A shallow water tensor AMT detection device and detection method
By using a tensor AMT detection device and method in shallow waters, combined with an above-water tensor electric field acquisition cable and an underwater three-component magnetic sensor, the problem of insufficient detection depth and accuracy in electromagnetic exploration of water areas has been solved, and high-resolution water area detection has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF GEOPHYSICAL & GEOCHEMICAL EXPLORATION CHINESE ACAD OF GEOLOGICAL SCI
- Filing Date
- 2023-08-28
- Publication Date
- 2026-07-17
AI Technical Summary
Existing electromagnetic exploration methods in water areas suffer from problems such as shallow detection depth, low accuracy, and compromised data quality. In particular, high-density electrical resistivity tomography, transient electromagnetic methods, and audio-frequency magnetotellurics are difficult to deploy, have insufficient detection depth, and produce incomplete data when applied in water areas.
The shallow water tensor AMT detection device, including a surface tensor electric field acquisition cable and an underwater three-component magnetic sensor, can simultaneously acquire electric field information in the direction of the measured profile and the vertical direction. Data acquisition is carried out through anchored and mobile observation methods, which solves the electromagnetic field separation observation error and improves the detection accuracy.
It enables high-resolution and rapid detection in shallow waters, improves detection depth and accuracy, expands the applicability of AMT detection, and is suitable for high-precision detection in various waters.
Smart Images
Figure CN116931099B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electromagnetic detection technology in water areas, specifically to a shallow water tensor AMT detection device and method. Background Technology
[0002] Electromagnetic methods, as commonly used geophysical techniques, have been widely applied in engineering exploration and mineral resource surveys, particularly suitable for detailed exploration of underground engineering projects in water bodies and the development of complex underground geological structures and fault formations. Traditional electromagnetic exploration equipment and methods, developed for terrestrial applications, are limited by the constraints of existing equipment and technology, making them difficult to apply effectively to water-covered areas such as large rivers and lakes. This underscores the necessity of developing electromagnetic detection devices and methods suitable for water bodies.
[0003] Currently, electromagnetic methods applied to water area exploration include high-density electrical methods using artificial sources, transient electromagnetic methods, and audio magnetotelluric (AMT) methods using passive sources. However, all current electromagnetic methods applicable to water area exploration have certain problems in practical applications.
[0004] High-density electrical resistivity tomography (EDT) uses direct current (DC) power. On land, the detection depth is generally only a few tens of meters and the resolution is not high. When applied to underwater detection, the data acquisition device is usually deployed on the seabed. However, the underwater topography is not visible, making the deployment of the data acquisition device difficult. Furthermore, since DC power is used during the detection process, if the underwater data acquisition cable leaks, it will directly affect the accuracy of the data. In addition, because the current tends to pass through the low-resistivity water layer and the bottom silt layer during the detection process, the detection depth of high-density EDT in water is shallower than that on land.
[0005] Transient electromagnetic methods typically involve underwater measurement devices towed at the stern of a vessel. During detection, the size limitations of the transmitting and receiving coils result in low transmission power and shallow detection depth. Although increasing the transmission current can improve the transmission power and thus the detection depth, this significantly increases the self-inductance and mutual inductance of the coils, prolonging the turn-off time and creating a detection blind zone in shallow water. Furthermore, the detection process is susceptible to interference from the hull, water layer, and current, which negatively impacts the quality of the acquired data.
[0006] Currently, the towed single-component electric field acquisition cable used in the commonly used audio-frequency magnetotelluric method can only acquire the electric field component along the profile direction, lacking the electric field component in the vertical direction of the profile. This results in insufficient acquisition of underground electrical information, thus affecting the detection accuracy. Furthermore, the electromagnetic field separation observation method, which combines the electric field of the water-based acquisition point with the magnetic field of the onshore base station, uses the magnetic field of the onshore base station to replace the magnetic field of the water-based acquisition point. This method is limited in practical application due to the uniformity of the magnetic fields on the shore and in the water.
[0007] Therefore, there is an urgent need to propose a shallow water tensor AMT detection device and method to improve the detection depth and accuracy of shallow water tensor audio-frequency magnetotelluric method detection, and to achieve high-resolution and rapid detection of shallow water. Summary of the Invention
[0008] This invention aims to detect and obtain richer electric field information and solve the errors caused by electromagnetic field separation observation. It proposes a shallow water tensor AMT detection device and detection method, which improves the detection depth and accuracy of shallow water tensor audio-frequency magnetotelluric method detection and is suitable for high-resolution rapid detection of shallow water layers in various waters.
[0009] To achieve the above objectives, the present invention adopts the following technical solution:
[0010] A shallow water tensor AMT detection device includes a magnetotelluric instrument, an electric field signal acquisition device, and a magnetic field signal acquisition device, wherein the electric field signal acquisition device and the magnetic field signal acquisition device are respectively connected to the magnetotelluric instrument.
[0011] The electric field signal acquisition device is a tensor-type electric field acquisition cable for water, including a non-polarized electrode, a GPS positioning device, a multi-core shielded cable, and a support. The support includes a first transverse support, a second transverse support, a third transverse support, and multiple longitudinal supports. Each longitudinal support is arranged at equal intervals along the transverse supports. The spacing between adjacent transverse supports is equal to the spacing between adjacent longitudinal supports. A float is installed on each longitudinal support between two adjacent transverse supports. The intersection of the longitudinal supports and the transverse supports is connected by a connecting bolt.
