A sea-floor dipole-dipole electromagnetic detection system and method mounted on a remote-controlled underwater robot

Abstract

The application discloses a seabed dipole-dipole electromagnetic detection system and method carried on a remote control underwater robot, and belongs to the technical field of fine exploration of seabed metal mineral resources. The system comprises a remote control underwater robot (ROV), a retractable receiving coil extension support, a transient electromagnetic transmitting coil and a receiving coil, a transient electromagnetic main cabin and an instrument fixing support. The extension support is controlled through a hydraulic contraction device, the receiving coil is arranged away from the ROV body, and the interference of the equipment body on the electromagnetic signal is obviously reduced. The ROV cruises at low altitude along a preset fine survey line on the seabed to collect transient electromagnetic data, and the measured data are corrected in real time by using the full-space seawater environment response in the diving process, so that the system interference is effectively inhibited. The method improves the high-resolution electromagnetic detection capability of seabed polymetallic sulfide ore bodies and is suitable for mineral resource investigation in complex terrain and small-scale areas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic exploration of seafloor polymetallic sulfide and other metal resources, in particular to a seafloor dipole-dipole electromagnetic detection system and method carried on a remotely operated underwater vehicle. BACKGROUND

[0002] The seafloor polymetallic sulfide deposit found in the mid-ocean ridge is rich in copper, zinc, silver, gold and other metals, and is an important seafloor mineral resource. At present, an effective electromagnetic exploration method is urgently needed to understand the three-dimensional distribution characteristics of seafloor polymetallic sulfide, and on this basis, to complete the quantitative evaluation of resources. Due to the high conductivity of seawater and the complex topography of the mid-ocean ridge, the instrument posture changes greatly during the transient electromagnetic tow body towing process, the height from the bottom is large, and the towing body is easily affected by the sea conditions to deviate from the designed survey line. More importantly, for small area seafloor polymetallic sulfide deposits, it is difficult to achieve fine line measurement, which affects the transient electromagnetic detection effect. Therefore, in order to obtain high-quality near-bottom transient electromagnetic data, it is necessary to consider combining transient electromagnetic equipment with near-bottom mobile platforms such as remotely operated vehicles (ROV), and at the same time, to reduce the interference of the mobile platform itself on data acquisition.

[0003] In order to overcome the above shortcomings, in recent years, researchers at home and abroad have actively explored the use of remotely operated vehicles (ROV) or autonomous underwater vehicles (AUV) as mobile carriers for transient electromagnetic exploration. ROV has good maneuverability and high control accuracy, can be close to the seafloor or even hover, and can flexibly deploy high-density lines to greatly improve spatial resolution. Technical reports and tests of some foreign literature (such as GEOMAR, NIOT, etc.) show that by modularizing the electromagnetic transmitter and receiver on the ROV, the preliminary identification of typical sulfide ore bodies has been achieved. However, due to the integration of a large amount of metal materials, propellers and various electrical equipment on the ROV, electromagnetic interference is more serious than the traditional tow body method, and without effective isolation and correction mechanism, it will seriously restrict the data quality. In addition, the space of the ROV platform is limited, and higher requirements are put forward for the weight, size and layout of the detection equipment.

[0004] Therefore, it is urgent to develop a transient electromagnetic detection system and method for fine electromagnetic exploration of seafloor metal sulfide and other mineral resources, which can fully exert the advantages of near-bottom precision operation and high maneuverability of ROV, effectively suppress the body electromagnetic interference, improve the signal-to-noise ratio and the reliability of data interpretation. This lays a technical foundation and practical demand for the present application. SUMMARY

[0005] The application aims at the problem of insufficient precision of conventional towed transient electromagnetic survey in seabed resource investigation and the problem of carrier electromagnetic interference in transient electromagnetic exploration operation, and proposes a seabed dipole-dipole electromagnetic detection system and method suitable for small-scale fine investigation operation and carried on a remote-controlled underwater robot.

