Error calibration method for aerial superconducting full-tensor magnetic gradient detection system

Abstract

The application belongs to an error calibration method of an aerial superconducting full tensor magnetic gradient detection system, aims to calibrate error parameters of the aerial superconducting full tensor magnetic gradient detection system, and realizes fine detection of the aerial superconducting full tensor magnetic gradient. A controllable standard magnetic field is generated by adopting a ground laid calibration coil through current, magnetic field components and full tensor magnetic gradient values in space at any position are calculated, flight height and adjustable excitation current are changed, and detection effects of the aerial superconducting full tensor receiving system are analyzed. Firstly, the environmental background magnetic field of the measurement experiment site under the condition of no excitation is measured, and the optimal flight height is found; according to the measured background magnetic field data of the calibration coil experiment area, the system error and the environmental background field and magnetic interference are removed, the known magnetic field components and full tensor magnetic gradient values are fitted, the validity of error correction parameters under the dynamic measurement of the system is verified, and the problem of low fine detection precision of the superconducting full tensor magnetic gradient is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aeromagnetic surveying, in particular to an error calibration method for an airborne superconducting full-tensor magnetic gradient detection system. BACKGROUND

[0002] A superconducting quantum interference device (SQUID) can effectively sense extremely weak magnetic signals of the order of fT and is one of the most sensitive magnetic sensors currently known. An airborne superconducting full-tensor magnetic gradient detection system based on a SQUID can effectively observe the gradient change of a geomagnetic vector field, thereby obtaining more abundant magnetic anomaly information, improving the resolution and positioning accuracy of magnetic anomaly body detection, reducing the multi-solution in inversion, and having obvious advantages in magnetic anomaly interpretation. With the sensing sensitivity of the order of fT of the SQUID, the airborne superconducting full-tensor magnetic gradient system has the ability of large-area rapid and refined surveying and has become an important development direction of international geophysical exploration equipment.

[0003] There are various errors in the dynamic measurement of the airborne superconducting full-tensor magnetic gradient detection system, such as system errors (probe non-orthogonal error, sensitivity error, zero offset error), magnetic interference, etc., which will seriously reduce the magnetic anomaly resolution of the detection system and the accuracy of data interpretation. Generally, the airborne superconducting full-tensor magnetic gradient system uses a calibration flight experiment to obtain error parameters to realize effective error correction. Due to the particularity of the air environment, the background geomagnetic vector gradient field in the calibration flight experiment area cannot be directly measured, and there is a lack of effective calibration benchmarks to evaluate the effectiveness of the error correction parameters. SUMMARY

[0004] The technical problem to be solved by the present application is to provide an error calibration method for an airborne superconducting full-tensor magnetic gradient detection system, which verifies the effectiveness of the error correction parameters in the dynamic measurement of the airborne superconducting full-tensor magnetic gradient detection system.

[0005] The present application is implemented in the following way,

[0006] An error calibration method for an airborne superconducting full-tensor magnetic gradient detection system, the method comprising:

[0007] 1) Selecting an experimental site, the experimental site being selected in an area with stable geomagnetic environment and no obvious magnetic interference objects around;

[0008] 2) Measuring the background geomagnetic vector gradient field of the experimental area by a helicopter carrying the superconducting full-tensor magnetic gradient detection system, taking 20-meter height difference as a step, measuring the background geomagnetic vector gradient field at different heights of 200-300 meters respectively, and finding an optimal flight height range;

[0009] 3) Under no incentive conditions, the helicopter-mounted superconducting full-tensor magnetic gradient detection system flies repeatedly at the same height, and the aircraft attitude and orientation are determined by the strapdown inertial navigation system;

[0010] 4) A square calibration coil is laid on the experimental site, and a standard magnetic gradient field is generated by exciting it with a 10A-100A adjustable current. The current collection device synchronously records the exciting current, and calculates the vector magnetic gradient field strength excited in the experimental area;

[0011] 5) On the basis of step 4), adjust the flight height of the aerial superconducting full-tensor magnetic gradient detection system, and measure the vector magnetic gradient field strength excited by the calibration coil at different flight heights;

[0012] 6) The data measured in steps 2), 3), 4), and 5) are input into the data quality evaluation system to remove background field information; the theoretical calculation values of the magnetic field components and the magnetic gradient at any position in space under the constant current excitation of the square calibration coil are calculated through theoretical calculation, and the theoretical calculation values, system errors, and measured data are fitted through a fitting equation to verify the system error correction parameters and calculate the system detection resolution.

