A lightning broadband very high frequency imaging method, system and readable medium

Abstract

The present invention discloses a lightning broadband VHF imaging method, system and readable medium, and relates to the technical fields of signal processing and lightning radiation source imaging. The present invention proposes a lightning broadband VHF imaging method, firstly constructing a non-uniform lightning VHF antenna array, collecting lightning broadband VHF signals and reconstructing them to obtain reconstructed signals; then constructing a dimension reduction orthogonal propagation operator based on the reconstructed signals; based on the dimension reduction orthogonal propagation operator, obtaining the incident angle information of the X-axis direction subarray and the Y-axis direction subarray; obtaining the azimuth and elevation of the radiation source based on the incident angle information of the X-axis direction subarray and the Y-axis direction subarray; finally obtaining the lightning broadband VHF imaging result based on the azimuth and elevation of the radiation source. The amount of calculation and memory usage are reduced, as well as the noise interference is reduced, the algorithm solution speed is improved, and the imaging accuracy is higher.

Description

Technical Field

[0001] The invention relates to the technical fields of signal processing and lightning radiation source imaging, in particular to a lightning broadband very high frequency imaging method, system and readable medium. Background Art

[0002] Lightning imaging methods are an important support for conducting research on lightning science and protection. Lightning imaging is a technology that uses multiple antennas to remotely measure electromagnetic radiation signals generated by atmospheric discharges, and inverts the direction or position of the radiation source based on a specific algorithm to generate two-dimensional or three-dimensional images of lightning activities. Based on lightning imaging results, the propagation characteristics of natural lightning are analyzed, which can serve to reveal the physical mechanism of the lightning discharge process and establish a lightning risk assessment model that takes into account key parameters such as the morphology and propagation speed of natural lightning channels, which helps to optimize the lightning protection design of ground infrastructure.

[0003] There are two main types of traditional lightning imaging methods: one is a detection technology based on the long baseline (20 km order) TDOA (Time Difference of Arrival) method, which is mainly used for locating ground lightning return stroke points and observing three-dimensional lightning processes; the second is a detection technology based on the short baseline (10 m order) interferometry method, which can invert the two-dimensional development process of lightning and has the advantage of single-station operation; however, the long baseline TDOA method requires multiple distributed detection stations to operate synchronously, with high time synchronization accuracy requirements, complex system architecture, and site selection and actual station layout are major difficulties; and when the time difference method and the interferometry method are used for lightning imaging, not only is the imaging time long, but they are also easily affected by noise interference, resulting in a significant decrease in algorithm accuracy. At the same time, the existing technology can only image the radiation source projected from the uniform lightning very high frequency antenna array. Summary of the invention

[0004] In order to overcome the defects of long imaging time and low precision in the above-mentioned prior art, the present invention proposes a lightning broadband very high frequency imaging method, system and readable medium.

[0005] To achieve the above object, the present invention adopts the following technical scheme, a lightning broadband very high frequency imaging method, comprising:

[0006] S1: Construct a non-uniform lightning VHF antenna array, collect lightning broadband VHF signals and reconstruct them to obtain reconstructed signals;

[0007] S2: Divide the lightning VHF antenna array into an X-axis direction sub-array and a Y-axis direction sub-array, and construct a dimension reduction orthogonal propagation operator based on the reconstructed signal; wherein the dimension reduction orthogonal propagation operator includes an X-axis orthogonal propagation operator and a Y-axis orthogonal propagation operator;

[0008] S3: Based on the dimension reduction orthogonal propagation operator, the incident angle information of the sub-array in the X-axis direction and the sub-array in the Y-axis direction is obtained;

[0009] S4: obtaining the azimuth and elevation of the radiation source based on the incident angle information of the sub-array in the X-axis direction and the sub-array in the Y-axis direction;

[0010] S5: Obtain lightning broadband VHF imaging results based on the azimuth and elevation of the radiation source.

