Forward modeling method for multidirectional sea wave induction electromagnetic field

Abstract

The invention discloses a forward modeling simulation method for a multidirectional sea wave induction electromagnetic field. The method comprises the following steps: expressing energy distribution of different propagation directions and frequency components through a spectral function; setting external environment input required by forward modeling according to the seawater depth and geomagnetic field parameters of the research area; after parameter setting is completed, electromagnetic response calculation is carried out on each frequency-direction sampling point; component response is called on a preset frequency set and a preset direction set, linear superposition is carried out by adopting a frequency direction correspondence method, and a total electromagnetic field is obtained; and outputting time sequences and frequency spectrum results of the wind wave induction electromagnetic field, the surge induction electromagnetic field and the mixed wave induction electromagnetic field, thereby providing a reference basis for noise analysis, background interference suppression and target signal identification in electromagnetic detection. According to the method, the limitation of a traditional model is broken through, the electromagnetic interference characteristics under the complex sea condition are represented more truly, and reliable support is provided for noise suppression and target recognition in electromagnetic detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ocean electromagnetic exploration and ocean dynamics, and particularly relates to a forward simulation method of multi-directional sea wave induced electromagnetic field. BACKGROUND

[0002] Ocean electromagnetic exploration technology has important application value in seabed resource exploration, ocean engineering safety and military target identification. However, in the complex environment of nearshore and shallow sea, the sea wave interacts with the geomagnetic field during propagation, and an induced electromagnetic field is generated. This kind of signal has a large intensity, and is often used as the main background interference source, which directly affects the reliability of electromagnetic exploration results, and even covers the target signal, thereby reducing the detection and identification accuracy.

[0003] Existing researches usually analyze the induced electromagnetic field based on regular wave models or one-way random wave models. The regular wave model assumes that the wave is single and regular, and cannot reflect the randomness of actual sea waves. The one-way random model considers the spectral characteristics, but the energy is concentrated in a single propagation direction, ignoring the superposition and coupling effect of multi-directional energy. These models are too simplified, resulting in obvious deviation between the simulation results and the real sea conditions, and it is difficult to accurately describe the amplitude and spectral characteristics of the interference signal, and the guiding effect on target detection and noise reduction processing is limited.

[0004] In the real marine environment, the sea wave is often formed by the joint action of wind wave, swell and their mixed forms, showing significant multi-directionality. The differences in propagation direction, frequency and energy level of different wave systems will superimpose in the electromagnetic response, making the induced electromagnetic field show complex spatio-temporal variation. If the multi-directionality and mixing effect are not described, not only the strength of the interference signal will be underestimated, but also part of the spectral structure cannot be explained, thereby affecting the target identification and data processing effect in electromagnetic exploration.

[0005] Therefore, the existing technology urgently needs to establish a modeling and simulation scheme that can fully consider the superposition effect of multi-directional sea waves, covering typical sea conditions such as wind wave, swell and mixed wave. SUMMARY

[0006] Therefore, the present application aims to provide a forward simulation method of multi-directional sea wave induced electromagnetic field, to break through the limitations of traditional models, more realistically represent the electromagnetic interference characteristics of complex sea conditions, and provide reliable support for noise suppression and target identification in electromagnetic exploration.

[0007] The technical problem solved by the present application adopts the following technical scheme:

[0008] A forward simulation method of multi-directional sea wave induced electromagnetic field, comprising the following steps:

[0009] Step S10, set the sea wave parameters and select a two-dimensional sea wave spectrum function to express the energy distribution of different propagation directions and frequency components through the spectrum function;

[0010] Step S20, configure the external environment and the geomagnetic field parameters, set the external environment input required by the forward simulation according to the seawater depth and the geomagnetic field parameters of the research area;

[0011] Step S30, calculate the electromagnetic response of single frequency-direction component, after completing the parameter setting, the electromagnetic response of each frequency-direction sampling point is calculated;

[0012] Step S40, total field synthesis based on the frequency direction corresponding method, on the preset frequency set and direction set, the component response obtained in step S30 is called respectively, and the frequency direction corresponding method is used for linear superposition to obtain the total electromagnetic field;

[0013] Step S50, output the multi-direction sea wave induced electromagnetic field result, through the total electromagnetic field obtained by synthesis, the time sequence and frequency spectrum result of the wind wave induced electromagnetic field, the swell induced electromagnetic field and the mixed wave induced electromagnetic field are output respectively, which provides reference basis for noise analysis, background interference suppression and target signal identification in electromagnetic detection.

