A multi-point measurement based magnetic target positioning method

Abstract

The application discloses a kind of magnetic target positioning methods based on multi-point measurement, belong to the target positioning technical field based on magnetic field. Including: S100, by motor-driven platform carries magnetic sensor array to certain movement mode, the measurement of magnetic gradient tensor is realized in multiple measurement points;S200, establish the positioning equation set that is decoupled with motor-driven platform attitude, calculate the positioning result of magnetic target under earth coordinate system.The application establishes the positioning equation set that is irrelevant with motor-driven platform attitude by multi-point measurement, realizes decoupling with attitude, eliminates the influence of motor-driven platform attitude on positioning accuracy, and then improves the positioning accuracy of tensor magnetic positioning technology.

Description

A Magnetic Target Localization Method Based on Multi-Point Measurement Technical Field

[0001] This invention relates to a magnetic target localization method based on multi-point measurement, belonging to the field of magnetic field-based target localization technology. Background Technology

[0002] Magnetic target localization technology is a non-contact, passive detection method based on magnetic fields. Theoretically, it can detect the presence of any ferromagnetic material on Earth. Compared to other detection methods, magnetic anomaly detection is largely unaffected by natural factors such as weather. Furthermore, water (oceans, rivers, lakes, etc.), air, the human body, and most soil and rocks do not shield the magnetic field. It also boasts advantages such as strong identification capabilities, short operating time, high positioning accuracy, and low cost. Therefore, magnetic target localization technology has wide applications in underwater exploration, biomedicine, archaeological excavation, and mineral exploration.

[0003] Mounting magnetic field detectors on mobile platforms (such as aerial survey aircraft and vehicles) for magnetic target localization can effectively improve detection efficiency. The main magnetic target localization techniques used on mobile platforms are scalar magnetic target localization and tensor magnetic target localization, but both methods have drawbacks to varying degrees.

[0004] 1. Due to the inability to accurately obtain the geomagnetic tilt and deflection angles, the positioning accuracy of scalar magnetic target positioning technology is limited.

[0005] Given the geomagnetic tilt and declination, and leveraging the near-zero scalar gradient of the geomagnetic field, a nonlinear equation system is constructed using a scalar magnetic sensor array. This allows for the accurate determination of the magnetic target's coordinates. However, the geomagnetic tilt and declination need to be calculated using a geomagnetic field model or measured by geomagnetic observatories. The fluctuations in the time-varying geomagnetic field are tens of nT on calm days and hundreds of nT on storm days, making it impossible to accurately determine the tilt and declination. Furthermore, the current global number of geomagnetic stations (only about 170) limits the geographical application of this technology. Therefore, the application of scalar magnetic target positioning technology is limited, and its positioning accuracy is insufficient.

[0006] 2. The positioning accuracy of tensor magnetic target localization technology is affected by the attitude error of the mobile platform.

[0007] Because the magnetic gradient tensor of the Earth's magnetic field is essentially zero, tensor magnetic target localization technology can accurately and quickly locate magnetic targets without requiring any prior knowledge of the Earth's magnetic field by measuring the magnetic gradient tensor generated by the magnetic target using a vector magnetic sensor array. During the detection process, the localization result must be projected onto the Earth coordinate system to accurately pinpoint the magnetic target's location. However, the attitude of the moving platform changes during movement, and the attitude sensor can only control the attitude error to around 1°. Due to the influence of the moving platform's attitude error, the localization result of tensor magnetic target localization technology cannot be accurately projected onto the Earth coordinate system. Taking the improved STAR method in tensor magnetic target localization technology as an example, the influence of the moving platform's attitude error on the localization error is analyzed when locating a magnetic target at 500m. As shown in Figure 1, the larger the attitude error, the larger the localization error of the magnetic target. Without attitude error, the localization error is 0.3608m; when the attitude error is 1°, the localization error is 1.1983m, becoming 232.13% of the original error. Therefore, due to the influence of the moving platform's attitude error, the localization accuracy of tensor magnetic target localization technology needs further improvement. Summary of the Invention

[0008] This invention proposes a magnetic target positioning method based on multi-point measurement, which decouples the positioning from the attitude of the platform and eliminates the influence of the attitude of the mobile platform on the positioning accuracy. This improves the positioning accuracy of the tensor magnetic positioning technology and solves the problem that the tensor magnetic target positioning technology is affected by the attitude error of the mobile platform and cannot accurately project the positioning results onto the Earth coordinate system, thus causing positioning errors.

[0009] A magnetic target localization method based on multi-point measurement, the magnetic target localization method based on a mobile platform includes the following steps:

[0010] S100: A magnetic sensor array is mounted on a mobile platform and moves in a certain manner to measure the magnetic gradient tensor at multiple measurement points.

