A towed transient electromagnetic gradient detection device and method based on a weakly coupled transmitting and receiving structure

Abstract

The present application belongs to the field of geophysical and geological exploration equipment and is a towed transient electromagnetic gradient detection device and method based on a weakly coupled transmitting and receiving structure, comprising: a transmitting coil for generating an excitation current; a receiving coil for receiving a secondary field signal, comprising a first receiving coil, a second receiving coil, and a third receiving coil, wherein the first receiving coil and the second receiving coil have the same size parameters, but are different from the size parameters of the third receiving coil; the first receiving coil and the second receiving coil are located in the same plane and at the same height from the plane where the transmitting coil is located; the first receiving coil and the second receiving coil are eccentrically arranged relative to the transmitting coil and are symmetrical about the central axis of the transmitting coil; the second receiving coil and the third receiving coil are coaxial and parallel. The present application can effectively suppress environmental noise interference, improve data signal-to-noise ratio, increase effective data length, and increase detection depth, thereby achieving blind-spot detection in all depths and depths.

Description

Technical Field

[0001] The present application relates to the field of geophysical and geological exploration equipment, and specifically to a towed transient electromagnetic gradient detection device and method based on a weakly coupled transceiver structure. Background Art

[0002] The towed transient electromagnetic method (TEM) is a highly efficient geophysical exploration and detection method based on the principle of electromagnetic induction. It primarily emits pulsed current through an ungrounded controlled transmitting coil, generating an induced current within the geological body. This gradually changing induced current then generates a secondary magnetic field around it. TEM explores and detects underground anomalies by detecting the differences in the secondary magnetic field.

[0003] At present, the main method of detecting the secondary magnetic field by towed transient electromagnetic method is to use a wound multi-turn metal coil as the induction device, but there are the following problems:

[0004] 1. In the early stage of work, the secondary field signal and the primary field are coupled with each other, resulting in the loss of early signals and the existence of shallow detection blind spots.

[0005] 2. Due to the dragging mobile measurement, the number of superpositions of a single equivalent measuring point is limited, the signal-to-noise ratio is low in the late stage, and the data quality is poor.

[0006] 3. When working in a fast-moving mode, the single-receiving working mode has insufficient lateral resolution due to the volume effect, and cannot identify small-sized targets.

[0007] In the field of transient electromagnetic receiver research, research on reducing detection blind spots has only solved the shallow blind spots caused by transmit-receive coupling, but has failed to improve the data signal-to-noise ratio and lateral resolution. Therefore, under the same transmission conditions, how to eliminate primary field coupling, obtain a wider spectrum of secondary field signals, and further increase the late signal-to-noise ratio have become key factors in improving the detection capabilities of towed transient electromagnetic (TEM) systems. Summary of the Invention

[0008] In a first aspect, an embodiment of the present application provides a towed transient electromagnetic gradient detection device based on a weakly coupled transceiver structure, which solves the problems of low signal-to-noise ratio, poor lateral and vertical resolution, and shallow detection blind spots caused by coupling of transceiver coils.

[0009] A second aspect of the embodiments of the present application provides a towed transient electromagnetic gradient detection method based on a weakly coupled transceiver structure.

[0010] This application is implemented in this way.

[0011] A first aspect of an embodiment of the present application provides a towed transient electromagnetic gradient detection device based on a weakly coupled transceiver structure, comprising:

[0012] a transmitting coil for generating an excitation current;

[0013] A receiving coil for receiving a secondary field signal, comprising a first receiving coil, a second receiving coil, and a third receiving coil. The first receiving coil and the second receiving coil have the same size parameters, but different size parameters from the third receiving coil. The first receiving coil and the second receiving coil are located in the same plane and at the same height from the plane where the transmitting coil is located. The first receiving coil and the second receiving coil are eccentrically arranged relative to the transmitting coil and are symmetrical about the central axis of the transmitting coil. The second receiving coil and the third receiving coil are coaxial and parallel.

[0014] Furthermore, the height of the first receiving coil from the plane where the transmitting coil is located and the eccentric distance of the first receiving coil relative to the transmitting coil satisfy the following conditions: an initial first height is selected, and an initial eccentric distance between the first receiving coil and the transmitting coil is selected based on the initial first height so that a first magnetic induction intensity is zero, where the first magnetic induction intensity is the first magnetic induction intensity of the first receiving coil inside and outside the transmitting coil.