[0014] Further, in step S10, according to the marine dynamic conditions of the research area, the effective wave height, the effective wave period and the main propagation direction of the sea wave are set, and the applicable two-dimensional direction spectrum function is selected.

[0015] Further, the two-dimensional direction spectrum function includes a wind wave spectrum, a swell spectrum or a mixed wave spectrum.

[0016] Further, in step S20, the geomagnetic field parameters include the magnetic inclination, the magnetic dip angle and the geomagnetic field strength, and the geomagnetic field parameters are derived from the international geomagnetic reference field or the world geomagnetic field model.

[0017] Further, step S30 of calculating the electromagnetic response of single frequency-direction component includes:

[0018] Step S31, two-dimensional Fourier transform is performed on the horizontal coordinates, and the frequency domain Maxwell equation set is converted into a constant differential equation related to only the vertical coordinates;

[0019] Step S32, the complex amplitude of the field quantity is solved in the wave number domain;

[0020] Step S33, inverse Fourier transform is performed on the result and a simple harmonic time factor is introduced to restore to the time-space domain to obtain the response of the six components of the electromagnetic field.

[0021] The forward simulation method of the multi-direction sea wave induced electromagnetic field disclosed by the application has the following beneficial effects:

[0022] Compared with the existing rule sea wave model and the one-way random sea wave model, the multi-direction sea wave induced electromagnetic field forward simulation method provided by the application can more truly reflect the energy superposition and coupling effect of sea waves under the condition of multi-direction propagation, and breaks through the limitation that the traditional model concentrates energy in a single direction; the application simultaneously covers complex sea conditions such as wind waves, swell waves and mixed waves, and improves the applicability of simulation in real marine environment; by using the frequency direction corresponding method for total field synthesis, the phase locking problem under the traditional superposition mode is effectively avoided, the simulation result is more uniform in spatial distribution, and has good ergodicity, which significantly improves the stability and rationality of simulation; meanwhile, the results of the electric field and the magnetic field six components in the time domain and the frequency domain can be output, the integrity of information is ensured, and reliable support is provided for noise analysis and target identification in electromagnetic detection. In summary, the application can significantly improve the electromagnetic interference characterization ability under complex sea conditions, and finally realize more accurate multi-direction sea wave induced electromagnetic field simulation. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a method flowchart of the application.

[0024] Figure 2 is a multi-direction sea wave induced electromagnetic field model diagram.

[0025] Figure 3 is a multi-direction sea wave induced electromagnetic field forward simulation technical route diagram.

[0026] Figure 4 is a wind wave induced electromagnetic field amplitude spectrum diagram.

[0027] Figure 5 is a swell wave induced electromagnetic field amplitude spectrum diagram.

[0028] Figure 6 is a mixed wave induced electromagnetic field amplitude spectrum diagram.

[0029] Figure 7 is a comparison diagram of the measured horizontal magnetic field amplitude spectrum and the simulation result. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0031] The present application aims to overcome the shortcomings of the existing sea wave induced electromagnetic field model, and proposes a scheme that can more truly reflect the multi-directional sea wave electromagnetic field response characteristics under complex sea conditions. The existing regular sea wave model and unidirectional random sea wave model are too simplified, and it is difficult to accurately describe the electromagnetic interference caused by the multi-directional superposition of sea waves, thereby limiting the accuracy of noise suppression and target identification in electromagnetic detection.

