Pull-type transient electromagnetic detection technology based on eccentric self-compensation and method thereof

Abstract

The invention discloses a pull-type transient electromagnetic detection technology based on eccentric self-compensation and a method thereof. The method comprises the following steps: 1) preliminarily laying a coil structure; 2), according to theoretical calculation and analysis of related parameters in an existing coil structure, selecting a relatively proper vertical distance H between the circular receiving coil and the circular transmitting coil; 3) according to the vertical distance L determined in the step 2), further theoretically calculating a horizontal distance L between the center of the circular receiving coil corresponding to the height and the center of the circular transmitting coil; (4) adjusting the position of the circular receiving coil in the coil structure according to the results in the step (2) and the step (3); and (5) transient electromagnetic detection is carried out through the coil structure adjusted in the step (4), in a certain size error range, interference of a primary field on signals is avoided, the signals sensed by the receiving coil can serve as pure secondary field signals to carry out subsequent data processing, so that the transient electromagnetic detection device has higher tolerance to physical size errors, and the accuracy of transient electromagnetic detection is improved. And the acquired signal is more fidelity.

Description

Technical Field

[0001] The invention relates to the field of geophysical exploration equipment, and in particular to a towed transient electromagnetic detection technology and method based on eccentricity self-compensation. Background Art

[0002] With the acceleration of urbanization in my country, urban space has expanded rapidly, and the development space is seriously insufficient. The demand for efficient and safe use of underground space has increased sharply. However, in the process of urban underground space development, major geological disasters such as road collapse caused by the failure to identify the underground geological structure have occurred from time to time, causing significant losses to people's lives and property. The development of urban underground space detection technology and the identification of urban underground geological structure are crucial to the reasonable and safe development of underground space and disaster warning. In the prior art, time domain electromagnetic transmission is usually used to complete the exploration of geological structures. However, the receiving signal of the time domain electromagnetic method is currently smaller than the transmitting voltage, especially for the integrated design structure of the towed transceiver coil. The receiving coil is more seriously affected by the coupling of the transmitting coil, that is, the coupling interference between the transmitting coil and the receiving coil causes the distortion of the electromagnetic signal in the time and frequency domains. The primary field coupling interference will not only change the attenuation characteristics of the received signal, causing errors in the later data interpretation, but also expand the dynamic range of the received signal, damage the receiving sensor's back-stage circuit, and the corresponding exploration structure is relatively complex and the production cost is high. Therefore, it is very necessary to propose a towed transient electromagnetic detection technology and method based on eccentric self-compensation. Summary of the invention

[0003] The purpose of the present invention is to provide a towed transient electromagnetic detection technology and method based on eccentric self-compensation, so that during exploration, within a certain error range, the influence of the transmitting coil and the receiving coil on the electromagnetic signal in the time and frequency domain can be ignored, so as to solve the existing technical defects and unattainable technical requirements.

[0004] To achieve the above object, the present invention provides the following technical solution: a towed transient electromagnetic detection technology based on eccentricity self-compensation, comprising:

[0005] A circular transmitting coil, wherein the circular transmitting coil is laid on a movable towing vehicle platform;

[0006] A circular receiving coil, wherein the circular receiving coil is laid on a platform that can move relative to the towing platform, the plane where the platform is located is located above the plane where the towing vehicle platform is located, and the two planes are arranged in parallel;

[0007] The host is arranged on the towing vehicle platform and is respectively connected to the circular transmitting coil and the circular receiving coil, and is used to transmit a pulse signal to the circular transmitting coil and simultaneously receive the primary field voltage information fed back to it by the circular receiving coil.

[0008] The vertical distance between the platform and the towing vehicle platform is adjustable, and the horizontal relative position of the circular receiving coil and the circular transmitting coil is also adjustable. The position of the circular receiving coil is determined by the position of the circular transmitting coil and the mutual inductance of the circular receiving coil being zero;

[0009] Preferably, the radius of the circular transmitting coil is greater than the radius of the circular receiving coil.

[0010] Preferably, the radius R of the circular transmitting coil is 0.5 m, and the radius r of the circular receiving coil is 0.125 m.

[0011] Preferably, the direction of the current emitted by the host to the circular transmitting coil is counterclockwise, the relative vertical height H between the circular receiving coil and the circular transmitting coil is 0.2m, and the horizontal distance L between the center of the circular receiving coil and the center of the circular transmitting coil is 0.6108m.