[0011] Preferably, in step S2, constructing a dimension reduction orthogonal propagation operator based on the reconstructed signal includes:

[0012] S21: Decompose the reconstructed signal to obtain several narrowband components s(t);

[0013] S22: Obtaining a steering vector a of the array based on a number of narrowband components s(t);

[0014] S23: Based on the array steering vector a, obtain the antenna array flow direction matrix A;

[0015] S24: Obtain a dimension reduction orthogonal propagation operator.

[0016] Preferably, in step S22, obtaining the steering vector a of the array based on the narrowband component s(t) includes:

[0017] Based on the narrowband component s(t), the array steering vector a is obtained by setting the first and second factors and the following equation:

[0018] ;

[0019] Where z(t) is the observed signal, i.e., the received signal of the non-uniform lightning VHF antenna array; z x (t), z y (t) are the observation signals of the sub-arrays in the X-axis and Y-axis directions, is a Gaussian white noise signal, N x (t) and N y (t) are Gaussian white noise signals on the X-axis and Y-axis respectively, and the superscript T is the transpose of the matrix;

[0020] The expression of the array's steering vector a is:

[0021] ;

[0022] Among them, a x and a y are the steering vectors of the subarrays in the X-axis and Y-axis directions respectively; j is an imaginary unit; ω0 represents the angular frequency; d mis the minimum distance between antennas in the non-uniform lightning VHF antenna array; k1 and k2 are proportionality coefficients; c is the speed of light; e represents a natural constant; θ is the azimuth; is the elevation angle, u and v are the first and second factors respectively;

[0023] The first and second factors are expressed as follows:

[0024] , ;

[0025] in, are equivalent symbols.

[0026] Preferably, in step S23, based on the array steering vector a, an antenna array flow direction matrix A is constructed, and the expression of the antenna array flow direction matrix A is:

[0027] ;

[0028] Among them, A x , A y are the sub-array matrices in the X-axis and Y-axis directions respectively, K is the total number of radiation sources, θ K is the azimuth of the Kth radiation source, is the elevation angle of the Kth radiation source, a x and a y These are the steering vectors for the X-axis and Y-axis arrays respectively.

[0029] Preferably, in step S24, obtaining a dimension reduction orthogonal propagation operator includes:

[0030] S241: Sub-matrix matrix in the X-axis direction A x Decomposition to obtain the matrix A 1 and matrix A 2 , the specific formula is as follows:

[0031] ;

[0032] Where K is the number of lightning radiation sources; M is the total number of antennas in the non-uniform lightning VHF antenna array; A 1 K×K Indicates that the dimension of matrix A1 is K×K; A 2 (M-K)×K Representation Matrix A 2 The dimension is (MK)×K;

[0033] S242: The matrix A 2 Using the matrix A 1 Linear representation, obtain the sub-matrix propagation operator in the X-axis direction P x ; The linear expression formula is as follows:

[0034] ;

[0035] Where, the superscript H is the conjugate transpose of the matrix;

[0036] S243: Based on the X-axis subarray propagation operator P x , get the unique propagation operator of the sub-matrix in the X-axis direction , the formula is:

[0037] ;

[0038] S244: Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis orthogonal propagation operator Q x0 ,include:

[0039] Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis noise matrix , the calculation formula is:

[0040] = ;

[0041] Among them, I M-K represents the MK-order identity matrix;

[0042] The X-axis noise matrix Q x Orthogonalization, obtain the X-axis orthogonal propagation operator Q x0 , the calculation formula is:

[0043] ;

[0044] S245: According to the method of steps S241-S244, the Y-axis sub-matrix matrix A y Make a matrix with sub-matrix in the X-axis direction A x The same operation is used to obtain the Y-axis orthogonal propagation operator. Q y0 .

