Submarine structure detection system and submarine structure detection method

Abstract

To provide a submarine structure body detection system capable of suppressing it from becoming difficult to detect a submarine structure body since magnetism emitted from the submarine structure body is small in magnitude and magnetic noise is present in a circumference of the submarine structure body.SOLUTION: A submarine structure body detection system 100 is to detect a submarine structure body 90 provided at the bottom 81 of the sea, and comprises: an electric wire 1 provided to the submarine structure body 90; a current source 2 having one terminal 2a connected to the electric wire 1; a magnetic sensor 3 outputting an electric signal 30 based upon magnetism in the sea; and a determination part 10a which determines whether there is the submarine structure body 90 based upon the magnetic signal 30 due to a current in a state in which the current flows through the electric wire 1 from the current source 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a seabed structure detection system and a seabed structure detection method, and more particularly to a seabed structure detection system for detecting a seabed structure provided on the seabed while moving a magnetic sensor along the seabed, and a seabed structure detection method.

Background Art

[0002] Conventionally, a seabed structure detection system for detecting a seabed structure provided on the seabed while moving a magnetic sensor along the seabed, and a seabed structure detection method have been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a magnetic exploration device (seabed structure detection system) that detects a seabed structure provided on the seabed using magnetism while moving along the seabed. The magnetic exploration device disclosed in Patent Document 1 includes a combined sensor in which magnetic sensors are combined in two or more upper and lower stages. The magnetic exploration device disclosed in Patent Document 1 arranges at least one pair of combined sensors so as to face each other in parallel on the same plane. Further, the magnetic exploration device disclosed in Patent Document 1 is configured to detect a seabed pipeline by detecting magnetism emitted from a seabed pipeline buried on the seabed while moving along the seabed by being towed by a survey ship.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the configuration disclosed in Patent Document 1 has the disadvantage that, since the detection of seabed structures is based on the magnetism emitted from the seabed pipeline (seabed structure), it becomes difficult to detect the seabed structure when the magnitude of the magnetism emitted from the seabed structure is small. Furthermore, in the configuration disclosed in Patent Document 1, if the magnitude of the magnetic noise around the seabed structure is large, the magnitude of the magnetism emitted from the seabed structure becomes relatively small, which also has the disadvantage of making it difficult to detect the seabed structure. Therefore, there is a problem in that the detection of seabed structures becomes difficult due to the small magnitude of the magnetism emitted from the seabed structure and the magnetic noise around the seabed structure.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide a seabed structure detection system and a seabed structure detection method that can suppress the difficulty in detecting seabed structures due to the small magnitude of magnetic fields emitted from seabed structures and magnetic noise around the seabed structures. [Means for solving the problem]

[0007] To achieve the above objective, the seabed structure detection system in the first aspect of this invention is a seabed structure detection system for detecting seabed structures installed on the seabed, wherein the power lines installed on the outside of the outermost surface of the seabed structure, Having a first terminal and a second terminal, It comprises a current source connected to a power line, a magnetic sensor that outputs a magnetic signal based on the magnetic field in the sea, and a discrimination unit that, when current flows through the power line due to the current source, determines the presence or absence of a seabed structure based on the magnetic signal caused by the current. The electric wire has one end connected to the first terminal of the current source on land, and the other end is located in the sea, with the other end electrically connected to the second terminal of the current source via seawater. ru. A second aspect of this invention is a seabed structure detection system for detecting seabed structures installed on the seabed, comprising: a wire installed on the seabed structure; a current source with one terminal connected to the wire; a magnetic sensor that outputs a magnetic signal based on the magnetism in the sea; a discrimination unit that determines the presence or absence of a seabed structure based on the magnetic signal caused by the current when current flows through the wire by the current source; and a metal plate connected to the other terminal of the current source and installed in the sea, wherein the end of the wire not connected to the current source is installed in the sea with its insulation stripped off, and is configured so that current flows between the end not connected to the current source and the metal plate via seawater.

[0008] A third aspect of this invention is a method for detecting seabed structures, which is a method for detecting seabed structures installed on the seabed, Having a first terminal and a second terminal current Source and The method comprises the steps of: sending an electric current through a wire connected to and located outside the outermost surface of a seabed structure; acquiring a magnetic signal based on the ocean's magnetic field, output by a magnetic sensor installed in the sea, while an electric current is flowing from the current source to the wire; and determining the presence or absence of a seabed structure based on the magnetic signal caused by the electric current. The electric wire has one end connected to the first terminal of the current source on land, and the other end is located in the sea, with the other terminal electrically connected to the second terminal of the current source via seawater. ru. [Effects of the Invention]

[0009] The seabed structure detection system in the first phase described above, and the first phase described above 3 In the seabed structure detection method in this phase, seabed structures The outermost surfaceAn electric current is passed through a wire installed in the seabed, and the presence or absence of a seabed structure is determined based on the magnetic signal generated by the current. Therefore, since the presence or absence of a seabed structure is determined using a relatively large magnetic signal generated by the current applied to the wire, the presence or absence of a seabed structure can be determined even if the magnetic signal based on the magnetism emitted from the seabed structure is small. Furthermore, by increasing the current applied to the wire, the magnitude of the magnetic signal generated by the current can be made larger than the magnetic noise around the seabed structure. As a result, the difficulty in detecting seabed structures due to the small magnitude of the magnetism emitted from the seabed structure and the magnetic noise around the seabed structure can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows the overall configuration of a seabed structure detection system according to one embodiment. [Figure 2] This is a block diagram showing the configuration of a seabed structure detection system according to one embodiment. [Figure 3] This is a schematic diagram illustrating the location where an electric wire is installed on an underwater structure according to one embodiment. [Figure 4] This is a schematic diagram illustrating the alternating magnetic field generated when alternating current flows through an electric wire. [Figure 5] This is a functional block diagram illustrating a configuration in which a discrimination unit according to one embodiment determines the presence or absence of a seabed structure. [Figure 6] This is a schematic diagram illustrating a configuration in which a discrimination unit according to one embodiment acquires the depth position of a seabed structure. [Figure 7] This graph illustrates the magnetic signal when the current source does not apply alternating current to the wire. [Figure 8] This graph illustrates the magnetic signal when a current source applies alternating current to a power line. [Figure 9] This graph illustrates the reference waveform generated by a reference waveform generation unit according to one embodiment. [Figure 10]A graph for explaining the synchronous detection signal generated by the discrimination unit according to an embodiment. [Figure 11] A flowchart for explaining the process of the discrimination unit according to an embodiment for discriminating the presence or absence of a seabed structure. [Figure 12] A block diagram showing the configuration of a seabed structure detection system according to the first modification example. [Figure 13] A graph for explaining the magnetic signal when a current source according to the first modification example applies a direct current to an electric wire. [Figure 14] A schematic diagram for explaining the position where an electric wire according to the second modification example is provided on a seabed structure.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0012] Referring to FIGS. 1 to 10, the configuration of a seabed structure detection system 100 according to an embodiment will be described.

