Magnetic anomaly pole-changing method based on equivalent source inversion

Abstract

The invention discloses an equivalent source inversion-based magnetic anomaly pole transformation method, which comprises the following steps of: performing uniform mesh generation on an underground space according to observation data, and constructing an equivalent source space by setting an inversion depth; according to the observation data and the equivalent source space parameters, obtaining a sensitivity matrix of forward and reverse calculation of the magnetic measurement data; according to the sensitivity matrix and the magnetic anomaly data, physical property parameters of an equivalent source space are calculated by using a generalized minimum residual method, and an equivalent source model is constructed; according to the sensitivity matrix and the equivalent source model, forward modeling of the vertical magnetization geomagnetic field is carried out, and a magnetic anomalous pole conversion result is obtained.According to the method, an inversion calculation framework of the equivalent source model is reconstructed on the basis of the generalized minimum residual method, and the problem that large equation sets are difficult to solve in similar inversion is solved; the efficiency and precision of equivalent field source inversion imaging are improved, the pole stabilization under any geomagnetic inclination angle condition can be well realized, and the method is suitable for pole conversion processing of magnetic anomalies in low geomagnetic latitude, especially magnetic equatorial regions.

Description

Technical Field

[0001] The present application relates to the field of geophysical exploration technology, and in particular to a magnetic anomaly pole method based on equivalent source inversion. Background Art

[0002] Magnetic data is an important geophysical basic data in geological survey and mineral exploration. However, in low-latitude areas, the shape of magnetic anomalies becomes complicated due to the influence of geomagnetic inclination, especially near the magnetic equator. This complexity brings great difficulties to the geological interpretation of magnetic data. Polarization processing of magnetic data can effectively reduce or eliminate the influence of oblique magnetization, which is crucial to improve the accuracy and reliability of magnetic data interpretation.

[0003] There are two methods for polarization of magnetic anomalies: spatial domain polarization and frequency domain polarization. The frequency domain polarization method is simple and fast to calculate, but the polarization accuracy is not high enough. The spatial domain polarization method has high accuracy, but its practical application is limited by the problem of solving a large set of equations. In addition, when using equivalent source technology for polarization, the traditional method of using magnetic dipoles and magnetic dipole elements as equivalent sources may affect the acquisition of low-frequency information due to its small extension in the depth direction, thereby reducing the accuracy of the equivalent source inversion method. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a magnetic anomaly pole localization method based on equivalent source inversion, which realizes stable and accurate pole localization under arbitrary geomagnetic inclination conditions through rapid inversion imaging of equivalent field sources, thereby solving the problems of complex calculation and poor stability in the calculation of magnetic anomaly pole localization in low latitudes, especially in the magnetic equatorial region.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is: a magnetic anomaly polarization method based on equivalent source inversion, comprising:

[0006] S1. Based on the observed data, the underground space is uniformly gridded and the equivalent source space is constructed by setting the inversion depth;

[0007] S2. Obtain the sensitivity matrix of forward and inversion calculation of magnetic survey data based on the observed data and equivalent source space parameters;

[0008] S3. Based on the sensitivity matrix and magnetic anomaly data, the generalized minimum residual method is used to calculate the physical parameters of the equivalent source space and construct an equivalent source model;

[0009] S4. According to the sensitivity matrix and equivalent source model, the vertical magnetization geomagnetic field is forward modeled to obtain the magnetic anomaly pole result.

[0010] Further: element A in the sensitivity matrix A in S2 i,j The expression is:

[0011]

[0012] k1=cosI0sinD0sinI+sinI0cosIsinD,k2=cosI0cosD0sinI+sinI0cosIcosD,

[0013] k3=cosI0cosD0cosIsinD+cosI0sinD0cosIcosD,

[0014] k4=cosI0cosD0cosIcosD, k5=cosI0sinD0cosIsinD, k6=-sinI0sinI

[0015] Among them, A i,j represents the (i, j)th unit of the sensitivity matrix A, k1, k2, k3, k4, k5 and k6 are all intermediate parameters, r is the distance from the rectangular unit to the observation point; μ0 is the vacuum permeability; I0 and D0 are the inclination and declination of the direction of the geomagnetic field, respectively, and I and D are the inclination and declination of the direction of the total magnetization intensity, respectively; (ξ, η, ζ) are the central coordinates of the volume element of the subdivided unit; ξ1, ξ2, η1, η2, ζ1 and ζ2 are the coordinate positions of the corner points of the underground rectangular unit; (x i ,y i ,z i ) are the coordinates of the observation point.

