Foundation lightning positioning method based on finite difference time domain model

Abstract

The invention relates to a ground-based lightning positioning method based on a time domain finite difference model, and belongs to the technical field of lightning detection. According to the method, based on a two-dimensional time domain finite difference algorithm model, different configurations of soil conductivity, an ionosphere and geomagnetic field parameters are considered, and a lag database of ground wave peak value arrival time when lightning electromagnetic waves are propagated along different directions and different distances is established; and taking the positioning result of the thunder and lightning positioning network as an initial value, considering the time lag of the position reaching different observation stations, repositioning by using a TOA time difference positioning method, and finally obtaining an optimized positioning result. According to the method, the two-dimensional time domain finite difference algorithm model is utilized for the first time, the influence of three factors including the soil conductivity, the ionosphere and the geomagnetic field is comprehensively considered, optimization processing of the thunder and lightning positioning result is achieved, and better technical support is provided for work in the aspects of foundation thunder and lightning positioning network construction, evaluation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of lightning detection, and particularly relates to a ground lightning location method based on a finite-difference time-domain model. Background Art

[0002] When the electromagnetic wave excited by lightning propagates along the Earth-ionosphere cavity, due to the influence of factors such as soil conductivity, ionosphere, geomagnetic field, and propagation distance, the propagation speed of the lightning electromagnetic wave is not equal to the speed of light. This propagation speed is related to different propagation directions, different propagation times, different propagation distances, and the soil conductivity on the propagation path. However, the current lightning location algorithm assumes that the propagation speed of the lightning electromagnetic signal is the speed of light, and locates by using the TOA time difference location algorithm through the arrival time of the lightning electromagnetic signals received synchronously by multiple stations. Obviously, this simple assumption is applicable to the case of an open space with infinite soil conductivity and no influence of the ionosphere on electromagnetic signals, which is very different from the actual situation. Then, how much does this simple assumption affect the location result? What measures should we take to make up for the deficiencies of this location algorithm?

[0003] Therefore, how to overcome the deficiencies of the existing technology is an urgent problem to be solved in the current technical field. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the existing technology and provide a ground lightning location method based on a finite-difference time-domain model.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A ground lightning location method based on a finite-difference time-domain model includes the following steps:

[0007] Based on a two-dimensional finite-difference time-domain algorithm model, considering different configurations of soil conductivity, ionosphere, and geomagnetic field parameters, establish a lag database of the arrival time of the ground wave peak when the lightning electromagnetic wave propagates in different directions and at different distances;

[0008] Taking the location result of the lightning location network as the initial value, considering the time lag from this position to different stations, re-locate by using the TOA time difference location method, and finally obtain the optimized location result.

[0009] Further, preferably, the specific method of considering different configurations of soil conductivity, ionosphere, and geomagnetic field parameters based on a two-dimensional finite-difference time-domain algorithm model is as follows:

[0010] When calculating the propagation characteristics of the lightning electromagnetic field by using a two-dimensional finite-difference time-domain algorithm model, consider three factors of soil conductivity, ionosphere, and geomagnetic field, and the parameter configurations are as follows:

[0011] (1) The size of the simulation domain of the two-dimensional finite-difference time-domain (FDTD) algorithm model is set to 1010 km × 100 km, the grid size is taken as Δr = Δz = 500 m, and the time step is taken as Δt = 1 μs; where, Δr is the horizontal scale and Δz is the vertical scale;

[0012] (2) The excitation source of the two-dimensional FDTD algorithm model is a vertical dipole, with a height of 10 km, and the current waveform I m (t) is a double-exponential expression:

[0013]

[0014] where: I 0 = 20 kA, v 0 = 8×10 7 m / s, γ = 3×10 4 s -1 , a = 2×10 4 s -1 , b = 2×10 5 s -1 , and t is time;

[0015] (3) The ground conductivity is set to: 0.001 S / m and 0.01 S / m;

[0016] (4) The electron density distribution N e (h) of the D layer of the ionosphere is represented by a two-parameter exponential function, and its expression is as follows:

[0017] N e (h) = 1.43×10 13 e -0.15h′ e (β-0.15)(h-h′) (m -3 )

[0018] where: h is the height from the ground, with a value range of 0 - 120 km, and the unit is km; h' is the reference height of the ionosphere, and the unit is km; β is the rate of change of the ionospheric electron density with height;

[0019] (5) The geomagnetic field intensity is 5×10 -5 T, and the magnetic dip angle is 45°. That is, in the simulation, the propagation directions of lightning electromagnetic signals in different directions are divided into 8 directions: 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°;

[0020] (6) The propagation distance ranges from 100 km to 3000 km, and for each 100 km, the cases of different conductivities, different ionospheres, and different azimuths are calculated once.

