A method for locating magnetic targets using vector difference array

Abstract

This invention discloses a method for locating magnetic targets using a vector difference array. It employs eight vector magnetic sensors with aligned triaxial directions. Sensors 1, 2, 3, and 4 are located at the four vertices of square array 1; sensors 5, 6, 7, and 8 are located at the four vertices of square array 2. Sensor 7 is located at the geometric center of square array 1, and sensor 1 is located at the geometric center of square array 2. Sensors 1, 3, 5, and 7 are aligned in a straight line, and the diagonals of the two square arrays are of equal length. The eight vector magnetic sensors measure all information of the three components of the geomagnetic field and the geomagnetic tensor at the center of the two square arrays. The influence of the geomagnetic background field is eliminated through difference, achieving target location. This invention offers relatively high resolution, enabling accurate target location even under complex geomagnetic conditions. It requires fewer sensors and provides a simple and rapid solution.

Description

Technical Field

[0001] This invention belongs to the field of geomagnetic detection technology and relates to a method for locating magnetic targets using a vector difference array. Background Technology

[0002] In various application fields, accurately determining the location of a target is a primary task and a prerequisite for subsequent work. For example, operations such as cargo salvage from sunken ships, mine clearance, beach rescue, port vessel monitoring, and anti-submarine warfare all require accurate and rapid location of underwater targets. In environments like the Yellow Sea and East China Sea in my country, sea state and target noise are the biggest factors determining the sonar detection range. However, magnetic field detection eliminates these factors. The presence of a magnetic target induces a magnetic field that alters the distribution of the Earth's magnetic field, creating magnetic anomalies in that space. Therefore, magnetic detection technology is a highly effective method; by inverting these magnetic anomalies, information about the target object (such as geometric parameters and positional parameters) can be obtained.

[0003] There are two types of sensors used to measure magnetic anomalies: scalar sensors and vector sensors. Scalar sensors can only measure the magnitude of the total geomagnetic field, providing incomplete information and requiring a large number of sensors. Furthermore, the resulting positioning equations are nonlinear, making analytical solutions nearly impossible, leading to spurious values ​​in the mathematical solution process. Scalar sensors also suffer from dead zones. When using vector sensors for target positioning, many center point geomagnetic components are measured indirectly, introducing approximation errors. This method also requires a large number of sensors and presents challenges in installation and operation. Summary of the Invention

[0004] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a method for locating magnetic targets by using a vector difference array to overcome the influence of the geomagnetic background field, effectively eliminating the influence of the geomagnetic background field and realizing accurate calculation of the target position.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for locating magnetic targets using a vector difference array, comprising:

[0006] Eight vector magnetic sensors with consistent triaxial orientation are used. Sensors 1, 2, 3, and 4 are located at the four vertices of square array 1, respectively; sensors 5, 6, 7, and 8 are located at the four vertices of square array 2, respectively. Sensor 7 is located at the geometric center of square array 1, and sensor 1 is located at the geometric center of square array 2. Sensors 1, 3, 5, and 7 are located on a straight line, and the diagonals of the two square arrays are of equal length.

[0007] When the target is in a changing geomagnetic field and a non-uniform geomagnetic background field, the target's position vector r satisfies:

[0008]

[0009] Wherein, G1 is the magnetic field tensor matrix of the center point of square array 1, G2 is the magnetic field tensor matrix of the center point of square array 2, the location of sensor 1 is the origin of the coordinate system, r1 represents the position vector of sensor 7, T1 and T7 represent the measurement values ​​of sensor 1 and sensor 7 respectively; t0 represents the initial time when the target is not in the area, G1(t0) and G2(t0) represent the magnetic field tensor matrices of the center point of square array 1 and the center point of square array 2 at time t0, and T1(t0) and T7(t0) represent the measurement values ​​of sensor 1 and sensor 7 at time t0.

