Method for inverting burial depth of target object by magnetic anomaly based on extreme value information of single sensor

Abstract

The invention relates to the technical field of marine surveying and mapping, investigation and detection, in particular to a magnetic anomaly target object burial depth inversion method based on extreme value information of a single sensor, which comprises the following steps: establishing a marine surveying and mapping space rectangular coordinate system; calculating the induced magnetization intensity formed by the point magnetic source under the action of the geomagnetic field and the gravitational potential generated at the observation point, and establishing the relationship between the magnetic potential and the gravitational potential based on the Poisson equation of the gravity-magnetic potential field; the corresponding relation between the magnetic field intensity and the magnetic potential is deduced by combining the electromagnetism principle, the geomagnetic inclination angle and the magnetic declination angle, and an underwater point magnetic source magnetic anomaly calculation model is constructed by using the total magnetic field intensity actually measured by a magnetometer and the normal geomagnetic field intensity; and extracting a maximum value and a minimum value in the magnetic anomaly, performing specific value operation, solving a vertical distance from the point magnetic source to the observation plane, and calculating the burial depth of the underwater target object through a geometrical relationship. The method is suitable for a detection scene of a ferromagnetic target object with a sandy substrate or a small scale.

Description

Technical Field

[0001] This invention relates to the field of marine surveying, investigation and exploration technology, and specifically to a method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor. Background Technology

[0002] In the fields of marine mapping and marine surveying and exploration, magnetic detection is one of the most effective methods and means to obtain spatial information on underwater ferromagnetic targets, such as abandoned anchors, subsea pipelines, shipwrecks, underwater vehicles, mines, and bombs. Regarding detection equipment, state-of-the-art marine magnetometers, such as proton precession type, optical pump type, and superconducting type, are widely used in marine geomagnetic measurements and the detection of underwater magnetic targets. Combined with high-precision differential navigation and positioning technology, this provides technical support for obtaining reliable measurement data.

[0003] Determining the burial depth of underwater buried objects is a challenge. For larger or long linear objects, the commonly used technique is the parametric array shallow seismic profiler (also known as a pipeline profiler), which often yields satisfactory results, especially in silty or clayey sediments. However, in sandy sediments, the success rate of shallow seismic profilers decreases significantly due to factors such as acoustic energy dissipation and reduced acoustic impedance differences. Therefore, for smaller buried objects or ferromagnetic objects buried in sand layers, magnetic probing is currently the only mature, efficient, and economical method.

[0004] Therefore, it is necessary to design a method for inverting the burial depth of a target object based on the magnetic anomaly information of a single sensor to solve the problems existing in the prior art. Through the derivation of the theoretical model of the magnetic anomaly of underwater target objects and the verification of the model by calculation examples, a method for rapidly inverting the burial depth of underwater buried target objects based on the magnetic anomaly extreme information obtained by a single sensor magnetometer with real-time water depth assistance is proposed. This provides a feasible solution for detecting the burial depth of underwater ferromagnetic target objects at the bottom of the water with a single magnetic sensor. Summary of the Invention

[0005] In view of this, the present invention proposes a method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, aiming to solve the problem of low success rate in detecting the burial depth of a target object in sandy sediments.

[0006] This invention proposes a method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, comprising: Establish a spatial rectangular coordinate system for marine mapping; take the observation plane where the magnetometer sensor is located as the XOY plane, determine the coordinates of the point magnetic source, the coordinates of the observation point, and the straight-line distance from the coordinates of the point magnetic source to the coordinates of the observation point; Calculate the induced magnetization and the gravitational potential generated by the point magnetic source at the observation point; determine the relationship between the magnetic potential and the gravitational potential based on Poisson's equation for the gravity and magnetic potential fields. Based on the relationship between magnetic potential and gravitational potential, as well as geomagnetic tilt and magnetic declination, the relationship between magnetic field strength and magnetic potential is determined; based on the total magnetic field strength measured by the magnetometer sensor and combined with the normal geomagnetic field strength, the magnetic field strength of the point magnetic source is determined; based on the relationship between magnetic field strength and magnetic potential and the magnetic field strength of the point magnetic source, a calculation model for the magnetic anomaly of the underwater point magnetic source target is determined. Identify the maximum and minimum values ​​of the total magnetic field anomaly; substitute the maximum and minimum values ​​into the calculation model of the underwater point magnetic source target magnetic anomaly, and perform ratio calculations to determine the vertical distance from the point magnetic source location coordinates to the observation plane; based on the real-time water depth measured synchronously, the draft of the magnetometer sensor, and the vertical distance, combined with geometric relationships, obtain the burial depth of the underwater target.

[0007] Furthermore, when establishing a marine surveying spatial rectangular coordinate system, the following should be included: The coordinates of the point magnetic source are Q ( x 0, y 0, z 0); the vertical distance from the point magnetic source position coordinates to the observation plane is R The coordinates of the observation point are P ( x , y , z The straight-line distance from the coordinates of the magnetic source to the coordinates of the observation point is... ; in, .

[0008] Furthermore, when determining the relationship between magnetic potential and gravitational potential based on Poisson's equation for the magnetic and gravitational potential fields, the following steps are taken: The gravitational potential of the point magnetic source at observation point P is: ; in, G It is the gravitational constant. The density of the point magnetic source, v Its volume; The Poisson equation relating magnetic potential and gravitational potential is: ; in, U ( x , y , z Let P be the magnetic potential. M Let grad be the total magnetization vector. P V ( x ,y , z )for V ( x , y , z The gradient at point P.