[0006] The application aims at the problem of insufficient precision of conventional towed transient electromagnetic survey in seabed resource investigation and the problem of carrier electromagnetic interference in transient electromagnetic exploration operation, and proposes a seabed dipole-dipole electromagnetic detection system and method suitable for small-scale fine investigation operation and carried on a remote-controlled underwater robot.

[0007] The receiving coil extension support group is composed of two supports and a hydraulic contraction device, including an extension support, an extension support and a hydraulic contraction device, the extension support is installed on the left side of the middle part of the ROV, the extension support is installed on the right side of the middle part of the ROV, and the hydraulic contraction device is installed at the root of the extension support to realize the extension and retraction of the extension support.

[0008] The transient electromagnetic transmitting coil is installed to the ROV body chassis, the transient electromagnetic receiving coil is installed to the extension support respectively, the transient electromagnetic main machine cabin is connected with the transient electromagnetic transmitting coil, the transient electromagnetic receiving coil group and the ROV body through the water-tight cable, and the installation specific position of the transient electromagnetic main machine cabin is adjusted according to the ROV counterweight state.

[0009] The transient electromagnetic receiving coil is installed and fixed through the instrument fixing support.

[0010] In one scheme, the extension support and the transient electromagnetic receiving coil are installed symmetrically along the ROV left and right, the electromagnetic interference of the ROV body on the transient electromagnetic detection signal is reduced, and the stable underwater operation of the ROV is ensured, the transient electromagnetic transmitting coil is installed on the ROV body chassis, the underwater movement burden of the ROV can be reduced while ensuring the signal transmission of the large magnetic moment.

[0011] In one scheme, the instrument fixing support is composed of a semicircular fixing plate in the shape of U, the transient electromagnetic transmitting coil is fixed between the U-shaped plates through fixing bolts, and is further installed on the extension support.

[0012] In one scheme, the extension support, the instrument fixing support and the fixing bolt 10 are made of high-strength lightweight non-metallic materials.

[0013] In one scheme, the transient electromagnetic device is connected with the ROV 1 through the water-tight cable, the ROV is further connected with the scientific research ship through the armored cable, so that the power supply and data transmission are ensured, and the real-time data monitoring is carried out on the deck unit of the scientific research ship during the underwater operation.

[0014] In still another aspect, a transient electromagnetic detection method and a full-space water body data correction method for a remote-controlled underwater robot are provided, the method being applicable to the system and comprising the following steps:

[0015] S1: After the transient electromagnetic components are checked and found to be correct, the transient electromagnetic deck test is performed to determine the detection function and the hydraulic retracting and releasing function are normal. After the scientific research ship reaches the starting position of the operation, the extension support and the extension support are ensured to be in the retracted state, and the ROV is lowered;

[0016] S2: During the lowering of the ROV, the extension support and the extension support 3 are opened by the hydraulic contraction device, and the full-space water body transient electromagnetic response is continuously collected, which is used as the measured data for subsequent processing and correction of the data.

[0017] S3: After the correction data collection is completed, the extension support and the extension support are retracted by the hydraulic contraction device, and the ROV continues to dive to the designed starting point of the measuring line.

[0018] S4: A seawater conductivity uniform medium model is established, and the theoretical response of the ROV transient electromagnetic method in the full-seawater environment is derived based on the emission current, coil pole distance, emission radius and effective receiving area of the ROV transient electromagnetic operation.

[0019] S5: For the time sequence t = [t o ,t1,…,t n ], n is the number of sampling time points, and the full-space seawater correction coefficient is defined as:

[0020]

[0021] Where P(t) is the full-space uniform medium transient electromagnetic theoretical response obtained by numerical simulation, and D(t) is the measured transient electromagnetic response of the ROV1 in the full-seawater environment.

[0022] In one scheme, the response characteristics of D(t) are considered to be affected only by the uniform seawater conductivity and the electromagnetic interference of the ROV body, and the data interference condition is quantified by the correction coefficient S(n);

[0023] The expression for water body correction of the complete measured transient electromagnetic data set D(m,n) is:

[0024]

[0025] Where m is the number of data set measuring points; the full-space seawater correction coefficient is applied to the complete measured data set, and the corrected data set D 校 On the basis of removing the interference of the ROV1, the electromagnetic anomaly caused by the change in the seabed conductivity structure is still retained.

