Lightning transient electric field detection system, method and time difference location network

Abstract

The application provides a lightning transient electric field detection system, method and time difference positioning network, which comprises a vertical spherical cap induction electrode and four horizontal spherical cap induction electrodes, is combined with a front-end signal conditioning channel and a digital signal processing unit, and can perform horizontal electric field component decomposition, single-station three-dimensional direction determination and radiation field polarization analysis based on five-way output signals. The scheme can realize synchronous measurement of three components of lightning transient electric field, and breaks through the fundamental limitation of traditional fast antennas which can only measure the vertical electric field component. Moreover, based on the vertical and horizontal electric field components, single-station three-dimensional direction determination can be realized, and real-time determination of the three-dimensional direction of lightning signals can be realized at a single station without the cooperation of multiple stations, and then, after the introduction of the pulse correlation of time difference positioning, the pulse mis-correlation rate can be reduced. In addition, the synchronous measurement of the vertical and horizontal electric field components also provides a complete data basis for the polarization analysis of the lightning radiation field, and perfect radiation field polarization parameters can be extracted.

Description

Technical Field

[0001] This invention relates to the field of atmospheric electrical detection technology, and more specifically, to a lightning transient electric field detection system, method, and time difference positioning network. Background Technology

[0002] Existing lightning transient electric field detection systems (fast antennas) are all scalar sensors. Their sensing electrodes (plates, spheres, or hemispheres) are symmetrical about the vertical axis, and can only measure the vertical component Ez of the atmospheric electric field. In a uniform electric field, the induced charges generated by the horizontal electric field components Ex or Ey on the symmetrical sensing electrodes cancel each other out about the axis of symmetry, resulting in zero net charge and zero output signal. This fundamental physical limitation causes traditional fast antenna systems to completely lose information about the horizontal component of the electric field.

[0003] However, the electric field of lightning is essentially a three-dimensional vector field E = (Ex, Ey, Ez), whose horizontal component carries rich physical information about the orientation of the lightning channel, the direction of horizontal propagation, and the polarization state of the radiation field.

[0004] Furthermore, in current multi-station lightning location networking (TDOA / TOA method), each station independently records the arrival time of lightning pulses and inverts the discharge location through time difference relationships. When multiple lightning processes are active simultaneously, the pulses recorded by different stations may come from different lightning events. The search space for pulse association grows exponentially with the number of stations and the intensity of lightning activity, becoming a core bottleneck restricting the speed of real-time location calculation.

[0005] If each station can independently determine the direction of arrival of the signal, the search space for pulse correlation will be reduced from all directions to a narrow sector consistent with the direction of arrival, significantly reducing the false match rate and improving computational efficiency. However, there is currently no commercially available or publicly reported broadband lightning fast antenna system capable of determining the direction of arrival at a single station.

[0006] In the fields of radio astronomy and communications, antenna polarization measurement technology is quite mature, but its operating frequency is usually above several hundred megahertz, and the antenna size is on the order of wavelength. Lightning fast antennas operate in the subhertz to 10 MHz frequency band, corresponding to wavelengths from tens of meters to almost infinity, and the design concepts of traditional polarized antennas cannot be directly applied.

[0007] It is evident that existing lightning fast antenna systems have shortcomings such as being able to measure only the vertical component of the electric field and being unable to determine the direction of arrival and perform polarization analysis at a single station. Summary of the Invention

[0008] The purpose of this invention is to provide a lightning transient electric field detection system, method, and time difference positioning network to achieve synchronous measurement of the three-component electric field, single-station three-dimensional direction determination, and radiation field polarization analysis.

[0009] In a first aspect, the present invention provides a lightning transient electric field detection system, comprising a vertical measurement unit, a horizontal measurement unit, a grounding reference plate assembly, a front-end signal conditioning channel, and a digital signal processing unit; The vertical measurement unit includes a vertical spherical cap induction electrode with its axis of symmetry set vertically and its opening facing upward, used to measure the vertical electric field component of the transient electric field of lightning. The horizontal measurement unit includes four horizontal spherical cap sensing electrodes, whose axes of symmetry are horizontally arranged along the four basic azimuth directions. The four horizontal spherical cap sensing electrodes are arranged back to back, with their convex surfaces facing the center of the array and their openings facing outwards in their respective azimuth directions. The grounding reference plate assembly includes two mutually perpendicular vertical conductive plates and a horizontal conductive plate. The two vertical conductive plates intersect orthogonally in the horizontal plane, and their orientations are at a 45° angle to the axis of symmetry of the two adjacent horizontal spherical cap induction electrodes. Each horizontal spherical cap induction electrode is located within a 90° dihedral reflector formed by the two vertical conductive plates. The horizontal conductive plate is disposed below the vertical spherical cap induction electrode and serves as a grounding reference plane for the vertical spherical cap induction electrode to measure the vertical electric field component. The front-end signal conditioning channel includes five channels for outputting the output signals of the five spherical cap sensing electrodes; The digital signal processing unit is used to receive five output signals and perform vector decomposition, single-station three-dimensional direction of arrival determination, and radiation field polarization analysis based on the five output signals.

