Target magnetic field data measurement and target magnetic field model construction method

Abstract

The invention provides a target magnetic field data measurement and target magnetic field model construction method, which comprises the following steps: firstly, providing a universal multi-layer grid target magnetic field data measurement method for acquiring target magnetic field data, secondly, arranging a multi-magnetic dipole array equivalent target magnetic field model based on target geometric information, and constructing a target magnetic field model according to a model precision requirement. And constructing a target simplest multi-magnetic dipole equivalent model for calculating a target magnetic field and obtaining target magnetic characteristic information by adaptively adding the number of magnetic dipoles.

Description

Technical Field

[0001] The present invention relates to the technical field of target magnetic field modeling, and in particular to a method for measuring target magnetic field data and building a target magnetic field model. Background Art

[0002] The geomagnetic field is the earth's inherent physical field, mainly composed of endogenous fields and exogenous fields. The endogenous field accounts for 99% and is a stable magnetic field that changes very slowly over time. When a ferromagnetic object is in the geomagnetic field, it can be magnetized by the geomagnetic field to produce a magnetic field. This magnetic field is superimposed on the background geomagnetic field to produce magnetic anomalies.

[0003] Magnetic anomaly detection refers to measuring the magnetic field distribution near ferromagnetic objects and inverting their spatial position and characteristics. This method has the advantages of not being affected by weather, seawater, soil, sediment and other media, and is one of the important ways to detect and identify ferromagnetic targets. With the development of magnetic detection technology, the sensitivity of magnetic sensors is getting higher and higher, and they have the ability to sense weak magnetic anomaly field signals. However, when detecting and identifying magnetic anomaly targets, it is difficult to accurately extract and identify the target due to the lack of target magnetic feature information. Obtaining magnetic feature information of different types of targets is the prerequisite for accurate detection and identification of magnetic anomaly targets. The main acquisition methods are target magnetic field measurement and target magnetic field modeling. Target magnetic field measurement can obtain target magnetic field data in the real environment, but it is necessary to collect target magnetic field data under different conditions, which is a huge workload and difficult to cover all situations; target magnetic field modeling is an economical and efficient method to obtain target magnetic feature information, which can obtain target magnetic feature information based on a small amount of magnetic measurement data and magnetic field model construction methods.

[0004] At present, the research objects in target magnetic field modeling at home and abroad are relatively single, mainly focusing on underwater target magnetic field modeling, and there is little research on the magnetic characteristics of other types of targets. There is an urgent need for a universal target magnetic field data measurement and target magnetic field model construction method to meet the application requirements of rapid acquisition of various types of target magnetic field data and rapid construction of magnetic field models. Summary of the invention

[0005] To achieve the above object, the present invention provides a method for measuring target magnetic field data and building a target magnetic field model, comprising the following steps:

[0006] Step 1: Select a site with small magnetic field gradient, small environmental interference, flat and open terrain as the measurement site, deploy the target to be measured, and set up a diurnal variation station at a location with small magnetic field gradient change at a distance of more than 100 times the target scale from the test site;

[0007] Step 2: Determine the magnetic field measurement scheme according to the target size, including the grid surface height, grid spacing and grid size;

[0008] Step 3: According to the magnetic field measurement plan, a high-precision magnetic measurement payload is used to perform two magnetic field measurements at each grid point on the multi-layer grid surface above the target. Each grid point on the grid surface is measured twice, once for the background magnetic field data when there is no target, and once for the magnetic measurement data when there is a target. The daily variable station data, the height and position data of the magnetic measurement payload are collected simultaneously, and the magnetic field measurement is performed on at least four targets placed in different directions;

[0009] Step 4: After completing the target magnetic field measurement, organize the daily station data and high-precision magnetic measurement payload magnetic measurement data, mark the magnetic measurement data state parameters, and after synchronous processing of the data, check and correct the acquired magnetic measurement data, and store the pre-processed data in the database for target magnetic field modeling;

[0010] Step 5: Arrange the magnetic dipole array according to the target geometry and the magnetic components it contains, take the target magnetic field model accuracy as input condition, and use the minimum number of magnetic dipoles to combine the equivalent target's spatial magnetic field distribution;

