Global magnetic interference compensation method in airborne magnetic surveying

Abstract

The disclosure provides a global magnetic interference compensation method in aerial magnetic survey, comprising: S1: high-altitude calibration flight is carried out through a motion platform, and total magnetic field data is obtained based on optical pumping magnetometer detection data; S2: geomagnetic background gradient information is obtained, and geomagnetic field data is obtained based on the geomagnetic background gradient information; S3: motion platform magnetic interference data is obtained according to the total magnetic field data and the geomagnetic field data; S4: motion platform attitude information, motion platform current information and fluxgate magnetometer detection data are obtained; S5: motion platform magnetic interference coefficients are obtained according to the motion platform magnetic interference data, the motion platform attitude information, the motion platform current information and the fluxgate magnetometer detection data; and S6: real-time data compensation is carried out on the total magnetic field data during actual aerial magnetic survey according to the geomagnetic background gradient information and the motion platform magnetic interference coefficients.

Description

Technical Field

[0001] This disclosure relates to the fields of airborne magnetic measurement and magnetic field interference compensation technology, and in particular to a global magnetic interference compensation method in airborne magnetic measurement. Background Technology

[0002] The Earth's magnetic field is an inherent physical field of the Earth. Any ferromagnetic target within it is magnetized. Combined with the target's remanence, this generates a quasi-static magnetic field with characteristics different from the Earth's magnetic field, known as a magnetic anomaly signal. Magnetic anomaly signals are quasi-static magnetic field signals. Their propagation characteristics in a medium are typically only affected by the medium's permeability. Since the permeability of propagation media such as air, water, and soil is very stable, magnetic anomaly signals are minimally affected by the environment. They are particularly suitable for detecting underwater and subsurface targets and are an important component of geophysical exploration methods.

[0003] Currently, commonly used magnetic anomaly detection technologies include airborne magnetic surveying, ground-based magnetic surveying, borehole magnetic surveying, and satellite magnetic surveying. Among these, airborne magnetic surveying utilizes mobile platforms (including helicopters and UAVs) equipped with high-precision magnetometers to detect weak magnetic anomaly signals from underground targets. Compared to ground-based magnetic surveying, airborne magnetic surveying offers advantages such as high operational efficiency, wide adaptability, flexibility, and rapid operation. Since the 1950s, the demand for mineral resources has spurred the rise of airborne magnetic surveying. After decades of development, airborne magnetic surveying, with its unique advantages, has not only become one of the main methods for mineral resource exploration but has also attracted significant attention from many countries worldwide as a new technology for target detection. With technological advancements, the resolution and sensitivity of magnetometers have continuously improved, but the magnetic interference problem of airborne platforms has also become increasingly prominent, severely restricting the detection performance of magnetometers. Therefore, magnetic compensation technology for airborne platforms, as a key technology in airborne magnetic surveying, has received widespread attention from scholars both domestically and internationally.

[0004] Current airborne magnetic compensation technologies are almost entirely based on the Tolles-Lawson Model (TL), primarily aimed at eliminating maneuvering magnetic interference caused by changes in aircraft attitude and materials. This is one source of magnetic interference for moving platforms, and years of engineering practice have proven its effectiveness. However, with technological advancements and continuous optimization of moving platform dimensions, the integration of electronic equipment within the aircraft is high, and much of it is electrically driven. This leads to a complex electromagnetic environment, making the magnetic interference caused by airborne electronic equipment (such as power drive systems, control and communication systems) very significant, constituting a second source of magnetic interference for moving platforms. Furthermore, the intensity of the Earth's magnetic field varies with distance; generally, the north-south gradient is much greater than the east-west gradient. The normal gradient value varies with latitude. The normal gradient value of the vertical component of the magnetic field is larger in low-latitude regions and smaller in high-latitude regions, while the normal gradient value of the horizontal component is the opposite. Moving platforms experience different magnetic fields at different locations within the Earth's magnetic field, constituting a third source of magnetic interference for moving platforms.