[0010] In an optional embodiment, the lightning transient electric field detection system further includes an insulating support assembly, which includes a gasket disposed between each spherical cap induction electrode and the grounding reference plate assembly, and the surface of the vertical conductive plate is provided with a groove. The opening edge of each horizontal spherical cap sensing electrode is embedded in the groove through the gasket.

[0011] In an optional implementation, the five spherical cap sensing electrodes are manufactured using the same mold and have the same spherical radius and radian angle; Among them, the four horizontal spherical cap sensing electrodes are arranged in a square when viewed from above. The opening edges of two adjacent horizontal spherical cap sensing electrodes are tangent, and the four tangent points form a square. The vertical spherical cap induction electrode appears circular when viewed from above, and its diameter is equal to the distance between two adjacent tangent points.

[0012] In an optional implementation, the digital signal processing unit is configured to perform horizontal electric field component decomposition in the following manner: Differential operation is performed on the output signals of two sets of opposing horizontal spherical cap induction electrodes among the four horizontal spherical cap induction electrodes to obtain the horizontal electric field component of the lightning transient electric field.

[0013] In an optional implementation, the digital signal processing unit is used to perform single-station three-dimensional orientation determination in the following manner: The azimuth angle of the signal in the horizontal plane is calculated based on the output signals of the four horizontal spherical cap induction electrodes. The horizontal electric field component is calculated by combining the horizontal electric field component to obtain the horizontal electric field magnitude. The elevation angle of the signal is calculated based on the horizontal electric field magnitude and the vertical electric field component.

[0014] In an optional implementation, the digital signal processing unit is further configured to determine weighting coefficients based on the azimuth angle of arrival, and to perform a weighted summation of the five output signals based on the weighting coefficients to enhance the signal-to-noise ratio.

[0015] In an optional implementation, the digital signal processing unit is used to perform radiation field polarization analysis in the following manner: The horizontal electric field components are subjected to Hilbert transform to obtain analytical signals. Instantaneous amplitude and instantaneous phase difference are calculated based on the analytical signals. Stokes parameters are calculated within the pulse time window based on the instantaneous amplitude and instantaneous phase difference. Radiation field polarization parameters are calculated based on the Stokes parameters. The radiation field polarization parameters include the azimuth angle of the major axis of the polarization ellipse, the ellipticity angle, the rotation direction, and the linear polarizability.

[0016] In an optional implementation, the digital signal processing unit is further configured to perform matrix inverse operation on the five output signals according to the mutual coupling calibration matrix, so as to eliminate the electromagnetic mutual coupling effect between adjacent spherical cap induction electrodes.

[0017] Secondly, the present invention provides a method for detecting transient electric fields during lightning strikes, applied to the transient electric field detection system for lightning strikes described in any of the foregoing embodiments, the method comprising: Five spherical cap induction electrodes are used to synchronously sense the transient electric field changes of lightning and output five output signals. Differential operation is performed on the four output signals corresponding to the four horizontal spherical cap induction electrodes in the five output signals to extract the horizontal electric field component of the lightning transient electric field. The signal arrival azimuth angle is calculated based on the horizontal electric field component, and the signal arrival elevation angle is estimated based on the horizontal electric field magnitude and the vertical electric field component. The weighting coefficients are determined based on the azimuth angle of arrival, and the five output signals are digitally beamformed and combined based on the weighting coefficients. The radiation field polarization parameters are extracted based on the horizontal electric field components and using Hilbert transform and Stokes parameters.

[0018] Thirdly, the present invention provides a time-difference positioning network, including a central processing station and a lightning transient electric field detection system as described in any one of the foregoing embodiments: Each of the lightning transient electric field detection systems is used to send the signal information obtained from the single-station three-dimensional determination for the same lightning event to the central processing station; The central processing station is used to filter out signal information pointing to the same area in space by combining the signal information sent by multiple lightning transient electric field detection systems, and to perform time difference of arrival positioning based on the filtered signal information to determine the lightning location information.

