An apparatus and method for measuring the vector geomagnetic field using an unmanned aerial vehicle (UAV).

Abstract

This application relates to the field of vector geomagnetic field surveying, and more particularly to a method and system for measuring vector geomagnetic fields using an unmanned aerial vehicle (UAV). The system includes a tetrahedral rigid support structure made of non-magnetic material, with four GNSS antennas mounted at its vertices and three base points respectively, forming an RTK-GNSS multi-antenna system for acquiring low-frequency attitude data in a geocentric-ground-fixed coordinate system. A sensor unit integrates a vector magnetic sensor and an inertial measurement unit for acquiring three-axis geomagnetic field data and high-frequency angular velocity data. A GNSS receiver receives the multi-antenna observation data. A calibration system is used to construct a reference coordinate system during the ground calibration stage and determine the first rotation matrix between the magnetometer coordinate system and the reference coordinate system. An attitude and magnetic field data processing unit fuses low-frequency attitude and high-frequency angular velocity information, calculates the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system, and outputs three-axis geomagnetic field data in the geocentric-ground-fixed coordinate system through multi-level rotation matrix transformation.

Description

Technical Field

[0001] This application relates to the field of vector geomagnetic field surveying, and in particular to an apparatus and method for measuring vector geomagnetic field using an unmanned aerial vehicle (UAV). Background Technology

[0002] In the field of geomagnetic exploration, airborne magnetic surveying, as an efficient and rapid means of acquiring large-scale geomagnetic field data, has been widely applied in geological surveys, mineral resource exploration, environmental monitoring, and the construction of geomagnetic navigation reference maps. Currently, most mainstream airborne magnetic surveying systems use fixed-wing aircraft or unmanned aerial vehicles (UAVs) as their platform, integrating high-sensitivity magnetometers for measurement.

[0003] Current common airborne magnetic surveying methods mainly rely on scalar magnetometry (i.e., measuring the total intensity of the geomagnetic field, or the modulus of the geomagnetic vector). Commonly used sensors include proton precession magnetometers, Overhauser magnetometers, and optically pumped magnetometers. However, scalar magnetometry can only provide information on the modulus of the geomagnetic field and cannot obtain the direction of the magnetic field vector, which has significant limitations in certain applications such as high-precision geophysical inversion and geomagnetic model construction.

[0004] To achieve more comprehensive geomagnetic field information, some solutions attempt to introduce vector magnetometry, which simultaneously measures the components of the geomagnetic field in three orthogonal directions. Typical vector magnetometers, such as fluxgate magnetometers, have become the primary choice for airborne vector magnetometry due to their small size, low power consumption, and fast response. However, the output of a vector magnetometer is essentially a projection of the geomagnetic field onto the sensor's body coordinate system. To transform this to an Earth-Centered Earth-Fixed (ECEF) coordinate system or a local geographic coordinate system (such as the North-East-Center coordinate system, NEC coordinate system), the precise three-dimensional orientation of the sensor's coordinate system relative to the reference coordinate system is required.

[0005] In existing technologies, inertial measurement units (IMUs) are typically used to provide the attitude of an aircraft. Specifically, the IMU obtains the direction of gravity by measuring the accelerometer, the magnetic north pole by measuring the magnetometer, and the attitude change by integrating the angular velocity by the gyroscope. A high-precision attitude can be obtained by fusing these three types of data through an attitude filter. This method is perfectly suitable for navigation of drones, robots, etc., in local areas. However, for rigorous geomagnetic field surveys and modeling, a serious problem may arise: the coordinate system calculated by the IMU is actually a "physically observed local navigation frame," and it does not have a strict mathematical transformation relationship with the coordinate systems commonly used in geomagnetic modeling (such as the ECEF or NEC coordinate systems). For example, the magnetometer in the IMU is used to measure the magnetic north pole to determine orientation; however, this is only a rough description of the Earth as a magnetic dipole. In reality, the geomagnetic field contains not only dipole components but also the magnetic fields of the lithosphere, ionosphere, and magnetosphere, and the magnetic fields of the ionosphere and magnetosphere also change over time. This means that the magnetic field vector measured by the magnetometer does not strictly point to the magnetic north pole; and even throughout the day, the direction of the vector measured by the magnetometer changes. In addition, the accelerometer measures the local gravity vector when at rest, and this vector may be affected by local gravity anomalies (such as iron ore), causing it not to point strictly to the Earth's center.

[0006] Therefore, while attitude calculation methods based on inertial measurement units (IMUs) perform well in general navigation tasks, the attitude reference frame they provide essentially relies on locally observable physical fields (i.e., local gravity and magnetic field directions). These directions do not have a precise and stable geometric correspondence with the global coordinate system (such as the ECEF coordinate system) upon which geomagnetic modeling depends. Especially in high-precision vector geomagnetic surveys, this reference frame bias directly leads to systematic errors in magnetic field vector coordinate transformation, severely impacting the absolute accuracy of geomagnetic data and the reliability of modeling.

[0007] In summary, current technologies lack a method for achieving high-precision and high-stability attitude determination in a global coordinate system (such as ECEF), making it difficult for vector magnetometers on airborne platforms to output geomagnetic field data with accurate directional information. Overcoming the dependence of traditional attitude measurement on local physical fields and establishing a precise transformation relationship between the sensor coordinate system and the global coordinate system has become a key bottleneck in achieving high-precision UAV vector geomagnetic surveys. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of insufficient attitude accuracy and inconsistent coordinate system reference in the existing UAV airborne magnetic measurement system for vector geomagnetic field measurement, and to provide a device and method for measuring vector geomagnetic field using UAV that can achieve high-precision attitude determination and complete accurate vector magnetic field conversion in the geocentric geofixed coordinate system (ECEF).

[0009] To solve the above-mentioned technical problems, the device for measuring vector geomagnetic field using an unmanned aerial vehicle (UAV) provided in this application includes:

[0010] A tetrahedral rigid support structure made of non-magnetic material, consisting of one vertex and three base points;

[0011] Four GNSS antennas are respectively installed at the apex and three base points of the tetrahedral rigid support structure to form an RTK-GNSS multi-antenna system, which is used to obtain low-frequency attitude measurement data of the tetrahedral rigid support structure in the geocentric coordinate system.

[0012] A GNSS receiver, mounted on the tetrahedral rigid support structure, is used to receive observation data from the RTK-GNSS multi-antenna system.

