Controllable source electromagnetic apparent parameter extraction method and system based on optimization algorithm

Abstract

The invention discloses a controllable source electromagnetic apparent parameter extraction method and system based on an optimization algorithm. The method comprises the following steps: acquiring a first type of apparent parameter of controllable source electromagnetic highest frequency; wherein the first apparent parameter is apparent resistivity or apparent permeability, and the other apparent parameter is a second apparent parameter; fixing a first apparent parameter of the highest frequency, and calculating a second apparent parameter of the highest frequency by adopting a uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and an optimization algorithm based on measuring each electromagnetic field component of the highest frequency as an observed quantity; according to the sequence of frequencies from high to low, taking the two apparent parameters of the previous frequency point as the initial value of the next frequency point in sequence, taking each electromagnetic field component measured at the next frequency point as the observed quantity, and adopting a uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and an optimization algorithm to calculate the electromagnetic field component of the next frequency point; and calculating two visual parameters of the next frequency point. According to the method, the apparent resistivity and apparent permeability parameters can be efficiently and accurately extracted.

Description

Technical Field

[0001] The present invention belongs to the field of controlled source electromagnetics, and in particular relates to a method and system for extracting controllable source electromagnetic visual parameters based on an optimization algorithm. Background Art

[0002] Frequency-domain controlled-source electromagnetic (CSEM) is an important tool for mineral resource exploration. This method can enhance signal strength by increasing the transmission power or source size, and the device configuration can be flexibly adjusted according to the target. It boasts advantages such as high resolution, deep exploration depth, wide observation range, high efficiency, and adaptability. It is widely used in resource surveys for oil and gas, geothermal energy, shale gas, and metal minerals, playing a vital role in deep-earth resource exploration. Stable and reliable techniques for extracting apparent parameters (such as apparent resistivity) can provide a qualitative description of the geological profile of the work area and offer important guidance for field data collection and processing.

[0003] Existing technologies mainly focus on the following aspects: (1) Extracting apparent resistivity parameters through electric and magnetic field components. In the early stages of the development of controlled source electromagnetic methods, the Cania apparent resistivity was introduced from the magnetotelluric method to obtain relevant sounding curves. However, it was based on the plane wave assumption, and the apparent resistivity results of the "near zone" could not reflect the actual underground structure. With the improvement of electromagnetic method theory, the wide-area apparent resistivity directly extracted from the electric or magnetic field has better avoided this phenomenon, greatly improving the efficiency of CSEM field detection and achieving good application results.

[0004] (2) Extracting apparent resistivity from wavenumbers. To further study the sounding performance of electromagnetic fields in the "near zone," another approach is to extract the apparent resistivity parameter from the "wavenumbers," namely, the wavenumber apparent resistivity. This approach first calculates the "wavenumbers" using the electromagnetic field, and then extracts the apparent resistivity parameter from the wavenumbers, which also yields better sounding results.

[0005] Although existing methods and technologies have made significant progress in frequency-domain CSEM visual parameter extraction, current refined geological exploration places higher demands on frequency-domain controlled source electromagnetic exploration technology. Complex geological scenarios pose greater challenges to existing technical means. Current technologies still have the following major defects and shortcomings: (1) The influence of magnetic permeability parameters on CSEM response has not been clarified. Currently, in CSEM exploration, it is generally assumed that the earth medium does not contain magnetism, that is, only apparent resistivity parameters are extracted from electromagnetic field data. However, the magnetic parameters of actual rocks and minerals can also have a significant impact on the electromagnetic response characteristics.

