Pull-type transient electromagnetic gradient detection device and method based on transmitting-receiving weak coupling structure

Abstract

The invention belongs to the field of geophysical geological exploration equipment, and relates to a pull-type transient electromagnetic gradient detection device and method based on a transmitting-receiving weak coupling structure, and the device comprises a transmitting coil which is used for generating excitation current; the receiving coil is used for receiving a secondary field signal and comprises a first receiving coil, a second receiving coil and a third receiving coil, and the size parameters of the first receiving coil and the second receiving coil are the same and are different from those of the third receiving coil; the first receiving coil and the second receiving coil are located on the same plane, have the same height from the plane where the transmitting coil is located, are eccentrically arranged relative to the transmitting coil and are symmetrical about the central axis of the transmitting coil; and the second receiving coil and the third receiving coil are coaxially arranged in parallel. According to the invention, environmental noise interference can be effectively suppressed, and the data signal-to-noise ratio is improved; and the effective data length is increased, and the detection depth is increased, so that non-blind area detection of the deep and shallow whole space is realized.

Description

Technical Field

[0001] This application belongs to the field of geophysical geological exploration equipment, and more specifically, it is a towed transient electromagnetic gradient detection device and method based on a weak transceiver coupling structure. Background Art

[0002] The towed transient electromagnetic method (TEM) is an efficient geophysical exploration and detection method based on the principle of electromagnetic induction. It mainly controls the transmitting coil to emit pulsed current without grounding, induces current inside the geological body, and generates a secondary magnetic field around the gradually changing induced current. TEM explores and detects underground anomalies by detecting the change differences of the secondary magnetic field.

[0003] Currently, the main method for detecting the secondary magnetic field by the towed transient electromagnetic method is to use a wound multi-turn loop metal coil as the induction device, but there are the following problems: 1. In the early stage of work, the secondary field signal is coupled with the primary field, resulting in the loss of early signals and a blind area in shallow layer detection.

[0004] 2. Due to towed mobile measurement, the stacking times of a single equivalent measurement point are limited, the signal-to-noise ratio in the late stage is low, and the data quality is poor.

[0005] 3. When working in a fast moving mode, in the single-receiver working mode, due to the volume effect, the lateral resolution is insufficient and small-sized target bodies cannot be identified.

[0006] In the research field of transient electromagnetic receiving devices, for the research on reducing the detection blind area, only the problem of the shallow blind area caused by transceiver coupling has been solved, and the data signal-to-noise ratio and lateral resolution cannot be improved. Therefore, how to eliminate the primary field coupling, obtain a secondary field signal with a wider spectrum, and further increase the signal-to-noise ratio of the late stage signal under the same emission conditions has become the key factor in improving the detection ability of the towed transient electromagnetic method. Summary of the Invention

[0007] The first aspect of the embodiments of this application provides a towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure, which solves the problems of low signal-to-noise ratio, poor lateral and longitudinal resolution, and the existence of a shallow detection blind area caused by transceiver coil coupling.

[0008] The second aspect of the embodiments of this application provides a towed transient electromagnetic gradient detection method based on a weak transceiver coupling structure.

[0009] This application is implemented as follows: A towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure in the first aspect of the embodiments of this application includes: The transmitting coil is used to generate an exciting current; The receiving coil is used to receive the secondary field signal, including 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, which are different from those of the third receiving coil. The first receiving coil and the second receiving coil are located in the same plane and have 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 symmetric about the central axis of the transmitting coil. The second receiving coil and the third receiving coil are coaxially and parallelly placed.

[0010] Further, 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: select an initial first height, and select an initial eccentric distance between the first receiving coil and the transmitting coil according to the initial first height, so that the first magnetic induction intensity is zero, and the first magnetic induction intensity is the first magnetic induction intensity of the first receiving coil inside and outside the transmitting coil.

[0011] Further, 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, select an initial second height so that the second magnetic induction intensity is zero, and the second magnetic induction intensity is the second magnetic induction intensity of the third receiving coil inside and outside the transmitting coil.