[0045] Preferably, in step S3, based on the dimension reduction orthogonal propagation operator, obtaining the incident angle information of the sub-arrays in the X-axis direction and the Y-axis direction includes:

[0046] S31: Based on the X-axis orthogonal propagation operator Qx0 Construct the X-axis weighted one-dimensional spatial spectrum function P x (α), the formula is:

[0047] ;

[0048] Among them, E tot is the sum of the energies of all effective narrowband components, equal to , E j is the energy of the jth effective narrowband component, J is the total number of effective narrowband components, is the orthogonal propagation operator of the observation signal of the sub-array in the X-axis direction on the jth effective narrowband component; α is the incident angle of the sub-array in the X-axis direction, j represents the number of effective narrowband components, ω j represents the frequency of the jth effective narrowband component; the effective narrowband component refers to the narrowband component in the set frequency band;

[0049] S32: When the X-axis weighted one-dimensional spatial spectrum function reaches the maximum value, obtain the estimated value of the incident angle of the sub-array in the X-axis direction ’ ;

[0050] S33: Based on the estimated incident angle of the sub-array in the X-axis direction ’ Get the estimated value of the incident angle cosine of the sub-array in the X-axis direction ;

[0051] S34: According to the method of steps S31-S33, the Y-axis orthogonal propagation operator Q y0 Perform the same processing as the X-axis orthogonal propagation operator to obtain the sub-array incident angle in the Y-axis direction β , and the cosine value u of the incident angle of the sub-array in the Y-axis direction;

[0052] Among them, the estimated value of the incident angle cosine of the sub-array in the X-axis direction is is the estimated value of the second factor, and the cosine value u of the incident angle of the sub-array in the Y-axis direction is the first factor.

[0053] Preferably, in step S4, based on the incident angle information of the sub-arrays in the X-axis direction and the Y-axis direction, the azimuth angle θ and the elevation angle of the radiation source are obtained. ,include:

[0054] The formula for calculating the elevation angle is:

[0055] ;

[0056] The calculation formula for the azimuth angle is:

[0057] .

[0058] Preferably, in step S5, based on the azimuth and elevation of the radiation source, obtaining a lightning broadband very high frequency imaging result includes:

[0059] S51: taking an azimuth and elevation value as a set of data, i.e., a cluster point, setting the minimum number of points and the proximity radius of the cluster, thereby forming an initial cluster;

[0060] S52: The distance between the two closest points in different clusters is taken as the inter-cluster distance;

[0061] S53: setting an inter-cluster distance threshold, removing cluster points whose inter-cluster distance is greater than the inter-cluster distance threshold, and obtaining true cluster points;

[0062] S54: Plot the azimuth and elevation angles contained in the real cluster points on a two-dimensional coordinate plane to obtain a lightning broadband very high frequency imaging result.

[0063] A lightning broadband very high frequency imaging system comprises a memory and a processor, wherein a computer program is stored in the memory, and the processor is connected to the memory, and the processor is used to execute the computer program to implement the lightning broadband very high frequency imaging method.

[0064] A lightning broadband very high frequency imaging readable medium stores a computer program, and when the computer program is executed, the lightning broadband very high frequency imaging method is implemented.

[0065] The advantages of the present invention are:

[0066] (1) The present invention reconstructs the lightning broadband very high frequency signal, and then constructs a dimension reduction orthogonal propagation operator based on the reconstructed signal, and constructs a weighted one-dimensional spatial spectrum function of the X-axis and the Y-axis based on the dimension reduction orthogonal propagation operator, obtains the incident angle information of the sub-array in the X-axis direction and the sub-array in the Y-axis direction, and reduces the dimension of the spatial spectrum of the azimuth-elevation two-dimensional plane into a one-dimensional spatial spectrum function composed of two spatial angles. The peak search range is smaller, the calculation complexity is reduced, the memory usage is reduced, and the solution speed of the algorithm is improved.

[0067] (2) The present invention constructs a non-uniform lightning VHF antenna array to collect lightning broadband VHF signals and processes them to obtain lightning broadband VHF imaging results. It can more flexibly capture the complex spatial distribution characteristics of lightning signals, thereby improving the accuracy of signal acquisition, enhancing the anti-ambiguity performance of the system, and improving the applicability of lightning monitoring.

[0068] (3) The method of the present invention adopts the joint density and hierarchical clustering method to remove discrete pseudo points, plots the azimuth and elevation of the radiation source on a two-dimensional plane, and generates intuitive lightning broadband very high frequency imaging results, which is convenient for users to analyze and understand the spatial distribution of lightning signals, making the positioning imaging accuracy more accurate.