[0006] (2) It is impossible to extract both apparent conductivity and apparent permeability parameters simultaneously. Currently, the extraction of apparent resistivity parameters is often based on the uniform half-space formula. Since the formula is relatively simple, the apparent resistivity parameters can be obtained by using a bisection method or an iterative solution. However, when considering both resistivity and permeability parameters, the electromagnetic field formula becomes more complex and has multiple solutions. Existing technical means make it difficult to extract both apparent parameters simultaneously. Summary of the Invention

[0007] The present invention provides a controlled source electromagnetic apparent parameter extraction method and system based on an optimization algorithm, which can efficiently and accurately extract apparent resistivity and apparent permeability parameters, and significantly improve the application accuracy and reliability of electromagnetic depth sounding curves under complex geological conditions.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: A method for extracting electromagnetic visual parameters of a controllable source based on an optimization algorithm, comprising: Step 1: Obtain a first apparent parameter of the highest frequency of the controllable source electromagnetic field; wherein the first apparent parameter is apparent resistivity or apparent permeability, and the other is a second apparent parameter; Step 2: Fix the first apparent parameter of the highest frequency, and based on the electromagnetic field components of the highest frequency measured as the observed quantity, use the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm to calculate the second apparent parameter of the highest frequency; Step 3: In descending order of frequency, the two apparent parameters of the previous frequency point are used as the initial values ​​of the next frequency point, and based on the electromagnetic field components measured at the next frequency point as the observed quantities, the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm are used to calculate the two apparent parameters of the next frequency point.

[0009] Further, if the first apparent parameter is apparent resistivity, the resistivity measured at the shallow surface is regarded as the highest frequency apparent resistivity.

[0010] Furthermore, if the first apparent parameter is apparent resistivity, the magnetic permeability is kept constant at vacuum permeability, and the highest frequency vertical magnetic field component is measured and the highest frequency apparent resistivity is calculated using the uniform half-space formula.

[0011] Furthermore, if the first apparent parameter is apparent magnetic permeability, the magnetic permeability measured at the shallow surface is regarded as the highest frequency apparent magnetic permeability.

[0012] Furthermore, the objective function of the optimization algorithm used to calculate the visual parameters at any frequency point is: ; Where, represents the objective function; is the apparent parameter vector, including apparent resistivity and apparent permeability; is the measured electromagnetic field data, is the electromagnetic field data obtained by forward modeling; is a diagonal matrix with diagonal elements The reciprocal of is used to normalize the data fitting error; is the initial value of the visual parameter vector; is the weight coefficient; is the Lagrange multiplier.

[0013] Furthermore, the objective function is minimized using the Oakham optimization algorithm, and the iterative update formula of the visual parameter vector at the k+1th iteration is obtained as follows: ; ; Where, is the visual parameter vector obtained at the kth iteration; are the apparent resistivity and permeability parameters of the kth iteration, I is the unit matrix, An intermediate temporary vector for ease of calculation.

[0014] Furthermore, the uniform half-space formula considering the influence of underground resistivity and magnetic permeability is calculated as follows: ; ; ; ; ; ; Where, is the wave number, satisfying , is the dielectric constant, is the circular frequency of the harmonic current; σ is the conductivity, which is the reciprocal of the resistivity; is the magnetic permeability of the medium; is the relative magnetic permeability of the underground medium, is the magnetic permeability of the underground half space; is the first-order Bessel function of the first kind; is the vertical wave number, which contains attenuation and phase information; 、 、 、 The subscript 1 in represents the underground parameters. 、 、 、 The subscript 0 in represents the air parameter; is the angle between the receiving point and the dipole direction; is the distance from the receiving point to the center of the dipole source; is the dipole source current intensity, is the transmitting dipole length; In the equation, z is the vertical distance of the receiving point relative to the transmitting source, that is, the depth coordinate of the receiving point; are the radial, normal and vertical components of the uniform half-space electric field considering the influence of underground resistivity and permeability, are the radial, normal and vertical components of the uniform half-space magnetic field considering the influence of underground resistivity and permeability;

[0015] In cylindrical coordinates and rectangular coordinates, the relationship between the horizontal electric and magnetic field components is: ; Where, and are the electric field components in the x-axis and y-axis directions in the rectangular coordinate system, and are the magnetic field components in the x-axis and y-axis directions in the rectangular coordinate system, respectively.

