A mobile platform electromagnetic survey system calibration device and method

Abstract

The application belongs to the technical field of electromagnetic exploration, and particularly relates to a mobile platform electromagnetic detection system calibration device and method. A coaxial and coplanar transmitting coil, a bucking coil and a receiving coil are provided. The bucking coil is located between the transmitting coil and the receiving coil and is connected and disconnected with the transmitting coil through a switch group. A controller controls the state of the switch group, receives response signals of the bucking coil and the transmitting coil when they are disconnected and work independently and the response signal of the transmitting coil when it works alone. The response signals collected twice are subtracted to obtain a measured bucking-receiving signal. A filter is used to remove the transmission characteristic data of the measured signal after training of the measured bucking-receiving signal and an ideal bucking-receiving signal. The influence of the receiving system on the signal can be continuously weakened, and the output signal after calibration tends to be close to the ideal response signal.

Description

Technical Field

[0001] This application belongs to the field of electromagnetic exploration technology, specifically a calibration device and method for a mobile platform electromagnetic detection system. Background Technology

[0002] Frequency-domain electromagnetic systems have been widely used in mineral resource exploration, cable and pipeline inspection, and underground hazard detection. Improving the amplitude and phase accuracy of frequency-domain electromagnetic detection systems is one of the key research focuses. To eliminate the influence of the receiving system's transmission characteristics on observation, methods typically include optimizing hardware circuits to reduce the distributed capacitance of the coils and thus suppress receiver link effects by lowering coil parameter errors. However, these methods can only weaken channel effects and cannot completely eliminate the influence of the receiving system's transmission characteristics on the induced signal.

[0003] The transfer function of the receiving system is explicitly estimated and compensated. However, noise and measurement errors can cause deviations in the estimation of the transfer function, thus affecting the correction effect.

[0004] Third, the response of the receiving coil is corrected through data processing. Existing methods have several drawbacks: they are highly dependent on geological conditions, cannot be applied to complex geological areas, and involve complex procedures, resulting in low efficiency and hindering field deployment. The method of calibrating the acquired data by introducing an anomaly loop as a calibration device and combining it with a Wiener filter increases the complexity of the detection system by requiring the additional introduction of the anomaly loop. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a calibration device and method for an electromagnetic detection system on a mobile platform.

[0006] A calibration apparatus for a mobile platform electromagnetic detection system according to a first aspect embodiment of this application includes:

[0007] A coaxial and coplanar transmitting coil, a bucking coil, and a receiving coil, wherein the bucking coil is located between the transmitting coil and the receiving coil and is connected and disconnected from the transmitting coil via a switch group;

[0008] The controller controls the state of the switch group to disconnect the bucking coil from the transmitting coil and allow it to work independently, or to allow the transmitting coil to work alone. It also receives the response signals of the bucking coil working independently and the transmitting coil working alone. The difference between the two acquired response signals is used to obtain the measured bucking-received signal.

[0009] A filter, trained with measured bucking-received signals and ideal bucking-received signals, is used to remove transmission characteristic data from the measured signals.

[0010] Furthermore, the switch group includes:

[0011] The first switch is set between the first break point and the second break point of the transmitting coil;

[0012] The second switch is set between the first and second breakpoints of the bucking coil;

[0013] The third switch is located between the first break point of the bucking coil and the first break point of the transmitting coil;

[0014] The fourth switch is located between the second break point of the bucking coil and the second break point of the transmitting coil.

[0015] Furthermore, the formula for calculating the ideal bucking-received signal is as follows:

[0016] , ,

[0017] in, For the mutual inductance of the bucking coil and the receiving coil, It is the mutual inductance between the transmitting coil and the bucking coil. It's the inductance of the bucking coil. It is a unit impulse function. It is a unit step function. For time variables, These are intermediate parameters. It is the resistance of the bucking coil. For ideal bucking-received signals, This is the emission current.