[0012] Non-polarized electrodes are provided at the intersections of the first, second, and third transverse supports with each longitudinal support. The second transverse support has an additional non-polarized electrode at its head end compared to the first and third transverse supports. Each non-polarized electrode is connected to the magnetotelluric instrument via a multi-core shielded cable to transmit natural electric field signals in two mutually perpendicular directions in the water to the magnetotelluric instrument.
[0013] The tensor electric field acquisition cable for water is provided with multiple transverse and longitudinal electric channels. The non-polarized electrodes on the second transverse support form multiple transverse electric channels. A non-polarized electrode is spaced apart between a pair of non-polarized electrodes on the same transverse electric channel. Each longitudinal support is provided with a longitudinal electric channel. A pair of non-polarized electrodes on the same longitudinal support on the first and third transverse supports form a longitudinal electric channel.
[0014] GPS positioning devices are installed on all non-polarized electrodes of the second transverse support. Each GPS positioning device is connected to a magnetotelluric instrument to record the real-time position of the transverse and longitudinal electric channels in the tensor electric field acquisition cable over water.
[0015] The magnetic field signal acquisition device is an underwater three-component magnetic sensor, including a fiberglass waterproof cover with a handle on the top, and an X-component magnetic sensor, a Y-component magnetic sensor, a Z-component magnetic sensor and an attitude locator installed inside the fiberglass waterproof cover. The X-component magnetic sensor, the Y-component magnetic sensor, the Z-component magnetic sensor and the attitude locator are respectively connected to a multi-core transmission line. The top end of the multi-core transmission line passes through the fiberglass waterproof cover and is connected to the magnetotelluric instrument.
[0016] The X-component magnetic sensor, Y-component magnetic sensor, and Z-component magnetic sensor are arranged perpendicularly to each other in pairs. The X-component magnetic sensor is used to measure the magnetic field component in the left-right direction, the Y-component magnetic sensor is used to measure the magnetic field component in the front-back direction, and the Z-component magnetic sensor is used to measure the magnetic field component in the up-down direction. The attitude directional device is fixed on the Y-component magnetic sensor and is used to measure the tilt angle and azimuth angle of the underwater three-component magnetic sensor for magnetic field correction.
[0017] Preferably, the distance between two adjacent non-polarized electrodes on the support is set to 5m to 20m.
[0018] Preferably, the top end of the multi-core transmission line is provided with a multi-core transmission line connector for connecting to a magnetotelluric instrument, and the top end of the multi-core shielded cable is provided with a multi-core shielded cable connector for connecting to a magnetotelluric instrument.
[0019] Preferably, a rope is attached to the handle at the top of the fiberglass waterproof cover.
[0020] A shallow water tensor AMT detection method employs the shallow water tensor AMT detection device as described above, specifically including an anchored observation method and a mobile observation method.
[0021] Preferably, the anchored observation method is based on a shallow water tensor AMT detection device and a mobile platform on water, and specifically includes the following steps:
[0022] Step 1: Obtain geological data and water conditions of the work area, and determine the profile to be measured and the location of each measuring point in the work area in conjunction with the detection target;
[0023] Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotellurist in the shallow water tensor AMT detection device are working properly.
[0024] Step 3: Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, determine the observation duration and observation period of the shallow water tensor AMT detection device in the working area, and adjust the electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device.
[0025] Step 4: Set up the observation device using a shallow water tensor AMT detection device and a floating platform. Set up the shallow water tensor AMT detection device on the floating platform, drag the floating tensor electric field acquisition cable to the tail end of the floating platform, fix the underwater three-component magnetic sensor to the floating platform with ropes, connect the non-polarized electrode in the floating tensor electric field acquisition cable, the GPS positioning device, and the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude orientation device in the underwater three-component magnetic sensor to the magnetotelluric instrument, and then deploy the underwater three-component magnetic sensor to the bottom of the water.
[0026] Step 5: Anchor the waterborne mobile platform equipped with the shallow water tensor AMT detection device at the first preset measurement point of the profile to be measured. During the set observation time and period, use the shallow water tensor AMT detection device to synchronously acquire electric field data of the transverse and longitudinal electric channels in the waterborne tensor electric field acquisition cable, as well as measurement data of the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude orientation device in the underwater three-component magnetic sensor. Acquire electric field data, X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data in the profile direction and two directions perpendicular to the profile direction. After the acquisition is completed, remove the rope and take the underwater three-component magnetic sensor out of the water. Move the waterborne mobile platform to the next preset measurement point and put the underwater three-component magnetic sensor back into the water for measurement. Continue until all preset measurement points of the profile to be measured have been measured and stop the measurement.
[0027] Step 6: Obtain electric field data, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point from the magnetotelluric instrument. Combine this with the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, and correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Based on the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point, determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
[0028] Preferably, the mobile observation method is based on a shallow water tensor AMT detection device and two mobile water platforms, and specifically includes the following steps:
[0029] Step 1: Obtain geological data and water conditions of the work area, and determine the profile to be measured and the location of each measuring point in the work area in conjunction with the detection target;
[0030] Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotellurist in the shallow water tensor AMT detection device are working properly.
[0031] Step 3: Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, determine the observation duration, observation time period and acquisition window of the measurement point in the working area, and adjust the electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device.
