JP2017161390A - Water bottom electromagnetic survey system and survey method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water bottom electromagnetic survey system that can accurately and efficiently search for metal mineral resources under the seabed.SOLUTION: In a seabed survey system, a transmission coil 100 and a reception unit 110 of an electromagnetic survey device are placed on a towed body 20 towed underwater via a towing rope 12 by a submerging mobile body 10. The reception unit 110 receives an electromagnetic wave caused by an electromagnetic induction phenomenon that occurs at a water bottom when current is made to flow through the transmission coil 100 in the state of the towed body 20 being towed to produce a magnetic field toward the water bottom, and the current is drastically cut off.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an underwater electromagnetic exploration system and a exploration method using the same.

  Exploration of mineral resources (for example, submarine hydrothermal deposits) existing under the seabed is actively conducted. For example, Patent Document 1 discloses a method of performing an electric survey under the sea floor by installing an electrode on the sea floor (Cited Document 1).

  However, since the seabed near the seafloor hydrothermal deposit is often undulating, it is often difficult to conduct electrical exploration in which an electrode is in direct contact with the seabed and current flows below the seabed.

  For this reason, an electromagnetic exploration device is mounted on a submersible (such as a remotely operated vehicle (ROV) or an autonomous underwater vehicle (AUV)), and the transmission current is transmitted to the transmission loop of the electromagnetic exploration device. It is possible to conduct electromagnetic surveys of the seabed without contact with the seabed by detecting changes in electromagnetic induction under the seabed that occur by cutting off the transmission current after supplying the (For example, cited reference 2).

JP 2001-305237 A JP 2014-98669 A

  According to this electromagnetic exploration system, electromagnetic exploration of metal mineral resources under the seabed can be efficiently performed while moving in the sea.

  However, when searching for metal mineral resources under the seabed by electromagnetic exploration, seawater with low resistivity exists as a medium, unlike land. Therefore, the induced current generated in extremely low resistivity metal elements (such as (remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV))) that must be placed close to the transmitter coil The problem is that the magnetic field caused by the noise becomes a large noise source.

  The present invention has been made in view of the problems as described above, and according to some aspects of the present invention, an electromagnetic survey for the bottom of the sea that can accurately and efficiently search for the bottom of the metal, for example, a metal mineral resource under the sea. A system and a search method using the system can be provided.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
The underwater electromagnetic exploration system according to this application example is
A submersible moving body that moves underwater in water,
A towed body towed underwater by the submersible moving body through a towline;
An electromagnetic exploration device in which a transmitting coil and a receiving unit are arranged on the towing body;
Including
The electromagnetic exploration device
The transmission coil is
With the towed body being towed, the transmission loop is disposed on the towed body so as to face the bottom of the water,
The receiver is
Arranged around the transmission coil;
A current is passed through the transmission coil to generate a magnetic field toward the bottom of the water, and an electromagnetic wave caused by an electromagnetic induction phenomenon generated at the bottom of the water by rapidly interrupting the current is received by the receiving unit.
It is an underwater electromagnetic exploration system.

  By adopting the above configuration, according to this application example, since the induced current generated by the transmission loop flows under the water bottom, the transient response after the cutoff of the transmission current included in the change over time of the received signal is measured. By doing so, you can explore the electrical properties under the bottom of the water. At this time, the loop surface of the transmission loop is disposed to face the water bottom. As a result, for example, conditions such as “when it is difficult to conduct electrical exploration in which an electrode is in direct contact with the ocean floor and current flows under the ocean floor, because the ocean floor near the ocean floor hydrothermal deposit is often undulating.” Even so, since the induced current generated by the transmission loop spreads in the depth direction below the seabed, the electrical property can be probed to a deep position below the seabed without contact.

  In addition, according to this application example, the transmitting coil and the receiving unit of the electromagnetic exploration device are mounted on the towing body separated from the submersible moving body as the metal element that greatly affects the accuracy of the electromagnetic exploration in water. Can reduce the induced current generated in a submersible moving body, which is a metal element that greatly affects the measurement accuracy, and can continuously search for metal mineral resources under the bottom of the water along the towing path of the towing body. .

  In particular, since the towed body does not need to be equipped with power for self-propelled underwater and equipment related thereto, the structure is a structure that is stably towed underwater and is equipped with the electromagnetic exploration device. If there is enough. Therefore, since the metal element used for the towed body is significantly smaller than that of the submersible mobile body, the influence is reduced to a level that can be almost ignored compared to the case where the electromagnetic exploration device is mounted on the submersible mobile body, The continuous and efficient electromagnetic search can be realized in a state where the search accuracy is improved to a level close to that when the electromagnetic search device is installed on the bottom of the water.

  Here, the “submersible moving body” may be, for example, a diving machine (remotely operated vehicle (ROV), autonomous underwater vehicle (AUV), etc.).

  In addition, the “towed body” may be configured to be stably towed in water and mounted with the electromagnetic exploration device.