[0009] Furthermore, the total magnetization vector M The formula for expressing it is: ; in, M i The magnetization intensity sensed for the target object. M r The residual magnetization retained after the target object has undergone magnetic field magnetization; ; T 0 represents the normal geomagnetic field strength. κ The magnetic susceptibility of the point magnetic source material. μ denoted as ρ_permeability.

[0010] Furthermore, determining the relationship between magnetic field strength and magnetic potential includes: The magnetic field strength is the negative gradient of the magnetic potential. Based on Poisson's equation relating magnetic potential and gravitational potential, the expressions for each component of the magnetic anomaly field can be obtained, i.e., the formula for the relationship between magnetic field strength and magnetic potential is: ; in: H ax , H ay , Z a These are the three components of the magnetic anomaly intensity vector. M x , M y , M z These are the three components of the total magnetization vector. V xx , V xy , V xz , V yy , V yz , V zz for V ( x , y , z The second-order partial derivative of ). The direction of the magnetization of a point magnetic source is the same as the direction of the Earth's magnetic field, expressed by magnetic declination.D This indicates that the magnetization inclination angle of the point magnetic source is related to the geomagnetic inclination angle. I Consistent, namely: ; When on the observation plane, z =0, z 0= R， After sorting, it becomes: .

[0011] Furthermore, determining the magnetic field strength of a point magnetic source includes: Point source magnetic anomaly intensity T a It is the total magnetic field strength T With normal geomagnetic field strength T The vector difference of 0 is expressed by the formula: ; The magnetometer sensor measures the total magnetic field strength, which includes the geomagnetic field strength at the observation point and the magnetic field strength of the point magnetic source. The total magnetic anomaly is obtained by subtracting the normal geomagnetic field strength from the measured total magnetic field strength. T This refers to the abnormal magnetic field strength of the point magnetic source, i.e. T yes T and T The modulus difference of 0 is given by the formula: ; Point source magnetic anomaly intensity T a With normal geomagnetic field strength T The vector angle between 0 and 0 is θ According to the cosine theorem for vector triangles, the formula is: ; Due to the magnetic anomaly intensity of the point magnetic source T a Much smaller than the normal geomagnetic field strength T 0, the formula is determined as follows: .

[0012] Furthermore, when determining the calculation model for the magnetic anomaly of the underwater point magnetic source target object, it includes: When the magnetic anomaly intensity of the point magnetic source T a When the total magnetic field anomaly is less than 1000 nT, the total magnetic field anomaly will be... T Considered as the magnetic anomaly intensity of a point magnetic source T a Under normal geomagnetic field strength TThe projection in the 0 direction, i.e., the total magnetic field anomaly T It is the magnetic anomaly intensity of the point magnetic source. T a The fixed-direction projection, the magnetic anomaly intensity of the point magnetic source T a The formulas for representing the components on the three coordinate axes are as follows: ; Based on the formula relating magnetic field strength and magnetic potential, the calculation model for the magnetic anomaly of the underwater point magnetic source target is determined as follows: ; Among them, △ T ( x , y () represents the magnetic anomaly value at the observation point. I It is the geomagnetic tilt angle. D It is the magnetic declination. T 0 represents the normal geomagnetic field strength. v The equivalent volume of the target object for the point magnetic source. κ Let be the magnetic susceptibility of the point magnetic source material, and let the coordinates of the point magnetic source be ( ). x 0, y 0, R ),in R The vertical distance from the point magnetic source target to the observation plane is denoted as .

[0013] Furthermore, identifying the maximum and minimum values ​​in the total magnetic field anomaly includes: The planar position Q of the target object is determined by combining magnetic anomaly curve information with real-time navigation and positioning information. x 0, y 0); and obtain information related to magnetic anomaly feature points, including the magnetic anomaly maximum value Δ. T max and the coordinates A of the maximum point ( x max , y max ) and the minimum value of magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min ).

[0014] Furthermore, determining the perpendicular distance from the point magnetic source location coordinates to the observation plane includes: Substituting the relevant information of the magnetic anomaly feature points into the magnetic anomaly calculation model of the underwater point magnetic source target object, the maximum value of the magnetic anomaly Δ is determined. T maxand the coordinates A of the maximum point ( x max , y max The relationship formula is: ; Determine the minimum value Δ of the magnetic anomaly T min and the coordinates B of the minimum point ( x min , y min The relationship formula is: ; Then, the ratio calculation is performed to determine the formula: ; Based on the known extreme point information, the vertical distance from the location coordinates of the point magnetic source to the observation plane is determined using the following formula: ; in, R The range of values ​​is [a, b]. All values ​​from a to b are iterated at intervals of 0.1, and solutions that satisfy the formula for the perpendicular distance from the point magnetic source location coordinates to the observation plane are selected, thus determining the... f ( R The closest to 0 R value.

[0015] Furthermore, when determining the burial depth of an underwater target, the following steps are taken: Based on geometric relationships, the formula for determining the relationship is: ; Right now: ; in, WD To measure water depth simultaneously with magnetic detection, d The draft of the magnetometer sensor. B The burial depth of underwater ferromagnetic targets.