[0013] (Configuration of Seabed Structure Detection Device) First, referring to FIG. 1, the configuration of a seabed structure detection system 100 according to an embodiment will be described.

[0014] The seabed structure detection system 100 is a seabed structure detection system that detects a seabed structure 90 provided on the seabed 81. The seabed structure 90 is a long object extending along the seabed 81. Specifically, the seabed structure 90 is a pipeline provided on the seabed 81. That is, the seabed structure detection system 100 is configured to detect a pipeline provided on the seabed 81. The pipeline includes, for example, a steel pipe provided so that an anticorrosion layer (not shown) for preventing rust covers the outer surface 90a (see FIG. 3). The anticorrosion layer includes, for example, insulators such as rubber and polyvinyl chloride. Note that the pipeline is an example of the "seabed structure" in the claims.

[0015] As shown in Figure 1, the seabed structure detection system 100 includes a power line 1, a current source 2, a magnetic sensor 3, and a computer 4. In this embodiment, the seabed structure detection system 100 includes a metal plate 5. In this embodiment, the seabed structure detection system 100 also includes a mobile body 6.

[0016] The electric wire 1 is installed on the seabed structure 90. The electric wire 1 is formed by a conductor that carries electric current and an insulating coating that covers the outer circumference of the conductor. The electric wire 1 includes, for example, cables, insulated wires, cords, etc. The location where the electric wire 1 is installed on the seabed structure 90 will be described later.

[0017] The current source 2 includes terminals 2a and 2b. One terminal 2a of the current source 2 is connected to the electric wire 1. The current source 2 is configured to cause current to flow through the electric wire 1 by applying a voltage to it, as shown by the dashed arrow 60. The other terminal 2b of the current source 2 is connected to the metal plate 5. In this embodiment, the current source 2 is configured to change the current applied to the electric wire 1 over time. Specifically, the current source 2 is configured to apply an alternating current to the electric wire 1. The current source 2 includes, for example, an AC power supply.

[0018] The magnetic sensor 3 is configured to detect the magnetic field in the sea. The magnetic sensor 3 is also configured to output a magnetic signal 30 (see Figure 2) based on the magnetic field in the sea. The magnetic sensor 3 is mounted on the moving body 6. In this embodiment, the magnetic sensor 3 is configured to output a magnetic signal 30 measured while being moved by the moving body 6. The magnetic sensor 3 is configured to output magnetic signals 30 in the vertical direction of the moving body 6 and in two mutually orthogonal directions within a plane perpendicular to the vertical direction. The magnetic sensor 3 includes, for example, a three-axis magnetometer.

[0019] Computer 4 is configured to supply current to the power line 1 by controlling the current source 2. Computer 4 is also configured to detect the seabed structure 90 based on the magnetic signal 30 output from the magnetic sensor 3. Furthermore, Computer 4 is configured to control the movement of the mobile body 6. Details of how Computer 4 detects the seabed structure 90 will be described later.

[0020] The metal plate 5 is connected to the other terminal 2b of the current source 2 and is installed in the sea. That is, the metal plate 5 is in contact with seawater 80. The metal plate 5 is made of a metal having a different ionization tendency than the electric wire 1. In this embodiment, the metal plate 5 is made of a metallic material with an ionization tendency greater than or equal to that of copper. In this embodiment, the metal plate 5 is, for example, a copper plate.

[0021] The mobile unit 6 is equipped with a magnetic sensor 3 and is configured to move the magnetic sensor 3. The mobile unit 6 is also equipped with a depth gauge (not shown) to acquire depth information of the mobile unit 6 in the sea, and a distance sensor (not shown) to acquire the distance from the mobile unit 6 to the object being measured. The mobile unit 6 is configured to autonomously travel underwater. Furthermore, the mobile unit 6 is configured to move underwater unmanned. The mobile unit 6 is a so-called AUV (Autonomous Underwater Vehicle). The detailed configuration of the mobile unit 6 will be described later.

[0022] As shown in Figure 1, a portion of the power line 1, the current source 2, and the computer 4 are located on land. The majority of the power line 1, the metal plate 5, and the mobile unit 6 are located underwater.

[0023] As shown in Figure 2, the computer 4 comprises a processor 10, a memory unit 11, a signal acquisition unit 12, and a notification unit 13. The computer 4 determines the presence or absence of the seabed structure 90 based on the magnetic signal 30 output from the magnetic sensor 3 installed on the mobile body 6. The computer 4 also controls the flow of current from the current source 2 to the power line 1.

[0024] The processor 10 comprises a discrimination unit 10a and a reference waveform generation unit 10b as functional blocks. In other words, the processor 10 functions as the discrimination unit 10a and the reference waveform generation unit 10b by executing programs stored in the memory unit 11. The processor 10 includes, for example, a CPU (Central Processing Unit), a microprocessor, and an FPGA (Field-Programmable Gate Array) configured for determining the position of the seabed structure 90.

[0025] The discrimination unit 10a is configured to determine the presence or absence of a seabed structure 90 based on a magnetic signal 30 caused by the current when current flows through the power line 1 by the current source 2. In this embodiment, the discrimination unit 10a is configured to determine the presence or absence of a seabed structure 90 based on the change in the signal waveform between the magnetic signal 30 before current flows through the power line 1 and the magnetic signal 31 (see Figure 8) when current flows through the power line 1. In this embodiment, the discrimination unit 10a is configured to determine the presence or absence of a pipeline. Furthermore, the discrimination unit 10a is configured to acquire the arrangement state of the seabed structure 90 based on the magnetic signal 30 measured while the magnetic sensor 3 is moving. Details of how the discrimination unit 10a determines the presence or absence of a seabed structure 90 will be described later.