  In addition, “the receiving unit generates an electromagnetic field caused by an electromagnetic induction phenomenon generated at the bottom of the water by causing a current to flow through the transmitting coil to generate a magnetic field toward the bottom of the water and abruptly interrupting the current”, for example, the receiving coil It may be a magnetic field sensor or a plurality of potential measuring electrodes arranged around the transmission loop. When using a plurality of potential measurement electrodes, it is only necessary to measure the transient response after the transmission current is interrupted, which is included in the change with time of the potential difference between two of the potential measurement electrodes. Here, as the magnetic field sensor, for example, the one described in JP-A-2009-300332 may be used.

The electromagnetic exploration device
You may further include the measurement part which calculates the specific resistance under a water bottom based on the transient response after the interruption | blocking of the said transmission current contained in the time-dependent change of the signal which the said receiving part received.

The electromagnetic exploration device
You may further include the measurement part which calculates the charging rate under a water bottom based on the transient response after the interruption | blocking of the said transmission current contained in the time-dependent change of the signal which the said receiving part received.

  The electromagnetic exploration device may include a transmission current supply source that supplies a transmission current to the transmission coil.

  In addition, elements other than the transmission coil and the reception unit of the electromagnetic exploration device (for example, the measurement unit and the transmission current supply source) may be mounted on the towing body, and if necessary, separated from the towing body. A configuration may be adopted in which the device is mounted on a location, for example, the submerged moving body, and current is supplied to or transmitted and received from the transmitting coil and the receiving unit via a cable.

[Application Example 2]
In the underwater electromagnetic exploration system according to this application example,
The towed body includes
A stabilizer for stabilizing the attitude during towing may be provided.

  Thereby, the posture during measurement of the electromagnetic exploration device mounted on the towing body is stabilized, and the measurement accuracy can be further increased.

  Here, the “stabilizer” may be a vertical stabilizer (for example, vertical wing) that stabilizes the traveling direction, or a horizontal stabilizer (for example, horizontal wing) that enhances stability in the horizontal direction.

[Application Example 3]
In the underwater electromagnetic exploration system according to this application example, the towed body is
The submersible moving body may support the one end side of the towing rope via a rotary joint and perform the towing with the other end side of the towing rope in an arbitrary towing direction.

  As a result, even if the relative position of the submersible moving body and the towed body towed by it changes, the towing line is also pulled easily toward the towed body, which is the direction in which the tension is applied, by the rotary joint. As a result, the towing can be performed stably.

[Application Example 4]
In the submarine electromagnetic exploration system according to this application example, the submersible moving body is:
An adjustment unit that adjusts the length of the towline may be included.

  Thereby, the position of the towed body is adjusted by adjusting the length of the tow line according to the topography of the water bottom and the change of the tidal current, and flexible electromagnetic exploration according to the surrounding situation can be realized.

  Here, for example, a winch may be used as the adjustment unit.

[Application Example 5]
In the underwater electromagnetic exploration system according to this application example, the electromagnetic exploration device is
The measurement may be repeated during the towing.

  Thereby, the continuous electromagnetic survey of the bottom of the water can be performed along the towing path of the towed body, and the electromagnetic survey in a wide range can be performed efficiently and in a short time.

  In particular, by repeatedly performing measurement by electromagnetic survey along the towing route in a short time, it is possible to perform underground electromagnetic survey with high spatial resolution using measurement results at a plurality of adjacent measurement points.

[Application Example 6]
In the underwater electromagnetic exploration system according to this application example,
You may provide the detection part which detects the positional relationship with a water bottom in the said submersible type mobile body or the said towing body.

  As a result, for example, the towing body is towed in a state where the positional relationship (for example, distance) between the towing body and the water bottom is maintained within a predetermined range, and continuous measurement along a given measurement line is performed with high accuracy. be able to.

  In addition, it is possible to avoid a risk that the submersible moving body or towing body collides with an obstacle on the bottom surface of the water, for example, chimney during the measurement operation.

  Here, “detecting the positional relationship with the water bottom” may be the positional relationship (for example, distance) between the submersible moving body and the water bottom, and the positional relationship between the towed body and the water bottom (for example, distance). ).

  In addition, the “detection unit that detects the positional relationship with the water bottom surface” may be, for example, a multi-beam sonar or a camera.

[Application Example 7]
In the underwater electromagnetic exploration system according to this application example,
The towed body is
You may include the detection part which detects the attitude | position of the said towing body.

  As a result, since the attitude of the electromagnetic exploration device is obtained from the detected attitude of the towed body, it is possible to measure the range while accurately recognizing the change in the exploration range caused by the attitude at each measurement point. It is possible to improve the reliability of measurement data.

[Application Example 8]
In the underwater electromagnetic exploration system according to this application example, the electromagnetic exploration device is
A receiving coil as the receiving unit,
At least during the towing,
The receiving coil may be arranged so as to overlap the transmitting coil or surround the transmitting coil in plan view.

[Application Example 9]
In the underwater electromagnetic exploration system according to this application example, the electromagnetic exploration device is
A magnetic field sensor as the receiving unit,
At least during the towing,
The transmission coil may be arranged so as to surround the magnetic field sensor in plan view.