[0016] Compared with existing technologies, the advantages of this invention are as follows: Based on the information of the extreme points of the magnetic anomaly in the main profile of underwater ferromagnetic targets detected by a single-sensor magnetometer, a method for inverting the burial depth of underwater buried targets under the constraint of synchronously measured water depth is proposed. The inversion effect of the method of this invention is analyzed through three calculation examples, and the results show that the inversion accuracy is better than 0.2m. The provided method has the advantages of simple data acquisition, strong operability, and high inversion accuracy, and is also applicable to the detection scenarios of sandy bottoms or small-scale ferromagnetic targets. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A flowchart of a method for retrieving the burial depth of a target object based on magnetic anomaly information from a single sensor, provided in an embodiment of the present invention; Figure 2 This is a spatial distribution map of the magnetization intensity vector of an underwater target object, provided by the method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the magnetic detection geometric relationship of the method for inverting the burial depth of a target object based on magnetic anomaly information of a single sensor, provided in an embodiment of the present invention. Figure 4 The method for retrieving the burial depth of a target object based on magnetic anomaly information from a single sensor, provided in this embodiment of the invention, includes the planar and profile features of the magnetic anomaly of the target object at an observation plane height of R=5m. Figure 5 The method for retrieving the burial depth of a target object based on magnetic anomaly information from a single sensor, provided in this embodiment of the invention, includes the planar and profile features of the magnetic anomaly of the target object at an observation plane height of R=10m. Figure 6 The method for retrieving the burial depth of a target object based on magnetic anomaly information from a single sensor, provided in this embodiment of the invention, includes the planar and profile features of the magnetic anomaly of the target object at an observation plane height of R=15m. Figure 7 This is a comparison of the main profile magnetic anomaly curves of the method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, provided in an embodiment of the present invention. Figure 8 The optimal R-value solution diagram is shown for Example 1 of the method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, as provided in this embodiment of the invention. Figure 9 The optimal R-value solution diagram is shown in Example 2 of the method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor provided in this embodiment of the invention. Figure 10 The optimal R-value solution diagram is shown in Example 3 of the method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor provided in this embodiment of the invention. Figure 11 This is a flowchart illustrating the specific implementation of the method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as provided in this embodiment of the invention. Detailed Implementation

[0018] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Traditional single-sensor magnetometers cannot obtain the burial depth information of underwater buried targets. Current reports suggest using interpolation cutting algorithms combined with magnetic anomaly contour maps and parametric array shallow profiling techniques to estimate the burial depth of targets, as well as using an improved Euler deconvolution method to perform depth inversion of underwater unexploded ordnance. These methods generally suffer from problems such as large data requirements, high data acquisition costs, and excessive computational load.

[0020] This invention, based on the magnetic anomaly extrema information of the main profile of underwater ferromagnetic targets detected by a single-sensor magnetometer, proposes a method for inverting the burial depth of underwater buried targets under the constraint of synchronously measured water depth. The inversion results of three computational examples were analyzed through modeling, and the results show that the inversion accuracy is better than 0.2m. The solution for detecting the burial depth of underwater buried targets based on magnetic detection provided by this invention has the advantages of simple data acquisition, strong operability, and high inversion accuracy. It is also applicable to the detection of ferromagnetic targets with sandy bottoms or smaller scales.

[0021] For this, please refer to Figure 1 As shown, this application proposes a method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, including: S100: Establish a spatial rectangular coordinate system for marine mapping; take the observation plane where the magnetometer sensor is located as the XOY plane, determine the coordinates of the point magnetic source, the coordinates of the observation point, and the straight-line distance from the coordinates of the point magnetic source to the coordinates of the observation point; S200: Calculate the induced magnetization and the gravitational potential generated by the point magnetic source at the observation point; determine the relationship between the magnetic potential and the gravitational potential based on the Poisson equation for the gravity and magnetic potential fields. S300: Based on the relationship between magnetic potential and gravitational potential, as well as geomagnetic tilt and magnetic declination, determine the relationship between magnetic field strength and magnetic potential; based on the total magnetic field strength measured by the magnetometer sensor and combined with the normal geomagnetic field strength, determine the magnetic field strength of the point magnetic source; based on the relationship between magnetic field strength and magnetic potential and the magnetic field strength of the point magnetic source, determine the calculation model for the magnetic anomaly of the underwater point magnetic source target. S400: Identify the maximum and minimum values ​​of the total magnetic field anomaly; substitute the maximum and minimum values ​​into the underwater point magnetic source target magnetic anomaly calculation model and perform ratio calculations to determine the vertical distance from the point magnetic source location coordinates to the observation plane; based on the real-time water depth measured synchronously, the draft of the magnetometer sensor, and the vertical distance, combined with geometric relationships, obtain the burial depth of the underwater target.

[0022] Specifically, firstly, a unified spatial rectangular coordinate system is established within the marine mapping area, and the observation plane where the magnetometer sensor is located is defined as the XOY plane. Under this coordinate system, the position coordinates of the equivalent point magnetic source of the underwater target are determined, along with the position coordinates of the observation point and the straight-line distance between the point magnetic source and the observation point. Subsequently, based on the geomagnetic environment conditions, the induced magnetization intensity of the underwater ferromagnetic target under the influence of the geomagnetic field is calculated, and the gravitational potential generated by the point magnetic source at the observation point is derived. Combining the Poisson equation for gravity and magnetic potential fields, a theoretical correspondence between magnetic potential and gravitational potential is established. Based on this, and according to the fundamental principles of electromagnetism, the geomagnetic tilt angle and magnetic... By using the deflection angle parameter, the functional relationship between magnetic field strength and magnetic potential is derived. The magnetic field strength generated by the point magnetic source is obtained by inverting the total magnetic field strength measured by the magnetometer sensor and the normal geomagnetic field strength, thus constructing a magnetic anomaly calculation model for the underwater point magnetic source target. Finally, the maximum and minimum values ​​in the total magnetic anomaly curve are automatically identified. The corresponding extreme value data are substituted into the magnetic anomaly calculation model and the ratio is calculated to determine the vertical distance from the point magnetic source location coordinates to the observation plane. Combined with the synchronously acquired real-time water depth data and the draft of the magnetometer sensor, the actual burial depth of the underwater ferromagnetic target below the seabed is calculated through geometric relationships.