[0019] This invention provides a lightning transient electric field detection system, method, and time-difference positioning network. The detection system, through a vertical measurement unit including a vertical spherical cap induction electrode and a horizontal measurement unit including four horizontal spherical cap induction electrodes, combined with a front-end signal conditioning channel and a digital signal processing unit, can perform horizontal electric field component decomposition, single-station three-dimensional direction of arrival determination, and radiation field polarization analysis based on five output signals. This scheme can achieve simultaneous measurement of the vertical and horizontal electric field components of the lightning transient electric field, overcoming the fundamental limitation of traditional fast antennas that can only measure the vertical electric field component. Furthermore, based on the horizontal and vertical electric field components, single-station three-dimensional direction of arrival determination can be achieved, enabling real-time determination of the three-dimensional direction of arrival of lightning signals at a single station without multi-station cooperation. Introducing pulse correlation for time-difference positioning further reduces the pulse false correlation rate. In addition, the simultaneous measurement of the vertical and horizontal electric field components provides a complete data foundation for the polarization analysis of the lightning radiation field, allowing for the extraction of comprehensive radiation field polarization parameters. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A top-view structural schematic diagram of the lightning transient electric field detection system provided in an embodiment of the present invention; Figure 2 A side-view structural schematic diagram of the lightning transient electric field detection system provided in an embodiment of the present invention; Figure 3This is a system block diagram of the five front-end signal conditioning channels and digital signal processing unit in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the principle of single-station direction determination in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the principle of radiation field polarization parameter extraction in an embodiment of the present invention; Figure 6 A flowchart of a lightning transient electric field detection method provided in an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the application of a multi-station time difference positioning network in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will now be described with reference to the accompanying drawings in the embodiments of the present invention.

[0023] Please refer to the following: Figure 1 and Figure 2 This invention provides a lightning transient electric field detection system, which includes a vertical measurement unit, a horizontal measurement unit, a grounding reference plate assembly, a front-end signal conditioning channel, and a digital signal processing unit.

[0024] The vertical measurement unit includes a vertical spherical cap induction electrode with its axis of symmetry set vertically and its opening facing upward, used to measure the vertical electric field component of the transient electric field of lightning.

[0025] The horizontal measurement unit includes four horizontal spherical cap induction electrodes, whose axes of symmetry are set horizontally along the four basic azimuth directions (East E, South S, West W, North N). The four horizontal spherical cap induction electrodes are arranged back to back, with their respective domes facing the center of the array and their openings facing outwards in their respective azimuth directions.

[0026] The grounding reference plate assembly includes two mutually perpendicular vertical conductive plates and a horizontal conductive plate. The two vertical conductive plates intersect orthogonally in the horizontal plane, with their orientations forming a 45° angle with the axis of symmetry of each of the two adjacent horizontal spherical cap induction electrodes. Each horizontal spherical cap induction electrode is located within a 90° dihedral reflector formed by the two vertical conductive plates.

[0027] A horizontal conductive plate is placed below the vertical spherical cap induction electrode, serving as a ground reference plane for the vertical spherical cap induction electrode to measure the vertical electric field component.

[0028] The front-end signal conditioning channel includes five channels for outputting the output signals of the five spherical cap sensing electrodes.

[0029] The digital signal processing unit is used to receive five output signals and perform horizontal electric field component decomposition, single-station three-dimensional direction of arrival determination, and radiation field polarization analysis based on the five output signals.

[0030] In this embodiment, the five spherical cap sensing electrodes are manufactured using the same mold and have the same spherical radius and radian angle. For example, the spherical radius can be R = 35 cm, and the radian angle can be α = 90°. Table 1 shows the relevant parameters and performance indicators of the detection system in this embodiment.

[0031] Table 1 System-related parameters and performance indicators

[0032] The four horizontal spherical cap sensing electrodes are arranged in a square from a top-down view. The opening edges of any two adjacent horizontal spherical cap sensing electrodes are tangent, and the four tangent points form a square. Each horizontal spherical cap sensing electrode is projected as a 90° arc, and the arcs of adjacent electrodes are tangent at their opening edges. The side length of the square formed is L = R × .

[0033] The vertical spherical cap induction electrode appears circular when viewed from above, and its diameter is equal to the distance between two adjacent tangent points.

[0034] like Figure 1 As shown, five spherical cap induction electrodes and a set of three-dimensional orthogonal ground reference plate assemblies constitute a spherical cap vector antenna array. The array center is provided with the aforementioned vertical spherical cap induction electrode. The diameter of the vertical spherical cap induction electrode is equal to the distance L between two adjacent tangent points, that is, the side length L = R × 10⁻⁶. ≈ 49.5 cm.

[0035] The grounding reference plate assembly consists of two mutually perpendicular vertical conductive plates and one horizontal conductive plate. These three plates intersect at the center of the array to form a three-dimensional orthogonal coordinate frame structure. The two vertical conductive plates intersect orthogonally in the horizontal plane, their orientation forming a 45° angle with the N / E / S / W azimuth directions, i.e., extending along the NW–SE and NE–SW directions respectively. This arrangement ensures that each horizontal spherical cap induction electrode is precisely located within the 90° dihedral angle formed by the two vertical conductive plates, with its opening direction directly opposite the diagonal bisector (i.e., the azimuth direction covered by that spherical cap induction electrode). The horizontal conductive plate is positioned below the vertical spherical cap induction electrodes, providing a grounding reference for Ez measurements.