[0005] However, current magnetic interference compensation methods are still difficult to take into account various magnetic interference sources, resulting in overlapping magnetic interference compensation effects. Therefore, there is an urgent need for a more effective method for compensating for airborne magnetic layer interference. Summary of the Invention

[0006] In view of the above, in order to at least partially solve at least one of the aforementioned technical problems, this disclosure provides a global magnetic interference compensation method for airborne magnetic surveys. The technical solution of this disclosure is as follows:

[0007] According to one embodiment of this disclosure, a method for global magnetic interference compensation in airborne magnetic surveys is provided, comprising: operation S1: performing high-altitude calibration flight via a motion platform and acquiring total magnetic field data based on data detected by an optically pumped magnetometer; operation S2: acquiring geomagnetic background gradient information and obtaining geomagnetic field data based on the geomagnetic background gradient information; operation S3: obtaining magnetic interference data of the motion platform based on the total magnetic field data and the geomagnetic field data; operation S4: acquiring attitude information of the motion platform, current information of the motion platform, and data detected by a fluxgate magnetometer; operation S5: obtaining a magnetic interference coefficient of the motion platform based on the magnetic interference data, attitude information, current information, and data detected by the fluxgate magnetometer; and operation S6: performing real-time data compensation on the total magnetic field data during actual airborne magnetic surveys based on the geomagnetic background gradient information and the magnetic interference coefficient of the motion platform.

[0008] According to an embodiment of this disclosure, in operation S2, the real-time longitude information, real-time latitude information, and real-time altitude information of the motion platform are acquired and used as input parameters of the IGRF model to obtain geomagnetic field data.

[0009] According to an embodiment of this disclosure, in operation S3, the geomagnetic field data is removed from the total magnetic field data to obtain the magnetic interference data of the motion platform.

[0010] According to embodiments of this disclosure, the attitude information of the motion platform includes the roll information, pitch information, yaw angle information, and flight speed information of the motion platform; the current information of the motion platform is the operating current information of the equipment carried on the motion platform during operation; the fluxgate magnetometer detection data includes three orthogonal components of the geomagnetic field data in the rectangular coordinate system of the motion platform.

[0011] According to an embodiment of this disclosure, operation S5 includes: obtaining first magnetic interference data with 18 interference coefficients related to the motion platform's attitude using the motion platform's attitude information and based on the Tolles-Lawson model, as follows:

[0012] (16);

[0013] in, For geomagnetic field data, , , These are the constant coefficients of the disturbance terms for the constant magnetic field, induced magnetic field, and eddy current magnetic field, respectively. It is the cosine of the angle between the platform's coordinate axes and the Earth's magnetic field, representing the platform's attitude. yes The time derivative.

[0014] According to an embodiment of this disclosure, operation S5 includes: obtaining second magnetic interference data with nine interference coefficients related to the working current of the motion platform based on the motion platform current information and the fluxgate magnetometer detection data, as follows;

[0015]

[0016] Where n represents the number of interference terms, Represents the coefficient of the interference term. This indicates the deformation of the operating current and its derivative of airborne electronic equipment.

[0017] According to an embodiment of this disclosure, the magnetic interference data of the motion platform is the superposition of the first magnetic interference data and the second magnetic interference data, which is equal to the difference between the total magnetic field data and the geomagnetic field data, thereby obtaining the magnetic interference coefficient in the first magnetic interference data and the second magnetic interference data.

[0018] According to the embodiments of this disclosure, when obtaining the three orthogonal components of the geomagnetic field in the rectangular coordinate system of the motion platform, it is necessary to determine the cosine value of the angle between the three coordinate axes of the rectangular coordinate system of the motion platform and the geomagnetic field, as well as the time derivative of the cosine value of the angle between the three coordinate axes of the rectangular coordinate system of the motion platform and the geomagnetic field.

[0019] According to embodiments of this disclosure, the motion platform includes any one of a fixed-wing aircraft, a helicopter, or a drone.

[0020] According to embodiments of this disclosure, calibration flight includes performing level flight, pitch, roll, yaw, and acceleration / deceleration in the four directions of east, west, south, and north, respectively. Attached Figure Description

[0021] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0022] Figure 1 This is a flowchart of a global magnetic interference compensation method in airborne magnetic surveying according to an embodiment of this disclosure.

[0023] Figure 2 This is a schematic diagram of the global geomagnetic field gradient distribution.