[0012] A towed transient electromagnetic detection method based on eccentricity self-compensation, comprising:

[0013] 1) Preliminary laying of coil structure;

[0014] 2) According to the theoretical calculation and analysis of relevant parameters in the existing coil structure, a more appropriate vertical distance H between the circular receiving coil and the circular transmitting coil is selected;

[0015] 3) According to the vertical distance L determined in step 2), further theoretically calculate the horizontal distance L between the center of the circular receiving coil and the center of the circular transmitting coil corresponding to this height;

[0016] 4) According to the results in step 2) and step 3), the position of the circular receiving coil in the coil structure is adjusted;

[0017] V) Perform transient electromagnetic detection using the coil structure adjusted in step 4). At this time, the signal induced by the circular receiving coil is used as a pure secondary field signal for subsequent data processing.

[0018] Preferably, in step 1), the specific contents of preliminary laying of the coil structure are:

[0019] The plane where the towing vehicle platform is located is arranged parallel to the plane where the high platform is located, the circular transmitting coil is laid on the towing vehicle platform, and the circular receiving coil is laid on the high platform.

[0020] Preferably, in step 2), the relevant parameters in the coil structure include:

[0021] The number of turns of the circular transmitting coil, the number of turns of the circular receiving coil, the radius R of the circular transmitting coil, the radius r of the circular receiving coil, the current intensity I emitted by the subject to the circular transmitting coil, the current direction and the horizontal distance L between the center of the circular receiving coil and the center of the circular transmitting coil.

[0022] Preferably, the specific content of step 2) is:

[0023] 2.1) Take different vertical distances H between the circular receiving coil and the circular transmitting coil, adjust the horizontal distance L between the center of the circular receiving line and the center of the circular transmitting coil, and obtain the relationship between the field strength of the primary field in the vertical direction and the horizontal distance L under different vertical distances H;

[0024] 2.2) Take the vertical distance H where the field changes less dramatically with different horizontal distances L;

[0025] 2.3) and take the approximate horizontal distance L1 where the field changes most dramatically with different vertical distances H.

[0026] Preferably, the specific content of step (3) is:

[0027] 3.1) Place the circular receiving coil at the vertical distance H in step 2.2) to the approximate horizontal distance L1 in step 2.3);

[0028] 3.2) By calculating the mutual inductance coefficient between the circular transmitting coil and the circular receiving coil, the horizontal distance L at zero coupling is obtained:

[0029] Preferably, in step 4), the requirement for adjusting the coil structure in step 1) according to the calculation result is:

[0030] In actual operation, the error between the adjusted horizontal distance between the center of the circular receiving coil and the center of the circular transmitting coil and the horizontal distance L between the center of the circular receiving coil and the center of the circular transmitting coil obtained by theoretical calculation in step 3) should not exceed 2 mm.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. Within a certain dimensional error range, the present application can ignore the influence of the primary field exposure sense, and consider that the transceiver coil is in a zero coupling state. The signal induced by the receiving coil can be used as a pure secondary field signal for subsequent data processing, avoiding the interference of the primary field on the signal, so that the present application has a higher tolerance to physical dimensional errors, making the acquired signal more fidelity, and the present application has the characteristics of simple structure and low manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1It is a simplified diagram of the overall structure of the present invention;

[0034] Figure 2 is a schematic diagram of a coordinate system in Embodiment 1 of the present invention;

[0035] Figure 3 The distribution diagram of the intensity of the transmitted magnetic field in the Z-axis direction at different heights as a function of the horizontal distance L in Example 1 of the present invention;

[0036] Figure 4 is the relationship between the mutual inductance coefficient of the transceiver coil and the horizontal distance L when the vertical distance H is 0.02 m in Example 1 of the present invention;

[0037] Figure 5 is a relationship diagram between the mutual inductance coefficient and the horizontal distance L of the transceiver coils when the vertical distance H is 0.1 m in Example 1 of the present invention;

[0038] Figure 6 is a relationship diagram between the mutual inductance coefficient and the horizontal distance L of the transceiver coils when the vertical distance H is 0.2 m in Example 1 of the present invention;

