Method and system for analyzing underground lightning electromagnetic field propagation by soil water content

Abstract

The invention relates to the technical field of underground lightning electromagnetic field propagation, and discloses a method and system for analyzing underground lightning electromagnetic field propagation by soil water content, and the analysis method comprises the steps: respectively constructing a vertical electric field distribution model, a horizontal electric field distribution model and an azimuth magnetic field distribution model of a lightning ideal smooth ground according to a moving charge electromagnetic field equation; acquiring the conductivity of the soil, the depth of the soil and the wavenumber of the soil; and determining underground lightning electromagnetic field distribution characteristics under the condition of soil water content in the soil depth direction according to the constructed vertical electric field distribution model, horizontal electric field distribution model and azimuth magnetic field distribution model and the obtained conductivity, depth and wavenumber of the soil. According to the invention, the lightning electromagnetic field propagation characteristics of the soil are accurately analyzed according to the moisture content of the soil, the conductivity of the soil and the depth of the soil, and the detection precision of underground cable protection and underground electromagnetic detection work is improved.

Description

Technical Field

[0001] The invention relates to the technical field of underground lightning electromagnetic field propagation, and in particular to an analysis method and system for the effect of soil moisture content on underground lightning electromagnetic field propagation. Background Art

[0002] The statements in this section merely provide background art related to the present disclosure and do not necessarily constitute prior art.

[0003] Lightning strike is a high-voltage and high-current discharge phenomenon in nature, involving physical effects of multiple field coupling such as impact force, electromagnetic force, and Joule heating effect, which poses a serious threat to communication systems. In mild cases, it affects the quality of communication, and in severe cases, it causes damage to communication base stations. Lightning ground lightning occurs between clouds and the ground, which has a huge impact on human production and life. Therefore, it is necessary to study lightning parameters. The lightning positioning system can determine the number, location, time and intensity of lightning in the effective area, which is of great significance for lightning disaster protection, lightning parameter statistics and research on lightning activity laws. Lightning positioning technology determines the spatial position, time and other discharge parameters of lightning by measuring multi-dimensional information such as sound, light, and electromagnetic fields generated by lightning. Among them, lightning electromagnetic fields are one of the indispensable characteristic quantities.

[0004] The ground-to-ground lightning process includes pre-breakdown, step leader, first return stroke, straight leader and subsequent return stroke. The return stroke process will generate the return stroke current with the largest intensity in the entire long gap discharge, and instantly radiate huge electromagnetic energy outward, that is, generate the lightning electromagnetic pulse with the largest amplitude and the strongest radiation effect in the entire ground-to-ground lightning process. After the lightning radiation electromagnetic pulse propagates to the surroundings, the electromagnetic field data is collected, and the corresponding lightning characteristic parameters can be inverted and calculated. The propagation process of lightning electromagnetic waves is easily affected by the space environment. Therefore, it is necessary to explore the propagation characteristics of lightning electromagnetic waves in typical scenarios, as well as the influence of environmental factors such as terrain and climate on the electromagnetic field.

[0005] At present, existing research mainly focuses on using FDTD to calculate the distribution of lightning electromagnetic fields above the ground. However, the numerical stability of FDTD causes electromagnetic fields to oscillate when the calculation distance exceeds 20km, which is difficult to solve. In addition, there is little research on the impact of soil moisture on the propagation of underground lightning electromagnetic fields. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method and system for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation, which obtains an underground lightning electromagnetic field model of smooth lossy soil based on the electromagnetic field equation of moving charges combined with the Wait formula, and then obtains an MTLE equivalent model of the lightning return channel in underground propagation characteristics based on the relationship between soil moisture content and resistivity.

[0007] The technical solution adopted by the present invention is: an analysis method for the effect of soil moisture on the propagation of underground lightning electromagnetic fields, comprising: constructing a vertical electric field distribution model, a horizontal electric field distribution model and an azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning according to a moving charge electromagnetic field equation; and obtaining the electrical conductivity of the soil, the depth of the soil and the wave number of the soil; and using the constructed vertical electric field distribution model, the horizontal electric field distribution model and the azimuthal magnetic field distribution model to obtain the electrical conductivity of the soil, the depth of the soil and the wave number of the soil to determine the underground lightning electromagnetic field distribution characteristics under the condition of soil moisture in the soil depth direction.