[0021] Further, preferably, during the day, the ionospheric reference height h' is set to: 68 km and 74 km; the electron density change rate β is set to 0.3 km -1 and 0.5 km -1 ;

[0022] During the night, the ionospheric reference height h' is set to: 83 km and 87 km; the electron density change rate β is set to 0.3 km -1 and 0.7 km -1 。

[0023] Further, preferably, the electron density distributions in the E and F layers of the ionosphere are calculated using the International Reference Ionosphere - IRI 2016 model.

[0024] Further, preferably, the specific method for establishing a lag database of the ground - wave peak arrival times when lightning electromagnetic waves propagate along different azimuths and different distances is as follows:

[0025] S1. Assume that lightning occurs at different distances and different azimuths. Using the 2D FDTD model, through the configured soil conductivity, ionosphere, and geomagnetic field parameters, obtain the arrival times of lightning electromagnetic waves under each parameter configuration;

[0026] S2. Subtract the arrival time of the lightning electromagnetic wave obtained in S1 from the corresponding arrival time propagating at the speed of light, then obtain the corresponding lag time; associate each parameter configuration with the corresponding time to form a lag - time database.

[0027] Further, preferably, taking the positioning result of the lightning location network as the initial value, considering the time lag from this position to different stations, use the TOA time - difference positioning method to re - position, and finally obtain an optimized positioning result; the specific method is as follows:

[0028] Step a, assume that the propagation speed of the lightning electromagnetic wave is the speed of light. According to the arrival times of the lightning electromagnetic waves obtained by multi - station synchronous stations, use the TOA time - difference positioning algorithm to obtain the initial solution of the lightning occurrence location;

[0029] Step b, according to the position and time information of the initial solution, obtain the distances, azimuths, and times from this lightning strike point to different stations; then directly look up the corresponding lag times from the established time - lag database;

[0030] Step c, according to the found lag times, revise the arrival times measured at each station, and then use the TOA time - difference positioning algorithm to re - position, so as to obtain an optimized positioning result.

[0031] To make up for the deficiencies of the current lightning location algorithm, the present invention proposes a ground-based lightning location method using a two-dimensional finite-difference time-domain algorithm model (2D-FDTD). The finite-difference time-domain algorithm is a method widely used to simulate the propagation of lightning electromagnetic waves, which can be applied to explore the propagation law of lightning VLF-band electromagnetic waves in the Earth-ionosphere waveguide cavity and to investigate the influence of ground conductivity, geomagnetic field, and ionospheric electron density on the time-domain waveform of lightning at long distances in the VLF band. Therefore, by setting reasonable parameter configurations on the propagation path, we can use the mature and widely used FDTD model to study the influence of factors such as soil conductivity, ionosphere, geomagnetic field, and propagation distance on the propagation of lightning electromagnetic fields, and then obtain the time lag data of lightning propagation signals under different propagation path conditions, so as to optimize the original location results.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention relates to a ground-based lightning location method based on a finite-difference time-domain model. Due to the influence of three factors: soil conductivity, ionosphere, and geomagnetic field, the speed of electromagnetic waves excited by lightning when propagating along the ground is not the speed of light. And this propagation speed varies at any time with different azimuths, different times, and different distances because the characteristic parameters of the ionosphere change hourly every day. The above-mentioned various factors ultimately result in different arrival times of lightning at the same distance along different directions when reaching the test, which is one of the main sources of the current lightning location error. Therefore, the present invention first uses the two-dimensional finite-difference time-domain algorithm model (2D FDTD), and by comprehensively considering the influence of the three factors of soil conductivity, ionosphere, and geomagnetic field, realizes the optimization of the lightning location results, providing better technical support for the construction and evaluation of ground-based lightning location networks and other aspects of work. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flowchart of the ground-based lightning location method based on the finite-difference time-domain model of the present invention;