[Application Example 10]
The method according to this application example is
A submersible moving body that moves underwater in water,
A towed body towed underwater by the submersible moving body through a towline;
An electromagnetic exploration device in which a transmitting coil and a receiving unit are arranged on the towing body;
Including
The transmission coil is
With the towed body being towed, the transmission loop is disposed on the towed body so as to face the bottom of the water,
The receiver is
An underwater electromagnetic exploration method using an underwater electromagnetic exploration system disposed around the transmission coil,
A towing step of towing the towed body in water along a given measurement line with the submerged moving body;
During the towing, a current is caused to flow through the transmission coil to generate a magnetic field toward the bottom of the water, and the current is suddenly interrupted to receive an electromagnetic wave caused by an electromagnetic induction phenomenon generated at the bottom of the water at the receiving unit. It may be a water bottom electromagnetic exploration method including repeated measurement steps.

[Application Example 11]
In the method according to this application example,
In the towing process,
A step of maintaining a positional relationship between the water bottom surface and the towed body in a given state during the towing may be included.

Here, “maintaining the positional relationship between the water bottom and the towed body in a given state” may be to maintain the distance between the towed body and the water bottom within a predetermined range.

FIG. 1A and FIG. 1B are schematic diagrams for explaining a conventional seabed exploration system. It is explanatory drawing of the seabed exploration system which concerns on 1st Embodiment. It is a more specific explanatory view of the seafloor exploration system according to the first embodiment. 4A is a side view schematically showing the arrangement of the transmission loop and the receiving unit of the seafloor exploration system according to the first embodiment, and FIG. 4B is the transmission loop of the system according to the first embodiment. It is a top view which shows typically arrangement | positioning of a receiving part. It is a functional block diagram of the seafloor exploration device used for the seafloor exploration system concerning a 1st embodiment. It is a flowchart which shows an example of the seabed search method using the seabed search system which concerns on 1st Embodiment. 7A is a timing chart of the transmission current I1, FIG. 7B is a timing chart of the counter electromotive force P generated in the transmission coil 100, and FIG. 7C is a timing of the magnetic field H generated by the transmission coil 100. It is a chart. It is a schematic diagram for demonstrating the induced current which the transmission coil 100 generates. It is explanatory drawing of the towed body which concerns on 1st Embodiment, and is explanatory drawing showing the state by which the towed body is towed. It is explanatory drawing of the towing body which concerns on 1st Embodiment, and is explanatory drawing showing the state in which a towing body is accommodated. FIG. 11A is an explanatory diagram showing an example of a state where the towing body is being towed by the ROV, and FIG. 11B is an example of an image of the seabed photographed by the camera light system mounted on the ROV. It is. It is a graph which shows an example of the response of the magnetic field detected by receiving magnetic field sensor 110-2. It is explanatory drawing which shows an example in the case of towing a towing body along an electromagnetic exploration side line, and performing an electromagnetic exploration.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The drawings used are for convenience of explanation. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

  FIG. 1A and FIG. 1B are schematic diagrams for explaining a conventional seabed exploration system.

  The seafloor exploration system in FIG. 1 (A) represents an installation-type seafloor exploration device in which an electromagnetic exploration device for seafloor exploration is installed on the seabed and measured away from a remotely operated vehicle (ROV). ing.

  The seafloor exploration system in FIG. 1 (B) represents a mobile submarine exploration apparatus that measures while moving by mounting an electromagnetic exploration apparatus for seafloor exploration on a remotely operated vehicle (ROV). .

  As described above, two types of seabed exploration systems, fixed and mobile, have been used for seabed exploration.

  In the fixed seafloor exploration system shown in FIG. 1 (A), since it can be installed on the seabed sufficiently away from the ROV, there is no influence of the ROV's shaking (due to the ocean current) and electromagnetic noise such as 60 Hz generated from the ROV. The ROV is not affected by the fact that it is made of a metal having a very low specific resistance.

  On the other hand, the seabed near the seafloor hydrothermal deposit is often undulating, so there is a problem that it is often difficult to pinpoint the seafloor exploration device at the point where it is required.

  The mobile submarine exploration system shown in Fig. 1 (B) is capable of continuous high-efficiency measurement, and since the measurement data can be observed on the ship in real time via the ROV cable, it is easy to deal with equipment troubles. There are advantages such as being able to cope with.

  On the other hand, extremely low resistivity metal elements (submersibles (remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), AUVs) that must be placed close to the transmitter coil ) Etc.))) The magnetic field caused by the induced current is a significant noise source in the exploration of metal mineral resources (eg, submarine hydrothermal deposits) existing under the seabed.

  The present embodiment relates to a seafloor exploration system having both the advantages of the fixed type and the mobile type.

  FIG. 2 is an explanatory diagram of the seafloor exploration system according to the present embodiment.

(Submarine exploration system)
The seafloor exploration system of the embodiment includes a ROV 10 as a submersible moving body and a towing body 20 towed underwater by the ROV 10 via a towline 12.

  The ROV 10 transmits and receives information to and from the survey mother ship 2 traveling on the sea via a cable, and is remotely operated by an operator who boarded the survey mother ship 2. In addition, as the diving type mobile body of the present embodiment, in addition to such a remote control type mobile body, for example, an AUV or a submersible type mobile body on which an occupant rides and steers can be used as necessary. Good.