[0013] Further:

[0014] The calculation of the theoretical value of the magnetic field component at any position in space in step 6) is as follows:

[0015] The expression of the three-component magnetic field generated by the calibration coil under constant current excitation in three-dimensional space is:

[0016]

[0017]

[0018]

[0019] In formulas (1), (2), and (3), l is the half side length of the calibration coil, μ0 is the magnetic permeability, I is the emission current of the calibration coil, and x, y, and z can be any position in space.

[0020] Further:

[0021] The calculation of the theoretical value of the magnetic gradient in step 6) is as follows:

[0022] From Maxwell's equations, the curl and divergence of the magnetic vector field in free space are both 0, i.e.:

[0023]

[0024]

[0025] From formula (4), G xy = Gyx , G xz = G zx , G yz = G zy ; from equation (5): G zz = -G xx -G yy ; partial derivative of equation (1), (2), (3) with respect to x, y, z respectively, 5 independent components of 9 components of magnetic gradient tensor T are: xx , G yy , G xy , G xz , G yz

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] Further:

[0032] The ground part of the aerial superconducting full tensor magnetic gradient detection system comprises a square calibration coil, a calibration coil signal recording device, a data quality evaluation system, a constant current transmitting device, and a transmitter GPS synchronization unit; wherein the constant current transmitting device transmits excitation current to the square calibration coil, and the transmitting current is recorded by the calibration coil signal recording device and input to the data quality evaluation system;

[0033] The aerial part of the aerial superconducting full tensor magnetic gradient detection system receives signals through the SQUID receiving system carried by the helicopter, and then transmits the signals to the full tensor receiver; the full tensor receiver receives auxiliary parameters measured by the auxiliary parameter measurement unit, and synchronizes with the transmitter GPS synchronization unit of the ground system through the receiving system GPS synchronization unit.

[0034] Further:

[0035] The auxiliary parameter measurement unit comprises an inertial navigation system, which is composed of an inertial measurement unit and a calculation unit; an accelerometer, which measures the acceleration of the object in the direction of motion; a gyroscope, which measures the angular velocity of the system to obtain the direction information of the system; an attitude calculation unit, which converts the inertial navigation system data from the coordinate system of itself to the coordinate system of the earth; an acceleration integration unit and an error compensation unit, which correct the flight attitude and obtain the accurate position information of the aircraft during flight.

[0036] Further:​

[0037] The calibration coil signal recording device selects a closed loop Hall current sensor, the number of turns is 1:500, the response time is less than 1 mu s, and the measurement resistance P M The output voltage is linearly related to the detection current, and the calibration coil current is observed from the voltage signal;

[0038] The 24-bit AD acquisition circuit imports the collected data into the memory of the single-chip microcomputer, and after the sampling is completed, the data in the memory is stored in the SD card for storage, and the analog part and the digital part are independently powered by an isolation power supply.

[0039] Compared with the prior art, the present application has the beneficial effects that:

[0040] The error parameter calibration method of the aerial superconducting full tensor magnetic gradient detection system calculates the magnetic field component and the full tensor magnetic gradient value at any position in space from the known first field value of the emission parameter, removes the system error from the system measured data, and performs fitting to calibrate the error parameters of the aerial superconducting full tensor magnetic gradient detection system; through analyzing the response detection effects of different flight altitudes and multiple emission current values, the working parameters of the detection system can be optimized, the reliability and accuracy of the detection data can be effectively improved, the interpretation and identification of underground anomaly body targets in practical applications are promoted, and the application of the time domain aerial superconducting full tensor magnetic gradient detection system in the field of aerial survey is promoted. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The aerial superconducting full tensor magnetic gradient detection system error calibration method provided by the embodiment of the present application is based on the structural block diagram of the detection system;

[0042] Figure 2 The calibration coil signal recording device structural block diagram in the present application is shown in FIG. 1. Figure 1

[0043] The constant current emission device structural block diagram in the present application is shown in FIG. 3. Figure 3 Figure 1 The data quality evaluation system flowchart in the present application is shown in FIG. 5.

[0044] Figure 4 Figure 1 The aerial superconducting full tensor magnetic gradient detection system error parameter calibration flowchart is shown in FIG. 6.