[0035] Figure 2 is a diagram showing the influence of ionospheric parameter changes on the arrival time of lightning electromagnetic signals; (a) night; (b) day;

[0036] Figure 3 is a diagram showing its influence on the peak time delay of ground waves when propagating in different directions at different distances; (a) night; (b) day;

[0037] Figure 4 is the influence of soil conductivity on the arrival time of lightning electromagnetic signals. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following further describes the present invention in detail with reference to embodiments.

[0039] Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the embodiments regarding specific techniques or conditions, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For those materials or equipment without indicating the manufacturer, they are all conventional products that can be obtained by purchase.

[0040] 1 General objectives and implementation steps

[0041] The objective of the present invention is to optimize the positioning result by constructing a lag database of the arrival time of the ground wave peak when the lightning electromagnetic wave propagates along different azimuths and different distances based on the 2D-FDTD model.

[0042] First, based on the two-dimensional finite-difference time-domain algorithm model (2D FDTD), considering different configurations of soil conductivity and ionospheric parameters, a lag database of the arrival time of the ground wave peak when the lightning electromagnetic wave propagates along different azimuths and different distances is established. Then, taking the positioning result of the lightning positioning network as the initial value, considering the time lag from this position to different stations, the TOA time difference positioning method is used for re-positioning, and finally the optimized positioning result is obtained.

[0043] 2 Establishment of the lag database

[0044] Based on the two-dimensional finite-difference time-domain algorithm model (2D FDTD), considering different configurations of soil conductivity and ionospheric parameters, a lag database of the arrival time of the ground wave peak when the lightning electromagnetic wave propagates along different azimuths and different distances is established. Based on the two-dimensional finite-difference time-domain algorithm model (2D-FDTD), considering different configurations of soil conductivity and ionospheric parameters, reasonable parameters are selected. The specific steps are as follows:

[0045] 2.1 Construction of the model

[0046] The model adopted in the present invention is the two-dimensional finite-difference time-domain algorithm model (2D-FDTD). For the detailed algorithm model expressions, refer to "Research on the Propagation Characteristics of Lightning Multi-Band Electromagnetic Waves in the Earth-Ionosphere Waveguide" by Hou Wenhao and "The Finite-Difference Time-Domain Method of Electromagnetic Waves" by Ge Debiao and Yan Yubo.

[0047] 2.2 Selection and configuration of reasonable parameters

[0048] When using this 2D-FDTD model to calculate the propagation characteristics of the lightning electromagnetic field in the Earth-ionosphere cavity, three factors, namely soil conductivity, ionosphere, and geomagnetic field, need to be considered. The parameter settings are as follows:

[0049] 1) In the simulation, the size of the FDTD simulation domain is set to 1010 km × 100 km, the grid size is taken as Δr = Δz = 500 m, and the time step is taken as Δt = 1 μs. The selection of this simulation area, grid size, and time step remains unchanged, which is the parameter setting considering many factors such as the running speed of the model and the stability of the calculation, and these parameters are fixed.

[0050] 2) The excitation source of the model is a vertical dipole, with a height of 10 km, and the current waveform I m (t) is a double-exponential expression:

[0051]

[0052] where: I 0 = 20 kA, v 0 = 8 × 10 7 m / s, γ = 3 × 10 4 s -1 , a = 2 × 10 4 s -1 , b = 2 × 10 5 s -1 , and t is time;

[0053] 3) The ground conductivity can be set to two cases: 0.001 S / m and 0.01 S / m;

[0054] 4) The electron density distribution of the D layer of the ionosphere is represented by a two-parameter exponential function, and its expression is as follows:

[0055] N e (h) = 1.43 × 10 13 e -0.15h′ e (β-0.15)(h-h′) (m -3 )

[0056] where: h is the height from the ground, with a value range of 0 - 120 km, and the unit is km; h’ is the ionosphere reference height, and the unit is km; β is the change rate of the ionosphere electron density with height;

[0057] During the day, the ionosphere reference height h’ is set to: 68 km and 74 km; the electron density change rate β is set to 0.3 km -1 and 0.5 km -1 ;

[0058] At night, the ionosphere reference height h’ is set to: 83 km and 87 km; the electron density change rate β is set to 0.3 km -1 and 0.7 km -1 .