[0011] Step 6: First, analyze the equivalent conditions of the magnetic moment size and distribution, then analyze the equivalent consistency of the magnetic field distribution of multiple magnetic dipoles to a single magnetic dipole under this spatial scale condition, and finally calculate the target simplest equivalent condition based on the multiple magnetic dipole array;

[0012] Step 7: Set different spatial scale parameters, analyze the total magnetic field distribution generated by multiple magnetic dipoles and the total field distribution diagram of a single magnetic dipole, as well as the equivalent consistency, and calculate and evaluate the equivalent effects of the magnetic field distribution of the magnetic measurement plane of multiple magnetic dipoles and a single magnetic dipole at different spatial scales;

[0013] Step 8: According to the simplest equivalent conditions of the target, construct the multi-magnetic dipole equivalent model of the target at different scales, as follows:

[0014]

[0015] Where k is the number of magnetic dipoles in the array, μ0 is the vacuum permeability, and R i and r i Respectively represent the distance and direction of each magnetic dipole to the measurement point, M i and m represent the magnitude and direction of the magnetic dipole moment, respectively, and u represents the direction of the Earth’s magnetic field;

[0016] Step nine: Use the multi-magnetic dipole equivalent model of the target at different scales as the target magnetic field model, use the target magnetic field model to calculate the target magnetic field, and perform target magnetic feature analysis.

[0017] Optionally, the step 2 specifically includes:

[0018] The grid surface height includes at least the order of magnitude of the target size, the order of magnitude of several times the target size, and the order of magnitude of ten times the target size, which is used for inversion of the target magnetic field near field and far field and evaluation of model accuracy; when the measurement altitude is high, the grid spacing is required to be no more than half of the target size, and the grid surface area is required to be at least one order of magnitude larger than the target area. When the measurement altitude is low, the grid spacing is required to be no more than one quarter of the target size, and the grid surface area is appropriately reduced.

[0019] Optionally, the step six specifically includes:

[0020] Using the magnetic dipole model, the magnetic moment conditions for multiple magnetic dipoles to be equivalent to a single magnetic dipole and the distribution of the magnetic moment of multiple magnetic dipoles and their relative positions to the equivalent single magnetic dipole are analyzed.

[0021] The height information H of the grid surface is obtained by the height sensor, and the horizontal scale information Lt of the target is obtained by the boundary equalization method based on the magnetic field image. The corresponding spatial scale value is calculated using the formula a=H / Lt.

[0022] Optionally, the step seven specifically includes:

[0023] Set different spatial scale parameters to analyze the total field distribution of the magnetic field generated by two magnetic dipoles and the total field distribution of a single magnetic dipole as well as their equivalent consistency;

[0024] Set different spatial scale parameters, analyze the total field distribution of the magnetic field generated by three magnetic dipoles and the total field distribution diagram of a single magnetic dipole, as well as the equivalent consistency, and so on;

[0025] The equivalent effect is quantitatively evaluated by the mean absolute percentage error (MAPE) of the total magnetic field value of each grid point on the grid surface, and the equivalent consistency (EC) is defined as EC = 1-MAPE.

[0026] After adopting the above technical solution, the present invention has the following beneficial effects:

[0027] The present invention proposes a universal multi-layer grid target magnetic field data measurement method for acquiring target magnetic field data, and arranges a multi-magnetic dipole array equivalent target magnetic field model based on target geometric information. According to the model accuracy requirements, the number of magnetic dipoles is adaptively added to construct a target simplest multi-magnetic dipole equivalent model, which is used to calculate the target magnetic field and obtain the target magnetic characteristic information. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 This is a schematic diagram of the target magnetic field data measurement process;

[0030] Figure 2 Schematic diagram of the scenario of the multi-layer grid target magnetic field data measurement method. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present disclosure provides a method for measuring target magnetic field data and building a target magnetic field model, including the following steps:

[0033] (1)Reference Figure 1 and 2 , target magnetic field data measurement, as follows:

[0034] Step 1: Select a site with small magnetic field gradient, small environmental interference, flat and open terrain as the measurement site, deploy the target to be measured, and select a location with small magnetic field gradient change near the test site to deploy a diurnal variation station;

[0035] Step 2: According to the target size, determine the magnetic field measurement plan, including grid surface height, grid spacing and grid size. The grid surface height includes at least the order of magnitude of the target size, the order of magnitude of several times the target size and the order of magnitude of ten times the target size, which is used for the inversion of the near-field and far-field of the target magnetic field and the evaluation of the model accuracy. When the measurement height is high, the grid spacing is required to be no more than half of the target size, and the grid surface area is required to be at least one order of magnitude larger than the target area. When the measurement height is low, the grid spacing is required to be no more than one-quarter of the target size, and the grid surface area is appropriately reduced. Taking the truck target as an example, its length is 10m and its width is 3m. The grid surface height can be selected from multiple heights such as 10m, 50m, and 100m.