[0012] Further, the first receiving coil and the second receiving coil have the same size parameters, which are different from those of the third receiving coil, including: the shape sizes and the number of turns of the first receiving coil and the second receiving coil are the same, the shape size of the first receiving coil is larger than that of the third receiving coil, and the number of turns of the first receiving coil is different from that of the third receiving coil.

[0013] Further, the first receiving coil, the second receiving coil and the third receiving coil work alone or in combination. The combination work 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.

[0014] In the second aspect of the embodiments of the present application, a towed transient electromagnetic gradient detection method based on a weak transceiver coupling structure is provided, including: Adjust the initial first height, the initial eccentric distance and the initial second height; The plane where the transmitting coil is located and the plane where the receiving coil is located are perpendicular to the ground plane. By transmitting a primary field through the transmitting coil, the interference of the primary field when the first receiving coil, the second receiving coil, and the third receiving coil work alone or in combination is obtained. The combined work includes: the first receiving coil and the second receiving coil working simultaneously, the second receiving coil and the third receiving coil working simultaneously, and the second receiving coil and the third receiving coil cascading. The plane where the transmitting coil is located and the plane where the receiving coil is located are parallel to the ground plane. Through the primary field transmitted by the transmitting coil, the first receiving coil is separately turned on to receive the first data, and the data for shallow detection is obtained by inverting the first data and the interference of the first receiving coil. The first receiving coil and the second receiving coil are turned on simultaneously. The second data and the third data are obtained through the first receiving coil and the second receiving coil respectively, and the lateral gradient data is obtained by inverting the difference between the second data and the third data. The second receiving coil and the third receiving coil are turned on simultaneously. The fourth data and the fifth data are obtained through the second receiving coil and the third receiving coil respectively, and the vertical gradient data is obtained by inverting the difference between the fourth data and the fifth data. The second receiving coil and the third receiving coil are cascaded to obtain the sixth data, and the data for deep detection is obtained by inverting the sixth data and the interference of the cascade of the second receiving coil and the third receiving coil. The full-level detection data is obtained based on the data for deep detection, the data for shallow detection, the lateral gradient data, and the vertical gradient data.

[0015] Further, the adjustment of the initial first height and the initial eccentricity distance includes: connecting the first receiving coil to the detector, transmitting a primary field through the transmitting coil, observing the waveform in the detector, and adjusting the initial first height and the initial eccentricity distance so that the waveform is stable, thereby obtaining the adjusted first height and the adjusted eccentricity distance.

[0016] Further, adjusting the initial second height according to the adjusted eccentricity distance includes connecting the third receiving coil to the detector, transmitting a primary field through the transmitting coil, observing the waveform in the detector, and adjusting the initial second height so that the waveform is stable, thereby obtaining the adjusted second height.

[0017] The multiple technical solutions provided by the embodiments of the present application have at least the following technical effects: By controlling the working modes of the three receiving coils, shallow detection, acquisition of lateral gradient differential data, acquisition of vertical gradient differential data, and deep detection can be realized. The acquisition of lateral gradient differential data and the acquisition of vertical gradient differential data can effectively suppress environmental noise interference and improve the signal-to-noise ratio of the data; the cascading of two vertical coils provides system sensitivity, increases the effective data length, and increases the detection depth, thereby realizing blind-zone-free detection in the entire shallow and deep space. Description of the Drawings

[0018] Figure 1 It is a structural block diagram of a towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure provided by an embodiment of the present application; Figure 2 It is a structural block diagram of a transmitting coil and a receiving coil in a towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure provided by an embodiment of the present application. Detailed Embodiment

[0019] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0020] The towed transient electromagnetic method in the embodiment of the present application refers to quickly and efficiently detecting an electromagnetic field in a target area by carrying a transmitting system and a receiving system on a towed platform. A transient electromagnetic pulse is transmitted by the transmitting system, and a secondary field signal is received by the receiving system to detect underground or underwater targets. Due to towed mobile measurement, the stacking times of a single equivalent measurement point are limited, the signal-to-noise ratio in the late stage is low, and the data quality is poor. When working in a fast moving mode, in the single-receiving working mode, due to the volume effect, the lateral resolution is insufficient and small-sized target bodies cannot be identified.