[0059] In this model, the electron density distributions in the E and F layers of the ionosphere are calculated using the International Reference Ionosphere - IRI 2016 model. This parameter is the same during the day and at night.

[0060] 5) The geomagnetic field strength is 5×10 -5 T, and the magnetic dip angle is 45° (taking the Nanjing station as an example)

[0061] In the simulation, taking the Nanjing station as a reference ((N32.0804160°, E118.6253202°), the propagation directions of lightning electromagnetic signals in different directions are divided into 8 directions: 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°.

[0062] 6) The propagation distance ranges from 100 km to 3000 km. For every 100 km interval, calculations are made for different conductivities, different ionospheres, and different azimuths, resulting in a total of 30 calculations.

[0063] In summary, considering the effects of soil conductivity, ionosphere, and geomagnetic field, the main parameter settings during the day and at night are as follows: 1) There are 2 cases for soil conductivity; 2) There are 2 cases for the reference height h' of the ionosphere; 3) There are 2 cases for the electron density change rate β; 4) There are 8 cases for the lightning occurrence azimuth; 5) There are 30 cases for the propagation distance. Therefore, there are 1920 combinations each for the day and at night.

[0064] 2.3 Establishment of the lag database

[0065] Assume that lightning electromagnetic waves propagate in an open space with infinite conductivity, without the influence of the ionosphere and geomagnetic field. Then the propagation speed of the lightning electromagnetic field is the speed of light. The initial solution of the lightning occurrence location is obtained using the Time of Arrival (TOA) method. Although there are errors in this initial solution, it roughly determines information such as the azimuth, time, and distance of the lightning occurrence. Thus, we can use the 2D FDTD model to simulate the time lag when this beam of electromagnetic waves propagates to the station location. However, considering the timeliness issue, it is impossible to perform real - time simulation separately for each lightning strike. This requires establishing a database in advance that can be called at any time.

[0066] Taking the Nanjing station as an example (N32.0804160°, E118.6253202°), assume that lightning strikes occur at different distances and different azimuths. Using the 2D FDTD model, by setting reasonable parameters for soil conductivity, ionosphere, and geomagnetic field, the arrival time of the lightning electromagnetic waves is obtained.

[0067] If we select the geometric mean of different combinations of two soil conductivities, two ionospheric reference heights, and two electron density change rates, only combinations of different azimuths and different distances remain. There are 240 combinations during the day and 240 combinations at night.

[0068] Subtract the arrival time of the lightning electromagnetic signal obtained from the above different combinations from the arrival time assuming propagation at the speed of light, and a lag time database can be obtained. This lag time database is related to the time of lightning occurrence (such as day and night), propagation distance, and azimuth. Once this database is established, we can call it at any time to optimize the positioning result.

[0069] Through a large number of simulation calculations, it is found that even if the station position is changed, this lag time database remains basically unchanged, and this database can be applied to stations in any location. Therefore, for lightning at any location, as long as the distance and azimuth information from it to several synchronous stations are known, the corresponding lag time database can be directly called for optimization processing (Note: The position and occurrence time of each lightning are determined by several stations that synchronously measure the data. Therefore, the distance and azimuth of this lightning to each station are known, and thus the corresponding lag time can be directly called for optimization processing).

[0070] Therefore, the lag time database established in the present invention (in two cases of day and night) only needs to input the distance, azimuth, and time of lightning occurrence to find the corresponding lag time.

[0071] 3 Positioning Optimization

[0072] Taking the positioning result of the lightning positioning network as the initial value, considering the time lag from this position to different stations, and using the TOA time difference positioning method to reposition, the optimized positioning result is finally obtained.

