Non-gimbaled magnetic pod magnetic compensation method and system

Abstract

The application discloses a kind of non-gyroscopic magnetic pod magnetic compensation method and system, comprising: S1. install non-gyroscopic pod, pod and carrier are connected by rotatable damper, three-axis magnetometer and attitude sensor are respectively installed on pod and carrier;S2. carrier makes complete magnetic compensation action in uniform, magnetic quiet area, so that three Euler angles change fully;S3. according to the measured carrier and pod Euler angle, calculate scalar magnetometer displacement;S4. according to scalar magnetometer displacement, carrier coordinate system measured geomagnetic field Heb, pod coordinate system measured geomagnetic field Hep, calculate dependent variable vector;S5. according to scalar magnetometer measured value h, pod coordinate system measured geomagnetic field Hep, calculate independent variable vector;S6. using linear fitting method obtains model coefficient;S7. calculate carrier interference magnetic field, after excluding carrier interference, obtain compensated magnetic field.The application realizes magnetic compensation in the field of magnetic detection by the model and solving method of magnetic interference compensation, reduces magnetic signal noise.

Description

Technical Field

[0001] This invention relates to the field of magnetic detection technology, specifically to a model and solution method for magnetic interference compensation, used for magnetic compensation in the field of magnetic detection to reduce magnetic signal noise. Background Technology

[0002] In airborne magnetic detection, non-strapped pod designs offer significant advantages over strapdown pods, including easier assembly, convenient takeoff and landing, and the ability to approach targets at near-limit distances due to reduced ground airflow interference, making them ideal for rapid takeoff and landing and detecting small magnetic targets on the ground. However, the inevitable swaying during movement of non-strapped pods introduces additional magnetic gradient interference from the carrier, posing significant challenges to magnetic detection signal processing and necessitating sophisticated magnetic compensation methods to mitigate this interference. Traditional airborne magnetic compensation methods are primarily based on the Tolles-Lawson (TL) model. This model categorizes the magnetic interference on the aircraft platform into a constant field, an induced field, and an eddy current field, using data from a three-axis vector magnetometer to determine the direction of the aircraft's magnetic field relative to the Earth's magnetic field, and establishing a phenomenological model to compensate for the optically pumped magnetometer measurements. However, the TL model is a strapdown model, where the scalar magnetometer's mounting position on the aircraft remains constant, making it unsuitable for magnetic compensation applications with non-strapped magnetic pods. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a magnetic compensation method and system for non-stripwire magnetic pods. Through a model and solution method for magnetic interference compensation, magnetic compensation in the field of magnetic detection is achieved, thereby reducing magnetic signal noise.

[0004] To achieve the above objectives, the present invention provides a magnetic compensation method for a non-straight-through magnetic pod, the method comprising the following steps:

[0005] S1. Install a non-strappable pod. The pod and the carrier are connected by a rotatable damper. Install a triaxial magnetometer and an attitude sensor on the pod and the carrier respectively. Align each triaxial sensor with its respective coordinate axis before starting work. The attitude sensor measures the attitude angle of the rigid body to solve for the relative attitude, that is, the rotation matrix Rr (Equation 3). The triaxial magnetometer measures the projection of the geomagnetic vector on the aircraft and the pod.

[0006] S2. The carrier performs a complete magnetic compensation maneuver in a uniform, magnetically quiet region to fully change the three Euler angles. The magnetic compensation maneuver is the Figure of Merit (FOM). The aircraft flies around the closed frame at a fixed altitude and performs three sets of maneuvers on each side: pitch, roll (left and right swaying), and sideslip (changing course). This is done to obtain magnetic interference field data under different attitudes.

[0007] S3. Calculate the scalar magnetometer displacement d based on the measured Euler angles of the carrier and pod;

[0008] S4. Calculate the dependent variable vector based on the scalar magnetometer displacement d, the geomagnetic field Heb measured in the carrier coordinate system, and the geomagnetic field Hep measured in the pod coordinate system;

[0009] S5. Calculate the independent variable vector based on the scalar magnetometer measurement value h and the geomagnetic field Hep measured in the pod coordinate system;

[0010] S6. Obtain the model coefficients using linear fitting methods;

[0011] S7. Calculate the carrier interference magnetic field, and obtain the compensated magnetic field after eliminating the carrier interference.

[0012] Furthermore, the carrier is a drone.