[0026] The reference waveform generation unit 10b is configured to generate a reference waveform 22 (see Figure 4) that the discrimination unit 10a uses to determine whether or not there is a seabed structure 90.

[0027] The storage unit 11 stores frequency data 20 and reference waveform 21. The storage unit 11 also stores various programs executed by the processor 10. The storage unit 11 includes a non-volatile storage device. Examples of non-volatile storage devices include hard disk drives and solid-state drives.

[0028] The frequency data 20 is the frequency of the alternating current applied from the current source 2 to the power line 1. The reference waveform 21 is acquired in advance when the seabed structure 90 is laid and stored in the memory unit 11. The reference waveform 21 is the waveform of the magnetic signal 30 output by the magnetic sensor 3 while the mobile body 6 is moved a predetermined distance from the seabed structure 90. The reference waveform 21 is used to acquire the depth position 52 (see Figure 6) of the seabed structure 90 when the seabed structure 90 is present. In other words, the reference waveform 21 is not used to determine whether or not the seabed structure 90 is present.

[0029] The signal acquisition unit 12 is configured to acquire a magnetic signal 30 from a magnetic sensor 3 provided on the mobile body 6. The signal acquisition unit 12 is also configured to output the acquired magnetic signal 30 to the processor 10. The signal acquisition unit 12 includes a wireless communication device and an input / output interface.

[0030] The notification unit 13 is configured to notify the discrimination result 40 (see Figure 5) of the discrimination unit 10a. The notification unit 13 is, for example, a liquid crystal display device. The notification unit 13 may also be an electroluminescent display device or a projector.

[0031] The mobile unit 6 includes a control unit 6a, a communication unit 6b, and a propulsion mechanism 6c.

[0032] The control unit 6a is configured to control the mobile body 6. The control unit 6a includes, for example, a CPU.

[0033] The communication unit 6b is configured to communicate with the computer 4 under the control of the control unit 6a. Specifically, the communication unit 6b is configured to receive information from the computer 4 regarding the direction in which the mobile body 6 should move, and to transmit the magnetic signal 30 output by the magnetic sensor 3 to the computer 4. The communication unit 6b includes, for example, a wirelessly connectable transceiver.

[0034] The propulsion mechanism 6c is configured to provide thrust to the moving body 6 under the control of the control unit 6a. The propulsion mechanism 6c includes a propeller (not shown) and a drive source (not shown) that drives the propeller. The propulsion mechanism 6c may be a so-called screw configuration that obtains thrust by scooping water by rotating the propeller, or it may be a so-called waterjet propulsion mechanism that obtains thrust by ejecting a high-pressure water stream backward.

[0035] <Planning of power lines> Next, with reference to Figure 3, the arrangement of the power line 1 relative to the seabed structure 90 will be explained. In the example shown in Figure 3, for illustrative purposes, the power line 1 and the seabed structure 90 are shown separated, but in reality, the power line 1 is installed in contact with the outer surface 90a of the seabed structure 90.

[0036] As shown in Figure 3, the electric wire 1 is installed on the outer surface 90a of the seabed structure 90 along the direction in which the axis 90b of the seabed structure 90 extends. Specifically, the electric wire 1 is installed in a straight line on the outer surface 90a of the seabed structure 90 along the direction in which the seabed structure 90 extends. Furthermore, the end 1a of the electric wire 1 that is not connected to the current source 2 is installed in the sea with its insulating coating stripped off. That is, the end 1a of the electric wire 1 that is not connected to the current source 2 has its conductor exposed and is installed in the sea with the conductor in contact with seawater 80 (see Figure 1). This configuration allows current to flow between the end 1a not connected to the current source 2 and the metal plate 5 (see Figure 1) via the seawater 80 (see Figure 1).

[0037] Note that in Figure 1, a dashed arrow 60 is shown to make it easier to visualize the state in which current flows through the wire 1 and the metal plate 5. However, in reality, current flows through the wire 1 because the seawater 80 is electrolyzed by the end 1a of the wire 1 and the metal plate 5. In other words, a current path is not formed between the end 1a of the wire 1 and the metal plate 5 as shown by the dashed arrow 60 in Figure 1.

[0038] <AC magnetic field detected by a magnetic sensor> Next, with reference to Figure 4, the alternating magnetic field 30a detected by the magnetic sensor 3 will be described. Figure 4 is a cross-sectional view of the seabed structure 90 and the power line 1.

[0039] When an electric current flows through the wire 1, a magnetic field is generated centered on the wire 1. Specifically, a magnetic field is generated in concentric circles centered on the wire 1. In this embodiment, since an alternating current flows through the wire 1, an alternating magnetic field 30a is generated due to the alternating current. In this embodiment, the magnetic sensor 3 (see Figure 1) is configured to detect the alternating magnetic field 30a caused by the alternating current emitted from the wire 1. The current source 2 applies current to the wire 1 such that the magnitude of the alternating magnetic field 30a is greater than the magnitude of the magnetism emitted from the seabed structure 90. The current source 2 also applies current to the wire 1 such that the magnitude of the alternating magnetic field 30a is greater than the magnitude of the magnetic noise around the seabed structure 90.

[0040] <Detection of seabed structures> Next, referring to Figure 5, we will describe the configuration in which the processor 10 determines the presence or absence of the seabed structure 90 (see Figure 1).

[0041] The reference waveform generation unit 10b acquires frequency data 20 from the storage unit 11. The reference waveform generation unit 10b generates a reference waveform 22 based on the frequency (frequency data 20) of the alternating current applied from the current source 2 to the power line 1. The frequency data 20 can be set by the user. In that case, it is preferable to set the frequency data 20 to a frequency different from the frequency of the alternating magnetic field around the seabed structure 90. Also, if the current source 2 is a commercial power supply, the frequency data 20 may be 50 Hz (Hertz) or 60 Hz. The reference waveform 22 is the waveform of the alternating magnetic field generated based on the frequency of the alternating current. The reference waveform generation unit 10b outputs the generated reference waveform 22 to the discrimination unit 10a.