[0008] In the present technical scheme, based on the relationship between the established vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning and the electrical conductivity of the soil, the depth of the soil and the wave number of the soil, the lossy ground electromagnetic field model of the lightning return stroke on the soil ground is determined; based on the lossy ground electromagnetic field model of the lightning return stroke on the soil ground, the lossy ground electromagnetic field model of the lightning return stroke on the soil ground surface is obtained; based on the lossy ground electromagnetic field model of the lightning return stroke on the soil ground surface, the distribution characteristics of the lightning radiation electromagnetic field propagating underground in the soil are obtained.

[0009] In this technical solution, when obtaining the lightning return lossy ground electromagnetic field model of the soil ground, the Wait formula and the vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of the ideal smooth ground struck by lightning are used to transform it into the lightning return lossy ground electromagnetic field model: ; ; ; in: ; ; ; ; Where: R is the horizontal distance from the channel; h is the vertical height from the ground; jω is a complex function; j is the imaginary unit; ω is the angular frequency; E z ( R, h, jω ) is the vertical electric field of lightning striking smooth lossy ground; E zp ( R, h, jω ) is the vertical electric field of lightning striking an ideal ground; E r ( R, h, jω) is the horizontal electric field when lightning strikes smooth and lossy ground; E rp ( R, h, jω ) is the horizontal electric field of an ideal ground struck by lightning; It is the azimuthal magnetic field of the smooth and lossy ground struck by lightning; The azimuth magnetic field of the ideal ground for lightning strike; erfc is the error correction function, J is the numerical distance; γ 0 is the free space wave number, Δ is the normalized surface impedance of the soil; σ The conductivity of the soil on a smooth and lossy surface; μ 0 is the vacuum permeability; ε 0 is the dielectric constant of vacuum; ε r is the relative dielectric constant; F(jω), Z(jω) Both are functions that vary with soil conductivity and angular frequency.

[0010] In this technical solution, when h is 0, the above formula is calculated to obtain the electromagnetic field model of the lightning return lossy ground surface on the soil surface; then the electromagnetic field model of the lightning return lossy ground surface on the soil surface is respectively substituted into the CR formula to obtain the underground lightning electromagnetic field distribution characteristics under the soil moisture content condition of the lightning-struck smooth lossy ground in the soil depth direction: ; ; ; in: ; Where: E z (R, s, jω) It is the vertical electric field of lightning striking smooth and lossy ground; It is the azimuthal magnetic field of the smooth and lossy ground struck by lightning; E r (R, s, jω) It is the horizontal electric field of lightning when it strikes smooth and lossy ground; E z (R, 0, jω) It is the vertical electric field of lightning when it strikes a smooth and lossy ground surface; It is the azimuthal magnetic field of the smooth and lossy ground surface struck by lightning; E r (R, 0, jω) It is the horizontal electric field of lightning when it strikes a smooth and lossy ground surface; s is the depth of the soil; γ is the wave number of soil; μ 0is the vacuum permeability; ε 0 is the dielectric constant of vacuum.

[0011] In this technical solution, when calculating the soil moisture content of the smooth lossy ground in the soil depth direction under the condition of lightning strike, the return current of the lightning return channel is I(z, t) The model used in the calculation is the MTLE model: ; Where: P(z) is the current attenuation factor, λ e is the current decay constant with height, v For the return speed ，i b (0,t) is the substrate current, z Charge element d z Height within the lightning channel, t - z / v represents time t minus the charge element d z Movement ground height z The distance of time; The double Heidler function is used to calculate the current distribution that conforms to the lightning channel: ; Where: I 01 and I 02 are the breakdown current peak and the corona current peak, respectively. and They are the breakdown current rising edge time and the corona current rising edge time, and They are the breakdown current falling edge time and the corona current falling edge time, n 1 and n 2 are the breakdown current steepness factor and the corona current steepness factor, η 1 and η 2 They are breakdown current peak correction factor and corona current peak correction factor respectively.