[0018] Furthermore, the process of training the filter includes:

[0019] The measured bucking-received signal was processed into a signal sequence;

[0020] The output signal of the filter is obtained by multiplying the signal sequence with the transpose of the filter weight vector.

[0021] Calculate the error signal between the ideal bucking-received signal and the filter output signal;

[0022] Update the filter weight vector based on the error signal;

[0023] Training stops once the error signal meets the set threshold.

[0024] A calibration method for a mobile platform electromagnetic detection system according to a second aspect of this application includes:

[0025] Disconnect the bucking coil from the transmitting coil, allowing the bucking coil and transmitting coil to operate independently, and acquire the first response signal through the receiving system;

[0026] Disconnect the bucking coil from the transmitting coil and disconnect the bucking coil, then acquire the second response signal through the receiving system;

[0027] The measured bucking-received signal is obtained by subtracting the first response signal from the second response signal.

[0028] The filter is trained using the measured bucking-received signal and the ideal bucking-received signal to obtain the trained filter;

[0029] The transmission characteristic data of the measured signal are removed using a trained filter.

[0030] Furthermore, the measured signal is obtained by placing the mobile platform electromagnetic detection system in the area to be measured, connecting the bucking coil and the transmitting coil in reverse series, and measuring the signal through the receiving system.

[0031] Furthermore, the measured bucking-received signal and the ideal bucking-received signal are used to train the filter, including:

[0032] The measured bucking-received signal was processed into a signal sequence;

[0033] The output signal of the filter is obtained by multiplying the signal sequence with the transpose of the filter weight vector.

[0034] Calculate the error signal between the ideal bucking-received signal and the filter output signal;

[0035] Update the filter weight vector based on the error signal;

[0036] Training stops once the error signal meets the set threshold.

[0037] Furthermore, the formula for calculating the ideal bucking-received signal is as follows:

[0038] , ,

[0039] in, For the mutual inductance of the bucking coil and the receiving coil, It is the mutual inductance between the transmitting coil and the bucking coil. It's the inductance of the bucking coil. It is a unit impulse function. It is a unit step function. For time variables, These are intermediate parameters. It is the resistance of the bucking coil. For ideal bucking-received signals, This is the emission current.

[0040] Compared with the prior art, the advantages of this application are as follows:

[0041] This application utilizes a bucking coil structure as an anomalous loop, avoiding additional coil design and effectively improving the consistency between the probed data and the ideal response with lower hardware complexity. By training the filter with the measured bucking-received signal and the ideal bucking-received signal, a trained filter is obtained. This filter can adaptively approximate the equivalent transfer characteristics of the receiving system and compensate for the response signal, thereby continuously reducing the influence of the receiving system on the signal and making the calibrated output signal approach the ideal response signal. Attached Figure Description

[0042] Figure 1 This is a structural block diagram of the calibration device for the electromagnetic detection system of a mobile platform provided in an embodiment of this application;

[0043] Figure 2 A diagram showing the positional relationship between the transmitting coil, the bucking coil, and the receiving coil provided in an embodiment of this application;

[0044] In this circuit, 1 is the transmitting coil, 2 is the bucking coil, 3 is the receiving coil, 41 is the first switch, 42 is the third switch, 43 is the fourth switch, and 44 is the second switch. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0046] In a mobile frequency domain electromagnetic detection system, the received signals include transmit-receive signals (TS response), bucket-receive signals (TBS response), transmit-to-ground-receive signals (TES response), and transmit-to-mobile-platform-receive signals (TMS response).