[0024] Figure 3 This is a schematic diagram of the aircraft body coordinate system according to an embodiment of the present disclosure. Detailed Implementation

[0025] This disclosure provides a global magnetic interference compensation method for airborne magnetic surveys. It considers the influence of real-time geomagnetic background gradient information on geomagnetic field data, and simultaneously considers the attitude and current information of the moving platform to obtain the magnetic interference coefficient of the moving platform. A global magnetic interference compensation method is proposed to perform real-time data compensation for the total magnetic field data during actual airborne magnetic surveys. Specifically, this disclosure considers noise interference sources caused by changes in the moving platform's attitude, including constant magnetic field, induced magnetic field, and eddy current magnetic field, as well as noise interference sources from on-board electronic (OBE) equipment current and changes in the geomagnetic background gradient field. A global interference analysis and compensation method incorporating the moving platform's attitude, current, and geomagnetic background gradient field is proposed, expanding the scope of magnetic compensation. A magnetic compensation model equation with 27 coefficients is proposed, improving the global magnetic interference compensation technology in airborne magnetic surveys.

[0026] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0027] The airborne magnetic measurement system mainly includes modules such as magnetometers (optically pumped magnetometers and fluxgate magnetometers), inertial navigation systems (INS), radar altimeters, and satellite navigation systems. Among them, the optically pumped magnetometer is used to achieve high-precision measurement of the total magnetic field; the fluxgate magnetometer is used to measure the three components of the external magnetic field; the radar altimeter uses radar echoes to measure the altitude of the flight platform above the ground; the INS is used to record motion parameters such as roll, pitch, yaw angles, and flight speed of the aircraft; and the satellite navigation system is used to record the longitude, latitude, and altitude information of the flight platform, monitor the flight trajectory of the flight platform in real time, and provide auxiliary information for data post-processing.

[0028] In this embodiment of the disclosure, a global magnetic interference compensation method for airborne magnetic surveys is provided, including the following operations S1-S6.

[0029] Operation S1: Perform high-altitude calibration flight via the motion platform and acquire total magnetic field data based on the detection data of the optically pumped magnetometer;

[0030] Operation S2: Obtain geomagnetic background gradient information and obtain geomagnetic field data based on the geomagnetic background gradient information;

[0031] Operation S3: Obtain magnetic interference data of the motion platform based on the total magnetic field data and the geomagnetic field data;

[0032] Operation S4: Acquire motion platform attitude information, motion platform current information, and fluxgate magnetometer detection data;

[0033] Operation S5: Obtain the magnetic interference coefficient of the motion platform based on the motion platform's magnetic interference data, attitude information, current information, and fluxgate magnetometer detection data; and

[0034] Operation S6: Based on the geomagnetic background gradient information and the magnetic interference coefficient of the moving platform, perform real-time data compensation for the total magnetic field data during actual airborne magnetic surveys.

[0035] According to embodiments of this disclosure, the motion platform can be, for example, any one of a fixed-wing aircraft, a helicopter, or a drone. Calibration flight includes sequentially performing level flight, pitch, roll, yaw, and acceleration / deceleration in the four directions: east, west, south, and north.

[0036] According to an embodiment of this disclosure, in operation S2, the real-time longitude information, real-time latitude information, and real-time altitude information of the motion platform are acquired and used as input parameters of the IGRF model to obtain geomagnetic field data.

[0037] To address magnetic interference caused by changes in geomagnetic background gradient information, this disclosure proposes a geomagnetic gradient field compensation method to reduce the influence of the geomagnetic gradient field. For example... Figure 2The image shows the global geomagnetic field gradient distribution map. The background gradient characteristics of the geomagnetic field include:

[0038] 1) The horizontal gradient of the north-south geomagnetic field is related to latitude, with the largest gradient in the mid-latitudes and relatively smaller gradients in the high and low latitudes. For example, the horizontal gradient values ​​in the southern, central and northern regions of my country are approximately 3.8 nT / km, 5.4 nT / km and 3.2 nT / km, respectively.

[0039] 2) The horizontal gradient of the east-west geomagnetic field is related to longitude. In western my country, the horizontal gradient is about -2.2 nT / km, while in eastern China it is about 1.1 nT / km. It can be seen that the gradient has different polarities with longitude.

[0040] 3) The vertical gradient of the total geomagnetic field mainly varies with latitude. In southern and northern my country, the vertical gradient is approximately -24 nT / km and -31 nT / km, respectively. As altitude increases, the vertical gradient tends to decrease; generally, for every 50 km increase in altitude, the absolute value of the vertical gradient decreases by approximately 1 nT / km.

[0041] The characteristics of the total geomagnetic field gradient show that the vertical gradient changes the most, followed by the north-south gradient, and the east-west gradient changes the least. Therefore, the magnetic interference field caused by the relative motion of the airborne magnetic survey platform (a few meters in the vertical direction) poses a significant threat to high-precision magnetic survey systems.