[0012] In this technical solution, based on the relationship between soil moisture content and electrical conductivity, a series of underground lightning electromagnetic field distribution characteristics of the same soil with different moisture contents in the soil depth direction are obtained; and a series of underground lightning electromagnetic field distribution characteristics of different soils with the same moisture content in the soil depth direction are obtained to obtain the lightning radiation electromagnetic field characteristics of soils with different moisture contents propagating underground, so as to analyze the lightning radiation electromagnetic field propagation characteristics of soils with different moisture contents and different types underground, thereby avoiding unnecessary design defects in advance in the design process involving water pipes, cables, valves, etc., and improving the accuracy and practicality of these designs.

[0013] In this technical solution, the resistivity of clay, silt and sand at different water contents obtained by the forced current method is used to obtain the relationship between the conductivity of clay, silt and sand and the change in water content according to the least squares fitting formula: ; Where: p is the soil moisture content, σ 粘土 , σ 粉土 , σ 砂土 Soil conductivity of clay, silt and sand, respectively.

[0014] In this technical solution, the Fourier transform technology is used to solve the conductivity and water content fitting formula to obtain the underground lightning electromagnetic field distribution characteristics in the soil depth direction.

[0015] An analysis system for the effect of soil moisture on underground lightning electromagnetic field propagation, the analysis system includes an ideal smooth ground electromagnetic distribution model for lightning strikes, a soil moisture and conductivity relationship model, a soil ground lightning return lossy ground electromagnetic field model, a soil ground lightning return lossy ground electromagnetic field model, and a soil ground lightning return lossy ground electromagnetic field model, wherein: The electromagnetic distribution model of an ideal smooth ground struck by lightning is used to construct a vertical electric field distribution model, a horizontal electric field distribution model and an azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning according to the electromagnetic field equation of moving charges; The soil moisture content and conductivity relationship model is used to obtain the influence factors of soil type, moisture content, soil depth and soil wave number on the actual lightning electromagnetic field of lightning striking smooth and lossy ground; The lightning return stroke lossy ground electromagnetic field model of the soil surface is used to obtain the lightning electromagnetic field characteristic distribution of the soil surface by associating the lightning ideal smooth ground electromagnetic distribution model with the soil moisture content and conductivity relationship model; The lightning return lossy ground electromagnetic field model under the soil is used to obtain the distribution characteristics of the lightning radiation electromagnetic field propagated underground in the soil in the lightning return channel according to the lightning return lossy ground electromagnetic field model on the soil surface.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1.According to the soil moisture content, soil conductivity, soil depth, and soil wave number, the soil lightning electromagnetic field propagation characteristics are accurately analyzed to improve the protection of underground cables and the detection accuracy of underground electromagnetic detection; 2. The underground attenuation characteristics of lightning electromagnetic fields under different soil moisture conditions were calculated, providing a certain reference for the protection of underground cables and underground electromagnetic detection; 3. Set the horizontal distance R , observation point P Height h , Soil moisture content on smooth and lossy ground p Substitute the Wait formula to obtain the distribution of the corresponding lightning electromagnetic field; R , observation point P Depth s , Soil moisture content on smooth and lossy ground p Substituting it into the CR formula, the corresponding underground distribution of lightning electromagnetic field can be obtained.

[0017] The analysis method and system of the present invention improve the FDTD numerical stability of the electromagnetic field when the lightning strike distance exceeds 20 km, and can accurately analyze the lightning electromagnetic field propagation characteristics of the soil according to the soil moisture content, soil conductivity, and soil depth, thereby improving the protection of underground cables and the detection accuracy of underground electromagnetic detection, providing a better reference basis for the protection of underground cables and underground electromagnetic detection, thereby expanding and enhancing its application in the protection of underground cables and underground electromagnetic detection.