[0016] A controllable source electromagnetic visual parameter extraction system based on an optimization algorithm includes an initial visual parameter acquisition module and a visual parameter iterative acquisition module; The initial visual parameter acquisition module is used to: obtain two visual parameters of the highest frequency of the controllable source electromagnetic; The first apparent parameter is the apparent resistivity or the apparent permeability, and the other is the second apparent parameter; the second apparent parameter is obtained by fixing the first apparent parameter at the highest frequency after obtaining the first apparent parameter at the highest frequency, and then calculating the second apparent parameter at the highest frequency based on the measured electromagnetic field components at the highest frequency as the observed quantities using a uniform half-space formula that takes into account the influence of underground resistivity and permeability; The apparent parameter iterative acquisition module is used to: use the two apparent parameters of the previous frequency point as the initial values ​​of the next frequency point in order from high to low frequency, and based on the electromagnetic field components measured at the next frequency point as the observed quantities, use the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm to calculate the two apparent parameters of the next frequency point.

[0017] Furthermore, if the first apparent parameter is apparent magnetic permeability, the magnetic permeability measured at the shallow surface is regarded as the highest frequency apparent magnetic permeability; If the first apparent parameter is apparent resistivity, it can be obtained by using any of the following methods: (1) The resistivity of the shallow surface is measured as the highest frequency apparent resistivity; (2) The magnetic permeability is kept constant at the vacuum permeability, and the highest frequency vertical magnetic field component is measured, and the highest frequency apparent resistivity is calculated using the uniform half-space formula.

[0018] Furthermore, the following objective function is minimized using the Oakham optimization algorithm to calculate the second visual parameter of the highest frequency in step 2 and the two visual parameters of the next frequency point in step 3: ; Where, represents the objective function; is the apparent parameter vector, including apparent resistivity and apparent permeability; is the measured electromagnetic field data, is the electromagnetic field data obtained by forward modeling; is a diagonal matrix with diagonal elements The reciprocal of is used to normalize the data fitting error; is the initial value of the visual parameter vector; is the weight coefficient; is the Lagrange multiplier.

[0019] Compared with the prior art, the present invention has the following beneficial effects: When considering both resistivity and permeability, the electromagnetic field formula becomes more complex and has multiple solutions. Existing techniques make it difficult to extract both apparent parameters simultaneously. This invention, based on the unique influence of permeability on vertical magnetic field Hz measurement data, uses the vertical component of the magnetic field to obtain high-frequency apparent resistivity and permeability, or obtains either of the highest-frequency apparent parameters based on the relationship between high-frequency data and the surface geological structure. It then cyclically uses an optimization algorithm to extract both apparent parameters at all frequencies, significantly improving the accuracy and reliability of electromagnetic depth sounding curves in complex geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The electric field components described in the embodiment of the present invention are affected by different relative magnetic permeabilities, wherein Figure 1 (a) and Figure 1 (b) The x-axis and y-axis components of the electric field are affected by different relative magnetic permeabilities.

[0021] Figure 2 The magnetic field components described in the embodiment of the present invention are affected by different relative magnetic permeabilities, wherein Figure 2 (a) Figure 2 (b) Figure 2 (c) The x-axis, y-axis, and z-axis components of the magnetic field are affected by different relative permeabilities.

[0022] above Figure 1 、 Figure 2In the figure, the horizontal axis represents the frequency in Hertz (Hz) and uses a logarithmic scale; the vertical axis represents the ratio of each electromagnetic field component under the influence of different magnetic permeabilities to the field value when the relative magnetic permeability is 1. In the legend, miur represents the relative magnetic permeability, that is, .

[0023] Figure 3 This is a flow chart of the controllable source electromagnetic visual parameter extraction method based on the optimization algorithm of the present invention.