[0023] This application further proposes the following for establishing a marine mapping spatial rectangular coordinate system: The coordinates of the point magnetic source position are Q ( x 0, y 0, z 0); The perpendicular distance from the point magnetic source location coordinates to the observation plane is R The coordinates of the observation point are P ( x , y , z The straight-line distance from the coordinates of the magnetic source to the coordinates of the observation point is... ; in, .

[0024] Specifically, such as Figure 2 As shown, the point magnetic source is considered as a uniformly magnetized magnetic body, and its remanent magnetization is neglected. In the spatial rectangular coordinate system of marine mapping, the observation plane where the magnetometer sensor (towed fish) is located is taken as... XOY Plane. The coordinates of the point magnetic source are Q (x 0, y 0, z 0), of which R Let P be the perpendicular distance from the point magnetic source to the observation plane, and let P be the coordinates of any observation point on the observation plane. x , y , z Then the distance between the point magnetic source and the observation point is... .

[0025] This application further proposes methods for determining the relationship between magnetic potential and gravitational potential based on Poisson's equation for gravity and magnetic potential fields, including: The gravitational potential of the point magnetic source at observation point P is: ; in, G It is the gravitational constant. The density of the point magnetic source, v Its volume; The Poisson equation relating magnetic potential and gravitational potential is: ; in, U ( x , y , z Let P be the magnetic potential. M Let grad be the total magnetization vector. P V ( x , y , z )for V ( x , y , z The gradient at point P.

[0026] Specifically, according to Poisson's equation for magnetic and gravitational potential fields, there is a certain relationship between the magnetic potential and gravitational potential of a uniformly magnetized and uniformly dense object. Based on this relationship, the magnetic field of the magnetic body can be calculated using the gravitational potential, and the Poisson equation for the relationship between magnetic potential and gravitational potential can be determined.

[0027] This application further proposes a total magnetization vector. M The formula for expressing it is: ; in, M i The magnetization intensity sensed for the target object. M r The residual magnetization retained after the target object has undergone magnetic field magnetization; ; T0 represents the normal geomagnetic field strength. κ The magnetic susceptibility of the point magnetic source material. μ denoted as ρ_permeability.

[0028] Specifically, when using magnetic methods to detect underwater targets, if the distance between the magnetometer sensor and the target is greater than three times the target's characteristic size, it can be approximated as a point magnetic source or a spherical magnetic source. The physical quantity that measures the degree of magnetization of a magnetic target at a certain point underwater is its total magnetization. M Generally, it is the result of the combined effect of its induced magnetization and remanent magnetization. The magnetization of a target object after being magnetized by the modern geomagnetic field under the influence of the Earth's magnetic field is its induced magnetization. M i The target object undergoes magnetization at various stages during its production, storage, transportation, and finally underwater placement. The magnetization intensity that remains at the end is its remanent magnetization intensity. M r . M r In this method, the value is 0 or can be ignored.

[0029] This application further proposes methods for determining the relationship between magnetic field strength and magnetic potential, including: The magnetic field strength is the negative gradient of the magnetic potential. Based on Poisson's equation relating magnetic potential and gravitational potential, the expressions for each component of the magnetic anomaly field can be obtained, i.e., the formula for the relationship between magnetic field strength and magnetic potential is: ; in: H ax , H ay , Z a These are the three components of the magnetic anomaly intensity vector. M x , M y , M z These are the three components of the total magnetization vector. V xx , V xy , V xz , V yy , V yz , V zz for V ( x , y , z The second-order partial derivative of ). The direction of the magnetization of a point magnetic source is the same as the direction of the Earth's magnetic field, expressed by magnetic declination. D This indicates that the magnetization inclination angle of the point magnetic source is related to the geomagnetic inclination angle. I Consistent, namely: ; When on the observation plane, z =0, z 0= R， After sorting, it becomes: .

[0030] Specifically, given the gravitational potential, the expressions for each component of the magnetic anomaly field can be obtained using Poisson's equation, thus determining the relationship between the magnetic field strength and the magnetic potential. Without considering remanent magnetization, the direction of the magnetization of the point magnetic source is consistent with the direction of the Earth's magnetic field, and magnetic declination can be used as the reference point. D This indicates that the magnetization inclination angle of the point magnetic source is related to the geomagnetic inclination angle. I Consistent, when on the observation plane, z =0, z 0= R, Z With the positive direction of the axis pointing underwater, the expression for the gravitational potential of the point magnetic source at the observation point P is combined with the formula for the relationship between magnetic field strength and magnetic potential to obtain the final formula for the relationship between magnetic field strength and magnetic potential.