[0018] Therefore, the study on the propagation characteristics of lightning electromagnetic fields on underground electromagnetic fields has important application value in the fields of lightning protection and geological exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of an embodiment of a method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation; Figure 2 A flowchart of another embodiment of the analysis method; Figure 3 A functional block diagram of an embodiment of an analysis system is provided; Figure 4 Schematic diagram of lightning channel structure; Figure 5 (a) shows the horizontal distance of the lightning channel R 200m, soil depth s is the vertical electric field component in clay with different water contents at 2 m underground; Figure 5 (b) shows the horizontal distance of the lightning channel R 200m, soil depth s is the horizontal electric field component in clay with different water contents 2 m underground; Figure 5 (c) shows the horizontal distance of the lightning channel R 200m, soil depth s is the azimuthal magnetic field component in clay with different water contents 2 m underground; Figure 6 (a) shows the horizontal distance of the lightning channel R 200m, soil depth s is the vertical electric field component in clay with different water contents at 2 m underground; Figure 6 (b) shows the horizontal distance of the lightning channel R 200m, soil depth s is the horizontal electric field component in clay with different water contents 2 m underground; Figure 6 (c) shows the horizontal distance of the lightning channel R 200m, soil depth s is the azimuthal magnetic field component in clay with different water contents 2 m underground; Figure 7 (a) shows the horizontal distance of the lightning channel R 200m, soil depth s is the vertical electric field component in sand with different water contents 2m underground; Figure 7 (b) shows the horizontal distance of the lightning channel R 200m, soil depth s is the horizontal electric field component in sand with different water contents 2m underground; Figure 7 (c) shows the horizontal distance of the lightning channel R 200m, soil depth s is the azimuthal magnetic field component in sand with different water contents 2 m underground; Among them: 100-ideal smooth ground electromagnetic distribution model of lightning strike, 200-soil moisture content and conductivity relationship model, 300-losative ground electromagnetic field model of lightning return stroke on soil ground, 400-losative ground electromagnetic field model of lightning return stroke on soil surface, 500-losative ground electromagnetic field model of lightning return stroke under soil. DETAILED DESCRIPTION

[0020] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout are the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0021] like Figure 1 As shown, the analysis method of soil moisture content on underground lightning electromagnetic field propagation includes the following steps: S1. According to the electromagnetic field equation of moving charges, a vertical electric field distribution model, a horizontal electric field distribution model and an azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning are respectively constructed; And step S2. obtain the electrical conductivity of the soil, the depth of the soil and the wave number of the soil; and step S3. use the constructed vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model to obtain the electrical conductivity of the soil, the depth of the soil and the wave number of the soil to determine the underground lightning electromagnetic field distribution characteristics under the soil moisture content conditions in the soil depth direction.

[0022] like Figure 2 As shown, the analysis method further includes step S4. determining a lightning return stroke lossy ground electromagnetic field model of the soil ground according to the relationship between the established vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of the ideal smooth ground struck by lightning and the electrical conductivity of the soil, the depth of the soil and the wave number of the soil; Step S5. According to the lossy ground electromagnetic field model of lightning return stroke on the soil surface, a lossy ground electromagnetic field model of lightning return stroke on the soil surface is obtained; Step S6. According to the lossy ground electromagnetic field model of lightning return stroke on the soil surface, the distribution characteristics of the electromagnetic field radiated by lightning propagating underground in the soil are obtained.

[0023] In addition, if Figure 3As shown, an analysis system for the effect of soil moisture content on underground lightning electromagnetic field propagation, the analysis system includes an ideal smooth ground electromagnetic distribution model 100 for lightning strike, a soil moisture content and conductivity relationship model 200, a lightning return lossy ground electromagnetic field model 300 on the soil ground, a lightning return lossy ground electromagnetic field model 400 on the soil ground surface, and a lightning return lossy ground electromagnetic field model 500 under the soil, wherein: the ideal smooth ground electromagnetic distribution model 100 for lightning strike is used to construct a vertical electric field distribution model, a horizontal electric field distribution model, and an azimuthal magnetic field distribution model of the ideal smooth ground struck by lightning according to a moving charge electromagnetic field equation; the soil moisture content The soil water content and conductivity relationship model 200 is used to obtain the influence factors of soil type, water content, soil depth and soil wave number on the lightning electromagnetic field of the actual lightning-struck smooth and lossy ground; the lightning return stroke lossy ground electromagnetic field model 300 of the soil ground is used to associate the ideal smooth ground electromagnetic distribution model of lightning strikes with the soil water content and conductivity relationship model to obtain the lightning electromagnetic field characteristic distribution of the soil ground surface; the lightning return stroke lossy ground electromagnetic field model 400 of the soil ground surface is used to obtain the lightning radiation electromagnetic field distribution characteristics of the soil propagating on the ground surface in the lightning return channel according to the lightning return stroke lossy ground electromagnetic field model of the soil ground surface. The lightning return stroke lossy ground electromagnetic field model 500 of the soil underground is used to obtain the lightning radiation electromagnetic field distribution characteristics of the soil propagating underground in the lightning return channel according to the lightning return stroke lossy ground electromagnetic field model of the soil underground.