[0042] The discrimination unit 10a is configured to determine the presence or absence of a seabed structure 90 based on changes in the magnetic signal 30 caused by electric current. Specifically, the discrimination unit 10a acquires a synchronous detection signal 32 (see Figure 10), which is the signal of the component of the AC magnetic field 30a caused by AC current, based on the AC magnetic field 30a detected by the magnetic sensor 3 and the reference waveform 22. The discrimination unit 10a multiplies the reference waveform 22 and the magnetic signal 30 and performs low-pass filtering to acquire the DC component in the magnetic signal 30 that is proportional to the amplitude of the AC magnetic field 30a as the synchronous detection signal 32.

[0043] Furthermore, the discrimination unit 10a is configured to determine the presence or absence of the seabed structure 90 based on the acquired synchronous detection signal 32. The discrimination unit 10a also outputs the discrimination result 40, which determines the presence or absence of the seabed structure 90 based on the synchronous detection signal 32, to the notification unit 13. In this embodiment, if the discrimination unit 10a determines that the seabed structure 90 is present, it outputs a message to the notification unit 13 indicating that the seabed structure 90 has been detected. If the discrimination unit 10a determines that the seabed structure 90 is not present, it outputs a message to the notification unit 13 indicating that the seabed structure 90 was not detected.

[0044] The notification unit 13 displays the discrimination result 40 input from the discrimination unit 10a.

[0045] <Detection of the depth location of seabed structures> Next, referring to Figure 6, the configuration in which the discrimination unit 10a (see Figure 2) acquires the depth position 52 of the seabed structure 90 will be described. In this embodiment, the discrimination unit 10a is configured to detect the depth position 52 of the seabed structure 90 based on the magnitude of the magnetic signal 30. Specifically, the discrimination unit 10a acquires the distance 50 between the seabed structure 90 and the mobile body 6 by comparing the reference waveform 21 with the magnetic signal 30. The reference waveform 21 is the waveform of the alternating magnetic field 30a when the seabed structure 90 is laid. When acquiring the reference waveform 21, the distance between the mobile body 6 and the seabed structure 90 is acquired by a distance sensor provided on the mobile body 6, and is stored in the storage unit 11 together with the reference waveform 21. Multiple reference waveforms 21 may be acquired by changing the distance between the mobile body 6 and the seabed structure 90.

[0046] Furthermore, the discrimination unit 10a acquires the distance 51 from the sea surface 82 to the mobile body 6 based on the depth gauge installed on the mobile body 6. The discrimination unit 10a then acquires the depth position 52 of the seabed structure 90 by adding the distance 50 between the seabed structure 90 and the mobile body 6 and the distance 51 from the sea surface 82 to the mobile body 6. In other words, the depth position 52 of the seabed structure 90 is the distance from the sea surface 82 to the seabed structure 90. With this configuration, for example, even if the seabed structure 90 is buried by sand on the seabed 81 and the distance 50 between the mobile body 6 and the seabed structure 90 cannot be acquired by a distance sensor or the like, the depth position 52 of the seabed structure 90 can still be acquired.

[0047] <Waveforms of each signal> Next, with reference to Figures 7 to 10, the magnetic signal 30 detected by the magnetic sensor 3 and the synchronous detection signal 32 generated by the discrimination unit 10a will be described.

[0048] Figure 7 is a graph 70 showing the waveform of the magnetic signal 30 before the alternating current is applied from the current source 2 to the wire 1. In graph 70, the vertical axis represents the total magnetic force, and the horizontal axis represents time. The total magnetic force is the sum of the magnetic forces in each axial direction acquired by the magnetic sensor 3.

[0049] As shown in Graph 70, the magnetic signal 30 includes a magnetic component 30b, which includes the magnetic component emitted from the seabed structure 90 (see Figure 1) and the DC magnetic component around the seabed structure 90, and an AC magnetic component 30c, which includes the AC magnetic component around the seabed structure 90. In other words, the magnetic sensor 3 (see Figure 1) outputs a magnetic signal 30 that includes the magnetic component from the magnetism emitted from the seabed structure 90 and the magnetic field around the seabed structure 90, when no current is applied to the wire 1 (see Figure 1) by the current source 2 (see Figure 1).

[0050] Figure 8 is a graph 71 showing the waveform of the magnetic signal 30 when an alternating current is applied from the current source 2 (see Figure 1) to the wire 1 (see Figure 1). In graph 70, the vertical axis represents the total magnetic force, and the horizontal axis represents time. In the example shown in Figure 8, an alternating current is applied from the current source 2 to the wire 1 at time 60.

[0051] As shown in Graph 71, the magnetic signal 31 after an alternating current is applied to the wire 1 also includes a magnetic component 30b, which includes the magnetic component emitted from the seabed structure 90 (see Figure 1) and the DC magnetic component around the seabed structure 90. Furthermore, the magnetic signal 31 after an alternating current is applied to the wire 1 also includes an alternating magnetic component 30d, which includes the alternating magnetic component around the seabed structure 90 and the alternating magnetic field 30a (see Figure 4) caused by the alternating current. In other words, the magnetic sensor 3 detects magnetism including the magnetic component caused by the alternating current when an alternating current is applied. Therefore, the magnetic signal 30 output from the magnetic sensor 3 changes to the magnetic signal 31.

[0052] Figure 9 is a graph 72 showing the reference waveform 22. In graph 72, the vertical axis represents the total magnetic force, and the horizontal axis represents time. The reference waveform 22 is an alternating magnetic field generated by the alternating current applied from the current source 2 (see Figure 1) to the wire 1 (see Figure 1). In other words, the reference waveform 22 is the waveform of the magnetic signal generated by the reference waveform generation unit 10b based on the frequency data 20 (see Figure 2) of the alternating current applied from the current source 2 to the wire 1.

[0053] Figure 10 is a graph 73 showing the synchronous detection signal 32 generated by the discrimination unit 10a (see Figure 2). In graph 73, the vertical axis represents the total magnetic force, and the horizontal axis represents time.