[0013] Furthermore, in step S2, the attitudes of the carrier and the pod are represented by Euler angles, which are defined as the three angles generated by rotating and aligning the fixed coordinate system around the z-axis, y-axis, and x-axis to the moving coordinate system.

[0014] Furthermore, the geodetic coordinate system is a fixed coordinate system x0-y0-z0, and the moving coordinate system is xyz, including the carrier coordinate system x. b -y b -z b and the pod coordinate system x p -y p -z p .

[0015] Furthermore, by adopting a z−y−x follow-through rotation around the motion axis, the geodetic coordinate system first rotates around the z-axis by α, then around the y-axis by β, and then around the x-axis by γ, finally aligning with the carrier coordinate system. At this point, the coordinate system rotation matrix R will be obtained; where α, β, and γ correspond to the three Euler angles of yaw, pitch, and roll, respectively.

[0016] Furthermore, the Euler angle of the carrier is α. b β b γ b The corresponding rotation matrix is ​​R. b The Euler angle of the pod is α. p β p γ p The corresponding rotation matrix is ​​R. p The rotation matrix of the pod relative to the carrier coordinate system is:

[0017] ;

[0018] Because the pod is vertically downward when stationary, the corresponding direction vector is the same in the geodetic coordinate system, the carrier coordinate system, and the pod coordinate system.

[0019] ;

[0020] During motion, the pod's direction vector in the carrier coordinate system is...

[0021] ;

[0022] This direction vector determines the position of the magnetometer in the pod within the carrier coordinate system; the position coordinates of the pod's swing are two-dimensional vectors, and the formula for calculating the scalar magnetometer displacement d is as follows:

[0023] ;

[0024] The distance between the scalar magnetometer in the pod and the UAV is measured in L time.

[0025] Furthermore, the signal change measured by the scalar magnetometer is the projection of the carrier's interfering magnetic field onto the Earth's magnetic field. The Earth's magnetic field measured in the pod coordinate system is H. ep The signal measured by the scalar magnetometer is

[0026] ;

[0027] The required equation is:

[0028]

[0029] The required 18 parameters are solved using fitting algorithms such as the least squares method.

[0030] On the other hand, the present invention provides a non-straight-through magnetic pod magnetic compensation system, the system being used to implement the method according to the present invention, the system comprising a drone and a pod, the drone and the pod being rotatably connected via a rotatable damping connector.

[0031] Furthermore, the drone is equipped with a carrier triaxial magnetometer and a carrier attitude sensor. The carrier triaxial magnetometer is used to accurately measure the geomagnetic field vector, and the carrier attitude sensor is used to monitor the carrier attitude.

[0032] Furthermore, a three-axis magnetometer and a pod attitude sensor are installed inside the pod. The pod includes a boom, an electronic box, and a scalar magnetometer. One end of the boom is connected to a damping connector, and the other end is connected to the electronic box. The three-axis magnetometer and the pod attitude sensor are installed in the electronic box. The scalar magnetometer is installed below the electronic box. The pod is strapped to the UAV via a rotatable damper. The distance L between the scalar magnetometer in the pod and the rotation center of the rotatable damper is 1.

[0033] Furthermore, each triaxial magnetometer and attitude sensor employs an Attitude and Bearing Reference System (AHRS).

[0034] The beneficial effects of this invention are as follows:

[0035] This invention achieves magnetic compensation in the field of magnetic detection through a model and solution method for magnetic interference compensation, effectively reducing magnetic signal noise. Taking measurement results from the Beijing area as an example, the noise on each axis of the three-axis fluxgate on the carrier and pod is 1 nT, and the noise of the attitude angle measuring equipment on the carrier and pod is 1°. The aircraft performed FOM (Forward-of-Mortar) flights with pitch ±5°, sideslip ±5°, and roll ±10°. According to the measurement results, the standard deviation of the interference magnetic field is reduced by 16 times after compensation. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of an unmanned aeromagnetic system with a non-straddlelink pod;

[0037] Figure 2 This is a schematic diagram showing the positional relationship between the magnetic pod and the carrier;

[0038] Figure 3 The diagram shows a comparison between the interfering magnetic field and the compensated magnetic field in the embodiment. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] The following combination Figures 1-3Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0043] The concept of this invention lies in extending the TL model by adding a horizontal gradient parameter. Considering that the aircraft carrier is far from the magnetometer in this invention, the eddy current term in the TL model is ignored. By monitoring the attitudes of the aircraft carrier and the pod separately, the influence of the horizontal magnetic field gradient of the carrier on the pod's oscillation is obtained through mathematical modeling, resulting in a clean target gradient field in the vertical direction.