[0042] To address the noise introduced by the geomagnetic gradient field, this disclosure introduces a high-order geomagnetic field reference model (IGRF-13). The longitude, latitude, and altitude information of the motion platform are obtained in real time from the inertial navigation system and input into the IGRF-13 model to estimate the geomagnetic gradient field, correct the magnetic field test data of the magnetometer in real time, and output the magnetic field data after geomagnetic background gradient correction.

[0043] The International Geomagnetic Reference Field Model (IGRF) uses spherical harmonic analysis to describe the Earth's main magnetic field and its long-term variations. Model data primarily comes from satellite magnetic measurements, ground-based observations from astronomical and geomagnetic observatories, marine magnetic measurements, and artificial geomagnetic surveys. The latest 13th generation IGRF model (IGRF-13) was released in December 2019, applicable from 1900 to 2025, with an accuracy of 0.1 nT. The IGRF model is widely used in scientific research (such as space meteorology and magnetic anomalies), civilian geomagnetic orientation (geomagnetic positioning), military applications, global or regional geomagnetic mapping, and calculation of geomagnetic elements in blank areas.

[0044] According to an embodiment of this disclosure, in operation S3, the geomagnetic field data is removed from the total magnetic field data to obtain the magnetic interference data of the motion platform.

[0045] Specifically, calibration flights are conducted in regions with a uniform geomagnetic field at high altitudes. In this case, the total field measured by the airborne magnetic field detector mainly includes the geomagnetic field and the interference field from the moving platform, i.e.:

[0046] (1);

[0047] Among them, H tot H represents the total magnetic field data signal measured by the magnetometer. geo For geomagnetic field data signals, H int This is the magnetic interference data signal from the motion platform. A bandpass filter (BPF) is used to process the signal within the detection bandwidth, thus removing the DC component of the detection signal, resulting in:

[0048] (2);

[0049] Traditional methods assume that geomagnetic field data are constant, i.e., BPF{H geo}≈0, therefore we conclude that:

[0050] (3);

[0051] However, in reality, the geomagnetic field is affected by gradient distribution and is not constant within the measurement area. Therefore, it is assumed that BPF{H geo}≈0 introduces calculation errors. This invention corrects for the influence of the geomagnetic field gradient by introducing an IGRF model, where the geomagnetic field data H geo H is generated by calculation from the IGRF model. geo =IGRF(longitude, latitude, altitude, time), therefore the magnetic interference data of the moving platform can be obtained as follows:

[0052] (4).

[0053] According to embodiments of this disclosure, the magnetic interference data of the motion platform mainly includes motion platform attitude interference data (i.e., first magnetic interference data) and motion platform operating current interference data (i.e., second magnetic interference data).

[0054] According to an embodiment of this disclosure, in operation S4, the motion platform attitude information, motion platform current information, and fluxgate magnetometer detection data are acquired; wherein, the motion platform attitude information includes the motion platform roll information, pitch information, yaw angle information, and flight speed information; the fluxgate magnetometer detection data includes three orthogonal components of the geomagnetic field data in the motion platform's rectangular coordinate system.

[0055] Regarding attitude disturbances of the motion platform: The disturbance field caused by attitude changes of the motion platform can be divided into three parts: a constant magnetic field, an induced field, and an eddy current field. Since the magnetic field is a vector, a coordinate system needs to be established for analysis. Figure 3As shown, with the location of the magnetometer on the motion platform (taking an aircraft as an example) as the origin, the X-axis points towards the nose along the fuselage axis or parallel to the fuselage axis, the Y-axis is perpendicular to the longitudinal section of the fuselage and points towards the right wing, and the Z-axis is perpendicular to the plane of the fuselage and points towards the bottom of the fuselage, thus establishing an aircraft coordinate system. Indicates the Earth's magnetic field. , , Let represent the angles between the geomagnetic field vector and the three axes of the body coordinate system, respectively. Then:

[0056] 1) Constant magnetic field: Generated by ferromagnetic materials within the aircraft body, it is the aircraft's own magnetic field effect and is generally considered a constant vector in the aircraft's coordinate system, which can be written as:

[0057] (5);

[0058] Represents the remanent magnetic field vector. , , The XYZ components of the constant magnetic field in the body coordinate system. , , This is the unit vector in the XYZ direction of the body coordinate system.