[0015] Furthermore, the height between the third receiving coil and the plane where the transmitting coil is located satisfies:

[0016] According to the initial eccentric distance between the third receiving coil and the transmitting coil, the initial second height is selected so that the second magnetic induction intensity is zero, where the second magnetic induction intensity is the second magnetic induction intensity of the third receiving coil inside and outside the transmitting coil.

[0017] Furthermore, the first receiving coil and the second receiving coil have the same size parameters, which are different from the size parameters of the third receiving coil, including: the first receiving coil and the second receiving coil have the same shape, size and number of turns, the shape and size of the first receiving coil are larger than the shape and size of the third receiving coil, and the number of turns of the first receiving coil is different from the number of turns of the third receiving coil.

[0018] Furthermore, the first receiving coil, the second receiving coil and the third receiving coil work individually or in combination, and the combined operation includes: the first receiving coil and the second receiving coil work simultaneously, the second receiving coil and the third receiving coil work simultaneously, and the second receiving coil and the third receiving coil work in cascade.

[0019] A second aspect of the embodiments of the present application provides a towed transient electromagnetic gradient detection method based on a weakly coupled transceiver structure, comprising:

[0020] Adjusting the initial first height, the initial eccentric distance, and the initial second height;

[0021] The plane where the transmitting coil and the plane where the receiving coil are located are perpendicular to the ground plane, and a primary field is emitted by the transmitting coil to obtain interference of the primary field when the first receiving coil, the second receiving coil, and the third receiving coil operate individually or in combination. The combined operation includes: the first receiving coil and the second receiving coil operate simultaneously, the second receiving coil and the third receiving coil operate simultaneously, and the second receiving coil and the third receiving coil operate in cascade.

[0022] The plane where the transmitting coil and the plane where the receiving coil are located are parallel to the ground plane, the primary field emitted by the transmitting coil is used to activate the first receiving coil to receive the first data, and the shallow detection data is obtained by inverting the interference between the first data and the first receiving coil;

[0023] Simultaneously turning on the first receiving coil and the second receiving coil, obtaining second data and third data through the first receiving coil and the second receiving coil respectively, and obtaining transverse gradient data by inverting the difference between the second data and the third data;

[0024] Simultaneously turning on the second receiving coil and the third receiving coil, obtaining fourth data and fifth data through the second receiving coil and the third receiving coil respectively, and obtaining vertical gradient data by inverting the difference between the fourth data and the fifth data;

[0025] cascade the second receiving coil and the third receiving coil to obtain sixth data, and invert the sixth data based on the interference between the cascaded second receiving coil and the third receiving coil to obtain deep detection data;

[0026] Full-level detection data are obtained based on deep-level detection data, shallow-level detection data, horizontal gradient data and vertical gradient data.

[0027] Furthermore, the adjustment of the initial first height and the initial eccentric distance includes: connecting the first receiving coil to the detector, transmitting a field through the transmitting coil, observing the waveform in the detector, adjusting the initial first height and the initial eccentric distance to stabilize the waveform, and obtaining the adjusted first height and the adjusted eccentric distance.

[0028] Further, the initial second height is adjusted according to the adjusted eccentric distance, including connecting the third receiving coil to the detector, transmitting a field through the transmitting coil, observing the waveform in the detector, adjusting the initial second height to stabilize the waveform, and obtaining the adjusted second height.

[0029] The multiple technical solutions provided in the embodiments of this application have at least the following technical effects:

[0030] By controlling the operating modes of the three receiving coils, shallow-level detection, lateral gradient differential data acquisition, vertical gradient differential data acquisition, and deep-level detection can be achieved. Transverse gradient differential data acquisition and vertical gradient differential data acquisition can effectively suppress environmental noise interference and improve the data signal-to-noise ratio. The cascade of the two vertical coils increases system sensitivity, increases effective data length, and increases detection depth, thus achieving blind-spot detection in all depths and shallows. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A structural block diagram of a towed transient electromagnetic gradient detection device based on a weakly coupled transceiver structure provided in an embodiment of the present application;

[0032] Figure 2 This is a structural block diagram of the transmitting coil and receiving coil in a towed transient electromagnetic gradient detection device based on a weakly coupled transmitting and receiving structure provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0034] The towed transient electromagnetic method in the embodiments of this application involves carrying a transmitting system and a receiving system on a towed platform to conduct rapid and efficient electromagnetic exploration of the target area. The transmitting system emits transient electromagnetic pulses, and the receiving system receives secondary field signals to detect underground or underwater targets. Due to towed mobile measurement, the number of times a single equivalent measurement point can be stacked is limited, resulting in a low signal-to-noise ratio in the late stage and poor data quality. When operating in a single receiving mode during rapid movement, the volume effect results in insufficient lateral resolution, making it impossible to identify small targets.

