A target positioning method based on geomagnetic anomaly and shaft frequency magnetic field

Abstract

The present application relates to the technical field of magnetic detection, in particular to a target positioning method based on geomagnetic anomaly and axial frequency magnetic field; comprising the following steps: S1. preparation before entering water; S2. approaching target; S3. target detection, when there is no target, the observation signal is composed of environmental magnetic field, the energy value of this part is very small; once the target appears, the energy of the observation signal will continue to increase significantly, when the energy value is greater than the preset decision threshold, it is judged as a suspected target point, and when the suspected point is continuously detected for a specified time, it is confirmed that the target exists; S4. joint positioning, under the Kalman filtering framework, the target is equivalent to a magnetic dipole and an electric dipole respectively, the position predicted by the target state equation is corrected by combining the measurement equations of the two models, the joint positioning of the target is realized, and more accurate target position information is obtained; S5. positioning result verification and output. The present application has the advantages of improving positioning accuracy and enhancing anti-interference ability.

Description

Technical Field

[0001] This invention relates to the field of magnetic detection technology, specifically to a target localization method based on geomagnetic anomalies and axial frequency magnetic fields. Background Technology

[0002] Surface target localization is a core technical challenge in the field of underwater detection, and it is widely used in scenarios such as marine monitoring and shipping safety. Surface targets generate static magnetic fields due to the magnetization of their own materials, and at the same time, the anti-corrosion current generates a characteristic low-frequency alternating magnetic field (axis frequency magnetic field) under the modulation of the propeller rotation. These significant electromagnetic characteristics provide a physical basis for magnetic detection.

[0003] However, existing magnetic detection positioning technology has limitations due to its reliance on a single magnetic field: when using only magnetic anomalies for positioning, it is susceptible to interference from dynamic changes in the geomagnetic field; when using only axis frequency magnetic fields for positioning, the signal strength is weak and easily overwhelmed by noise. Neither of these two positioning methods, when used alone, can achieve high-precision positioning in complex environments. Summary of the Invention

[0004] This invention provides a target positioning method based on geomagnetic anomalies and axial frequency magnetic fields. Its purpose is to solve the problems of geomagnetic interference in positioning by a single magnetic anomaly and the easy submersion of positioning signals by noise by a single axial frequency magnetic field by co-detecting geomagnetic anomalies and axial frequency magnetic fields, thereby overcoming the limitations of positioning by a single magnetic field and achieving high-precision positioning in complex environments.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a target localization method based on geomagnetic anomalies and axial frequency magnetic fields, comprising the following steps: S1. Pre-entry preparation: Use external sensors to obtain the target's heading, speed and initial position. Based on the assumption that the target is moving at a constant speed in a straight line for a short period of time, construct a state equation to calculate and predict the target's future position and provide an initial reference for the underwater platform's movement. S2. Approaching the target: With the assistance of real-time attitude and acceleration information provided by the inertial navigation module, the underwater motion platform approaches the predicted target position from a distance, and performs magnetic calibration and noise suppression preprocessing on the raw magnetic field data collected by the magnetic sensor to eliminate environmental interference. S3. Target detection: When no target appears, the observation signal consists of the ambient magnetic field, and the energy value of this part is very small; once a target appears, the energy of the observation signal will continuously and significantly increase. When the energy value is greater than the preset decision threshold, it is judged as a suspected target point. If suspected points are continuously detected for a specified time, the existence of the target is confirmed. S4. Joint localization: Under the Kalman filter framework, the target is equivalent to a magnetic dipole and an electric dipole, respectively. The position predicted by the target state equation is corrected by combining the measurement equations of the two models, so as to achieve joint localization of the target and obtain more accurate target position information. S5. Verify and output the positioning results. Compare the positioning results with the target location information derived from the state equation and calculate the degree of consistency between the two. If they do not match, set the confidence level of the positioning results to zero and repeat S1~S5. If they match, output the positioning results.