[0021] Based on the above problems, the towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure proposed in the present application can achieve shallow detection, acquisition of lateral gradient difference data, acquisition of vertical gradient difference data, and deep detection through the structures of three receiving coils and a transmitting coil provided. The acquisition of lateral gradient difference data and vertical gradient difference data can effectively suppress environmental noise interference and improve the signal-to-noise ratio of data; the cascading of two vertical coils provides system sensitivity, increases the effective data length, and increases the detection depth, thereby achieving blind area-free detection in the entire shallow and deep space.

[0022] See Figure 1 As shown in the structural schematic diagram of the towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure provided by an embodiment of the present application, a towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure according to an embodiment of the present application. Includes: Including: a transmitting coil 4 for generating an excitation current; A receiving coil for receiving secondary field signals, including 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, which are different from those of the third receiving coil. The first receiving coil 3 and the second receiving coil 5 are located in the same plane and have 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 symmetric about the central axis of the transmitting coil 4. The second receiving coil 5 and the third receiving coil 6 are coaxially and parallelly placed.

[0023] The central axis of the transmitting coil 4 here refers to the line passing through the geometric center of the transmitting coil 4 and perpendicular to the plane where the transmitting coil 4 is located. Being symmetric 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 on both sides of the central axis and at the same distance from the central axis. And the line connecting the geometric centers of the first receiving coil 3 and the second receiving coil 5 is perpendicular to the central axis.

[0024] The shape of the transmitting coil 4 here is not limited and can be rectangular or circular. The shape of the receiving coil is not limited either and can be rectangular or circular. When the shape of the transmitting coil 4 is selected, the shape of the receiving coil can be the same as or different from that of the transmitting coil 4. Figure 1 Take the transmitting coil 4 and the receiving coil in [reference] as rectangular coils as an example.

[0025] 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 an exciting current in the transmitting coil 4. Through the synchronization signal between the receiver 1 and the transmitter 2, the secondary field signal is received, and the received signal is processed by the circuit of the receiver 1.

[0026] In order to fix the transmitting coil 4 and the receiving coil, in one embodiment, both the transmitting system and the receiving system are arranged on a support platform, and the support platform is installed on a towing platform. Taking the towing platform as a reference, the transmitting coil 4 is arranged on the towing platform, and the height is At this position, a first support platform and a second support platform are set, and taking the first support platform as a reference, the height is At this position, a third support platform is set parallel to the first support platform. The heights of the three support platforms are adjustable. For easy adjustment, adjustable support legs can be set. The transmitting coil 4 is fixed on the towing platform. Taking a rectangle as an example: the length is 2a and the width is 2b; the first receiving coil 3 is fixed on the first support platform. Taking a square as an example: the side length is 2c and the number of turns is , the second receiving coil 5 is fixed on the second support 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 support 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 all , where the second receiving coil 5 and the third receiving coil 6 are parallel and coaxial in plane.

[0027] In the projection of the first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 on the transmitting coil 4, part is located within the area surrounded by the transmitting coil 4, and part is located outside the area surrounded by the transmitting coil 4.

[0028] As Figure 2 shown, taking circular coils as examples for both the transmitting coil 4 and the receiving coils, the transmitting coil 4 is connected to the transmitter 2 through twisted pair wires. The transmitter 2 and the receiver 1 are connected through 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 channels of the receiver 1 through signal shielding wires. There are three receiving channels, which respectively receive the data of the first receiving coil 3, the second receiving coil 5, and the third receiving coil 6. There is a control switch in the middle of the signal shielding wire to control the on and off of the signal; Cascade connection between the second receiving coil 5 and the third receiving coil 6 is achieved through a control switch; The receiver 1 and the industrial computer are connected through an Ethernet connection line.