[0035] To address these issues, the present application proposes a towed transient electromagnetic gradient detection device based on a weakly coupled transmitter-receiver structure. By employing three receiving coils and one transmitting coil, this device can achieve shallow-level detection, lateral gradient differential data acquisition, vertical gradient differential data acquisition, and deep-level detection. This can effectively suppress environmental noise interference and improve the data signal-to-noise ratio through lateral gradient differential data acquisition and vertical gradient differential data acquisition. The cascaded two vertical coils increase system sensitivity, increase effective data length, and extend the detection depth, thus achieving blind-spot detection across all depths and depths.

[0036] See also Figure 1 The structure diagram of the towed transient electromagnetic gradient detection device based on the weakly coupled transmitting and receiving structure provided by the embodiment of the present application is shown as follows. The towed transient electromagnetic gradient detection device based on the weakly coupled transmitting and receiving structure provided by the embodiment of the present application comprises:

[0037] It includes: a transmitting coil 4, used to generate an excitation current;

[0038] The receiving coil is used to receive the secondary field signal and includes a first receiving coil 3, a second receiving coil 5, and a third receiving coil 6. The first receiving coil 3 and the second receiving coil 5 have the same size parameters, but different size parameters from the third receiving coil. The first receiving coil 3 and the second receiving coil 5 are located in the same plane and at the same height from the plane where the transmitting coil 4 is located. The first receiving coil 3 and the second receiving coil 5 are eccentrically arranged relative to the transmitting coil 4 and are symmetrical about the central axis of the transmitting coil 4. The second receiving coil 5 and the third receiving coil 6 are coaxial and parallel.

[0039] The central axis of the transmitting coil 4 here refers to a line drawn from the geometric center of the transmitting coil 4 perpendicular to the plane in which the transmitting coil 4 lies. Symmetry about the central axis of the transmitting coil 4 means that the geometric centers of the first receiving coil 3 and the second receiving coil 5 are located on either side of the central axis, at the same distance from the central axis. Furthermore, the line connecting the geometric centers of the first receiving coil 3 and the second receiving coil 5 is perpendicular to the central axis.

[0040] The shape of the transmitting coil 4 is not limited and can be rectangular or circular. The shape of the receiving coil is not limited and can be rectangular or circular. Once the shape of the transmitting coil 4 is selected, the shape of the receiving coil can be consistent with or inconsistent with the shape of the transmitting coil 4. Figure 1 The transmitting coil 4 and the receiving coil in the embodiment are rectangular coils as an example.

[0041] It can be understood that the transmitting coil 4 and the transmitter 2 form a transmitting system, and the receiving coil and the receiver 1 form a receiving system. The transmitter 2 is provided to control the generation of a transmitting current or excitation current in the transmitting coil 4. Through the synchronization signal between the receiver 1 and the transmitter 2, the receiving signal receives the secondary field signal and is processed by the circuit of the receiver 1.

[0042] In order to achieve the fixation of the transmitting coil 4 and the receiving coil, in one embodiment, the transmitting system and the receiving system are both arranged on a support platform, and the support platform is mounted on the towing platform. Taking the towing platform as a reference, the transmitting coil 4 is arranged on the towing platform at a height of The first supporting platform and the second supporting platform are set up at A third support platform is set up parallel to the first support platform. The heights of the three support platforms are adjustable. In order to facilitate adjustment, adjustable support legs can be set up. The transmitting coil 4 is fixed on the towing platform. For example, the length is 2a and the width is 2b. The first receiving coil 3 is fixed on the first support platform. For example, the side length is 2c and the number of turns is 2c. The second receiving coil 5 is fixed on the second supporting platform, which is the same as the first receiving coil 3. Taking a square as an example: the side length is 2c, and the number of turns is The third receiving coil 6 is fixed on the third supporting platform. Taking a square as an example: the side length is 2d and the number of turns is The eccentric distances between the three receiving coils and the transmitting coil 4 are , wherein the second receiving coil 5 and the third receiving coil 6 are plane-parallel and coaxial.