[0007] Furthermore, the specific steps of target detection described in S3 include: S31. From From time 10:00 onwards, the energy value of the input signal is estimated and stored using the following formula;

[0008] In the formula:

[0009]

[0010] in, The length of the data window; The step size for sliding the data window; coefficient Control the sliding of the window, K = 0, 1, 2...; S32. Continuously convert the energy value obtained in S31 With threshold Compare the energy values. Greater than the threshold If so, then the point is considered a suspected target point; S33. Continuous If a suspected target point is detected within seconds, the existence of the target is confirmed.

[0011] Furthermore, the specific steps of joint positioning described in S4 include: S41. Magnetic anomaly localization based on the magnetic dipole model: The magnetic dipole model for measuring magnetic anomalies using a three-component magnetometer is as follows: (1)

[0012] In the formula: For sensor output; This refers to the system status; To mitigate noise during the measurement process, the magnetic target is treated as a point magnetic dipole, and a tracking reference coordinate system is established using a three-component magnetometer coordinate system, located at... The magnetic field of the magnetic target at point A at the three-component magnetometer is calculated by equation (2): (2)

[0013] In the formula: The vacuum permeability; Let be the position vector of the target relative to the three-component magnetometer; The target magnetic moment; the target magnetic moment parameters. Due to the inherent magnetic moment and induced magnetic moment Composition; during the target's movement, The measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is:

[0014] (3)

[0015] In the formula: for The target location at any given time; for Target magnetic moment at any given moment; for Measure noise at all times. ; for The position vector of the target relative to the three-component magnetometer at any given moment;

[0016] Assume the relative position difference between the two measurement points is Then the measurement model of the three-component magnetometer at the second point is: (4)

[0017] S42. Axis-frequency magnetic field localization based on the electric dipole model: The target static magnetic source can be equivalent to an electric dipole. Assuming the electric dipole is... The radiated magnetic field is calculated using the following formula: (5)

[0018] in, It is the wavenumber of electromagnetic waves. These are the magnetic permeability and dielectric constant of the propagation medium, respectively. For receiving point The distance from the magnetic dipole To receive the radius and The included angle of the axes; the magnetic field calculated above is the result in the electric dipole spherical coordinate system, which is then converted to the value in the sensor's rectangular coordinate system: (6)

[0019] in Let be the transformation matrix from the electric dipole coordinate system to the magnetic sensor coordinate system. The axis frequency magnetic field measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is as follows: (7)

[0020] In the formula: for The target location at any given time; for The target electric dipole moment at any given time, for The axial components of the electric dipole moment in its own coordinate system at any given moment; for Measure noise at all times; The relative position difference between the two measurement points is Under the premise that, the shaft frequency measurement model of the magnetic sensor at the second measurement point is: (8)

[0021] S43. Joint target localization based on the Kalman filter framework: Since the speed of the underwater platform far exceeds that of the target, it is assumed that the target moves at a constant linear velocity for a short period of time. Therefore, the target's motion model can be represented as follows: (9)

[0022] In the formula, Sampling time; It is the velocity of the platform relative to the target at time k. Let be the velocity of the platform relative to the target at time (k-1); as the target passes the sensor at a constant velocity, assuming the target does not deflect during its motion, the target's magnetic moment and electric dipole moment will hardly change in a short time, i.e.: (10)

[0023] Based on the measurement equation, the target state variable at time k is defined as: (11)

[0024] The state equation for the target motion can be written as: (12)

[0025] The state transition matrix A in the formula is: (13)

[0026] Equation (13) can also be expressed as: (14)

[0027] In the formula This represents the initial state of the target. Therefore, a three-component magnetometer positioning model is established based on the measurement model of magnetic anomaly and axis frequency magnetic field, and the state equation: (15)

[0028] This localization model locates the target within a Kalman filter framework, thereby obtaining the accurate target position.

[0029] Furthermore, the surface target positioning method is implemented based on a magnetic detection device, which is installed on an underwater motion platform; the magnetic detection device includes a magnetic sensor, a magnetic detection control unit, an inertial navigation module, a data transmission radio, and a secondary power supply.

[0030] Furthermore, there are two types of magnetic sensors: a three-component magnetometer and a total field magnetometer; the three-component magnetometer is specifically a fluxgate magnetometer, and the total field magnetometer is specifically an optically pumped magnetometer.