[0069] (4) The present invention obtains the incident angle information of the X-axis sub-array and the Y-axis sub-array based on the dimension reduction orthogonal propagation operator, reduces the time complexity and improves the imaging speed.

[0070] (5) Based on the incident angle information of the X-axis subarray and the Y-axis subarray, the present invention obtains the azimuth angle by considering the relationship between the incident angle cosine estimate value of the X-axis subarray and the incident angle cosine value of the Y-axis subarray and 0 in many aspects, thereby achieving higher imaging accuracy.

[0071] (6) The present invention adopts a fully adaptive noise ensemble empirical mode decomposition method to preprocess the lightning broadband very high frequency signal to obtain a reconstructed signal; in the calculation of the steering vector, by introducing a Gaussian white noise model, it is possible to effectively distinguish between the signal and the noise, thereby improving the robustness of the signal processing, reducing noise interference, and enhancing the anti-noise capability.

[0072] (7) The present invention can effectively reduce noise interference in lightning broadband very high frequency signal processing and improve the spatial resolution of the signal by reconstructing the lightning broadband very high frequency signal and constructing a dimensionality reduction orthogonal propagation operator. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 It is a non-uniform L-shaped array diagram of the present invention;

[0074] Figure 2 is a flow chart of the method of the present invention;

[0075] Figure 3 This is a lightning VHF data chart;

[0076] Figure 4 This is the imaging result diagram of the method of the present invention;

[0077] Figure 5 This is the imaging result diagram of the multiple signal classification method. DETAILED DESCRIPTION

[0078] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0079] like Figure 1-4 As shown, the present invention proposes a lightning broadband very high frequency imaging method.

[0080] Example 1

[0081] Step 1: Construct a non-uniform lightning VHF antenna array to collect lightning broadband VHF signals (Very High Frequency, VHF signals) from array elements;

[0082] The present invention adopts a non-uniform L-shaped lightning VHF antenna array, which is divided into an X-axis direction sub-array and a Y-axis direction sub-array, and non-equidistant antennas (array elements) are arranged on both the X-axis and the Y-axis. The specific non-uniform L-shaped array is shown in FIG. Figure 1 The array is L-shaped in the XOY plane, with the X axis being due south and the Y axis being due east.

[0083] In this embodiment, there are 4 antennas on the X-axis and Y-axis (including the antenna at the origin), where V1, V2, V3, V4, V5, V6, and V7 represent numbered antennas. The horizontal coordinates of the antennas arranged on the X-axis are , where d m represents the distance between antenna V1 and antenna V2. The antennas on the Y-axis are arranged in the same manner as the antennas on the X-axis.

[0084] Assume that The radiation source (lightning radiation signal S) is at different azimuth angles θ and elevation angles. From the far field incident to the non-uniform lightning VHF antenna array containing M array elements, the array element position is In this embodiment, M is 7. Figure 1 The N in the formula represents that N non-equidistant antennas are arranged on both the X-axis and the Y-axis (including the antenna at the origin).

[0085] Step 2: Preprocess the lightning broadband VHF signal using the fully adaptive noise ensemble empirical mode decomposition method to obtain the reconstructed signal;

[0086] The Complementary Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method is based on the lightning broadband very high frequency signal. It first solves the first-order intrinsic mode function (IMF) component, then adds the last-order IMF component to white noise, obtains the mean of all IMF components, further splits the mean of all IMF components and adds white noise, obtains the mean of all IMF components and iterates multiple times, and adds all the decomposed IMF components to obtain the reconstructed signal.

[0087] Step 3: Decompose the reconstructed signal through Discrete Fourier Transform (DFT) to obtain several narrowband components s(t); t is time;

[0088] Step 4: Based on the narrowband component s(t), the steering vector a of the array is obtained by setting the first and second factors and the following equation:

[0089] ;

[0090] Where z(t) is the observed signal, i.e., the received signal of the non-uniform lightning VHF antenna array, z x (t), z y (t) are the observation signals of the sub-arrays in the X-axis and Y-axis directions, is a Gaussian white noise signal, N x (t) and N y (t) are Gaussian white noise signals on the X-axis and Y-axis respectively, and the superscript T is the transpose of the matrix.