[0026] In one scheme, the S3 is contracted by a hydraulic contraction device, the extension support is opened, and the ROV is made to perform transient electromagnetic detection along a pre-planned survey line.

[0027] The present application has the following beneficial effects:

[0028] The transient electromagnetic equipment carried by the remotely operated vehicle (ROV) effectively overcomes the influence of sea conditions such as ocean currents, greatly improves the stability of the instrument, and ensures that the coil posture remains stable during the measurement process and the height of the survey line from the seabed is stable under complex seabed conditions.

[0029] The remotely operated vehicle (ROV) has an independent power system and positioning function, so that the transient electromagnetic equipment can realize small-area and small-scale detection and meet the requirements of high-precision exploration.

[0030] The transient electromagnetic dipole-dipole detection based on the remotely operated vehicle (ROV) can effectively reduce the electromagnetic interference of the ROV body on the transient electromagnetic signal reception, while ensuring the signal transmission of a large magnetic moment, and effectively increasing the transient electromagnetic detection capability.

[0031] By comparing the actual operation of the full-seawater transient electromagnetic response and the theoretical transient electromagnetic response of the uniform medium, the interference characteristics of the measured data can be effectively quantified, the full-space water data correction method is used to further reduce the electromagnetic interference of the detection equipment body and retain effective anomalies, and the signal-to-noise ratio is improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description, and of course the drawings in the description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0033] Figure 1 FIG. 1 is a structural schematic diagram of a seabed dipole-dipole electromagnetic detection system carried by a remotely operated vehicle (ROV) according to the present application;

[0034] Figure 2 FIG. 4 is a schematic diagram of each component.

[0035] Figure 3 FIG. 5 is a schematic diagram of instrument fixation.

[0036] Figure 4 FIG. 6 is a schematic diagram of a seabed dipole-dipole electromagnetic detection method carried by a remotely operated vehicle (ROV) according to the present application.

[0037] Figure 5For ROV offshore operation survey line path planning, ROV along the preset route for detection operation.

[0038] Figure 6 For ROV offshore operation time-depth variation chart, near the bottom section ROV cruise detection operation to keep stable height from the bottom.

[0039] Figure 7 For the whole space water body data correction method effect diagram.

[0040] In the figure: 1-remote control underwater robot ROV, 2-ROV left extension bracket, 3-ROV right extension bracket, 4-hydraulic telescopic device, 5-transient electromagnetic transmitting coil, 6-transient electromagnetic left receiving coil, 7-transient electromagnetic right receiving coil, 8-transient electromagnetic main computer cabin, 9-instrument fixing bracket, 10-fixed bolt, 11-survey ship, 12-deck unit, 13-armored cable, 14-float ball. DETAILED DESCRIPTION

[0041] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The drawings show typical embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described in the present application. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0042] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as understood by those skilled in the art to which the present application belongs. The terms used in the present application in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The drawings show typical embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described in the present application. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0043] Example 1

[0044] As Figure 1 shown, the present application provides a seabed dipole-dipole electromagnetic detection system carried on a remote control underwater robot, which comprises a remote control underwater robot ROV 1, a receiving coil extension bracket 2, 3, a hydraulic device 4, a transient electromagnetic transmitting coil 5, a transient electromagnetic receiving coil 6, 7, a transient electromagnetic main computer cabin 8 and an instrument fixing bracket 9.

[0045] The receiving coil extension bracket set is composed of two brackets and a hydraulic contraction device, the two extension brackets are respectively installed on the left side and the right side of the middle part of the ROV, and the hydraulic contraction device is installed at the root of the extension bracket to realize the extension and retraction of the extension bracket; the transient electromagnetic transmitting coil is installed on the ROV body chassis; the two transient electromagnetic receiving coils are respectively installed on the two extension bracket ends; the transient electromagnetic main machine cabin is connected with the transient electromagnetic transmitting coil, the transient electromagnetic receiving coil and the ROV body through a water-tight cable, and the installation position of the transient electromagnetic main machine cabin is adjusted according to the ROV counterweight state; the transient electromagnetic receiving coil is fixedly installed through the instrument fixing bracket.