[0031] Furthermore, the magnetic detection control section includes a processor, a data storage unit, and a signal acquisition module.

[0032] The beneficial effects achieved by this invention are as follows: 1) Improved positioning accuracy: By using a three-axis fluxgate magnetometer and an optical pump magnetometer to collect magnetic anomaly and axis frequency magnetic field data, and combining it with a Kalman filter fusion algorithm, dynamic correction of the target position is achieved, and the positioning error is significantly reduced compared with single magnetic field positioning.

[0033] 2) Enhanced anti-interference capability: By utilizing the complementary characteristics of strong magnetic anomaly signal intensity and filterable axial frequency magnetic field, interference such as geomagnetic field fluctuations and environmental noise is effectively suppressed, significantly improving detection accuracy and success rate. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0035] Figure 1 This is a data processing flowchart of the present invention.

[0036] Figure 2 This is a block diagram illustrating the principle of the energy-based magnetic anomaly detection algorithm of this invention.

[0037] Figure 3 This is the overall positioning flowchart of the present invention. Detailed Implementation

[0038] The technical solutions in 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 a part of the embodiments of the present invention, and not all of them. 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.

[0039] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0040] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, if the word "and / or" appears throughout the text, it means including three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0041] Surface targets have a static magnetic field (i.e., a magnetic anomaly relative to the Earth's magnetic field) against the background of the Earth's magnetic field. At the same time, their anti-corrosion current and other components will form an axis frequency magnetic field after being modulated by the propeller. The detection of the target can be achieved by using these two magnetic fields.

[0042] Target localization using either magnetic anomalies or axial frequency magnetic fields each has its advantages and disadvantages: the magnetic anomaly value generated by the target is much larger than that of the axial frequency magnetic field, but since the magnetic anomaly value is superimposed on the Earth's magnetic field, interference from the Earth's magnetic field must be considered when the target is in motion; although the value of the axial frequency magnetic field is smaller than that of the magnetic anomaly, most low-frequency interference can be removed through filtering, thus serving as a supplement to the magnetic anomaly field. To address the problems of existing technologies, this invention combines the advantages and disadvantages of both magnetic field localization methods, simultaneously measuring both magnetic anomalies and axial frequency magnetic fields using a three-axis fluxgate magnetometer, thereby achieving target localization.

[0043] This invention provides a target localization method based on geomagnetic anomalies and axial frequency magnetic fields. This method is implemented using a magnetic detection device mounted on an underwater platform. As the underwater platform approaches the target from a distance, the magnetic detection device collects relevant magnetic field data, which is then processed by a localization algorithm to provide the target's location information in real time.

[0044] The underwater motion platform can be an autonomous underwater vehicle (AUV), a tethered remotely operated underwater vehicle (ROV), a hybrid underwater vehicle (ARV), or an underwater glider, etc.; the underwater motion platform generally includes a hull, a buoyancy and stabilization system, a power system, and an electrical system (including batteries and primary power supply circuits, etc.). Since the underwater motion platform involved in this invention uses existing technology and is not related to the innovation of this invention, its specific principles and technical details will not be elaborated further.

[0045] The magnetic detection device includes a magnetic sensor, a magnetic detection control unit, an inertial navigation module, a data transmission radio, and a secondary power supply.

[0046] There are two types of magnetic sensors: a three-component magnetometer and a total field magnetometer. The three-component magnetometer is specifically a fluxgate magnetometer (note: the three-component magnetometer is not limited to fluxgate magnetometers; it can be other magnetic sensors with comparable performance. Using fluxgate magnetometer in this article is just a descriptive term). The fluxgate magnetometer is used to detect triaxial magnetic field data. The fluxgate magnetometer is a magnetic field measuring element (also called a magnetometer) that works by utilizing the nonlinear variation characteristics of the magnetic permeability of ferromagnetic materials. The total field magnetometer is specifically an optically pumped magnetometer (note: the total field magnetometer is not limited to optically pumped magnetometers; it can be other magnetic sensors with comparable performance. Using optically pumped magnetometer in this article is just a descriptive term). The optically pumped magnetometer is used to detect total magnetic field data. The optically pumped magnetometer is a high-sensitivity magnetic field measuring instrument designed based on the optically pumped magnetic resonance principle, mainly used to accurately detect the total magnetic field strength (i.e., the absolute value of the magnetic field).