[0039] Figure 7 is a relationship diagram between the mutual inductance coefficient and the horizontal distance L of the transceiver coils when the vertical distance H is 0.3 m in Example 1 of the present invention;

[0040] Figure 8 is a curve diagram of the change of the conductive ring in Example 1 of the present invention;

[0041] Fig. 9 This is a pure secondary field voltage curve diagram without considering the influence of the receiving coil parasitic parameters in Example 1 of the present invention;

[0042] Fig.10 It is a schematic diagram of the simulation results of the signals induced when the receiving coil deviates toward the center direction of the transmitting coil under different deviation conditions in Example 1 of the present invention;

[0043] Fig.11 It is a schematic diagram of the simulation results of the signals induced when the receiving coil is offset away from the center of the transmitting coil under different deviation conditions in Example 1 of the present invention;

[0044] In the figure: a circular transmitting coil 1, a towing vehicle platform 2, a circular receiving coil 3, a platform 4, and a host 5. DETAILED DESCRIPTION

[0045] The following will be combined with the attached embodiment of the present invention Figure 1-11, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] See also Figure 1-11 , embodiments of the present invention:

[0047] Embodiment 1:

[0048] like Figure 1 Shown: A towed transient electromagnetic detection technology based on eccentricity self-compensation, including:

[0049] A circular transmitting coil 1, wherein the circular transmitting coil 1 is laid on a movable towing vehicle platform 2;

[0050] A circular receiving coil 3, wherein the circular receiving coil 3 is laid on a platform 4 that can move relative to the towing platform, wherein the plane where the platform 4 is located is located above the plane where the towing vehicle platform 2 is located, and the two planes are arranged in parallel;

[0051] A host 5, wherein the host 5 is disposed on the towing vehicle platform 2, and the host 5 is respectively connected to the circular transmitting coil 1 and the circular receiving coil 3;

[0052] The vertical distance between the platform 4 and the towing vehicle platform 2 is adjustable, and the horizontal relative position of the circular receiving coil 3 and the circular transmitting coil 1 is also adjustable. The position of the circular receiving coil 3 is determined by the position of the circular transmitting coil 1 and the mutual inductance of the circular receiving coil being zero;

[0053] The radius of the circular transmitting coil 1 is greater than the radius of the circular receiving coil 3 .

[0054] Specifically, the radius R of the circular transmitting coil 1 is 0.5 m, and the radius r of the circular receiving coil 3 is 0.125 m.

[0055] like Figure 2-11 As shown: A towed transient electromagnetic detection method based on eccentricity self-compensation, comprising:

[0056] 1) Preliminary laying of coil structure;

[0057] The specific contents of the preliminary laying of the coil structure are:

[0058] The plane where the towing vehicle platform 2 is located is arranged parallel to the plane where the platform 4 is located, the circular transmitting coil 1 is laid on the towing vehicle platform 2 , and the circular receiving coil 3 is laid on the platform 4 .

[0059] 2) According to the theoretical calculation and analysis of relevant parameters in the existing coil structure, a more appropriate vertical distance H between the circular receiving coil 3 and the circular transmitting coil 1 is selected;

[0060] The relevant parameters in the coil structure include:

[0061] The number of turns of the circular transmitting coil 1, the number of turns of the circular receiving coil 3, the radius R of the circular transmitting coil 1, the radius r of the circular receiving coil 3, the current intensity I emitted by the subject to the circular transmitting coil 1, the current direction and the horizontal distance L between the center of the circular receiving coil 3 and the center of the circular transmitting coil 1.

[0062] 2.1) Take different vertical distances H between the circular receiving coil 3 and the circular transmitting coil 1, adjust the horizontal distance L between the center of the circular receiving line and the center of the circular transmitting coil 1, and obtain the relationship between the field strength of the primary field in the vertical direction and the horizontal distance L under different vertical distances H;

[0063] like Figure 3 As shown: Specifically, in this embodiment, a theoretical calculation is performed by taking the model parameters of a single-turn circular transmitting coil 1, a transmitting radius R=0.5m, a single-turn circular receiving coil 3, a receiving radius r=0.125m, a transmitting current intensity I=10A, and a current direction being counterclockwise as an example, and the primary field distribution at different plane positions of H of 0.02m, 0.1m, 0.2m, and 0.3m is analyzed and calculated.