[0036] Figure 2The spatial relationship between the top vertical spherical cap sensing electrode and the two horizontal spherical cap sensing electrodes at the W and E positions is shown. The arc of the vertical spherical cap sensing electrode extends from the left tangent point, through the bottom (dome facing down), to the right tangent point, forming a downward-concave 90° arc. The two horizontal spherical cap sensing electrodes on both sides extend downward from the tangent points, with their respective domes concave inwards, forming a 90° arc with the same curvature as the top spherical cap. The three arcs connect seamlessly at the tangent points.

[0037] The opening edge (rim) of each horizontal spherical cap induction electrode is an arc, with the two ends of the arc located on both sides of the vertical conductive plate.

[0038] In this embodiment, the lightning transient electric field detection system further includes an insulating support assembly. The insulating support assembly includes a gasket disposed between each spherical cap induction electrode and the grounding reference plate assembly. A groove is formed on the surface of the vertical conductive plate. The opening edge of each horizontal spherical cap induction electrode is embedded in the groove via the gasket. This gasket can be a polytetrafluoroethylene (PTFE) insulating gasket. Its thickness can be 2–5 mm, and its insulation withstand voltage is not less than 100 kV.

[0039] In this embodiment, a uniform gap of 2–5 mm is maintained between the opening edge of the horizontal spherical cap induction electrode and the surface of the vertical conductive plate through a PTFE insulating gasket. The opening edge is embedded in a groove, and the PTFE gasket is laid at the bottom of the groove to achieve precise positioning and uniform gap control.

[0040] In this embodiment, the two orthogonal vertical conductive plates behind each horizontal spherical cap induction electrode form a classic 90° dihedral reflector structure. In antenna theory, a 90° dihedral reflector is equivalent to generating three virtual image sources (one on each of the two reflecting surfaces, plus one at the corner) through the mirror effect. It has the maximum response to signals coming directly in front of the opening, and the response to signals coming from the back side (through the direction of the vertical conductive plates) and the sides is significantly attenuated.

[0041] Empirical estimates suggest that the front-to-back ratio of a 90° angle reflector can reach 15–20 dB, significantly higher than the 6–10 dB of a single planar ground plane. This means that each horizontally oriented spherical cap sensing electrode is 30–100 times more sensitive in the direction directly in front than in the direction behind, exhibiting excellent directional selectivity.

[0042] It should be noted that in the operating frequency band of fast antennas (subhertz to 10 MHz), the array size (approximately 1 m) is much smaller than the shortest operating wavelength (30 m @ 10 MHz), and the entire array is in the electrically quasi-static region. In this case, the enhancement effect of the corner reflector is mainly manifested in the improvement of the boundary conditions of the electrostatic and induced fields, rather than the far-field pattern concept based on path difference in traditional antenna theory. The specific enhancement amount of directional selectivity needs to be determined through full-wave electromagnetic simulation (such as HFSS).

[0043] In the aforementioned spherical cap vector antenna array, five spherical cap sensing electrodes can synchronously sense transient electric field changes during lightning strikes, outputting five signals. Based on this, the front-end signal conditioning channel of the detection system includes five channels for processing these five signals and outputting the output signals from the five spherical cap sensing electrodes.

[0044] Please refer to the following: Figure 3 In this embodiment, each of the five spherical cap sensing electrodes is equipped with an independent front-end signal conditioning channel. Each channel includes a proximal buffer module (located near the proximal end of the cap), an analog signal cable, and amplification and digitization circuitry integrated into the base-end signal processing and interface host chassis. The proximal buffer module includes a junction field-effect transistor source follower, a bootstrap bias circuit, and a graded protection circuit, and is located near the proximal end of the corresponding spherical cap sensing electrode.

[0045] Five digital output signals are fed into a digital signal processing unit (DSP), which can be implemented using an FPGA or an embedded processor. The DSP can perform tasks such as horizontal electric field component decomposition, single-station three-dimensional direction of arrival determination, and radiation field polarization analysis. In addition, it can also perform digital beamforming and mutual coupling correction.

[0046] Specifically, the digital signal processing unit can perform horizontal electric field component decomposition in the following manner: Differential operation is performed on the output signals of two sets of opposing horizontal spherical cap induction electrodes among the four horizontal spherical cap induction electrodes to obtain the horizontal electric field component of the lightning transient electric field.

[0047] In this embodiment, the horizontal electric field components include Ex and Ey, wherein Ex is proportional to the difference between the output signals of the spherical cap induction electrode in the east-west direction and Ey is proportional to the difference between the output signals of the spherical cap induction electrode in the north-south direction.

[0048] Specifically, the calculation formula is as follows:

[0049] in, VN , VE , VS , VWThe output signals of the four horizontally shaped spherical cap induction electrodes are respectively located in the north, east, south, and west directions. kE and kN The proportional coefficient is determined by calibration. The output signals of each pair of opposing spherical cap induction electrodes are differentially processed to eliminate common-mode interference and simultaneously extract the electric field component along that direction.