[0043] In the projection of the transmitting coil 4 , the first receiving coil 3 , the second receiving coil 5 and the third receiving coil 6 are partially located within the area surrounded by the transmitting coil 4 , and partially located outside the area surrounded by the transmitting coil 4 .

[0044] like Figure 2 As shown, both the transmitting coil 4 and the receiving coil are circular coils. The transmitting coil 4 is connected to the transmitter 2 via a twisted pair cable. The transmitter 2 and the receiver 1 are connected via a synchronization signal line. The first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 are connected to the receiving channel of the receiver 1 via a signal shielding cable. There are three receiving channels, which receive data from the first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 respectively. A control switch is provided in the middle of the signal shielding cable to control the on / off of the signal. The second receiving coil 5 and the third receiving coil 6 are cascaded via a control switch. The receiver 1 is connected to the industrial computer via an Ethernet cable.

[0045] Transmitter 2 includes a transmission control unit, an H-bridge drive circuit, a power supply, a DC-DC adjustable constant current source, and an H-bridge chopper circuit. Furthermore, the power supply provides power to each module in transmitter 2. The transmission control unit transmits a 25Hz bipolar PWM wave to the H-bridge drive circuit. The H-bridge drive circuit drives the H-bridge chopper circuit to convert the constant wave source provided by the DC-DC adjustable constant current source into a bipolar trapezoidal wave. The bipolar trapezoidal wave excites a primary field through the transmitting coil 4 and propagates underground.

[0046] Receiver 1 includes a power supply and three receiving channels. Each receiving channel includes an overvoltage protection circuit, a preamplifier, and a signal conditioning circuit. The three receiving channels are connected to a multi-channel synchronous data acquisition module, which is in turn connected to a microcontroller.

[0047] The first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 are connected to the three receiving channels of the receiver 1 via shielded cables. Each receiving channel filters and amplifies the received signal and then connects to a multi-channel synchronous data acquisition module. The multi-channel synchronous data acquisition module is connected to the microcontroller via a control bus. When the microcontroller receives the synchronization signal from the transmitting control unit, the microcontroller sends a control sequence to the multi-channel synchronous data acquisition module to start collecting the received signal.

[0048] In one embodiment, the height of the first receiving coil 3 from the plane where the transmitting coil 4 is located and the eccentric distance of the first receiving coil 3 relative to the transmitting coil 4 satisfy the following conditions: an initial first height is selected, and an initial eccentric distance between the first receiving coil 3 and the transmitting coil 4 is selected based on the initial first height so that a first magnetic induction intensity is zero, where the first magnetic induction intensity is the first magnetic induction intensity of the first receiving coil 3 inside and outside the transmitting coil 4.

[0049] The first receiving coil 3 and the second receiving coil 5 have the same dimensional parameters, but differ from the dimensional parameters of the third receiving coil. These parameters include: the first receiving coil 3 and the second receiving coil 5 have the same shape, size, and number of turns; the shape and size of the first receiving coil 3 are larger than those of the third receiving coil; and the number of turns of the first receiving coil 3 is different from that of the third receiving coil. For example, the first receiving coil 3 and the second receiving coil 5 are both square, with identical sides and the same number of turns; the third receiving coil is square, with smaller sides than the first receiving coil 3, and has a different number of turns than the first receiving coil 3.

[0050] Taking the rectangular transmitting coil 4 and the square receiving coil as an example, the initial position of the receiving coil is explained;

[0051] like Figure 2 As shown, the long side length of the transmitting coil 4 is 2b, the short side length is 2a, and the number of turns is , the number of turns of the first receiving coil 3 and the second receiving coil 5 is , the number of turns of the second receiving coil 5 is , the side length is 2c, and the eccentricity with the transmitting coil 4 is The height difference between the first receiving coil 3 and the second receiving coil 5 and the transmitting coil 4 is , the height difference between the third receiving coil 6 and the transmitting coil 4 is , the height difference between the first receiving coil 3 and the third receiving coil 6 is ;

[0052] The transmitting coil 4 is placed in parallel with the three receiving coils and is only sensitive to the transmitting magnetic induction intensity in the Z direction in space. The magnetic field intensity superposition of the four sides of the transmitting coil 4 at any point in space is obtained. The first receiving coil 3 and the second receiving coil 5 are symmetrical about the central axis of the transmitting coil 4, and have the same height and the same number of turns. Taking the first receiving coil 3 as an example, see Figure 2 As shown:

[0053] The magnetic induction intensity within the range covered by the first receiving coil 3 and the transmitting coil 4 is:

[0054] ,

[0055] The coverage range refers to the portion where the projection of the first receiving coil 3 on the plane where the transmitting coil 4 is located overlaps with the transmitting coil 4 , and the magnetic induction intensity of the transmitting coil 4 in the first receiving coil 3 corresponding to the overlapping portion is calculated.