[0031] This application further proposes methods for determining the magnetic field strength of a point magnetic source, including: Point source magnetic anomaly intensity T a It is the total magnetic field strength T With normal geomagnetic field strength T The vector difference of 0 is expressed by the formula: ; The magnetometer sensor measures the total magnetic field strength, which is the sum of the geomagnetic field strength at the observation point and the magnetic field strength of the point magnetic source. The total magnetic anomaly is obtained by subtracting the normal geomagnetic field strength from the measured total magnetic field strength. T This refers to the abnormal magnetic field strength of the point magnetic source, i.e. T yes T and T The modulus difference of 0 is given by the formula: ; Point source magnetic anomaly intensity T a With normal geomagnetic field strength T The vector angle between 0 and 0 is θ According to the cosine theorem for vector triangles, the formula is: ; Due to the magnetic anomaly intensity of the point magnetic sourceT a Much smaller than the normal geomagnetic field strength T 0, the formula is determined as follows: .

[0032] Specifically, in the magnetic detection of underwater targets, ignoring the magnetic anomalies of the Earth's magnetic field itself, the magnetic anomaly intensity vector of the point magnetic source is... T a It is the total magnetic field strength T With normal geomagnetic field T The vector difference of 0; in magnetic detection, the magnetometer measures the total magnetic field strength, which is the sum of the geomagnetic field strength at the observation point and the magnetic field strength of the point magnetic source. The total magnetic anomaly is obtained by subtracting the normal geomagnetic field from the measured total magnetic field strength. T The magnetic field strength of the point magnetic source is denoted as . T yes T and T The difference in modulus is 0; T a and T The angle between the two vectors is 0 θ According to the cosine theorem for vector triangles, we have: ; Right now: ; Squaring both sides of the above equation and rearranging, we can obtain: ; Due to the magnetic anomaly intensity of the point magnetic source T a Much smaller than the normal geomagnetic field strength T 0. The square term in the above formula can be omitted, and it can be simplified to: .

[0033] This application further proposes a calculation model for determining the magnetic anomaly of an underwater point magnetic source target object, including: When the magnetic anomaly intensity of the point magnetic source T a When the total magnetic field anomaly is less than 1000 nT, the total magnetic field anomaly will be... T Considered as the magnetic anomaly intensity of a point magnetic source T a Under normal geomagnetic field strength T The projection in the 0 direction, i.e., the total magnetic field anomaly T It is the magnetic anomaly intensity of the point magnetic source. T aThe fixed-direction projection, the magnetic anomaly intensity of the point magnetic source T a The formulas for representing the components on the three coordinate axes are as follows: ; Based on the formula relating magnetic field strength and magnetic potential, the calculation model for the magnetic anomaly of the underwater point magnetic source target is determined as follows: ; Among them, △ T ( x , y () represents the magnetic anomaly value at the observation point. I It is the geomagnetic tilt angle. D It is the magnetic declination. T 0 represents the normal geomagnetic field strength. v The equivalent volume of the target object for the point magnetic source. κ Let be the magnetic susceptibility of the point magnetic source material, and let the coordinates of the point magnetic source be ( ). x 0, y 0, R ),in R The vertical distance from the point magnetic source target to the observation plane is denoted as .

[0034] Specifically, when the magnetic anomaly intensity T a When it is less than 1000nT, it can be approximated as T Seen as T a exist T Projection in the 0 direction. Moreover, generally speaking, over a fairly large area, T The zero direction is approximately constant, therefore it can be considered that... T Seen as T a The projection in a fixed direction. That is to say, approximately, T The physical meaning and H ax , H ay , Z a Similar, all T a Projection in a fixed direction. Since... T yes T a Projection in a fixed direction.

[0035] This application further proposes methods for identifying maxima and minima in the total magnetic field anomaly, including: The planar position Q of the target object is determined by combining magnetic anomaly curve information with real-time navigation and positioning information. x 0, y 0); and obtain information related to magnetic anomaly feature points, including the magnetic anomaly maximum value Δ. T max and the coordinates A of the maximum point ( x max , y max ) and the minimum value of magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min ).

[0036] This application further proposes methods for determining the perpendicular distance from the point magnetic source location coordinates to the observation plane, including: Substituting information related to magnetic anomaly characteristic points into the underwater point magnetic source target magnetic anomaly calculation model, the maximum magnetic anomaly value Δ is determined. T max and the coordinates A of the maximum point ( x max , y max The relationship formula is: ; Determine the minimum value of the magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min The relationship formula is: ; Then, the ratio calculation is performed to determine the formula: ; Based on the known extreme point information, the vertical distance from the location coordinates of the point magnetic source to the observation plane is determined using the following formula: ; in, R The value range is [a, b]. Iterate through all values ​​from a to b at intervals of 0.1. R The range of values ​​[a, b] is determined by WD, d, and the possible burial depth range. Solutions that satisfy the formula for the vertical distance from the point magnetic source location coordinates to the observation plane are selected, thus determining the [value]. f ( R The closest to 0 R value.

[0037] Specifically, such as Figure 4-6 As shown, the planar and profile features of the magnetic anomaly of the same target at different observation plane heights R are calculated and displayed using the underwater point magnetic source target magnetic anomaly calculation model, as well as... Figure 7 As shown, the regional characteristics of the magnetic anomaly distribution of the target object are similar, and the magnetic anomaly profile exhibits a "quasi-sine wave" shape. With the increase of R, the magnetic anomaly amplitude decreases sharply and decays rapidly. The positions of the magnetic anomaly maxima and minima also change. In other words, changes in the observation plane height R not only cause changes in the magnetic anomaly amplitude but also lead to changes in its planar distribution characteristics, including the relative positions and sizes of the extreme points. Figure 7 In the diagram, A-A' is the main profile magnetic anomaly curve when the observation plane height R is 5m, B-B' is the main profile magnetic anomaly curve when the observation plane height R is 10m, and C-C' is the main profile magnetic anomaly curve when the observation plane height R is 15m.