[0013] The sensor unit, mounted on the tetrahedral rigid support structure, integrates a vector magnetic sensor and an inertial measurement unit, wherein:

[0014] The vector magnetic sensor is used to collect triaxial magnetic field data of the Earth's magnetic field in the coordinate system of the magnetometer.

[0015] The inertial measurement unit is used to collect high-frequency angular velocity measurement data of the tetrahedral rigid support structure in the magnetometer coordinate system;

[0016] The drone is used to move the tetrahedral rigid support structure during the flight measurement phase;

[0017] The connecting component is connected at one end to the UAV and at the other end to the vertex of the tetrahedral rigid support structure.

[0018] The calibration system is used to construct a tetrahedral rigid support structure coordinate system as the REF reference coordinate system during the ground calibration stage, and to determine the first rotation matrix between the magnetometer coordinate system and the reference coordinate system.

[0019] The attitude and magnetic field data processing unit, connected to the GNSS receiver and sensor unit, is used during the flight measurement phase for:

[0020] By integrating the low-frequency attitude measurement data and the high-frequency angular velocity measurement data, the high-frequency attitude information of the tetrahedral rigid support structure in the geocentric-ground-fixed coordinate system is obtained.

[0021] Based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the directions of all baseline vectors in the geocentric-ground-fixed coordinate system are calculated, and the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system is obtained.

[0022] Based on the first rotation matrix, the three-axis geomagnetic field data in the magnetometer coordinate system is transformed to the reference coordinate system, and then based on the second rotation matrix, the three-axis geomagnetic field data in the reference coordinate system is transformed to the geocentric-geo-fixed coordinate system, thereby obtaining high-frequency three-axis geomagnetic field data in the geocentric-geo-fixed coordinate system.

[0023] As an improvement to the above-mentioned device, the tetrahedral rigid support structure is a symmetrical structure.

[0024] As an improvement to the above-mentioned device, the rigid support structure is a spatial tetrahedral frame, including three base sides and three side sides; a GNSS antenna is installed at each of the four corners of the spatial tetrahedral frame, and the sensor unit is installed at the center of gravity of the spatial tetrahedral frame; the length of each base side of the spatial tetrahedral frame is greater than or equal to 1.5 meters, and the length of each side side of the spatial tetrahedral frame is greater than or equal to 2.0 meters.

[0025] As an improvement to the above-mentioned device, the four GNSS antennas are connected to the same GNSS receiver, which supports real-time dynamic differential positioning technology; the inertial measurement unit includes a gyroscope.

[0026] As an improvement to the above-mentioned device, a non-magnetic tail fin device is also included. The non-magnetic tail fin device is installed at the bottom of the tetrahedral rigid support structure or behind the center of gravity to provide air damping, thereby suppressing the random swaying and rotation of the tetrahedral rigid support structure during flight and improving measurement stability. The connecting component includes a flexible non-magnetic cable.

[0027] To achieve another objective of the present invention, the present invention also provides a method for measuring vector geomagnetic fields using a drone, implemented based on the above-described apparatus for measuring vector geomagnetic fields using a drone, comprising:

[0028] Installation phase: Install the four GNSS antennas, GNSS receiver, sensor unit, and attitude and magnetic field data processing unit onto the tetrahedral rigid support structure;

[0029] Ground calibration stage: Construct a tetrahedral rigid support structure coordinate system as the REF reference coordinate system, and determine the first rotation matrix between the magnetometer coordinate system and the reference coordinate system;

[0030] Flight Measurement Phase: The UAV is mounted to the apex of the tetrahedral rigid support structure via connecting components, enabling movement of the tetrahedral rigid support structure during flight measurement. Low-frequency attitude measurement data of the tetrahedral rigid support structure in a geocentric coordinate system is obtained via four GNSS antennas and transmitted to the attitude and magnetic field data processing unit via a GNSS receiver. Three-axis geomagnetic field data in a magnetometer coordinate system is acquired via a vector magnetic sensor, and high-frequency angular velocity measurement data of the tetrahedral rigid support structure in a magnetometer coordinate system is acquired via an inertial measurement unit and transmitted to the attitude and magnetic field data processing unit. The attitude and magnetic field data processing unit then fuses the tetrahedral data. Low-frequency attitude measurement data and high-frequency angular velocity measurement data of the rigid support structure are used to obtain high-frequency attitude information of the REF reference coordinate system in the geocentric-ground-fixed coordinate system. Based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the directions of all baseline vectors in the geocentric-ground-fixed coordinate system are calculated to obtain the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system. Based on the first rotation matrix, the three-axis geomagnetic field data in the magnetometer coordinate system are transformed to the reference coordinate system, and then based on the second rotation matrix, the three-axis geomagnetic field data in the reference coordinate system are transformed to the geocentric-ground-fixed coordinate system, thereby obtaining high-frequency three-axis geomagnetic field data in the geocentric-ground-fixed coordinate system.

[0031] As an improvement to the above method, the ground calibration stage specifically includes:

[0032] Ground static calibration phase: Measure the six baseline vectors between the four GNSS antennas, determine the geometric configuration of the tetrahedron formed by the phase center points of the four GNSS antennas, construct the tetrahedron rigid support structure coordinate system as the REF reference coordinate system, and obtain the coordinates of the six baseline vectors of the four GNSS antenna arrays in the REF reference coordinate system.

[0033] Ground-based joint calibration phase: The tetrahedral rigid support structure is fixed on a non-magnetic turntable. The non-magnetic turntable is rotated at a constant speed. Using low-frequency attitude measurement data of the tetrahedral rigid support structure in the geocentric-ground coordinate system measured by the RTK-GNSS multi-antenna system and the three-axis magnetic field data of the geomagnetic field in the magnetometer coordinate system measured by the vector magnetic sensor, the coordinates of the rotation axis of the non-magnetic turntable in the REF reference coordinate system and the vector in the magnetometer coordinate system are calculated. The attitude of the non-magnetic turntable is changed and the rotation measurement process is repeated to obtain the coordinates of the rotation axis of at least two non-collinear non-magnetic turntables in the REF reference coordinate system and the vector in the magnetometer coordinate system. The first rotation matrix between the REF reference coordinate system and the magnetometer coordinate system is solved using the TRIAD algorithm or SVD algorithm.