[0032] To this end, the present application provides a forward simulation method of multi-directional sea wave induced electromagnetic field, which introduces multi-directional energy distribution and coupling effect in the model to systematically depict the electromagnetic response law under the conditions of wind wave, swell wave and mixed wave sea state. This method can effectively improve the accuracy of sea wave induced electromagnetic field simulation, provide more reliable theoretical support and data basis for electromagnetic detection in complex marine environment, and thus realize accurate characterization of background interference and effective extraction of target signal.

[0033] Reference Figure 1 A forward simulation method of multi-directional sea wave induced electromagnetic field, comprising the following steps:

[0034] Step S10, setting sea wave parameters and selecting two-dimensional sea wave spectrum function, according to the marine dynamic conditions of the research area, setting the effective wave height, effective wave period and main propagation direction of the sea wave, and selecting the applicable two-dimensional directional spectrum function (such as wind wave spectrum, swell spectrum or mixed wave spectrum). The energy distribution of different propagation directions and frequency components is expressed by the spectrum function, which provides the input basis for the subsequent electromagnetic response calculation.

[0035] For different sea conditions of the research area, the classic JONSWAP (Joint North Sea Wave Project) spectrum can be selected to describe the wind wave, the PM (Pierson-Moskowitz) spectrum can be selected to describe the mature swell, or the mixed wave superposition sea wave spectrum model can be selected to describe the mixed wave. If the main propagation direction needs to be constrained, the directional function can be combined to realize the directional concentration of energy distribution.

[0036] Step S20, configuring external environment and geomagnetic field parameters, according to the water depth conditions and geomagnetic field parameters of the research area, setting the external environment input required for forward simulation. The geomagnetic field parameters include magnetic inclination, magnetic dip angle and geomagnetic field strength, which can be obtained from the International Geomagnetic Reference Field (IGRF) or the World Magnetic Model (WMM). The water depth is set according to the hydrological and topographical data of the target sea area.

[0037] By querying the IGRF or WMM database, the geomagnetic field strength, magnetic inclination and magnetic dip angle of the target sea area are obtained, and they are used as the boundary input conditions for electromagnetic field calculation.

[0038] Step S30, calculating electromagnetic response of single frequency-direction component, after completing parameter setting, electromagnetic response calculation is carried out to each frequency-direction sampling point, and the specific steps include:

[0039] Step S31, two-dimensional Fourier transform is carried out to horizontal coordinates, and frequency domain Maxwell equation set is converted into constant differential equation only related to vertical coordinates;

[0040] Step S32, complex amplitude of field quantity is solved in wave number domain;

[0041] Step S33, inverse Fourier transform is carried out to the result and a simple harmonic time factor is introduced, and recovery to time-space domain is carried out, and the response of six components (Ex, Ey, Ez, Bx, By, Bz) of electromagnetic field is obtained.The results of six components (Ex, Ey, Ez, Bx, By, Bz) in time domain and frequency domain can be directly used for comparison analysis and interference identification of marine electromagnetic detection data.

[0042] In actual simulation, if single stack method or double stack method is used, coherent coupling of same frequency components can easily lead to "phase locking" phenomenon.The frequency-direction corresponding method used in the application effectively avoids this problem by point-by-point stacking of field responses in frequency-direction space, so that the stability and rationality of electromagnetic field simulation results are significantly improved.

[0043] Step S40, total field synthesis based on frequency-direction corresponding method, respectively calls the component response obtained in step S30 on the preset frequency set and direction set, and linearly stacks by using the frequency-direction corresponding method to obtain total electromagnetic field;This method avoids the problem of phase locking of same frequency components in traditional single stack or double stack, so that the simulation result is more uniform in spatial distribution, and has ergodicity, and is closer to the electromagnetic response characteristics of real marine environment.

