Subsea structure detection system

Abstract

To provide a submarine structure detection system that can detect presence or absence of a submarine structure and can accurately detect presence or absence of damage to a corrosion-proof layer provided on the submarine structure.SOLUTION: A submarine structure detection system 100 detects a metal submarine structure 90 provided on a sea bed 80, or detects presence or absence of damage 6a to a corrosion-proof layer 6 provided on the submarine structure 90 and formed of metal different in an ionization tendency from the submarine structure 90, and the submarine structure detection system comprises: a potential difference sensor 1 that detects a potential difference caused by a current flowing between the submarine structure 90 and the corrosion-proof layer 6; a magnetic sensor 2 that detects a magnetism in the sea; a submarine structure detection unit 10a that detects presence or absence of the submarine structure 90 on the basis of, a magnetic signal 31 output by the magnetic sensor 2; and a damage detection unit 10b that detects the presence or absence of the damage 6a to the corrosion-proof layer 6 on the basis of, the magnetic signal 31 and an electric field signal 30 output by the potential difference sensor 1.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a subsea structure detection system, and more particularly to a subsea structure detection system that detects subsea structures provided on the seabed while moving a magnetic sensor along the seabed.

Background Art

[0002] Conventionally, a subsea structure detection system that detects subsea structures while moving a magnetic sensor along the seabed is known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a magnetic exploration device (subsea structure detection system) that detects subsea structures 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 is arranged such that at least one pair of combined sensors are opposed to each other in parallel on the same plane. Further, the magnetic exploration device disclosed in Patent Document 1 is configured to detect a subsea pipeline by detecting magnetism emitted from a subsea 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] Here, although not disclosed in the above Patent Document 1, it is considered that the subsea pipeline (subsea structure) is composed of steel pipes (iron), and it is considered that an anticorrosion layer formed of a metal other than iron for preventing rust is provided so as to cover the outer peripheral surface of the steel pipe. When the anticorrosion layer is damaged, the surface of the subsea structure is exposed at the damaged portion of the anticorrosion layer. In this case, there is a disadvantage that corrosion of the subsea structure occurs from the exposed portion of the subsea structure. When damage occurs to the anticorrosion layer, due to the difference in ionization tendency between the metal constituting the subsea structure and the anticorrosion layer, an electric current flows between the exposed damaged portion of the subsea structure and the anticorrosion layer. In a configuration including a magnetic sensor as in the above Patent Document 1, it is possible to detect the damaged portion by detecting a magnetic field generated due to the electric current flowing between the damaged portion and the anticorrosion layer. However, the detection accuracy of the magnetic field generated due to the electric current flowing between the damaged portion and the anticorrosion layer may decrease due to noise such as geomagnetism. Therefore, in the configuration disclosed in the above Patent Document 1, there is a problem that it is difficult to accurately detect the presence or absence of the subsea structure and the presence or absence of damage to the anticorrosion layer.

[0006] The present invention has been made to solve the above problems, and it is an object of the present invention to provide a subsea structure detection system capable of detecting the presence or absence of a subsea structure and accurately detecting the presence or absence of damage to an anticorrosion layer provided on the subsea structure.

Means for Solving the Problems

[0007] To achieve the above object, a subsea structure detection system according to one aspect of the present invention is a subsea structure detection system for detecting a metal subsea structure provided on the seabed and detecting the presence or absence of damage to a corrosion protection layer formed of a metal having an ionization tendency different from that of the metal constituting the subsea structure. The system includes a potential difference sensor that detects a potential difference caused by a current flowing between the subsea structure and the corrosion protection layer, a magnetic sensor that detects magnetism in the sea, a subsea structure detection unit that detects the presence or absence of a subsea structure based on a magnetic signal output by the magnetic sensor, and a damage detection unit that detects the presence or absence of damage to the corrosion protection layer based on the magnetic signal and an electric field signal output by the potential difference sensor.

Advantages of the Invention

[0008] In the subsea structure detection system according to the first aspect, a subsea structure detection unit is provided that detects the presence or absence of a subsea structure based on a magnetic signal output by the magnetic sensor. Thus, by acquiring the magnetic signal, the presence or absence of a subsea structure can be detected. Further, in the subsea structure detection system according to the first aspect, a damage detection unit is provided that detects the presence or absence of damage to the corrosion protection layer based on the magnetic signal output by the magnetic sensor and an electric field signal output by a potential difference sensor that detects a potential difference caused by a current flowing between the subsea structure and the corrosion protection layer. Thus, unlike a configuration that detects the presence or absence of damage to the corrosion protection layer only by the magnetic signal, the presence or absence of damage to the corrosion protection layer can be detected by both the magnetic signal generated due to the current flowing between the subsea structure and the corrosion protection layer and the electric field signal based on the potential difference caused by the current flowing between the subsea structure and the corrosion protection layer. Therefore, compared with a configuration that detects the presence or absence of damage to the corrosion protection layer only by the magnetic signal, the presence or absence of damage to the corrosion protection layer can be detected with higher accuracy. As a result, it is possible to provide a subsea structure detection system that can detect the presence or absence of a subsea structure and can accurately detect the presence or absence of damage to the corrosion protection layer provided on the subsea structure.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.

[0011] With reference to FIGS. 1 to 8, the configuration of a submarine structure detection system 100 according to an embodiment will be described.

[0012] (Configuration of Subsea Structure Detection Device) First, with reference to FIG. 1, the configuration of a subsea structure detection system 100 according to an embodiment will be described.

[0013] The subsea structure detection system 100 is a subsea structure detection system that detects a metal subsea structure 90 provided on the seabed 80. The subsea structure 90 is a pipeline provided on the seabed 80. That is, the subsea structure detection system 100 is configured to detect the presence or absence of a pipeline provided on the seabed 80. Further, the subsea structure detection system 100 is a subsea structure detection system that is provided on the subsea structure 90 and detects the presence or absence of damage 6a to a corrosion protection layer 6 formed of a metal having an ionization tendency different from that of the metal constituting the subsea structure 90. That is, the subsea structure detection system 100 is configured to detect the presence or absence of damage to a pipeline provided on the seabed 80. Note that the subsea structure 90 is formed of, for example, steel (iron material).

[0014] The pipeline includes, for example, a steel pipe provided with a corrosion protection layer 6 for preventing rust covering the outer surface. The corrosion protection layer 6 is formed of, for example, a zinc alloy. When damage 6a occurs in the corrosion protection layer 6, as shown by the arrow 7, due to the difference in ionization tendency between the metal constituting the subsea structure 90 and the corrosion protection layer 6, a current flows through the seawater from the damaged portion 6a to the corrosion protection layer 6. Note that the pipeline is an example of the "subsea structure" in the claims. In the example shown in FIG. 1, for convenience, the corrosion protection layer 6 provided on the subsea structure 90 is hatched.

[0015] As shown in FIG. 1, the subsea structure detection system 100 includes a potential difference sensor 1, a magnetic sensor 2, and a computer 3. Further, in the present embodiment, the subsea structure detection system 100 includes a mobile body 4. The potential difference sensor 1 and the magnetic sensor 2 are provided on the mobile body 4. Also, the computer 3 is provided on a ship 5.

[0016] The potential difference sensor 1 is configured to detect the potential difference caused by the current flowing between the subsea structure 90 and the anticorrosion layer 6. The potential difference sensor 1 is configured to output an electric field signal 30 (see FIG. 2) based on the potential difference caused by the current flowing in the sea water between the subsea structure 90 and the anticorrosion layer 6. In the present embodiment, the potential difference sensor 1 is configured to output the electric field signal 30 measured while being moved by the moving body 4. The potential difference sensor 1 includes, for example, a silver / silver chloride electrode. The position where the potential difference sensor 1 is provided on the moving body 4 and the like will be described later.