[0073] Specifically as follows:

[0074] Step a, assume that the propagation speed of the lightning electromagnetic wave is the speed of light. According to the arrival time of the lightning electromagnetic wave obtained from multi-station synchronous measurements, use the TOA time difference positioning algorithm to obtain the initial solution of the lightning occurrence position.

[0075] Step b, according to the position and time information of the initial solution, obtain the distance, azimuth, and time from this lightning strike point to different stations; then directly search for the corresponding lag time from the established time lag database.

[0076] Step c, according to the found lag time, revise the arrival time measured by each station, and then use the TOA time difference positioning algorithm to reposition, so as to obtain the optimized positioning result.

[0077] The present invention utilizes the TOA time difference positioning technology. Through synchronous data from at least five stations or more, the initial position and time of lightning occurrence can be obtained. Based on this position, the distances and azimuths from this point to several synchronous measurement stations can be determined; based on the time, it can be determined whether it is day or night. By inputting the distance, azimuth, and time information of the initial lightning strike point, the lag times from this point to several synchronous measurement stations can be found from the lag time database. According to the lag times obtained from each synchronous measurement station, the originally measured time is revised, and the TOA time difference positioning algorithm is used for repositioning, thereby obtaining an optimized positioning result. For the TOA time difference positioning method described in the present invention, see Li, J.; Dai, B.; Zhou, J.; Zhang, J.; Zhang, Q.; Yang, J.; Wang, Y.; Gu, J.; Hou, W.; Zou, B.; et al. Preliminary Application of Long-Range Lightning Location Network with Equivalent Propagation Velocity in China. Remote Sens. 2022, 14, 560. https: / / doi.org / 10.3390 / rs14030560.

[0078] 4 Application Examples

[0079] Using the method of the present invention to simulate the propagation of lightning electromagnetic waves in the Earth-ionosphere waveguide cavity, the influence of various parameters on the ground wave time delay is simulated by the method of controlling variables, as follows:

[0080] A ground-based lightning location method based on the finite-difference time-domain model includes the following steps:

[0081] Based on the two-dimensional finite-difference time-domain algorithm model, considering different configurations of soil conductivity, ionosphere, and geomagnetic field parameters, a lag database of the ground wave peak arrival time is established when lightning electromagnetic waves propagate along different azimuths and different distances;

[0082] Taking the positioning result of the lightning location network as the initial value, considering the time lag from this position to different measurement stations, the TOA time difference positioning method is used for repositioning, and finally an optimized positioning result is obtained.

[0083] Based on the two-dimensional finite-difference time-domain algorithm model, the specific method for considering different configurations of soil conductivity, ionosphere, and geomagnetic field parameters is as follows:

[0084] When calculating the propagation characteristics of lightning electromagnetic fields using the two-dimensional finite-difference time-domain algorithm model, three factors of soil conductivity, ionosphere, and geomagnetic field are considered, and the parameter configurations are as follows:

[0085] (1) The size of the simulation domain of the two-dimensional finite-difference time-domain algorithm model is set to 1010 km × 100 km, the grid size is taken as Δr = Δz = 500 m, and the time step is taken as Δt = 1 μs; where, Δr is the horizontal scale and Δz is the vertical scale;

[0086] (2) The excitation source of the two-dimensional finite-difference time-domain algorithm model is a vertical dipole, with a height of 10 km, and the current waveform I m (t) is a double-exponential expression:

[0087]

[0088] where: I 0 = 20 kA, v 0 = 8 × 10 7 m / s, γ = 3 × 10 4 s -1 , a = 2 × 10 4 s -1 , b = 2 × 10 5 s -1 , and t is time;

[0089] (3) The ground conductivity is set to: 0.001 S / m and 0.01 S / m;

[0090] (4) The electron density distribution N e (h) of the D layer of the ionosphere is represented by a two-parameter exponential function, and its expression is as follows:

[0091] N e (h) = 1.43 × 10 13 e -0.15h′ e (β-0.15)(h-h′) (m -3 )

[0092] where: h is the height from the ground, with a value range of 0 - 120 km, and the unit is km; h' is the reference height of the ionosphere, and the unit is km; β is the rate of change of the ionospheric electron density with height;

[0093] (5) The geomagnetic field intensity is 5 × 10 -5 T, and the magnetic dip angle is 45°. That is, in the simulation, the propagation directions of lightning electromagnetic signals in different directions are divided into 8 directions: 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°;

[0094] (6) The propagation distance ranges from 100 km to 3000 km, and for each 100 km, the cases of different conductivities, different ionospheres, and different azimuths are calculated once.