[0047] based on Figure 1 The diagram shown is a structural block diagram of a calibration device for an electromagnetic detection system on a mobile platform. Figure 2The diagram shows the positional relationship between the transmitting coil 1, the bucking coil 2, and the receiving coil 3. This is a calibration device for a mobile platform electromagnetic detection system. It includes a coaxial and coplanar transmitting coil 1, a bucking coil 2, and a receiving coil 3. The bucking coil 2 is located between the transmitting coil 1 and the receiving coil 3, and its connection to the transmitting coil 1 is controlled by a switch group. The transmitting coil 1, bucking coil 2, and receiving coil 3 utilize the structure of a mobile platform electromagnetic detection system. The connection between the bucking coil 2 and the transmitting coil 1 is achieved by adding a switch group, allowing for anti-series joint operation, independent operation, or operation of one coil at a time. The bucking coil 2, also known as a compensation coil, is used in the mobile platform electromagnetic detection system to cancel out the primary field.

[0048] The controller controls the state of the switch group to disconnect the bucking coil 2 from the transmitting coil 1 and make it work independently, or to make the transmitting coil 1 work alone. It also receives the response signals of the bucking coil 2 and the transmitting coil 1 working independently. The difference between the two acquired response signals is used to obtain the measured bucking-receive signal. Separation means that the transmitting coil 1 and the bucking coil 2 are not connected, that is, they work independently of each other.

[0049] The filter, trained with measured bucked-received signals and ideal bucked-received signals, is used to remove transmission characteristic data from the measured signals. The filter is a Normalized Least Mean Square (NLMS) filter, where the filter weights are adjusted to minimize the error signal value; in this embodiment, an NLMS filter is used.

[0050] In one embodiment, the switch group includes a first switch 41 disposed between a first break and a second break of the transmitting coil 1; a second switch 44 disposed between a first break and a second break of the bucking coil 2; a third switch 42 disposed between a first break of the bucking coil 2 and a first break of the transmitting coil 1; and a fourth switch 43 disposed between a second break of the bucking coil 2 and a second break of the transmitting coil 1. When the third switch 42 and the fourth switch 43 are open, the bucking coil 2 and the transmitting coil 1 are independent of each other. At this time, the first switch 41 is normally closed, and the transmitting coil 1 is closed. When the second switch 44 is closed, the bucking coil 2 is closed; when the second switch 44 is open, the bucking coil 2 is open. When the first switch 41 and the second switch 44 are open, and the third switch 42 and the fourth switch 43 are closed, the bucking coil 2 and the transmitting coil 1 are connected in anti-series connection.

[0051] Buckling coil 2 is isolated from transmitting coil 1 via a switch and calibrated as an abnormal loop. When buckling coil 2 is isolated and closed, the response signal in the receiving system mainly consists of the TS response, TMS response, TES response, TBS response, and noise. When buckling coil 2 is isolated and open, the response signal includes the TS response, TMS response, TES response, and noise. Referring to the secondary field extraction method, the measured signal of the TBS response can be obtained by subtracting the closed-loop response from the open-loop response.

[0052] When the bucking coil 2 is independent and closed (i.e., the first switch 41 is closed, the third switch 42 and the fourth switch 43 are open, and the second switch 44 is closed), assume the resistance of the bucking coil 2 is... The inductance is Considering that the current in the inductor cannot change abruptly, according to Kirchhoff's circuit laws, the ideal time-domain expression for the bucking-received signal can be obtained:

[0053] , ,

[0054] The ideal response signal of TBS is derived using the above formula. For the mutual inductance of the bucking coil 2 and the receiving coil 3, It is the mutual inductance between transmitting coil 1 and bucking coil 2. It is the inductance of the bucking coil 2. It is a unit impulse function. It is a unit step function. For time variables, These are intermediate parameters. It is the resistance of the bucking coil 2. For ideal bucking-received signals, This is the emission current.

[0055] The actual measurement signal obtained after transmission by the receiving system With ideal signal The expression can be organized as follows:

[0056] ,

[0057] in, These are signals actually measured during the exploration process. It is an ideal signal during the exploration process. It is the induced voltage of the receiving coil. It is the transmission characteristic of the receiving system. It is the system gain. , , , , and It is the resistor in the amplifier section of the receiving system. , , These are the resistance, inductance, and capacitance of the receiving coil. It is the matching resistor for receiving coil 3. ω is the angular frequency.