[0032] Step 4: Set up the observation device using the shallow water tensor AMT detection device and two floating platforms. Tow the floating tensor electric field acquisition cable of the shallow water tensor AMT detection device to the tail end of the first floating platform. Fix the underwater three-component magnetic sensor of the shallow water tensor AMT detection device to the second floating platform by rope. Both floating platforms are equipped with magnetotellurics. Connect the non-polarized electrode and GPS positioning device in the floating tensor electric field acquisition cable to the magnetotellurics on the first floating platform. After connecting the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude directional device in the underwater three-component magnetic sensor to the magnetotellurics on the second floating platform, the underwater three-component magnetic sensor is deployed to the bottom of the water at the middle position of the profile to be measured.
[0033] Step 5: Use the underwater three-component magnetic sensor mounted on the second waterborne mobile platform to collect X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data. Use the X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data as the magnetic field data of the section to be measured. Then use the first waterborne mobile platform to tow the waterborne tensor electric field acquisition cable to move along the section to be measured to collect electric field information in the direction of the section to be measured and in the two vertical directions of the section to be measured. Move the first waterborne mobile platform until the section to be measured is completely measured and stop the measurement.
[0034] Step 6: Obtain electric field data for each set of transverse and longitudinal electric channels in the tensor electric field acquisition cable from the magnetotelluric instrument on the first floating platform, as well as the time and location recorded by each GPS positioning device. Extract the electric field time series segments of each measuring point from the electric field data of each set of transverse and longitudinal electric channels according to the acquisition window of each measuring point, and splice them in chronological order to obtain the complete electric field data of each measuring point. Then, obtain the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data of each measuring point from the magnetotelluric instrument on the second floating platform. Combine the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Combine the complete electric field data of each measuring point with the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
[0035] Preferably, the waterborne mobile platform is configured as a ship hull.
[0036] Preferably, both the mobile platform and the tensor electric field acquisition cable are equipped with anchors to stabilize the tensor AMT detection device in shallow water.
[0037] The beneficial technical effects of this invention are as follows:
[0038] (1) In the shallow water tensor AMT detection device proposed in this invention, the electric field signal acquisition device is set as a tensor electric field acquisition cable on the water. The tensor electric field acquisition cable on the water can simultaneously acquire electric field information in two mutually orthogonal directions, namely the direction of the test profile and the direction perpendicular to the test profile, thus realizing the acquisition of tensor electric field. Compared with scalar acquisition, the electric field information obtained is richer and the detection accuracy is higher.
[0039] (2) The underwater three-component magnetic sensor in the shallow water tensor AMT detection device proposed in this invention is easy to deploy on the bottom of the water near the measurement point and collect data synchronously with the electric field at the same location. This solves the error caused by the separation of electromagnetic field observation during the detection process, improves the detection accuracy of shallow water tensor AMT detection, and is applicable to detection in various water areas, thus expanding the scope of application of AMT detection.
[0040] (3) The present invention also proposes a shallow water tensor AMT detection method, which specifically includes an anchored observation method and a mobile observation method. In the actual detection process, the staff selects the appropriate observation method according to the detection purpose, which improves the applicability of the shallow water tensor AMT detection method. Attached Figure Description
[0041] Figure 1This is a schematic diagram of the structure of a tensor electric field acquisition cable over water.
[0042] Figure 2 This is a schematic diagram of the overall structure of an underwater three-component magnetic sensor.
[0043] Figure 3 This is a schematic diagram of the internal structure of an underwater three-component magnetic sensor.
[0044] Figure 4 This is a schematic diagram of the anchored observation method in the tensor AMT detection method for shallow water.
[0045] Figure 5 This is a schematic diagram of the mobile observation method in the tensor AMT detection method for shallow water.
[0046] In the diagram: 1. Tensor electric field acquisition cable for water, 101. First transverse support, 102. Second transverse support, 103. Third transverse support, 104. Longitudinal support, 105. Float, 106. Non-polarizing electrode, 107. GPS positioning device, 108. Multi-core shielded cable, 109. Multi-core shielded cable connector, 2. Underwater three-component magnetic sensor, 201. Fiberglass waterproof cover, 202. Handle, 203. Multi-core transmission line, 204. Multi-core transmission line connector, 205. X-component magnetic sensor, 206. Y-component magnetic sensor, 207. Z-component magnetic sensor, 208. Attitude directional device, 3. Magnetoelectric instrument, 4. Waterborne mobile platform, 401. First waterborne mobile platform, 402. Second waterborne mobile platform, 5. Water body, 6. Underwater strata. Detailed Implementation
[0047] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:
[0048] Example 1
[0049] This invention proposes a shallow water tensor AMT detection device, which includes a magnetotelluric instrument, an electric field signal acquisition device, and a magnetic field signal acquisition device, wherein the electric field signal acquisition device and the magnetic field signal acquisition device are respectively connected to the magnetotelluric instrument.
[0050] The electric field signal acquisition device is a tensor-type electric field acquisition cable 1 for waterborne applications, such as... Figure 1As shown, the system includes a non-polarized electrode 106, a GPS positioning device 107, a multi-core shielded cable 108, and a support. The support includes a first transverse support 101, a second transverse support 102, a third transverse support 103, and multiple longitudinal supports 104. Each longitudinal support is arranged at equal intervals along the transverse supports, and the spacing between adjacent transverse supports is equal to the spacing between adjacent longitudinal supports. Each longitudinal support between two adjacent transverse supports is equipped with a float 105 to provide buoyancy so that the tensor electric field acquisition cable floats on the water surface. The intersection of the longitudinal supports and the transverse supports is connected by a connecting bolt for easy assembly and disassembly of the support.