[0017] The magnetic sensor 2 is configured to detect the magnetism in the sea water. Further, the magnetic sensor 2 is configured to output a magnetic signal 31 (see FIG. 2) based on the magnetism in the sea water. The magnetic sensor 2 is provided on the moving body 4. In the present embodiment, the magnetic sensor 2 is configured to output the magnetic signal 31 measured while being moved by the moving body 4. The magnetic sensor 2 is configured to output the magnetic signals 31 in two directions orthogonal to each other in the vertical direction of the moving body 4 and in a plane orthogonal to the vertical direction. The magnetic sensor 2 includes, for example, a three-axis magnetometer.

[0018] The computer 3 is configured to detect the subsea structure 90 based on the magnetic signal 31 output from the magnetic sensor 2. Further, the computer 3 is configured to detect the presence or absence of damage 6a of the anticorrosion layer 6 based on the magnetic signal 31 and the electric field signal 30 output from the potential difference sensor 1. In the present embodiment, the damage 6a of the anticorrosion layer 6 is, for example, corrosion of the anticorrosion layer 6. That is, in the present embodiment, the computer 3 is configured to detect the presence or absence of corrosion of the anticorrosion layer 6. The computer 3 detects the presence or absence of damage 6a of the anticorrosion layer 6 by detecting whether a current (corrosion current) flows between the surface of the subsea structure 90 and the anticorrosion layer 6 due to the corrosion of the anticorrosion layer 6. Further, the computer 3 is configured to control the movement of the moving body 4. The details of the configuration in which the computer 3 detects the presence or absence of the subsea structure 90 and the configuration in which the computer 3 detects the presence or absence of damage 6a of the anticorrosion layer 6 will be described later.

[0019] The mobile body 4 is provided with a magnetic sensor 2 and a potential difference sensor 1, and is configured to be movable in water. In the present embodiment, the mobile body 4 is configured to integrally move both the potential difference sensor 1 and the magnetic sensor 2. Further, the mobile body 4 is provided with a depth gauge (not shown) for acquiring depth information of the mobile body 4 in the sea, and a distance sensor (not shown) for acquiring the distance from the mobile body 4 to the measurement target. The mobile body 4 is configured to be able to travel in the sea. Further, the mobile body 4 is configured to be able to move in the sea unmanned. The mobile body 4 is a so-called AUV (Autonomous Underwater Vehicle). Details of the configuration of the mobile body 4 will be described later.

[0020] As shown in FIG. 2, the computer 3 includes a processor 10, a storage unit 11, a mobile body information acquisition unit 12, a signal acquisition unit 13, and a notification unit 14.

[0021] The processor 10 is configured to detect the presence or absence of the underwater structure 90 (see FIG. 1). Further, the processor 10 is configured to detect the presence or absence of damage 6a (see FIG. 1) to the anticorrosion layer 6 provided on the underwater structure 90. The processor 10 includes, for example, a CPU (Central Processing Unit), a microprocessor, an FPGA (Field-Programmable Gate Array) configured for position determination of the underwater structure 90, and the like. Details of the configuration in which the processor 10 detects the presence or absence of the underwater structure 90 and the presence or absence of damage 6a to the anticorrosion layer 6 will be described later.

[0022] The memory unit 11 stores the reference magnetic signal 20 acquired in advance. Further, the memory unit 11 is configured to store the reference distance 21, which is the distance between the magnetic sensor 2 and the underwater structure 90 when the reference magnetic signal 20 is acquired. Further, the memory unit 11 stores various programs executed by the processor 10. The memory unit 11 includes a non-volatile memory device. The non-volatile memory device is, for example, a hard disk drive, a solid state drive, or the like.

[0023] The reference magnetic signal 20 is a magnetic signal output by the magnetic sensor 2 at a position where the distance between the moving body 4 and the underwater structure 90 is the reference distance 21. The reference distance 21 is the distance between the moving body 4 and the underwater structure 90 when the reference magnetic signal 20 is acquired. The reference magnetic signal 20 and the reference distance 21 are acquired in advance and stored in the memory unit 11. Note that the reference magnetic signal 20 is used for detecting the presence or absence of the underwater structure 90 and the presence or absence of the damage 6a of the anticorrosion layer 6. Further, the reference magnetic signal 20 and the reference distance 21 are used for acquiring the depth position 25 (see FIG. 6) of the underwater structure 90 when the underwater structure 90 is present. Note that the reference distance 21 is not used for detecting the presence or absence of the damage 6a of the anticorrosion layer 6.

[0024] The moving body information acquisition unit 12 is configured to acquire moving body information 22 including information on the acceleration and attitude of the moving body 4. Further, the moving body information acquisition unit 12 is configured to output the acquired moving body information 22 to the processor 10. The moving body information acquisition unit 12 includes, for example, a wireless communication device and an input / output interface.

[0025] The signal acquisition unit 13 is configured to acquire an electric field signal 30 from the potential difference sensor 1 provided in the moving body 4. Further, the signal acquisition unit 13 is configured to acquire a magnetic signal 31 from the magnetic sensor 2. Further, the signal acquisition unit 13 is configured to output the acquired electric field signal 30 and magnetic signal 31 to the processor 10. The signal acquisition unit 13 includes, for example, a wireless communication device and an input / output interface.

[0026] The notification unit 14 is configured to notify the first detection result 40a (see FIG. 5), which is the detection result of the presence or absence of the underwater structure detection unit 10a. Further, the notification unit 14 is configured to notify the second detection result 40b (see FIG. 5), which is the detection result of the presence or absence of the damage 6a of the anticorrosion layer 6. The notification unit 14 is, for example, a liquid crystal display device. The notification unit 14 may be an electroluminescence display device or a projector.

[0027] The moving body 4 includes a control unit 4a, a communication unit 4b, a moving body information measurement unit 4c, and a propulsion mechanism 4d.

[0028] The control unit 4a is configured to control the moving body 4. The control unit 4a includes, for example, a CPU.

[0029] The communication unit 4b is configured to communicate with the computer 3 under the control of the control unit 4a. Specifically, the communication unit 4b is configured to receive information on the direction in which the moving body 4 is to be moved from the computer 3, and to transmit the electric field signal 30 output by the potential difference sensor 1, the magnetic signal 31 output by the magnetic sensor 2, and the moving body information 22 to the computer 3. The communication unit 4b includes, for example, a wirelessly connectable transceiver.

[0030] The moving body information measurement unit 4c is configured to acquire information on the acceleration and attitude of the moving body 4. The attitude information is a vector representing the attitude of the moving body 4 in the sea. The moving body information measurement unit 4c includes, for example, triaxial acceleration sensors in two directions orthogonal to each other in the vertical direction of the moving body 4 and in a plane orthogonal to the vertical direction.

[0031] The propulsion mechanism 4d is configured to apply a propulsion force to the moving body 4 under the control of the control unit 4a. The propulsion mechanism 4d includes a propeller (not shown) and a drive source (not shown) for driving the propeller. The propulsion mechanism 4d may have a so-called screw configuration in which water is stirred by rotating the propeller to obtain a propulsion force, or a so-called water jet propulsion mechanism in which a high-pressure water flow is ejected rearward to obtain a propulsion force.

[0032] <Arrangement of Potential Difference Sensor and Magnetic Sensor> Next, with reference to FIG. 3, the arrangement of the potential difference sensor 1 and the magnetic sensor 2 in the moving body 4 will be described.

[0033] As shown in FIG. 3, the potential difference sensor 1 includes a pair of electrodes. Specifically, the potential difference sensor 1 includes a first electrode 1a and a second electrode 1b as a pair of electrodes. The potential difference sensor 1 is configured to detect the potential difference between the first electrode 1a and the second electrode 1b.