[0059] The scalar magnetometer (optically pumped magnetometer) measures the Earth's magnetic field. The superposition of the magnetic anomaly field and its projection onto the geomagnetic field direction means that the constant magnetic field disturbance can be expressed as:

[0060] (6);

[0061] in, , , These represent the angles between the three axes of the platform coordinate system and the geomagnetic field.

[0062] 2) Induced Magnetic Field: This is mainly generated by the magnetization of soft magnetic materials on the aircraft by the Earth's magnetic field. The soft iron materials on the aircraft have diverse shapes and complex distributions; in modeling, they are equivalent to three soft magnetic rods magnetized only in the X, Y, and Z directions. Due to demagnetization, the total magnetization of the soft magnetic rods is not in the same direction as the magnetizing magnetic field. Therefore, after the soft magnetic rod in the X direction is magnetized by the X component of the Earth's magnetic field, it will induce magnetic fields along the X, Y, and Z directions. The induced magnetic field of the soft magnetic rod in the X direction can be obtained as follows:

[0063] (7);

[0064] , , Represents the geomagnetic field in the body coordinate system Three components. , , These represent the magnetic field coefficients of the equivalent soft magnetic rod in the X direction magnetized by the X component of the Earth's magnetic field.

[0065] Similarly, the induced magnetic fields of the soft magnetic rods in the Y and Z directions can be obtained as follows:

[0066] (8);

[0067] (9);

[0068] (10);

[0069] (11);

[0070] (12);

[0071] , , These represent the induced magnetic fields of the three equivalent soft magnetic rods. , , These represent the magnetic field coefficients of the equivalent soft magnetic rod in the Y direction magnetized by the Y component of the Earth's magnetic field. , , Let X, Y, and Z represent the magnetic field coefficients of the equivalent soft magnetic rod magnetized by the Z component of the Earth's magnetic field in the Z direction, respectively. Therefore, there are a total of 9 interference coefficients in the X, Y, and Z directions. Combined with equations (7)-(12), the induced magnetic field interference can be expressed as:

[0072] (13);

[0073] According to equation (13), the attitude-related disturbance term is: , , , , , There are a total of 6 terms, therefore, the scalar induced magnetic field interference coefficient has 6 terms.

[0074] 3) Eddy current field: Originating from the eddy current effect generated when the conductive materials of the aircraft cut through the Earth's magnetic field during movement. Based on the properties of the eddy current field, its interference value is related to the external magnetic field and the rate of change of aircraft attitude, as shown below:

[0075] (14);

[0076] Therefore, the disturbance of the eddy current field can be expressed as:

[0077] (15);

[0078] It can be seen that the eddy current field disturbance includes b 11 b 12 b 13 b 21 b 22 b 23 b 31 b 32 b 33 There are a total of 9 interference coefficients.

[0079] According to an embodiment of this disclosure, operation S5 includes: obtaining first magnetic interference data related to the attitude of the motion platform through the attitude information of the motion platform and based on the Tolles-Lawson model (TL model for short).

[0080] Combining equations (6), (13), and (15), we can obtain the expression for the motion platform-related interference data based on the TL model, which includes 18 coefficients, i.e., the first magnetic interference data:

[0081] (16);

[0082] in, For geomagnetic field data, , , These are the constant coefficients of the disturbance terms for the constant magnetic field, induced magnetic field, and eddy current magnetic field, respectively. It is the cosine of the angle between the platform's coordinate axes and the Earth's magnetic field, representing the platform's attitude. yes The time derivative, when i takes the values ​​1, 2, or 3:

[0083] (17)

[0084] According to embodiments of this disclosure, the motion platform current information is the operating current information of the equipment carried by the motion platform during operation.

[0085] According to an embodiment of this disclosure, operation S5 includes: obtaining second magnetic interference data with nine interference coefficients related to the working current of the motion platform based on the motion platform current information and the fluxgate magnetometer detection data.

[0086] Since the magnetic interference data of the motion platform is the superposition of the first magnetic interference data and the second magnetic interference data, it is equal to the difference between the total magnetic field data and the geomagnetic field data. Thus, the first magnetic interference data and the second magnetic interference data are calculated, and the magnetic interference coefficient is further calculated.