[0024] Figure 4 is the visual parameter extracted according to the x-axis direction component of the electric field according to the embodiment of the present invention, wherein Figure 4 (a) is the apparent resistivity extraction result, Figure 4 (b) is the apparent relative permeability extraction result.

[0025] Figure 5 is the visual parameter extracted according to the y-axis component of the magnetic field according to the embodiment of the present invention, wherein Figure 5 (a) is the apparent resistivity extraction result, Figure 5 (b) is the apparent relative permeability extraction result.

[0026] above Figure 4 、 Figure 5 In the figure, the horizontal axis represents the frequency in Hertz (Hz) using a logarithmic scale; the vertical axis represents the value of the extracted visual parameter. DETAILED DESCRIPTION

[0027] The following is a detailed description of an embodiment of the present invention. This embodiment is based on the technical solution of the present invention, provides a detailed implementation method and a specific operation process, and further explains the technical solution of the present invention.

[0028] Example 1

[0029] Magnetic permeability It can be expressed as: , is the vacuum permeability, is the relative magnetic permeability. When the underground magnetic permeability distribution is not considered, the relative magnetic permeability is always 1. Since the CSEM forward calculation formula that considers both resistivity and magnetic permeability is very complicated and it is difficult to obtain the asymptotic expressions for the far and near zones, its response characteristics are analyzed directly through numerical calculations. In land mineral exploration, the five components of the electromagnetic field are often involved, namely the horizontal electric field, 、 and magnetic field 、 、 Since the influence of resistivity on each component has been thoroughly analyzed in the industry's scientific research and work, the influence of magnetic permeability on each parameter will be briefly analyzed below.

[0030] 1) Magnetic permeability versus electric field 、 impact.

[0031] Suppose there is an electric dipole source, the measuring point coordinates are (5000, 8000, 0), the first underground layer is 300m thick, the resistivity is 100Ωm, and the relative permeability is changed to 0.5, 1, 2, 4, 6, 8, 10 respectively. The second layer is 100Ωm, and the relative permeability is 1. Figure 1 The bathymetric curve shown.

[0032] Figure 1 The vertical axis represents the ratio of the electric field amplitude calculated under different relative magnetic permeabilities (symbolized as miur in the figure) to the case when the relative magnetic permeability is 1, and the horizontal axis is the frequency used in conventional field measurements. When there is an anomaly in the underground magnetic permeability, the electric field will directly increase at high frequencies. times, and gradually approaches 1 at low frequencies. This shows that if there is an anomaly in the underground magnetic permeability, ignoring the effect of the magnetic permeability when calculating the electric field apparent resistivity will result in a false anomaly. For example, when When it is greater than 1, the electric field will increase, resulting in a false high-resistance anomaly.

[0033] 2) Magnetic permeability versus magnetic field 、 、 impact.

[0034] Similarly, the magnetic field response characteristics of the above model are analyzed, such as Figure 2 When there is an anomaly in the underground magnetic permeability, the horizontal magnetic field component will directly increase at high frequencies. times, and gradually approaches 1 at low frequencies. This means that if there is an anomaly in the underground magnetic permeability, ignoring the effect of magnetic permeability when calculating the magnetic field apparent resistivity will result in a false anomaly. The high frequency components will be able to reflect the real underground conditions.

[0035] The phenomena discovered above are universal and can be summarized as follows: 1) When the relative permeability of the formation at the measuring point is not 1, the horizontal electromagnetic field, from high frequency to low frequency, will be severely affected by the relative permeability, while the high-frequency data of the vertical magnetic field component will be unaffected by the relative permeability. 2) When the relative permeability of the formation at the measuring point is 1, while the relative permeability of the remaining formations is not 1, the high-frequency apparent resistivity of all electromagnetic field components will reflect the true subsurface conditions, but the low-frequency data will be affected by the permeability. High permeability will lead to an increase in the electromagnetic field, resulting in a false high-resistance anomaly. In actual field work, since the relative permeability of the formation at the measuring point is unknown, simply ignoring the influence of permeability may result in an incorrect apparent resistivity curve.