[0029] The 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. Further, the power supply provides power for each module in the 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 is propagated underground by exciting a primary field through the transmitting coil 4; The receiver 1 includes a power supply and three groups of receiving channels. Each group of receiving channels includes an overvoltage protection circuit, a preamplifier, and a signal conditioning circuit. The three groups of receiving channels are connected to a multi-channel synchronous data acquisition module, and the multi-channel synchronous data acquisition module is connected to a microcontroller; 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 through shielding wires. After each receiving channel filters and amplifies the received signal, it is connected to the multi-channel synchronous data acquisition module. The multi-channel synchronous data acquisition module and the microcontroller are connected through a control bus. When the microcontroller receives the synchronization signal from the transmission control unit, the microcontroller sends a control timing to the multi-channel synchronous data acquisition module to start collecting the received signal.

[0030] 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: an initial first height is selected, and an initial eccentric distance between the first receiving coil 3 and the transmitting coil 4 is selected according to the initial first height, such that the 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.

[0031] The first receiving coil 3 and the second receiving coil 5 have the same size parameters and different size parameters from those of the third receiving coil, including: the first receiving coil 3 and the second receiving coil 5 have the same shape size and number of turns, the shape size of the first receiving coil 3 is larger than that 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: both the first receiving coil 3 and the second receiving coil 5 are square, the side lengths of the square are exactly the same, and the number of turns of the coil is also exactly the same; the third receiving coil is square, the side length of the square is smaller than the side length of the first receiving coil 3, and the number of turns is different from that of the first receiving coil 3.

[0032] Taking the rectangular transmitting coil 4 and the square receiving coil as an example, the initial position of the receiving coil is described; As Figure 2 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 lengths are all 2c, the eccentric distance from 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 ; The transmitting coil 4 and the three receiving coils are placed in parallel, and are only sensitive to the transmitted magnetic induction intensity in the Z direction in space, and 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 symmetric 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 shown: The magnetic induction intensity within the range covered by the first receiving coil 3 and the transmitting coil 4 is: , The covered range refers to the overlapping part between the projection of the first receiving coil 3 on the plane where the transmitting coil 4 is located and the transmitting coil 4, and the magnetic induction intensity in the first receiving coil 3 corresponding to the overlapping part of the transmitting coil 4 is calculated.

[0033] The magnetic induction intensity outside the covered range of the first receiving coil 3 and the transmitting coil 4 is calculated as: , The outside of the covered range refers to the magnetic induction intensity in the corresponding first receiving coil 3 outside the overlapping part between the projection of the first receiving coil 3 on the plane where the transmitting coil 4 is located and the transmitting coil 4.

[0034] Among them, is a coordinate system established with the center of the transmitting coil 4 as the origin. Let , and what is obtained is a function about and . represents axis coordinate. Using to replace , what is obtained is a function about and : , First, determine the initial first height . Generally, it is taken as 0.1m - 0.3m and determined according to the size of the transmitting coil 4. When the maximum size of the transmitting coil 4 is less than 2m, take 0.1 - 0.2m. When the maximum size of the transmitting coil 4 is greater than 2m, take 0.3m, generally taking 1 / 10 of the maximum size of the transmitting coil 4. For example, for a circular coil, the maximum size is the diameter; for a rectangular coil, the maximum size is the maximum side length.

[0035] Select the initial eccentric distance between the first receiving coil 3 and the transmitting coil 4 according to the initial first height.

[0036] In the same way, according to the initial eccentric distance between the third receiving coil 6 and the transmitting coil 4, select the initial second height to make the second magnetic induction intensity 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.

[0037] The initial first height and the initial second height here are both the heights relative to the towing platform.