[0046] The two extension brackets and the two transient electromagnetic receiving coils are respectively installed along the left-right symmetry of the ROV, so that the electromagnetic interference of the ROV body on the transient electromagnetic detection signal is reduced, and the stable underwater operation of the ROV is ensured; the transient electromagnetic transmitting coil is installed on the ROV body chassis, so that the signal transmission with large magnetic moment is ensured while the underwater movement burden of the ROV is reduced.

[0047] The instrument fixing bracket is composed of a semicircular fixing plate in U shape, the transient electromagnetic transmitting coil is fixed between the U-shaped plates through fixing bolts, and the transient electromagnetic transmitting coil is further installed on the extension bracket.

[0048] The receiving coil extension bracket, the instrument fixing bracket and the fixing bolt are all made of high-strength lightweight non-metallic materials.

[0049] The transient electromagnetic device is connected with the ROV through a water-tight cable, the ROV is further connected with the research ship through an armored cable, so that power supply and data transmission are ensured, and real-time data monitoring is realized on the research ship during underwater operation.

[0050] The electromagnetic interference generated by the ROV1 is collected and tested in the laboratory, the extension bracket set is designed to make the transient electromagnetic measurement away from the interference of the ROV1 without affecting the operation of the carrier. Meanwhile, in order to protect the equipment and personnel safety during the deployment and recovery of the ROV1, the hydraulic device is arranged to keep the extension bracket in the retracted state during non-operation. The system does not affect the operation of the traditional ROV1, and can additionally obtain high-precision transient electromagnetic data near the seabed. In addition, the system can also monitor the electromagnetic data in real time, effectively protect the data quality, improve the efficiency of marine investigation, and provide scientific data support for the delineation of seabed mining areas.

[0051] Evaluation of transient electromagnetic interference of ROV body

[0052] The control group is set, and the interference range is determined by taking ROV1 power on and off, propeller running and shutdown, and the horizontal distance between the transient electromagnetic coil and ROV1 as variables. When ROV1 is not powered on, the transient electromagnetic signal will produce electromagnetic anomalies due to the metal structure of ROV1 itself. The anomaly decreases with the increase of the horizontal distance between the transient electromagnetic receiving coil and ROV1. Combined with the force bearing capacity of the extension bracket itself, the length of the extension bracket is determined so that the electromagnetic interference of ROV1 can be considered as insufficient to affect the transient electromagnetic data. When ROV1 is powered on, its transformer becomes the main interference source. Test data show that the distortion of the transient electromagnetic signal caused by this interference source is stable over time, and the running and shutdown of the propeller will not produce additional effects on the transient electromagnetic signal, so the transient electromagnetic method can still identify the abnormal structure of the seabed resistivity.

[0053] Installation mode of transient electromagnetic method

[0054] As shown in Figure 2 , the cable of the transient electromagnetic transmitting coil 5 is wound along the rectangular frame groove, and the overall frame is directly fixed to the ROV1 body chassis; the transient electromagnetic main cabin 8 has five interfaces, including power supply and communication interfaces, which are connected with ROV1 through water-tight cables, two receiving interfaces are respectively connected with the transient electromagnetic receiving coils 6 and 7 through water-tight cables, and one transmitting interface is connected with the transient electromagnetic transmitting coil through a water-tight cable.