[0036] Therefore, this embodiment provides a method for extracting controllable source electromagnetic apparent parameters based on an optimization algorithm, which simultaneously considers the influence of underground resistivity and permeability on frequency domain controllable source electromagnetic, such as Figure 3 As shown, the following steps are included: Step 1: Obtain a first apparent parameter of the highest frequency of the controllable source electromagnetic field; wherein the first apparent parameter is apparent resistivity or apparent permeability, and the other is a second apparent parameter.

[0037] If the first apparent parameter is apparent magnetic permeability and the second apparent parameter is apparent resistivity: since the high-frequency apparent resistivity mainly reflects the shallow surface resistivity structure, the shallow surface magnetic permeability can be measured near the measuring point and the shallow surface magnetic permeability can be regarded as the highest-frequency apparent magnetic permeability.

[0038] If the first apparent parameter is apparent resistivity and the second apparent parameter is apparent permeability, there are two ways to obtain the apparent resistivity: (1) The resistivity measured at the shallow surface is regarded as the highest frequency apparent resistivity.

[0039] Since high-frequency data are mainly affected by the shallow surface geological structure, the resistivity of the shallow surface can be measured near the measuring point and regarded as the highest-frequency apparent resistivity.

[0040] (2) The magnetic permeability is kept constant at the vacuum permeability. By measuring the highest frequency vertical magnetic field component, the highest frequency apparent resistivity is calculated using the uniform half-space formula that takes into account the influence of underground resistivity and magnetic permeability.

[0041] In this embodiment, the uniform half-space formula considering the influence of underground resistivity and permeability will be explained in the subsequent step 2. This step (2) is based on the vertical component of the magnetic field at high frequency. It is not affected by the magnetic permeability and can be constant as vacuum magnetic permeability, that is, relative magnetic permeability , and thus the highest frequency apparent resistivity is calculated using the uniform half-space formula described in step 2, which takes into account the influence of underground resistivity and permeability.

[0042] Step 2: Fix the first apparent parameter at the highest frequency, and based on the electromagnetic field components at the highest frequency measured as the observed quantity, use the uniform half-space formula and optimization algorithm that consider the influence of underground resistivity and permeability to calculate the second apparent parameter at the highest frequency. Specifically, it includes:

[0043] Step 2.1: Fixedly use the first apparent parameter with the highest frequency obtained in step 1, and forward calculate the forward data of each electromagnetic field component under the current two apparent parameters using the uniform half-space calculation formula that considers the influence of underground resistivity and permeability.

[0044] In the first iteration, an empirical initial value is given for the second visual parameter.

[0045] Step 2.2: Evaluate the degree of fit between the forward modeled data obtained in step 2.1 and the corresponding observations. If the fit requirements are not met, proceed to step 2.3; otherwise, terminate the visual parameter extraction and regard the current value of the second visual parameter as the highest-frequency second visual parameter value to be calculated.

[0046] In step 2.3, the sensitivity matrix is ​​solved using the perturbation method, and it is iteratively updated as follows, returning to step 2.1.