[0051] Non-polarized electrodes are provided at the intersections of the first, second, and third transverse supports with each longitudinal support. The second transverse support has an additional non-polarized electrode at its head end compared to the first and third transverse supports. Each non-polarized electrode is connected to the magnetotelluric instrument 3 via a multi-core shielded cable to transmit natural electric field signals in two mutually perpendicular directions in the water to the magnetotelluric instrument.
[0052] The tensor electric field acquisition cable for water is equipped with multiple transverse and longitudinal electric channels for measuring the natural electric field signal of the target profile in water and its vertical direction. The non-polarized electrodes on the second transverse support form multiple transverse electric channels, and a non-polarized electrode is spaced apart from a pair of non-polarized electrodes on the same transverse electric channel. Each longitudinal support is equipped with a longitudinal electric channel, and a pair of non-polarized electrodes on the first and third transverse supports on the same longitudinal support form a longitudinal electric channel.
[0053] GPS positioning devices are installed on all non-polarized electrodes of the second transverse support. Each GPS positioning device is connected to a magnetotelluric instrument to record the real-time position of the transverse and longitudinal electric channels in the tensor electric field acquisition cable over water.
[0054] The non-polarized electrode is a lead chloride non-polarized electrode with good conductivity. The GPS positioning device uses a high-precision GPS locator. The multi-core shielded cable has the characteristics of high tensile strength and good conductivity. The top end of the multi-core shielded cable is provided with a multi-core shielded cable connector 109 for connecting to the magnetotelluric instrument. The multi-core shielded cable connector is conductive and waterproof and sealed, and has excellent conductivity and waterproofness.
[0055] This embodiment of the tensor electric field acquisition cable for water contains several sets of mutually perpendicular intersecting electric channels, which can simultaneously acquire electric field component information in the direction of the measured profile and its perpendicular direction, realizing the acquisition of tensor electric fields. Since it contains multiple sets of mutually orthogonal electric channels, it realizes simultaneous observation of multiple channels, improving the detection efficiency of tensor AMT detection in shallow water. At the same time, since the tensor electric field acquisition cable for water is towed to the tail end of the floating platform and floats in the water, the deployment does not need to consider the influence of the underwater strata, making it more convenient and faster.
[0056] The magnetic field signal acquisition device is an underwater three-component magnetic sensor 2, such as... Figure 2 and Figure 3 As shown, it includes a fiberglass waterproof cover 201 with a handle 202 on the top, and an X-component magnetic sensor 205, a Y-component magnetic sensor 206, a Z-component magnetic sensor 207 and an attitude locator 208 disposed inside the fiberglass waterproof cover 201. The X-component magnetic sensor, the Y-component magnetic sensor, the Z-component magnetic sensor and the attitude locator are respectively connected to a multi-core transmission line 203. The top end of the multi-core transmission line passes through the fiberglass waterproof cover and is connected to the magnetotelluric instrument 3.
[0057] The X-component magnetic sensor, Y-component magnetic sensor, and Z-component magnetic sensor are arranged perpendicularly to each other in pairs. The X-component magnetic sensor is used to measure the magnetic field component in the left-right direction, the Y-component magnetic sensor is used to measure the magnetic field component in the front-back direction, and the Z-component magnetic sensor is used to measure the magnetic field component in the up-down direction. The attitude directional device is fixed on the Y-component magnetic sensor and is used to measure the tilt angle and azimuth angle of the underwater three-component magnetic sensor for magnetic field correction, which facilitates the subsequent magnetic field correction of the magnetic field data measured by the X-component magnetic sensor, Y-component magnetic sensor, and Z-component magnetic sensor.
[0058] In this embodiment, the fiberglass waterproof cover of the underwater three-component magnetic sensor is made of fiberglass material and has a bell-shaped structure. The bell-shaped structure design reduces the resistance encountered by the underwater three-component magnetic sensor underwater. The fiberglass waterproof cover is waterproof and pressure-resistant after being treated with a waterproof seal. The top of the fiberglass waterproof cover is provided with a handle for attaching ropes, which facilitates the lowering of the underwater three-component magnetic sensor to the bottom of the water. The top of the multi-core transmission line is provided with a multi-core transmission line connector for connecting to the magnetotelluric instrument. The multi-core transmission line connector 204 is conductive and waterproof and sealed, which can quickly transmit the magnetic field data measured by the X-component magnetic sensor, Y-component magnetic sensor and Z-component magnetic sensor.
[0059] In this embodiment, the underwater three-component magnetic sensor achieves simultaneous measurement of magnetic field components in two vertical directions and the vertical direction on the horizontal plane by setting three mutually orthogonal single-component magnetic sensors inside. In conjunction with the attitude orientation device, the tilt angle and azimuth angle of the underwater three-component magnetic sensor are measured simultaneously, and the magnetic field data measured by the underwater three-component magnetic sensor are corrected to ensure the accuracy of subsequent underwater stratum electrical structure inversion.
[0060] This invention also proposes a shallow water tensor AMT detection method, which uses the shallow water tensor AMT detection device as described above, specifically including an anchored observation method and a mobile observation method.
[0061] The anchored observation method proposed in this invention is based on a shallow water tensor AMT detection device and a mobile water platform 4, such as Figure 4 As shown, the specific steps include:
[0062] Step 1: Obtain geological data and water conditions of the work area, and determine the location of the profile to be measured and each measuring point in the work area in conjunction with the detection target.
[0063] Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device, and magnetotellurist in the shallow water tensor AMT detection device are working properly.