[0050] Furthermore, the digital signal processing unit is used to perform single-station three-dimensional orientation determination in the following manner: The azimuth angle of the signal in the horizontal plane is calculated based on the output signals of the four horizontal spherical cap induction electrodes. The horizontal electric field magnitude is calculated by combining the horizontal electric field components. The elevation angle of the signal is calculated based on the horizontal electric field magnitude and the vertical electric field components.

[0051] Please refer to the following: Figure 4 When the lightning radiation signal reaches the array, it produces responses of different amplitudes on the four horizontally shaped spherical cap induction electrodes. Because each spherical cap induction electrode is directionally selective, the one facing the signal source has the strongest response, while the one facing away has the weakest.

[0052] Taking a signal from a direction 30° north of east as an example: the N-shaped cap sensing electrode has the strongest response, followed by the E-shaped cap sensing electrode, the S-shaped cap sensing electrode has the weakest response (facing away), and the W-shaped cap sensing electrode is also relatively weak.

[0053] The horizontal electric field components are obtained through the difference operation shown below:

[0054] Based on the horizontal electric field component, the azimuth angle of arrival of the signal in the horizontal plane is calculated using the following formula. θ (theta):

[0055] The magnitude of the horizontal electric field is calculated using the following formula based on the horizontal electric field component. Eh :

[0056] The elevation angle of arrival (φ) of the signal can be further estimated using the ratio of the vertical electric field component Ez to the horizontal electric field component Eh, which is φ = arctan(Eh / Ez). This relationship is based on the decomposition of the vertically polarized radiation field: for a vertically polarized plane wave arriving from the elevation angle φ (phi), the ratio of its vertical electric field component to the horizontal electric field component is Ez / Eh = cos(φ) / sin(φ). The azimuth angle θ and the elevation angle φ together constitute the three-dimensional direction of arrival (DOA) estimate of the signal.

[0057] This elevation angle estimate is most reliable under far-field radiation conditions (distances much greater than the lightning channel length) and when the lightning channel is dominated by a vertical component. For far-field vertically polarized radiation (such as long-range return stroke radiation fields), this elevation angle estimate can provide a rough indication of the lightning discharge height. Under near-field conditions (distances <50 km), the electrostatic and induced field components are significant, reducing the reliability of the elevation angle estimate, and it needs to be distinguished in conjunction with waveform characteristics.

[0058] The accuracy of the azimuth determination depends on: (a) the steepness of the directional response function of each spherical cap induction electrode (enhanced by the 90° angle reflector); (b) the signal-to-noise ratio; and (c) the amplitude and delay consistency of the four channels. Under typical operating conditions (signal-to-noise ratio > 20 dB), an azimuth determination accuracy better than ±15° is expected to be achieved.

[0059] In this embodiment, the digital signal processing unit is also used to determine the weighting coefficients based on the azimuth angle of arrival, and to perform weighted summation on the five output signals based on the weighting coefficients to enhance the signal-to-noise ratio.

[0060] Specifically, the digital signal processing unit performs digital beamforming combining, and performs a weighted summation of the five output signals based on the estimated azimuth angle θ of arrival, which can be characterized as follows:

[0061] in, V_combined This represents the result of a weighted summation of the five output signals, with weighting coefficients. wtop, wN, wE, wS, wW Based on the direction θ, the components in the signal direction are coherently superimposed, while noise in other directions is not coherently superimposed. Theoretically, this can improve the signal-to-noise ratio by up to [percentage missing]. 10 times (approximately 7 dB).

[0062] In this embodiment, the digital signal processing unit is used to perform radiation field polarization analysis in the following manner: Hilbert transforms are performed on the horizontal electric field components to obtain analytical signals. Instantaneous amplitude and instantaneous phase difference are calculated based on the analytical signals. Stokes parameters are calculated within the pulse time window based on the instantaneous amplitude and instantaneous phase difference. Radiation field polarization parameters are calculated based on the Stokes parameters. The radiation field polarization parameters include the azimuth angle of the major axis of the polarization ellipse, the ellipticity angle, the rotation direction, and the linear polarizability.

[0063] Please refer to the following: Figure 5 The digital signal processing unit performs Hilbert transform on the synchronously acquired horizontal electric field components Ex(t) and Ey(t) to obtain analytic signals, and then obtains the instantaneous amplitude Ax(t), Ay(t) and instantaneous phase difference delta(t), delta(t) = phi_x(t) - phi_y(t).

[0064] Within a lightning pulse duration window (typically several microseconds), the Stokes parameters S0, S1, S2, and S3 are calculated to extract all parameters of the polarization ellipse. The formulas for calculating the Stokes parameters are as follows: S0 =<Ax²> +<Ay²> S1 =<Ax²> -<Ay²> S2 = 2<Ax × Ay × cos(delta)> S3 = 2<Ax × Ay × sin(delta)> Where <> represents the time average within a pulse time window.

[0065] The calculated Stokes parameters are used to further extract the radiation field polarization parameters, which include the azimuth angle of the major axis of the polarization ellipse, the ellipticity angle, the rotation direction, and the linear polarizability.