[0038] In magnetic detection, if the survey line is the main profile magnetic anomaly curve (the survey line direction is consistent with the magnetic north direction, and the survey line passes directly above the target), then the accurate planar position Q of the target can be determined by combining the magnetic anomaly curve information with real-time navigation and positioning information. x 0, y 0), and at the same time, we can also obtain relevant information about some magnetic anomaly characteristic points, such as: magnetic anomaly maxima Δ T max and the coordinates A of the maximum point ( x max , y max ) and the minimum value of magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min For these two extreme points, their location coordinates and values ​​also satisfy the relationship of the underwater point magnetic source target magnetic anomaly calculation model.

[0039] Magnetic anomaly maximum Δ T max and the coordinates A of the maximum point ( x max , y max The relationship formula and the minimum value of magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min In the relationship formula, the geomagnetic field parameters T 0、 D ,I The parameters are constants and are known parameters; the target object parameters are... v , κ Although it is also a constant, it is generally unknown during detection. To facilitate the elimination of unknowns, we compare both sides of the above formula. When the extreme point information is known, the only unknown in the ratio calculation formula is the height of the observation plane. R One item.

[0040] Considering the complex form of the formula for the perpendicular distance from the point magnetic source location coordinates to the observation plane, and the presence of unknowns... R The highest order is 5, making analytical solutions difficult to obtain. Therefore, a numerical exhaustive search method using programming can be considered, i.e., given the actual situation... R The range of values ​​for is [a, b], in reality... R The value must be within this interval. By iterating through all values ​​from a to b at 0.1 intervals, and substituting them sequentially into the formula for the perpendicular distance from the point magnetic source position coordinates to the observation plane, we can select the solution that satisfies the equation, thus obtaining the result. f ( R The closest to 0 R value.

[0041] This application further proposes methods for obtaining the burial depth of underwater targets, including: Based on geometric relationships, the formula for determining the relationship is: ; Right now: ; in, WD To measure water depth simultaneously with magnetic detection, d The draft of the magnetometer sensor. B The burial depth of underwater ferromagnetic targets.

[0042] Specifically, such as Figure 3 As shown, the geometric relationships and formulas are determined based on the schematic diagram of the magnetic detection geometry, and then solved to obtain... R Afterwards, WD (Simultaneously measured water depth) and d Given that the draft of the magnetometer sensor is known, determine the burial depth of the target object. B .

[0043] The detailed implementation flowchart of the method for inverting the burial depth of a target object based on the extreme value of magnetic anomalies constrained by synchronous water depth in this invention is shown below. Figure 11 As shown; 1. First, collect data on the survey area, including: information on the target object, geomagnetic background parameters, water depth and topography, etc.

[0044] 2. Develop a magnetic detection plan, preferably by first laying out a grid-like survey line to determine the accurate planar position of the target object. x 0, y 0). Sometimes, if the planar location of the target object is known and only its burial depth needs to be determined, this step can be omitted, and you can proceed directly to the next step.

[0045] 3. Based on the determined planar position of the target object, design the main profile survey line, conduct main profile magnetic detection, and simultaneously measure the water depth using an acoustic depth sounder to obtain the real-time water depth at the target object's location. WD .

[0046] 4. Process magnetic detection data to obtain information on the maximum and minimum points of the magnetic anomaly in the main profile and the real-time draft of the towed fish at the target object. d Substituting the extreme point information into the formula for the vertical distance from the point magnetic source position coordinates to the observation plane, the height of the observation plane is calculated. R Note that the formula for the perpendicular distance from the magnetic source location coordinates to the observation plane is quite complex and has no analytical solution. An approximate numerical solution can be obtained using a programming method.

[0047] 5. Based on the geometric formulas, and the measured water depth at the target location... WD and the draft of the troll d Substitute the values ​​to determine the burial depth of the target object. B .

[0048] The feasibility of this method is illustrated below through three simulation examples.

[0049] Example 1: T 0 = 50000nT D =0°, I =45° is the geomagnetic field parameter, with the volume directly below the origin as the reference point. v =0.10m 3 Material magnetic susceptibility κ =100SI, burial depth B The target object is 3m deep, which is used as the basis for the model. The real-time water depth at the time of detection is assumed. WD =6m, magnetometer dragging fish draws water d =2m, then: R =7m.

[0050] First, forward modeling is used to obtain relevant information about the extreme points of the magnetic anomaly in the main profile: Magnetic anomaly maximum: △ T max =142.97nT, coordinates of the maximum point: ( x max , y max ) = (-3, 0); Magnetic anomaly minimum: △ T min =-60.21nT, coordinates of the minimum point: ( x min , y min = (4.1, 0).

[0051] Then assume the burial depth B It is unknown; extreme point information is used for inversion. The known quantity is: real-time water depth. WD =6m, magnetometer dragging fish draws water d =2m, therefore a solution is needed. R .

[0052] like Figure 8 As shown, f ( R ) images and f ( R ) = 0 is approximately in R The magnetic source is tangent to the observation plane near point 7. The distance is calculated using the formula for the perpendicular distance from the point magnetic source position coordinates to the observation plane. R There are two values: 6.65m and 7.19m, with an average of 6.92m. Substituting these values ​​into the geometric formula, the burial depth is... B =2.92m, which is consistent with the preset value. B Compared to 3m, the error is 0.08m.