[0054] The synchronous detection signal 32 indicates whether or not the magnetic signal 30 (see Figure 2) contains a magnetic component of the alternating magnetic field 30a (see Figure 4) generated by the alternating current. If the synchronous detection signal 32 contains a magnetic component of the alternating magnetic field 30a generated by the alternating current, it outputs an output value of the magnitude of the DC component proportional to the amplitude of the alternating magnetic field 30a. Conversely, if the synchronous detection signal 32 does not contain a magnetic component caused by the alternating current, for example, it will be "0 (zero)". In this embodiment, an alternating current is applied to the wire 1 (see Figure 1) at time 60 (see Figure 8), so the value of the synchronous detection signal 32 is 0 (zero) until time 60. After time 60, the synchronous detection signal 32 becomes an output value of the magnitude of the DC component proportional to the amplitude of the alternating magnetic field 30a.

[0055] <Detection process for underwater structures> Next, with reference to Figure 11, the process by which the seabed structure detection system 100 detects the seabed structure 90 will be described. Note that the process shown in Figure 11 is performed with the metal plate 5 (see Figure 1) placed in the sea.

[0056] In step 101, the current source 2 (see Figure 1) is connected to one of its terminals 2a (see Figure 1) and supplies current to the electric wire 1 installed on the seabed structure 90. The current source 2 continues to apply current to the electric wire 1 while determining whether or not the seabed structure 90 is present.

[0057] In step 102, the signal acquisition unit 12 (see Figure 2) acquires a magnetic signal 30 (see Figure 2) based on the magnetic field in the sea, which is output by a magnetic sensor 3 (see Figure 1) installed in the sea, while current is flowing from the current source 2 to the wire 1 (see Figure 1).

[0058] In step 103, the discrimination unit 10a (see Figure 2) acquires a synchronous detection signal 32 (see Figure 10). Specifically, the discrimination unit 10a generates a synchronous detection signal 32 based on the reference waveform 22 (see Figure 9) generated by the reference waveform generation unit 10b (see Figure 2) and the magnetic signal 30 acquired by the signal acquisition unit 12.

[0059] In step 104, the discrimination unit 10a determines whether or not there is a seabed structure 90 (see Figure 1). Specifically, the discrimination unit 10a determines whether or not there is a seabed structure 90 based on a magnetic signal 30 caused by an electric current. More specifically, the discrimination unit 10a determines whether or not there is a seabed structure 90 based on a synchronous detection signal 32 (see Figure 10). If the discrimination unit 10a determines that there is a seabed structure 90, the process proceeds to step 105. If the discrimination unit 10a determines that there is no seabed structure 90, the process proceeds to step 108.

[0060] In step 105, the discrimination unit 10a obtains a discrimination result 40 (see Figure 2) indicating that the seabed structure 90 has been detected.

[0061] In step 106, the discrimination unit 10a acquires the depth position 52 of the seabed structure 90, as shown in Figure 6.

[0062] In step 107, the notification unit 13 (see Figure 2) notifies the depth position 52 of the seabed structure 90 and the determination result 40 indicating that the seabed structure 90 has been detected. After that, the process ends.

[0063] Furthermore, if the process proceeds from step 104 to step 108, in step 108, the discrimination unit 10a obtains a discrimination result 40 indicating that the seabed structure 90 was not detected.

[0064] In step 109, the notification unit 13 notifies the determination result 40 that no seabed structure 90 was detected. The process then ends.

[0065] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0066] In this embodiment, as described above, the seabed structure detection system 100 is a seabed structure detection system for detecting a seabed structure 90 installed on the seabed 81, and comprises a wire 1 installed on the seabed structure 90, a current source 2 with one terminal 2a connected to the wire 1, a magnetic sensor 3 that outputs a magnetic signal 30 based on the magnetism in the sea, and a discrimination unit 10a that determines the presence or absence of the seabed structure 90 based on the magnetic signal 30 caused by the current when current flows through the wire 1 by the current source 2.

[0067] As a result, the discrimination unit 10a applies current to the wire 1 installed on the seabed structure 90 and uses the relatively large magnetic signal 30 caused by the current applied to the wire 1 to determine whether or not the seabed structure 90 is present. Therefore, even if the magnetic signal based on the magnetism emitted from the seabed structure 90 is small, the presence or absence of the seabed structure 90 can be determined. Furthermore, by increasing the current applied to the wire 1, the magnitude of the magnetic signal 30 caused by the current can be made larger than the magnetic noise around the seabed structure 90. As a result, it is possible to suppress the difficulty in detecting the seabed structure 90 due to the small magnitude of the magnetism emitted from the seabed structure 90 and the magnetic noise around the seabed structure 90.

[0068] Furthermore, for example, in a configuration where a magnetic field is detected by passing an electric current through a seabed structure 90 that is provided with a corrosion-preventive layer to prevent rust, if there is peeling or other damage to the corrosion-preventive layer of the seabed structure 90, the electric current will not flow beyond the point where the corrosion-preventive layer has peeled off. In the seabed structure detection system 100 according to the above embodiment, an electric current is applied to the electric wire 1 installed on the seabed structure 90, so even if peeling occurs in the corrosion-preventive layer of the seabed structure 90, the seabed structure 90 can be detected by the magnetic field emitted from the electric wire 1.

[0069] Furthermore, in this embodiment, as described above, the seabed structure detection method is a seabed structure detection method for detecting a seabed structure 90 provided on the seabed 81, and comprises the steps of: passing current through a wire 1 connected to one terminal 2a of a current source 2 and provided on the seabed structure 90; acquiring a magnetic signal 30 based on the magnetism in the sea, output by a magnetic sensor 3 provided in the sea, while current is flowing from the current source 2 to the wire 1; and determining the presence or absence of the seabed structure 90 based on the magnetic signal 30 caused by the current.

[0070] This makes it possible to provide a seabed structure detection method that, similar to the seabed structure detection system 100 described above, can suppress the difficulty in detecting the seabed structure 90 caused by the magnitude of the magnetic field emitted from the seabed structure 90 and the magnetic noise surrounding the seabed structure 90.

[0071] Furthermore, in the above embodiment, the following additional effects can be obtained by configuring it as follows.