[0087] Regarding magnetic interference from airborne electronic equipment on motion platforms: Airborne electronic equipment on motion platforms radiates complex electromagnetic fields and generates interfering magnetic fields during operation. High-frequency interference, such as from stroboscopic interference, communication equipment, and radar, primarily generates higher-frequency interference. These interferences differ significantly in frequency band from other interfering magnetic fields and magnetic anomalies; therefore, low-pass filtering can eliminate this interference. The main types of airborne electronic equipment interference that can cause problems within the detection frequency band are as follows:

[0088] 1) Interference magnetic fields generated by the power unit during the process of providing power to the carrier motion platform and equipment power supply. This type of electromagnetic interference is related to current, has a wide spectrum, and a large amplitude.

[0089] 2) Interfering magnetic fields generated by control circuits, such as switching circuits and pulse digital circuits, can cause rapid changes in current during operation, resulting in electromagnetic interference with a wide spectrum. Therefore, it is generally believed that magnetic interference from airborne equipment is mainly generated by current.

[0090] According to electromagnetic field theory, electric current generates a magnetic field. In the low-frequency range, the magnetic interference generated by the current of airborne electronic equipment such as engines and control links on the carrier platform can be calculated using the Biot-Savart law, expressed by the following equation:

[0091] (18);

[0092] (19);

[0093] Where I is the source current and L is the integration path. It is a tiny line element of the source current. Let r be the unit vector pointing from the current element to the point where the field is to be determined, and let r be the distance between the current element and the point where the field is to be determined. Let be the free permeability, and its value is . The three vector directions conform to the right-hand rule. It can be seen that the magnetic interference generated by the current in the low-frequency band is related to the current itself, the shape of the conductor, and the observation distance.

[0094] Magnetic interference testing of the platform revealed that the high current during engine operation generates significant magnetic interference. Since the engine is a power source, it needs to operate continuously as long as the aircraft is in flight. Therefore, without intervention, magnetic interference from the airborne electronic equipment will persist. Its characteristics can be summarized as follows:

[0095] 1) The engine requires a large current to operate, which will generate a lot of magnetic interference and affect the quality of magnetic measurement data.

[0096] 2) Magnetic interference from airborne electronic equipment is mainly generated by the power supply current. The resulting magnetic interference vector is similar to the characteristics of permanent magnet materials. It is not affected by the magnetization of the Earth's magnetic field, but it will be superimposed with the Earth's magnetic field vector.

[0097] 3) The magnetic interference waveform caused by the sudden current change during engine start-up and shutdown is similar to the magnetic target waveform after filtering, which will seriously interfere with subsequent target identification.

[0098] According to embodiments of this disclosure, the fluxgate magnetometer detection data includes three orthogonal components of the geomagnetic field data in the Cartesian coordinate system of the moving platform. When obtaining these three orthogonal components, it is necessary to determine the cosine values ​​of the angles between the three axes of the moving platform's Cartesian coordinate system and the geomagnetic field, as well as the time derivatives of these cosine values. Taking a human-machine interface as an example, based on the analysis of magnetic interference on UAV platforms, the magnetic interference of UAV-borne electronic equipment is mainly caused by the power supply current, and its interfering magnetic field is similar to that of permanent magnet materials. Therefore, this invention proposes a linear compensation model based on current interference sources. This model uses the operating current data of the moving platform, fluxgate data, and optically pumped magnetic field data obtained during flight experiments to calculate the compensation model coefficients. The magnetic interference is estimated using the coefficients and the current interference source matrix, and the modeling interference is subtracted from the optically pumped magnetic field data to eliminate the magnetic interference of the airborne electronic equipment.

[0099] The magnetic interference generated by the operating current of the motion platform is expressed as follows:

[0100] (20);

[0101] in, This represents the sum of magnetic interference generated by the operating current of the motion platform. The interfering magnetic field caused by a constant current. The interfering magnetic field caused by the change of current over time. The interference magnetic field caused by the change in current turn-off velocity is projected onto the direction of the Earth's magnetic field. Therefore, the magnetic field model of the magnetic interference (i.e., the second magnetic interference data) generated by the actual operating current of the motion platform can be written as:

[0102] (twenty one);

[0103] in, It is electric current. It is the derivative of current with respect to time. It is the second derivative of the current with respect to time. Coefficient. These are the magnetic compensation coefficients related to the operating current of airborne electronic equipment, totaling 9 terms. Then:

[0104]

[0105] Where n represents the number of interference terms, Represents the coefficient of the interference term. This indicates the deformation of the operating current and its derivative of airborne electronic equipment.