[0034] As an improvement to the above method, the process of constructing the coordinate system of the tetrahedral rigid support structure includes:

[0035] In the static state of the tetrahedral rigid support structure, the points where the phase centers of the four GNSS antennas are located are denoted as points A, B, C, and D, respectively, where point D is the vertex and points A, B, and C are the base points. Based on baseline measurements, the baseline vectors between adjacent points in the geocentric geofixed coordinate system are obtained, including: the first baseline vector AB between points A and B, the second baseline vector AC between points A and C, the third baseline vector AD between points A and D, the fourth baseline vector BC between points B and C, the fifth baseline vector BD between points B and D, and the sixth baseline vector CD between points C and D.

[0036] Construct a REF reference coordinate system using the first baseline vector AB and the second baseline vector AC: let the X-axis of the REF reference coordinate system coincide with the direction of the first baseline vector AB, let the Z-axis of the REF reference coordinate system point to the cross product direction of the first baseline vector AB and the second baseline vector AC, and let the Y-axis of the REF reference coordinate system form a right-handed system with the X-axis and Z-axis.

[0037] As an improvement to the above method, the process of calculating the directions of all baseline vectors in the geocentric-ground-fixed coordinate system based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, and obtaining the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system includes:

[0038] Under the motion state of the tetrahedral rigid support structure, based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the geocentric-ground-fixed coordinate system are obtained: First ECEF baseline vector Second ECEF baseline vector Third ECEF baseline vector Fourth ECEF baseline vector Fifth ECEF baseline vector and the sixth ECEF baseline vector ;

[0039] Based on the REF reference coordinate system and the first rotation matrix, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the REF reference coordinate system are obtained: First REF baseline vector Second REF baseline vector Third REF baseline vector Fourth REF baseline vector Fifth REF baseline vector and the sixth REF baseline vector ;

[0040] Solve for the attitude of the REF reference coordinate system relative to the geocentric-ground-fixed coordinate system, and find the optimal second rotation matrix. :

[0041]

[0042] in, , This represents a group consisting of three-dimensional rotation matrices. This indicates that the second rotation matrix belongs to the group consisting of three-dimensional rotation matrices, and st indicates that the constraint condition is met. This indicates that the constraints are met. In the case where the second rotation matrix minimizes the sum of squared residuals for all vector pairs, the second rotation matrix is ​​the optimal second rotation matrix. .

[0043] As an improvement to the above method, it is characterized by further comprising: aligning the low-frequency attitude measurement data with the high-frequency angular velocity measurement data in time using a unified clock source or hardware trigger signal, so as to avoid magnetic field data distortion caused by attitude lag.

[0044] The technical solution provided by this invention has the following significant advantages compared with the prior art:

[0045] 1. Eliminate the problem of inconsistent coordinate system references: The attitude is calculated directly in the ECEF coordinate system by using RTK-GPS (Real-Time Kinematic Global Positioning System), which avoids the systematic deviation caused by the reliance of traditional IMU on local gravity and magnetic north direction.

[0046] 2. Improve the absolute accuracy of vector magnetic field measurement: By combining ground geometric calibration, redundant baseline calculation and multi-sensor joint calibration, a high-fidelity conversion of the entire link from sensor output to the ECEF coordinate system is realized, ensuring that the measurement results have good absolute directional consistency, which is suitable for the construction of regional and even global geomagnetic maps.

[0047] 3. Enhanced system robustness and anti-interference capability: The four GNSS antenna design provides redundant observations, which can maintain attitude calculation even when individual GNSS antenna signals are lost; the flexible sling and tail fin design effectively isolates the UAV platform from vibration and electromagnetic interference, ensuring a clean working environment for the magnetometer.

[0048] 4. Achieve high-frequency continuous attitude output: Introduce a fusion mechanism of gyroscope and multiplicative extended Kalman filter (MEKF) to make up for the low attitude update rate of RTK-GPS, meet the time synchronization requirements of high-speed sampling magnetometer, and avoid data distortion caused by attitude lag.

[0049] 5. Suitable for small and medium-sized UAV platforms: The device adopts a lightweight carbon fiber design, with a weight controllable to within 5kg. Combined with a flexible suspension method, it can be adapted to a variety of multi-rotor UAVs, and has good engineering deployability and operational flexibility. Attached Figure Description

[0050] Figure 1 A schematic diagram of a drone and a magnetic measurement device;

[0051] Figure 2 Here is a flowchart of the magnetic measurement data conversion process;

[0052] Figure 3 A schematic diagram of the geometric calibration and coordinate system construction for a GPS attitude measurement device;

[0053] Figure 4 A schematic diagram showing the alignment and calibration of the coordinate systems of the attitude measurement unit, magnetometer, and gyroscope.

[0054] Figure 5 This is a flowchart illustrating a method for measuring the vector geomagnetic field using a drone. Detailed Implementation

[0055] The technical solutions provided in this application are further illustrated below with reference to the embodiments.

[0056] To address the shortcomings of existing technologies that rely on inertial measurement units (IMUs), which cause the attitude reference system to depend on the direction of local gravity and magnetic fields and make it difficult to meet the requirements of global coordinate system consistency for geomagnetic modeling, this embodiment aims to use a high-precision RTK-GPS receiver to construct a rigid tetrahedral measurement unit and calculate its baseline vector in the ECEF coordinate system to obtain the three-dimensional attitude of the device, thereby avoiding dependence on the direction of the gravitational field and geomagnetic field.

[0057] Furthermore, to address the issue of installation deviations between the coordinate systems of multiple source sensors, this embodiment also provides an alignment method between the RTK-GPS attitude measurement system and the fluxgate magnetometer coordinate system. By calibrating the coordinate transformation relationship between the two (i.e., the installation matrix), a step-by-step coordinate transformation of magnetic measurement data from the sensor coordinate system to the ECEF coordinate system without cumulative error is achieved.

[0058] Through the above-mentioned technical means, this embodiment can achieve a high-fidelity representation of the vector geomagnetic field in the ECEF coordinate system under the UAV platform, effectively reduce the magnetic field component conversion deviation caused by attitude error and coordinate system misalignment, and improve the absolute accuracy and data consistency of vector geomagnetic measurement.

[0059] This embodiment provides a device and method for measuring vector geomagnetic fields using an unmanned aerial vehicle (UAV), aiming to solve the problem of large magnetic field vector transformation errors caused by insufficient attitude measurement accuracy and inconsistent coordinate system references in existing airborne vector magnetic surveys. The device directly determines the three-dimensional attitude of a rigid structure in the Earth-centered Earth-fixed (ECEF) coordinate system using a multi-GNSS antenna RTK-GPS system, and combines multi-sensor data fusion and coordinate system alignment calibration methods to achieve accurate representation of the magnetometer output in the ECEF coordinate system.