[0044] The system structure of this invention is as follows:

[0045] like Figure 1 As shown, the non-straight-through magnetic pod magnetic compensation method according to the present invention is applied to an unmanned aeromagnetic system with a non-straight-through pod. The system includes an unmanned aerial vehicle (UAV) 1 and a pod, which are rotatably connected via a rotatable damping connector 2. The pod includes a boom 3, an electronics box 4, and a scalar magnetometer 5. One end of the boom 3 is connected to the damping connector 2, and the other end is connected to the electronics box 4. The electronics box 4 houses the pod's triaxial magnetometer and pod attitude sensors, among other electronic equipment. The scalar magnetometer 5 is mounted below the electronics box 4. The pod is strapped to the UAV 1 via the rotatable damper 2, and the distance L between the scalar magnetometer 5 and the rotation center of the rotatable damper is 1.

[0046] A three-axis magnetometer is installed on the aircraft carrier (i.e., UAV 1) to accurately measure the geomagnetic field vector. A carrier attitude sensor is also installed on the aircraft carrier to monitor its attitude, ensuring strict alignment of the coordinate axes of the three-axis magnetometer and the attitude sensor. The three-axis magnetometer detects the geomagnetic field, while the attitude sensor detects Euler angles. The coordinate system of the carrier three-axis magnetometer is the same as the aircraft coordinate system, and the projection of the geomagnetic field into this coordinate system determines the magnitude of the induced magnetic field. A scalar magnetometer 5 is installed on the pod. A pod three-axis magnetometer is housed in an electronic box 4 on the pod to accurately measure the geomagnetic field vector. A pod attitude sensor is also installed in the electronic box 4 to monitor the pod's attitude, ensuring strict alignment of the coordinate axes of the three-axis magnetometer and the attitude sensor. The direction of the geomagnetic field projection into the pod three-axis magnetometer coordinate system determines the magnitude of the magnetic field measured by the scalar magnetometer 5. The relative attitude between the carrier coordinate system and the pod coordinate system is determined by the carrier attitude sensor and the pod attitude sensor. This attitude determines the magnitude of the magnetic interference sensed by the scalar magnetometer. The triaxial magnetometer and attitude sensor in this invention preferably use a high-precision Attitude and Heading Reference System (AHRS). While the AHRS includes a triaxial magnetometer and attitude sensor, the triaxial magnetometer in the AHRS has lower accuracy and is not used to measure the Earth's magnetic field. This invention requires two triaxial magnetometers and two attitude sensors. At a comparable price, the triaxial magnetometer in the attitude sensor has lower accuracy, but it is sufficient for measuring angles. Since the Earth's magnetic field is 50,000 nT, a triaxial magnetometer with an accuracy of 100 nT can accurately measure an angle of 100 / 50,000 * 180 / 3.14 = 0.1 degrees. However, 100 nT accuracy already represents the intensity of the magnetic anomaly signal. This invention compensates for this 100 nT magnetic field; a 0.1 degree angle error only introduces a 0.5 nT compensation error. The triaxial magnetometer and the optically pumped magnetometer directly participate in the magnetic field measurement, requiring even higher accuracy. It consists of an accelerometer, a three-axis magnetometer, and a gyroscope. The AHRS's reference comes from the Earth's gravitational and magnetic fields. The sensor coordinate axes inside the AHRS are pre-aligned, and its three-axis magnetometer accuracy meets the requirements of this scheme for vector magnetometer accuracy.

[0047] The non-strap-connected magnetic pod magnetic compensation method of the present invention obtains a clean target gradient field in the vertical direction by separately monitoring the attitude of the aircraft carrier (e.g., UAV) and the pod, and mathematically modeling the effect of the horizontal magnetic field gradient of the carrier on the pod's oscillation. The non-strap-connected magnetic pod magnetic compensation method of the present invention includes the following steps:

[0048] S1. Install a non-strappable pod, with the pod and UAV connected by a rotatable damper. Install a three-axis magnetometer and an attitude sensor on the pod and UAV respectively. Align each three-axis sensor with its respective coordinate axis before starting operation. The attitude sensor is used to measure the attitude angles (i.e., Euler angles) of the rigid body, with the purpose of solving the relative attitude, i.e., the rotation matrix Rr. The three-axis magnetometer is used to measure the projection of the geomagnetic vector on the aircraft and the pod.