[0034] Also, a pair of potential difference sensors 1 (the first electrode 1a and the second electrode 1b) are provided in the moving body 4 so as to be arranged vertically at a predetermined interval. The magnetic sensor 2 is provided at a position between the pair of electrodes. That is, the first electrode 1a, the second electrode 1b, and the magnetic sensor 2 are provided in the moving body 4 so as to be arranged vertically at a predetermined interval. In other words, the first electrode 1a, the second electrode 1b, and the magnetic sensor 2 are provided in the moving body 4 such that their positions in the traveling direction of the moving body 4 are substantially equal.

[0035] <Acquisition of Reference Magnetic Signal> Next, with reference to FIG. 4, the configuration in which the undersea structure detection system 100 (see FIG. 1) acquires the reference magnetic signal 20 will be described.

[0036] The undersea structure detection system 100 is configured to acquire the reference magnetic signal 20, for example, when laying the undersea structure 90. Specifically, the undersea structure detection system 100 acquires the reference magnetic signal 20 by detecting the magnetism emitted from the undersea structure 90 while moving the moving body 4. At this time, the distance acquired by the distance sensor provided in the moving body 4 is stored in the storage unit 11 (see FIG. 2) together with the reference magnetic signal 20 as the reference distance 21.

[0037] In addition, after the undersea structure 90 is laid, the undersea structure detection system 100 acquires a reference magnetic signal 20 before a damage 6a (see FIG. 1) occurs in the anticorrosion layer 6 of the undersea structure 90.

[0038] 〈Detection of Undersea Structure and Detection of Damage to Anticorrosion Layer〉 Next, with reference to FIG. 5, a configuration in which the processor 10 detects the presence or absence of the undersea structure 90 (see FIG. 1) and a configuration in which the processor 10 detects the presence or absence of a damage 6a (see FIG. 1) in the anticorrosion layer 6 (see FIG. 1) will be described.

[0039] As shown in FIG. 5, the processor 10 includes an undersea structure detection unit 10a, a damage detection unit 10b, and a signal correction unit 10c as functional blocks. In other words, the processor 10 functions as the undersea structure detection unit 10a, the damage detection unit 10b, and the signal correction unit 10c by executing a program stored in the storage unit 11.

[0040] In the present embodiment, the undersea structure detection system 100 acquires an electric field signal 30 and a magnetic signal 31 while moving the moving body 4 (see FIG. 1). Therefore, the electric field signal 30 and the magnetic signal 31 may change depending on the attitude of the moving body 4. Thus, in the present embodiment, the signal correction unit 10c is configured to correct the attitude of the moving body 4 with respect to the magnetic signal 31 and the electric field signal 30 based on the moving body information 22. Specifically, the signal correction unit 10c acquires the information on the acceleration and attitude of the moving body 4 by acquiring the moving body information 22 from the moving body information acquisition unit 12. Then, the signal correction unit 10c performs a filtering process and an orthogonality correction process on the electric field signal 30 using the acquired information on the acceleration and attitude of the moving body 4, thereby acquiring a corrected electric field signal 30a. That is, the signal correction unit 10c performs a correction process on the electric field signal 30 to perform a coordinate transformation from the coordinate system of the potential difference sensor 1 to an absolute coordinate system in the horizontal and vertical directions. Thereby, the signal correction unit 10c can acquire corrected electric field signals 30a in two directions orthogonal to each other in the vertical direction and in the horizontal plane.

[0041] Further, the signal correction unit 10c acquires a corrected magnetic signal 31a by performing filter processing and orthogonality correction processing on the magnetic signal 31 using the acquired acceleration and attitude information of the moving body 4. That is, the signal correction unit 10c performs correction processing on the magnetic signal 31 to perform coordinate conversion from the coordinate system of the magnetic sensor 2 to the absolute coordinate system in the horizontal and vertical directions. Thereby, the signal correction unit 10c can acquire corrected magnetic signals 31a in two directions orthogonal to each other in the vertical direction and in the horizontal plane. The signal correction unit 10c outputs the corrected electric field signal 30a to the damage detection unit 10b. Further, the signal correction unit 10c outputs the corrected magnetic signal 31a to the subsea structure detection unit 10a and the damage detection unit 10b.

[0042] The subsea structure detection unit 10a is configured to detect the presence or absence of the subsea structure 90 based on the magnetic signal 31 output by the magnetic sensor 2. In the present embodiment, the subsea structure detection unit 10a is configured to detect the presence or absence of the subsea structure 90 based on the corrected magnetic signal 31a which is the magnetic signal 31 after the attitude correction is performed by the signal correction unit 10c.

[0043] The subsea structure detection unit 10a acquires the corrected magnetic signal 31a acquired by the signal correction unit 10c. The subsea structure detection unit 10a determines the presence or absence of the subsea structure 90 (see FIG. 1) based on the amplitude 51 (see FIG. 7(B)) of the corrected magnetic signal 31a. Specifically, the subsea structure detection unit 10a determines that there is a subsea structure 90 when the amplitude 51 of the corrected magnetic signal 31a is equal to or greater than a predetermined magnitude. Further, the subsea structure detection unit 10a determines that there is no subsea structure 90 when the amplitude 51 of the corrected magnetic signal 31a is smaller than the predetermined magnitude.

[0044] Further, when the undersea structure detection unit 10a determines that there is an undersea structure 90, it acquires the depth position 25 (see FIG. 6) of the undersea structure 90 based on the reference magnetic signal 20 and the magnetic signal 31. In the present embodiment, the undersea structure detection unit 10a acquires the reference magnetic signal 20 and the reference distance 21 from the storage unit 11. The undersea structure detection unit 10a acquires the depth position 25 of the undersea structure 90 by using the reference magnetic signal 20, the reference distance 21, and the corrected magnetic signal 31a.

[0045] 〈Detection of the depth position of the undersea structure〉 Next, with reference to FIG. 6, a configuration in which the undersea structure detection unit 10a (see FIG. 2) acquires the depth position 25 of the undersea structure 90 will be described. In the present embodiment, the undersea structure detection unit 10a is configured to detect the depth position 25 of the undersea structure 90 based on the magnitude of the magnetic signal 31 (see FIG. 2). Specifically, the undersea structure detection unit 10a is configured to detect the depth position 25 of the undersea structure 90 based on the amplitude 50 of the waveform of the reference magnetic signal 20 (see FIG. 2), the reference distance 21 (see FIG. 2), and the amplitude 51 of the magnetic signal 31 (see FIG. 7(B)).

[0046] Here, it is known that the magnitude of the magnetic signal 31 is inversely proportional to the cube of the distance between the undersea structure 90 and the moving body 4. Therefore, by comparing the amplitude 50 of the reference distance 21 and the amplitude 51 of the magnetic signal 31, it is possible to acquire the ratio of the reference distance 21 to the distance 23 between the undersea structure 90 and the moving body 4, so that the distance 23 between the undersea structure 90 and the moving body 4 can be acquired.

[0047] Further, the undersea structure detection unit 10a (see FIG. 2) acquires the distance 24 from the sea surface 81 to the moving body 4 based on a depth gauge provided in the moving body 4. Then, the undersea structure detection unit 10a acquires the depth position 25 of the undersea structure 90 by adding the distance 23 between the undersea structure 90 and the moving body 4 and the distance 24 from the sea surface 81 to the moving body 4. That is, the depth position 25 of the undersea structure 90 is the distance from the sea surface 81 to the undersea structure 90.

[0048] Referring again to FIG. 5, the seabed structure detector 10a outputs a first detection result 40a, which is a detection result of the presence or absence of the seabed structure 90, to the notification unit 14. In the present embodiment, when the seabed structure detector 10a determines that there is a seabed structure 90, it outputs a message indicating that the seabed structure 90 has been detected to the notification unit 14 as the first detection result 40a. Further, when the seabed structure detector 10a determines that there is no seabed structure 90, it outputs a message indicating that the seabed structure 90 has not been detected to the notification unit 14 as the first detection result 40a. When there is a seabed structure 90, the seabed structure detector 10a also outputs the depth position 25 of the seabed structure 90 as the first detection result 40a.