[0064] 2.2) Take the vertical distance H where the field changes less dramatically with different horizontal distances L;

[0065] Establish a coordinate system: take the plane where the circular transmitting coil 1 is located as the zero plane, the center of the circular transmitting coil 1 as the coordinate origin, the offset direction of the circular receiving coil 3 relative to the circular transmitting coil 1 as the X-axis direction, and the direction perpendicular to the zero plane and upward as the Z-axis direction. In the figure, Φ1 is the angle between the circular transmitting coil microelement and the x-axis, Φ2 is the angle between the circular receiving coil microelement and the x-axis, Q is an arbitrary microelement point of the circular transmitting coil, and P is an arbitrary microelement point of the circular receiving coil.

[0066] The magnitude of the magnetic field intensity is represented by both the numerical value of the z-axis and the color bar on the right side of the image. Therefore, by calculating the primary field distribution in the z-direction of planes at different heights, it can be seen that as the plane height increases, not only does the maximum value of the magnetic field intensity gradually decay, but the degree of change of the magnetic field also becomes more gradual, so the vertical distance H is taken as 0.2m.

[0067] 2.3) and take the approximate horizontal distance L1 where the field changes most dramatically with different vertical distances H.

[0068] It can be found that the field strength is weaker at a position far away from the transmitting line, and the field strength changes most dramatically near the transmitting line position (x=±0.5m), where the positive and negative H alternate. The field strength changes most dramatically at the height H=0.02m, but the intensity of the field change decreases significantly as H increases. Therefore, when the receiving coil is placed near x=±0.5m, the receiving coil senses the transmitting magnetic field in both positive and negative directions, so the position x=±0.5m is taken as the approximate horizontal distance L1.

[0069] 3) According to the vertical distance L determined in step 2), further theoretically calculate the horizontal distance L between the center of the circular receiving coil 3 and the center of the circular transmitting coil 1 corresponding to this height;

[0070] Since the coupling degree of the two coils is related to the mutual inductance coefficient, when the mutual inductance coefficient is zero, the two coils have no coupling relationship with each other. Therefore, the mutual inductance coefficient of the transmitting and receiving line coils is calculated to obtain the size of L at zero coupling.

[0071] 3.1) Place the circular receiving coil at the vertical distance H in step 2.2) to the approximate horizontal distance L1 in step 2.3);

[0072] 3.2) By calculating the mutual inductance coefficient between the circular transmitting coil 1 and the circular receiving coil, the horizontal distance L at zero coupling is obtained:

[0073] Calculation results Figure 6 As shown, the horizontal distance L is 0.6108m.

[0074] When the mutual inductance is zero, the receiving coil is divided into two parts, inner and outer, by the transmitting coil. The outer area of ​​the transmitting coil with weaker magnetic field strength is significantly larger. At this position, the positive and negative magnetic fluxes B*S sensed by the receiving coil are offset and are completely unaffected by the primary field.

[0075] In this embodiment, in order to facilitate data verification and comprehensive analysis, the parameters other than L=0.2m are also calculated:

[0076] According to the existing technology (Neumann formula), the relationship between the offset distance L and the mutual inductance coefficient is calculated when the relative vertical distance H between the single-turn transmitting coil and the single-turn receiving coil is 0.02m, 0.1m, 0.2m, and 0.3m respectively, as shown in the following figure: Figure 4-7As shown. It can be found that, in theory, when the transmitting and receiving coils are at different H, an L can be found to make the mutual inductance coefficient zero. When the mutual inductance coefficient of the transmitting and receiving coils is 0, the offset distances L corresponding to H of 0.02m, 0.1m, 0.2m, and 0.3m are 0.5308m, 0.5544m, 0.6108m, and 0.6916m, respectively. At zero mutual inductance, the receiving coil is divided into two parts, inner and outer, by the transmitting coil. The outer area of ​​the transmitting coil with weaker magnetic field strength is significantly larger. At this position, the positive and negative magnetic fluxes B*S sensed by the receiving coil to the transmitting coil are offset, and are completely unaffected by the primary field. As H increases, the change curve of the mutual inductance coefficient at the zero position becomes smoother, and the offset distance L corresponding to zero mutual inductance also gradually increases.