[0056] The magnetic induction intensity outside the range covered by the first receiving coil 3 and the transmitting coil 4 is calculated as:

[0057] ,

[0058] The outside of the coverage range refers to the magnetic induction intensity in the first receiving coil 3 outside the portion where the projection of the first receiving coil 3 on the plane where the transmitting coil 4 is located overlaps with the transmitting coil 4 .

[0059] Among them, the coordinate system is established with the center of the transmitting coil 4 as the origin, and , what we get is about and function, express Axis coordinates, using replace What you get is about and Function:

[0060] ,

[0061] First determine the initial first height , generally 0.1m-0.3m, determined based on the size of transmitting coil 4. If the maximum size of transmitting coil 4 is less than 2m, use 0.1-0.2m. If the maximum size of transmitting coil 4 is greater than 2m, use 0.3m. Generally, use 1 / 10 of the maximum size of transmitting coil 4. For example, for a circular coil, the maximum size is the diameter, and for a rectangular coil, the maximum size is the longest side length.

[0062] An initial eccentric distance between the first receiving coil 3 and the transmitting coil 4 is selected according to the initial first height.

[0063] In the same way, based on the initial eccentric distance between the third receiving coil 6 and the transmitting coil 4, an initial second height is selected so that the second magnetic induction intensity is zero. The second magnetic induction intensity is the second magnetic induction intensity of the third receiving coil 6 inside and outside the transmitting coil 4.

[0064] Here, the initial first height and the initial second height are both relative to the height of the towing platform.

[0065] However, since the dimensional errors of the transmitting coil 4 and the receiving coil are inevitable during the winding and installation process, it is necessary to slightly move the receiving coil near the theoretical position value, and observe the secondary field signal received by the receiving coil through an oscilloscope until it reaches the optimal state, and finally fix it.

[0066] Connect the first receiving coil 3 to the detector, transmit a primary field through the transmitting coil 4, observe the waveform in the detector, and adjust the initial first height and initial eccentricity to achieve the optimal waveform, obtaining the adjusted first height and adjusted eccentricity. Set the eccentricity between the third receiving coil 6 and the transmitting coil 4 based on the adjusted eccentricity. Connect the third receiving coil 6 to the detector, transmit a primary field through the transmitting coil 4, observe the waveform in the detector, and adjust the initial second height to achieve the optimal or stable waveform, obtaining the adjusted second height. The waveform here refers to the secondary field signal waveform, and the secondary field signal state is determined based on the waveform. The optimal state refers to a clear waveform with no jitter of abnormal frequency components, etc., exhibited during multiple movements. This refers to the other waveforms during the adjustment process.

[0067] By controlling the operating modes of the three receiving coils, shallow-level detection data, lateral gradient data, vertical gradient data, and deep-level detection data can be acquired. The resulting detection data not only provides more accurate early information, but also increases the effective data length and the detection depth. At the same time, the lateral gradient data and vertical gradient data can effectively suppress environmental noise interference and improve the data signal-to-noise ratio.

[0068] A towed transient electromagnetic gradient detection method based on a weakly coupled transceiver structure according to an embodiment of the present application includes:

[0069] Adjusting the initial first height, the initial eccentric distance, and the initial second height;

[0070] The plane where the transmitting coil 4 and the plane where the receiving coil are located are perpendicular to the ground plane, and a primary field is emitted by the transmitting coil 4 to obtain interference of the primary field when the first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 are working individually or in combination. The combined operation includes: the first receiving coil 3 and the second receiving coil 5 working simultaneously, the second receiving coil 5 and the third receiving coil 6 working simultaneously, and the second receiving coil 5 and the third receiving coil 6 working in cascade.

[0071] The plane where the transmitting coil 4 and the plane where the receiving coil are located are parallel to the ground plane. The first receiving coil 3 is turned on separately to receive the first data through the primary field emitted by the transmitting coil 4. The shallow detection data is obtained by inverting the interference between the first data and the first receiving coil 3.