[0095] The electron density distributions in the E and F layers of the ionosphere will be calculated using the International Reference Ionosphere - IRI 2016 model.

[0096] The specific method for establishing a database of the lag of the ground - wave peak arrival time when lightning electromagnetic waves propagate in different directions and at different distances is as follows:

[0097] S1. Assume that lightning occurs at different distances and in different directions. Using the 2D FDTD model, and through the configured soil conductivity, ionosphere, and geomagnetic field parameters, obtain the arrival times of lightning electromagnetic waves under each parameter configuration.

[0098] S2. Subtract the arrival time of the lightning electromagnetic wave obtained in S1 from the corresponding arrival time propagating at the speed of light, then the corresponding lag time can be obtained; associate each parameter configuration with the corresponding time to form a lag - time database.

[0099] Taking the positioning result of the lightning location network as the initial value, considering the time lag from this location to different stations, use the TOA time - difference positioning method to re - position, and finally obtain the optimized positioning result; the specific method is as follows:

[0100] Step a, assume that the propagation speed of lightning electromagnetic waves is the speed of light. According to the arrival times of lightning electromagnetic waves obtained by multi - station synchronous measurements, use the TOA time - difference positioning algorithm to obtain the initial solution of the lightning occurrence location.

[0101] Step b, according to the position and time information of the initial solution, obtain the distances, azimuths, and times from this lightning strike point to different stations; then directly look up the corresponding lag times from the established lag - time database.

[0102] Step c, according to the found lag times, revise the arrival times measured at each station, and then use the TOA time - difference positioning algorithm to re - position, so as to obtain the optimized positioning result.

[0103] 1) The influence of the ionosphere on the ground - wave peak time delay

[0104] Figure 2 (a) shows the influence of the change of ionosphere parameters on the arrival time of lightning electromagnetic signals at night. Among them, β is 0.3 km -1 , 0.5 km -1 , 0.7 km -1 , and h′ is 83 km. It can be seen that within about 1500 km, the change of ionosphere parameters has little influence on the arrival time of lightning electromagnetic waves; but when it exceeds 1500 km, the influence brought by the change of ionosphere parameters becomes more and more significant. Figure 2(b) shows the influence of the variation of ionospheric parameters on the arrival time of lightning electromagnetic signals under daytime conditions. Among them, h′ is 68 km, 70 km, 72 km, and 74 km, and β is 0.3 km -1 . It can be seen that due to the relatively low ionospheric height during the day, its influence on lightning electromagnetic fields is significantly greater.

[0105] 2) Influence of the geomagnetic field on the peak delay of ground waves

[0106] Figure 3 shows the influence of the anisotropic geomagnetic field on the arrival time of lightning electromagnetic signals under nighttime ( Figure 3 (a)) and daytime ( Figure 3 (b)) conditions. From the nighttime perspective, when the propagation distance exceeds 1200 km, the influence of the geomagnetic field begins to gradually become significant. From the daytime perspective, when the propagation distance exceeds 1500 km, the influence of the geomagnetic field becomes obvious.

[0107] 3) Influence of ground conductivity on the peak delay of ground waves

[0108] Figure 4 shows the influence of soil conductivity on the arrival time of lightning electromagnetic signals, with the conductivity set to 0.01 S / m and 0.001 S / m. It can be clearly seen from the figure that as the observation distance increases, the peak delay of ground waves approximately increases linearly.

[0109] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A ground-based lightning location method based on a finite-difference time-domain model, characterized in that: The steps include: Based on the two-dimensional finite-difference time-domain algorithm model, considering different configurations of soil conductivity, ionosphere and geomagnetic field parameters, a hysteresis database of ground wave peak arrival time when lightning electromagnetic waves propagate along different directions and distances is established; Taking the positioning result of the lightning positioning network as the initial value and considering the time lag of the location reaching different measuring stations, the TOA time difference positioning method is used to reposition the location, and finally the optimized positioning result is obtained.