[0047] The equation for simultaneously extracting apparent resistivity and apparent permeability using a uniform half-space formula that simultaneously considers the effects of underground resistivity and permeability is underdetermined. For example, for Ex data collected in the field, it may be caused by resistivity, permeability, or more likely a combination of resistivity and permeability. Therefore, this will cause the process of synchronously extracting apparent parameters to be extremely unstable (for example, using Newton's method for extraction). To solve this problem, the embodiment of the present invention draws on the optimization solution idea of ​​underdetermined problems, that is, introducing reference value constraints, and constructing the objective function of the optimization problem of simultaneously extracting apparent resistivity and apparent permeability as follows: ; In the above formula, the first term on the right side is the data fitting term, is the apparent parameter vector of each frequency point (including apparent resistivity and apparent permeability parameters), The electromagnetic field data of each frequency point obtained by field measurement, The forward modeling data of the electromagnetic field at each frequency point is obtained by using the forward modeling formula of the uniform half space. , a diagonal matrix The diagonal elements of The reciprocal of the vector is used to normalize the data fitting error; the second term is the reference value constraint term, is the initial value or prior value; is the weight coefficient, which is used to adjust the weight of the reference value constraint; is the Lagrange multiplier, which is obtained using the golden section method in this embodiment.

[0048] The initial value in step 2 of this embodiment , which is composed of the fixed highest frequency first visual parameter and the given empirical initial value of the second visual parameter.

[0049] In addition, in this embodiment, the objective function is minimized by using the Oakham optimization algorithm, and the iterative update formula of the visual parameter vector at the k+1th iteration can be obtained: ; ; Where, is the visual parameter vector obtained at the kth iteration; are the apparent resistivity and permeability parameters of the kth iteration, I is the unit matrix, An intermediate temporary vector for ease of calculation.

[0050] Since the apparent parameters are extracted from the uniform half-space formula, each frequency point only contains an apparent resistivity and an apparent permeability. The present invention uses the perturbation method to solve the sensitivity matrix The perturbation method is used to solve the sensitivity matrix, that is, a small perturbation is performed on the formation, the partial derivatives are approximated by the finite difference method, and the approximate values ​​of the partial derivatives are filled into the corresponding columns of the matrix, thereby obtaining the sensitivity matrix.

[0051] The uniform half-space formula considering the influence of underground resistivity and permeability is calculated as follows: ; ; ; ; ; ; Where, is the wave number, satisfying , is the dielectric constant, is the circular frequency of the harmonic current; σ is the conductivity, which is the reciprocal of the resistivity; is the magnetic permeability of the medium; is the relative magnetic permeability of the underground medium, is the magnetic permeability of the underground half space; is the first-order Bessel function of the first kind; is the vertical wave number, which contains attenuation and phase information; 、 、 、 The subscript 1 in represents the underground parameters. 、 、 、 The subscript 0 in represents the air parameter; is the angle between the receiving point and the dipole direction; is the distance from the receiving point to the center of the dipole source; is the dipole source current intensity, is the transmitting dipole length; In the equation, z is the vertical distance of the receiving point relative to the transmitting source, that is, the depth coordinate of the receiving point; are the radial, normal and vertical components of the uniform half-space electric field considering the influence of underground resistivity and permeability, are the radial, normal and vertical components of the uniform half-space magnetic field considering the influence of underground resistivity and permeability.

[0052] Converting the above electromagnetic field components in the cylindrical coordinate system to the rectangular coordinate system, the horizontal electric field and magnetic field components are obtained as follows: ; Where, and are the electric field components in the x-axis and y-axis directions in the rectangular coordinate system, and are the magnetic field components in the x-axis and y-axis directions in the rectangular coordinate system, respectively.

[0053] Step 3: In order of frequency from high to low, the two apparent parameters of the previous frequency point are used as the initial values ​​of the next frequency point, and based on the electromagnetic field components measured at the next frequency point as the observation quantity, the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm are used to calculate the two apparent parameters of the next frequency point until the apparent resistivity and apparent permeability of all frequency points are obtained, thereby obtaining a complete apparent parameter sounding curve.

[0054] In this step, the optimization algorithm is used to minimize the objective function to obtain the two visual parameters of the next frequency point. As in step 2, the Oakham optimization algorithm is used to minimize the objective function to obtain the visual parameter vector at the k+1th iteration: ; .

[0055] The difference between the methods used in step 3 and step 2 in this embodiment is that the initial value , which is obtained by combining the two visual parameters of the previous frequency point, and the difference in the number of visual parameters solved.