[0066] Specifically, the formula for calculating the azimuth angle of the major axis of the polarization ellipse is as follows:

[0067] The formula for calculating the ellipticity angle is as follows:

[0068] The corresponding axis ratio is tan(chi).

[0069] The direction of rotation is determined by the sign of S3: S3>0 indicates right-hand rotation, and S3<0 indicates left-hand rotation.

[0070] The formula for calculating linear polarizability is as follows:

[0071] Radiation field polarization parameters can be used to distinguish different types of lightning discharge processes and analyze the characteristics of electromagnetic wave propagation paths.

[0072] Linear polarization: When the phase difference delta approaches 0 or pi, S3 approaches zero, and the polarization ellipse degenerates into a line segment (ellipticity angle chi approaches 0), and the major axis azimuth angle psi indicates the direction of signal arrival. The main radiation field of a lightning return is vertically polarized, and under far-field conditions, the horizontal component is mainly along the radial direction (pointing towards the signal source), exhibiting high linear polarization PL.

[0073] Elliptic polarization: When a lightning channel is curved or has tilted branches, a non-zero phase difference delta appears between the two orthogonal horizontal components of the radiation field, and S3 is not zero, so the polarization changes from linear to elliptic. The ellipticity |tan(chi)| reflects the degree to which the channel deviates from a straight line, and the rotation direction (symbol of S3) carries information about the direction of channel curvature.

[0074] Different types of lightning processes (initial breakdown, step leader, return stroke, K-change, M-component, etc.) have different polarization fingerprint characteristics, which can be used as auxiliary criteria for automatic classification.

[0075] In this embodiment, because the five metal spherical cap sensing electrodes are placed close to each other, the induced charge distribution on one spherical cap sensing electrode is affected by the adjacent spherical cap sensing electrodes, resulting in a mutual coupling effect. Mutual coupling reduces the orthogonality between the channels—for example, the north-facing cap may also have a weak response to an east-west oriented electric field.

[0076] Therefore, in this embodiment, the digital signal processing unit is also used to perform matrix inverse operation on the five output signals according to the mutual coupling calibration matrix, so as to eliminate the electromagnetic mutual coupling effect between adjacent spherical cap induction electrodes.

[0077] The mutual coupling calibration matrix is ​​a fixed parameter matrix uniquely determined by the array geometry and can be calibrated in the following ways: (a) by accurately calculating the theoretical mutual coupling matrix using full-wave electromagnetic simulation (HFSS / CST); and (b) by experimental calibration in a standard electric field with known directions. After obtaining the mutual coupling calibration matrix, matrix inversion can be performed in the digital signal processing unit to eliminate the mutual coupling effect and restore the orthogonality of each channel.

[0078] The gain, delay, and frequency response of the five front-end signal conditioning channels must be highly consistent. It is recommended that the five front-end PCBs use components from the same batch and the same layout, and that channel consistency be calibrated using a standard signal source before shipment.

[0079] Based on the lightning transient electric field detection system provided above, please refer to Figure 6 This invention also provides a method for detecting transient electric fields during lightning, which includes the following steps: S11 synchronously senses the transient electric field changes of lightning through five spherical cap induction electrodes and outputs five output signals. S12 performs differential operation on the four output signals corresponding to the four horizontal spherical cap induction electrodes in the five output signals to extract the horizontal electric field component of the lightning transient electric field. S13, calculate the signal arrival azimuth angle based on the horizontal electric field component, and estimate the signal arrival elevation angle based on the horizontal electric field magnitude and the vertical electric field component obtained from the horizontal electric field component. S14, determine the weighting coefficients according to the azimuth angle of arrival, and perform digital beamforming and combining on the five output signals based on the weighting coefficients; S15, the radiation field polarization parameters are extracted based on the horizontal electric field components and through Hilbert transform and Stokes parameters.

[0080] It should be noted that the lightning transient electric field detection method provided in this embodiment can achieve the same, similar or corresponding functions as the lightning transient electric field detection system in the above embodiments. For details not covered in this embodiment, please refer to the relevant content in the above embodiments. This embodiment will not elaborate further here.

[0081] In this embodiment, when the aforementioned lightning transient electric field detection system is used as a single station, it can achieve the above-mentioned functions such as horizontal electric field component decomposition, single-station three-dimensional direction of arrival determination, radiation field polarization analysis, digital beamforming, and mutual coupling correction. When the detection system is used as a node in a time-difference positioning network, each station completes the direction of arrival estimation locally and sends it to the central processing station. The central processing station then performs summary analysis and processing, thereby reducing the search space for time-difference positioning and lowering the pulse false correlation rate.

[0082] Based on this, embodiments of the present invention also provide a time difference positioning network, which includes a central processing station and multiple lightning transient electric field detection systems as described in the above embodiments.

[0083] Please refer to the following: Figure 7 Each of the lightning transient electric field detection systems is used to send the signal direction information obtained from the single-station three-dimensional direction determination performed for the same lightning event to the central processing station.