[0049] The damage detector 10b is configured to detect the presence or absence of damage 6a (see FIG. 1) in the anticorrosion layer 6 (see FIG. 1) based on the magnetic signal 31 and the electric field signal 30 output by the potential difference sensor 1.

[0050] The damage detector 10b is configured to detect the presence or absence of damage 6a in the anticorrosion layer 6 based on the magnetic component of the current flowing between the location where the damage 6a in the anticorrosion layer 6 of the seabed structure 90 has occurred and the anticorrosion layer 6, and the current component included in the electric field signal 30. Specifically, the damage detector 10b is configured to obtain the magnetic component due to the current based on the reference magnetic signal 20 and the magnetic signal 31. In the present embodiment, the damage detector 10b obtains the corrected electric field signal 30a and the corrected magnetic signal 31a obtained by the signal correction unit 10c. The damage detector 10b is configured to detect the presence or absence of damage 6a in the anticorrosion layer 6 based on the corrected magnetic signal 31a and the corrected electric field signal 30a, which is the electric field signal 30 after the attitude has been corrected by the signal correction unit 10c.

[0051] When the subsea structure detection unit 10a determines that there is a subsea structure 90, the damage detection unit 10b determines whether there is damage 6a in the anticorrosion layer 6 provided on the subsea structure 90. Specifically, the damage detection unit 10b detects the presence or absence of the damage 6a based on the corrected electric field signal 30a output by the signal correction unit 10c, the corrected magnetic signal 31a output by the signal correction unit 10c, and the reference magnetic signal 20 stored in the storage unit 11.

[0052] In this embodiment, the anticorrosion layer 6 is formed of a metal with an ionization tendency different from that of the metal constituting the subsea structure 90. Therefore, when there is damage 6a in the anticorrosion layer 6, based on the difference in ionization tendency, as shown by the arrow 7 (see FIG. 1), a current flows from the damage 6a to the anticorrosion layer 6. In this case, magnetism is generated due to the current flowing from the damage 6a to the anticorrosion layer 6. The magnetic sensor 2 (see FIG. 1) outputs a magnetic signal 31 including the magnetism generated due to the current flowing from the damage 6a to the anticorrosion layer 6.

[0053] Here, the magnetic signal 31 includes noise caused by components such as geomagnetism in addition to the magnetic component generated due to the current flowing from the damage 6a to the anticorrosion layer 6. In a state including noise, it is difficult to distinguish the magnetism generated due to the current flowing from the damage 6a to the anticorrosion layer 6. Therefore, in this embodiment, the damage detection unit 10b is configured to detect the presence or absence of the damage 6a of the anticorrosion layer 6 based on the differential magnetic signal 32 (see FIG. 7(C)), which is a signal obtained by differentiating the reference magnetic signal 20 from the magnetic signal 31. The damage detection unit 10b acquires the differential magnetic signal 32, which is the difference between the corrected magnetic signal 31a and the reference magnetic signal 20.

[0054] In this embodiment, the damage detection unit 10b is configured to detect the presence or absence of the damage 6a of the anticorrosion layer 6 based on the first peak 60 (see FIG. 7(C)) of the differential magnetic signal 32 and the second peak 62 (see FIG. 8(B)) of the electric field signal 30. Specifically, the damage detection unit 10b determines whether there is damage 6a based on whether the first peak 60 based on the magnetism generated due to the current flowing from the damage 6a to the anticorrosion layer 6 is included in the differential magnetic signal 32.

[0055] Also, in the present embodiment, the damage detection unit 10b is configured to detect the position of the damage 6a of the anticorrosion layer 6 based on the first acquisition position 61 (see FIG. 7(C)), which is the acquisition position of the first peak 60, and the second acquisition position 63 (see FIG. 8(B)), which is the acquisition position of the second peak 62. Specifically, the damage detection unit 10b acquires the first acquisition position 61 based on the time when the detection of the damage 6a is started and the moving distance of the moving body 4 when the first peak 60 is acquired. Further, the damage detection unit 10b acquires the second acquisition position 63 based on the time when the detection of the damage 6a is started and the moving distance of the moving body 4 when the second peak 62 is acquired.

[0056] When there is a damage 6a in the anticorrosion layer 6, the damage detection unit 10b acquires, as the second detection result 40b, a message indicating that there is a damage 6a in the anticorrosion layer 6. Also, when there is a damage 6a in the anticorrosion layer 6, the damage detection unit 10b acquires, as the second detection result 40b, the position of the damage 6a. Further, when there is no damage 6a in the anticorrosion layer 6, the damage detection unit 10b acquires, as the second detection result 40b, a message indicating that there is no damage 6a in the anticorrosion layer 6. Also, the damage detection unit 10b outputs the acquired second detection result 40b to the notification unit 14. Note that when there is no undersea structure 90, the damage detection unit 10b does not determine whether there is a damage 6a in the anticorrosion layer 6, and thus does not acquire the second detection result 40b. That is, when there is no undersea structure 90, the damage detection unit 10b does not output the second detection result 40b to the notification unit 14.

[0057] The notification unit 14 displays the first detection result 40a input from the undersea structure detection unit 10a. Also, when the second detection result 40b is input from the damage detection unit 10b, the notification unit 14 displays the second detection result 40b together with the first detection result 40a.

[0058] 〈Each signal waveform〉 Next, with reference to FIGS. 7 and 8, the magnetic signal 31 detected by the magnetic sensor 2 and the electric field signal 30 detected by the potential difference sensor 1 will be described. Note that the example shown in FIG. 7 is a conceptual diagram, and in reality, the magnetic signal 31 includes noise such as geomagnetism. Also, the example shown in FIG. 8 is also a conceptual diagram, and in reality, the electric field signal 30 includes noise such as the potential difference in the surrounding environment.

[0059] FIG. 7(A) is a graph 70 showing a reference magnetic signal 20 acquired in advance and stored in the storage unit 11 (see FIG. 2). In the graph 70, the vertical axis represents magnetic force, and the horizontal axis represents the moving distance of the moving body 4 (see FIG. 1).

[0060] The reference magnetic signal 20 shown in the graph 70 is a magnetic signal detected by the magnetic sensor 2 (see FIG. 1) at the reference distance 21 (see FIG. 2). That is, since the reference magnetic signal 20 is a signal acquired in a state where there is no damage 6a (see FIG. 1) in the anticorrosion layer 6 (see FIG. 1), it does not include peaks caused by the damage 6a.

[0061] FIG. 7(B) is a graph 71 showing a corrected magnetic signal 31a output by the magnetic sensor 2 (see FIG. 1) and corrected by the signal correction unit 10c (see FIG. 5). In the graph 71, the vertical axis represents magnetic force, and the horizontal axis represents the moving distance of the moving body 4 (see FIG. 1). The example shown in FIG. 7(B) is the corrected magnetic signal 31a when there is damage 6a (see FIG. 1) in the anticorrosion layer 6 (see FIG. 1). Therefore, the corrected magnetic signal 31a shown in FIG. 7(B) includes a first peak 60 that is a magnetic component caused by the current flowing from the damage 6a to the anticorrosion layer 6. Note that the first peak 60 includes a positive first peak 60a and a negative first peak 60b. The positive first peak 60a is a peak that appears at the position of the starting point of the current flowing from the damage 6a to the anticorrosion layer 6. Also, the negative first peak 60b is a peak that appears at the position of the ending point of the current flowing from the damage 6a to the anticorrosion layer 6.