[0038] However, due to inevitable dimensional errors in the winding and installation processes of the transmitting coil 4 and the receiving coil, it is still necessary to slightly move the receiving coil near the theoretical position value and observe the state of the secondary field signal received by the receiving coil through an oscilloscope until it reaches the optimal state, and finally fix it. When in use: Connect the first receiving coil 3 to the detector, transmit the primary field through the transmitting coil 4, observe the waveform in the detector, adjust the initial first height and the initial eccentric distance so that the waveform is in the best state, and obtain the adjusted first height and the adjusted eccentric distance. Set the eccentric distance between the third receiving coil 6 and the transmitting coil 4 according to the adjusted eccentric distance, connect the third receiving coil 6 to the detector, transmit the primary field through the transmitting coil 4, observe the waveform in the detector, and adjust the initial second height so that the waveform is in the best state or a stable state, and obtain the adjusted second height. The waveform here refers to the waveform of the secondary field signal. Determine the state of the secondary field signal according to the waveform. The best state refers to that the waveform is clear and there is no jitter of abnormal frequency components when moving multiple times. It is relative to other waveforms during the adjustment process.

[0039] By controlling the working modes of the three receiving coils, it is possible to obtain data for shallow detection, lateral gradient data, vertical gradient data, and data for deep detection. The obtained detection data can not only take into account more accurate early information, but also increase the effective data length, increase the detection depth. At the same time, the lateral gradient data and the vertical gradient data can effectively suppress environmental noise interference and improve the data signal-to-noise ratio.

[0040] A towed transient electromagnetic gradient detection method based on a weak transceiver coupling structure according to an embodiment of the present application includes: Adjust the initial first height, the initial eccentric distance, and the initial second height; Make the plane where the transmitting coil 4 is located and the plane where the receiving coil is located perpendicular to the ground plane, transmit the primary field through the transmitting coil 4, and obtain the interference of the primary field when the first receiving coil 3, the second receiving coil 5, and the third receiving coil 6 work alone or in combination. The combined work includes: the first receiving coil 3 and the second receiving coil 5 work simultaneously, the second receiving coil 5 and the third receiving coil 6 work simultaneously, and the second receiving coil 5 and the third receiving coil 6 work in cascade; Make the plane where the transmitting coil 4 is located and the plane where the receiving coil is located parallel to the ground plane. Through the primary field transmitted by the transmitting coil 4, independently turn on the first receiving coil 3 to receive the first data, and obtain the data for shallow detection by inverting the first data and the interference of the first receiving coil 3; Turn on the first receiving coil 3 and the second receiving coil 5 simultaneously, obtain the second data and the third data through the first receiving coil 3 and the second receiving coil 5 respectively, and obtain the lateral gradient data by inverting the difference between the second data and the third data; Turn on the second receiving coil 5 and the third receiving coil 6 simultaneously, obtain the fourth data and the fifth data through the second receiving coil 5 and the third receiving coil 6 respectively, and obtain the vertical gradient data by inverting the difference between the fourth data and the fifth data; Cascade the second receiving coil 5 and the third receiving coil 6 to obtain the sixth data, and invert the data based on the interference of the sixth data with the cascading of the second receiving coil 5 and the third receiving coil 6 to obtain the data for deep detection; Obtain the full-layer detection data based on the data for deep detection, the data for shallow detection, the horizontal gradient data, and the vertical gradient data.

[0041] Among them, adjusting the initial first height, the initial eccentricity distance, and the initial second height includes adjusting the initial first height and the initial eccentricity distance, including: Connect the first receiving coil 3 to the detector, transmit the primary field through the transmitting coil 4, observe the waveform in the detector, and adjust the initial first height and the initial eccentricity distance so that the waveform is in the best state to obtain the adjusted first height and the adjusted eccentricity distance.

[0042] Adjust the initial second height according to the adjusted eccentricity distance, including connecting the third receiving coil 6 to the detector, transmitting the primary field through the transmitting coil 4, observing the waveform in the detector, and adjusting the initial second height so that the waveform is in the best state to obtain the adjusted second height.

[0043] Among them, during calibration, the plane where the transmitting coil 4 is located and the plane where the receiving coil is located need to be perpendicular to the ground plane. In an open area, vertically lift the towing platform to a certain height, control each control switch, and control the connection or disconnection of the receiving coil to / from the receiver 1. The transmitter 2 transmits a bipolar trapezoidal wave, and transmits the primary field through the transmitting coil 4.