[0106] In summary, this invention proposes a global interference compensation algorithm that includes the attitude of the moving platform, the operating current of the moving platform, and the magnetic field interference related to the geomagnetic background gradient. Based on the TL model which includes three types of interferences—constant magnetic field, induced magnetic field, and eddy current magnetic field—caused by the attitude change of the moving platform, the algorithm introduces the noise source of the operating current of the equipment on the moving platform, which is physically equivalent to constant magnetic field and induced magnetic field. This expands the coefficients of the magnetic compensation model equation from the existing 18 terms to 27 terms, greatly improving the detection accuracy.

[0107] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and are not described in detail. Furthermore, the definitions of the various elements and methods described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

[0108] Furthermore, unless specifically described or required to occur in a specific order, the order of the above steps is not limited to those listed above and can be varied or rearranged according to the desired design. Moreover, the above embodiments can be used in combination with each other or with other embodiments based on design and reliability considerations; that is, technical features from different embodiments can be freely combined to form more embodiments.

[0109] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of this disclosure. It should be understood that the above are only specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for global magnetic interference compensation in airborne magnetic surveying, comprising: Operation S1: Perform high-altitude calibration flight via the motion platform and acquire total magnetic field data based on the detection data of the optically pumped magnetometer; Operation S2: Obtain geomagnetic background gradient information and obtain geomagnetic field data based on the geomagnetic background gradient information; Operation S3: Obtain magnetic interference data of the motion platform based on the total magnetic field data and the geomagnetic field data; Operation S4: Acquire motion platform attitude information, motion platform current information, and fluxgate magnetometer detection data. The motion platform attitude information includes the motion platform's roll, pitch, yaw angle, and flight speed information. The motion platform current information is the operating current information of the equipment carried on the motion platform during operation. The fluxgate magnetometer detection data includes three orthogonal components of the geomagnetic field data in the motion platform's rectangular coordinate system. Operation S5: Obtain the magnetic interference coefficient of the motion platform based on the magnetic interference data of the motion platform, the attitude information of the motion platform, the current information of the motion platform, and the detection data of the fluxgate magnetometer; and Operation S6: Based on the geomagnetic background gradient information and the magnetic interference coefficient of the motion platform, perform real-time data compensation on the total magnetic field data during actual airborne magnetic surveys; In operation S2, the real-time longitude, latitude, and altitude information of the motion platform are acquired and used as input parameters for the IGRF model to obtain geomagnetic field data. Operation S5 includes: Using the motion platform's attitude information and based on the Tolles-Lawson model, the first magnetic interference data with 18 interference coefficients related to the motion platform's attitude is obtained as follows: (16)； in, For geomagnetic field data, , , These are the constant coefficients of the disturbance terms for the constant magnetic field, induced magnetic field, and eddy current magnetic field, respectively. It is the cosine of the angle between the platform's coordinate axes and the Earth's magnetic field, representing the platform's attitude. yes The time derivative; Based on the motion platform current information and the fluxgate magnetometer detection data, the second magnetic interference data with nine interference coefficients related to the motion platform's operating current is obtained as follows: Where n represents the number of interference terms, Represents the coefficient of the interference term. This represents the equivalent transformation of the operating current and its derivative of airborne electronic equipment. The magnetic interference data of the motion platform is the superposition of the first magnetic interference data and the second magnetic interference data, which is equal to the difference between the total magnetic field data and the geomagnetic field data. Thus, the magnetic interference coefficient in the first magnetic interference data and the second magnetic interference data can be obtained.

2. In the global magnetic interference compensation method according to claim 1, in operation S3, the geomagnetic field data is removed from the total magnetic field data to obtain the magnetic interference data of the moving platform.

3. According to the global magnetic interference compensation method of claim 1, when obtaining the three orthogonal components of the geomagnetic field in the rectangular coordinate system of the moving platform, it is necessary to determine the cosine value of the angle between the three coordinate axes of the rectangular coordinate system of the moving platform and the geomagnetic field, as well as the time derivative of the cosine value of the angle between the three coordinate axes of the rectangular coordinate system of the moving platform and the geomagnetic field.

4. The global magnetic interference compensation method according to claim 1, wherein the motion platform includes any one of a fixed-wing aircraft, a helicopter, or a drone.

5. The global magnetic interference compensation method according to claim 1, wherein the calibration flight includes performing level flight, pitch, roll, yaw, and acceleration / deceleration flight sequentially in the four directions of east, west, south, and north.

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