[0056] Since the apparent parameter curve changes smoothly and continuously, the apparent permeability and resistivity parameters obtained at the previous high-frequency point can be used as the initial values ​​of the next low-frequency point. The value is set according to the reliability of the initial value (generally set between 0.1 and 1, the smaller the value, the more reliable the initial value), and the apparent parameters of the next frequency point are solved.

[0057] The three-layer formation model shown in Table 1 is set up, with the measurement points at (5000, 8000, 0) m. The field source is an electric dipole in the x-direction at the origin. The middle layer has high resistivity and high permeability.

[0058]

[0059] set up = 0.1, the electric field horizontal component Ex data parameter extraction effect is as follows Figure 4 As shown in the figure, the effect of the parameter extraction of the magnetic field horizontal component Hy data is as follows: Figure 5 As shown in the figure. When using the first scheme, it is assumed that the relative permeability of the ground surface is 1; when using the second scheme, it is assumed that the surface resistivity is 100Ωm; when using the third scheme, it is assumed that there is Hz measurement data. The extraction results of the three schemes are consistent with Figure 4 、 Figure 5 The results are consistent and will not be repeated. From the extraction results, it can be seen that the visual parameters of the middle frequency band can better reflect the high resistivity and high magnetism of the actual middle abnormal strata.

[0060] The above embodiments are preferred embodiments of the present application. Ordinary technicians in this field can also make various changes or improvements on this basis. Without departing from the overall concept of the present application, these changes or improvements should fall within the scope of protection required by the present application.

Claims

1. A method for extracting controllable source electromagnetic visual parameters based on an optimization algorithm, characterized in that: include: Step 1: Obtain a first apparent parameter of the highest frequency of the controllable source electromagnetic field; wherein the first apparent parameter is apparent resistivity or apparent permeability, and the other is a second apparent parameter; Step 2: Fix the first apparent parameter of the highest frequency, and based on the electromagnetic field components of the highest frequency measured as the observed quantity, use the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm to calculate the second apparent parameter of the highest frequency; Step 3: In descending order of frequency, the two apparent parameters of the previous frequency point are used as the initial values ​​of the next frequency point, and based on the electromagnetic field components measured at the next frequency point as the observed quantities, the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm are used to calculate the two apparent parameters of the next frequency point.

2. The method for extracting controllable source electromagnetic visual parameters according to claim 1, characterized in that: If the first apparent parameter is apparent resistivity, the resistivity measured at the shallow surface is regarded as the highest frequency apparent resistivity.

3. The method for extracting controllable source electromagnetic visual parameters according to claim 1, characterized in that: If the first apparent parameter is apparent resistivity, the magnetic permeability is kept constant at vacuum permeability, and the highest frequency vertical magnetic field component is measured and the highest frequency apparent resistivity is calculated using the uniform half-space formula.

4. The method for extracting controllable source electromagnetic visual parameters according to claim 1, characterized in that: If the first apparent parameter is apparent magnetic permeability, the magnetic permeability measured at the shallow surface is regarded as the highest frequency apparent magnetic permeability.

5. The method for extracting controllable source electromagnetic visual parameters according to claim 1, characterized in that: The objective function of the optimization algorithm used to calculate the visual parameters at any frequency point is: ； Where, represents the objective function; is the apparent parameter vector, including apparent resistivity and apparent permeability; is the measured electromagnetic field data, is the electromagnetic field data obtained by forward modeling; is a diagonal matrix with diagonal elements The reciprocal of is used to normalize the data fitting error; is the initial value of the visual parameter vector; is the weight coefficient; is the Lagrange multiplier.

6. The method for extracting controllable source electromagnetic visual parameters according to claim 5, characterized in that: Using the Oakham optimization algorithm to minimize the objective function, the iterative update formula of the visual parameter vector at the k+1th iteration is obtained as follows: ； ； Where, is the visual parameter vector obtained at the kth iteration; are the apparent resistivity and permeability parameters of the kth iteration, I is the unit matrix, An intermediate temporary vector for ease of calculation.