[0024] When using the above analysis method, firstly, the vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning are constructed: (1) Based on the electromagnetic field equation of moving charges, the vertical electric field distribution model formula of lightning striking an ideal smooth ground is obtained: (1); (2); (3); (4); (5); Where: The electromagnetic field geometric model of the lightning return channel is as follows: Figure 4 According to the geometric model, in the above formula, is the vertical component of the electric field of the accelerating radiation; is the vertical component of the velocity field; is the vertical component of the deceleration radiation electric field; is the vertical component of the electrostatic field; is the current at the height z of the lightning channel; t is the time; is the angle between the bottom of the lightning channel and the observation point P; Charge element Angle with observation point P; Image charge element Angle with observation point P; is the vacuum dielectric constant; z is the charge element Height within the lightning channel; r 1 is the distance from the observation point to the charge element distance; r 2 is the distance from the observation point to the image charge element The distance between the observation point and the return stroke point of the lightning return stroke channel is r. is the current attenuation factor; c is the speed of light, take 3×10 8 m / s, v For the speed of return; H is the lightning channel length.

[0025] (2) Based on the electromagnetic field equation of moving charges, the horizontal electric field distribution model formula of lightning striking an ideal smooth ground is obtained: (6); (7); (8); (9); (10); in, is the horizontal component of the electric field of the accelerating radiation; is the horizontal component of the velocity field; is the horizontal component of the deceleration radiation electric field; is the horizontal component of the electrostatic field, and the other parameters are consistent with equations (1) to (4).

[0026] (3) Based on the electromagnetic field equation of moving charges, the azimuthal magnetic field distribution formula of lightning striking an ideal smooth ground is obtained: (11); (12); (13); (14); To accelerate the radiation magnetic field; is the velocity magnetic field; To decelerate the radiation magnetic field.

[0027] Secondly, the Wait formula is then used to transform the ideal ground electromagnetic field model of lightning return stroke obtained by equations (5), (10) and (14) into a lossy ground electromagnetic field model of lightning return stroke. The Wait formula is as follows: (15); (16); (17); In formulas (15), (16) and (17), R is the horizontal distance from the channel; h is the vertical height from the ground; is a complex function; is an imaginary unit; is the angular frequency; It is the vertical electric field of lightning striking smooth and lossy ground; is the vertical electric field of an ideal ground struck by lightning; It is the horizontal electric field of lightning striking smooth and lossy ground; is the horizontal electric field of an ideal ground struck by lightning; It is the azimuthal magnetic field of the smooth and lossy ground struck by lightning; It is the azimuth magnetic field of the ideal ground for lightning strike.

[0028] Among them, in formulas (15), (16) and (17) The expression is as follows: (18); In formula (18), is the error correction function, J is the numerical distance, and the expression is: (19); In formula (19), is the free space wave number, is the normalized surface impedance of the soil, and the expressions are: (20); (twenty one); In formula (21), The expression is: (twenty two); In formula (22), The conductivity of the soil on a smooth and lossy surface; is the vacuum magnetic permeability, which is 4π×10 -7 H / m; is the vacuum dielectric constant, which is ; is the relative dielectric constant, which can be a certain value or a certain range. The value is related to the frequency and is taken as 10 here.