[0016] Further: S3 includes:

[0017] S31, calculating the initial error r0 according to the sensitivity matrix A and the magnetic anomaly data d in the observation data;

[0018] S32. According to the initial error r0, the generalized minimum residual method is used to iterate and obtain the standard orthogonal basis element v j ;

[0019] S33, based on standard orthogonal basis elements v j , by solving the least squares problem, the physical property parameter m of the equivalent source space is obtained;

[0020] S34. Construct an equivalent source model according to the physical property parameter m of the equivalent source space.

[0021] Further: The forward expression of the vertical magnetization geomagnetic field in S4 is:

[0022] dRTP=A·m

[0023] Among them, d RTPTo transform the polar magnetic anomaly, m is the equivalent source model, and the sensitivity matrix A is calculated using the vertical magnetization geomagnetic field with a magnetic inclination of 90° and a magnetic declination of 0°.

[0024] The beneficial effects of the present invention are:

[0025] 1. The generalized minimum residual method is used to solve the equivalent source parameters, which solves the problem of difficulty in solving large-scale equations in similar inversions and improves the efficiency and accuracy of equivalent field source inversion imaging;

[0026] 2. The stability and accuracy of magnetic anomaly polarization based on equivalent source technology are improved by using uniformly magnetized regular shapes to approximate equivalent sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the magnetic anomaly pole method based on equivalent source inversion.

[0028] Figure 2 Schematic diagram of model magnetic anomaly under horizontal magnetization and vertical magnetization conditions in an embodiment of the present invention.

[0029] Figure 3 Schematic diagram of the magnetic anomaly polarization result and inversion error of the noisy model in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0031] like Figure 1 As shown, in one embodiment of the present invention, a magnetic anomaly polarization method based on equivalent source inversion is provided, comprising:

[0032] S1. Based on the observed data, the underground space is uniformly gridded and the equivalent source space is constructed by setting the inversion depth;

[0033] S2. Obtain the sensitivity matrix of forward and inversion calculation of magnetic survey data based on the observed data and equivalent source space parameters;

[0034] S3. Based on the sensitivity matrix and magnetic anomaly data, the generalized minimum residual method is used to calculate the physical parameters of the equivalent source space and construct an equivalent source model;

[0035] S4. According to the sensitivity matrix and equivalent source model, the vertical magnetization geomagnetic field is forward modeled to obtain the magnetic anomaly pole result.

[0036] Specifically, the (i,j)th matrix element A in the sensitivity matrix A is i,j It is determined by the distance between the jth cuboid unit and the i-th observation point, and its A i,j The expression is:

[0037]

[0038] k1=cosI0sinD0sinI+sinI0cosIsinD,k2=cosI0cosD0sinI+sinI0cosIcosD,

[0039] k3=cosI0cosD0cosIsinD+cosI0sinD0cosIcosD,

[0040] k4=cosI0cosD0cosIcosD, k5=cosI0sinD0cosIsinD, k6=-sinI0sinI

[0041] Among them, A i,j represents the (i, j)th unit of the sensitivity matrix A, k1, k2, k3, k4, k5 and k6 are all intermediate parameters, r is the distance from the rectangular unit to the observation point; μ0 is the vacuum permeability; I0 and D0 are the inclination and declination of the direction of the geomagnetic field, respectively, and I and D are the inclination and declination of the direction of the total magnetization intensity, respectively; (ξ, η, ζ) are the central coordinates of the volume element of the subdivided unit; ξ1, ξ2, η1, η2, ζ1 and ζ2 are the coordinate positions of the corner points of the underground rectangular unit; (x i ,y i ,z i ) are the coordinates of the observation point.

[0042] Specifically, S3 includes:

[0043] S31, calculating the initial error r0 according to the sensitivity matrix A and the magnetic anomaly data d in the observation data;

[0044] S32. According to the initial error r0, the generalized minimum residual method is used to iterate and obtain the standard orthogonal basis element v j ;

[0045] S33, based on standard orthogonal basis elements v j , by solving the least squares problem, the physical property parameter m of the equivalent source space is obtained;

[0046] S34. Construct an equivalent source model according to the physical property parameter m of the equivalent source space.

[0047] The forward modeling expression of the vertical magnetization geomagnetic field in S4 is:

[0048] dRTP=A·m

[0049] Among them, d RTP To transform the polar magnetic anomaly, m is the equivalent source model, and the sensitivity matrix A is calculated using the vertical magnetization geomagnetic field with a magnetic inclination of 90° and a magnetic declination of 0°.