[0011] S200. Establish a set of positioning equations decoupled from the attitude of the mobile platform, and calculate the positioning results of the magnetic target in the Earth coordinate system.

[0012] Furthermore, in S100, specifically: the motion mode of the motorized platform is: it moves on m motion planes, where m ≥ 2; on motion plane P i During the upward motion, 1 ≤ i ≤ m, there are n paths, each path is parallel to the others, and the angle between each path and the X-axis of the Earth coordinate system is θ. i , 0°≤θ i ≤180°; Plane of motion P i (1≤i≤m) and the plane of motion P i+1 The distance between them is h i(i+1) .

[0013] Furthermore, in S200, specifically: at the j-th (1≤j≤N) measurement point, the positioning distance obtained by the tensor magnetic target localization technique is r. j The position coordinates of the mobile platform in the Earth coordinate system are (x... j ,y j ,z j The position coordinates are obtained through a positioning system. Let the position coordinates of the magnetic target in the Earth coordinate system be (x0, y0, z0). Then, at the j-th measurement point, the distance equation is obtained as follows:

[0014]

[0015] A set of distance equations independent of the attitude of the maneuvering platform was established through multi-point measurements, as shown in equation (2).

[0016]

[0017] The position coordinates of the magnetic target in the Earth coordinate system are obtained by solving equation (2) using a nonlinear optimization method.

[0018] The beneficial effects of this invention are:

[0019] (1) Tensor magnetic target positioning technology is affected by the error of the maneuvering platform, which makes it impossible to accurately project the positioning results onto the Earth coordinate system, thus leading to positioning errors. To address this issue, a magnetic target positioning method based on multi-point measurement is proposed. By planning the motion path of the maneuvering platform and performing multi-point measurements, a set of equations for the distance between the maneuvering platform and the magnetic target is established. This decouples the magnetic target positioning results from the attitude of the maneuvering platform, compensates for the positioning errors caused by the attitude errors of the maneuvering platform, and thus improves the positioning accuracy of the magnetic target.

[0020] (2) When the attitude error of the mobile platform is ±1°, the positioning error of the magnetic target before compensation is 1.141m. After compensation using the magnetic target positioning method based on the mobile platform proposed in this invention, the positioning error of the magnetic target is 0.304m, which improves the positioning accuracy by 73.36%, effectively improving the positioning accuracy. Attached Figure Description

[0021] Figure 1 shows the impact of the attitude error of the mobile platform on the magnetic target positioning error;

[0022] Figure 2 is a schematic diagram of magnetic target localization based on a mobile platform;

[0023] Figure 3 shows the effect of the motion path on the positioning error of the magnetic target. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Referring to Figures 1-3, this invention proposes a magnetic target localization method based on multi-point measurement. The magnetic target localization method based on a mobile platform includes the following steps:

[0026] S100: A magnetic sensor array is mounted on a mobile platform and moves in a certain manner to measure the magnetic gradient tensor at multiple measurement points.

[0027] S200. Establish a set of positioning equations decoupled from the attitude of the mobile platform, and calculate the positioning results of the magnetic target in the Earth coordinate system.

[0028] Furthermore, in S100, specifically: the motion mode of the motorized platform is: it moves on m motion planes, where m ≥ 2; on motion plane P i During the upward motion, 1 ≤ i ≤ m, there are n paths, each path is parallel to the others, and the angle between each path and the X-axis of the Earth coordinate system is θ. i , 0°≤θ i ≤180°; Plane of motion P i (1≤i≤m) and the plane of motion P i+1 The distance between them is h i(i+1) .

[0029] Specifically, a mobile platform carrying a magnetic sensor array moves in a specific manner to measure the magnetic gradient tensor at multiple locations, ultimately accurately locating the magnetic target, as shown in Figure 2. The motion of the mobile platform can be summarized as follows: moving on m (m≥2) motion planes; and on motion plane P... i When moving on (1≤i≤m), there are n paths, each parallel to the others, and the angle between each path and the X-axis of the Earth coordinate system is θ. i (0°≤θ i ≤180°); Plane of motion P i (1≤i≤m) and the plane of motion P i+1 The distance between them is h i(i+1) In practical use, the movement mode of the mobile platform should be planned according to actual conditions and requirements. Increasing the number of motion planes can increase positioning accuracy. However, the number should not be too large; 2-3 motion planes are ideal, otherwise the entire detection process will take too long. It is recommended that θ... iThe motion paths are uniformly distributed within the range of 0° to 180°. The number of motion paths, n, is related to the positioning accuracy. It is necessary to calculate the impact of the number of motion paths, n, on the positioning accuracy and select the appropriate path based on the requirements.