[0047] The magnetic detection control section is responsible for internal signal acquisition and control, and performs algorithmic calculations on the detection data to complete the magnetic anomaly target localization function; specifically including: The processor, including DSP, FPGA or ARM chips, is the core carrier for data processing and algorithm execution, responsible for executing positioning algorithms and coordinating the workflow of the entire system; The data storage unit includes RAM and non-volatile storage (such as Flash and hard disk) for real-time storage of raw magnetic data, platform status information (such as inertial navigation data), intermediate calculation results and final positioning solution data; The signal acquisition module includes an analog-to-digital converter (ADC) that converts the analog signals output by the magnetic sensor (optical pump magnetometer, fluxgate) into digital signals for processing by the processor.

[0048] The inertial navigation module is mainly used to measure the real-time motion state parameters (including real-time attitude and acceleration information) of the underwater motion platform, providing basic data support for target positioning; it includes a gyroscope, an accelerometer, a data processing unit, and an interface circuit; the data processing unit contains an embedded processor that performs integration, calibration, and other calculations on the output data of the gyroscope and accelerometer, and outputs the real-time attitude and acceleration information of the platform; the interface circuit communicates with the data storage and processing unit of the magnetic detection control section to transmit measurement data (such as through SPI, UART, and other interfaces).

[0049] The secondary power supply is responsible for converting the 28V primary power provided by the underwater motion platform into the secondary power required by the internal circuit modules of the magnetic detection device, and providing a power-on / off switch for the sensor.

[0050] The data transmission module sends the real-time calculated position data to the terminal computer for testing personnel to view in real time. In underwater environments, the data transmission module typically uses underwater acoustic communication technology (such as acoustic modulation and demodulation) to transmit data through the water medium, offering strong anti-interference capabilities but with a relatively low transmission rate. If the platform is close to the water surface, data can be transmitted via a radio frequency module (such as WiFi or 4G), suitable for short-distance, high-speed scenarios. Since this invention utilizes existing technology, and this module is not the focus of this invention, specific technical details and principles will not be elaborated further.

[0051] like Figures 1-3 As shown, the water surface target positioning method specifically includes the following steps: S1. Pre-entry preparation: Use external sensors such as radar and GNSS to obtain information such as the target's heading, speed and initial position. Based on the assumption that the target is moving at a constant speed in a straight line for a short period of time, construct a state equation to calculate and predict the target's future position and provide an initial reference for the underwater platform's movement. S2. Approaching the target: With the assistance of real-time attitude and acceleration information provided by the inertial navigation module, the underwater motion platform approaches the predicted target position from a distance. The raw magnetic field data collected by the magnetic sensor is preprocessed with magnetic calibration and noise suppression to eliminate environmental interference. The magnetic calibration and noise suppression adopt existing technologies, which will not be described in detail in this paper.

[0052] S3. Target detection: When no target appears, the observation signal consists of the ambient magnetic field, and the energy value of this part is very small; once a target appears, the energy of the observation signal will continuously and significantly increase. When the energy value is greater than the preset decision threshold, it is judged as a suspected target point. If suspected points are continuously detected for a specified time, the existence of the target is confirmed. S4. Joint localization: Under the Kalman filter framework, the target is equivalent to a magnetic dipole (for magnetic anomaly localization) and an electric dipole (for axis frequency magnetic field localization), respectively. The position predicted by the target state equation is corrected by combining the measurement equations of the two models, thereby achieving joint localization of the target and obtaining more accurate target position information.

[0053] S5. Verify and output the positioning results. Compare the positioning results with the target location information derived from the state equation and calculate the degree of consistency between the two. If they do not match, set the confidence level of the positioning results to zero and repeat steps S1 to S5. If they match, output the positioning results. The degree of consistency is based on the distance between the positioning results and the derived location. If the distance is too large (a threshold is given based on experience) and does not conform to the actual situation, the confidence level is set to zero.