2. The ground-based lightning location method based on the finite difference time domain model according to claim 1 is characterized in that: Based on the two-dimensional finite-difference time-domain algorithm model, the specific method considering different configurations of soil conductivity, ionosphere and geomagnetic field parameters is as follows: When using the two-dimensional finite-difference time-domain algorithm model to calculate the propagation characteristics of lightning electromagnetic fields, three factors, soil conductivity, ionosphere and geomagnetic field, are considered. The configuration of its parameters is as follows: (1) The size of the simulation domain of the 2D FDTD model is set to 1010 km × 100 km, the grid size is Δr = Δz = 500 m, and the time step is Δt = 1 μs; where Δr is the horizontal scale and Δz is the vertical scale; (2) The excitation source of the 2D FDTD model is a vertical dipole with a height of 10 km and a current waveform I m (t) is a double exponential expression: Where: I0 = 20kA, v0 = 8 × 10 7 m / s,γ=3×10 4 s -1 , a=2×10 4 s -1 , b = 2 × 10 5 s -1 , t is the time; (3) The ground conductivity is set to: 0.001S / m and 0.01S / m; (4) Electron density distribution N in the D layer of the ionosphere e (h) is expressed by a two-parameter exponential function, and its expression is as follows: N e (h)=1.43×10 13 e -0.15h′ e (β-0.15)(h-h′) (m -3 ) Where: h is the height from the ground, ranging from 0 to 120 km, in km; h' is the ionospheric reference height, in km; β is the rate of change of ionospheric electron density with altitude; (5) The Earth's magnetic field strength is 5×10 -5 T, the magnetic inclination is 45°, that is, in the simulation, the propagation directions of lightning electromagnetic signals in different directions are divided into 8 directions: 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315°; (6) The propagation distance ranges from 100km to 3000km, and calculations are performed every 100km for different conductivity, different ionosphere, and different azimuth conditions.

3. The ground-based lightning location method based on the finite difference time domain model according to claim 2 is characterized in that: During the day, the ionospheric reference altitude h' is set to 68km and 74km; the electron density change rate β is set to 0.3km -1 and 0.5km -1 ; At night, the ionospheric reference altitude h' is set to 83km and 87km; the electron density change rate β is set to 0.3km -1 and 0.7km -1 .

4. The ground-based lightning location method based on the finite difference time domain model according to claim 2 is characterized in that: The electron density distribution in the E and F layers of the ionosphere will be calculated using the International Reference Ionosphere-IRI 2016 model.

5. The ground-based lightning location method based on the finite difference time domain model according to claim 2, characterized in that: The specific method for establishing a hysteresis database of the ground wave peak arrival time when lightning electromagnetic waves propagate along different directions and different distances is as follows: S1. Assuming that lightning occurs at different distances and directions, the 2D FDTD model is used to obtain the arrival time of lightning electromagnetic waves under various parameter configurations through the configured soil conductivity, ionosphere and geomagnetic field parameters; S2. Subtract the arrival time of the lightning electromagnetic wave obtained in S1 from the corresponding arrival time propagating at the speed of light to obtain the corresponding lag time; associate each parameter configuration with the corresponding time to form a lag time database.

6. The ground-based lightning location method based on the finite difference time domain model according to claim 2 is characterized in that: Taking the positioning result of the lightning positioning network as the initial value, considering the time lag of the location reaching different measuring stations, the TOA time difference positioning method is used to reposition, and finally the optimized positioning result is obtained; the specific method is as follows: Step a, assuming that the propagation speed of lightning electromagnetic waves is the speed of light, according to the arrival time of lightning electromagnetic waves obtained by multiple synchronous measurement stations, the TOA time difference positioning algorithm is used to obtain the initial solution of the lightning occurrence location; Step b, obtaining the distance, direction and time from the lightning strike point to different measuring stations according to the position and time information of the initial solution; Then the corresponding lag time is directly searched from the established time lag database; Step c: According to the found lag time, the arrival time measured by each station is revised, and then the TOA time difference positioning algorithm is used to reposition, so as to obtain the optimized positioning result.

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