[0010] Furthermore, when the target is in a uniform geomagnetic background field, G1(t0)=G2(t0)=0, T1(t0)=T7(t0), and the target's position vector r satisfies:

[0011]

[0012] Wherein, B1 represents the magnetic field vector generated by the magnetic target at the location of sensor 1, B7 represents the magnetic field vector generated by the magnetic target at the location of sensor 7, and B1-B7=T1-T7.

[0013] The beneficial effects of this invention are as follows: Compared with the prior art, this invention has a relatively high resolution and can still achieve accurate positioning of the target under complex geomagnetic conditions. The array algorithm proposed uses a relatively small number of sensors. It cleverly uses a double square structure to overcome the influence of the geomagnetic background field at the array center point and uses a double gradient algorithm to eliminate the influence of uneven geomagnetic field distribution, making the solution simple and fast. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a vector difference magnetic target positioning array. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] Combination Figure 1 The present invention is implemented as follows: Based on the target far-field magnetic dipole model, a double square array is constructed using two sets of vector sensor square planar arrays. The array consists of eight three-axis vector sensors. With eight sensors, all information of the three components of the geomagnetic field and the geomagnetic tensor at the center of the two sets of square arrays can be measured. The influence of the geomagnetic background field can be eliminated through difference calculation, and the target positioning can be achieved.

[0017] The method for locating magnetic targets using a magnetic vector difference array includes the following steps:

[0018] Step 1: Use eight vector magnetic sensors to form a sensor array. The three axes of the eight sensors are aligned (Cartesian right-hand coordinate system). Sensors 1, 2, 3, and 4 are located at the four vertices of a square, forming square array 1. Sensors 5, 6, 7, and 8 are located at the four vertices of another square, forming square array 2. Sensor 7 is located at the geometric center of square array 1, and sensor 1 is located at the geometric center of square array 7. Sensors 1, 3, 5, and 7 are on a straight line (x-axis). The location of sensor 1 is the origin of the coordinate system. The diagonal length of both squares is 2d. Figure 1 .

[0019] Step 2: Based on the sensor array and the magnetic dipole far-field model, establish the relationship between the three components of the geomagnetic field, their respective geomagnetic tensors, and the position of the magnetic target:

[0020]

[0021] Wherein: G1 is the magnetic field tensor matrix at the center point of square array 1, G2 is the magnetic field tensor matrix at the center point of square array 2, r represents the target's position vector, r1 represents the sensor 7's position vector, B1 represents the magnetic field vector generated by the magnetic target at the sensor 1's position, and B7 represents the magnetic field vector generated by the magnetic target at the sensor 7's position.

[0022] Step 3: Subtract the left and right sides of the two equations in the system of positioning equations obtained in Step 2 to get:

[0023]

[0024] Considering that when the geomagnetic background field is uniformly distributed, B1-B7 = T1-T7, the influence of the uniform geomagnetic background field on target positioning is eliminated. Where: T i T j The measured values ​​of sensors i (i = 1, 2, ..., 8) and j (j = 1, 2, ..., 8) are represented by i ≠ j. i and j are the sensor serial numbers.

[0025] Step 4: Eliminate the influence of changing geomagnetic field and inhomogeneous geomagnetic background field on target positioning.

[0026] Because of T i Real-time measurement

[0027] T i =T0(t0)+ΔT0(t-t0)+ΔT0(t0,x i ,y i ,z i )+Bi (3)

[0028] Where: T0(t0) represents the initial geomagnetic field value without a target, ΔT0(t-t0) is the change of the geomagnetic field with time due to various factors such as thunderstorms, and ΔT0(t0,x) is the change of the geomagnetic field with time. i ,y i ,z i The increment at time t0 is caused by the uneven spatial distribution of the geomagnetic field. i This represents the magnetic field vector generated by the magnetic target at the location of sensor i.

[0029] T i -T j =ΔT0(t0,x i ,y i ,z i )-ΔT0(t0,x j ,y j ,z j )+B i -B j (4)

[0030] It is evident that the effects of spatial non-uniformity in the geomagnetic background field have not yet been eliminated.