[0044] Step S50, outputting multi-directional sea wave induced electromagnetic field result, through the total electromagnetic field obtained by synthesis, time sequence and frequency spectrum results of wind wave induced electromagnetic field, swell wave induced electromagnetic field and mixed wave induced electromagnetic field can be respectively outputted, so as to provide reference basis for noise analysis, background interference suppression and target signal identification in electromagnetic detection.

[0045] Compared with existing regular wave models and unidirectional random wave models, the forward modeling method for multidirectional wave-induced electromagnetic fields proposed in this invention can more realistically reflect the energy superposition and coupling effects of waves under multidirectional propagation conditions, breaking through the limitation of traditional models where energy is concentrated in a single direction. This invention also covers complex sea conditions such as wind waves, swells, and mixed waves, improving the applicability of the simulation in real marine environments. By employing the frequency-direction correspondence method for total field synthesis, the "phase-locking" problem under traditional superposition methods is effectively avoided, resulting in a more uniform spatial distribution of simulation results and good ergodicity, significantly improving the stability and rationality of the simulation. Simultaneously, it can output the results of the six components of the electric and magnetic fields in the time and frequency domains, ensuring the integrity of the information and providing reliable support for noise analysis and target identification in electromagnetic detection. In summary, this invention can significantly improve the characterization capability of multidirectional wave electromagnetic interference under complex sea conditions, ultimately achieving a more accurate simulation of multidirectional wave-induced electromagnetic fields.

[0046] Example

[0047] To improve the ability to identify background interference and extract target signals in marine electromagnetic detection, and to more accurately describe the characteristics of multi-directional wave-induced electromagnetic fields under complex sea conditions, this invention provides a forward modeling method for multi-directional wave-induced electromagnetic fields. This method introduces a multi-directional wave direction spectrum, comprehensively considers the coupling effects of wind waves, swells, and mixed waves, and combines geomagnetic parameters and marine environmental conditions to achieve accurate simulation of wave-induced electromagnetic fields under complex sea conditions, thus providing reliable support for noise reduction and target identification in electromagnetic detection. The method includes the following steps:

[0048] S1: Establish a multi-directional wave-induced electromagnetic field model and set parameters.

[0049] Based on wave observation data of the study area, parameters such as significant wave height, significant wave period, and main wave propagation direction are set, and a suitable two-dimensional wave spectrum function is selected. Common wave spectra include the JONSWAP spectrum suitable for wind and wave conditions, the PM spectrum suitable for swells, and mixed wave spectra obtained through superposition methods. In this embodiment, as... Figure 1 As shown, ocean waves are composed of multiple component waves in different directions, but they generally share a dominant propagation direction. The wave direction spectrum can be represented as .in For the spectrum function, This represents the directional distribution function. By setting different spectral types and parameters, wind wave spectra, swell spectra, and mixed wave spectra can be obtained. Based on this, combined with... Figure 2The multi-directional wave-induced electromagnetic field model in this paper uses wave parameters as input conditions, which interact with external environmental parameters (such as water depth, seawater conductivity, and geomagnetic field parameters) to provide a foundation for subsequent forward modeling of the induced electromagnetic field response. In the model, the waves are composed of superimposed component waves from multiple directions and have a main propagation direction, which can be arbitrary. Above the sea surface is the air layer (…). ), with a seawater layer of thickness d underneath ( Below this are the seabed and the subsurface space. The coordinate system is X, Y, Z, where Y points to geographic north and Z points vertically upward. The angle between the geomagnetic north pole and geographic north is the magnetic declination D, and the red arrow indicates the direction of the geomagnetic field with a tilt angle of I.