[0049] S2. The UAV performs a complete magnetic compensation maneuver in a uniform, magnetically quiet region, allowing the three Euler angles to change sufficiently. This invention uses the data from this step to obtain compensation coefficients for subsequent compensation. These compensation maneuvers during flight constitute FOM (Figure of Merit) flight. The magnetic compensation maneuver is FOM flight, in which the aircraft flies one revolution along a closed frame at a fixed altitude, performing three sets of maneuvers on each side: pitch, roll (left and right swaying), and sideslip (changing course), thereby acquiring magnetic interference field data under different attitudes.

[0050] S3. Based on the measured Euler angles of the carrier and pod, calculate the scalar magnetometer displacement d according to formulas 1, 3, 4, and 5;

[0051] Specifically, the measured Euler angles of the carrier are used as α. b β b γ b , α b β b γ b Replacing α, β, and γ in Formula 1, the carrier rotation matrix is ​​calculated as R. b Using the measured Euler angles of the pod as α p β p γ p , α p β p γ p Replace α, β, and γ in Formula 1 to calculate the pod rotation matrix R. p .

[0052] Using the pod rotation matrix R p and the carrier rotation matrix R b The rotation matrix R of the pod relative to the carrier coordinate system is calculated according to Formula 3. r .

[0053] Using the rotation matrix R of the pod relative to the carrier coordinate system r The displacement d of the variable magnetometer is calculated using formula 456.

[0054] S4. Based on the displacement d of the scalar magnetometer, the geomagnetic field Heb measured in the carrier coordinate system, and the geomagnetic field Hep measured in the pod coordinate system, calculate the dependent variable vector according to Formula 1.

[0055] S5. Calculate the independent variable vector based on the scalar magnetometer measurement value h and the geomagnetic field Hep measured in the pod coordinate system;

[0056] S6. According to Formula 13, obtain the model coefficients using the linear fitting method. A is an abbreviation for 18 parameters.

[0057] S7. Calculate the carrier interference magnetic field according to Formula 17, and obtain the magnetic field after eliminating carrier interference, i.e., the compensated magnetic field, according to Formula 18.

[0058] Specifically, in step S1, the pod includes a boom 3, an electronic box 4, and a scalar magnetometer 5. One end of the boom 3 is connected to a damping connector 2, and the other end is connected to the electronic box 4. The electronic box 4 houses the pod's triaxial magnetometer and attitude sensors, among other electronic equipment. The scalar magnetometer 5 is installed below the electronic box 4. The pod is strapped to the UAV 1 via a rotatable damper 2. The distance L between the scalar magnetometer 5 and the rotation center of the rotatable damper in the pod is [missing information].

[0059] In step S2, the attitudes of the carrier (body, such as a drone) and the pod are represented by Euler angles, which are defined as three angles generated by rotating and aligning the fixed coordinate system (geocentric coordinate system) around the z-axis, y-axis, and x-axis to the moving coordinate system.

[0060] In step S3, the specific implementation process for calculating the scalar magnetometer displacement d is as follows:

[0061] Transformations between two Cartesian coordinate systems can be linked using a coordinate system rotation matrix, which can be represented by three Euler angles. For example... Figure 2 As shown, the geodetic coordinate system is defined as a fixed coordinate system x0-y0-z0, and the moving coordinate system is xyz, including the carrier coordinate system z. b -y b -z b and the pod coordinate system x p -y p -z p .take Following the direction of motion and rotating around the axis of motion, the geodetic coordinate system first rotates by α around the z-axis, then by β around the y-axis, and then by γ around the x-axis, finally aligning with the carrier coordinate system. This yields the coordinate system rotation matrix R. Here, α, β, and γ correspond to the three Euler angles: yaw, pitch, and roll, respectively. The final rotation matrix R is:

[0062] ;

[0063] The Euler angle of the carrier is α b β b γ b The corresponding rotation matrix is ​​R.b The Euler angle of the pod is α. p β p γ p The corresponding rotation matrix is ​​R. p The rotation matrix of the pod relative to the carrier coordinate system is:

[0064] ;

[0065] Because the pod is vertically downward when stationary, the corresponding direction vector is the same in the geodetic coordinate system, the carrier coordinate system, and the pod coordinate system:

[0066] ;

[0067] It is the direction vector of the pod when it is stationary.