[0077] 4) According to the results of step 2) and step 3), the position of the circular receiving coil 3 in the coil structure is adjusted;

[0078] In actual operation, the error between the adjusted horizontal distance between the center of the circular receiving coil 3 and the center of the circular transmitting coil 1 and the horizontal distance L between the center of the circular receiving coil 3 and the center of the circular transmitting coil 1 obtained by theoretical calculation in step 3) should not exceed 2 mm.

[0079] V) Perform transient electromagnetic detection using the coil structure adjusted in step 4).

[0080] In summary, the theory shows that when the zero flux position of the RX coil is determined, the present embodiment can receive a pure secondary field signal that is not interfered by the primary field. However, in practical applications, any error (processing error, size error, position error) will reintroduce primary field interference. The receiving area must include the area where the positive and negative alternations of the field strength change most dramatically, and the existence of errors may have a significant impact on the compensation effect.

[0081] Therefore, in order to verify the effect of the above structure in eliminating the coupling of the primary field, the simulation experiment based on the above method is as follows:

[0082] The specific parameters of the simulation system are as follows: the radius of the transmitting coil is 0.5m, 1 turn, the transmitting current is 1A, and the shutdown time is 20us (linear shutdown); the radius of the receiving coil is 0.125m, 160 turns; the conductive ring has 1 turn, a radius of 1m, a self-inductance of 0.168uF, an internal resistance of 0.0056Ω, and a height difference with the transmitting coil of H0=1m. The relative height of the transmitting and receiving coils is fixed at H=0.2m. From the theoretical calculation in the previous article, it can be seen that when the transmitting and receiving coils are zero-coupled, the theoretical horizontal offset distance L=0.6108m. Adjust the offset distance of the receiving coil to simulate the system receiving signal under different horizontal position errors.

[0083] The experimental simulation results are as follows Figure 8-11 As shown, during the off period (0~20us), the conductive loop current ( Figure 8 ) is gradually strengthened by the transmitting current, which is the process of eddy current establishment. After being completely shut down, it gradually decreases due to its own energy consumption, which is the process of eddy current attenuation. Due to the coupling between the conductive ring and the receiving coil, without considering the influence of the parasitic parameters of the receiving coil, the pure secondary field voltage waveform generated by the conductive ring induced by the receiving coil during the process of eddy current establishment and attenuation of the conductive ring is as follows Fig. 9 As shown in the figure, its waveform trend is related to the derivative of the conductive loop current. In the process of eddy current establishment, the current growth is gradually slow, that is, the derivative of the conductive loop current gradually decreases, resulting in a decrease in the secondary field voltage. After the transmitting current is completely turned off, the eddy current changes suddenly from the establishment process to the attenuation process, that is, the polarity of the derivative of the conductive loop current suddenly changes, causing the positive and negative jump of the secondary field voltage, and the voltage gradually decreases as the eddy current decays slowly. Overall, when the offset of the receiving coil of the eccentric self-compensation system does not exceed 2mm, the system offset direction is different, but the fault tolerance curve is similar and always above 99%. In the simulation results, the influence of the primary field is extremely limited and can be ignored. The signal induced by the receiving coil can be used as a pure secondary field signal for subsequent data processing.

[0084] In summary, the experimental results are consistent with the theoretical results, which verifies that the eccentric self-compensating TEM structure can ignore the influence of the primary field leakage inductance within a certain dimensional error range (within 2mm horizontal error), and assumes that the transceiver coil is in a zero coupling state. The signal induced by the receiving coil can be used as a pure secondary field signal for subsequent data processing. Compared with the existing technology, the present application has a lower cost and a higher tolerance to physical dimensional errors.

[0085] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0086] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that those skilled in the art can understand.

Claims

1. A towed transient electromagnetic detection technology based on eccentricity self-compensation, characterized in that: include: A circular transmitting coil (1), wherein the circular transmitting coil (1) is laid on a movable towing vehicle platform (2); A circular receiving coil (3), the circular receiving coil (3) being laid on a high platform (4) movable relative to the towing platform, the plane where the high platform (4) is located is located above the plane where the towing vehicle platform (2) is located, and the two planes are arranged in parallel; A host (5), the host (5) being arranged on a towing vehicle platform (2), and the host (5) being respectively connected to a circular transmitting coil (1) and a circular receiving coil (3); The vertical distance between the platform (4) and the towing vehicle platform (2) is adjustable, and the horizontal relative position of the circular receiving coil (3) and the circular transmitting coil (1) is also adjustable. The position of the circular receiving coil (3) is determined when the mutual inductance of the circular transmitting coil (1) and the circular receiving coil is zero.