[0044] Specifically include: Connect the first receiving coil 3 to a receiving channel of the receiver 1 through a lead wire, the transmitter 2 transmits a bipolar trapezoidal wave, and record the waveform of the first receiving coil 3 ; 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 interference of the primary field transmitted by the transmitting coil 4 on the first receiving coil 3; it is also the interference of the primary field transmitted by the transmitting coil 4 on the second receiving coil 5.

[0045] Connect the third receiving coil 6 to a receiving channel of the receiver 1 through a lead wire, the transmitter 2 transmits a bipolar trapezoidal wave, and record the waveform of the third receiving coil 6 ; The waveform of the third receiving coil 6 is the interference of the primary field transmitted by the transmitting coil 4 on the third receiving coil 6; 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 bipolar trapezoidal wave, and record 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 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 symmetric about the central axis of the transmitting coil 4, so = .

[0046] Connect the second receiving coil 5 and the third receiving coil 6 to different receiving channels of the receiver 1. The transmitter 2 emits a bipolar trapezoidal wave, and record 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 the waveform ; Cascade the second receiving coil 5 and the third receiving coil 6, that is, connect the second receiving coil 5 and the third receiving coil 6 in series, and then connect them to one of the receiving channels of the receiver 1, and record the waveform of the cascade of the second receiving coil 5 and the third receiving coil 6 . The interference of the primary field emitted by the transmitting coil 4 on the cascade of the second receiving coil 5 and the third receiving coil 6 is obtained as the waveform .

[0047] In an embodiment, the plane where the transmitting coil 4 is located and the plane where the receiving coil is located are parallel to the ground plane. Through the primary field emitted by the transmitting coil 4, the first receiving coil 3 is separately turned on to receive the first data, and the data for shallow detection is obtained by inverting the first data and the interference of the first receiving coil 3.

[0048] Record the waveform of the first receiving coil 3 as the first data , , where is the response of the geological body structure obtained by the first receiving coil 3, is the first noise data, and perform inversion on the waveform data - .

[0049] In one embodiment, the first receiving coil 3 and the second receiving coil 5 are simultaneously turned on, and the second data and the third data are obtained through the first receiving coil 3 and the second receiving coil 5 respectively. The horizontal gradient data is obtained by inverting the difference between the second data and the third data; The first receiving coil 3 and the second receiving coil 5 are connected to different receiving channels of the receiver 1, and the transmitter 2 transmits a primary field signal to the ground through the 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 the third data , , , wherein, and are the geological body response signals obtained by the first receiving coil 3 and the second receiving coil 5 respectively, and are equal, and are the second noise data. Since the two receiving coils are in the same environment, so . The waveform of the horizontal gradient differential data is obtained : , The waveform of the horizontal gradient differential data is inverted. It can eliminate environmental noise interference, improve the signal-to-noise ratio, weaken the volume effect, obtain horizontal gradient data, and improve the horizontal resolution of the detection system.

[0050] In one embodiment, the second receiving coil 5 and the third receiving coil 6 are simultaneously turned on, and the fourth data and the fifth data are obtained through the second receiving coil 5 and the third receiving coil 6 respectively. The vertical gradient data is obtained by inverting the difference between the fourth data and the fifth data; The second receiving coil 5 and the third receiving coil 6 are connected to different receiving channels of the receiver 1, and the transmitter 2 transmits a primary field signal to the ground 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 the fifth data , , , wherein, and are the geological body response signals obtained by the second receiving coil 5 and the third receiving coil 6 respectively, and is the third noise data. Since the two receiving coils are in the same environment, so = . Obtain the waveform of the vertical gradient difference data : , for the waveform of the vertical gradient difference data perform inversion to obtain the vertical gradient data. It can eliminate environmental noise interference, improve the signal-to-noise ratio, weaken the volume effect, realize the acquisition of vertical gradient data, and improve the vertical resolution of the detection system.