[0062] FIG. 7(C) is a graph 72 showing the differential magnetic signal 32 acquired by the undersea structure detection unit 10a (see FIG. 5). In graph 72, the vertical axis represents magnetic force, and the horizontal axis represents the moving distance of the moving body 4 (see FIG. 1). The differential magnetic signal 32 includes a first peak 60 which is a magnetic component caused by the current flowing from the damage 6a (see FIG. 1) to the anticorrosion layer 6 (see FIG. 1). Also, since the differential magnetic signal 32 is a signal obtained by differentiating the reference magnetic signal 20 from the corrected magnetic signal 31a (see FIG. 5), noise due to geomagnetism etc. around the undersea structure 90 (see FIG. 1) is removed. That is, the differential magnetic signal 32 is a signal with a high SNR (Signal Noise Ratio) of the magnetic component (first peak 60) caused by the current flowing from the damage 6a to the anticorrosion layer 6.

[0063] FIG. 8(A) is a graph 73 showing the electric field signal 30b when there is no damage 6a in the anticorrosion layer 6 (see FIG. 1). In graph 73, the vertical axis represents magnetic force, and the horizontal axis represents the moving distance of the moving body 4 (see FIG. 1). When there is no damage 6a, no current flows from the undersea structure 90. Therefore, the electric field signal 30b shown in graph 73 is a signal without a peak.

[0064] FIG. 8(B) shows the corrected electric field signal 30a when there is damage 6a in the anticorrosion layer 6 (see FIG. 1). In graph 74, the vertical axis represents magnetic force, and the horizontal axis represents the moving distance of the moving body 4 (see FIG. 1). When there is damage 6a, current flows from the damage 6a to the anticorrosion layer 6. Therefore, the electric field signal 30b includes a second peak 62 caused by the current flowing from the damage 6a to the anticorrosion layer 6. Note that the second peak 62 includes a positive second peak 62a and a negative second peak 62b. The positive second peak 62a is a peak that appears at the position of the start point of the current flowing from the damage 6a to the anticorrosion layer 6. Also, the negative second peak 62b is a peak that appears at the position of the end point of the current flowing from the damage 6a to the anticorrosion layer 6.

[0065] When there is a damage 6a in the anticorrosion layer 6, a first peak 60 (see FIG. 7(C)) caused by the current flowing from the damage 6a to the anticorrosion layer 6 is detected, and a second peak 62 is also detected. Since the potential difference sensor 1 and the magnetic sensor 2 are integrally moved by the moving body 4 (see FIG. 1), based on the position of the first peak 60 (the first acquisition position 61 (see FIG. 7(C))) and the position of the second peak 62 (the second acquisition position 63), the position of the damage 6a in the anticorrosion layer 6 can be acquired.

[0066] Note that the first acquisition position 61 includes a first acquisition position 61a corresponding to the positive first peak 60a and a first acquisition position 61b corresponding to the negative first peak 60b. Therefore, the damage detection unit 10b can acquire the start point and the end point of the current flowing between the anticorrosion layer 6 and the damage 6a (the surface of the undersea structure 90) by acquiring the first acquisition position 61a corresponding to the positive first peak 60a and the first acquisition position 61b corresponding to the negative first peak 60b.

[0067] Also, the second acquisition position 63 includes a second acquisition position 63a corresponding to the positive second peak 62a and a second acquisition position 63b corresponding to the negative second peak 62b. Therefore, the damage detection unit 10b can acquire the start point and the end point of the current flowing between the anticorrosion layer 6 and the damage 6a (the surface of the undersea structure 90) by acquiring the second acquisition position 63a corresponding to the positive second peak 62a and the second acquisition position 63b corresponding to the negative second peak 62b.

[0068] 〈Detection Process of Undersea Structure〉 Next, with reference to FIG. 9, the process by which the undersea structure detection system 100 detects the presence or absence of the undersea structure 90 will be described.

[0069] In step 101, the undersea structure detection unit 10a (see FIG. 5) acquires the magnetic signal 31 (see FIG. 2) output by the magnetic sensor 2 (see FIG. 1). Specifically, the undersea structure detection unit 10a acquires the corrected magnetic signal 31a (see FIG. 5) corrected by the signal correction unit 10c (see FIG. 5).

[0070] In step 102, the seabed structure detection unit 10a (see FIG. 2) determines whether the seabed structure 90 (see FIG. 1) has been detected. Specifically, the seabed structure detection unit 10a determines whether the seabed structure 90 has been detected based on whether the magnitude of the amplitude 51 (see FIG. 7(B)) of the corrected magnetic signal 31a is equal to or greater than a predetermined magnitude. If the seabed structure 90 is detected, the process proceeds to step 103. If the seabed structure 90 is not detected, the process proceeds to step 107.

[0071] In step 103, the seabed structure detection unit 10a obtains, as the first detection result 40a (see FIG. 5), a message indicating that the seabed structure 90 has been detected.

[0072] In step 104, the seabed structure detection unit 10a obtains the reference magnetic signal 20 (see FIG. 2) stored in the storage unit 11 (see FIG. 2).

[0073] In step 105, as shown in FIG. 6, the seabed structure detection unit 10a obtains the depth position 25 of the seabed structure 90.

[0074] In step 106, the notification unit 14 (see FIG. 2) notifies the first detection result 40a. Specifically, the notification unit 14 notifies the depth position 25 of the seabed structure 90 and a message indicating that the seabed structure 90 has been detected. Thereafter, the process ends.

[0075] Also, when the process proceeds from step 102 to step 107, in step 107, the seabed structure detection unit 10a obtains, as the first detection result 40a, a message indicating that the seabed structure 90 has not been detected.

[0076] In step 108, the notification unit 14 notifies the first detection result 40a. Specifically, the notification unit 14 notifies a message indicating that the seabed structure 90 has not been detected. Thereafter, the process ends. Note that the seabed structure detection unit 10a repeatedly performs the processes of steps 101 to 108 at predetermined intervals.

[0077] Next, referring to FIG. 10, a process in which the seabed structure detection system 100 detects the presence or absence of damage 6a (see FIG. 1) to the anticorrosion layer 6 (see FIG. 1) provided on the seabed structure 90 (see FIG. 1) will be described. Note that the process shown in FIG. 10 is executed when it is determined that there is a seabed structure 90 in the process shown in FIG. 9. That is, when starting the process shown in FIG. 10, the processor 10 (see FIG. 2) is in a state of having acquired the magnetic signal 31 (see FIG. 2) and the reference magnetic signal 20 (see FIG. 2).

[0078] In step 200, the damage detection unit 10b (see FIG. 5) acquires the differential magnetic signal 32 (see FIG. 7(C)). Specifically, the damage detection unit 10b acquires the differential magnetic signal 32 based on the difference between the corrected magnetic signal 31a (see FIG. 2) and the reference magnetic signal 20.

[0079] In step 201, the damage detection unit 10b acquires the position of the first peak 60 (the first acquisition position 61 (see FIG. 7(C))). Specifically, the damage detection unit 10b acquires the first acquisition position 61 based on the moving distance of the moving body 4 when the first peak 60 is detected.

[0080] In step 202, the damage detection unit 10b acquires the electric field signal 30 (see FIG. 2). Specifically, the damage detection unit 10b acquires the corrected electric field signal 30a (see FIG. 5) corrected by the signal correction unit 10c (see FIG. 5).

[0081] In step 203, the damage detection unit 10b acquires the position of the second peak 62 (the second acquisition position 63 (see FIG. 8(B))). Specifically, the damage detection unit 10b acquires the second acquisition position 63 based on the moving distance of the moving body 4 when the second peak 62 is detected. Note that the processes of step 200 and step 201 and the processes of step 202 and step 203 may be performed in either order.

[0082] In step 204, the damage detection unit 10b determines whether there is a first peak 60 or a second peak 62. Specifically, the damage detection unit 10b determines whether the first peak 60 is detected in the differential magnetic signal 32, or whether the second peak 62 is detected in the corrected electric field signal 30a. If either the first peak 60 or the second peak 62 is detected, the process proceeds to step 205. If neither the first peak 60 nor the second peak 62 is detected, the process proceeds to step 208.