[0060] 1. The device comprises the following components:

[0061] Rigid support structure: A spatial tetrahedral frame made of lightweight, high-strength non-magnetic material (preferably carbon fiber composite material), with the four vertices of the tetrahedron used to mount the GNSS antenna. This structure is self-stabilizing and can maintain structural stability during geomagnetic surveys. The tetrahedron is not limited to a regular tetrahedral configuration, but three of its base sides should be at least 1.0 meter (preferably greater than 1.5 meters), and the three side sides should be longer than the base sides (preferably greater than 2.0 meters) to enhance the geometric sensitivity of attitude calculation, especially in compensating for the relatively large measurement error of the GPS elevation component in the vertical direction. Theoretically, the attitude calculation error can be further reduced by increasing the side lengths.

[0062] 2. Obtaining Precise Geometric Configuration during Ground Static Calibration: Before the device is first put into use, it is placed in an open, unobstructed, flat outdoor area and kept stationary for more than 24 hours. During this period, each RTK-GPS receiver continuously collects carrier phase data. Through long-term static differential calculation, the absolute positions of the phase centers of the four GNSS antennas in the ECEF coordinate system are accurately determined, thereby reconstructing the true geometric shape of the tetrahedral structure (i.e., the length of each side, the included angle, etc.), which serves as the rigid body constraint prior information for subsequent attitude calculation.

[0063] 3. Multi-GNSS Antenna RTK-GPS System: A high-precision dual-frequency or multi-frequency GNSS antenna is installed at each of the four vertices of a tetrahedron and connected to the same RTK-GPS receiver module. The system supports real-time dynamic baseline measurement mode and can output the coordinates of multiple baseline vectors in ECEF space at an update frequency of 1Hz.

[0064] 4. Attitude calculation method based on redundant baselines and geometric constraints: Using four GNSS antennas, up to six sets of spatial baseline vectors (i.e., vectors between any two points) can be constructed. Although theoretically, three sets of linearly independent baselines can uniquely determine the three-dimensional attitude of a rigid body, this embodiment utilizes the redundant observations provided by four GNSS antennas to introduce least squares optimization or weighted least squares estimation in the attitude calculation process. Combined with the precise geometric dimensions obtained in step 2 as hard or soft constraints, this significantly improves the robustness and outlier resistance of the attitude calculation.

[0065] 5. Additional Inertial Measurement Unit (IMU) for High-Frequency Attitude Interpolation: Since the attitude update rate of RTK-GPS is limited (typically 1Hz), insufficient to meet the requirements of high-frequency magnetic field sampling, this embodiment also integrates a high-precision three-axis gyroscope within the structure for measuring angular velocity. By establishing a Multiplicative Extended Kalman Filter (MEKF), the low-frequency, high-precision RTK-GPS attitude observation is used as the filter update quantity, and the high-frequency gyroscope angular velocity is used as the prediction quantity, achieving continuous and smooth attitude estimation and effectively compensating for the attitude blind spot within the GPS update interval.

[0066] 6. Vector Magnetometer Module: A triaxial magnetometer is installed in the central region of the bottom surface of the tetrahedral structure to measure the three orthogonal components of the geomagnetic field in the sensor's body coordinate system. This magnetometer features high sensitivity (better than 0.1 nT), low drift, and wide frequency response characteristics. It is fixed with a non-magnetic bracket, away from metal connectors, to reduce structural residual magnetism and eddy current interference.

[0067] 7. Multi-sensor collaborative coordinate system alignment and calibration method: After the device is assembled, the attitude measurement system needs to be aligned with the magnetometer coordinate system and the gyroscope coordinate system. Specifically, using a specially designed non-magnetic turntable, the entire assembled system is placed on the turntable and rotated at a constant speed to obtain the coordinates of the rotation axis vector in the three coordinate systems. The attitude of the turntable is then changed and measured again. Using two or more sets of rotation axis information, the relative rotation matrix between the three coordinate systems can be obtained using classical methods such as TRIAD or QUEST. Figure 4 As shown, the non-magnetic turntable includes a turntable rotation plane, a turntable support plane, several adjusting screws, movable connectors, and a base. The turntable rotation plane is located on and rotatably connected to the turntable support plane, driving the assembled system to rotate at a uniform speed. Several adjusting screws are positioned between the turntable support plane and the base, with one end connected to the turntable support plane via a movable connector, and the other end connected to the base via a movable connector. By adjusting the length of the adjusting screws, the orientation or posture of the rotation support plane is changed, thereby adjusting the posture of the turntable rotation plane.

[0068] 8. Aerodynamic Stabilization Structure: A non-magnetic tail fin device (such as a carbon fiber plate or lightweight plastic wing) is installed at the bottom or behind the center of gravity of the tetrahedral structure. Its shape can be cross-shaped, T-shaped, or flat. This tail fin provides aerodynamic damping and directional stability during the UAV's suspended flight, suppressing random swaying and rotation of the device, allowing it to maintain a generally stable orientation naturally during flight, which is beneficial to the convergence and accuracy maintenance of the attitude system.

[0069] 9. UAV Suspension System: The entire measuring device is suspended below the UAV by a flexible, non-magnetic cable (preferably 5-10m in length). One end of the cable is connected to a vertex of a tetrahedron, and the other end is fixed to the bottom of the UAV fuselage. This design keeps the measuring device away from electromagnetic interference sources of the UAV (such as motors, batteries, ESCs, etc.), while the flexible connection effectively isolates the influence of flight vibrations on attitude measurement.