[0058] In one embodiment, a final filter is obtained by training the filter, which is used to correct the measured signal. The process of training the filter includes:

[0059] The measured bucking-received signal is processed into a signal sequence, represented as follows: ; This represents a discrete-time index.

[0060] Multiplying the signal sequence by the transpose of the filter weight vector yields the filter output signal, i.e. , This represents the filter output signal. Indicates the first Weight vector of time-iteration filter transpose;

[0061] The error signal between the ideal bucking-received signal and the filter output signal is calculated and expressed as: , This represents the ideal sequence form of the bucking-received signal;

[0062] The filter weight vector is updated based on the error signal, expressed as: ; This represents the step size parameter, 0 < ≤2, Indicates the first A filter weight vector for each time iteration. This represents a parameter to prevent the denominator from being zero.

[0063] Training stops once the error signal meets the set threshold.

[0064] This method effectively avoids the influence of internal system and measurement errors, enhancing overall accuracy and shallow detection capabilities. The weight vector of the filter, obtained through training, serves as the correction parameter. The measured signal is passed through the filter to obtain reliable data free from the transmission characteristics of the receiving system. Indoor and outdoor field tests verified that this device can effectively suppress the influence of the receiving system's transmission characteristics on the measurement signal. After applying NLMS (Normalized Least Mean Square) filtering to the measurement signal, the offset of the main frequency signal is reduced, and the maximum accuracy of amplitude and phase is effectively improved.

[0065] The filter divides the step size parameter μ by the instantaneous power of the input signal, achieving adaptive normalization. The filter can be introduced into the data acquisition process to process the data received by the receiving system in real time and eliminate the influence of the transmission characteristics of the receiving system.

[0066] Filter training yields the theoretical and actual signal responses of the calibration device, which is a crucial step in obtaining appropriate correction coefficients for the filter. The filter minimizes the error between the input signal and the desired signal by adjusting the coefficient ω[n].

[0067] On the other hand, embodiments of this application also provide a calibration method for a mobile platform electromagnetic detection system, including:

[0068] Disconnect the bucking coil 2 from the transmitting coil 1, so that the bucking coil 2 and the transmitting coil 1 can work independently, and collect the first response signal through the receiving system;

[0069] Disconnect the bucking coil 2 from the transmitting coil 1, and disconnect the bucking coil 2. Acquire the second response signal through the receiving system.

[0070] The measured bucking-received signal is obtained by subtracting the first response signal from the second response signal.

[0071] The filter is trained using the measured bucking-received signal and the ideal bucking-received signal to obtain the trained filter;

[0072] The transmission characteristic data of the measured signal are removed using a trained filter; the filter used is an NLMS filter.

[0073] The measured signal is obtained by placing the mobile platform electromagnetic detection system in the area to be measured, connecting the bucking coil 2 and the transmitting coil 1 in reverse series, and measuring the signal obtained by the receiving coil 3 through the receiving system.

[0074] In one embodiment, training the filter with the measured bucking-received signal and the ideal bucking-received signal includes:

[0075] The measured bucking-received signal was processed into a signal sequence;

[0076] The output signal of the filter is obtained by multiplying the signal sequence with the transpose of the filter weight vector.

[0077] Calculate the error signal between the ideal bucking-received signal and the filter output signal;

[0078] Update the filter weight vector based on the error signal;

[0079] Training stops once the error signal meets the set threshold.

[0080] By training the filter with the measured bucking-received signal and the ideal bucking-received signal, a trained filter is obtained. It can adaptively approximate the equivalent transfer characteristics of the receiving system and compensate for the response signal, thereby continuously reducing the influence of the receiving system on the signal and making the calibrated output signal approach the ideal response signal.