[0031] At the initial time t0, the target is not within the area, and the measurement value T of sensor i at this time is... i =T i (t0), at this time B i =B j =0 (i≠j), from equation (4),

[0032] T i (t0)-T j (t0)=ΔT0(t0,x i ,y i ,z i )-ΔT0(t0,x j ,y j ,z j (5)

[0033] Substituting equation (5) into equation (4), we get

[0034] B i -B j =T i -T j -(T i (t0)-T j (t0)) (6)

[0035] The right side of equation (6) represents the sensor measurements. The magnetic field at a point in space is a linear superposition of the target's far-field dipole magnetic field and the Earth's magnetic field. At the initial time t0 without a target, the target is located at (x... i ,y i ,z i The sensor i measures a value of T. i Substituting the geomagnetic tensors G1(t0) and G2(t0) corresponding to the initial time t0 without a target into equation (2), the influence of the uneven distribution of the geomagnetic field at the location of the array is eliminated, and the target positioning function is obtained:

[0036]

[0037] Ultimately, the magnetic field of the target is located.

[0038] To verify the anti-interference capability of the method, a magnetic field target localization experiment was conducted in the laboratory. An array of eight ColiyF902 fluxgate magnetometers was used, with an array aperture d = 0.284 m. Figure 1 A vector magnetic sensor array was constructed, from which r1 was obtained, with a magnetic moment of 37 Am. 2 The permanent magnet is used as the target, with a magnetic moment tilt angle of π / 2, and a sampling rate of 1Hz. The target is initially located at (-2.4m, 1.6m, 0.557m) and remains there for about 30 seconds. Then, the target is moved to the point (-20m, 0.8m, 0.557m) and kept in the same position, which is time t0. The sensor measurements T1(t0) and T7(t0), T1 and T2, the magnetic field tensor matrices G1(t0) and G2(t0), and G1 and G2 are obtained from the array measurement data. These data are then substituted into equation (7).

[0039]

[0040] The position of the magnetic target is obtained through calculation.

[0041] The laboratory's magnetic environment is complex and harsh, with magnetic anomalies ranging from 500 to 10000 nT / m. Under these unfavorable conditions, the three-dimensional positioning results (-2.3m, 1.9m, 0.34m) show relatively small positioning errors. Experiments demonstrate that the proposed method effectively eliminates the significant influence of the indoor geomagnetic field, achieving effective positioning of magnetic targets.

Claims

1. A method for locating magnetic targets using a vector difference array, characterized in that, include: Eight vector magnetic sensors with consistent triaxial orientation are used. Sensors 1, 2, 3, and 4 are located at the four vertices of square array 1, respectively; sensors 5, 6, 7, and 8 are located at the four vertices of square array 2, respectively. Sensor 7 is located at the geometric center of square array 1, and sensor 1 is located at the geometric center of square array 2. Sensors 1, 3, 5, and 7 are located on a straight line, and the diagonals of the two square arrays are of equal length. When the target is in a changing geomagnetic field and a non-uniform geomagnetic background field, the target's position vector r satisfies: Wherein, G1 is the magnetic field tensor matrix of the center point of square array 1, G2 is the magnetic field tensor matrix of the center point of square array 2, the location of sensor 1 is the origin of the coordinate system, r1 represents the position vector of sensor 7, T1 and T7 represent the measurement values ​​of sensor 1 and sensor 7 respectively; t0 represents the initial time when the target is not in the area, G1(t0) and G2(t0) represent the magnetic field tensor matrices of the center point of square array 1 and the center point of square array 2 at time t0, and T1(t0) and T7(t0) represent the measurement values ​​of sensor 1 and sensor 7 at time t0.

2. The method for locating magnetic targets using a vector difference array according to claim 1, characterized in that: When the target is in a uniform geomagnetic background field, G1(t0)=G2(t0)=0, T1(t0)=T7(t0), and the target's position vector r satisfies: Wherein, B1 represents the magnetic field vector generated by the magnetic target at the location of sensor 1, B7 represents the magnetic field vector generated by the magnetic target at the location of sensor 7, and B1-B7=T1-T7.

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