[0070] like Figure 5 As shown, the method provided in this embodiment includes the following steps:

[0071] Ground preparation phase: Complete the static calibration of the device and obtain the precise geometric configuration of the four GNSS antennas; specifically, a tetrahedral rigid support structure is made using non-magnetic materials (such as carbon fiber composites). This structure serves as the mechanical reference for the entire measurement system and is also the physical carrier of the "attitude reference coordinate system" in this invention. To achieve high-precision three-dimensional attitude measurement, four GNSS antennas are installed at the vertices of the rigid support structure, forming a multi-GNSS antenna RTK-GNSS array. The preferred tetrahedral configuration in this invention is based on the optimal trade-off between accuracy and practicality. Theoretically, three non-collinear GNSS antennas can solve the three-dimensional attitude, but the solution results exhibit significant accuracy attenuation in the direction of the normal to the plane formed by the three points. By using four GNSS antennas to form a non-coplanar tetrahedron, the overall accuracy and robustness of the three-dimensional attitude solution are significantly improved through geometric redundancy, especially greatly improving the attitude accuracy of the weakest dimension. Meanwhile, compared to solutions with five or more GNSS antennas, the tetrahedral configuration achieves an optimal balance in terms of system weight, complexity, cost, and data processing load, making it particularly suitable for payload-sensitive applications such as UAVs. To further optimize the system's center of gravity, the tetrahedral configuration is preferably symmetrical or approximately symmetrical. An integrated vector magnetometer and inertial measurement unit are fixed to the rigid support structure. This integrated module (e.g., Twinleaf VMR) is precisely calibrated by the manufacturer before shipment. Its included three-axis vector magnetometer and gyroscope sensors share the same coordinate system and output time-synchronized observation data. The core advantage of using such an integrated module is that it eliminates the need for joint calibration of the magnetometer and inertial measurement unit, thus simplifying the system calibration process. The four GNSS antennas are connected to a GNSS receiver supporting RTK (Real-Time Kinematic) technology via cables. The integrated vector magnetometer, inertial measurement unit, and GNSS receiver are connected to the data acquisition system via data cables. Ultimately, all equipment is integrated and the mechanical connections are ensured to form a complete measuring unit that can be used for suspended operations.

[0072] Coordinate system calibration phase: Through multi-axis rotation experiments, the joint alignment of the magnetometer, gyroscope, and GPS attitude system is completed. Specifically, in the ground static calibration phase: the six baseline vectors between the four GNSS antennas are measured to determine the precise geometric configuration of the tetrahedron formed by the phase center points of the four GNSS antennas, and a local attitude reference coordinate system is constructed to obtain the coordinates of the six baseline vectors of the four GNSS antenna array in this attitude reference coordinate system. In the ground joint calibration phase: the above device is fixed on a non-magnetic turntable, the turntable is rotated at a constant speed, and the rotation axis is calculated using the measurements of the GNSS antenna array and the magnetic field measurement of the vector magnetometer, respectively, to obtain the vector coordinates of the rotation axis in the attitude reference coordinate system and the vector coordinates of the rotation axis in the vector magnetometer coordinate system; the turntable attitude is changed and the rotation measurement process is repeated to obtain at least two pairs of non-collinear rotation axis vectors; the rotation matrix between the attitude reference coordinate system and the vector magnetometer coordinate system is solved using the TRIAD algorithm or SVD algorithm.

[0073] Flight Measurement Phase: The UAV, carrying a sling, flies along a preset route within the target area, and the system collects multi-source data in real time. Specifically, a rigid support structure is suspended below the UAV platform via flexible non-magnetic cables. After takeoff, the coordinates of the six baseline vectors between the four GNSS antennas in the ECEF coordinate system are calculated in real time. Combined with the precise coordinates of these six baseline vectors in the attitude reference coordinate system obtained during the static calibration phase, an optimal rotation matrix can be fitted, representing the attitude of the attitude reference coordinate system in the ECEF coordinate system. GNSS measurement frequencies are relatively low, while the angular velocity measurement frequency of the inertial measurement unit (IMU) is higher. By using an attitude filter to fuse the high-frequency angular velocity measurement data collected by the IMU with the low-frequency attitude measurement data obtained by the GNSS antenna array, high-frequency attitude information of the attitude reference coordinate system in the ECEF coordinate system can be obtained. Using the rotation matrix between the attitude reference coordinate system and the vector magnetometer coordinate system obtained during the ground joint calibration phase, the magnetic field vector measured by the vector magnetometer can be transformed into the attitude reference coordinate system, and then the measured attitude can be used to further transform the magnetic field vector into the ECEF coordinate system. In this embodiment, the attitude and magnetic field data processing unit is configured for real-time fusion calculation. However, in other embodiments, depending on the different requirements of the task for real-time performance and accuracy, the attitude and magnetic field data processing unit can be configured either for real-time fusion calculation or for post-processing.

[0074] Post-processing stage: Combining installation matrix, geometric constraints and filtering algorithms, the raw magnetometer data is transformed into the ECEF coordinate system to generate a high-precision vector geomagnetic field dataset.

[0075] This embodiment proposes several technological innovations in the field of UAV airborne vector geomagnetic measurement, specifically including:

[0076] 1. Attitude measurement method for rigid structures based on multi-GNSS antenna RTK-GPS: The multi-point RTK-GPS system is applied to the tetrahedral structure, and the three-dimensional attitude of the device is obtained through multiple baseline vectors, which eliminates the dependence of traditional IMU on gravity direction and magnetic north direction.

[0077] 2. Accurate Geometric Configuration Acquired Through Long-Term Ground-Based Static Calibration: Before the device is put into use, it is continuously statically placed for over 24 hours. Static RTK calculations are then used to accurately determine the absolute positions of the phase centers of the four GNSS antennas, thus retrieving the true geometric shape of the structure. This prior geometric information serves as a constraint for subsequent dynamic attitude calculations, improving the stability and accuracy of attitude estimation.

[0078] 3. Attitude calculation algorithm based on redundant baseline and geometric constraints: By utilizing the redundancy of six sets of spatial baseline vectors constructed by four GNSS antennas, and combining the known precise geometric dimensions, attitude calculation is performed under the least squares or weighted optimization framework, which enhances the system's robustness to observation noise and other factors.

[0079] 4. Multi-sensor fusion attitude continuous estimation mechanism: The gyroscope and RTK-GPS are combined to form a MEKF (multiplicative extended Kalman filter) to achieve the fusion of low-frequency high-precision attitude and high-frequency angular velocity data, and output a continuous attitude sequence with high time resolution to meet the high requirements of vector magnetic measurement for synchronization.

[0080] 5. Coordinate system alignment method for magnetometer and GPS attitude system: A multi-sensor collaborative calibration method including RTK-GPS attitude measurement device, gyroscope and vector magnetometer is proposed to accurately calibrate the installation matrix between the fluxgate magnetometer coordinate system and the structural coordinate system defined by the RTK-GPS attitude measurement system, so as to ensure that there is no systematic deviation in the final magnetic field vector transformation.