  FIG. 3 schematically shows the towed body 20 and the electromagnetic exploration device 60 mounted on the towed body 20. The towing body 20 is provided with the transmission coil 100 and the reception unit 110 of the electromagnetic exploration device 60.

(Towing body 20)
9 and 10 show a specific configuration of the towed body 20 of the present embodiment. The towed body 20 of the present embodiment has a first base plate 30 and a second base plate 36 that are square, and the first and second base plates 30 and 36 are provided at four corners. The columns 34 are fixed to each other at a predetermined interval.

  The first base plate 30 is provided with four legs 32 around the first base plate 30. The first base plate 30 is horizontally installed on the floor surface with a predetermined distance by the four legs 32 while being installed on the floor surface. It is arranged.

  A plurality of pressure-resistant containers 22 and a light camera unit 23 are fixed on the upper surface of the second base plate 36, and various components are accommodated in each pressure-resistant container 22. In particular, in the present embodiment, main circuit members such as a power source of the electromagnetic exploration device 60 are accommodated. Further, the light camera unit 23 shoots the traveling direction of the towed body 20 while illuminating with a light as shown in FIG. 3, and the shooting signal is transmitted to the ROV 10 side by a cable (not shown) arranged along the towline 12. Is done. Various controls such as the photographing direction of the light camera unit 23 are executed by control signals from the ROV 10 side.

  Four horizontal blades 40-1, 40-2, 40-3, and 40-4 are rotated upward along the four sides of the first base plate 30 as stabilizers in the horizontal direction. It is mounted and fixed freely.

  Each of the horizontal blades 40-1, 40-2, 40-3, 40-4 is formed in an elongated plate shape, and the inner end side thereof is freely rotatable to the end surface side of the base plate 30 by a rotation support member. It is fixed and attached to.

  On the second base plate 36, a vertical rod 48 is erected upward from the central portion thereof, and the cylindrical body 50 is fitted into the vertical rod 48 so as to be slidable in the axial direction. Has been.

  Around the cylindrical body 50, one end sides of four support arms 52-1, 52-2, 52-3, 52-4 are rotatably attached and fixed.

  The other end sides of the support arms 52-1, 52-2, 52-3, 52-4 are rotated to the surface sides of the corresponding horizontal blades 40-1, 40-2, 40-3, 40-4. It is attached and fixed freely.

  These four horizontal blades 40-1, 40-2, 40-3, 40-4 are normally fixed in a state of being horizontally deployed as shown in FIG. 9 by their own weight. For example, when transporting or storing a towed body, these four horizontal wings 40-1, 40-2, 40-3, 40-4 are configured to be folded and stored as shown in FIG. Yes.

  When the four horizontal blades 40-1, 40-2, 40-3, 40-4 are folded and stored, the cylindrical body 50 is slid toward the upper end side of the vertical lot 48, and the support arm 52-1, The horizontal blades 40-1, 40-2, 40-3, 40-4 are pulled upward by 52-2, 52-3, 52-4 and rotated to the position shown in FIG.

  As shown in FIG. 9, when the horizontal blades 40 are deployed horizontally, this state is maintained by a lock mechanism (not shown), and the horizontal blades 40 are stored as shown in FIG. The movement of the cylinder 50 is restricted by a lock mechanism (not shown) so as to maintain this state.

  Then, the towed body 20 is held by a holding mechanism (not shown) of the ROV 10 in a state where the horizontal wings 40 are housed as shown in FIG. 10, is transported in the sea, and reaches the given measurement region. And towed by the towline 12 as shown in FIG.

  Also, as a vertical stabilizer, a relatively large vertical tail 42 is erected on the horizontal blade 40-1 located on the rear side of the four horizontal blades, and the horizontal blades 40 on both the left and right sides. -3 and 40-4 are provided with vertical tails 42-3 and 42-4 in the traveling direction.

  As a result, when the towed body 20 moves in the direction of the arrow in the drawing, that is, in the forward direction, the vertical tails 42-1, 42-2, 42-3, 42-4 function as stabilizers, This means that the movement is performed stably.

  In addition, an arc-shaped cover 46 is attached to the front side of the second base plate 36, and when the towed body 20 moves forward, the cover 46 reduces water resistance in the traveling direction. In addition, the towed body 20 can be moved smoothly.

  A transmission coil 100 is attached and fixed to the tip side of the four horizontal blades 40-1, 40-2, 40-3, 40-4, and is positioned so as to surround the transmission coil 100. The receiving coil 110-1 as the receiving unit 110 is attached and fixed.

  As a result, as shown in FIG. 9, in the state where the four horizontal blades 40-1, 40-2, 40-3, 40-4 are deployed horizontally, the transmission coil is positioned outside the first base plate 30. 100 is disposed, and in the vicinity of the transmission coil 100, the reception coil 110-1 that functions as a reception unit is disposed.

(Towing rope 12 etc.)
In the towed body 20 of the present embodiment, one end side of the tow rope 12 is attached and fixed to the front end side of the vertical lot 48 and towed by the ROV 10 as shown in FIG. 3 or FIG.