[0054] Furthermore, S3 employs a signal detection method based on magnetic anomaly detection technology, such as... Figure 2 As shown, the specific steps of the energy-based ship magnetic anomaly signal detection method are as follows: S31. From From time 10:00 onwards, the energy value of the input signal is estimated and stored using the following formula;

[0055] In the formula:

[0056] in, The energy value is based on the OBF algorithm, representing the sum of squares of the target signal in the orthogonal basis space; The length of the data window; The step size for sliding the data window; coefficient Control the sliding of the window, K = 0, 1, 2...

[0057] In addition, to reduce the estimation variance of higher-order moments, The value of should not be too small; The value of should not be too large, otherwise some noise energy will be added, thereby weakening the signal energy value and reducing the test performance.

[0058] S32. Continuously convert the energy value obtained in S31 With threshold Compare the energy values. Greater than the threshold If so, then the point is considered a suspected target point; S33. Continuous If a suspected target point is detected within seconds, the existence of the target is confirmed.

[0059] in, and threshold The values ​​of these values ​​depend on the required false alarm probability and false negative probability for detection. and threshold As the value increases, the probability of a false alarm decreases, while the probability of a missed alarm increases.

[0060] Furthermore, the localization scheme based on the Kalman filter framework in S4 uses two localization methods: a localization method based on the target's magnetic anomaly and a localization method based on the target's axial frequency magnetic field, to jointly locate the target; for example... Figure 3 As shown, the specific steps include: S41. Magnetic anomaly localization based on the magnetic dipole model: The magnetic dipole model for measuring magnetic anomalies using a three-component magnetometer is as follows: (1)

[0061] In the formula: For sensor output; This refers to the system status; Noise during the measurement process; The target magnetic moment; typically, a magnetic target can be considered as a point magnetic dipole, and a tracking reference coordinate system is established using a three-component magnetometer coordinate system, located at... The magnetic field of the magnetic target at the three-component magnetometer can be calculated by equation (2): (2)

[0062] In the formula: The vacuum permeability; Let be the position vector of the target relative to the three-component magnetometer; Let be the target magnetic moment. The target's magnetic moment parameters. Typically determined by the intrinsic magnetic moment and induced magnetic moment Composition: The inherent magnetic moment is the magnetization formed during the target's construction and is an invariant vector in the target's volume coordinate system; the induced magnetic moment is generated by the target being magnetized by an external magnetic field during its motion, and the magnitude of this magnetic moment is related to the magnitude of the external magnetic field; during the target's motion... The measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is:

[0063] (3)

[0064] In the formula: for The target location at any given time; for Target magnetic moment at any given moment; for The noise measured at any given time is typically independent Gaussian noise. ; for The position vector of the target relative to the three-component magnetometer at any given time.

[0065] Assume the relative position difference between the two measurement points is Then the measurement model of the three-component magnetometer at the second point is: (4)

[0066] S42. Axis-frequency magnetic field localization based on the electric dipole model: Research based on measured data reveals that the target static magnetic source can be equivalently represented as an electric dipole, and its distribution field can be calculated from the electric dipole distribution field. Assuming the electric dipole is... The radiated magnetic field can be calculated using the following formula: (5)

[0067] in, It is the wavenumber of electromagnetic waves. These are the magnetic permeability and dielectric constant of the propagation medium, respectively. For receiving point The distance from the magnetic dipole To receive the radius and The included angle of the axis, The value is a unit complex number (representing a unit vector in complex space). The magnetic field calculated above is in the electric dipole spherical coordinate system, which can be converted to a value in the sensor's Cartesian coordinate system. (6)

[0068] in Let be the transformation matrix from the electric dipole coordinate system to the magnetic sensor coordinate system. The axis frequency magnetic field measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is as follows: (7)

[0069] In the formula: for The target location at any given time; for The target electric dipole moment at any given time, for The axial components of the electric dipole moment in its own coordinate system at any given moment; for The noise measured at any given time is typically independent Gaussian noise. .