[0045] Figure 5 The aerial superconducting full tensor magnetic gradient detection system calibration coil side length L=100 m, I=50 A, flight height z=200 m and z=250 m, and the magnetic gradient full tensor theoretical value calculation can generate a pT / m order of magnitude magnetic gradient value.

[0046] Figure 6 The aerial superconducting full tensor magnetic gradient detection system calibration coil side length L=100 m, I=50 A, flight height z=200 m and z=250 m, and the magnetic gradient full tensor theoretical value calculation can generate a pT / m order of magnitude magnetic gradient value. DETAILED DESCRIPTION​​

[0047] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0048] Referring to Figure 1 In combination Figure 4 And Figure 5 A calibration method of an aerial superconducting full-tensor magnetic gradient detection system, comprising:

[0049] 1) Selecting an experimental site, the experimental site being selected in an area with stable geomagnetic environment and no obvious magnetic interference objects around;

[0050] 2) Measuring the background geomagnetic vector gradient field of the experimental area by the superconducting full-tensor magnetic gradient detection system mounted on a helicopter, with a height difference of 20 meters as a step, measuring the background geomagnetic vector gradient field at different heights of 200-300 meters respectively, and finding the optimal flight height;

[0051] 3) Under the condition of no excitation, repeatedly flying the full-tensor detection system mounted on the helicopter at the same height, and determining the attitude and orientation of the aircraft by the strapdown inertial navigation system;

[0052] 4) Laying a square calibration coil in the experimental site, exciting a standard magnetic gradient field by the square calibration coil with a 10A-100A adjustable current, recording the excitation current by a current collection device synchronously, calculating the intensity of the vector magnetic gradient field excited in the experimental area in combination with the established full-tensor magnetic gradient field model, calibrating the parameters of the square calibration coil, the side length L=100m, the transmission current I=50A, the flight height of the helicopter z=200m and z=250m, and the number of turns is 4.

[0053] 5) On the basis of step 4), adjusting the flight height of the aerial superconducting full-tensor magnetic gradient detection system, and measuring the magnetic vector gradient field excited by the square calibration coil at different flight heights;

[0054] 6) Inputting the data measured in steps 2), 3), 4) and 5) into a data quality evaluation system, removing the background field information, calculating the magnetic field components and the theoretical values of the magnetic gradient at any position in space under the constant current excitation of the square calibration coil, fitting the theoretical calculation values, system errors and measured data by a fitting equation, verifying the system error correction parameters and calculating the detection resolution of the system;

[0055] Referring to Figure 1 A full-tensor magnetic gradient receiving system based on a SQUID gradiometer, which is composed of at least 5 planar gradiometers arranged on 3 mutually non-parallel planes to form a full-tensor magnetic gradiometer, and measures the full-tensor information of the magnetic gradient.

[0056] The airborne superconducting full-tensor magnetic gradient detection system includes a ground segment and an air segment. The ground segment includes a square calibration coil, a calibration coil signal recording device, a data quality evaluation system, a constant current transmitting device, and a transmitter GPS synchronization unit. The constant current transmitting device transmits an excitation current to the square calibration coil, the calibration coil signal recording device records the transmitted current, and the data is input into the data quality evaluation system.

[0057] The airborne portion receives signals from a SQUID receiving system carried by a helicopter and transmits them to a full tensor receiver. The full tensor receiver receives auxiliary parameters measured by an auxiliary parameter measurement unit and synchronizes them with the transmitter's GPS synchronization unit on the ground system via the receiver system's GPS synchronization unit.

[0058] The auxiliary parameter measurement unit includes an inertial navigation system, which consists of an inertial measurement unit and a calculation unit; an accelerometer to measure the acceleration in the direction of the object's motion; a gyroscope to measure the angular velocity of the system and obtain the system's orientation information; an attitude calculation unit to convert the inertial navigation system data from its own coordinate system to the Earth's coordinate system; and an acceleration integration unit and an error compensation unit to correct the flight attitude and obtain precise position information of the aircraft during flight.