[0029] Set h in equations (15), (16), and (17) to 0 to obtain the lossy ground electromagnetic field of lightning return stroke on the ground surface. Then, substitute them into equations (23) to (25) to obtain the distribution characteristics of electromagnetic field radiated by lightning propagating underground. The distribution characteristics of electromagnetic field radiated by lightning propagating underground are expressed by the CR formula as follows: (twenty three); (twenty four); (25); in E z (R, s, jω) It is the vertical electric field of lightning that strikes smooth and lossy ground underground; E r (R, s, jω) It is the horizontal electric field of lightning that strikes smooth and lossy ground. It is the azimuthal magnetic field of the smooth and lossy ground under the lightning strike; s is the depth of the soil; γ is the wave number of the soil.

[0030] (26); in μ 0 is the vacuum magnetic permeability, which is 4π×10 -7 H / m. By inverse Fourier transforming equations (23), (24) and (25), we can finally obtain the time domain electromagnetic field of the electromagnetic field distribution characteristics of lightning radiation propagating underground in the soil.

[0031] In the specific implementation process, the return current is calculated I(z, t) The model selected is the MTLE model. When the return stroke current develops upward along the channel, its current amplitude decays exponentially with the height, which is more in line with the actual current distribution of the lightning channel. Its current distribution expression is as follows: (27); The above formula P(z) is the current attenuation factor. λ e is the current attenuation constant with height, taken as 2000. v Assuming the return velocity is constant, we take 1.5×10 8 m / s. i b (0,t) is the base current. Here, the double Heidler function is used, which includes the breakdown current and the corona current. The expression is as follows: (28);

[0032] In the formula I 01 and I 02 are the breakdown current and the corona current peak, and They are the breakdown current rising edge time and the corona current rising edge time, and They are the breakdown current falling edge time and the corona current falling edge time, n 1 and n 2 are the breakdown current steepness factor and the corona current steepness factor, η 1 and η 2 are the peak correction factor of breakdown current and the peak correction factor of corona current respectively. The parameters corresponding to the base current are shown in Table 1. Substitute the return stroke current in equation (27) into equation (1)-(14) to replace the return stroke current in the formula.

[0033] Table 1 Base current parameters

[0034] In the specific implementation process, the relationship model between water content and soil conductivity is generally the resistivity of clay, silt and sand at different soil moisture contents obtained by the forced current method. The relationship between the conductivity of the three soils and the change of water content is obtained by fitting according to the least squares method. By analyzing the residuals, it is found that the fitting situation is very consistent with the measured situation. The fitting formula is as follows: (29); Where p is the soil moisture content, σ 粘土 , σ 粉土 , σ 砂土 for σ A specific embodiment, that is to say σ 粘土 , σ 粉土 , σ 砂土 Soil conductivity of clay, silt and sand, respectively.

[0035] In the specific numerical calculation process, Fourier transform technology is used to solve equations (23) to (25) to obtain the underground lightning electromagnetic field distribution under different soil moisture conditions.

[0036] Through numerical simulation of examples, the present invention analyzes the influence of the water content of clay, silt and sand on the underground propagation of lightning electromagnetic field when the water content is 5%, 10%, 15%, 20% and 25% respectively. The experimental verification results are shown in Figure 5 (a), Figure 5 (b) and Figure 5 (c) for the horizontal distance of the lightning channel. R 200m, soil depth s Characteristic diagrams of vertical electric field component, horizontal electric field component, and azimuthal magnetic field component in clay with different water contents 2 m underground; and horizontal distances of lightning channels in Figures 6 (a), 6 (b), and 6 (c) R 200m, soil depth s Characteristic diagrams of vertical electric field component, horizontal electric field component, and azimuthal magnetic field component in clay with different water contents 2 m underground; and horizontal distance of lightning channel in Figure 7 (a), Figure 7 (b), and Figure 7 (c) R 200m, soil depth s The characteristic diagram of the vertical electric field component, horizontal electric field component, and azimuthal magnetic field component in sand with different water contents 2m underground.

