is determined based on the effective area of ​​the main beam, the ground scattering coefficient in the ground multipath effect area of ​​the main beam, and the antenna gain at the corresponding elevation angle. The sidelobe multipath radar cross-section is determined based on the sidelobe effective area, the ground scattering coefficient within the sidelobe ground multipath effect region, and the sidelobe level. The radar cross-sections of the main beam multipath and the sidelobe multipath are combined to obtain the equivalent multipath radar cross-section, and the signal-to-clutter ratio is determined by combining it with the reference radar cross-section, which serves as a multipath interference indicator.

5. The method for separating far-field multipath interference from a weather radar antenna as described in claim 3, characterized in that, Based on multipath interference indicators, the weather radar antenna is scanned at elevation angles to collect the echo power of the calibrated target at different elevation angles. The target elevation angle for suppressing incoherent multipath interference is determined based on the echo power characteristics, and the weather radar antenna is adjusted to the target elevation angle, including: When the multipath interference index meets the preset scanning conditions, the elevation angle of the weather radar antenna is scanned, and the reference elevation angle of the weather radar antenna pointing to the calibration target is determined based on the height difference between the feed center of the weather radar antenna and the calibration target and the slant distance between the weather radar antenna and the calibration target. Multiple candidate elevation angles are determined within a preset range centered on the reference elevation angle. The weather radar antenna is then adjusted to each candidate elevation angle in sequence, and a test pulse sequence is transmitted to the calibration target and the corresponding echo signal is collected. Based on the frequency domain power of the echo signal at each candidate pitch angle, the pitch power distribution is determined, and the frequency domain power variance of the echo signal at each candidate pitch angle is calculated to obtain the pitch variance distribution. The candidate pitch angle corresponding to the minimum echo power is determined based on the pitch power distribution, or the candidate pitch angle corresponding to the minimum frequency domain variance is determined based on the pitch variance distribution, and the determined candidate pitch angle is used as the target pitch angle. Adjust the weather radar antenna to the target elevation angle so that the elevation angle corresponding to the ground reflection point is located at or close to the position of minimum sidelobe gain or null position in the antenna gain corresponding to different elevation angles, thereby minimizing the spatial gain of the ground reflected wave.

6. The method for separating far-field multipath interference from a weather radar antenna as described in claim 3, characterized in that, Based on the frequency diversity parameters determined by the path difference, the echo power of the calibration target at different frequencies is collected, and statistical power statistics are obtained through statistical processing, including: The multipath fading frequency period between the direct echo and the multipath echo reflected from the ground is determined based on the path difference between the direct path and the multipath echo reflected from the ground. The frequency step and frequency diversity bandwidth are determined based on the multipath fading frequency period. The frequency step is no more than one-third of the multipath fading frequency period, and the frequency diversity bandwidth covers at least three multipath fading frequency periods. The number of frequency sampling points is determined based on the frequency diversity bandwidth and frequency step, and the frequency diversity pulse sequence is configured according to the frequency step and the number of frequency sampling points to configure the weather radar into inter-pulse frequency diversity mode. Keep the weather radar antenna at the target elevation angle, change the operating frequency of the weather radar between adjacent pulses in the frequency diversity pulse sequence according to the frequency step, collect the linear echo power of the target at each operating frequency, and obtain the echo power sequence arranged according to the operating frequency. The echo power sequence is statistically processed to obtain power statistics.

7. The method for separating far-field multipath interference from a weather radar antenna as described in claim 6, characterized in that, Based on power statistics, coherent multipath interference correction is performed, and the radar cross-section of the calibration target is retrieved to obtain the interference separation results, including: Obtain the surface type of the location of the ground reflection point, and determine the ground reflection coefficient according to the preset correspondence between surface type and ground reflection coefficient; Based on the coherent superposition relationship between direct echo and multipath echo reflected from the ground, the coherent multipath gain term in the echo power at each operating frequency is determined. The coherent multipath gain term is characterized by the ground reflection coefficient and the path phase difference, and the path phase difference is determined by the path difference and the corresponding operating frequency. Based on the coherent cross term in the coherent multipath gain term that varies with the operating frequency, the power bias relationship between the power statistics and the direct echo power corresponding to the calibration target is determined under the frequency diversity bandwidth and frequency step. Based on the power offset relationship, the sum of the square of the modulus of the ground reflection coefficient and 1 is determined as the multipath power offset factor, and the ratio of the power statistics value to the multipath power offset factor is determined as the direct echo power corresponding to the calibration target. Based on the transmit power, the antenna gain corresponding to the direction of the calibration target, the operating wavelength corresponding to the center frequency determined by the operating frequency, the slant range between the weather radar antenna and the calibration target, and the system loss, the inversion relationship between the direct echo power and the radar cross-section of the calibration target is determined. The radar cross-section of the calibration target is determined based on the inversion relationship and the direct echo power, and the radar cross-section of the calibration target is used as the result of interference separation.

8. A far-field multipath interference separation system for a weather radar antenna, characterized in that, include: The parameter acquisition module is used to acquire the measurement geometric parameters, radar operating parameters, and antenna pattern parameters in the far-field calibration of the weather radar antenna. The multipath geometry establishment module is used to establish the multipath geometric relationship between the weather radar antenna and the calibration target based on the measured geometric parameters, so as to determine the path difference between the direct path from the weather radar antenna to the calibration target and the multipath path reflected from the ground. The multipath interference evaluation module is used to determine the ground multipath effect zone based on the measured geometric parameters, radar operating parameters and antenna pattern parameters, determine the equivalent multipath radar cross-section based on the ground multipath effect zone and the corresponding ground scattering characteristics, and determine the multipath interference index in combination with the reference radar cross-section of the calibration target. The elevation angle adjustment module is used to scan the elevation angle of the weather radar antenna based on the multipath interference index, collect the echo power of the calibration target at different elevation angles, determine the target elevation angle to suppress incoherent multipath interference based on the echo power characteristics, and adjust the weather radar antenna to the target elevation angle. The frequency diversity processing module is used to collect the echo power of the calibration target at different frequencies according to the frequency diversity parameters determined by the path difference, and obtain the power statistics value through statistical processing. The interference correction and inversion module is used to perform coherent multipath interference correction based on power statistics and invert the radar cross-section of the calibration target to obtain the interference separation result.

9. A far-field multipath interference separation device for a weather radar antenna, characterized in that, include: At least one processor; And, a memory that is communicatively connected to at least one processor; The memory stores instructions that can be executed by at least one processor. When the instructions are executed by at least one processor, the at least one processor performs the weather radar antenna far-field multipath interference separation method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing computer-executable instructions thereon, characterized in that, When the computer-executable instructions are executed by the processor, they implement the weather radar antenna far-field multipath interference separation method as described in any one of claims 1 to 7.

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