[0064] Step 3 involves conducting electrode distance tests, observation duration tests, and electromagnetic interference background tests on the shallow water tensor AMT detection device. Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, the observation duration and observation period within the working area are determined, and the electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device is adjusted. The electrode distance test, observation duration test, and electromagnetic interference background test are conventional techniques used by those skilled in the art to determine the observation duration, observation period, and electrode distance between adjacent non-polarized electrodes during the measurement process.
[0065] Step 4: Set up the observation device using a shallow water tensor AMT detection device and a mobile platform. The mobile platform is a boat. The shallow water tensor AMT detection device is set on the mobile platform. The tensor electric field acquisition cable is towed to the stern of the mobile platform. Anchors are installed at the stern of both the mobile platform and the tensor electric field acquisition cable to stabilize the shallow water tensor AMT detection device. The underwater three-component magnetic sensor is fixed to the mobile platform by ropes. After connecting the non-polarized electrode in the tensor electric field acquisition cable, the GPS positioning device, and the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor, and attitude orientation device in the underwater three-component magnetic sensor to the magnetotelluric instrument, the underwater three-component magnetic sensor is deployed to the bottom of the water. The correctness of the deployment and connection of the shallow water tensor AMT detection device is checked one by one.
[0066] Step 5: Anchor the floating platform equipped with the shallow water tensor AMT detection device at the first preset measurement point of the profile to be measured. During the set observation time, use the shallow water tensor AMT detection device to synchronously acquire electric field data of the transverse and longitudinal electric channels in the floating tensor electric field acquisition cable, as well as measurement data of the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor, and attitude orientation device at the same location. Acquire electric field data, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data in the profile direction and the two directions perpendicular to the profile direction. After the acquisition is completed, remove the rope and take the underwater three-component magnetic sensor out of the water. Move the floating platform to the next preset measurement point and put the underwater three-component magnetic sensor back into the water for measurement. Continue until all preset measurement points of the profile to be measured have been measured, and then stop the measurement.
[0067] Step 6: Obtain electric field data, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point from the magnetotelluric instrument. Combine this with the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, and correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Based on the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point, determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
[0068] The mobile observation method proposed in this invention is based on a shallow water tensor AMT detection device and two mobile water platforms, such as... Figure 5 As shown, the specific steps include:
[0069] Step 1: Obtain geological data and water conditions of the work area, and determine the location of the profile to be measured and each measuring point in the work area in conjunction with the detection target.
[0070] Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device, and magnetotellurist in the shallow water tensor AMT detection device are working properly.
[0071] Step 3 involves conducting electrode distance tests, observation duration tests, and electromagnetic interference background tests on the shallow water tensor AMT detection device. Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, the observation duration, observation time period, and measurement point acquisition window within the working area are determined. The electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device is then adjusted. In this embodiment, the measurement point acquisition window is set as a square area centered on the measurement point. Electric field data acquired by any circuit moving into the measurement point acquisition window area are considered the electric field data at that measurement point. The electrode distance test, observation duration test, and electromagnetic interference background test are conventional techniques used by those skilled in the art to determine the observation duration, observation time period, measurement point acquisition window, and electrode distance between adjacent non-polarized electrodes during the measurement process.
[0072] Step 4: Set up the observation device using the shallow water tensor AMT detection device and two floating platforms. Both floating platforms are boats. The floating tensor electric field acquisition cable of the shallow water tensor AMT detection device is towed to the stern of the first floating platform 401. The underwater three-component magnetic sensor of the shallow water tensor AMT detection device is fixed to the second floating platform 402 by ropes. Both floating platforms are equipped with magnetotellurics, and anchors are installed at the sterns of both floating platforms and the floating tensor electric field acquisition cable to stabilize the shallow water tensor AMT detection device. Connect the non-polarized electrode and GPS positioning device in the floating tensor electric field acquisition cable to the magnetotelluric instrument on the first floating platform. After connecting the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude directional device in the underwater three-component magnetic sensor to the magnetotelluric instrument on the second floating platform, the underwater three-component magnetic sensor is deployed to the bottom of the water at the middle position of the profile to be measured.
[0073] Step 5: The underwater three-component magnetic sensor mounted on the second mobile platform is used to collect X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data. The X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data are used as the magnetic field data of the section to be measured. Then, the first mobile platform is used to tow the underwater tensor electric field acquisition cable to move along the section to be measured to collect electric field information in the direction of the section to be measured and in the two vertical directions of the section to be measured. The first mobile platform is moved until the section to be measured is completely measured, and then the measurement is stopped.
[0074] If the profile to be measured is too long, it will be divided into several short profiles. After each short profile is measured, the tensor electric field acquisition cable and the underwater three-component magnetic sensor will be moved to the next short profile using the first and second waterborne mobile platforms to re-deploy and measure, until the entire profile to be measured is completed by mobile measurement.
[0075] Step 6: Obtain electric field data for each set of transverse and longitudinal electric channels in the tensor electric field acquisition cable from the magnetotelluric instrument on the first floating platform, as well as the time and location recorded by each GPS positioning device. Extract the electric field time series segments of each measuring point from the electric field data of each set of transverse and longitudinal electric channels according to the acquisition window of each measuring point, and splice them in chronological order to obtain the complete electric field data of each measuring point. Then, obtain the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data of each measuring point from the magnetotelluric instrument on the second floating platform. Combine the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Combine the complete electric field data of each measuring point with the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
[0076] Example 2
[0077] In this embodiment, the anchored observation method and the moving observation method in the shallow water tensor AMT detection method proposed in Embodiment 1 are used for detection in a shallow water area. The top layer of the shallow water area is water body 5, and the bottom layer is underwater stratum 6. The shallow water tensor AMT detection device proposed in Embodiment 1 is used during the detection process.