[0036] Step 3: According to the magnetic field measurement plan, a magnetic detection drone is used to perform two magnetic field measurements at each grid point on the multi-layer grid surface above the target, one for background magnetic field data when there is no target, and one for magnetic measurement data when there is a target. The daily station data, the altitude data and the position data of the drone are collected simultaneously, and the magnetic field measurement is performed on at least four targets placed in different directions;

[0037] Step 4: After completing the target magnetic field measurement, sort out the daily station data and magnetic measurement payload magnetic measurement data, mark the magnetic measurement data state parameters, and after synchronous processing of the data, check and correct the acquired magnetic measurement data, and store the pre-processed data in the database for target magnetic field modeling;

[0038] (2) Target magnetic field modeling, as follows:

[0039] Step 5: Arrange the magnetic dipole array according to the target geometry and the magnetic components it contains, take the target magnetic field model accuracy as input condition, and use the minimum number of magnetic dipoles to combine the equivalent target's spatial magnetic field distribution;

[0040] Step 6: First, analyze the equivalent conditions of the magnetic moment size and distribution. Using the magnetic dipole model, analyze the magnetic moment conditions for multiple magnetic dipoles to be equivalent to a single magnetic dipole and the relative position of the distribution of the magnetic moment size of multiple magnetic dipoles and the equivalent single magnetic dipole.

[0041] Then, the equivalent consistency of the magnetic field distribution of multiple magnetic dipoles to a single magnetic dipole under this spatial scale condition is analyzed. The equivalent consistency analysis of the magnetic field distribution of ferromagnetic objects is based on the height of the magnetic measurement surface and the structural size of the target. The height information H of the grid surface is obtained by the height sensor. The horizontal scale information Lt of the target is obtained based on the magnetic field image using the boundary equalization method. The corresponding spatial scale value is calculated using the formula a=H / Lt.

[0042] Finally, the target simplest equivalent condition based on the multi-magnetic dipole array is calculated;

[0043] Step 7: Set different spatial scale parameters to analyze the total magnetic field distribution generated by multiple magnetic dipoles and the total field distribution diagram of a single magnetic dipole as well as the equivalent consistency. Specifically, set different spatial scale parameters to analyze the total magnetic field distribution generated by two magnetic dipoles and the total field distribution diagram of a single magnetic dipole as well as the equivalent consistency; set different spatial scale parameters to analyze the total magnetic field distribution generated by three magnetic dipoles and the total field distribution diagram of a single magnetic dipole as well as the equivalent consistency, and so on; at different spatial scales, calculate and evaluate the equivalent effects of the magnetic field distribution of the magnetic measurement plane of multiple magnetic dipoles and a single magnetic dipole. The equivalent effect is quantitatively evaluated by the mean absolute percentage error MAPE of the total magnetic field value of each grid point on the grid surface, and the equivalent consistency EC is defined as EC=1-MAPE;

[0044] Step 8: According to the simplest equivalent conditions of the target, construct the multi-magnetic dipole equivalent model of the target at different scales, as follows:

[0045]

[0046] Where k is the number of magnetic dipoles in the array, μ0 is the vacuum permeability, and R i and r i Respectively represent the distance and direction of each magnetic dipole to the measurement point, M i and m represent the magnitude and direction of the magnetic dipole moment, respectively, and u represents the direction of the Earth’s magnetic field;

[0047] Step nine: Use the multi-magnetic dipole equivalent model of the target at different scales as the target magnetic field model, use the target magnetic field model to calculate the target magnetic field, and perform target magnetic feature analysis.

[0048] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the claims.