[0091] Wherein, the array's steering vector, in this embodiment, the array's steering vector a is expressed as:

[0092] ;

[0093] ;

[0094] Among them, a x and a y are the steering vectors of the X-axis and Y-axis arrays respectively; j is an imaginary unit; ω0 represents the angular frequency; d m is the distance between antenna V1 and antenna V2 in the non-uniform lightning VHF antenna array; c is the speed of light; e represents a natural constant; θ is the azimuth; is the elevation angle; u and v are the first and second factors respectively.

[0095] The first and second factors are expressed as follows:

[0096] , ;

[0097] in, are equivalent symbols.

[0098] Step 5: Based on the array's steering vector a, construct the antenna array flow direction matrix A, including:

[0099] ;

[0100] in, Ax 、A y are the sub-array matrices in the X-axis and Y-axis directions respectively, K is the total number of radiation sources, θ K is the azimuth of the Kth radiation source, is the elevation angle of the Kth radiation source.

[0101] The covariance matrix R is constructed based on the array's steering vector a. The covariance matrix R includes the X-axis covariance matrix and the Y-axis covariance matrix R y , the specific formula is:

[0102] ;

[0103] ;

[0104] in, represents the noise intensity, represents the identity matrix, the superscript is the conjugate transpose of the matrix, represents the noise power, represents the covariance matrix of the radiation source, Express expectations.

[0105] Step 6: Obtain the dimension reduction orthogonal propagation operator, including the X-axis orthogonal propagation operator and the Y-axis orthogonal propagation operator. The specific process includes:

[0106] The X-axis sub-matrix matrix A x Decomposed, the specific formula is as follows:

[0107] ;

[0108] Where K is the number of lightning radiation sources; M is the total number of antennas in the non-uniform lightning VHF antenna array; A 1 K×K Indicates that the dimension of matrix A1 is K×K; A 2 (M-K)×K It means that the dimension of matrix A2 is (MK)×K;

[0109] Assuming that the lightning radiation source signals are independent of each other, the sub-array matrix A in the X-axis direction is x is of full column rank, then the X-axis submatrix matrix A x have The rows are linearly independent, and the others This can be done Linear representation of rows.

[0110] Matrix A2 can be linearly represented by matrix A1. The specific formula is as follows:

[0111] ;

[0112] Among them, the superscript is the conjugate transpose of the matrix; P x It is called the X-axis subarray propagation operator, which can also be expressed as follows:

[0113] ;

[0114] in, Q x is the noise matrix of the sub-array in the X-axis direction, express The unit matrix, express Zero-order matrix.

[0115] Based on the decomposed X-axis sub-matrix matrix (ie matrix and ), construct the cost function , solve the cost function and obtain the unique propagation operator of the sub-matrix in the X-axis direction , the calculation formula is:

[0116] ;

[0117] in, Represents the square of the Frobenius norm.

[0118] Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis orthogonal propagation operator ,include:

[0119] Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis noise matrix , the calculation formula is:

[0120] = ;

[0121] The X-axis noise matrix Q x Orthogonalization, obtain the X-axis orthogonal propagation operator , the specific formula is as follows:

[0122] ;

[0123] Similarly, according to the above method, the same operation is performed on the Y-axis sub-matrix as on the X-axis sub-matrix to obtain the Y-axis orthogonal propagation operator Q y0 .

[0124] Step 7: Based on the dimension reduction orthogonal propagation operator, obtain the estimated value of the incident angle cosine of the sub-array in the X-axis direction and the incident angle cosine value of the sub-array in the Y-axis direction, including:

[0125] Based on the X-axis orthogonal propagation operator Construct the X-axis weighted one-dimensional spatial spectrum function P x (α), the formula is:

[0126] ;

[0127] in, E tot is the sum of the energies of all effective narrowband components, equal to , E j is the energy of the jth effective narrowband component, is the total number of effective narrowband components, is the observation signal of the sub-array in the X-axis direction Orthogonal propagation operators on the effective narrowband components; α is the incident angle of the sub-array in the X-axis direction, j represents the number of effective narrowband components, ω j Indicates the frequency of the jth effective narrowband component; the effective narrowband component refers to the narrowband component in the energy distribution frequency band ranging from 27.5MHz to 60MHz;