[0030] Furthermore, at each measurement point, the tensor magnetic target localization technique can obtain the position vector of the magnetic target in the mobile platform coordinate system. However, due to the attitude error of the mobile platform, projecting the localization result to the Earth coordinate system by measuring the attitude of the mobile platform will lead to localization errors. Because the localization distance is a scalar, the rotation of the coordinate system does not change the localization distance. In both the mobile platform coordinate system and the Earth coordinate system, the localization distance between the mobile platform and the magnetic target is the same, meaning that the calculated localization distance is accurate at this point.

[0031] In S200, specifically: at the j-th (1≤j≤N) measurement point, the positioning distance obtained by the tensor magnetic target localization technique is r. j The position coordinates of the mobile platform in the Earth coordinate system are (x... j ,y j ,z j The position coordinates are obtained through a positioning system. Let the position coordinates of the magnetic target in the Earth coordinate system be (x0, y0, z0). Then, at the j-th measurement point, the distance equation is obtained as follows:

[0032]

[0033] A set of distance equations independent of the attitude of the maneuvering platform was established through multi-point measurements, as shown in equation (2).

[0034]

[0035] The position coordinates of the magnetic target in the Earth coordinate system are obtained by solving equation (2) using a nonlinear optimization method.

[0036] The following is a specific implementation method of the present invention:

[0037] In the research of tensor magnetic target localization methods, some scholars have proposed the STAR method based on magnetic gradient contraction, whose positioning accuracy is unaffected by the geomagnetic field. Other scholars have compensated for the aspherical error of the STAR method, proposing an improved STAR method that further enhances positioning accuracy. The implementation method of this invention will be illustrated using the improved STAR method as an example.

[0038] Step 1: Plan the movement mode of the mobile platform.

[0039] Take the number of motion planes m as 2, and the plane distance h. 21The value is 0m; in motion plane P1, the angle θ1 between the motion path and the X-axis is 0°; in motion plane P2, the angle θ2 between the motion path and the X-axis is 90°. The settings of each simulation parameter in the magnetic target positioning simulation are shown in Table 1.

[0040] Magnetic target magnetic moment, magnetic target position coordinates, magnetic sensor resolution array baseline distance, and maneuvering platform attitude error (0.2×10⁻⁶). 6 ,0)A·m 2 (0,0,500)m10fT15m±1° surface

[0041] Table 1. Parameter settings in magnetic target localization simulation

[0042] The effect of the number of motion paths, n, on the magnetic target positioning error is shown in Figure 3. As can be seen from the figure, the positioning error first decreases and then increases with the increase of the number of motion paths, n. The positioning error is minimized when n = 5. Therefore, the number of motion paths, n, is chosen to be 5.

[0043] Step 2: Establish a set of positioning equations decoupled from the attitude of the maneuvering platform, and calculate the positioning result of the magnetic target in the Earth coordinate system.

[0044] Assuming the position coordinates of the mobile platform under the geomagnetic field during its movement have been accurately obtained by GPS, the Levenberg-Marquardt method is chosen as the nonlinear optimization method for solving the distance equations, with a convergence error set to 0.15m. Calculation results show that the positioning error of the magnetic target before compensation is 1.141m. After compensation using the proposed mobile platform-based magnetic target positioning method, the positioning error is reduced to 0.304m, improving the positioning accuracy by 73.36%, effectively enhancing the positioning precision.

Claims

1. A magnetic target localization method based on multi-point measurement, characterized in that, The magnetic target localization method based on multi-point measurement includes the following steps: S100, a magnetic sensor array mounted on a mobile platform is used to measure the magnetic gradient tensor at multiple measurement points in a certain motion manner. In S100, the motion manner of the mobile platform is as follows: it moves on m motion planes, where m ≥ 2; on motion plane P i During the upward motion, 1 ≤ i ≤ m, there are n paths, each path is parallel to the others, and the angle between each path and the X-axis of the Earth coordinate system is θ. i 0° ≤θ i ≤ 180°; Plane of motion P i and the plane of motion P i+1 The distance between them is h i(i+1) S200: Establish a set of positioning equations decoupled from the attitude of the maneuvering platform, and calculate the positioning result of the magnetic target in the Earth coordinate system. In S200, at the j-th measurement point, 1 ≤ j ≤ N, the positioning distance obtained by the tensor magnetic target positioning technique is r. j The position coordinates of the mobile platform in the Earth coordinate system are (x... j ,y j ,z j The position coordinates are obtained through a positioning system. Let the position coordinates of the magnetic target in the Earth coordinate system be (x0, y0, z0). Then, at the j-th measurement point, the distance equation is obtained as follows: (1) A set of distance equations independent of the attitude of the maneuvering platform is established through multi-point measurements, as shown in equation (2). (2) Solve the system of equations (2) by nonlinear optimization method to obtain the position coordinates of the magnetic target in the Earth coordinate system.

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