Claims

1. A method for measuring target magnetic field data and constructing a target magnetic field model, characterized in that: The following steps are involved: Step 1: Select a site with small magnetic field gradient, small environmental interference, flat and open terrain as the measurement site, deploy the target to be measured, and set up a diurnal variation station at a location with small magnetic field gradient change at a distance of more than 100 times the target scale from the test site; Step 2: Determine the magnetic field measurement scheme according to the target size, including the grid surface height, grid spacing and grid size; Step 3: According to the magnetic field measurement plan, a high-precision magnetic measurement payload is used to perform two magnetic field measurements at each grid point on the multi-layer grid surface above the target, one for background magnetic field data when there is no target, and one for magnetic measurement data when there is a target. The daily variable station data, the height and position data of the magnetic measurement payload are collected simultaneously, and the magnetic field measurement is performed on at least four targets placed in different directions; Step 4: After completing the target magnetic field measurement, organize the daily station data and high-precision magnetic measurement payload magnetic measurement data, mark the magnetic measurement data state parameters, and after synchronous processing of the data, check and correct the acquired magnetic measurement data, and store the pre-processed data in the database for target magnetic field modeling; Step 5: Arrange the magnetic dipole array according to the target geometry and the magnetic components it contains, take the target magnetic field model accuracy as input condition, and use the minimum number of magnetic dipoles to combine the equivalent target's spatial magnetic field distribution; Step 6: First, analyze the equivalent conditions of the magnetic moment size and distribution, then analyze the equivalent consistency of the magnetic field distribution of multiple magnetic dipoles to a single magnetic dipole under this spatial scale condition, and finally calculate the target simplest equivalent condition based on the multiple magnetic dipole array; Step 7: Set different spatial scale parameters, analyze the total magnetic field distribution generated by multiple magnetic dipoles and the total field distribution diagram of a single magnetic dipole, as well as the equivalent consistency, and calculate and evaluate the equivalent effects of the magnetic field distribution of the magnetic measurement plane of multiple magnetic dipoles and a single magnetic dipole at different spatial scales; Step 8: According to the simplest equivalent conditions of the target, construct the multi-magnetic dipole equivalent model of the target at different scales, as follows: Where k is the number of magnetic dipoles in the array, μ0 is the vacuum permeability, and R i and r i Respectively represent the distance and direction of each magnetic dipole to the measurement point, M i and m represent the magnitude and direction of the magnetic dipole moment, respectively, and u represents the direction of the Earth’s magnetic field; Step nine: Use the multi-magnetic dipole equivalent model of the target at different scales as the target magnetic field model, use the target magnetic field model to calculate the target magnetic field, and perform target magnetic feature analysis.

2. The method for measuring target magnetic field data and constructing a target magnetic field model according to claim 1, characterized in that: The step 2 specifically includes: The grid surface height includes at least the order of magnitude of the target size, the order of magnitude of several times the target size, and the order of magnitude of ten times the target size, which is used for inversion of the target magnetic field near field and far field and evaluation of model accuracy; when the measurement altitude is high, the grid spacing is required to be no more than half of the target size, and the grid surface area is required to be at least one order of magnitude larger than the target area. When the measurement altitude is low, the grid spacing is required to be no more than one quarter of the target size, and the grid surface area is appropriately reduced.

3. The target magnetic field data measurement and target magnetic field model construction method according to claim 1, characterized in that: The step six specifically includes: Using the magnetic dipole model, the magnetic moment conditions for multiple magnetic dipoles to be equivalent to a single magnetic dipole and the distribution of the magnetic moment of multiple magnetic dipoles and their relative positions to the equivalent single magnetic dipole are analyzed. The height information H of the grid surface is obtained by the height sensor, and the horizontal scale information Lt of the target is obtained by the boundary equalization method based on the magnetic field image. The corresponding spatial scale value is calculated using the formula a=H / Lt.

4. The method for measuring target magnetic field data and building a target magnetic field model according to claim 1, characterized in that: The step seven specifically includes: Set different spatial scale parameters to analyze the total field distribution of the magnetic field generated by two magnetic dipoles and the total field distribution of a single magnetic dipole as well as their equivalent consistency; Set different spatial scale parameters, analyze the total field distribution of the magnetic field generated by three magnetic dipoles and the total field distribution diagram of a single magnetic dipole, as well as the equivalent consistency, and so on; The equivalent effect is quantitatively evaluated by the mean absolute percentage error (MAPE) of the total magnetic field value of each grid point on the grid surface, and the equivalent consistency (EC) is defined as EC = 1-MAPE.

Images