[0072] Simultaneously turning on the first receiving coil 3 and the second receiving coil 5, obtaining second data and third data through the first receiving coil 3 and the second receiving coil 5 respectively, and obtaining transverse gradient data by inverting the difference between the second data and the third data;

[0073] Simultaneously turning on the second receiving coil 5 and the third receiving coil 6, obtaining fourth data and fifth data through the second receiving coil 5 and the third receiving coil 6 respectively, and obtaining vertical gradient data by inverting the difference between the fourth data and the fifth data;

[0074] The second receiving coil 5 and the third receiving coil 6 are cascaded to obtain sixth data, and the deep detection data is obtained by inverting the sixth data and the interference of the cascaded second receiving coil 5 and the third receiving coil 6;

[0075] Full-level detection data are obtained based on deep-level detection data, shallow-level detection data, horizontal gradient data and vertical gradient data.

[0076] The adjustment of the initial first height, the initial eccentric distance and the initial second height includes: connecting the first receiving coil 3 to the detector, transmitting a field through the transmitting coil 4, observing the waveform in the detector, adjusting the initial first height and the initial eccentric distance so that the waveform is in an optimal state, and obtaining the adjusted first height and the adjusted eccentric distance.

[0077] The initial second height is adjusted according to the adjusted eccentric distance, including connecting the third receiving coil 6 to the detector, transmitting a field through the transmitting coil 4, observing the waveform in the detector, adjusting the initial second height so that the waveform is in the optimal state, and obtaining the adjusted second height.

[0078] During calibration, the planes of the transmitting coil 4 and the receiving coil must be perpendicular to the ground. The towed platform is hoisted vertically to a certain height in an open area, and various control switches are controlled to connect or disconnect the receiving coil from receiver 1. Transmitter 2 emits a bipolar trapezoidal wave, transmitting a primary field through transmitting coil 4.

[0079] Specifically, the first receiving coil 3 is connected to a receiving channel of the receiver 1 through a lead, the transmitter 2 transmits a bipolar trapezoidal wave, and the waveform of the first receiving coil 3 is recorded. Since the first receiving coil 3 and the second receiving coil 5 are completely symmetrical, the waveform of the second receiving coil 5 is the same as the waveform of the first receiving coil 3. The waveform of the first receiving coil 3 is the same. It is the interference of the primary field emitted by the transmitting coil 4 on the first receiving coil 3; it is also the interference of the primary field emitted by the transmitting coil 4 on the second receiving coil 5.

[0080] Connect the third receiving coil 6 to a receiving channel of the receiver 1 through a lead. Transmitter 2 transmits a bipolar trapezoidal wave and records the waveform of the third receiving coil 6. ; Waveform of the third receiving coil 6 It is the interference of the primary field emitted by the transmitting coil 4 on the third receiving coil 6;

[0081] Connect the first receiving coil 3 and the second receiving coil 5 to different receiving channels of the receiver 1. Transmitter 2 transmits a bipolar trapezoidal wave and records the waveform of the first receiving coil 3. and the waveform of the second receiving coil 5 , the waveform of the first receiving coil 3 It is the sum of the interference of the primary field emitted by the transmitting coil 4 on the first receiving coil 3 and the mutual interference between the first receiving coil 3 and the second receiving coil 5. At the same time, the sum of the interference of the primary field emitted by the transmitting coil 4 on the second receiving coil 5 and the mutual interference between the first receiving coil 3 and the second receiving coil 5 is the waveform , the first receiving coil 3 and the second receiving coil 5 have the same size and number of turns, and are symmetrical about the central axis of the transmitting coil 4, so = .

[0082] Connect the second receiving coil 5 and the third receiving coil 6 to different receiving channels of the receiver 1. Transmitter 2 transmits a bipolar trapezoidal wave and records the waveform of the second receiving coil 5. and the waveform of the third receiving coil 6 The sum of the interference of the primary field emitted by the transmitting coil 4 on the second receiving coil 5 and the mutual interference between the second receiving coil 5 and the third receiving coil 6 is The sum of the interference of the primary field emitted by the transmitting coil 4 on the third receiving coil 6 and the mutual interference between the second receiving coil 5 and the third receiving coil 6 is waveform ;

[0083] The second receiving coil 5 and the third receiving coil 6 are cascaded, that is, the second receiving coil 5 and the third receiving coil 6 are connected in series, and then connected to one of the receiving channels of the receiver 1. The waveform of the cascade connection of the second receiving coil 5 and the third receiving coil 6 is recorded. The cascade interference of the primary field emitted by the transmitting coil 4 on the second receiving coil 5 and the third receiving coil 6 is obtained as the waveform .