[0083] In step 205, the damage detection unit 10b obtains the position of the damage 6a of the anticorrosion layer 6 based on the peak. When both the first peak 60 and the second peak 62 are detected, the damage detection unit 10b obtains the position of the damage 6a of the anticorrosion layer 6 based on the first acquisition position 61 and the second acquisition position 63. When only one of the first peak 60 and the second peak 62 is detected, the damage detection unit 10b obtains the position of the damage 6a of the anticorrosion layer 6 based on the acquisition position of either peak.

[0084] In step 206, the damage detection unit 10b obtains, as the second detection result 40b (see FIG. 5), a message indicating that the damage 6a of the anticorrosion layer 6 has been detected.

[0085] In step 207, the notification unit 14 (see FIG. 5) notifies the second detection result 40b.

[0086] When the process proceeds from step 204 to step 208, in step 208, the damage detection unit 10b obtains, as the second detection result 40b, a message indicating that the damage 6a of the anticorrosion layer 6 has not been detected. Thereafter, the process proceeds to step 207.

[0087] That is, when the process proceeds from step 206 to step 207, in step 207, a message indicating that the damage 6a of the anticorrosion layer 6 has been detected is reported as the second detection result 40b. Further, when the process proceeds from step 208 to step 207, in step 207, a message indicating that the damage 6a of the anticorrosion layer 6 has not been detected is reported as the second detection result 40b.

[0088] (Effects of this Embodiment) In this embodiment, the following effects can be obtained.

[0089] In this embodiment, as described above, the subsea structure detection system 100 is a subsea structure detection system that detects a metal subsea structure 90 provided on the seabed 80 and detects the presence or absence of damage 6a to an anticorrosion layer 6 provided on the subsea structure 90 and formed of a metal having an ionization tendency different from that of the subsea structure 90. The system includes a potential difference sensor 1 that detects a potential difference caused by a current flowing between the subsea structure 90 and the anticorrosion layer 6, a magnetic sensor 2 that detects magnetism in the sea, a subsea structure detection unit 10a that detects the presence or absence of the subsea structure 90 based on a magnetic signal 31 output by the magnetic sensor 2, and a damage detection unit 10b that detects the presence or absence of damage 6a to the anticorrosion layer 6 based on the magnetic signal 31 and an electric field signal 30 output by the potential difference sensor 1.

[0090] As a result, since the subsea structure detection system 100 includes a subsea structure detection unit 10a that detects the presence or absence of the subsea structure 90 based on the magnetic signal 31 output by the magnetic sensor 2, the presence or absence of the subsea structure 90 can be detected by acquiring the magnetic signal 31. Further, the subsea structure detection system 100 includes a damage detection unit 10b that detects the presence or absence of damage 6a to the anticorrosion layer 6 based on the magnetic signal 31 output by the magnetic sensor 2 and the electric field signal 30 output by the potential difference sensor 1 that detects the potential difference resulting from the current flowing between the subsea structure 90 and the anticorrosion layer 6. Thus, unlike a configuration that detects the presence or absence of damage 6a to the anticorrosion layer 6 only based on the magnetic signal 31, the presence or absence of damage 6a to the anticorrosion layer 6 can be detected based on both the magnetic signal 31 generated due to the current flowing between the subsea structure 90 and the anticorrosion layer 6 and the electric field signal 30 based on the potential difference resulting from the current flowing between the subsea structure 90 and the anticorrosion layer 6. Therefore, the presence or absence of damage 6a to the anticorrosion layer 6 can be detected with higher accuracy compared to a configuration that detects the presence or absence of damage 6a to the anticorrosion layer 6 only based on the magnetic signal 31. As a result, it is possible to provide the subsea structure detection system 100 that can detect the presence or absence of the subsea structure 90 and can accurately detect the presence or absence of damage 6a to the anticorrosion layer 6 provided on the subsea structure 90.

[0091] Further, in the above embodiment, by configuring as follows, the following further effects can be obtained.

[0092] That is, in the present embodiment, as described above, the damage detection unit 10b detects the presence or absence of the damage 6a of the anticorrosion layer 6 based on the magnetic component caused by the current flowing between the location where the damage 6a of the anticorrosion layer 6 has occurred in the undersea structure 90 and the anticorrosion layer 6, and the current component included in the electric field signal 30. Thereby, since the damage detection unit 10b detects the presence or absence of the damage 6a of the anticorrosion layer 6 based on the magnetic component caused by the current flowing between the location where the damage 6a of the anticorrosion layer 6 has occurred and the anticorrosion layer 6, and the current component included in the electric field signal 30, compared with the configuration of detecting the damage 6a of the anticorrosion layer 6 using only one of the magnetic signal 31 and the electric field signal 30, the detection accuracy of the damage 6a of the anticorrosion layer 6 can be improved.

[0093] Further, in the present embodiment, as described above, it further includes a storage unit 11 that stores the reference magnetic signal 20 acquired in advance, and the damage detection unit 10b is configured to acquire the magnetic component caused by the current based on the reference magnetic signal 20 and the magnetic signal 31. Thereby, even when the magnetic signal 31 includes noise such as geomagnetism, the magnetic component caused by the current flowing between the location where the damage 6a of the anticorrosion layer 6 has occurred and the anticorrosion layer 6 can be easily acquired. As a result, it is possible to suppress a decrease in the detection accuracy of the damage 6a of the anticorrosion layer 6 due to noise such as geomagnetism.

[0094] Further, in the present embodiment, as described above, the damage detection unit 10b is configured to detect the presence or absence of the damage 6a of the anticorrosion layer 6 based on the first peak 60 of the differential magnetic signal 32, which is a signal obtained by differentiating the reference magnetic signal 20 from the magnetic signal 31, and the second peak 62 of the electric field signal 30. Thereby, the presence or absence of the damage 6a of the anticorrosion layer 6 can be detected by whether or not the first peak 60 is included in the differential magnetic signal 32 and whether or not the second peak 62 is included in the electric field signal 30. As a result, the presence or absence of the damage 6a of the anticorrosion layer 6 can be easily detected.

[0095] Also, in the present embodiment, as described above, the damage detection unit 10b is configured to detect the position of the damage 6a of the anticorrosion layer 6 based on the first acquisition position 61 which is the acquisition position of the first peak 60 and the second acquisition position 63 which is the acquisition position of the second peak 62. Thereby, by acquiring the first acquisition position 61 and the second acquisition position 63, the position of the damage 6a of the anticorrosion layer 6 can be easily acquired.

[0096] Also, in the present embodiment, as described above, the storage unit 11 is configured to store the reference distance 21 which is the distance between the magnetic sensor 2 and the subsea structure 90 when the reference magnetic signal 20 is acquired, and the subsea structure detection unit 10a is configured to detect the depth position 25 of the subsea structure 90 based on the amplitude 50 of the waveform of the reference magnetic signal 20, the reference distance 21, and the amplitude 51 of the magnetic signal 31. Thereby, for example, even when the subsea structure 90 is buried in sand or the like on the seabed 80 and cannot be visually observed, the depth position 25 of the subsea structure 90 can be acquired, so that the position of the subsea structure 90 can be accurately acquired.

[0097] Also, in the present embodiment, as described above, the magnetic sensor 2 and the potential difference sensor 1 are provided, and the moving body 4 which can move in water is further provided. Thereby, the magnetic sensor 2 and the potential difference sensor 1 can be integrally moved. Therefore, when there is a damage 6a in the anticorrosion layer 6, the detection timing of the first peak 60 in the magnetic signal 31 and the detection timing of the second peak 62 in the electric field signal 30 become substantially equal. As a result, for example, compared with a configuration in which the magnetic sensor 2 and the potential difference sensor 1 are separately moved, the position of the damage 6a of the anticorrosion layer 6 can be easily acquired based on the position of the first peak 60 and the position of the second peak 62.