[0081] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A mobile platform electromagnetic survey system calibration apparatus, characterized by, include: A coaxial and coplanar transmitting coil, a bucking coil, and a receiving coil, wherein the bucking coil is located between the transmitting coil and the receiving coil and is connected and disconnected from the transmitting coil via a switch group; The controller controls the state of the switch group to disconnect the bucking coil from the transmitting coil and allow it to work independently, or to allow the transmitting coil to work alone. It also receives the response signals of the bucking coil working independently and the transmitting coil working alone. The difference between the two acquired response signals is used to obtain the measured bucking-received signal. A filter, trained with measured bucking-received signals and ideal bucking-received signals, is used to remove transmission characteristic data from the measured signals.

2. The calibration device for a mobile platform electromagnetic survey system of claim 1, wherein, The switch group includes: The first switch is set between the first break point and the second break point of the transmitting coil; The second switch is set between the first and second breakpoints of the bucking coil; The third switch is located between the first break point of the bucking coil and the first break point of the transmitting coil; The fourth switch is located between the second break point of the bucking coil and the second break point of the transmitting coil.

3. The calibration device for a mobile platform electromagnetic survey system of claim 1, wherein, The formula for calculating the ideal bucking-received signal is as follows: ， ， wherein is the mutual inductance of the bucking coil and the receiving coil, is the mutual inductance of the transmitting coil and the bucking coil, is the inductance of the bucking coil, is the unit impulse function, is the unit step function, is the time variable, is the intermediate parameter, is the resistance of the bucking coil, is the ideal bucking-receiving signal, is the transmitting current.

4. The calibration device for a mobile platform electromagnetic detection system according to claim 1, characterized in that, The process of training a filter includes: The measured bucking-received signal was processed into a signal sequence; The output signal of the filter is obtained by multiplying the signal sequence with the transpose of the filter weight vector. Calculate the error signal between the ideal bucking-received signal and the filter output signal; Update the filter weight vector based on the error signal; Training stops once the error signal meets the set threshold.

5. A calibration method for a mobile platform electromagnetic detection system, using the mobile platform electromagnetic detection system calibration device according to any one of claims 1-4, characterized in that, include: Disconnect the bucking coil from the transmitting coil, allowing the bucking coil and transmitting coil to operate independently, and acquire the first response signal through the receiving system; Disconnect the bucking coil from the transmitting coil and disconnect the bucking coil, then acquire the second response signal through the receiving system; The measured bucking-received signal is obtained by subtracting the first response signal from the second response signal. The NLMS filter is trained using the measured bucking-received signal and the ideal bucking-received signal to obtain the trained filter; The transmission characteristic data of the measured signal are removed using a trained filter.

6. The calibration method for the electromagnetic detection system of a mobile platform according to claim 5, characterized in that, The measured signal is obtained by placing the mobile platform electromagnetic detection system in the area to be measured, connecting the bucking coil and the transmitting coil in reverse series, and measuring the signal through the receiving system.

7. The calibration method for the electromagnetic detection system of a mobile platform according to claim 5, characterized in that, The filter is trained using the measured bucking-received signal and the ideal bucking-received signal, including: The measured bucking-received signal was processed into a signal sequence; The output signal of the filter is obtained by multiplying the signal sequence with the transpose of the filter weight vector. Calculate the error signal between the ideal bucking-received signal and the filter output signal; Update the filter weight vector based on the error signal; Training stops once the error signal meets the set threshold.

8. The calibration method for the electromagnetic detection system of a mobile platform according to claim 5, characterized in that, The formula for calculating the ideal bucking-received signal is as follows: ， ， in, For the mutual inductance of the bucking coil and the receiving coil, It is the mutual inductance between the transmitting coil and the bucking coil. It's the inductance of the bucking coil. It is a unit impulse function. It is a unit step function. For time variables, These are intermediate parameters. It is the resistance of the bucking coil. For ideal bucking-received signals, This is the emission current.

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