[0070] The relative position difference between the two measurement points is Under the premise that, the shaft frequency measurement model of the magnetic sensor at the second measurement point is: (8)

[0071] S43. Joint target localization based on the Kalman filter framework, specifically using the magnetic anomaly and axis frequency magnetic field model to form a measurement equation, and correcting the target position predicted by the target's state equation: Since the speed of the underwater platform far exceeds that of the target, the target can be assumed to be moving at a constant velocity in a straight line for a short period of time. Therefore, the target's motion model can be represented as follows: (9)

[0072] In the formula, Sampling time; It is the velocity of the platform relative to the target at time k. Let be the platform's velocity relative to the target at the previous sampling point (k-1). The velocity of the underwater platform is provided by the inertial navigation system on the platform, while the velocity and initial position information of the surface target are provided by other sensors, such as radar, before the underwater platform enters the water. Assuming the target does not deflect during its uniform passage past the sensors, the target's magnetic moment and electric dipole moment will remain almost unchanged for a short period of time.

[0073] (10)

[0074] Based on the measurement equation, the target state variable at time k is defined as: (11)

[0075] The state equation for the target motion can be written as: (12)

[0076] The state transition matrix A in the formula is: (13)

[0077] Equation (13) can also be expressed as: (14)

[0078] In the formula This represents the initial state of the target.

[0079] Therefore, a three-component magnetometer positioning model can be established based on the measurement model of magnetic anomalies and axis frequency magnetic fields, and the state equation: (15)

[0080] The positioning model locates the target within the Kalman filter framework. Equation (14) serves as the target's state equation, which can be used to calculate the target's trajectory and predict its position at a future time. Then, two positioning methods, magnetic anomaly positioning and axis frequency magnetic field positioning, are used to jointly locate the target based on equations (3) and (7), forming a measurement equation. This equation corrects the target position predicted by the target's state equation, thereby obtaining the accurate target position.

[0081] High-precision magnetometers and fluxgate magnetometers are used to detect magnetic anomalies and axis-frequency magnetic fields generated by ships. Combined with real-time attitude and acceleration information provided by inertial navigation, the target position is calculated using two positioning algorithms: one based on the magnetic anomaly and the other on the axis-frequency magnetic field. Simultaneously, prior information about the target before it enters the water, such as heading and speed, is obtained through other means. This information is used to construct a target state equation, estimate the initial target position, and correct the real-time calculation results to obtain more accurate target position information.