[0050] Based on the magnetic anomaly polarization method based on equivalent source inversion described in this embodiment, a simulation experiment was conducted, and the simulation parameters were designed as follows: the uniform magnetic body was 3000m long, 3000m wide, 500m thick, the magnetization intensity was 1A / M, and the center position was (-1500, -1500, 1750)m;

[0051] In this embodiment, the magnetic anomaly under two conditions of horizontal magnetization and vertical magnetization is simulated and analyzed, and the results are as follows: Figure 2 As shown in Figure 2, and the polarization results of the noisy horizontal magnetization anomaly data, as shown in Figure 2 Figure 3 shown; combined Figure 2 and Figure 3 As can be seen from the results, the polarization result obtained in this embodiment is not much different from the magnetic anomaly of vertical magnetization, and both are highly consistent in morphology and amplitude, indicating that the present invention has a good application effect. The generalized minimum residual method is used in the equivalent field source inversion to solve the physical parameter model, which solves the problem of difficulty in solving large-scale equations in similar inversions. It is a simple and novel physical property inversion method. The calculation amount is small when performing polarization processing based on this method. By setting a suitable equivalent model space, the offset caused by oblique magnetization can be eliminated, and a stable and accurate polarization result can be obtained. Even under noise interference conditions, a good polarization effect can be obtained, which meets the actual needs of magnetic anomaly polarization in low-latitude areas.

[0052] In summary, the present invention can solve the problems of unstable low-latitude magnetic anomaly pole location calculation and insufficient pole location accuracy in the original pole location method, and improve the stability and accuracy of magnetic anomaly pole location.

[0053] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A magnetic anomaly polarization method based on equivalent source inversion, characterized in that: include: S1. Based on the observed data, the underground space is uniformly gridded and the equivalent source space is constructed by setting the inversion depth; S2. Obtain the sensitivity matrix of forward and inversion calculation of magnetic survey data based on the observed data and equivalent source space parameters; S3. Based on the sensitivity matrix and magnetic anomaly data, the generalized minimum residual method is used to calculate the physical parameters of the equivalent source space and construct an equivalent source model; S4. According to the sensitivity matrix and equivalent source model, the vertical magnetization geomagnetic field is forward modeled to obtain the magnetic anomaly pole result.

2. The magnetic anomaly polarization method based on equivalent source inversion according to claim 1 is characterized in that: The element A in the sensitivity matrix A in S2 i,j The expression is: k1=cosI0sinD0sinI+sinI0cosIsinD,k2=cosI0cosD0sinI+sinI0cosIcosD, k3=cosI0cosD0cosIsinD+cosI0sinD0cosIcosD, k4=cosI0cosD0cosIcosD, k5=cosI0sinD0cosIsinD, k6=-sinI0sinI Among them, A i,j represents the (i, j)th unit of the sensitivity matrix A, k1, k2, k3, k4, k5 and k6 are all intermediate parameters, r is the distance from the rectangular unit to the observation point; μ0 is the vacuum permeability; I0 and D0 are the inclination and declination of the direction of the geomagnetic field, respectively, and I and D are the inclination and declination of the direction of the total magnetization intensity, respectively; (ξ, η, ζ) are the central coordinates of the volume element of the subdivided unit; ξ1, ξ2, η1, η2, ζ1 and ζ2 are the coordinate positions of the corner points of the underground rectangular unit; (x i ,y i ,z i ) are the coordinates of the observation point.

3. The magnetic anomaly polarization method based on equivalent source inversion according to claim 1 is characterized in that S3 include: S31, calculating the initial error r0 according to the sensitivity matrix A and the magnetic anomaly data d in the observation data; S32. According to the initial error r0, the generalized minimum residual method is used to iterate and obtain the standard orthogonal basis element v j ; S33, based on standard orthogonal basis elements v j , by solving the least squares problem, the physical property parameter m of the equivalent source space is obtained; S34. Construct an equivalent source model according to the physical property parameter m of the equivalent source space.

4. The magnetic anomaly polarization method based on equivalent source inversion according to claim 1 is characterized in that: The forward modeling expression of the vertical magnetization geomagnetic field in S4 is: dRTP=A·m Among them, d RTP To transform the polar magnetic anomaly, m is the equivalent source model, and the sensitivity matrix A is calculated using the vertical magnetization geomagnetic field with a magnetic inclination of 90° and a magnetic declination of 0°.

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