[0053] Example 2: T 0 = 50000nT D =45°, I =45° is the geomagnetic field parameter, with the volume directly below the origin as the reference point. v =0.10m 3 Material magnetic susceptibility κ =100SI, burial depth B The target object, at a depth of 2 meters, was used as the base model. Real-time water depth during detection. WD =11m, magnetometer dragging fish draws water d =1m, then: R =12m.

[0054] First, forward modeling is used to obtain relevant information about the extreme points of the magnetic anomaly in the main profile: Magnetic anomaly maximum: △ T max =28.36nT, coordinates of the maximum point: ( x max , y max ) = (-3.7, -3.7); Magnetic anomaly minimum: △ T min=-11.96nT, coordinates of the minimum point: ( x min , y min = (5, 5).

[0055] Then assume the burial depth B It is unknown; extreme point information is used for inversion. The known quantity is: real-time water depth. WD =11m, magnetometer dragging fish draws water d =1m are all measured values, therefore a solution is needed. R .

[0056] like Figure 9 As shown, f ( R ) images and f ( R ) = 0 is approximately in R The magnetic source is tangent to the observation plane at approximately 12, and the distance is calculated using the formula for the perpendicular distance from the point magnetic source position coordinates to the observation plane. R There are two values: 11.58m and 12.09m. R The average value is 11.84m. Substituting this into the geometric formula, then... B =1.84m, compared to the preset value B Compared to 2m, the error is 0.16m.

[0057] Example 3: T 0 = 50000nT D =30°, I =30° is the geomagnetic field parameter, with the volume directly below the origin as the reference point. v =0.10m 3 Material magnetic susceptibility κ =100SI, burial depth B The target object, 1m in diameter, was used as the base model. Real-time water depth during detection. WD =15m, magnetometer dragging fish draws water d =2m, then: R =14m.

[0058] First, forward modeling is used to obtain relevant information about the extreme points of the magnetic anomaly in the main profile: Magnetic anomaly maximum: △ T max =11.84nT, coordinates of the maximum point: ( x max , y max = (-7.5, -4.4); Magnetic anomaly minimum: △ T min=-10.94nT, coordinates of the minimum point: ( x min , y min = (4.5, 2.5).

[0059] Then assume the burial depth B It is unknown; extreme point information is used for inversion. The known quantity is: real-time water depth. WD =15m, magnetometer dragging fish draws water d =2m are all measured values, therefore a solution is needed. R .

[0060] like Figure 10 As shown, f ( R ) images and f ( R ) = 0 is approximately in R The point of tangency is at point 14, and the perpendicular distance from the point magnetic source position coordinates to the observation plane is calculated using a programming method. R There are two values: 13.77m and 14.09m. R The average value is 13.93m. Substituting this into the geometric formula, then... B =0.93m, which is consistent with the preset value. B Compared to 1m, the error is 0.07m.

[0061] In summary, this invention uses magnetic methods to detect the extreme points of magnetic anomalies in the main profile of underwater ferromagnetic targets. Under the constraint of synchronously measured water depth, the method for inverting the burial depth of the target can be realized by using only a single-sensor magnetometer simultaneously equipped with a depth sounder during data acquisition. It has the advantages of simple data acquisition, strong operability, and high inversion accuracy.

[0062] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, characterized in that, include: Establish a spatial rectangular coordinate system for marine mapping; take the observation plane where the magnetometer sensor is located as the XOY plane, determine the coordinates of the point magnetic source, the coordinates of the observation point, and the straight-line distance from the coordinates of the point magnetic source to the coordinates of the observation point; Calculate the induced magnetization and the gravitational potential generated by the point magnetic source at the observation point; determine the relationship between the magnetic potential and the gravitational potential based on Poisson's equation for the gravity and magnetic potential fields. Based on the relationship between magnetic potential and gravitational potential, as well as geomagnetic tilt and magnetic declination, the relationship between magnetic field strength and magnetic potential is determined; based on the total magnetic field strength measured by the magnetometer sensor and combined with the normal geomagnetic field strength, the magnetic field strength of the point magnetic source is determined. Based on the relationship between magnetic field strength and magnetic potential, and the magnetic field strength of the point magnetic source, a calculation model for the magnetic anomaly of the target object of the underwater point magnetic source is determined. Identify the maximum and minimum values ​​of the total magnetic field anomaly; substitute the maximum and minimum values ​​into the calculation model of the underwater point magnetic source target magnetic anomaly, and perform ratio calculations to determine the vertical distance from the point magnetic source location coordinates to the observation plane; based on the real-time water depth measured synchronously, the draft of the magnetometer sensor, and the vertical distance, combined with geometric relationships, obtain the burial depth of the underwater target.

2. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 1, is characterized in that... When establishing a spatial rectangular coordinate system for marine mapping, the following steps are included: The coordinates of the point magnetic source are Q ( x 0, y 0, z 0); the vertical distance from the point magnetic source position coordinates to the observation plane is R The coordinates of the observation point are P ( x , y , z The straight-line distance from the coordinates of the magnetic source to the coordinates of the observation point is... ; in, .

3. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 2, is characterized in that... When determining the relationship between magnetic potential and gravitational potential based on Poisson's equation for gravity and magnetic potential, the following steps are included: The gravitational potential of the point magnetic source at observation point P is: ； in, G It is the gravitational constant. The density of the point magnetic source, v Its volume; The Poisson equation relating magnetic potential and gravitational potential is: ； in, U ( x , y , z Let P be the magnetic potential. M Let grad be the total magnetization vector. P V ( x , y , z )for V ( x , y , z The gradient at point P.

4. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 3, is characterized in that... include: Total magnetization vector M The formula for expressing it is: ； in, M i The magnetization intensity sensed for the target object. M r The residual magnetization retained after the target object has undergone magnetic field magnetization; ； T 0 represents the normal geomagnetic field strength. κ The magnetic susceptibility of the point magnetic source material. μ denoted as ρ, where ρ is the permeability of the medium.

5. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 4, is characterized in that... Determining the relationship between magnetic field strength and magnetic potential includes: The magnetic field strength is the negative gradient of the magnetic potential. Based on Poisson's equation relating magnetic potential and gravitational potential, the expressions for each component of the magnetic anomaly field can be obtained, i.e., the formula for the relationship between magnetic field strength and magnetic potential is: ； in: H ax , H ay , Z a These are the three components of the magnetic anomaly intensity vector. M x , M y , M z These are the three components of the total magnetization vector. V xx , V xy , V xz , V yy , V yz , V zz for V ( x , y , z The second-order partial derivative of ). The direction of the magnetization of a point magnetic source is the same as the direction of the Earth's magnetic field, expressed by magnetic declination. D This indicates that the magnetization inclination angle of the point magnetic source is related to the geomagnetic inclination angle. I Consistent, namely: ； When on the observation plane, z =0, z 0= R， After sorting, it becomes: 。 6. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 5, is characterized in that... Determining the magnetic field strength of a point magnetic source includes: Point source magnetic anomaly intensity T a It is the total magnetic field strength T With normal geomagnetic field strength T The vector difference of 0 is expressed by the formula: ； The magnetometer sensor measures the total magnetic field strength, which includes the geomagnetic field strength at the observation point and the magnetic field strength of the point magnetic source. The total magnetic anomaly is obtained by subtracting the normal geomagnetic field strength from the measured total magnetic field strength. T This refers to the abnormal magnetic field strength of the point magnetic source, i.e. T yes T and T The modulus difference of 0 is given by the formula: ； Point source magnetic anomaly intensity T a With normal geomagnetic field strength T The vector angle between 0 and 0 is θ According to the cosine theorem for vector triangles, the formula is: ； Due to the magnetic anomaly intensity of the point magnetic source T a Much smaller than the normal geomagnetic field strength T 0, the formula is determined as follows: 。 7. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 6, is characterized in that... When determining the calculation model for the magnetic anomaly of the target object at the underwater point magnetic source, the following should be included: When the magnetic anomaly intensity of the point magnetic source T a When the total magnetic field anomaly is less than 1000 nT, the total magnetic field anomaly will be... T Considered as the magnetic anomaly intensity of a point magnetic source T a Under normal geomagnetic field strength T The projection in the 0 direction, i.e., the total magnetic field anomaly T It is the magnetic anomaly intensity of the point magnetic source. T a The fixed-direction projection, the magnetic anomaly intensity of the point magnetic source T a The formulas for representing the components on the three coordinate axes are as follows: ； Based on the formula relating magnetic field strength and magnetic potential, the calculation model for the magnetic anomaly of the underwater point magnetic source target is determined as follows: ； Among them, △ T ( x , y () represents the magnetic anomaly value at the observation point. I It is the geomagnetic tilt angle. D It is the magnetic declination. T 0 represents the normal geomagnetic field strength. v The equivalent volume of the target object for the point magnetic source. κ Let be the magnetic susceptibility of the point magnetic source material, and let the coordinates of the point magnetic source be ( ). x 0, y 0, R ),in R The vertical distance from the point magnetic source target to the observation plane is denoted as .

8. The method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 7, is characterized in that... When identifying the maximum and minimum values ​​of the total magnetic field anomaly, the following steps are included: The planar position Q of the target object is determined by combining magnetic anomaly curve information with real-time navigation and positioning information. x 0, y 0); and obtain information related to magnetic anomaly feature points, including the magnetic anomaly maximum value Δ. T max and the coordinates A of the maximum point ( x max , y max ) and the minimum value of magnetic anomaly Δ T min and the coordinates B of the minimum point ( x min , y min ).

9. The method for determining the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 8, is characterized in that... Determining the perpendicular distance from the point magnetic source's location coordinates to the observation plane includes: Substituting the relevant information of the magnetic anomaly feature points into the magnetic anomaly calculation model of the underwater point magnetic source target object, the maximum value of the magnetic anomaly Δ is determined. T max and the coordinates A of the maximum point ( x max , y max The relationship formula is: ； Determine the minimum value Δ of the magnetic anomaly T min and the coordinates B of the minimum point ( x min , y min The relationship formula is: ； Then, the ratio calculation is performed to determine the formula: ； Based on the known extreme point information, the vertical distance from the location coordinates of the point magnetic source to the observation plane is determined using the following formula: ； in, R The range of values ​​is [a, b]. All values ​​from a to b are iterated at intervals of 0.1, and solutions that satisfy the formula for the perpendicular distance from the point magnetic source location coordinates to the observation plane are selected, thus determining the solution. f ( R The closest to 0 R value.

10. The method for inverting the burial depth of a target object based on magnetic anomaly information from a single sensor, as described in claim 9, is characterized in that... When determining the burial depth of an underwater target, the following is included: Based on geometric relationships, the formula for determining the relationship is: ； Right now: ； in, WD To measure water depth simultaneously with magnetic detection, d The draft of the magnetometer sensor. B The burial depth of underwater ferromagnetic targets.

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