[0050] S2: Configure external environment and geomagnetic field parameters

[0051] like Figure 3 (a) to Figure 3 As shown in (f), to ensure the realism and applicability of the multi-directional wave-induced electromagnetic field simulation, external environmental parameters and geomagnetic field parameters need to be further configured based on the established directional spectrum model. External environmental parameters mainly include seawater depth and seawater conductivity. The former is determined by the hydrological and topographical conditions of the target sea area, while the latter can be set based on regional measured data or empirical averages. Geomagnetic field parameters include geomagnetic field strength, magnetic declination, and magnetic inclination, the values ​​of which can be obtained from the International Geomagnetic Reference Field (IGRF) or the World Geomagnetic Model (WMM). Magnetic declination represents the angle between geomagnetic north and geographic north, magnetic inclination represents the angle between the geomagnetic field direction and the horizontal plane, and geomagnetic field strength reflects the overall field energy level.

[0052] In this embodiment, wave parameters (significant wave height, significant wave period, and main propagation direction), along with external environmental parameters (seawater depth, seawater conductivity) and geomagnetic field parameters (geomagnetic field strength, magnetic declination, and magnetic inclination), are jointly input into the multi-directional wave-induced electromagnetic field forward modeling module (see...). Figure 3 (The orange box in the middle) forms the complete conditions for calculating the driving electromagnetic field. This step not only ensures that the simulation results can accurately reflect the energy and direction characteristics of ocean waves, but also incorporates the water properties and geomagnetic background of the study area, thus providing support for obtaining an electromagnetic response that is closer to actual sea conditions.

[0053] S3: Calculate the single-component electromagnetic field and perform frequency-direction synthesis.

[0054] After setting the wave direction spectrum (S1) and configuring the external environment and geomagnetic field parameters (S2), it is necessary to calculate the electromagnetic response of the waves for each frequency-direction component. The core idea is to first discretize the two-dimensional direction spectrum into a finite number of frequency sampling points. and direction angle sampling points Then, the corresponding electromagnetic field components are solved separately, and finally synthesized into a total field using the frequency-direction correspondence method.

[0055] In electromagnetic field calculations, a two-dimensional Fourier transform of the governing equations is first performed to obtain a system of ordinary differential equations concerning depth z. Solving these equations yields the complex amplitudes of the electric and magnetic fields for individual components, denoted as follows: and Substituting it back into the spacetime domain, we get the expression:

[0056]

[0057] In the formula, μ is the magnetic permeability of seawater. and These are complex vector functions of the electric and magnetic fields, respectively. and Let x and y be the horizontal wavenumbers of the n-th frequency and k-th direction wave components, respectively. Let be the angular frequency of the nth frequency component in the kth direction. This indicates taking the real part.

[0058] The above expressions correspond to the responses of single-frequency-direction component waves in an electromagnetic field. Since the contributions of each component are independent, further synthesis is required to obtain the total electromagnetic field. To avoid the coherent phase-locking problem of the same-frequency components caused by traditional double or single superposition methods, this embodiment employs the frequency-direction correspondence method. This method is applicable to discrete... and The above component solutions are called one by one at each sampling point, and then linearly superimposed to obtain the final multidirectional wave-induced electromagnetic field:

[0059] .

[0060] Where N and M are the number of samples in frequency and direction, respectively. and These represent the indices of the nth frequency component and the sampling point in the kth direction, respectively.

[0061] This method ensures a one-to-one correspondence between each frequency component in the spatiotemporal domain, resulting in a synthesized electromagnetic field with good spatial homogeneity and ergodicity, thus more realistically reflecting the electromagnetic response characteristics under complex sea conditions. Based on this, this embodiment simulates three typical sea wave scenarios and outputs their induced electromagnetic field amplitude spectra: Figure 4 (a) to Figure 4 (f) is the amplitude spectrum of the induced electromagnetic field under wind and wave conditions. The response is mainly concentrated in the high-frequency range, which is consistent with the characteristics of short-period wind and waves. Figure 5 (a) to Figure 5(f) is the amplitude spectrum of the induced electromagnetic field under swell conditions. The peak appears in the low frequency range, reflecting the significant influence of long-period swells. Figure 6 (a) to Figure 6 (f) shows the amplitude spectrum of the induced electromagnetic field under mixed wave conditions, exhibiting a bimodal structure that simultaneously reflects the superposition effect of wind waves and swells. Therefore, this method can not only accurately calculate the single-component electromagnetic response under uniform external environmental conditions, but also obtain the complete multi-directional wave-induced electromagnetic field through the frequency-direction correspondence method, outputting the typical amplitude spectrum characteristics of wind waves, swells, and mixed waves, providing a reliable basis for subsequent electromagnetic noise identification and target signal extraction.