[0078] When using the anchored observation method to conduct exploration in this shallow water area, the specific steps include:
[0079] Step 1: Using the shallow water area as the work area, obtain geological data and water conditions of the work area. Combined with the detection target, determine the section to be measured AA' in the work area. The section to be measured AA' is oriented east-west and has a length of 1140m. There are 20 measuring points set in the section to be measured, and the distance between each measuring point is 60m.
[0080] Step 2: Before observation, the equipment performance of the shallow water tensor AMT detection device is tested. Before construction, the magnetotelluric instrument and the independently developed underwater three-component magnetic sensor are calibrated and tested for consistency to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotelluric instrument in the shallow water tensor AMT detection device are working properly.
[0081] Step 3: Conduct electrode distance tests, observation duration tests, and electromagnetic interference background tests on the shallow water tensor AMT detection device. Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device and the actual situation of the water area, determine that the electrode distance between adjacent non-polarized electrodes is 20m. According to the electromagnetic environment of the working area, select the afternoon time to carry out AMT detection, with an observation duration of 30 minutes and an observation frequency set to 0.35Hz~10400Hz.
[0082] Step 4: Set up the observation device using a shallow water tensor AMT detection device and a floating platform. The shallow water tensor AMT detection device is set up on the floating platform, and the floating tensor electric field acquisition cable is towed to the stern of the platform. Anchors are installed at the sterns of both the platform and the cable to stabilize the device. The underwater three-component magnetic sensor is fixed to the platform via ropes. The non-polarizing electrode in the floating tensor electric field acquisition cable, the GPS positioning device, and the X, Y, and Z component magnetic sensors and attitude orienteering device of the underwater three-component magnetic sensor are connected to the magnetotelluric instrument. After deploying the underwater three-component magnetic sensor to the bottom, each component is checked to ensure the correctness of the shallow water tensor AMT detection device's deployment and connection.
[0083] Step 5: Anchor the waterborne mobile platform equipped with the shallow water tensor AMT detection device at the first preset measurement point of the profile to be measured. Observe for 30 minutes at the preset observation frequency. Use the shallow water tensor AMT detection device to synchronously collect electric field data of the two components of the profile direction and its vertical direction, and magnetic field data of the three components at the same point. After the data collection is completed, remove the rope and take the underwater three-component magnetic sensor out of the water. Move the waterborne mobile platform to the next preset measurement point and put the underwater three-component magnetic sensor back into the water for measurement. Repeat the data collection process until 20 measurement points have been measured, and then stop the measurement.
[0084] Step 6: Obtain electric field data, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point from the magnetotelluric instrument. Combine this with the tilt and azimuth angles measured by the attitude orienter at each measuring point, and correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Based on the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data from the electric field data at each measuring point, use the magnetotelluric instrument's software to process the electric field data and the corrected magnetic field data to obtain the apparent resistivity and impedance phase of each measuring point. Then, use MTEditor software to edit the data and use the two-dimensional magnetotelluric inversion software SCS2D to invert and obtain the electrical structure of the underwater strata.
[0085] When using a mobile observation method to conduct exploration in this shallow water area, the specific steps include:
[0086] Step 1: Using this shallow water area as the work area, obtain geological data and water conditions for the work area. Combined with the detection target, determine the section to be measured AA' within the work area. The section to be measured AA' is oriented east-west and has a length of 1140m. To compare with the anchored observation method, a measuring point is set every 60m on the section to be measured AA', resulting in 20 measuring points at the same location.
[0087] Step 2: Before observation, the equipment performance of the shallow water tensor AMT detection device is tested. Before construction, the magnetotelluric instrument and the independently developed underwater three-component magnetic sensor are calibrated and tested for consistency to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotelluric instrument in the shallow water tensor AMT detection device are working properly.
[0088] Step 3: Conduct electrode distance tests, observation duration tests, and electromagnetic interference background tests on the shallow water tensor AMT detection device. Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device and the actual situation of the water area, determine that the electrode distance between adjacent non-polarized electrodes is 20m. According to the electromagnetic environment of the working area, select the afternoon time to carry out AMT detection, with an observation duration of 20 minutes and an observation frequency set to 0.35Hz~10400Hz. Based on the electrode distance length, select a square area with a length of 20m and a width of 20m for the acquisition window of the measurement point.
[0089] Step 4: Utilize the shallow water tensor AMT detection device and two mobile water platforms to set up the observation equipment. Both platforms are boat-shaped. The underwater tensor electric field acquisition cable of the shallow water tensor AMT detection device is towed to the stern of the first mobile water platform. The underwater three-component magnetic sensor of the shallow water tensor AMT detection device is fixed to the second mobile water platform via ropes. Both mobile water platforms are equipped with magnetotellurics, and anchors are installed at the sterns of both platforms and the underwater tensor electric field acquisition cable for... To stabilize the shallow water tensor AMT detection device, the non-polarized electrode and GPS positioning device in the tensor electric field acquisition cable on the surface are connected to the magnetotelluric instrument on the first surface mobile platform. After connecting the X-component, Y-component, and Z-component magnetic sensors and the attitude directional device in the underwater three-component magnetic sensor to the magnetotelluric instrument on the second surface mobile platform, the underwater three-component magnetic sensor is deployed to the bottom of the water at the middle position of the profile to be measured. The correctness of the deployment and connection of the shallow water tensor AMT detection device is then checked one by one.