[0128] When the X-axis weighted one-dimensional spatial spectrum function reaches the maximum value, the estimated value of the incident angle of the sub-array in the X-axis direction is obtained. ’ ;

[0129] Based on the estimated incident angle of the sub-array in the X-axis direction ’ Get the estimated value of the incident angle cosine of the sub-array in the X-axis direction ;

[0130] According to the above method, the Y-axis orthogonal propagation operator Q y0 Perform the same processing as the X-axis orthogonal propagation operator to obtain the Y-axis sub-array incident angle β and the Y-axis sub-array incident angle cosine value u. is the estimated value of the second factor, and the cosine value u of the incident angle of the sub-array in the Y-axis direction is the first factor.

[0131] Step 8: Based on the estimated value of the incident angle cosine of the sub-array in the X-axis direction and the incident angle cosine of the sub-array in the Y-axis direction, the azimuth and elevation of the radiation source are obtained. The calculation formula for the elevation angle is:

[0132] ;

[0133] The calculation formula for the azimuth angle is:

[0134] ;

[0135] Step 9: Based on the azimuth and elevation angles of multiple radiation sources, obtain broadband VHF imaging results of lightning, including:

[0136] The value of an azimuth and elevation angle is taken as a set of data, i.e. a cluster point, and the minimum number of points and the neighboring radius of the cluster are set to form an initial clustering cluster;

[0137] The distance between the two closest points in different clusters is taken as the inter-cluster distance;

[0138] Set the inter-cluster distance threshold, remove the cluster points whose inter-cluster distance is greater than the inter-cluster distance threshold, and obtain the real cluster points;

[0139] The azimuth and elevation angles contained in the real cluster points are plotted on a two-dimensional coordinate plane to obtain the lightning broadband very high frequency imaging results.

[0140] In this embodiment, after obtaining the azimuth and elevation, there will be discrete pseudo points; the present invention uses a joint density and hierarchical clustering method to remove discrete pseudo points. The values ​​of the azimuth and elevation are a set of numerical data, i.e., a cluster. The minimum number of points in the cluster is set to 5, and the neighboring radius is set to 0.03, thereby forming an initial cluster cluster. The initial cluster cluster is used as input, and the distance between clusters is calculated by the minimum connection distance method. The distance is set to 0.01, thereby judging the compactness of the radiation source point, thereby removing pseudo points. Finally, each set of two-dimensional coordinates obtained is plotted one by one on the azimuth-elevation plane, and a two-dimensional projection of the lightning channel on the plane is obtained, which is the imaging result.

[0141] Example 2

[0142] As a second implementation of the present invention, the acquisition of the unique propagation operator on the X-axis ,include:

[0143] The covariance matrix of the sub-matrix in the X-axis direction Divide into blocks, the block formula is as follows:

[0144] ;

[0145] Among them, G x represents the signal covariance sub-block matrix of the sub-array in the X-axis direction, H x represents the noise covariance sub-block matrix of the sub-array in the X-axis direction;

[0146] When the cost function When it is minimum, solve it and get the unique propagation operator on the X axis , the calculation formula is:

[0147] ;

[0148] A lightning broadband very high frequency imaging system comprises a memory and a processor. The memory stores a computer program. The processor is connected to the memory and is used to execute the computer program to implement a lightning broadband very high frequency imaging method.

[0149] A lightning broadband very high frequency imaging readable medium, characterized in that a computer program is stored thereon, and when the computer program is executed, a lightning broadband very high frequency imaging method is implemented.

[0150] To illustrate the feasibility of the method of the present invention, 100ms lightning VHF data is used for imaging. Figure 4 and Figure 5 The positioning imaging results of the method of the present invention and the existing multiple signal classification method are respectively shown. Figure 4 For example, the horizontal axis represents the azimuth, and the angle range is [0°, 360°], and the vertical axis represents the elevation, and the angle range is [0°, 90°]. This figure depicts the position and change of the radiation source in the two-dimensional coordinate system, and the color change indicates the time sequence. By comparison, it is found that the method of the present invention locates more radiation source points, especially at the grounding position, showing the superiority of the method. This section of VHF data is 100ms in total, and the method of the present invention takes a total of 2 minutes, and the multiple signal classification method takes 8 minutes.