[0084] In one embodiment, the plane where the transmitting coil 4 and the plane where the receiving coil are located are parallel to the ground plane. The first receiving coil 3 is turned on separately to receive the first data through the primary field emitted by the transmitting coil 4. The shallow detection data is obtained by inverting the interference between the first data and the first receiving coil 3.

[0085] Record the waveform of the first receiving coil 3 as the first data , ,in, is the response of the geological structure obtained by the first receiving coil 3, is the first noise data, and the waveform data - Perform inversion.

[0086] In one embodiment, the first receiving coil 3 and the second receiving coil 5 are turned on simultaneously, and the second data and the third data are obtained through the first receiving coil 3 and the second receiving coil 5 respectively, and the transverse gradient data is obtained by inverting the difference between the second data and the third data;

[0087] Connect the first receiving coil 3 and the second receiving coil 5 to different receiving channels of the receiver 1. The transmitter 2 transmits a field signal to the underground through the ground transmitting coil 4 to detect the underground structure. The waveforms of the first receiving coil 3 and the second receiving coil 5 are recorded as the second data. and third-party data ,

[0088] ,

[0089] ,

[0090] in, and The geological body response signals obtained by the first receiving coil 3 and the second receiving coil 5 are respectively, and equal, and For the second noise data, the two receiving coils are in the same environment, so . Get the waveform of the transverse gradient difference data :

[0091] ,

[0092] Waveform of transverse gradient difference data Perform inversion. It can eliminate environmental noise interference, improve the signal-to-noise ratio, reduce volume effects, achieve lateral gradient data acquisition, and improve the lateral resolution of the detection system.

[0093] In one embodiment, the second receiving coil 5 and the third receiving coil 6 are turned on simultaneously, and fourth data and fifth data are obtained through the second receiving coil 5 and the third receiving coil 6 respectively, and vertical gradient data is obtained by inverting the difference between the fourth data and the fifth data;

[0094] The second receiving coil 5 and the third receiving coil 6 are connected to different receiving channels of the receiver 1. The transmitter 2 transmits a field signal to the underground through the transmitting coil 4 to detect the underground structure. The waveforms of the second receiving coil 5 and the third receiving coil 6 are recorded as the fourth data. and Fifth Data ,

[0095] ,

[0096] ,

[0097] in, and are the geological body response signals obtained by the second receiving coil 5 and the third receiving coil 6 respectively, and For the third noise data, the two receiving coils are in the same environment, so = . Get the waveform of vertical gradient difference data : , waveform of vertical gradient difference data Performing inversion to obtain vertical gradient data can eliminate environmental noise interference, improve the signal-to-noise ratio, reduce volume effects, achieve vertical gradient data acquisition, and enhance the vertical resolution of the detection system.

[0098] In one embodiment, the second receiving coil 5 and the third receiving coil 6 are cascaded to obtain sixth data, and the deep detection data is obtained by inverting the sixth data and the interference of the cascade of the second receiving coil 5 and the third receiving coil 6; the transmitter 2 transmits a field signal into the ground through the transmitting coil 4, and records the sixth data detected by the cascade combination of the second receiving coil 5 and the third receiving coil 6. ,

[0099] ,

[0100] in, The second receiving coil 5 and the third receiving coil 6 are cascaded and combined to detect the geological body response signal. is the fourth noise data, for the waveform data Inversion is performed to obtain deep-level detection data, which is used to improve system sensitivity, increase effective data length, increase detection depth, and complete deeper exploration of underground structures.

[0101] Finally, full-level detection data is obtained and imaging is performed based on the deep-level detection data, shallow-level detection data, lateral gradient data and vertical gradient data.

[0102] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A towed transient electromagnetic gradient detection device based on a weakly coupled transceiver structure, characterized in that: include: a transmitting coil for generating an excitation current; A receiving coil for receiving a secondary field signal, comprising a first receiving coil, a second receiving coil, and a third receiving coil. The first receiving coil and the second receiving coil have the same size parameters, but different size parameters from the third receiving coil. The first receiving coil and the second receiving coil are located in the same plane and at the same height from the plane where the transmitting coil is located. The first receiving coil and the second receiving coil are eccentrically arranged relative to the transmitting coil and symmetrically arranged about the central axis of the transmitting coil. The second receiving coil and the third receiving coil are coaxial and parallel. The first receiving coil, the second receiving coil and the third receiving coil work individually or in combination. The combined operation includes: the first receiving coil and the second receiving coil work simultaneously, the second receiving coil and the third receiving coil work simultaneously, and the second receiving coil and the third receiving coil work in cascade.