7. The method for extracting controllable source electromagnetic visual parameters according to claim 1, characterized in that: The uniform half-space formula considering the influence of underground resistivity and permeability is calculated as follows: ； ； ； ； ； ； Where, is the wave number, satisfying , is the dielectric constant, is the circular frequency of the harmonic current; σ is the conductivity, which is the reciprocal of the resistivity; is the magnetic permeability of the medium; is the relative magnetic permeability of the underground medium, is the magnetic permeability of the underground half space; is the first-order Bessel function of the first kind; is the vertical wave number, which contains attenuation and phase information; 、 、 、 The subscript 1 in represents the underground parameters. 、 、 、 The subscript 0 in represents the air parameter; is the angle between the receiving point and the dipole direction; is the distance from the receiving point to the center of the dipole source; is the dipole source current intensity, is the transmitting dipole length; In the equation, z is the vertical distance of the receiving point relative to the transmitting source, that is, the depth coordinate of the receiving point; are the radial, normal and vertical components of the uniform half-space electric field considering the influence of underground resistivity and permeability, are the radial, normal and vertical components of the uniform half-space magnetic field considering the influence of underground resistivity and permeability; In cylindrical coordinates and rectangular coordinates, the relationship between the horizontal electric and magnetic field components is: ； Where, and are the electric field components in the x-axis and y-axis directions in the rectangular coordinate system, and are the magnetic field components in the x-axis and y-axis directions in the rectangular coordinate system, respectively.

8. A controllable source electromagnetic visual parameter extraction system based on optimization algorithm, characterized in that: It includes an initial visual parameter acquisition module and a visual parameter iterative acquisition module; The initial visual parameter acquisition module is used to: obtain two visual parameters of the highest frequency of the controllable source electromagnetic; The first apparent parameter is the apparent resistivity or the apparent permeability, and the other is the second apparent parameter. The second apparent parameter is obtained by fixing the first apparent parameter at the highest frequency after obtaining the first apparent parameter at the highest frequency. The second apparent parameter at the highest frequency is then calculated using a uniform half-space formula that takes into account the influence of underground resistivity and permeability, based on the electromagnetic field components at the highest frequency measured as observed quantities. The apparent parameter iterative acquisition module is used to: use the two apparent parameters of the previous frequency point as the initial values ​​of the next frequency point in order from high to low frequency, and based on the electromagnetic field components measured at the next frequency point as the observed quantities, use the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm to calculate the two apparent parameters of the next frequency point.

9. The controllable source electromagnetic visual parameter extraction system according to claim 8, characterized in that: If the first apparent parameter is apparent magnetic permeability, the magnetic permeability measured at the shallow surface is regarded as the highest frequency apparent magnetic permeability; If the first apparent parameter is apparent resistivity, it can be obtained by using any of the following methods: (1) The resistivity of the shallow surface is measured as the highest frequency apparent resistivity; (2) The magnetic permeability is kept constant at the vacuum permeability, and the highest frequency vertical magnetic field component is measured, and the highest frequency apparent resistivity is calculated using the uniform half-space formula.

10. The controllable source electromagnetic visual parameter extraction system according to claim 8, characterized in that: Use the Oakham optimization algorithm to minimize the following objective function to calculate the second visual parameter of the highest frequency in step 2 and the two visual parameters of the next frequency point in step 3: ； Where, represents the objective function; is the apparent parameter vector, including apparent resistivity and apparent permeability; is the measured electromagnetic field data, is the electromagnetic field data obtained by forward modeling; is a diagonal matrix with diagonal elements The reciprocal of is used to normalize the data fitting error; is the initial value of the visual parameter vector; is the weight coefficient; is the Lagrange multiplier.

Images