[0098] Also, in the present embodiment, as described above, the potential difference sensor 1 includes a pair of electrodes (the first electrode 1a and the second electrode 1b), and the pair of potential difference sensors 1 are provided in the moving body 4 so as to be arranged vertically at a predetermined interval. The magnetic sensor 2 is provided at a position between the pair of electrodes. Thereby, the pair of electrodes and the magnetic sensor 2 can be arranged in a direction orthogonal to the traveling direction of the moving body 4. Therefore, for example, when performing detection while moving the moving body 4 along the direction in which the underwater structure 90 extends, the pair of electrodes and the magnetic sensor 2 can be easily arranged at a position orthogonal to the underwater structure 90. As a result, the positions of the first peak 60 and the second peak 62 can be made substantially equal, so that the position of the damage 6a of the anticorrosion layer 6 can be obtained more easily.

[0099] Also, in the present embodiment, as described above, a moving body information acquisition unit 12 that acquires moving body information 22 including information on the acceleration and attitude of the moving body 4, and based on the moving body information 22, a signal correction unit 10c that corrects the attitude of the moving body 4 with respect to the magnetic signal 31 and the electric field signal 30 are further provided. The underwater structure detection unit 10a is configured to detect the presence or absence of the underwater structure 90 based on the corrected magnetic signal 31a, which is the magnetic signal 31 after the attitude correction is performed by the signal correction unit 10c. The damage detection unit 10b is configured to detect the presence or absence of the damage 6a of the anticorrosion layer 6 based on the corrected magnetic signal 31a and the corrected electric field signal 30a, which is the electric field signal 30 after the attitude correction is performed by the signal correction unit 10c. Thereby, without correcting the attitude of the moving body 4, it is possible to detect the presence or absence of the underwater structure 90 and the presence or absence of the damage 6a of the anticorrosion layer 6. Therefore, unlike a configuration in which the presence or absence of the underwater structure 90 and the presence or absence of the damage 6a of the anticorrosion layer 6 are detected while correcting the attitude of the moving body 4, it is possible to detect the presence or absence of the underwater structure 90 and the presence or absence of the damage 6a of the anticorrosion layer 6 without performing attitude control of the moving body 4. As a result, the degree of freedom of movement of the moving body 4 can be improved, so that the degree of freedom of detecting the presence or absence of the underwater structure 90 and the presence or absence of the damage 6a of the anticorrosion layer 6 can be improved.

[0100] Also, in the present embodiment, as described above, the mobile body 4 is provided with the magnetic sensor 2, the potential difference sensor 1, and the propulsion mechanism 4d that applies a propulsion force to the mobile body 4, and is configured to be able to travel in the sea. Thereby, for example, compared with a configuration in which the mobile body 4 is moved by towing the mobile body 4 by the ship 5, the degree of freedom of movement of the mobile body 4 can be improved.

[0101] Also, in the present embodiment, as described above, the seabed structure 90 is a pipeline provided on the seabed 80, the seabed structure detection unit 10a is configured to determine the presence or absence of the pipeline, the damage 6a of the anticorrosion layer 6 is corrosion of the anticorrosion layer 6, and the damage detection unit 10b is configured to detect the presence or absence of corrosion of the pipeline. Thereby, a seabed structure detection system 100 suitable for detecting the presence or absence of a pipeline and the presence or absence of corrosion of the pipeline can be provided.

[0102] (Modification example) It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and further includes all changes (modification examples) within the meaning and scope equivalent to the claims.

[0103] For example, in the above embodiment, an example of a configuration in which the damage detection unit 10b acquires the magnetic component caused by the current based on the reference magnetic signal 20 and the magnetic signal 31 and detects the presence or absence of the damage 6a of the anticorrosion layer 6 has been shown, but the present invention is not limited to this. For example, the damage detection unit 10b may be configured to detect the presence or absence of the damage 6a of the anticorrosion layer 6 without using the reference magnetic signal 20.

[0104] Also, in the above-described embodiment, an example of the configuration in which the damage detection unit 10b acquires the differential magnetic signal 32 has been shown, but the present invention is not limited to this. For example, the damage detection unit 10b may not acquire the differential magnetic signal 32. However, when the damage detection unit 10b does not acquire the differential magnetic signal 32, the detection accuracy of the presence or absence of the damage 6a of the anticorrosion layer 6 decreases due to noise such as geomagnetism. Therefore, it is preferable that the damage detection unit 10b is configured to acquire the differential magnetic signal 32.

[0105] Also, in the above-described embodiment, an example of the configuration in which the undersea structure detection unit 10a acquires the depth position 25 of the undersea structure 90 has been shown, but the present invention is not limited to this. For example, the undersea structure detection unit 10a may not acquire the depth position 25 of the undersea structure 90.

[0106] Also, in the above-described embodiment, an example of the configuration in which the moving body 4 is configured to be capable of autonomous driving has been shown, but the present invention is not limited to this. For example, the moving body 4 may be configured to move in the sea by being towed by a ship 5.

[0107] Also, in the above-described embodiment, an example of the configuration in which the undersea structure detection system 100 includes the signal correction unit 10c has been shown, but the present invention is not limited to this. For example, the undersea structure detection system 100 may not include the signal correction unit 10c. However, when the undersea structure detection system 100 does not include the signal correction unit 10c, the detection accuracy of the presence or absence of the undersea structure 90 and the detection accuracy of the presence or absence of the damage 6a of the anticorrosion layer 6 decrease. Therefore, it is preferable that the undersea structure detection system 100 includes the signal correction unit 10c.

[0108] Also, in the above-described embodiment, an example of the configuration in which the computer 3 and the moving body 4 communicate with each other by wireless communication has been shown, but the present invention is not limited to this. For example, the computer 3 and the moving body 4 may be wired-connected and configured to perform wired communication.

[0109] In the above-described embodiment, an example of a configuration in which the damage detection unit 10b determines that there is damage 6a in the anticorrosion layer 6 when either the first peak 60 or the second peak 62 is detected has been shown. However, the present invention is not limited to this. For example, the damage detection unit 10b may be configured to determine that there is damage 6a in the anticorrosion layer 6 when both the first peak 60 and the second peak 62 are detected.

[0110] In the above-described embodiment, for the sake of convenience of explanation, an example in which the control process of the undersea structure detection unit 10a and the control process of the damage detection unit 10b are described using a flow-driven type flowchart that processes in order along the processing flow has been shown. However, the present invention is not limited to this. In the present invention, the control process of the undersea structure detection unit 10a and the control process of the damage detection unit 10b may be performed by an event-driven type (event-driven type) process that executes the process in units of events. In this case, it may be performed in a completely event-driven manner, or may be performed by combining event driving and flow driving.

[0111] [Aspect] It is understood by those skilled in the art that the above-exemplified embodiments are specific examples of the following aspects.

[0112] (Item 1) An undersea structure detection system for detecting a metal undersea structure provided on the seabed and detecting the presence or absence of damage to an anticorrosion layer provided on the undersea structure and formed of a metal having a different ionization tendency from the metal constituting the undersea structure, a potential difference sensor that detects a potential difference caused by a current flowing between the undersea structure and the anticorrosion layer; a magnetic sensor that detects magnetism in the sea; an undersea structure detection unit that detects the presence or absence of the undersea structure based on a magnetic signal output by the magnetic sensor; and a damage detection unit that detects the presence or absence of damage to the anticorrosion layer based on the magnetic signal and an electric field signal output by the potential difference sensor.