[0081] 6. Aerodynamically Stabilized Suspension Structure with Tail Wing: A non-magnetic tail wing is added to the bottom of the tetrahedron to suppress random swaying and rotation during flight using the air damping effect, thereby improving the natural stability of the device in the suspended state and contributing to the convergence of the attitude system and the improvement of data quality.

[0082] Alternative embodiments:

[0083] 1. The tetrahedral structure can be replaced with other rigid structures. Theoretically, three-dimensional attitude calculation can be achieved as long as there are no fewer than three non-collinear GNSS antennas.

[0084] 2. Data fusion filters can use particle filtering, complementary filtering, or deep learning models to replace Kalman filtering in order to adapt to complex dynamic environments.

[0085] 3. The magnetometer can be replaced with other types of vector magnetic sensors (such as AMR and GMR magnetic sensors).

[0086] 4. Four GNSS antennas require high-performance RTK-GPS receivers. Alternatively, two dual-GNSS antenna RTK-GPS receivers or four single-GNSS antenna RTK-GPS receivers can be used, but the performance will be reduced accordingly.

[0087] 5. Depending on the different requirements of the task for real-time performance and accuracy, the attitude and magnetic field data processing unit can be configured as a real-time fusion solution mode or as a post-processing mode.

[0088] The present invention will be further described below with reference to a specific embodiment, but the present invention is not limited to this embodiment.

[0089] Example: UAV-mounted vector geomagnetic measurement device based on four-point RTK-GPS

[0090] See appendix Figure 1 This embodiment provides a vector geomagnetic field measurement device for an unmanned aerial vehicle (UAV) platform, mainly including: a rigid support structure, a distributed RTK-GPSGNSS antenna system, an inertial measurement unit (IMU), a three-axis vector magnetometer, a data acquisition and processing module, a non-magnetic suspension cable, and an aerodynamically stabilized tail fin. The IMU is placed inside the three-axis vector magnetometer, such as the Twinleaf VMR high-precision vector magnetometer. Therefore, the IMU and the three-axis vector magnetometer are in the same position in the same group, and there is no need to consider the rotation matrix calibration between the coordinate system of the vector magnetometer and the coordinate system of the IMU.

[0091] The rigid support structure is a spatial tetrahedral frame made of carbon fiber composite material, with the four vertices connected to carbon fiber tubing via non-magnetic joints. The tetrahedron has three base sides of 1.5m in length and three lateral sides of 2.0m in length to enhance the geometric sensitivity of attitude calculations in the vertical direction. The entire structure weighs approximately 1kg and possesses good rigidity and wind resistance.

[0092] A high-precision GPS / GNSS antenna is installed at each of the four vertices of the tetrahedron, with the phase center of the GNSS antenna located at each vertex. These antennas are connected to a dual-frequency GPS receiver module via low-noise feed lines. Each receiver module supports L1 / L2 / L5 band signal reception and has carrier phase output capability. In RTK mode, it can achieve sub-centimeter relative positioning accuracy (horizontal ≤1cm, elevation ≤2cm), with a data update frequency of 1Hz.

[0093] Before putting the device into use, place it in an open, unobstructed location and keep it stationary for more than 24 hours. Figure 3As shown. During this period, the GNSS receiving module continuously collects observation data to accurately determine the absolute coordinates of the phase centers of the four GNSS antennas in the ECEF coordinate system. Based on these coordinates, the actual geometric configuration of the tetrahedron is derived, including parameters such as the length of each side and the included angle, which serve as the prior geometric constraints for subsequent dynamic attitude calculations.

[0094] With the tetrahedral rigid support structure at rest, a REF reference coordinate system is constructed based on the GNSS antenna array. Assume the phase centers of the four GNSS antennas are located at points A, B, C, and D, respectively. The three base vertices of the tetrahedron can be designated as A, B, and C, and the top vertex as D. Baseline vectors between adjacent points in the geocentric-fixed coordinate system can be obtained through baseline measurements. For example, the baseline vectors between points A and B are: First Baseline Vector AB; between points A and C: Second Baseline Vector AC; between points A and D: Third Baseline Vector AD; between points B and C: Fourth Baseline Vector BC; between points B and D: Fifth Baseline Vector BD; and between points C and D: Sixth Baseline Vector CD. These six baselines represent the attitude of the tetrahedral rigid support structure in the geocentric-fixed coordinate system. It is worth noting that the three-axis vector magnetometer is fixed to a tetrahedral rigid support structure. Therefore, the coordinate system of the three-axis vector magnetometer and the coordinate system of the tetrahedral rigid support structure have a fixed rotational relationship, obtained through calibration. A REF reference coordinate system is constructed using the first baseline vector AB and the second baseline vector AC: the X-axis of the coordinate system is aligned with the direction of the first baseline vector AB, the Z-axis points in the direction of the cross product of the first baseline vector AB and the second baseline vector AC, and the Y-axis forms a right-handed system with the X-axis and Z-axis.

[0095] Since the REF reference coordinate system is constructed based on these baseline vectors, the coordinates of these points (point A, point B, point C, point D) and the baseline vectors (AB, AC, AD, BC, BD, CD) in the REF reference coordinate system are known.

[0096] A three-axis vector magnetometer is installed inside the tetrahedron near the center of gravity. The three axes of the magnetometer are orthogonally arranged, and the sensitivity is 300 pT / Hz. 1 / 2 The measurement range is ±1 Gauss, and the sampling rate is set to 50Hz. This magnetometer incorporates a gyroscope and accelerometer. The gyroscope's angular velocity measurement range is ±500° / s, and its zero-bias stability is better than 0.1° / h. The magnetometer is fixed using a non-magnetic bracket, away from metal connectors and cable routing areas to reduce structural residual magnetism and eddy current interference.

[0097] The GPS receiver module and the three-axis vector magnetometer are connected to an embedded data acquisition system. All sensor data are acquired and marked with a unified time base (PPS pulse synchronization) to ensure time alignment accuracy better than 1ms.

[0098] The attitude calculation process is as follows:

[0099] During the ground-based joint calibration and flight measurement phases, i.e., under the motion state of the tetrahedral rigid support structure, the coordinates of these baseline vectors (AB, AC, AD, BC, BD, CD) in the geocentric-ground-fixed coordinate system are measured in real time. Combined with the coordinates of these baseline vectors obtained during the ground static calibration phase in the REF reference coordinate system, the attitude of the REF reference coordinate system relative to the geocentric-ground-fixed coordinate system can be calculated in real time. Specifically, based on RTK-GNSS measurements, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the ECEF coordinate system can be obtained: First ECEF baseline vector... Second ECEF baseline vector Third ECEF baseline vector Fourth ECEF baseline vector Fifth ECEF baseline vector and the sixth ECEF baseline vector .