[0055] The installation position and length of the instrument bracket group are determined by the above-mentioned test: two extension brackets 2 and 3 and two transient electromagnetic receiving coils 6 and 7 are respectively installed symmetrically on the left and right of the middle of ROV1, which reduces the electromagnetic interference of ROV1 body on the transient electromagnetic detection signal and ensures the stable operation of ROV1 underwater; the hydraulic contraction device 4 is installed at the root of the extension bracket 2, 3 to realize the extension and retraction of the extension bracket; the transient electromagnetic transmitting coil 5 is installed to the ROV1 body chassis, which can reduce the underwater movement burden of ROV1 while ensuring the signal transmission of large magnetic moment; the two transient electromagnetic receiving coils 6 and 7 are respectively installed to the ends of the two extension brackets 2 and 3; the transient electromagnetic main cabin 8 is connected with the transient electromagnetic transmitting coil 5, the transient electromagnetic receiving coils 6 and 7 and the ROV1 body through water-tight cables, and the specific installation position of the transient electromagnetic main cabin 8 is adjusted according to the state of the ROV1 counterweight; the transient electromagnetic receiving coil is fixedly installed through the instrument fixing bracket 9. The materials of the extension bracket 2, 3, the instrument fixing bracket 9 and the fixing screw 10 should be high-strength lightweight non-metallic materials, which can meet the use requirements of the high-pressure environment of the seabed while preventing additional electromagnetic interference.

[0056] Figure 3Figure 1 is a schematic diagram of installation of the transient electromagnetic receiving coil 6, 7, the instrument fixing support 9, and the extension support 2, 3. First, the transient electromagnetic receiving coil 6, 7 is installed on the "U" shaped instrument fixing support 9. The diameter of the U-shaped instrument fixing support 9 should match the diameter of the receiving coil 6, 7. The receiving coil 6, 7 is clamped by the two U-shaped plates through the grooves, and is fixed by the fixing bolt 10. When the receiving coil 6, 7 and the instrument fixing support 9 are installed, the instrument fixing support 9 is installed on the end of the extension support 2, 3 by the fixing bolt 10.

[0057] Embodiment 2

[0058] Based on the system of embodiment 1, a seabed transient electromagnetic detection method carried on a remote control underwater robot and a full space water data correction method are constructed, as shown in Figures 4-7 , which comprises the following steps:

[0059] S1: The ROV 1 is connected with the deck unit 12 on the survey ship 11 through the armored cable 13, and the armored cable 13 is installed with a float ball 14. Before being launched into water, each part of the transient electromagnetic device is checked to be correct, and then the transient electromagnetic deck test is performed to determine that the detection function and the hydraulic retracting function are normal. When the scientific research ship reaches the on-line position, it is ensured that the extension support 2 and the extension support 3 are in the retracted state, and the ROV 1 is lowered.

[0060] S2: When the ROV 1 is lowered halfway (the distance from the seabed and the distance from the sea surface of the ROV 1 are both much greater than the transient electromagnetic detection distance), the extension support 2 and the extension support 3 are opened by the hydraulic contraction device 4, and the continuous acquisition of the full space seawater transient electromagnetic response is started. After the correction data acquisition is completed, the extension support 2 and the extension support 3 are retracted by the hydraulic contraction device 4, and the ROV 1 continues to dive to the designed starting point of the survey line.

[0061] S3: The extension support 2 and the extension support 3 are opened by the hydraulic contraction device 4, and the ROV 1 is allowed to perform the transient electromagnetic detection along the pre-planned survey line (as shown in Figure 5 ), and the scientific research ship 11 is kept in the state of dynamic positioning and moves slowly to keep the cooperative operation with the ROV 1. The ROV 1 advances at a speed of 0.5-1 knot, and the height from the seabed is adjusted in real time according to the height gauge data of the ROV 1 during the advancing process (as shown in Figure 6 ), so as to ensure that the transient electromagnetic detection process is always close to the seabed surface. After the survey line is completed, the extension support 2 and the extension support 3 are retracted by the hydraulic contraction device 4, and the ROV 1 is recovered to the deck of the scientific research ship 11.

[0062] S4: A seawater conductivity (~3S / m) uniform medium model is established, and the theoretical response of the ROV transient electromagnetic device in the full seawater environment is derived according to the information such as the transmission current, the transmission radius and the effective receiving area of the ROV transient electromagnetic operation diving.