[0037] From Figures 5(a), 5(b), 5(c), 6(a), 6(b), 6(c), 7(a), 7(b), and 7(c), it can be verified that: (1) The attenuation of lightning electromagnetic fields in different soils is significantly different. The attenuation in clay is significantly greater than that in silt and sand. There are also significant differences in the attenuation of electric and magnetic fields. The attenuation of the electric field is significantly greater than that of the magnetic field, and the attenuation of the vertical electric field is the most significant. (2) Regardless of clay, silt, or sand, when the water content is 5% to 10%, the attenuation effect on the underground electromagnetic field is the strongest, the attenuation of the vertical electric field is the largest, followed by the horizontal electric field, and the azimuthal magnetic field has the smallest effect. When the water content is 10% to 25%, as the water content approaches saturation, the soil conductivity tends to be stable, and the attenuation effect on the electromagnetic field weakens.

[0038] In summary, the present invention provides a method and system for analyzing the effect of soil moisture content on underground lightning electromagnetic field propagation. By constructing a lightning electromagnetic field propagation model and combining it with numerical calculation technology, the lightning electromagnetic field distribution of different soils under the same moisture content or different moisture content conditions is accurately calculated. The lightning electromagnetic field distribution of the same soil under different moisture content conditions can also be accurately calculated. This method provides important theoretical support for lightning electromagnetic pulse protection and geological exploration.

[0039] The embodiments of the present invention disclose preferred embodiments, but are not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. The method for analyzing the effect of soil moisture on the propagation of underground lightning electromagnetic fields is characterized by: include: According to the electromagnetic field equation of moving charges, the vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of lightning striking ideal smooth ground are constructed respectively; as well as Obtain soil conductivity, soil depth, and soil wave number; and The constructed vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model are used to obtain the soil conductivity, soil depth and soil wave number to determine the underground lightning electromagnetic field distribution characteristics under the soil moisture content conditions in the soil depth direction.

2. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 1, characterized in that: According to the relationship between the vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of ideal smooth ground struck by lightning and the conductivity of the soil, the depth of the soil and the wave number of the soil, the lossy ground electromagnetic field model of lightning return stroke on the soil ground is determined; According to the lightning return lossy ground electromagnetic field model of the soil ground, the lightning return lossy ground electromagnetic field model of the soil ground surface is obtained; According to the lossy ground electromagnetic field model of lightning return stroke on the soil surface, the distribution characteristics of the electromagnetic field radiated by lightning propagating underground in the soil are obtained.

3. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 2, characterized in that: When obtaining the lightning return lossy ground electromagnetic field model of the soil ground, the Wait formula and the vertical electric field distribution model, horizontal electric field distribution model and azimuthal magnetic field distribution model of the ideal smooth ground struck by lightning are used to transform it into the lightning return lossy ground electromagnetic field model: ； ； ； in: ; ; ; ； Where: R is the horizontal distance from the channel; h is the vertical height from the ground; jω is a complex function; j is an imaginary unit; ω is the angular frequency; E z (R,h,jω) It is the vertical electric field of lightning striking smooth and lossy ground; E zp (R,h,jω) is the vertical electric field of an ideal ground struck by lightning; E r (R,h,jω) E is the horizontal electric field of lightning striking smooth and lossy ground; rp (R,h,jω) is the horizontal electric field of the ideal ground struck by lightning; It is the azimuthal magnetic field of the smooth and lossy ground struck by lightning; The azimuth magnetic field of the ideal ground for lightning strike; erf is the error correction function, J is the numerical distance; γ 0 is the free space wave number, Δ is the normalized surface impedance of the soil; σ is the conductivity of smooth lossy ground soil; μ0 is the vacuum magnetic permeability; ε 0 is the dielectric constant of vacuum; ε r is the relative dielectric constant; F(jω), Z(jω) Both are functions that vary with soil conductivity and angular frequency.

4. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 3 is characterized by: when h When is 0, the above formula is calculated to obtain the electromagnetic field model of the lightning return stroke lossy ground surface on the soil surface; then the electromagnetic field model of the lightning return stroke lossy ground surface on the soil surface is respectively substituted into the CR formula to obtain the underground lightning electromagnetic field distribution characteristics under the soil moisture content condition of the lightning-struck smooth lossy ground in the soil depth direction: ； ； ； in: ; Where: E z (R,s,jω) It is the vertical electric field of lightning striking smooth and lossy ground; It is the azimuthal magnetic field of the smooth and lossy ground struck by lightning; E r (R,s,jω) It is the horizontal electric field of lightning when it strikes smooth and lossy ground; E z (R,0,jω) It is the vertical electric field of lightning when it strikes a smooth and lossy ground surface; It is the azimuthal magnetic field of the smooth and lossy ground surface struck by lightning; E r (R,0,jω) It is the horizontal electric field of lightning when it strikes a smooth and lossy ground surface; s is the depth of the soil; γ is the wave number of soil; μ 0 is the vacuum permeability; ε 0 is the dielectric constant of vacuum.

5. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 3 is characterized by: When calculating the soil moisture content of a smooth lossy ground struck by lightning in the soil depth direction, the return current of the lightning return path I(z,t) The model used in the calculation is the MTLE model: ； Where: P(z) is the current attenuation factor, λ e is the current decay constant with height, v For the return speed, i b (0,t) is the substrate current, z Charge element d z Height within the lightning channel, tz / v represents time t minus the charge element d z The time it takes to travel the distance z above the ground; The double Heidler function is used to calculate the current distribution that conforms to the lightning channel: ； Where: I 01 and I 02 are the breakdown current peak and the corona current peak, respectively. τ 11 and τ 21 They are the breakdown current rising edge time and the corona current rising edge time, τ 12 and τ 22 They are the breakdown current falling edge time and the corona current falling edge time, n 1 and n 2 are the breakdown current steepness factor and the corona current steepness factor, η 1 and η 2 They are breakdown current peak correction factor and corona current peak correction factor respectively.

6. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to any one of claims 1 to 5, characterized in that: According to the relationship between soil moisture content and electrical conductivity, a series of underground lightning electromagnetic field distribution characteristics in the soil depth direction under different moisture contents of the same soil are obtained; and a series of underground lightning electromagnetic field distribution characteristics in the soil depth direction under the same moisture contents of different soils are obtained.

7. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 6, characterized in that: The resistivity of clay, silt and sand at different water contents obtained by the forced current method, and the relationship between the conductivity of clay, silt and sand and water content according to the least squares fitting formula ； Where: p is the soil moisture content, σ 粘土 , σ 粉土 , σ 砂土 Soil conductivity of clay, silt and sand, respectively.

8. The method for analyzing the effect of soil moisture on underground lightning electromagnetic field propagation according to claim 7, characterized in that: The Fourier transform technique is used to solve the fitting formula of conductivity and water content, and the distribution characteristics of underground lightning electromagnetic field in the soil depth direction are obtained.

9. The analysis system of soil moisture content on underground lightning electromagnetic field propagation is characterized by: The analysis system includes an ideal smooth ground electromagnetic distribution model for lightning strikes, a soil moisture content and conductivity relationship model, a soil ground lightning return lossy ground electromagnetic field model, a soil ground lightning return lossy ground electromagnetic field model, and a soil underground lightning return lossy ground electromagnetic field model, wherein: The electromagnetic distribution model of an ideal smooth ground struck by lightning is used to construct a vertical electric field distribution model, a horizontal electric field distribution model and an azimuthal magnetic field distribution model of an ideal smooth ground struck by lightning according to the electromagnetic field equation of moving charges; The soil moisture content and conductivity relationship model is used to obtain the influence factors of soil type, moisture content, soil depth and soil wave number on the actual lightning electromagnetic field of lightning striking smooth and lossy ground; The lightning return stroke lossy ground electromagnetic field model of the soil surface is used to obtain the lightning electromagnetic field characteristic distribution of the soil surface by associating the lightning ideal smooth ground electromagnetic distribution model with the soil moisture content and conductivity relationship model; The lightning return lossy ground electromagnetic field model under the soil is used to obtain the distribution characteristics of the lightning radiation electromagnetic field propagated underground in the soil in the lightning return channel according to the lightning return lossy ground electromagnetic field model on the soil surface.

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