[0072] In other words, in this embodiment, as described above, the current source 2 is configured to change the current applied to the electric wire 1 over time, and the discrimination unit 10a is configured to determine the presence or absence of the seabed structure 90 based on the change in the magnetic signal 30 caused by the current. As a result, even if the magnetic signal 30 contains magnetism emitted from the seabed structure 90 and noise based on the Earth's magnetic field, the discrimination unit 10a can effectively determine the presence or absence of the seabed structure 90 by the magnetic signal 30 that changes due to the change in the current over time. As a result, it is possible to suppress a decrease in the discrimination accuracy of the seabed structure 90 due to magnetism emitted from the seabed structure 90 and noise such as the Earth's magnetic field.

[0073] Furthermore, in this embodiment, as described above, the current source 2 is configured to apply an alternating current to the power line 1, and the magnetic sensor 3 is configured to detect the alternating magnetic field 30a caused by the alternating current emitted from the power line 1. As a result, even when a direct current magnetic field is emitted from the seabed structure 90, the magnetic sensor 3 can output a magnetic signal 30 based on the alternating magnetic field 30a. Consequently, the influence of the direct current magnetic field emitted from the seabed structure 90 and noise based on the Earth's magnetic field can be reduced in the magnetic signal 30 output to the discrimination unit 10a.

[0074] Furthermore, in this embodiment, as described above, the discrimination unit 10a acquires a synchronous detection signal 32, which is a signal of the component of the alternating magnetic field 30a caused by the alternating current, based on the alternating magnetic field 30a detected by the magnetic sensor 3 and the frequency (frequency data 20) of the alternating current applied from the current source 2 to the power line 1. Based on the acquired synchronous detection signal 32, the discrimination unit 10a is configured to determine whether or not there is a seabed structure 90. As a result, since the discrimination unit 10a determines whether or not there is a seabed structure 90 using the synchronous detection signal 32, it is possible to further suppress a decrease in the accuracy of the seabed structure 90 discrimination.

[0075] Furthermore, in this embodiment, as described above, a metal plate 5 is provided, which is connected to the other terminal 2b of the current source 2 and installed in the sea. The end 1a of the electric wire 1 that is not connected to the current source 2 is installed in the sea with its insulation stripped off, and current is configured to flow between the end 1a not connected to the current source 2 and the metal plate 5 via seawater 80. As a result, by making a U-turn in the electric wire 1, current can be passed through the electric wire 1 without connecting the electric wire 1 to one terminal 2a and the other terminal 2b of the current source 2. Consequently, the length of the electric wire 1 installed in the seabed structure 90 can be reduced compared to a configuration in which the electric wire 1 is connected to both terminals of the current source 2.

[0076] Furthermore, in this embodiment, as described above, the metal plate 5 is formed of a metal having a different ionization tendency than the electric wire 1. This allows current to easily flow between the end 1a, which is not connected to the current source 2, and the metal plate 5 via seawater 80.

[0077] Furthermore, in this embodiment, as described above, the seabed structure 90 is a long structure extending along the seabed 81, and the electric wire 1 is provided in a straight line on the outer surface 90a of the seabed structure 90 along the direction in which the seabed structure 90 extends. This makes it possible to minimize the length of the electric wire 1 provided by the seabed structure 90.

[0078] Furthermore, in this embodiment, as described above, a magnetic sensor 3 is provided, and a moving body 6 is further provided to move the magnetic sensor 3. The magnetic sensor 3 is configured to output a magnetic signal 30 measured while being moved by the moving body 6, and the discrimination unit 10a is configured to acquire the arrangement state of the seabed structure 90 based on the magnetic signal 30 measured while the magnetic sensor 3 is being moved. As a result, even when the magnetic field emitted from the seabed structure 90 is small, the arrangement state of the seabed structure 90, which indicates where and in what direction the seabed structure 90 is positioned on the seabed 81, can be easily acquired.

[0079] Furthermore, in this embodiment, as described above, the seabed structure 90 is a pipeline installed on the seabed 81, and the discrimination unit 10a is configured to determine the presence or absence of the pipeline. This makes it possible to provide a seabed structure detection system 100 suitable for determining the presence or absence of a pipeline.

[0080] Furthermore, in this embodiment, as described above, the discrimination unit 10a is configured to detect the depth position 52 of the seabed structure 90 based on the magnitude of the magnetic signal 30. This makes it possible to obtain the depth position 52 of the seabed structure 90 even if, for example, the seabed structure 90 is buried in the sand of the seabed 81 and cannot be seen, thereby enabling the position of the seabed structure 90 to be obtained with high accuracy.

[0081] (modified version) It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and further includes all modifications (exceptions) within the meaning and scope equivalent to the claims.

[0082] For example, in the above embodiment, an example was shown in which the seabed structure detection system 100 is equipped with a current source 2 that applies alternating current to the power line 1, but the present invention is not limited thereto. For example, as shown in the first modified example in Figure 12, the seabed structure detection system 200 may be equipped with a current source 14 that applies direct current to the power line 1.

[0083] The seabed structure detection system 200 has the same configuration as the seabed structure detection system 100 in the above embodiment, except that it is equipped with a current source 14 instead of a current source 2.

[0084] The current source 14 is configured to apply a direct current to the wire 1. The current source 14 includes, for example, a DC power supply.

[0085] Graph 74 in Figure 13 shows the magnetic signal 30 after a DC current is applied to the wire 1 by the current source 14. In Graph 74, the vertical axis represents the total magnetic force, and the horizontal axis represents time. In the example shown in Figure 13, the DC current is applied at time 61.

[0086] As shown in Graph 74, the magnetic signal 30 includes a magnetic component 30b that includes the magnetic component emitted from the seabed structure 90 and the DC magnetic component around the seabed structure 90. Furthermore, the magnetic signal 33 after a DC current is applied to the power line 1 has a DC magnetic field component 30e, which is caused by the DC current, added to it.

[0087] The discrimination unit 10a may be configured to determine the presence or absence of the seabed structure 90 based on the change in waveform between the magnetic signal 33 after a direct current is applied and the magnetic signal 30 before a direct current is applied. Specifically, the discrimination unit 10a may be configured to determine the presence or absence of the seabed structure 90 based on the difference between the amplitude of the magnetic signal 30 after a direct current is applied and the amplitude of the magnetic signal 30 before a direct current is applied.