[0090] Step 5: The underwater three-component magnetic sensor mounted on the second mobile platform is used to collect X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data. The X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data are used as the magnetic field data of the section to be measured. Then, the first mobile platform is used to tow the tensor electric field acquisition cable along the head end of the section to be measured AA' to the tail end. The electric field information in the direction of the section to be measured and the two vertical directions of the section to be measured is collected according to the preset observation frequency. The first mobile platform is moved until the 20 measuring points on the section to be measured are measured, and the measurement is stopped.
[0091] Step 6: Obtain electric field data for each set of horizontal and vertical electric fields in the tensor electric field acquisition cable from the magnetotelluric instrument on the first floating platform, as well as the time and location recorded by each GPS positioning device. Based on the acquisition window of each measuring point, extract the electric field time series segments of each measuring point from the electric field data of each set of horizontal and vertical electric fields, and splice them in chronological order to obtain the complete electric field data of each measuring point.
[0092] Next, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point are acquired from the magnetotelluric instrument on the second floating platform. Combined with the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data are corrected to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Based on the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point, the magnetotelluric instrument software is used to process the electric field data and the corrected magnetic field data to obtain the apparent resistivity and impedance phase of each measuring point. Then, the data is edited using MTEditor software, and the electrical structure of the underwater strata is obtained by inversion using the two-dimensional magnetotelluric inversion software SCS2D.
[0093] In this embodiment, the anchored observation method and the mobile observation method in the shallow water tensor AMT detection method proposed in this invention were used to successfully obtain the underwater stratum electrical structure of a certain water area profile, which can achieve the detection purpose and verify the effectiveness of the shallow water tensor AMT detection method and shallow water tensor AMT detection device in this invention for shallow water tensor AMT detection.
[0094] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.
Claims
1. A shallow water tensor AMT detection device, characterized in that, It includes a magnetotelluric instrument, an electric field signal acquisition device, and a magnetic field signal acquisition device, with the electric field signal acquisition device and the magnetic field signal acquisition device respectively connected to the magnetotelluric instrument; The electric field signal acquisition device is a tensor-type electric field acquisition cable for water, including a non-polarized electrode, a GPS positioning device, a multi-core shielded cable, and a support. The support includes a first transverse support, a second transverse support, a third transverse support, and multiple longitudinal supports. Each longitudinal support is arranged at equal intervals along the transverse supports. The spacing between adjacent transverse supports is equal to the spacing between adjacent longitudinal supports. A float is installed on each longitudinal support between two adjacent transverse supports. The intersection of the longitudinal supports and the transverse supports is connected by a connecting bolt. Non-polarized electrodes are provided at the intersections of the first, second, and third transverse supports with each longitudinal support. The second transverse support has an additional non-polarized electrode at its head end compared to the first and third transverse supports. Each non-polarized electrode is connected to the magnetotelluric instrument via a multi-core shielded cable to transmit natural electric field signals in two mutually perpendicular directions in the water to the magnetotelluric instrument. The tensor electric field acquisition cable for water includes several sets of mutually perpendicular intersecting transverse and longitudinal electric channels, used to simultaneously acquire electric field component information in the direction of the measured profile and its perpendicular direction, thereby realizing the acquisition of tensor electric fields. Among them, the non-polarized electrodes on the second transverse support form multiple transverse electric channels, and a non-polarized electrode is spaced apart between a pair of non-polarized electrodes located on the same transverse electric channel. Each longitudinal support is provided with a longitudinal electric channel, and a pair of non-polarized electrodes located on the same longitudinal support on the first transverse support and the third transverse support form a longitudinal electric channel. GPS positioning devices are installed on all non-polarized electrodes of the second transverse support. Each GPS positioning device is connected to a magnetotelluric instrument to record the real-time position of the transverse and longitudinal electric channels in the tensor electric field acquisition cable over water. The magnetic field signal acquisition device is an underwater three-component magnetic sensor, including a fiberglass waterproof cover with a handle on the top, and an X-component magnetic sensor, a Y-component magnetic sensor, a Z-component magnetic sensor and an attitude locator installed inside the fiberglass waterproof cover. The X-component magnetic sensor, the Y-component magnetic sensor, the Z-component magnetic sensor and the attitude locator are respectively connected to a multi-core transmission line. The top end of the multi-core transmission line passes through the fiberglass waterproof cover and is connected to the magnetotelluric instrument. The X-component magnetic sensor, Y-component magnetic sensor, and Z-component magnetic sensor are arranged perpendicularly to each other in pairs. The X-component magnetic sensor is used to measure the magnetic field component in the left-right direction, the Y-component magnetic sensor is used to measure the magnetic field component in the front-back direction, and the Z-component magnetic sensor is used to measure the magnetic field component in the up-down direction. The attitude directional device is fixed on the Y-component magnetic sensor and is used to measure the tilt angle and azimuth angle of the underwater three-component magnetic sensor for magnetic field correction. The distance between two adjacent non-polarized electrodes on the support is set to 5m~20m; The top end of the multi-core transmission line is provided with a multi-core transmission line connector for connecting to the magnetotelluric instrument, and the top end of the multi-core shielded cable is provided with a multi-core shielded cable connector for connecting to the magnetotelluric instrument. A rope is attached to the handle at the top of the fiberglass waterproof cover.