[0151] Of course, it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0152] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0153] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A lightning broadband very high frequency imaging method, characterized in that: include: S1: Construct a non-uniform lightning VHF antenna array, collect lightning broadband VHF signals and reconstruct them to obtain reconstructed signals; S2: Divide the lightning VHF antenna array into an X-axis direction sub-array and a Y-axis direction sub-array, and construct a dimensionality reduction orthogonal propagation operator based on the reconstructed signal; wherein the dimensionality reduction orthogonal propagation operator includes an X-axis orthogonal propagation operator and a Y-axis orthogonal propagation operator; S3: Based on the dimension reduction orthogonal propagation operator, the incident angle information of the sub-array in the X-axis direction and the sub-array in the Y-axis direction is obtained; S4: obtaining the azimuth and elevation of the radiation source based on the incident angle information of the sub-array in the X-axis direction and the sub-array in the Y-axis direction; S5: Obtain lightning broadband VHF imaging results based on the azimuth and elevation of the radiation source.

2. A lightning broadband very high frequency imaging method as claimed in claim 1, characterized in that: In step S2, constructing a dimension reduction orthogonal propagation operator based on the reconstructed signal includes: S21: Decompose the reconstructed signal to obtain several narrowband components s(t); S22: Obtaining a steering vector a of the array based on a number of narrowband components s(t); S23: Based on the array steering vector a, obtain the antenna array flow direction matrix A; S24: Obtain a dimension reduction orthogonal propagation operator.

3. A lightning broadband very high frequency imaging method as claimed in claim 2, characterized in that: In step S22, the steering vector a of the array is obtained based on the narrowband component s(t), including: Based on the narrowband component s(t), the array steering vector a is obtained by setting the first and second factors and the following equation: ； Where z(t) is the observed signal, i.e., the received signal of the non-uniform lightning VHF antenna array; z x (t), z y (t) are the observation signals of the sub-arrays in the X-axis and Y-axis directions, is a Gaussian white noise signal, N x (t) and N y (t) are Gaussian white noise signals on the X-axis and Y-axis respectively, and the superscript T is the transpose of the matrix; The expression of the array's steering vector a is: ； Among them, a x and a y are the steering vectors of the subarrays in the X-axis and Y-axis directions respectively; j is an imaginary unit; ω0 represents the angular frequency; d m is the minimum distance between antennas in the non-uniform lightning VHF antenna array; k1 and k2 are proportionality coefficients; c is the speed of light; e represents a natural constant; θ is the azimuth; is the elevation angle, u and v are the first and second factors respectively; The first and second factors are expressed as follows: ， ； in, are equivalent symbols.

4. A lightning broadband very high frequency imaging method as claimed in claim 2, characterized in that: In step S23, based on the array steering vector a, an antenna array flow direction matrix A is constructed. The expression of the antenna array flow direction matrix A is: ； in, A x 、A y are the sub-array matrices in the X-axis and Y-axis directions respectively, K is the total number of radiation sources, θ K is the azimuth of the Kth radiation source, is the elevation angle of the Kth radiation source, a x and a y These are the steering vectors for the X-axis and Y-axis arrays respectively.