[0084] The central processing station is used to filter out signal information pointing to the same area in space by combining the signal information sent by multiple lightning transient electric field detection systems, and to perform time difference of arrival positioning based on the filtered signal information to determine the lightning location information.

[0085] In this embodiment, each station completes the direction of arrival estimation locally and reports the signal direction of arrival information (including the azimuth angle θ) to the central processing station along with the timestamp.

[0086] When performing pulse correlation, the central processing station first checks whether the direction of arrival information of each station is consistent: for pulses from the same lightning event, the direction of arrival estimates of each station should point to the same area in space. Pulse combinations with inconsistent directions of arrival are immediately eliminated, and the search space is significantly reduced.

[0087] In complex scenarios where multiple thunderstorms are active simultaneously, this direction-assisted pulse correlation strategy has a particularly prominent advantage. It can effectively avoid incorrectly associating pulses from different thunderstorms and eliminate false location results.

[0088] In summary, the lightning transient detection system, detection method, and time-difference positioning network provided in this embodiment have at least the following advantages compared to existing technologies: (1) Realize the measurement of three-component vector electric field: While maintaining the broadband characteristics of traditional fast antenna (subhertz to above 10 MHz), the simultaneous measurement of the three components of lightning transient electric field Ex, Ey and Ez is realized for the first time, breaking through the fundamental limitation of traditional fast antennas that can only measure the vertical component.

[0089] (2) Realize three-dimensional direction of arrival determination of a single station: calculate the azimuth of arrival of the signal by the ratio of the two horizontal electric field components, and estimate the elevation angle of arrival of the signal by the ratio of the horizontal electric field component to the vertical electric field component. Real-time determination of three-dimensional direction of arrival of lightning signals can be achieved at a single station without the need for multi-station cooperation.

[0090] (3) Multi-station networking efficiency is doubled: By introducing the signal direction information into the pulse correlation process of time difference positioning, the search space is reduced from all directions to a narrow sector, the pulse false correlation rate is significantly reduced, and the real-time positioning calculation speed is greatly improved, especially in complex scenarios where multiple thunderstorms are active at the same time.

[0091] (4) Three-dimensional orthogonal ground plane architecture: Two vertical conductive plates form 90° dihedral reflectors in each quadrant, providing 15–20 dB front-to-back ratio enhancement for each horizontal spherical cap induction electrode; the horizontal conductive plates provide a ground reference for the top vertical spherical cap induction electrode. The three plates converge at the center of the array and simultaneously serve as structural supports, resulting in good overall rigidity.

[0092] (5) Same mold design: The five spherical cap sensing electrodes are manufactured using the same mold (same spherical radius R, same arc angle α), which can reduce manufacturing costs and ensure channel consistency; adjacent spherical cap sensing electrodes are tangent at the opening edge to achieve full sky coverage without dead angles.

[0093] (6) Compact structure: The total size of the array is much smaller than the working wavelength (10 MHz corresponds to a wavelength of 30 m, and the array size is about 1 m). The electric field seen by all the spherical cap sensing electrodes has almost no spatial phase difference, so there is no need to consider the phase calibration between array elements, which simplifies signal processing.

[0094] (7) Differential common-mode suppression: The differential operation of each pair of opposing spherical cap induction electrodes naturally suppresses common-mode interference (such as 50Hz power frequency, changes in far-field uniform electrostatic field, etc.), improving signal quality.

[0095] (8) Digital beamforming gain: The weighted combiner of the five output signals can achieve a signal-to-noise ratio improvement of about 7dB under known direction of arrival.

[0096] (9) Radiation field polarization analysis: The three-component synchronous measurement provides a complete data foundation for the polarization analysis of the lightning radiation field. All parameters of the polarization ellipse can be extracted through Hilbert transform and Stokes parameter, which can be used to distinguish different discharge types, analyze the characteristics of electromagnetic wave propagation paths, and study the three-dimensional geometric structure of lightning channels.

[0097] In the embodiments provided by this invention, it should be understood that the disclosed apparatus and method can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0098] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0099] Furthermore, the functional modules in the various embodiments of the present invention can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0100] It should be noted that if the functionality is implemented as a software module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0101] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lightning transient electric field detection system, characterized in that, It includes a vertical measurement unit, a horizontal measurement unit, a grounding reference board assembly, a front-end signal conditioning channel, and a digital signal processing unit; The vertical measurement unit includes a vertical spherical cap induction electrode with its axis of symmetry set vertically and its opening facing upward, used to measure the vertical electric field component of the transient electric field of lightning. The horizontal measurement unit includes four horizontal spherical cap sensing electrodes, whose axes of symmetry are horizontally arranged along the four basic azimuth directions. The four horizontal spherical cap sensing electrodes are arranged back to back, with their convex surfaces facing the center of the array and their openings facing outwards in their respective azimuth directions. The grounding reference plate assembly includes two mutually perpendicular vertical conductive plates and a horizontal conductive plate. The two vertical conductive plates are orthogonally intersecting in the horizontal plane, and their orientations are at a 45° angle to the axis of symmetry of the two adjacent horizontal spherical cap induction electrodes. Each horizontal spherical cap induction electrode is located in a 90° dihedral reflector formed by the two vertical conductive plates. The horizontal conductive plate is disposed below the vertical spherical cap induction electrode and serves as the grounding reference plane for the vertical spherical cap induction electrode to measure the vertical electric field component. The front-end signal conditioning channel includes five channels for outputting the output signals of the five spherical cap sensing electrodes; The digital signal processing unit is used to receive five output signals and perform horizontal electric field component decomposition, single-station three-dimensional direction of arrival determination, and radiation field polarization analysis based on the five output signals.