2. The towed transient electromagnetic detection technology based on eccentricity self-compensation according to claim 1 is characterized in that: The radius of the circular transmitting coil (1) is greater than the radius of the circular receiving coil (3).

3. The towed transient electromagnetic detection technology based on eccentricity self-compensation according to claim 1 is characterized in that: The radius R of the circular transmitting coil (1) is 0.5 m, and the radius r of the circular receiving coil (3) is 0.125 m.

4. The towed transient electromagnetic detection technology based on eccentricity self-compensation according to claim 1 is characterized in that: The direction of the current emitted by the host (5) to the circular transmitting coil (1) is counterclockwise, the relative vertical height H between the circular receiving coil (3) and the circular transmitting coil (1) is 0.2 m, and the horizontal distance L between the center of the circular receiving coil (3) and the center of the circular transmitting coil (1) is 0.6108 m.

5. A towed transient electromagnetic detection method based on eccentricity self-compensation, characterized in that: include: 1) Preliminary laying of coil structure; 2) According to theoretical calculation and analysis of relevant parameters in the existing coil structure, a more appropriate vertical distance H between the circular receiving coil (3) and the circular transmitting coil (1) is selected; 3) Based on the vertical distance L determined in step 2), further theoretically calculate the horizontal distance L between the center of the circular receiving coil (3) and the center of the circular transmitting coil (1) corresponding to the height; 4) According to the results of step 2) and step 3), the position of the circular receiving coil (3) in the coil structure is adjusted; V) Perform transient electromagnetic detection using the coil structure adjusted in step 4).

6. The towed transient electromagnetic detection method based on eccentricity self-compensation according to claim 5 is characterized in that: In the step 1), the specific contents of the preliminary laying of the coil structure are as follows: The plane where the towing vehicle platform (2) is located is arranged parallel to the plane where the high platform (4) is located, the circular transmitting coil (1) is laid on the towing vehicle platform (2), and the circular receiving coil (3) is laid on the high platform (4).

7. The towed transient electromagnetic detection method based on eccentricity self-compensation according to claim 5 is characterized in that: In step 2), the relevant parameters in the coil structure include: The number of turns of the circular transmitting coil (1), the number of turns of the circular receiving coil (3), the radius R of the circular transmitting coil (1), the radius r of the circular receiving coil (3), the current intensity I emitted by the subject to the circular transmitting coil (1), the current direction and the horizontal distance L between the center of the circular receiving coil (3) and the center of the circular transmitting coil (1).

8. The towed transient electromagnetic detection method based on eccentricity self-compensation according to claim 5 is characterized in that: The specific contents of step 2) are: 2.1) Taking different vertical distances H between the circular receiving coil (3) and the circular transmitting coil (1), adjusting the horizontal distance L between the center of the circular receiving line and the center of the circular transmitting coil (1), and obtaining the relationship between the field strength of the primary field in the vertical direction and the horizontal distance L at different vertical distances H; 2.2) Take the vertical distance H where the field changes less dramatically with different horizontal distances L; 2.3) and take the approximate horizontal distance L1 where the field changes most dramatically with different vertical distances H.

9. The towed transient electromagnetic detection method based on eccentricity self-compensation according to claim 5 is characterized in that: The specific contents of step 3 are: 3.1) Place the circular receiving coil at the vertical distance H in step 2.2) to the approximate horizontal distance L1 in step 2.3); 3.2) By calculating the mutual inductance coefficient between the circular transmitting coil (1) and the circular receiving coil, the size of the horizontal distance L when zero coupling is obtained.

10. The towed transient electromagnetic detection method based on eccentricity self-compensation according to claim 5, characterized in that: In step 4), the requirements for adjusting the coil structure in step 1) according to the calculation results are: In actual operation, the error between the adjusted horizontal distance between the center of the circular receiving coil (3) and the center of the circular transmitting coil (1) and the horizontal distance L between the center of the circular receiving coil (3) and the center of the circular transmitting coil (1) obtained by theoretical calculation in step 3) should not exceed 2 mm.

Images