5. A lightning broadband very high frequency imaging method as claimed in claim 4, characterized in that: In step S24, a dimension reduction orthogonal propagation operator is obtained, including: S241: Sub-matrix A in the X-axis direction x Decomposition to obtain the matrix A 1 and matrix A 2 , the specific formula is as follows: ； Where K is the number of lightning radiation sources; M is the total number of antennas in the non-uniform lightning VHF antenna array; A 1 K×K Representation Matrix A 1 The dimension is K×K; A 2 (M-K)×K Representation Matrix A 2 The dimension is (MK)×K; S242: Linearly represent matrix A2 with matrix A1 to obtain the sub-matrix propagation operator P in the X-axis direction x ; The linear expression formula is as follows: ； Where, the superscript H is the conjugate transpose of the matrix; S243: Based on the X-axis subarray propagation operator P x , get the unique propagation operator of the sub-matrix in the X-axis direction , the formula is: ； S244: Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis orthogonal propagation operator Q x0 ,include: Based on the unique propagation operator of the sub-array in the X-axis direction , get the X-axis noise matrix , the calculation formula is: = ； Among them, I M-K represents the MK-order identity matrix; The X-axis noise matrix Q x Orthogonalization, obtain the X-axis orthogonal propagation operator Q x0 , the calculation formula is: ； S245: According to the method of steps S241-S244, the Y-axis sub-matrix matrix A y Make the sub-matrix matrix A in the X-axis direction x The same operation is performed to obtain the Y-axis orthogonal propagation operator Q y0 .

6. A lightning broadband very high frequency imaging method as claimed in claim 2, characterized in that: In step S3, based on the dimension reduction orthogonal propagation operator, the incident angle information of the sub-arrays in the X-axis direction and the Y-axis direction is obtained, including: S31: Based on the X-axis orthogonal propagation operator Q x0 Construct the X-axis weighted one-dimensional spatial spectrum function P x (α), the formula is: ； Among them, E tot is the sum of the energies of all effective narrowband components, equal to , E j is the energy of the jth effective narrowband component, J is the total number of effective narrowband components, is the orthogonal propagation operator of the observation signal of the X-axis sub-array on the jth effective narrowband component; α is the incident angle of the X-axis sub-array, j represents the number of effective narrowband components, ω j represents the frequency of the jth effective narrowband component; the effective narrowband component refers to the narrowband component in the set frequency band; S32: When the X-axis weighted one-dimensional spatial spectrum function reaches the maximum value, obtain the estimated value of the incident angle of the sub-array in the X-axis direction ’ ; S33: Based on the estimated incident angle of the sub-array in the X-axis direction ’ Get the estimated value of the incident angle cosine of the sub-array in the X-axis direction ; S34: According to the method of steps S31-S33, the Y-axis orthogonal propagation operator Q y0 Perform the same processing as the X-axis orthogonal propagation operator to obtain the sub-array incident angle in the Y-axis direction β , and the cosine value u of the incident angle of the sub-array in the Y-axis direction; Among them, the estimated value of the incident angle cosine of the sub-array in the X-axis direction is is the estimated value of the second factor, and the cosine value u of the incident angle of the sub-array in the Y-axis direction is the first factor.

7. A lightning broadband very high frequency imaging method as claimed in claim 6, characterized in that: In step S4, based on the incident angle information of the sub-arrays in the X-axis direction and the Y-axis direction, the azimuth angle θ and the elevation angle of the radiation source are obtained. ,include: The formula for calculating the elevation angle is: ； The calculation formula for the azimuth angle is: 。 8. A lightning broadband very high frequency imaging method as claimed in claim 7, characterized in that: In step S5, based on the azimuth and elevation of the radiation source, a lightning broadband very high frequency imaging result is obtained, including: S51: taking an azimuth and elevation value as a set of data, i.e., a cluster point, setting the minimum number of points and the proximity radius of the cluster, thereby forming an initial cluster; S52: The distance between the two closest points in different clusters is taken as the inter-cluster distance; S53: setting an inter-cluster distance threshold, removing cluster points whose inter-cluster distance is greater than the inter-cluster distance threshold, and obtaining true cluster points; S54: Plot the azimuth and elevation angles contained in the real cluster points on a two-dimensional coordinate plane to obtain a lightning broadband very high frequency imaging result.

9. A lightning broadband very high frequency imaging system, characterized in that: It comprises a memory and a processor, wherein a computer program is stored in the memory, the processor is connected to the memory, and the processor is used to execute the computer program to implement a lightning broadband very high frequency imaging method as described in any one of claims 1 to 8.

10. A lightning broadband very high frequency imaging readable medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the lightning broadband very high frequency imaging method described in any one of claims 1 to 8 is implemented.

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