2. The lightning transient electric field detection system according to claim 1, characterized in that, The lightning transient electric field detection system also includes an insulating support assembly, which includes a gasket disposed between each spherical cap induction electrode and the grounding reference plate assembly, and the surface of the vertical conductive plate is provided with a groove; The opening edge of each horizontal spherical cap sensing electrode is embedded in the groove through the gasket.

3. The lightning transient electric field detection system according to claim 1, characterized in that, The five spherical cap sensing electrodes are manufactured using the same mold and have the same spherical radius and arc angle; Among them, the four horizontal spherical cap sensing electrodes are arranged in a square when viewed from above. The opening edges of two adjacent horizontal spherical cap sensing electrodes are tangent, and the four tangent points form a square. The vertical spherical cap induction electrode appears circular when viewed from above, and its diameter is equal to the distance between two adjacent tangent points.

4. The lightning transient electric field detection system according to claim 1, characterized in that, The digital signal processing unit is used to perform horizontal electric field component decomposition in the following manner: Differential operation is performed on the output signals of two sets of opposing horizontal spherical cap induction electrodes among the four horizontal spherical cap induction electrodes to obtain the horizontal electric field component of the lightning transient electric field.

5. The lightning transient electric field detection system according to claim 4, characterized in that, The digital signal processing unit is used to perform single-station three-dimensional orientation determination in the following manner: The azimuth angle of the signal in the horizontal plane is calculated based on the output signals of the four horizontal spherical cap induction electrodes. The horizontal electric field component is calculated by combining the horizontal electric field component to obtain the horizontal electric field magnitude. The elevation angle of the signal is calculated based on the horizontal electric field magnitude and the vertical electric field component.

6. The lightning transient electric field detection system according to claim 5, characterized in that, The digital signal processing unit is further configured to determine weighting coefficients based on the azimuth angle of arrival, and to perform weighted summation on the five output signals based on the weighting coefficients to enhance the signal-to-noise ratio.

7. The lightning transient electric field detection system according to claim 4, characterized in that, The digital signal processing unit is used to perform radiation field polarization analysis in the following manner: The horizontal electric field components are subjected to Hilbert transform to obtain analytical signals. Instantaneous amplitude and instantaneous phase difference are calculated based on the analytical signals. Stokes parameters are calculated within the pulse time window based on the instantaneous amplitude and instantaneous phase difference. Radiation field polarization parameters are calculated based on the Stokes parameters. The radiation field polarization parameters include the azimuth angle of the major axis of the polarization ellipse, the ellipticity angle, the rotation direction, and the linear polarizability.

8. The lightning transient electric field detection system according to claim 1, characterized in that, The digital signal processing unit is also used to perform matrix inverse operation on the five output signals according to the mutual coupling calibration matrix, so as to eliminate the electromagnetic mutual coupling effect between adjacent spherical cap induction electrodes.

9. A method for detecting transient electric fields during lightning, characterized in that, The method, applied to the lightning transient electric field detection system according to any one of claims 1-8, comprises: Five spherical cap induction electrodes are used to synchronously sense the transient electric field changes of lightning and output five output signals. Differential operation is performed on the four output signals corresponding to the four horizontal spherical cap induction electrodes in the five output signals to extract the horizontal electric field component of the lightning transient electric field. The signal arrival azimuth angle is calculated based on the horizontal electric field component, and the signal arrival elevation angle is estimated based on the horizontal electric field magnitude and the vertical electric field component. The weighting coefficients are determined based on the azimuth angle of arrival, and the five output signals are digitally beamformed and combined based on the weighting coefficients. The radiation field polarization parameters are extracted based on the horizontal electric field components and using Hilbert transform and Stokes parameters.

10. A time-difference positioning network, characterized in that, Includes a central processing station and a lightning transient electric field detection system as described in any one of claims 1-8: Each of the lightning transient electric field detection systems is used to send the signal information obtained from the single-station three-dimensional determination for the same lightning event to the central processing station; The central processing station is used to filter out signal information pointing to the same area in space by combining the signal information sent by multiple lightning transient electric field detection systems, and to perform time difference of arrival positioning based on the filtered signal information to determine the lightning location information.

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