[0100] Based on the constructed REF reference coordinate system and the precisely measured geometric configuration of the four GNSS antennas, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the REF reference coordinate system are obtained: First REF baseline vector Second REF baseline vector Third REF baseline vector Fourth REF baseline vector Fifth REF baseline vector , Sixth REF baseline vector .

[0101] Solving for the pose of the REF reference coordinate system relative to the ECEF coordinate system involves finding the optimal rotation matrix. , so that:

[0102]

[0103] in, This represents a group consisting of three-dimensional rotation matrices. This indicates that the second rotation matrix belongs to the group consisting of three-dimensional rotation matrices. These are constraint symbols. This indicates that the constraints are met. In the case where the second rotation matrix minimizes the sum of squared residuals for all vector pairs, the second rotation matrix is ​​the optimal second rotation matrix. .

[0104] Attitude filtering:

[0105] The attitude is used as an observation input to a multiplicative Kalman filter (MEKF), which is fused with the integral result of the gyroscope angular velocity to output a continuous attitude quaternion sequence with a frequency of 50 Hz, while simultaneously estimating the gyroscope drift.

[0106] During the ground calibration phase, the entire device is fixed at, for example... Figure 4 Calibration experiments were conducted on a non-magnetic turntable in an open environment free from magnetic interference and obstructions. The turntable was fixed in a first orientation A by adjusting the lead screw, and the turntable disk was slowly and uniformly rotated around the axis (angular velocity < 5° / s). The attitude, gyroscope data, and magnetometer output calculated by RTK-GPS were recorded simultaneously. Using the attitude, gyroscope angular velocity vector, and magnetic field vector measurements, the coordinates of the first rotation axis a in various coordinate systems were obtained. The lead screw was adjusted to obtain a second orientation, and the above measurements were repeated to obtain the coordinates of the second rotation axis b in various coordinate systems. The lead screw was adjusted to obtain a third orientation C, and the above measurements were repeated to obtain the coordinates of the third rotation axis c in various coordinate systems. Then, classical algorithms such as TRIAD or QUEST were used to obtain the rotation matrices from the gyroscope coordinate system to the attitude coordinate system, and from the magnetometer coordinate system to the attitude coordinate system.

[0107] During flight operations, the device is suspended below the octagonal drone by an 8-meter-long non-magnetic cable. One end of the cable is connected to the vertex of the tetrahedron, and the other end is fixed to the center of the drone's fuselage. A stabilizing tail fin with a wingspan of approximately 40cm is installed at the rear of the bottom of the tetrahedron to provide air damping and suppress swaying and spinning during flight.

[0108] The UAV carrying the device flies along a preset route within the target area at an altitude of 10–50 m above the ground and a speed of 10–15 m / s. The system collects multi-source data in real time and, in post-processing, transforms the raw magnetometer output to the ECEF coordinate system (e.g., using an installation matrix and real-time attitude conversion). Figure 2 As shown in the figure, a high-precision vector geomagnetic dataset containing time, position, attitude, and three-dimensional magnetic field components is generated.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A device for measuring vector geomagnetic fields using a drone, characterized in that, include: A tetrahedral rigid support structure made of non-magnetic material, consisting of one vertex and three base points; Four GNSS antennas are respectively installed at the apex and three base points of the tetrahedral rigid support structure to form an RTK-GNSS multi-antenna system, which is used to obtain low-frequency attitude measurement data of the tetrahedral rigid support structure in the geocentric coordinate system. A GNSS receiver, mounted on the tetrahedral rigid support structure, is used to receive observation data from the RTK-GNSS multi-antenna system. The sensor unit, mounted on the tetrahedral rigid support structure, integrates a vector magnetic sensor and an inertial measurement unit, wherein: The vector magnetic sensor is used to collect triaxial magnetic field data of the Earth's magnetic field in the coordinate system of the magnetometer. The inertial measurement unit is used to collect high-frequency angular velocity measurement data of the tetrahedral rigid support structure in the magnetometer coordinate system; The drone is used to move the tetrahedral rigid support structure during the flight measurement phase; The connecting component is connected at one end to the UAV and at the other end to the vertex of the tetrahedral rigid support structure. The calibration system is used to construct a tetrahedral rigid support structure coordinate system as the REF reference coordinate system during the ground calibration stage, and to determine the first rotation matrix between the magnetometer coordinate system and the REF reference coordinate system. The attitude and magnetic field data processing unit, connected to the GNSS receiver and sensor unit, is used during the flight measurement phase for: By integrating the low-frequency attitude measurement data and the high-frequency angular velocity measurement data, the high-frequency attitude information of the tetrahedral rigid support structure in the geocentric-ground-fixed coordinate system is obtained. Based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the directions of all baseline vectors in the geocentric-ground-fixed coordinate system are calculated, and the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system is obtained. Based on the first rotation matrix, the three-axis geomagnetic field data in the magnetometer coordinate system is transformed to the reference coordinate system, and then based on the second rotation matrix, the three-axis geomagnetic field data in the reference coordinate system is transformed to the geocentric-geo-fixed coordinate system, thereby obtaining high-frequency three-axis geomagnetic field data in the geocentric-geo-fixed coordinate system.

2. The device for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 1, characterized in that, The tetrahedral rigid support structure is a symmetrical structure.

3. The device for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 2, characterized in that, The rigid support structure is a spatial tetrahedral frame, including three base sides and three side sides; a GNSS antenna is installed at each of the four corners of the spatial tetrahedral frame, and the sensor unit is installed at the center of gravity of the spatial tetrahedral frame; the length of each base side of the spatial tetrahedral frame is greater than or equal to 1.5 meters, and the length of each side side of the spatial tetrahedral frame is greater than or equal to 2.0 meters.

4. The device for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 1, characterized in that, The four GNSS antennas are connected to the same GNSS receiver, which supports real-time dynamic differential positioning technology; the inertial measurement unit includes a gyroscope.

5. The device for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 1, characterized in that, It also includes a non-magnetic tail fin device, which is installed at the bottom of the tetrahedral rigid support structure or behind the center of gravity to provide air damping to suppress the random swaying and rotation of the tetrahedral rigid support structure during flight and improve measurement stability; the connecting component includes a flexible non-magnetic cable.