[0059] The constant current transmitting device mainly includes a control board, a driver board, a transmitting bridge, a calibration coil, and a power supply module. Transmission parameters are determined via buttons and a display screen. Then, a synchronization module provides a time base to the control unit, which uses an STM32 microcontroller as its core, and sends a PWM wave control signal. After passing through the driver unit, which consists of a transformer module and an optocoupler isolation module, the voltage and current of the control signal meet the requirements for driving the power switching devices, thus controlling the transmitting bridge. Figure 3 The circuit is designed to prevent manual shut-off, which could pose a danger under high voltage and high current conditions. The control circuit uses a low-power power supply, while the transmitting circuit uses a high-power battery pack, and the two do not interfere with each other.

[0060] A 100×100-meter return wire with 4 turns and a resistance of less than 4Ω is selected. A high-power battery pack is used for high-stability constant current transmission, achieving a stable 400V output voltage. Q1, Q2, and Q3 are used as switches, and timing signals from a microcontroller control the switching on and off, achieving circuit on / off control and enabling constant current transmission under constant load. R0 is an adjustable power resistor with an adjustable resistance range of 0–50Ω, enabling current adjustment. D1 is a high-power reverse protection diode to prevent the transmission current from returning to the power supply via a freewheeling diode after current cutoff. The transmitting coil is replaced by a resistor and an inductor.

[0061] The commonly used switching devices are IGBT and MOSFET, the MOSFET has the characteristics of small size, low power consumption, low breakdown voltage and low saturation current, the IGBT has the characteristics of large size, fast heat dissipation, large breakdown voltage and large saturation current, according to the design requirements of high-power emission, a high-power IGBT module is selected as the switching device of the emission circuit to realize the target of 100A emission current.

[0062] Referring to Figure 2 As shown in the figure, the calibration coil signal recording device selects a closed-loop Hall current sensor, the turns ratio is 1:500, the reaction time is less than 1μs, the measurement resistance P M The output voltage is linearly related to the detection current, the current of the calibration coil is observed by the voltage signal, the 24-bit AD acquisition circuit imports the collected data into the single-chip microcomputer memory, and after the sampling is completed, the data in the memory is stored in the SD card, the analog part and the digital part are independently powered by an isolation power supply; The ground is paved with the calibration coil, the current value of the calibration coil is adjusted to change between 10A-100A with 10A step, the magnetic field three components and the magnetic gradient data of the calibration coil are measured;

[0063] By changing the flight height of the helicopter, it repeatedly flies between 200-300 meters high with 20 meters high difference, and measures the full tensor magnetic gradient information excited by the calibration coil;

[0064] The error calibration method of the aerial superconducting full tensor magnetic gradient detection system uses the emission device to emit a constant current to the calibration coil to generate a controllable magnetic vector gradient field in space, calculates the gradient field information of any point in space, inputs the measured data into the data quality evaluation system, removes the dynamic error of the detection system from the actual measurement value, and compares and fits the theoretical value to calibrate the error parameters and detection resolution of the aerial superconducting full tensor magnetic gradient detection system;

[0065] The three-component magnetic field generated by the calibration coil in three-dimensional space under the excitation of constant current is expressed as:

[0066]

[0067]

[0068]

[0069] In formulas (1), (2), and (3), l is the half side length of the calibration coil, μ0 is the magnetic permeability, I is the emission current of the calibration coil, and x, y, and z can be any point in space.

[0070] From the Maxwell equations, the curl and divergence of the magnetic vector field in free space are both 0, that is:

[0071]

[0072]

[0073] From formula (4), we get: G xy =G yx G xz =G zx G yz =G zy From formula (5), we get: G zz =-G xx -G yy Taking the partial derivatives of formulas (1), (2), and (3) with respect to x, y, and z respectively, we can obtain the G component of the nine components of the magnetic gradient tensor T. xx G yy G xy G xz G yz The five independent components are:

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] The test results are as follows Figure 6 As shown, when the calibration coil side length of the airborne superconducting full tensor magnetic gradient detection system is L=100m, I=50A, and the flight altitude is z=200m and z=250m, the theoretical value of the full tensor magnetic gradient can be calculated, and a magnetic gradient value on the order of pT / m can be generated.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An error calibration method for an airborne superconducting full-tensor magnetic gradiometric system, characterized in that, The method comprises: 1) selecting an experimental site, the experimental site being selected in an area with stable geomagnetic environment and no obvious magnetic interference around; 2) measuring the background geomagnetic vector gradient field of the experimental area by a helicopter-mounted superconducting full-tensor magnetic gradient detection system, taking 20-meter height difference as a step, measuring the background geomagnetic vector gradient field at different heights of 200-300 meters respectively, and finding the optimal flight height range; 3) under the condition of no excitation, the helicopter-mounted superconducting full-tensor magnetic gradient detection system repeatedly flies at the same height, and the aircraft attitude and orientation are determined by a strapdown inertial navigation system; 4) a square calibration coil is laid on the experimental site, a standard magnetic gradient field is generated by exciting the square calibration coil with a 10A-100A adjustable current, a current collection device synchronously records the excitation current, and the intensity of the vector magnetic gradient field excited by the experimental area is calculated; 5) on the basis of step 4), the flight height of the aerial superconducting full-tensor magnetic gradient detection system is adjusted, and the intensity of the vector magnetic gradient field excited by the calibration coil at different flight heights is measured; 6) the data measured in steps 2), 3), 4) and 5) are input into a data quality evaluation system, and the background field information is removed; the theoretical calculation value of the magnetic field component and the magnetic gradient at any position in space under the constant current excitation of the square calibration coil is calculated through theoretical calculation, the theoretical calculation value, the system error and the measured data are fitted through a fitting equation, and the system error correction parameter and the system detection resolution are verified.

2. The error calibration method of the aerial superconducting full-tensor magnetic gradient detection system according to claim 1, characterized in that: the calculation of the theoretical value of the magnetic field component at any position in space in step 6) is as follows: the expression of the three-component magnetic field generated by the calibration coil in three-dimensional space under constant current excitation is as follows: in formulas (1), (2) and (3), l is the half length of the calibration coil, μ0 is the magnetic permeability, I is the emission current of the calibration coil, and x, y and z can be any position in space.

3. The error calibration method of the aerial superconducting full-tensor magnetic gradient detection system according to claim 2, characterized in that: the calculation of the theoretical value of the magnetic gradient in step 6) is as follows: According to Maxwell's equations, the curl and divergence of the magnetic vector field in free space are both 0, i.e. From equation (4) we have: G xy = G yx , G xz = G zx , G yz = G zy ; from equation (5) we have: G zz = -G xx - G yy ; partial derivatives of equation (1), (2), (3) with respect to x, y, z respectively, we have 5 independent components of 9 components of magnetic gradient tensor T, G xx , G yy , G xy , G xz , G yz :

4. The error calibration method of the aerial superconducting full-tensor magnetic gradient detection system according to claim 1, characterized in that: the ground part of the aerial superconducting full-tensor magnetic gradient detection system comprises a square calibration coil, a calibration coil signal recording device, a data quality evaluation system, a constant current emission device and a transmitter GPS synchronization unit; the constant current emission device emits excitation current to the square calibration coil, the calibration coil signal recording device records the emission current, and the data quality evaluation system inputs the data; the aerial part of the aerial superconducting full-tensor magnetic gradient detection system receives signals by the SQUID receiving system carried by the helicopter, transmits the signals to the full-tensor receiver, receives the auxiliary parameters measured by the auxiliary parameter measurement unit, and synchronizes with the transmitter GPS synchronization unit of the ground system through the receiving system GPS synchronization unit.

5. The error calibration method of an aerial superconducting full-tensor magnetic gradient detection system according to claim 4, characterized in that: The auxiliary parameter measurement unit comprises an inertial navigation system, which is composed of an inertial measurement unit and a calculation unit; an accelerometer for measuring the acceleration of the object in motion, a gyroscope for measuring the angular velocity of the system to obtain the directional information of the system, a pose solution unit for converting the data of the inertial navigation system from the self-coordinate system to the earth coordinate system, an acceleration integration unit and an error compensation unit for correcting the flight attitude to obtain the accurate position information of the aircraft during flight.

6. The error calibration method of an aerial superconducting full-tensor magnetic gradient detection system according to claim 4, characterized in that: The calibration coil signal recording device selects a closed loop Hall current sensor, the number of turns ratio is 1:500, the reaction time is less than 1 mu s, and the measurement resistance R M The output voltage is linearly related to the detection current by selecting 40 omega, and the calibration coil current is observed from the voltage signal; The 24-bit AD acquisition circuit imports the collected data into the single-chip microcomputer memory, and after the sampling is completed, the data in the memory is transferred to the SD card for storage. The analog part and the digital part are independently powered by an isolation power supply.

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