Here, a wire having a given strength may be used as the towline 12, and the ROV 10 is provided with a winch 24 as an adjusting unit for adjusting the distance from the towed body 20. . And by winding up the towline 12 with the winch 24, the length of the towline 12 is adjusted as shown in FIG. 11, for example, and the distance between the ROV 10 and the towed body 20 can be adjusted. Yes.

  For example, as shown in FIG. 11, when the ROV 1010 is moving along the seabed, the towline 12 is elongated so that the distance between the towed body 20 and the seabed is reduced. By controlling 12 to be short, the distance between the towed body 20 and the seabed can be controlled to be large.

  In addition, one end side of the tow rope 12 is supported in the ROV 10 via a rotary joint (not shown), so that the towed body 20 can be stabilized even if the relative position of the ROV 10 and the towed body 20 in water changes. It is configured to be towed. That is, the towed rope 12 is pulled without difficulty by the rotary joint in the direction in which the towed body 20 is located, which is the direction in which the towed rope 12 is tensioned, and the towed body 20 can be towed stably. Become.

  In addition, the ROV 10 has the front light camera units 26-1 and 26-2, the multi-beam sonar unit 27, and the towed body so that the towed body 20 can be towed and the seafloor can be searched smoothly. A front light camera unit 28 is provided.

  The light camera units 26-1 and 26-2 are configured to capture a moving direction image with a camera while illuminating the front of the ROV 10 with a light. For example, as illustrated in FIG. 11A, the ROV 10 moves. The state of the seabed in the direction can be photographed and viewed on a monitor. FIG. 11B is an image when the submarine hydrothermal deposit chimney group is in the traveling direction.

  When conducting electromagnetic exploration of the seabed, there are many terrain rich in undulations such as mounds and chimneys in the seabed that is the exploration area. Therefore, for efficient exploration, it is important to conduct the exploration while monitoring the seabed topography using the ROV light camera units 26-1, 26-2 and the like.

  In addition, the multi-beam sonar unit 27 can search for the undulations of the sea floor using the multi-beam sonar and accurately grasp the topography of the sea floor as a measurement region.

  The towed body forward light camera unit 28 illuminates the towed body 20 to which the ROV 10 is towed, and is used to photograph the towed state of the towed body 20 from a camera mounted on the ROV 10 to make the seabed exploration smooth.

(Electromagnetic exploration device 60)
FIG. 4A is a side view schematically showing the arrangement of the electromagnetic exploration device 60 according to the present embodiment, and FIG. 4B schematically shows the arrangement of the electromagnetic exploration device 60 of the present embodiment. It is a top view.

  FIG. 5 shows a functional block diagram of the electromagnetic exploration device 60 of the present embodiment. The electromagnetic exploration device 60 of the present embodiment includes a transmission coil 100, a transmission current supply source 120, a reception unit 110, The measurement unit 130, the analysis unit 140, and the control unit 150 are included.

  The transmission coil 100 is configured as a coil through which the transmission current I1 output from the transmission current supply source 120 flows. The cable constituting the transmission coil 100 may be covered with an insulating film. As a result, it is possible to cause an induced current to flow under the seabed with the transmission coil 100 and seawater insulated. In the example shown in FIGS. 4B and 9, the number of turns of the transmission coil 100 is one, but the number of turns may be plural.

In the present embodiment, the coil surface of the transmission coil 100 may be disposed to face the seabed. The arrangement where the coil surface and the seabed face each other is such that the seabed exists in the normal direction of the coil surface.

  In the example shown in FIG. 4A and FIG. 9, the transmission coil 100 is disposed on the lower side of the pressure vessel 22 (side near the seabed to be searched).

  In the present embodiment, a transmission current supply source 120, a measurement unit 130, and an analysis unit 140 are accommodated in the pressure vessel 22.

  According to the present embodiment, since the induced current generated by the transmission coil 100 spreads in the depth direction below the seabed, the electrical property at a deep position below the seabed can be explored.

  The transmission current supply source 120 supplies a transmission current to the transmission coil 100. In the present embodiment, the transmission current supply source 120 repeats a state in which the transmission current I1 is supplied to the transmission coil 100 and a state in which the transmission current I1 is cut off. After the transmission current I1 is supplied to the transmission coil 100, the transmission current I1 is cut off, thereby generating an induced current around the transmission coil 100. The transmission current I1 output from the transmission current supply source 120 may be, for example, about several tens of amperes to several hundreds of amperes according to the purpose of exploration.

  The receiving unit 110 detects the amount of change (time differentiation) of the magnetic field or the magnitude of the magnetic field itself. In the present embodiment, the receiving unit 110 includes a receiving coil 110-1 that detects the amount of change (time differentiation) of the magnetic field. In the present embodiment, the reception coil 110-1 is provided so that the coil surface of the reception coil 110-1 and the coil surface of the transmission coil 100 are parallel to each other. In the example shown in FIG. 4B and FIG. 9, the number of turns of the receiving coil 110-1 is one, but the number of turns may be plural. The receiving unit 110 may include a receiving magnetic field sensor 110-2 that detects the magnitude of the magnetic field itself. In the example shown in FIG. 4, the reception magnetic field sensor 110-2 is provided near the center of the coil surface of the reception coil 110-1.