[0051] In one embodiment, the second receiving coil 5 and the third receiving coil 6 are cascaded to obtain the sixth data. Invert according to the interference of the sixth data and the cascade of the second receiving coil 5 and the third receiving coil 6 to obtain the data for deep detection; the transmitter 2 transmits a primary field signal to 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 , , wherein is the geological body response signal detected by the cascade combination of the second receiving coil 5 and the third receiving coil 6, is the fourth noise data, and perform inversion on the waveform data to obtain the data for deep detection. It is used to improve the sensitivity of the system, increase the effective data length, increase the detection depth, and complete the deeper exploration of the underground structure.

[0052] Finally, obtain the full-level detection data based on the deep-level detection data, shallow-level detection data, horizontal gradient data and vertical gradient data and perform imaging.

[0053] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure, characterized in that Comprising: A transmitting coil for generating an exciting current; Receiving coils for receiving secondary field signals, including 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, which are different from those of the third receiving coil. The first receiving coil and the second receiving coil are located in the same plane and have 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 symmetric about the central axis of the transmitting coil. The second receiving coil and the third receiving coil are coaxially and parallelly placed.

2. The towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure according to claim 1, wherein 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: Select an initial first height, and select an initial eccentric distance between the first receiving coil and the transmitting coil according to the initial first height, such that the 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 weak transceiver coupling structure according to claim 2, wherein 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, select an initial second height, such 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 weak transceiver coupling structure according to claim 1, wherein The first receiving coil and the second receiving coil have the same size parameters, which are different from those 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 size of the first receiving coil is larger than that of the third receiving coil, and the number of turns of the first receiving coil is different from that of the third receiving coil.

5. The towed transient electromagnetic gradient detection device based on a weak transceiver coupling structure according to claim 1, wherein The first receiving coil, the second receiving coil, and the third receiving coil work alone or in combination. The combined work 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.

6. A drag-type transient electromagnetic gradient detection method based on a weak transceiver coupling structure, which uses the drag-type transient electromagnetic gradient detection device based on the weak transceiver coupling structure described in any one of claims 1-5, characterized in that Comprising: Adjust the initial first height, the initial eccentric distance, and the initial second height; Make the plane where the transmitting coil is located and the plane where the receiving coil is located perpendicular to the ground plane. Transmit a primary field through the transmitting coil to obtain the interference of the primary field when the first receiving coil, the second receiving coil, and the third receiving coil work alone or in combination. The combined work 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; Make the plane where the transmitting coil is located and the plane where the receiving coil is located parallel to the ground plane. Transmit a primary field through the transmitting coil. Individually turn on the first receiving coil to receive the first data, and obtain the data for shallow detection by inverting the first data and the interference of the first receiving coil; Simultaneously turn on the first receiving coil and the second receiving coil, obtain the second data and the third data through the first receiving coil and the second receiving coil respectively, and obtain the lateral gradient data by inverting the difference between the second data and the third data; Turn on the second receiving coil and the third receiving coil simultaneously, obtain the fourth data and the fifth data through the second receiving coil and the third receiving coil respectively, and obtain the 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 the sixth data, and invert the data of deep detection according to the interference of the sixth data and the cascade of the second receiving coil and the third receiving coil; Obtain the full-level detection data according to the data of deep detection, the data of shallow detection, the horizontal gradient data and the vertical gradient data.

7. A towed transient electromagnetic gradient detection method based on a weak transceiver coupling structure according to claim 6, characterized in that The adjustment of the initial first height and the initial eccentricity distance includes: connecting the first receiving coil to the detector, transmitting the primary field through the transmitting coil, observing the waveform in the detector, and adjusting the initial first height and the initial eccentricity distance to make the waveform stable, so as to obtain the adjusted first height and the adjusted eccentricity distance.

8. A towed transient electromagnetic gradient detection method based on a weak transceiver coupling structure according to claim 7, characterized in that, Adjust the initial second height according to the adjusted eccentricity distance, including connecting the third receiving coil to the detector, transmitting the primary field through the transmitting coil, observing the waveform in the detector, and adjusting the initial second height to make the waveform stable, so as to obtain the adjusted second height.

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