2. The towed transient electromagnetic gradient detection device based on a weakly coupled transmitting and receiving structure according to claim 1 is characterized in that: The height of the first receiving coil from the plane where the transmitting coil is located and the eccentric distance of the first receiving coil relative to the transmitting coil satisfy the following conditions: an initial first height is selected, and an initial eccentric distance between the first receiving coil and the transmitting coil is selected based on the initial first height so that a first magnetic induction intensity is zero, where the first magnetic induction intensity is the first magnetic induction intensity of the first receiving coil inside and outside the transmitting coil.

3. The towed transient electromagnetic gradient detection device based on a weakly coupled transmitting and receiving structure according to claim 2 is characterized in that: The height between the third receiving coil and the plane where the transmitting coil is located satisfies: According to the initial eccentric distance between the third receiving coil and the transmitting coil, the initial second height is selected so that the second magnetic induction intensity is zero, where the second magnetic induction intensity is the second magnetic induction intensity of the third receiving coil inside and outside the transmitting coil.

4. The towed transient electromagnetic gradient detection device based on a weakly coupled transmitting and receiving structure according to claim 1 is characterized in that: The first receiving coil and the second receiving coil have the same size parameters, which are different from the size parameters of the third receiving coil, including: the first receiving coil and the second receiving coil have the same shape, size and number of turns, the shape and size of the first receiving coil are larger than the shape and size of the third receiving coil, and the number of turns of the first receiving coil is different from the number of turns of the third receiving coil.

5. A towed transient electromagnetic gradient detection method based on a weakly coupled transmitter-receiver structure, using the towed transient electromagnetic gradient detection device based on a weakly coupled transmitter-receiver structure according to any one of claims 1 to 4, characterized in that: include: Adjusting the initial first height, the initial eccentric distance, and the initial second height; The plane where the transmitting coil and the plane where the receiving coil are located are perpendicular to the ground plane, and a primary field is emitted by the transmitting coil to obtain interference of the primary field when the first receiving coil, the second receiving coil, and the third receiving coil operate individually or in combination. The combined operation includes: the first receiving coil and the second receiving coil operate simultaneously, the second receiving coil and the third receiving coil operate simultaneously, and the second receiving coil and the third receiving coil operate in cascade. The plane where the transmitting coil and the plane where the receiving coil are located are parallel to the ground plane, the primary field emitted by the transmitting coil is used to activate the first receiving coil to receive the first data, and the shallow detection data is obtained by inverting the interference between the first data and the first receiving coil; Simultaneously turning on the first receiving coil and the second receiving coil, obtaining second data and third data through the first receiving coil and the second receiving coil respectively, and obtaining transverse gradient data by inverting the difference between the second data and the third data; Simultaneously turning on the second receiving coil and the third receiving coil, obtaining fourth data and fifth data through the second receiving coil and the third receiving coil respectively, and obtaining vertical gradient data by inverting the difference between the fourth data and the fifth data; cascade the second receiving coil and the third receiving coil to obtain sixth data, and invert the sixth data based on the interference between the cascaded second receiving coil and the third receiving coil to obtain deep detection data; Full-level detection data are obtained based on deep-level detection data, shallow-level detection data, horizontal gradient data and vertical gradient data.

6. The towed transient electromagnetic gradient detection method based on a weakly coupled transmitting and receiving structure according to claim 5 is characterized in that: The adjustment of the initial first height and the initial eccentric distance includes: connecting the first receiving coil to the detector, transmitting a field through the transmitting coil, observing the waveform in the detector, adjusting the initial first height and the initial eccentric distance to stabilize the waveform, and obtaining the adjusted first height and the adjusted eccentric distance.

7. The towed transient electromagnetic gradient detection method based on a weakly coupled transmitting and receiving structure according to claim 6 is characterized in that: The initial second height is adjusted according to the adjusted eccentric distance, including connecting the third receiving coil to the detector, transmitting a field through the transmitting coil, observing the waveform in the detector, adjusting the initial second height to stabilize the waveform, and obtaining the adjusted second height.

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