2. A shallow water tensor AMT detection method, characterized in that, The shallow water tensor AMT detection device as described in claim 1 specifically includes an anchored observation method and a mobile observation method.
3. The shallow water tensor AMT detection method according to claim 2, characterized in that, The anchored observation method is based on a shallow water tensor AMT detection device and a mobile platform on water, and specifically includes the following steps: Step 1: Obtain geological data and water conditions of the work area, and determine the profile to be measured and the location of each measuring point in the work area in conjunction with the detection target; Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotellurist in the shallow water tensor AMT detection device are working properly. Step 3: Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, determine the observation duration and observation period of the shallow water tensor AMT detection device in the working area, and adjust the electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device. Step 4: Set up the observation device using a shallow water tensor AMT detection device and a floating platform. Set up the shallow water tensor AMT detection device on the floating platform, drag the floating tensor electric field acquisition cable to the tail end of the floating platform, fix the underwater three-component magnetic sensor to the floating platform with ropes, connect the non-polarized electrode in the floating tensor electric field acquisition cable, the GPS positioning device, and the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude orientation device in the underwater three-component magnetic sensor to the magnetotelluric instrument, and then deploy the underwater three-component magnetic sensor to the bottom of the water. Step 5: Anchor the waterborne mobile platform equipped with the shallow water tensor AMT detection device at the first preset measurement point of the profile to be measured. During the set observation time and period, use the shallow water tensor AMT detection device to synchronously acquire electric field data of the transverse and longitudinal electric channels in the waterborne tensor electric field acquisition cable, as well as measurement data of the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude orientation device in the underwater three-component magnetic sensor. Acquire electric field data, X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data in the profile direction and two directions perpendicular to the profile direction. After the acquisition is completed, remove the rope and take the underwater three-component magnetic sensor out of the water. Move the waterborne mobile platform to the next preset measurement point and put the underwater three-component magnetic sensor back into the water for measurement. Continue until all preset measurement points of the profile to be measured have been measured and stop the measurement. Step 6: Obtain electric field data, X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point from the magnetotelluric instrument. Combine this with the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, and correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Based on the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data at each measuring point, determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
4. The shallow water tensor AMT detection method according to claim 2, characterized in that, The mobile observation method, based on a shallow water tensor AMT detection device and two mobile platforms on water, specifically includes the following steps: Step 1: Obtain geological data and water conditions of the work area, and determine the profile to be measured and the location of each measuring point in the work area in conjunction with the detection target; Step 2: Before observation, conduct equipment performance tests on the shallow water tensor AMT detection device to ensure that the electric field signal acquisition device, magnetic field signal acquisition device and magnetotellurist in the shallow water tensor AMT detection device are working properly. Step 3: Based on the test results of the acquisition parameters of the shallow water tensor AMT detection device, determine the observation duration, observation time period and acquisition window of the measurement point in the working area, and adjust the electrode distance between adjacent non-polarized electrodes in the shallow water tensor AMT detection device. Step 4: Set up the observation device using the shallow water tensor AMT detection device and two floating platforms. Tow the floating tensor electric field acquisition cable of the shallow water tensor AMT detection device to the tail end of the first floating platform. Fix the underwater three-component magnetic sensor of the shallow water tensor AMT detection device to the second floating platform by rope. Both floating platforms are equipped with magnetotellurics. Connect the non-polarized electrode and GPS positioning device in the floating tensor electric field acquisition cable to the magnetotellurics on the first floating platform. After connecting the X-component magnetic sensor, Y-component magnetic sensor, Z-component magnetic sensor and attitude directional device in the underwater three-component magnetic sensor to the magnetotellurics on the second floating platform, the underwater three-component magnetic sensor is deployed to the bottom of the water at the middle position of the profile to be measured. Step 5: Use the underwater three-component magnetic sensor mounted on the second waterborne mobile platform to collect X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data. Use the X-component magnetic field data, Y-component magnetic field data and Z-component magnetic field data as the magnetic field data of the section to be measured. Then use the first waterborne mobile platform to tow the waterborne tensor electric field acquisition cable to move along the section to be measured to collect electric field information in the direction of the section to be measured and in the two vertical directions of the section to be measured. Move the first waterborne mobile platform until the section to be measured is completely measured and stop the measurement. Step 6: Obtain electric field data for each set of transverse and longitudinal electric channels in the tensor electric field acquisition cable from the magnetotelluric instrument on the first floating platform, as well as the time and location recorded by each GPS positioning device. Extract the electric field time series segments of each measuring point from the electric field data of each set of transverse and longitudinal electric channels according to the acquisition window of each measuring point, and splice them in chronological order to obtain the complete electric field data of each measuring point. Then, obtain the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data of each measuring point from the magnetotelluric instrument on the second floating platform. Combine the tilt angle and azimuth angle measured by the attitude orienter at each measuring point, correct the X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to the profile direction, the vertical direction of the profile, and the vertical direction of the horizontal plane where the profile is located, respectively. Combine the complete electric field data of each measuring point with the corrected X-component magnetic field data, Y-component magnetic field data, and Z-component magnetic field data to determine the apparent resistivity and impedance phase at each measuring point, and invert the electrical structure of the underwater strata.
5. The shallow water tensor AMT detection method according to claim 3 or 4, characterized in that, The waterborne mobile platform is configured as a ship hull.
6. The shallow water tensor AMT detection method according to claim 3 or 4, characterized in that, Both the floating mobile platform and the end of the floating tensor electric field acquisition cable are equipped with anchors to stabilize the shallow water tensor AMT detection device.