[0088] Furthermore, while the above embodiment shows an example in which the electric wire 1 is provided linearly on the outer surface 90a of the seabed structure 90 along the direction in which the seabed structure 90 extends, the present invention is not limited to this. For example, as shown in the second modified example in Figure 14, the electric wire 1 may be provided on the outer surface 90a of the seabed structure 90 so as to be wound around the axis in which the seabed structure 90 extends. That is, the electric wire 1 may be provided spirally on the outer surface 90a of the seabed structure 90.

[0089] In the second modified example, as described above, the seabed structure 90 is a long structure extending along the seabed 81, and the electric wire 1 is provided on the outer surface 90a of the seabed structure 90 so as to be wound around the axis of extension of the seabed structure 90 in a rotational direction. Here, if the electric wire 1 is provided in a straight line on the outer surface 90a of the seabed structure 90, depending on the arrangement of the seabed structure 90, the electric wire 1 may be positioned between the seabed structure 90 and the seabed 81. In this case, the distance between the electric wire 1 and the magnetic sensor 3 increases, and the magnitude of the magnetic field detected by the magnetic sensor 3 decreases. On the other hand, when an electric current is passed through the electric wire 1 which is wound around the seabed structure 90, a magnetic field caused by the current is generated in a direction along the direction in which the seabed structure 90 extends. In other words, it is possible to suppress changes in the position where the magnetic field caused by the current is generated depending on the arrangement of the electric wire 1 relative to the seabed structure 90. Therefore, by configuring it as described above, it is possible to suppress changes in the magnitude of the magnetic field detected by the magnetic sensor 3 due to changes in the position where a magnetic field is generated due to electric current caused by the arrangement of the power lines 1 in the seabed structure 90.

[0090] Furthermore, in the above embodiment, an example was shown in which the current source 2 applies an alternating current to the electric wire 1 as an example of changing the current applied to the electric wire 1 over time, but the present invention is not limited to this. For example, the current source 2 may change the current applied to the electric wire 1 over time by applying a pulsed direct current to the electric wire 1.

[0091] Furthermore, although the above embodiment shows an example in which the discrimination unit 10a determines the presence or absence of the seabed structure 90 using the synchronous detection signal 32, the present invention is not limited thereto. For example, the discrimination unit 10a may determine the presence or absence of the seabed structure 90 without using the synchronous detection signal 32.

[0092] Furthermore, although the above embodiment shows an example in which the seabed structure detection system 100 includes a metal plate 5, the present invention is not limited to this. For example, the seabed structure detection system 100 does not have to include a metal plate 5. However, if the seabed structure detection system 100 does not include a metal plate 5, the length of the power line 1 will increase. Therefore, it is preferable that the seabed structure detection system 100 includes a metal plate 5.

[0093] Furthermore, although the above embodiment shows an example in which the discrimination unit 10a acquires the depth position 52 of the seabed structure 90, the present invention is not limited to this. For example, the discrimination unit 10a does not need to acquire the depth position 52 of the seabed structure 90.

[0094] Furthermore, although the above embodiment shows an example of an AUV (Autonomous Underwater Vehicle) where the mobile body 6 autonomously travels underwater, in the present invention, for example, the mobile body 6 may be moved underwater by being towed by a ship or the like.

[0095] Furthermore, although the above embodiment shows an example in which the seabed structure detection system 100 includes a mobile body 6, the present invention is not limited to this. For example, the seabed structure detection system 100 does not have to include a mobile body 6. If the seabed structure detection system 100 does not include a mobile body 6, a person can dive into the sea and move the magnetic sensor 3. However, depending on the depth at which the seabed structure 90 is located, it may not be possible for a person to dive. Therefore, it is preferable that the seabed structure detection system 100 includes a mobile body 6.

[0096] Furthermore, in the above embodiment, for the sake of explanation, an example was shown in which the control processing of the discrimination unit 10a was explained using a flow-driven flowchart that processes sequentially according to the processing flow, but the present invention is not limited to this. In the present invention, the control processing of the discrimination unit 10a may be performed by event-driven processing that executes processing on an event-by-event basis. In this case, it may be performed as a completely event-driven system, or a combination of event-driven and flow-driven systems may be used.

[0097] [Aspect] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0098] (Item 1) A seabed structure detection system for detecting seabed structures installed on the seabed, The electric wires installed on the aforementioned underwater structure, One terminal is connected to the aforementioned wire and is a current source, A magnetic sensor that outputs a magnetic signal based on the magnetic field in the ocean, A seabed structure detection system comprising: a discrimination unit that determines the presence or absence of the seabed structure based on the magnetic signal caused by the current when the current flows through the wire by the current source.

[0099] (Item 2) The current source is configured to change the current applied to the electric wire over time. The seabed structure detection system according to item 1, wherein the discrimination unit is configured to determine the presence or absence of the seabed structure based on the change in the magnetic signal caused by the electric current.

[0100] (Item 3) The current source is configured to apply alternating current to the electric wire. The submarine structure detection system according to item 1 or 2, wherein the magnetic sensor is configured to detect an alternating magnetic field caused by an alternating current emitted from the electric wire.

[0101] (Item 4) The seabed structure detection system according to item 3, wherein the discrimination unit is configured to acquire a synchronous detection signal, which is a signal of the component of the alternating magnetic field caused by the alternating current, based on the alternating magnetic field detected by the magnetic sensor and the frequency of the alternating current applied to the wire from the current source, and to determine the presence or absence of the seabed structure based on the acquired synchronous detection signal.

[0102] (Item 5) The other terminal of the current source is connected to a metal plate that is installed in the sea, Of the aforementioned electric wires, the ends not connected to the current source are installed in the sea with their insulation stripped off. A seabed structure detection system according to any one of items 1 to 4, configured such that an electric current flows between the end not connected to the current source and the metal plate via seawater.

[0103] (Item 6) The seabed structure detection system according to item 5, wherein the metal plate is formed of a metal having an ionization tendency of a different size than that of the electric wire.

[0104] (Item 7) The aforementioned seabed structure is a long structure that extends along the seabed, The submarine structure detection system according to any one of items 1 to 6, wherein the electric wire is provided in a straight line on the outer surface of the submarine structure along the direction in which the submarine structure extends.