[0063] S5: For time series t = [t o ,t1,…,t n ], n is the number of sampling time points, define the full-space seawater correction coefficient:

[0064]

[0065] Where P(t) is the full-space uniform medium transient electromagnetic theory response obtained by numerical simulation calculation, D(t) is the measured transient electromagnetic response of ROV1 in the full seawater environment. The response characteristics of D(t) can be considered to be affected only by the uniform seawater conductivity and the electromagnetic interference of ROV1 body, so the data interference condition is quantified by the correction coefficient S(n). Then the expression for water body correction of the complete measured transient electromagnetic data set D(m, n) is:

[0066]

[0067] Where m is the number of data set measurement points. Apply the full-space seawater correction coefficient to the complete measured data set, and the corrected data set D 校 On the basis of removing the interference of ROV1, the electromagnetic anomaly caused by the change of seabed conductivity structure is still retained. Figure 7

[0068] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above-mentioned embodiment methods. The storage medium can be a magnetic disc, an optical disc, a read-only memory (ROM) or a random access memory (RAM), etc.

[0069] It should be understood that the above detailed description of the technical solutions of the present application by means of preferred embodiments is illustrative rather than limiting. Those skilled in the art can modify the technical solutions recorded in each embodiment on the basis of the present application, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present application.​

Claims

1. A seabed dipole-dipole electromagnetic detection method mounted on a remotely operated underwater vehicle, characterized in that: The transient electromagnetic transmitting coil is installed on the ROV chassis, and two extension brackets are installed symmetrically on the left and right sides of the ROV. The transient electromagnetic receiving coils are installed on the two extension brackets respectively. The method includes the following steps: S1: Before the remotely operated underwater vehicle (ROV) is launched, all components of the transient electromagnetic system are checked and confirmed to be in good working order. Then, the transient electromagnetic deck test is performed to confirm that the detection function and hydraulic deployment and retraction function are normal. Once the research vessel reaches the starting position of the operation, ensure that both extension supports are in the retracted state before lowering the ROV. S2: Halfway down the ROV, the two extension supports are opened by the hydraulic retraction device, and continuous acquisition of transient electromagnetic response of the water body in the whole space begins. This data is used as the measured response under uniform seawater medium for subsequent data correction. S3: After the calibration data acquisition is completed, the two extension supports are retracted by the hydraulic retraction device, and the ROV continues to descend to the starting point of the designed survey line; S4: Establish a uniform conductivity medium model for seawater, and derive the theoretical response of ROV transient electromagnetic operation in a full seawater environment by performing forward modeling based on the transmission current, coil pole spacing, transmission radius and effective receiving area information of the ROV transient electromagnetic operation. S5: For a time series t = [t o ,t1,…,t n ], where n is the number of sampling time points, and the full-space seawater correction coefficient is defined as follows: ； Wherein, P(t) is the theoretical transient electromagnetic response of the homogeneous medium in the whole space obtained by numerical simulation, and D(t) is the measured transient electromagnetic response of the ROV in the whole seawater environment.

2. The seabed dipole-dipole electromagnetic detection method mounted on a remotely operated underwater vehicle according to claim 1, characterized in that: The response characteristics of D(t) are considered to be affected only by the uniform conductivity of seawater and the electromagnetic interference of the ROV itself. The data interference is quantified by the correction coefficient S(n). The expression for water body correction for the complete measured transient electromagnetic dataset D(m,n) is as follows: ； Where m is the number of measurement points in the dataset; the full-space seawater correction coefficient is applied to the complete measured dataset, thus obtaining the correction dataset D. 校 While removing ROV interference, the electromagnetic anomalies caused by changes in seabed conductivity structure are still retained.

3. The seabed dipole-dipole electromagnetic detection method mounted on a remotely operated underwater vehicle according to claim 1, characterized in that: In S3, a hydraulic retraction device is used to open the two extension supports and allow the ROV to perform transient electromagnetic detection along a pre-planned measurement line.

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