  As shown in FIG. 4B, in this embodiment, the transmission coil 100 is disposed so as to surround the pressure-resistant container 22 serving as a metal element in a plan view, and the reception coil 110- is surrounded so as to surround the transmission coil 100. 1 is arranged. Note that the reception coil 110-1 may be arranged so as to overlap the transmission coil 100. Moreover, the receiving coil 110-1 may be arrange | positioned inside the transmission coil 100 as needed.

  The measurement unit 130 measures a transient response after the transmission current I1 is interrupted, which is included in the change over time of the magnetic field detected by the reception coil 110-1. In particular, it is preferable to measure the change in the magnetic field over time immediately after the transmission current supply source 120 switches from the state in which the transmission current I1 is supplied to the transmission coil 100 to the state in which the transmission current I1 is cut off.

  According to the present embodiment, since the induced current generated by the transmission coil 100 flows below the seabed, the transient response after the interruption of the transmission current I1 included in the change over time of the magnetic field detected by the reception coil 110-1. By measuring, the electrical properties under the seafloor can be explored. That is, according to the present embodiment, time domain electromagnetic exploration on the sea floor can be performed. The electromagnetic exploration device 60 can also be applied when performing electromagnetic exploration in the frequency domain on the sea floor.

The analysis unit 140 calculates the specific resistance under the seabed based on the transient response after the interruption of the transmission current I1 included in the change over time of the magnetic field detected by the reception coil 110-1. As will be described later, the smaller the specific resistance under the seabed, the more slowly the induced current decays, so the magnetic field caused by the induced current also slowly decays. Therefore, according to the present embodiment, the receiving coil 110-1
The specific resistance under the seabed can be calculated based on the transient response after the interruption of the transmission current I1 included in the change in the magnetic field detected with time.

  The control unit 150 controls the transmission current supply source 120 and the measurement unit 130. For example, the control unit 150 controls the timing at which the transmission current I1 is cut off, or controls the operation of the measurement unit 130 in accordance with the timing at which the transmission current I1 is cut off.

  FIG. 6 is a flowchart showing an example of the seabed exploration method using the electromagnetic exploration device 60 according to the first embodiment.

  In the example shown in FIG. 6, first, the transmission current supply source 120 supplies the transmission current I1 to the transmission coil 100, and then blocks the transmission current I1 (step S100).

  In step S <b> 100, an induced current is generated around the transmission coil 100 by cutting off the transmission current I <b> 1 after supplying the transmission current I <b> 1 to the transmission coil 100.

  7A is a timing chart of the transmission current I1, FIG. 7B is a timing chart of the counter electromotive force P generated in the transmission coil 100, and FIG. 7C is a timing of the magnetic field H generated by the transmission coil 100. It is a chart. FIG. 8 is a schematic diagram for explaining the induced current generated by the transmission coil 100. In FIG. 8, when the transmission current I1 is positive, the current flows through the transmission coil 100 in the direction of the arrow.

  First, as shown in FIG. 7A, a positive transmission current I1 is output from the transmission current supply source 120 to the transmission coil 100. Next, the transmission current I1 is suddenly cut off. As a result, as shown in FIG. 7B, an electromotive force E is generated to maintain the same magnetic field before the interruption by the law of electromagnetic induction, and an induced current is generated on the sea floor. Thereafter, a negative transmission current I1 is output from the transmission current supply source 120 to the transmission coil 100. Next, the transmission current I1 is suddenly cut off. Such an operation is repeated at a period T.

  The induced current at the bottom of the sea is attenuated in accordance with the specific resistance below the sea floor, but a new induced current is generated in the ground to prevent the change of the current. This process is repeated, and a phenomenon occurs as if the induced current 500 propagates to the induced current 501 and the induced current 502 to the deep part under the seabed.

  These induced currents attenuate according to the specific resistance of the current path formation. For this reason, it is possible to detect the attenuation of the induced current as a time change of the magnetic field as shown in FIG. 7C by using the receiving coil 110-1 disposed in the vicinity of the seabed, and to know the specific resistance under the seabed. For example, when the underground has a high resistivity, the induced current decays rapidly, but when the underground has a low resistivity, it slowly decays.

  Returning to FIG. 6, after step S100, the transient response of the magnetic field after the transmission current I1 is cut off is measured (step S102). This enables exploration of electrical properties beneath the seabed.

  After step S102, the specific resistance under the seabed is calculated based on the transient response of the magnetic field after the transmission current I1 is cut off (step S104). As described above, the smaller the specific resistance under the seabed, the slower the induced current decays, so the magnetic field caused by the induced current also slowly decays. Therefore, the specific resistance under the seabed can be calculated based on the transient response of the magnetic field after the transmission current I1 is cut off.

Although the induced current under the seabed has been described with reference to FIG. 8, induced current is also generated in seawater and metal elements based on the same principle. Since the metal element has a small specific resistance, it becomes a large noise when searching for a metal mineral resource under the seabed having a small specific resistance.