6. A method for measuring vector geomagnetic fields using a drone, implemented based on the apparatus for measuring vector geomagnetic fields using a drone as described in any one of claims 1-5, characterized in that, include: Installation phase: Install the four GNSS antennas, GNSS receiver, sensor unit, and attitude and magnetic field data processing unit onto the tetrahedral rigid support structure; Ground calibration stage: Construct a tetrahedral rigid support structure coordinate system as the REF reference coordinate system, and determine the first rotation matrix between the magnetometer coordinate system and the reference coordinate system; Flight measurement phase: The UAV is installed at the apex of the tetrahedral rigid support structure via connecting components, which is used to drive the tetrahedral rigid support structure to move during the flight measurement phase; Low-frequency attitude measurement data of the tetrahedral rigid support structure in the geocentric-ground-fixed coordinate system is obtained through four GNSS antennas and transmitted to the attitude and magnetic field data processing unit via a GNSS receiver. Three-axis magnetic field data of the geomagnetic field in the magnetometer coordinate system are collected by a vector magnetic sensor, and high-frequency angular velocity measurement data of the tetrahedral rigid support structure in the magnetometer coordinate system are collected by an inertial measurement unit and transmitted to the attitude and magnetic field data processing unit. The attitude and magnetic field data processing unit fuses the low-frequency attitude measurement data and the high-frequency angular velocity measurement data of the tetrahedral rigid support structure to obtain high-frequency attitude information of the REF reference coordinate system in the geocentric-ground-fixed coordinate system. Based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the directions of all baseline vectors in the geocentric-ground-fixed coordinate system are calculated, and the second rotation matrix between the REF reference coordinate system and the geocentric-ground-fixed coordinate system is obtained. Based on the first rotation matrix, the three-axis geomagnetic field data in the magnetometer coordinate system is transformed to the reference coordinate system, and then based on the second rotation matrix, the three-axis geomagnetic field data in the reference coordinate system is transformed to the geocentric-geo-fixed coordinate system, thereby obtaining high-frequency three-axis geomagnetic field data in the geocentric-geo-fixed coordinate system.

7. The method for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 6, characterized in that, The ground calibration phase specifically includes: Ground static calibration phase: Measure the six baseline vectors between the four GNSS antennas, determine the geometric configuration of the tetrahedron formed by the phase center points of the four GNSS antennas, construct the tetrahedron rigid support structure coordinate system as the REF reference coordinate system, and obtain the coordinates of the six baseline vectors of the four GNSS antenna arrays in the REF reference coordinate system. Ground-based joint calibration phase: The tetrahedral rigid support structure is fixed on a non-magnetic turntable. The non-magnetic turntable is rotated at a constant speed. Using low-frequency attitude measurement data of the tetrahedral rigid support structure in the geocentric-ground coordinate system measured by the RTK-GNSS multi-antenna system and the three-axis magnetic field data of the geomagnetic field in the magnetometer coordinate system measured by the vector magnetic sensor, the coordinates of the rotation axis of the non-magnetic turntable in the REF reference coordinate system and the vector in the magnetometer coordinate system are calculated. The attitude of the non-magnetic turntable is changed and the rotation measurement process is repeated to obtain the coordinates of the rotation axis of at least two non-collinear non-magnetic turntables in the REF reference coordinate system and the vector in the magnetometer coordinate system. The first rotation matrix between the REF reference coordinate system and the magnetometer coordinate system is solved using the TRIAD algorithm or SVD algorithm.

8. The method for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 7, characterized in that, The process of constructing the coordinate system of the tetrahedral rigid support structure includes: In the static state of the tetrahedral rigid support structure, the points where the phase centers of the four GNSS antennas are located are denoted as points A, B, C, and D, respectively, where point D is the vertex and points A, B, and C are the base points. Based on baseline measurements, the baseline vectors between adjacent points in the geocentric geofixed coordinate system are obtained, including: the first baseline vector AB between points A and B, the second baseline vector AC between points A and C, the third baseline vector AD between points A and D, the fourth baseline vector BC between points B and C, the fifth baseline vector BD between points B and D, and the sixth baseline vector CD between points C and D. Construct a REF reference coordinate system using the first baseline vector AB and the second baseline vector AC: let the X-axis of the REF reference coordinate system coincide with the direction of the first baseline vector AB, let the Z-axis of the REF reference coordinate system point to the cross product direction of the first baseline vector AB and the second baseline vector AC, and let the Y-axis of the REF reference coordinate system form a right-handed system with the X-axis and Z-axis.

9. The method for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 8, characterized in that, The process of calculating the directions of all baseline vectors in the geocentric-fixed coordinate system based on the real-time coordinates of the four GNSS antennas in the geocentric-fixed coordinate system, and obtaining the second rotation matrix between the REF reference coordinate system and the geocentric-fixed coordinate system includes: Under the motion state of the tetrahedral rigid support structure, based on the real-time coordinates of the four GNSS antennas in the geocentric-ground-fixed coordinate system, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the geocentric-ground-fixed coordinate system are obtained: First ECEF baseline vector Second ECEF baseline vector Third ECEF baseline vector Fourth ECEF baseline vector Fifth ECEF baseline vector and the sixth ECEF baseline vector ; Based on the REF reference coordinate system and the first rotation matrix, the corresponding representations of the first baseline vector AB, the second baseline vector AC, the third baseline vector AD, the fourth baseline vector BC, the fifth baseline vector BD, and the sixth baseline vector CD in the REF reference coordinate system are obtained: First REF baseline vector Second REF baseline vector Third REF baseline vector Fourth REF baseline vector Fifth REF baseline vector and the sixth REF baseline vector ; Solve for the attitude of the REF reference coordinate system relative to the geocentric-ground-fixed coordinate system, and find the optimal second rotation matrix. : in, , This represents a group consisting of three-dimensional rotation matrices. This indicates that the second rotation matrix belongs to the group consisting of three-dimensional rotation matrices, and st indicates that the constraint condition is met. This indicates that the constraints are met. In the case where the second rotation matrix minimizes the sum of squared residuals for all vector pairs, the second rotation matrix is ​​the optimal second rotation matrix. .

10. The method for measuring vector geomagnetic field using an unmanned aerial vehicle according to claim 6, characterized in that, The feature is that it further includes: aligning the low-frequency attitude measurement data with the high-frequency angular velocity measurement data in time using a unified clock source or hardware trigger signal to avoid magnetic field data distortion caused by attitude lag.

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