[0113] (Item 2) The damage detection unit is configured to detect the presence or absence of damage to the anticorrosion layer based on a magnetic component resulting from an electric current flowing between a location where damage has occurred to the anticorrosion layer among the undersea structures and the anticorrosion layer, and a component of the electric current included in the electric field signal. The undersea structure detection system according to Item 1.

[0114] (Item 3) The system further includes a storage unit that stores a reference magnetic signal acquired in advance. The damage detection unit is configured to acquire the magnetic component resulting from the electric current based on the reference magnetic signal and the magnetic signal. The undersea structure detection system according to Item 2.

[0115] (Item 4) The damage detection unit is configured to detect the presence or absence of damage to the anticorrosion layer based on a first peak of a differential magnetic signal, which is a signal obtained by differentiating the reference magnetic signal from the magnetic signal, and a second peak of the electric field signal. The undersea structure detection system according to Item 3.

[0116] (Item 5) The damage detection unit is configured to detect the location of damage to the anticorrosion layer based on a first acquisition position, which is the acquisition position of the first peak, and a second acquisition position, which is the acquisition position of the second peak. The undersea structure detection system according to Item 4.

[0117] (Item 6) The storage unit is configured to store a reference distance, which is the distance between the magnetic sensor and the undersea structure when the reference magnetic signal was acquired. The undersea structure detection unit is configured to detect the depth position of the undersea structure based on the amplitude of the waveform of the reference magnetic signal, the reference distance, and the amplitude of the magnetic signal. The undersea structure detection system according to any one of Items 3 to 5.

[0118] (Item 7) The subsea structure detection system according to any one of items 1 to 6, further comprising a moving body provided with the magnetic sensor and the potential difference sensor and capable of moving underwater.

[0119] (Item 8) The potential difference sensor includes a pair of electrodes. The pair of potential difference sensors are provided on the moving body so as to be arranged vertically at a predetermined interval. The magnetic sensor is provided at a position between the pair of electrodes. The subsea structure detection system according to item 7.

[0120] (Item 9) A moving body information acquisition unit that acquires moving body information including information on the acceleration and attitude of the moving body; Based on the moving body information, a signal correction unit that corrects the attitude of the moving body with respect to the magnetic signal and the electric field signal. The subsea structure detection system further comprises: The subsea structure detection unit is configured to detect the presence or absence of the subsea structure based on the corrected magnetic signal, which is the magnetic signal after the attitude correction is performed by the signal correction unit. The damage detection unit is configured to detect the presence or absence of damage to the anticorrosion layer based on the corrected magnetic signal and the corrected electric field signal, which is the electric field signal after the attitude correction is performed by the signal correction unit. The subsea structure detection system according to item 7 or 8.

[0121] (Item 10) The moving body is provided with the magnetic sensor, the potential difference sensor, and a propulsion mechanism that applies a propulsion force to the moving body, and is configured to be able to travel in the sea. The subsea structure detection system according to any one of items 7 to 9.

[0122] (Item 11) The subsea structure is a pipeline provided on the seabed. The subsea structure detection unit is configured to determine the presence or absence of the pipeline. The damage to the anticorrosion layer is corrosion of the anticorrosion layer. The damage detection unit is configured to detect the presence or absence of corrosion in the pipeline. The subsea structure detection system according to any one of Items 1 to 10.

Explanation of Signs

[0123] 1 Potential difference sensor 1a First electrode (pair of electrodes) 1b Second electrode (pair of electrodes) 2 Magnetic sensor 4 Mobile body 4d Propulsion mechanism 6 Anti-corrosion layer 6a Damage 10a Subsea structure detection unit 10b Damage detection unit 10c Signal correction unit 12 Mobile body information acquisition unit 20 Reference magnetic signal 21 Reference distance 25 Depth position 30 Electric field signal 30a Corrected electric field signal 31 Magnetic signal 31a Corrected magnetic signal 32 Differential magnetic signal 50 Amplitude of reference magnetic signal 51 Amplitude of magnetic signal 60, 60a, 60b First peak 61, 61a, 61b First acquisition position 62, 62a, 62b Second peak 63, 63a, 63b Second acquisition position 80 Seabed 90 Subsea structure (pipeline) 100 Subsea structure detection system

Claims

1. A subsea structure detection system for detecting a metal subsea structure provided on the seabed and detecting the presence or absence of damage to a corrosion protection layer provided on the subsea structure and formed of a metal having an ionization tendency different from that of the metal constituting the subsea structure, comprising: a potential difference sensor for detecting a potential difference caused by a current flowing between the subsea structure and the corrosion protection layer; a magnetic sensor for detecting magnetism in the sea; a subsea structure detection unit for detecting the presence or absence of the subsea structure based on a magnetic signal output by the magnetic sensor; a damage detection unit for detecting the presence or absence of damage to the corrosion protection layer based on the magnetic signal and an electric field signal output by the potential difference sensor.

2. The damage detection unit is configured to detect the presence or absence of damage to the corrosion protection layer based on a magnetic component caused by the current flowing between a location where damage has occurred to the corrosion protection layer of the subsea structure and the corrosion protection layer, and a component of the current included in the electric field signal. The subsea structure detection system according to claim 1.

3. further comprising a storage unit for storing a reference magnetic signal acquired in advance, wherein the damage detection unit is configured to acquire the magnetic component caused by the current based on the reference magnetic signal and the magnetic signal. The subsea structure detection system according to claim 2.

4. The damage detection unit is configured to detect the presence or absence of damage to the corrosion protection layer based on a first peak of a differential magnetic signal, which is a signal obtained by differentiating the reference magnetic signal from the magnetic signal, and a second peak of the electric field signal. The subsea structure detection system according to claim 3.

5. The damage detection unit is configured to detect the location of damage to the corrosion protection layer based on a first acquisition position, which is the acquisition position of the first peak, and a second acquisition position, which is the acquisition position of the second peak. The subsea structure detection system according to claim 4.

6. the storage unit is configured to store a reference distance, which is the distance between the magnetic sensor and the subsea structure when the reference magnetic signal is acquired, wherein the subsea structure detection unit is configured to detect the depth position of the subsea structure based on the amplitude of the waveform of the reference magnetic signal, the reference distance, and the amplitude of the magnetic signal. The subsea structure detection system according to any one of claims 3 to 5.

7. The subsea structure detection system according to any one of claims 1 to 6, further comprising a moving body provided with the magnetic sensor and the potential difference sensor and capable of moving underwater.

8. The potential difference sensor includes a pair of electrodes. The pair of potential difference sensors are provided in the moving body so as to be arranged vertically at a predetermined interval. The magnetic sensor is provided at a position between the pair of electrodes. The subsea structure detection system according to claim 7.

9. A moving body information acquisition unit that acquires moving body information including information on the acceleration and attitude of the moving body; Based on the moving body information, further comprising a signal correction unit that corrects the attitude of the moving body with respect to the magnetic signal and the electric field signal. The subsea structure detection unit is configured to detect the presence or absence of the subsea structure based on the corrected magnetic signal, which is the magnetic signal after the attitude correction is performed by the signal correction unit. The damage detection unit is configured to detect the presence or absence of damage to the anticorrosion layer based on the corrected magnetic signal and the corrected electric field signal, which is the electric field signal after the attitude correction is performed by the signal correction unit. The subsea structure detection system according to claim 7 or 8.

10. The moving body is provided with the magnetic sensor, the potential difference sensor, and a propulsion mechanism that applies a propulsion force to the moving body, and is configured to be able to travel in the sea. The subsea structure detection system according to any one of claims 7 to 9.

11. The subsea structure is a pipeline provided on the seabed. The subsea structure detection unit is configured to determine the presence or absence of the pipeline. The damage to the anticorrosion layer is corrosion of the anticorrosion layer. The damage detection unit is configured to detect the presence or absence of corrosion of the pipeline. The subsea structure detection system according to any one of claims 1 to 10.

Images