[0068] During motion, the direction vector of the pod in the carrier coordinate system is:

[0069] ;

[0070] n is the direction vector of the pod relative to the aircraft during its motion.

[0071] This direction vector determines the position of the magnetometer in the pod within the carrier coordinate system. Assuming the pod's swing angle is small, the z-coordinate remains almost constant, with only the x and y coordinates changing. The position coordinates are approximated as a two-dimensional vector. The formula for calculating the scalar magnetometer displacement d is as follows:

[0072] ;

[0073] Where L is the distance between the scalar magnetometer in the pod and the UAV. d1 and d2 are the horizontal components of displacement d.

[0074] In step S6, the model coefficients are obtained using a linear fitting method, specifically as follows:

[0075] The TL model without eddy current magnetic fields is as follows:

[0076] ;

[0077] Wherein, H1 is a constant field and H2 is an induced field. M is the geomagnetic field measured in the carrier coordinate system, and M is the magnetic induction tensor, which is a 3x3 matrix. H is the interference magnetic field of the aircraft.

[0078] Performing a Taylor expansion on H1 at the pod's equilibrium position, we obtain:

[0079] ;

[0080] in, G is a fixed vector with 3*1 parameters; G is a first-order tensor, represented by a 3*2 matrix, which is the gradient constant of the constant field; the displacement d of the scalar magnetometer is a 2*1 vector, which is the position of the scalar magnetometer in the xy plane of the carrier coordinate system.

[0081] Written in matrix form:

[0082] ;

[0083] Because the induced field is relatively weak, the induced magnetic field H2 can be kept constant. Equation 9 is an expansion of Equation 8, where a, b, and c correspond to... , - Corresponding to G. a, b, and c are the three components of the constant disturbance magnetic field. - Let be the partial derivatives of the three components of the constant disturbing magnetic field in the x and y directions. , The displacement of the optically pumped magnetometer in the xy-axis direction caused by vibration.

[0084] ;

[0085] Equation 10 is the expansion of H2 in Equation 7, and m1-m9 are the M matrix in Equation 7. , , Corresponding to formula 7 . , , It refers to the three axes of a three-axis fluxgate magnetometer, which are the xyz axes of the magnetometer.

[0086] Since the signal change measured by the scalar magnetometer is the projection of the carrier's interfering magnetic field onto the Earth's magnetic field, it is assumed that the Earth's magnetic field measured in the pod coordinate system is... The signal measured by the scalar magnetometer is:

[0087] ;

[0088] The final equation is:

[0089] ;

[0090] The required 18 parameters can be solved using fitting algorithms such as the least squares method. The formula above can be simplified as follows:

[0091] ;

[0092] Where Y is the dependent variable, X is the independent variable, and A is the coefficient. The solution is to solve for the coefficient A. X is calculated based on the measured values, and the calculation methods are Formula 14 and Formula 16.

[0093] ;

[0094] A represents the coefficients to be fitted.

[0095]

[0096] After obtaining the coefficient A through linear fitting, the interference magnetic field is calculated according to Formula 17:

[0097] ;

[0098] The actual magnetic field is calculated using formula 18:

[0099] ;

[0100] Taking the measurement results from the Beijing area as an example, the noise level on each axis of the three-axis fluxgate on the carrier and pod is 1 nT, and the noise level of the attitude angle measurement equipment on the carrier and pod is 1°. The aircraft performed FOM (Forward Motion) flights with pitch ±5°, sideslip ±5°, and roll ±10° respectively. Based on the measurement results, the interfering magnetic field and the compensated magnetic field are as follows: Figure 3 As shown, the standard deviation of the interference magnetic field is reduced by 16 times after compensation.

[0101] Any process or method described in the flowcharts of this invention or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, which can be implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device. The computer-readable medium can be any medium containing a program for storage, communication, propagation, or transmission for use by the execution system, apparatus, or device, including read-only memory, magnetic disks, or optical disks.

[0102] In the description of this specification, references to terms such as "embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, those skilled in the art can combine or combine the different embodiments or examples described in this specification and the features therein without causing contradiction.

[0103] While embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and alterations to the above embodiments within the scope of the present invention.