[0082] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A target localization method based on geomagnetic anomalies and axial frequency magnetic fields, characterized in that, Includes the following steps: S1. Pre-entry preparation: Use external sensors to obtain the target's heading, speed and initial position. Based on the assumption that the target is moving at a constant speed in a straight line for a short period of time, construct a state equation to calculate and predict the target's future position and provide an initial reference for the underwater platform's movement. S2. Approaching the target: With the assistance of real-time attitude and acceleration information provided by the inertial navigation module, the underwater motion platform approaches the predicted target position from a distance, and performs magnetic calibration and noise suppression preprocessing on the raw magnetic field data collected by the magnetic sensor to eliminate environmental interference. S3. Target detection: When no target is present, the observation signal consists of the ambient magnetic field, and the energy value of this part is very small. Once a target appears, the energy of the observation signal will continuously and significantly increase. When the energy value exceeds the preset decision threshold, it is judged as a suspected target point. If suspected points are continuously detected for a specified time, the existence of the target is confirmed. S4. Joint localization: Under the Kalman filter framework, the target is equivalent to a magnetic dipole and an electric dipole, respectively. The position predicted by the target state equation is corrected by combining the measurement equations of the two models, so as to achieve joint localization of the target and obtain more accurate target position information. S5. Verify and output the positioning results. Compare the positioning results with the target location information derived from the state equation and calculate the degree of consistency between the two. If they do not match, set the confidence level of the positioning results to zero and repeat S1~S5. If they match, output the positioning results. The specific steps of joint positioning described in S4 include: S41. Magnetic anomaly localization based on the magnetic dipole model: The magnetic dipole model for measuring magnetic anomalies using a three-component magnetometer is as follows: （1） In the formula: For sensor output; This refers to the system status; To mitigate noise during the measurement process, the magnetic target is treated as a point magnetic dipole, and a tracking reference coordinate system is established using a three-component magnetometer coordinate system, located at... The magnetic field of the magnetic target at point A at the three-component magnetometer is calculated by equation (2): （2） In the formula: The vacuum permeability; Let be the position vector of the target relative to the three-component magnetometer; The target magnetic moment; the target magnetic moment parameters. Due to the inherent magnetic moment and induced magnetic moment Composition; during the target's movement, The measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is: （3） In the formula: for The target location at any given time; for Target magnetic moment at any given time; for Measure noise at all times. ; for The position vector of the target relative to the three-component magnetometer at any given moment; Assume the relative position difference between the two measurement points is Then the measurement model of the three-component magnetometer at the second point is: （4） S42. Axis-frequency magnetic field localization based on the electric dipole model: The target static magnetic source can be equivalent to an electric dipole. Assuming the electric dipole is... The radiated magnetic field is calculated using the following formula: （5） in, It is the wavenumber of electromagnetic waves. These are the magnetic permeability and dielectric constant of the propagation medium, respectively. For receiving point Distance from the magnetic dipole To receive the radius and The included angle of the axes; the magnetic field calculated above is the result in the electric dipole spherical coordinate system, which will be converted to the value in the sensor's rectangular coordinate system: （6） in Let be the transformation matrix from the electric dipole coordinate system to the magnetic sensor coordinate system. The axis frequency magnetic field measurement model of the three-component magnetometer located at the origin of the reference coordinate system at time t is as follows: （7） In the formula: for The target location at any given time; for The target electric dipole moment at any given time, for The axial components of the electric dipole moment in its own coordinate system at any given moment; for Measure noise at all times; The relative position difference between the two measurement points is Under the premise that, the shaft frequency measurement model of the magnetic sensor at the second measurement point is: （8） S43. Joint target localization based on the Kalman filter framework: Since the speed of the underwater platform far exceeds that of the target, it is assumed that the target moves at a constant linear velocity for a short period of time. Therefore, the target's motion model can be represented as follows: （9） In the formula, Sampling time; It is the platform's speed relative to the target. Let be the platform's velocity relative to the target at the previous sampling point. Assuming the target does not deflect during its uniform passage past the sensor, the target's magnetic moment and electric dipole moment will remain almost unchanged in a short time, i.e.: （10） Based on the measurement equation, the target state variable at time k is defined as: （11） The state equation for the target motion can be written as: （12） The state transition matrix A in the formula is: （13） Equation (13) can also be expressed as: （14） In the formula This represents the initial state of the target. Therefore, a three-component magnetometer positioning model is established based on the measurement model of magnetic anomaly and axis frequency magnetic field, and the state equation: （15） This localization model locates the target within a Kalman filter framework, thereby obtaining the accurate target position.

2. The target positioning method based on geomagnetic anomalies and axial frequency magnetic fields according to claim 1, characterized in that, The specific steps for target detection described in S3 include: S31. From From time 10:00 onwards, the energy value of the input signal is estimated and stored using the following formula; In the formula: in, The length of the data window; The step size for sliding the data window; coefficient Control the sliding of the window, K = 0, 1, 2...; S32. Continuously convert the energy value obtained in S31 With threshold Compare the energy values. Greater than the threshold If so, then the point is considered a suspected target point; S33. Continuous If a suspected target point is detected within seconds, the existence of the target is confirmed.

3. A target positioning method based on geomagnetic anomalies and axial frequency magnetic fields according to any one of claims 1 to 2, implemented using a magnetic detection device; characterized in that: The magnetic detection device is installed on an underwater moving platform; the magnetic detection device includes a magnetic sensor, a magnetic detection control part, an inertial navigation module, a data transmission radio, and a secondary power supply.

4. The target positioning method based on geomagnetic anomalies and axial frequency magnetic fields according to claim 3, characterized in that: There are two types of magnetic sensors: a three-component magnetometer and a total field magnetometer; the three-component magnetometer is specifically a fluxgate magnetometer, and the total field magnetometer is specifically an optically pumped magnetometer.

5. The target positioning method based on geomagnetic anomalies and axial frequency magnetic fields according to claim 3, characterized in that: The magnetic detection control unit includes a processor, a data storage unit, and a signal acquisition module.

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