[0062] Furthermore, to verify the applicability of this method under actual sea conditions, this embodiment compares the simulation results with measured data, such as... Figure 7 As shown, Figure 7 (a) Figure 7 (b) The original amplitude spectra of the horizontal magnetic field components Bx and By are shown respectively. It can be seen that there are significant energy peaks in the 0.10~0.20Hz frequency band. This frequency band is the main response range of the wave-induced magnetic field, and is marked with a red dashed box. The frequency band outside the box is mainly dominated by the regional magnetotelluric background. Figure 7 (c) Figure 7 (d) shows the result after bandpass filtering the original signal at 0.10~0.20Hz. The black curve is the measured amplitude spectrum, and the red curve is the simulation result of this method. The comparison shows that the two are highly consistent in amplitude level and spectrum shape, and can effectively reproduce the energy distribution characteristics of the observed signal, thus proving that this method has good rationality and effectiveness under actual sea conditions.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A forward modeling method for multi-directional wave-induced electromagnetic fields, characterized in that, Includes the following steps: Step S10: Set wave parameters and select a two-dimensional wave spectrum function to express the energy distribution of different propagation directions and frequency components through the spectrum function; Step S20: Configure external environment and geomagnetic field parameters. Based on the seawater depth and geomagnetic field parameters of the study area, set the external environment input required for forward modeling. Step S30: Calculate the electromagnetic response of a single frequency-direction component. After setting the parameters, calculate the electromagnetic response for each frequency-direction sampling point. Step S40: Based on the frequency-direction correspondence method, the component responses obtained in step S30 are called on the preset frequency set and direction set respectively, and linear superposition is performed using the frequency-direction correspondence method to obtain the total electromagnetic field. Step S50: Output the multi-directional wave-induced electromagnetic field results. By synthesizing the total electromagnetic field, output the time series and frequency spectrum results of the wind wave-induced electromagnetic field, the swell-induced electromagnetic field, and the mixed wave-induced electromagnetic field, respectively, to provide a reference for noise analysis, background interference suppression, and target signal identification in electromagnetic detection.

2. The forward modeling simulation method for multi-directional wave-induced electromagnetic fields according to claim 1, characterized in that, In step S10, based on the marine dynamic conditions of the study area, the significant wave height, significant wave period, and main propagation direction are set, and an applicable two-dimensional directional spectrum function is selected.

3. The forward modeling simulation method for multi-directional wave-induced electromagnetic fields according to claim 2, characterized in that, Two-dimensional directional spectral functions include wind wave spectrum, surge wave spectrum, or mixed wave spectrum.

4. The forward modeling simulation method for multi-directional wave-induced electromagnetic fields according to claim 3, characterized in that, In step S20, the geomagnetic field parameters include magnetic declination, magnetic inclination, and geomagnetic field intensity. These parameters are derived from the International Geomagnetic Reference Field or the World Geomagnetic Magnetic Field Model.

5. The forward modeling simulation method for multi-directional wave-induced electromagnetic fields according to claim 4, characterized in that, Step S30, the steps for calculating the electromagnetic response of a single frequency-direction component include: Step S31: Perform a two-dimensional Fourier transform on the horizontal coordinates to transform the frequency domain Maxwell's equations into ordinary differential equations that depend only on the vertical coordinates. Step S32: Solve for the complex amplitude of the field quantity in the wavenumber domain; Step S33: Perform an inverse Fourier transform on the result and introduce a harmonic time factor to restore it to the time-space domain, obtaining the response of the six components of the electromagnetic field.

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