Claims

1. A magnetic compensation method for a non-straight-through magnetic pod, characterized in that, The method includes the following steps: S1. Install a non-strappable pod. The pod and the carrier are connected by a rotatable damper. Install a triaxial magnetometer and an attitude sensor on the pod and the carrier respectively. Align each triaxial sensor with its respective coordinate axis before starting work. S2. The carrier performs a complete magnetic compensation operation in a uniform, magnetically quiet region, allowing the three Euler angles to change fully; S3. Calculate the scalar magnetometer displacement d based on the measured Euler angles of the carrier and pod; S4. Calculate the dependent variable vector based on the scalar magnetometer displacement d, the geomagnetic field Heb measured in the carrier coordinate system, and the geomagnetic field Hep measured in the pod coordinate system; S5. Calculate the independent variable vector based on the scalar magnetometer measurement value h and the geomagnetic field Hep measured in the pod coordinate system; S6. Obtain the model coefficients using linear fitting methods; S7. Calculate the carrier interference magnetic field, and obtain the compensated magnetic field after eliminating the carrier interference.

2. The magnetic compensation method for a non-straight-through magnetic pod according to claim 1, characterized in that, The carrier is an unmanned aerial vehicle (UAV).

3. The magnetic compensation method for a non-straight-through magnetic pod according to claim 1, characterized in that, In step S2, the attitudes of the carrier and the pod are represented by Euler angles. Euler angles are defined as the three angles generated when the fixed coordinate system is rotated and aligned with the moving coordinate system around the z-axis, y-axis, and x-axis respectively. The fixed coordinate system is x0-y0-z0, the moving coordinate system is x-y-z, including the carrier coordinate system x b -y b -z b and the pod coordinate system x p -y p -z p ; adopt z-y-x order and rotate around the motion axis.

4. The magnetic compensation method for a non-straight-through magnetic pod according to claim 3, characterized in that, The geodetic coordinate system is first rotated around the z-axis by α, then around the y-axis by β, and then around the x-axis by γ, finally aligning with the carrier coordinate system. This gives us the coordinate system rotation matrix R, where α, β, and γ correspond to the three Euler angles of yaw, pitch, and roll, respectively.

5. The magnetic compensation method for a non-straight-through magnetic pod according to claim 4, characterized in that, The Euler angle of the carrier is α b β b γ b The corresponding carrier rotation matrix is ​​R. b The Euler angle of the pod is α. p β p γ p The corresponding pod rotation matrix is ​​R. p According to the carrier rotation matrix R b and pod rotation matrix R p Calculate the rotation matrix of the pod relative to the carrier coordinate system. And the displacement d of the scalar magnetometer is calculated.

6. The magnetic compensation method for a non-straight-through magnetic pod according to claim 5, characterized in that, The signal change measured by the scalar magnetometer is the projection of the carrier interference magnetic field onto the Earth's magnetic field. The Earth's magnetic field measured in the pod coordinate system is H. ep Based on the signal h measured by the scalar magnetometer, the 18 required parameters are obtained by using the least squares method.

7. A non-straight-through magnetic pod magnetic compensation system, characterized in that, The system is used to implement the method according to any one of claims 1-6, the system comprising a drone and a pod, the drone and the pod being rotatably connected via a rotatable damping connector.

8. The non-straight-through magnetic pod magnetic compensation system according to claim 7, characterized in that, The drone is equipped with a carrier triaxial magnetometer and a carrier attitude sensor. The carrier triaxial magnetometer is used to accurately measure the geomagnetic field vector, and the carrier attitude sensor is used to monitor the carrier attitude.

9. The non-straight-through magnetic pod magnetic compensation system according to claim 8, characterized in that, The pod is equipped with a three-axis magnetometer and an attitude sensor. The pod includes a boom, an electronic box, and a scalar magnetometer. One end of the boom is connected to a damping connector, and the other end is connected to the electronic box. The electronic box houses the three-axis magnetometer and the attitude sensor. The scalar magnetometer is installed below the electronic box. The pod is strapped to the UAV via a rotatable damper. The distance L between the scalar magnetometer in the pod and the rotation center of the rotatable damper is 1.

10. The non-straight-through magnetic pod magnetic compensation system according to claim 9, characterized in that, Each triaxial magnetometer and attitude sensor uses an attitude reference system (AHRS).

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