  As shown in FIG. 2 and FIG. 3, in this embodiment, the transmission coil 100 and the receiver of the electromagnetic exploration device 60 are connected to the towed body 20 separated from the ROV 10 as a metal element that greatly affects the accuracy of electromagnetic exploration. By mounting 110, the induced current generated in the ROV 10, which is a metal element that greatly affects the measurement accuracy, can be reduced, and the metal mineral resources under the water bottom can be continuously and accurately distributed along the towing path of the towed body 20. To explore.

  In particular, since the towed body 20 does not need to be equipped with power for self-propelled underwater and equipment related thereto, the structure is stably towed underwater and has the electromagnetic exploration device 60 mounted thereon. A configuration is sufficient. Therefore, since the metal elements used for the towed body 20 are much smaller than those of the ROV 10, the influence thereof is reduced to a level that can be almost ignored as compared with the conventional system in which the electromagnetic exploration device 60 is mounted on the ROV 10. The continuous and efficient electromagnetic search can be realized with the search accuracy improved to a level close to that when the device 60 is installed on the bottom of the water.

(Data acquired in actual sea area)
FIG. 12 is a graph showing an example of the response of the change rate of the magnetic field detected by the receiving coil 110-1. The horizontal axis of FIG. 12 represents the elapsed time (logarithmic scale) after the transmission current I1 is cut off, and the vertical axis represents the response of the change rate of the magnetic field (linear scale).

  In FIG. 12, data 1001 is a measurement result (system shown in FIG. 1A) when the electromagnetic exploration device 60 is installed on the seabed as shown in FIG. 1A, and data 1002 is shown in FIG. As shown in FIG. 4, the measurement result when the electromagnetic exploration device 60 is installed in the ROV 10 and the data 1003 indicate the measurement result in the system of this embodiment.

  Data 1001 is the response of the rate of change of the magnetic field detected by the receiving coil 110-1 when the electromagnetic exploration device 60 is installed on the seabed and the ROV 10 is separated from the horizontal direction by 20 m or more (in the case of the seabed and seawater). 1002 indicates that the electromagnetic exploration device 60 is installed on the ROV 10 and the response of the rate of change of the magnetic field detected by the receiving coil 110-1 at an altitude of 600 m (in the case of seawater only) from the seabed. The response of the rate of change of the magnetic field detected by the receiving coil 110-1 when the towed body 20 is towed by the ROV 10 at a height of 100 m from the seabed (only in the case of seawater).

  As shown in FIG. 12, the rate of change in the magnetic field of data 1002 is attenuated more slowly than that of data 1001. This is because an induced current is generated in the ROV 10 which is a large metal element. On the other hand, in the data 1003, the influence of the induced current generated in the ROV 10 serving as the metal element is reduced and approaches the data 1001. The difference between the slopes of the waveforms of data 1001 and data 1003 is that data 1001 is a response to the rate of change of the magnetic field due to the induced current generated in the seabed and seawater, and data 1003 is the induced current generated only in seawater. This is because the response is due to the change rate of the magnetic field caused by.

  As described above, according to the system of the present embodiment, it has been clarified that the influence caused by the induced current generated in the metal element can be reduced, and a seafloor exploration apparatus capable of accurately searching for a metal mineral resource under the seafloor can be realized.

That is, the difference between the data 1003 and 1002 is a noise component of the ROV 10 as a large metal element, and the towed vehicle in which the transmitting coil 100 and the receiving unit 110 of the electromagnetic exploration device 60 are separated from the ROV 10 as in the present embodiment. It was clarified that the electromagnetic exploration system that can significantly reduce this noise component and can accurately explore the metal mineral resources under the seabed can be realized by providing it on the 20 side.

(Electromagnetic exploration of the sea floor using an electromagnetic exploration system)
Next, a specific example in the case where the sea bottom electromagnetic survey is performed using the electromagnetic survey system of the present embodiment will be described with reference to FIG.

  First, as shown in FIG. 13A, an electromagnetic survey line 2000 is set on the survey region of the seabed 4000. Here, the electromagnetic survey line 2000 has a total length of 1000 m. Then, along this electromagnetic survey line 2000, a total of 500 measurement points A, B, C... Are set at intervals of 2 m.

  Then, the measurement along the electromagnetic survey line 2000 is performed using the electromagnetic survey system of the present embodiment.

  First, as shown in FIG. 13B, the towed body 20 is towed along the electromagnetic survey line 2000 using the ROV 10. And it searches using the winch 24, adjusting the length of the towline 12 in the range of 3-10 m.

  In this embodiment, the towed body 20 is moved at a predetermined speed along the electromagnetic survey line 2000 while adjusting the length of the towed cable 12 so that the distance of the towed body 20 from the seabed is about 4 m. . Here, it shall move at a speed of 0.5 m / s.

  Thereby, the measurement of 500 points along the electromagnetic survey line 2000 can be completed in about 33 minutes.

  As described above, according to the system of the present embodiment, the influence of the ROV 10 as a large metal element can be reduced, and the electromagnetic exploration can be repeatedly performed while moving along the electromagnetic exploration survey line 2000 at a given speed. Therefore, it is possible to efficiently perform highly accurate submarine electromagnetic survey.