[0105] (Item 8) The aforementioned seabed structure is a long structure that extends along the seabed, The submarine structure detection system according to any one of items 1 to 6, wherein the electric wire is provided on the outer surface of the submarine structure so as to be wound around the axis of rotation of the submarine structure from which the submarine structure extends.

[0106] (Item 9) The magnetic sensor is provided, and the system further comprises a movable body for moving the magnetic sensor, The magnetic sensor is configured to output the magnetic signal measured while being moved by the moving body, The seabed structure detection system according to item 5 or 6, wherein the discrimination unit is configured to acquire the arrangement state of the seabed structure based on the magnetic signal measured while the magnetic sensor is being moved.

[0107] (Item 10) The aforementioned submarine structure is a pipeline installed on the seabed. The seabed structure detection system according to any one of items 7 to 9, wherein the discrimination unit is configured to determine the presence or absence of the pipeline. (Item 11) The seabed structure detection system according to any one of items 1 to 10, wherein the discrimination unit is configured to detect the depth position of the seabed structure based on the magnitude of the magnetic signal.

[0108] (Item 12) A method for detecting seabed structures located on the seabed, The process involves connecting to one terminal of a current source and supplying current to a wire installed in the underwater structure, The steps include acquiring a magnetic signal based on the magnetic field in the sea, which is output by a magnetic sensor installed in the sea, while current is flowing from the current source to the electric wire, A method for detecting a seabed structure, comprising the step of determining the presence or absence of the seabed structure based on the magnetic signal caused by an electric current. [Explanation of Symbols]

[0109] 1 electric wire 1a End (the end of the wire that is not connected to the current source) 2, 14 current source 2a terminal (one of the terminals of the current source) 2b terminal (the other terminal of the current source) 3 Magnetic Sensor 5 metal plate 6 Mobile Unit 10a Discriminant section 30, 31 Magnetic signals 30A AC magnetic field 32 Synchronous detection signal 52 Depth position 80 Seawater 81 Undersea 90. Underwater structures (pipelines) 90a Outer surface (outer surface of seabed structures) 100, 200 Seafloor Structure Detection Systems

Claims

1. A seabed structure detection system for detecting seabed structures installed on the seabed, The electric wires provided on the outermost surface of the aforementioned seabed structure, A current source having a first terminal and a second terminal, and connected to the electric wire, A magnetic sensor that outputs a magnetic signal based on the magnetic field in the ocean, The system includes a discrimination unit that, when current flows through the wire due to the current source, determines the presence or absence of the seabed structure based on the magnetic signal caused by the current, A seabed structure detection system wherein one end of the electric wire is connected to the first terminal of the current source on land, and the other end of the wire is located in the sea and is electrically connected to the second terminal of the current source via seawater.

2. The current source is configured to change the current applied to the electric wire over time. The seabed structure detection system according to claim 1, wherein the discrimination unit is configured to determine the presence or absence of the seabed structure based on the change in the magnetic signal caused by the electric current.

3. The current source is configured to apply alternating current to the electric wire. The seabed structure detection system according to claim 1 or 2, wherein the magnetic sensor is configured to detect an alternating magnetic field caused by an alternating current emitted from the electric wire.

4. The seabed structure detection system according to claim 3, wherein the discrimination unit is configured to acquire a synchronous detection signal, which is a signal of the component of the alternating magnetic field caused by the alternating current, based on the alternating magnetic field detected by the magnetic sensor and the frequency of the alternating current applied to the wire from the current source, and to determine the presence or absence of the seabed structure based on the acquired synchronous detection signal.

5. A seabed structure detection system for detecting seabed structures installed on the seabed, The electric wires installed on the aforementioned underwater structure, One terminal is connected to the aforementioned wire and is a current source, A magnetic sensor that outputs a magnetic signal based on the magnetic field in the ocean, When current flows through the wire due to the current source, a determination unit determines the presence or absence of the seabed structure based on the magnetic signal caused by the current, The other terminal of the current source is connected to a metal plate that is installed in the sea, Of the aforementioned electric wires, the ends not connected to the current source are installed in the sea with their insulation stripped off. A seabed structure detection system configured such that an electric current flows between the end not connected to the current source and the metal plate via seawater.

6. The seabed structure detection system according to claim 5, wherein the metal plate is formed of a metal having an ionization tendency of a different size than that of the electric wire.

7. The aforementioned seabed structure is a long structure that extends along the seabed, The submarine structure detection system according to any one of claims 1 to 6, wherein the electric wire is provided in a straight line along the direction in which the submarine structure extends, outside the outermost surface of the submarine structure.

8. The aforementioned seabed structure is a long structure that extends along the seabed, The submarine structure detection system according to any one of claims 1 to 6, wherein the electric wire is provided outside the outermost surface of the submarine structure so as to be wound around the axis of rotation of the submarine structure from which the submarine structure extends.

9. The magnetic sensor is provided, and the system further comprises a movable body for moving the magnetic sensor, The magnetic sensor is configured to output the magnetic signal measured while being moved by the moving body, The seabed structure detection system according to claim 5 or 6, wherein the discrimination unit is configured to acquire the arrangement state of the seabed structure based on the magnetic signal measured while the magnetic sensor is being moved.

10. The aforementioned submarine structure is a pipeline installed on the seabed. The seabed structure detection system according to any one of claims 7 to 9, wherein the discrimination unit is configured to determine the presence or absence of the pipeline.

11. The seabed structure detection system according to any one of claims 1 to 10, wherein the discrimination unit is configured to detect the depth position of the seabed structure based on the magnitude of the magnetic signal.

12. A method for detecting seabed structures located on the seabed, The process involves connecting a current source having a first terminal and a second terminal to an electric wire provided on the outermost surface of the submarine structure and supplying current to it. The steps include acquiring a magnetic signal based on the magnetic field in the sea, which is output by a magnetic sensor installed in the sea, while current is flowing from the current source to the electric wire, The step of determining the presence or absence of the seabed structure based on the magnetic signal caused by the electric current, A method for detecting seabed structures, wherein one end of the electric wire is connected to the first terminal of the current source on land, and the other end is provided in the sea, with the other terminal electrically connected to the second terminal of the current source via seawater.

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