  As mentioned above, although this embodiment was described, this invention is not limited to these this embodiment, In the range which does not deviate from the summary, it is possible to implement in various aspects.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

  For example, in the above-described embodiment, the electromagnetic exploration device 60 itself is disposed on the towed body 20, but members other than the transmission coil 100 and the receiving unit 110 may be provided at a place other than the towed body 20 as necessary, for example, the ROV 10. May be provided.

  For example, a power source unit of an electromagnetic exploration apparatus that becomes one of noise sources during electromagnetic exploration may be arranged in the ROV 10 as necessary, and current may be supplied from the ROV 10 side to the transmission coil.

Further, a gyro may be arranged on the towed body 20, and the measurement data of the electromagnetic exploration device 60 may be stored together with the measurement data of the gyro and analyzed. Accordingly, since the attitude of the electromagnetic exploration device 60 is obtained from the detected attitude of the towed body 20, the range is measured while accurately recognizing the change in the exploration range caused by the attitude at each measurement point. It is possible to improve the reliability of measurement data.

Further, as the receiving unit 110, a plurality of electrodes, preferably three or more electrodes, are provided around the transmission loop, and a transient after a transmission current interruption included in a change with time of a potential difference between two of the plurality of electrodes. You may employ | adopt the structure which measures a response.
Moreover, it can be widely used not only for the bottom of the sea but also for the bottom of a lake such as a lake.

10 ... ROV,
20 ... Towing body,
22 ... pressure vessel,
24 ... Towing rope winch,
26 ... Camera light unit,
27 ... Multi-beam sonar unit,
42, 44-3, 44-4 ... vertical tail,
60 ... Submarine exploration device,
DESCRIPTION OF SYMBOLS 100 ... Transmission coil, 120 ... Transmission current supply source, 110 ... Reception part, 110-1 ... Reception coil, 110-2 ... Reception magnetic field sensor, 130 ... Measurement part, 140 ... Analysis part, 150 ... Control part, 500,501 , 502 ... induced current, 1001, 1002, 1003 ... data,
2000 ... Electromagnetic exploration side line,

Claims (11)

A submersible moving body that moves underwater in water,
A towed body towed underwater by the submersible moving body through a towline;
An electromagnetic exploration device in which a transmitting coil and a receiving unit are arranged on the towing body;
Including
The electromagnetic exploration device
The transmission coil is
With the towed body being towed, the transmission loop is disposed on the towed body so as to face the bottom of the water,
The receiver is
Arranged around the transmission coil;
A current is passed through the transmission coil to generate a magnetic field toward the bottom of the water, and an electromagnetic wave caused by an electromagnetic induction phenomenon generated at the bottom of the water by rapidly interrupting the current is received by the receiving unit.
Underwater electromagnetic exploration system. In claim 1,
The towed body includes
A stabilizer is provided to stabilize the attitude during towing.
Underwater electromagnetic exploration system. In claim 1 or 2,
The towed body is
The submersible moving body supports one end portion side of the towing rope via a rotary joint, and performs the towing with the other end side of the towing rope in an arbitrary towing direction.
Underwater electromagnetic exploration system. In any one of Claims 1-3,
The submerged moving body is:
Including an adjusting unit for adjusting the length of the towing line,
Underwater electromagnetic exploration system. In any one of Claims 1-4,
The electromagnetic exploration device
Repeating the measurement during the towing,
Underwater electromagnetic exploration system. In any one of Claims 1-5,
A detection unit for detecting the positional relationship with the bottom of the water is provided in the submersible moving body or the towing body,
Underwater electromagnetic exploration system. In any one of Claims 1-6,
The towed body is
Including a detector for detecting the attitude of the towed vehicle,
Underwater electromagnetic exploration system. In any one of Claims 1-7,
The electromagnetic exploration device
A receiving coil as the receiving unit,
At least during the towing,
The receiving coil is arranged so as to overlap the transmitting coil or surround the transmitting coil in a plan view.
Underwater electromagnetic exploration system. In any one of Claims 1-7,
The electromagnetic exploration device
A magnetic field sensor as the receiving unit,
At least during the towing,
The transmission coil is disposed so as to surround the magnetic field sensor in a plan view.
Underwater electromagnetic exploration system. A submersible moving body that moves underwater in water,
A towed body towed underwater by the submersible moving body through a towline;
An electromagnetic exploration device in which a transmitting coil and a receiving unit are arranged on the towing body;
Including
The transmission coil is
With the towed body being towed, the transmission loop is disposed on the towed body so as to face the bottom of the water,
The receiver is
An underwater electromagnetic exploration method using an underwater electromagnetic exploration system disposed around the transmission coil,
A towing step of towing the towed body in water along a given measurement line with the submerged moving body;
During the towing, a current is caused to flow through the transmission coil to generate a magnetic field toward the bottom of the water, and the current is suddenly interrupted to receive an electromagnetic wave caused by an electromagnetic induction phenomenon generated at the bottom of the water at the receiving unit. An underwater electromagnetic exploration method including repeated measurement steps. In claim 10,
In the towing process,
A water bottom electromagnetic exploration method including a step of maintaining a positional relationship between a water bottom and the towed body in a given state during the towing.