Seabed structure survey system

Abstract

We provide a seabed structure survey system that can efficiently investigate the seabed structure. [Solution] The seabed structure survey system 100 includes an underwater speaker 1 that is placed underwater and emits sound wave vibrations toward the seabed SF, a vibration receiving unit 31 that receives vibrations corresponding to the sound wave vibrations from the seabed SF, and a speaker control unit that controls the underwater speaker 1.

Description

【Technical Field】 【0001】 The present invention relates to a submarine structure survey system. 【Background Art】 【0002】 As a system for investigating geological structures, Patent Document 1 discloses a seismic survey system. The seismic survey system includes a seismic source device that is disposed on the ground and generates vibrations by eccentrically rotating a rotating body, a signal acquisition device that acquires vibration signals based on the vibrations generated by the seismic source device, and a management device that manages the seismic source device and the signal acquisition device. The management device analyzes the geology using the vibration signals from the signal acquisition device. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2024-39369 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 On the other hand, as a system for investigating geological structures (submarine structures) in water, a method using an air gun as a seismic source device is known. In the method using the air gun, a compressor is disposed on a ship, and compressed air by the compressor is instantaneously discharged into water by the air gun to generate vibrations, and a vibration receiving unit receives the reflected wave of this vibration. 【0005】 In the method using the air gun, since it is necessary to dispose devices such as a compressor on the ship, it is necessary to use a relatively large ship to investigate the geological structure in water. Therefore, the operation of the ship is laborious, and there is a problem that the investigation of the submarine structure is inefficient. 【0006】 The present invention has been made in view of the above problems, and provides a submarine structure survey system capable of efficiently surveying submarine structures. [Means for solving the problem] 【0007】 One aspect of the present invention provides a seabed structure survey system comprising: an underwater speaker positioned in water and emitting sound wave vibrations toward the seabed; a vibration receiving unit that receives vibrations corresponding to the sound wave vibrations from the seabed; and a speaker control unit that controls the underwater speaker. 【0008】 According to the above configuration, when investigating the seabed structure using an underwater speaker, equipment such as a compressor attached to the air gun becomes unnecessary. Therefore, the seabed structure can be investigated without operating a relatively large vessel, allowing for efficient investigation of the seabed structure. 【0009】 The system may further include an anchoring device for fixing the underwater speaker in a fixed position underwater. Here, "fixed position" means ensuring that the underwater speaker does not move from a predetermined location, or that the underwater speaker remains in a predetermined location and its surrounding area. 【0010】 According to the above configuration, the underwater speaker, which is the source of sound wave vibrations, is fixed in place underwater, thus improving the accuracy of the seabed structure survey. 【0011】 The anchoring device includes a weight that is submerged in the water together with the underwater speaker, and when the weight lands on the bottom of the water, the underwater speaker may be positioned near the bottom of the water. Here, arranging an underwater speaker near the bottom of the water means, for example, arranging the underwater speaker such that when the lower end surface of the speaker emits sound wave vibrations, the lower end surface of the speaker falls within a predetermined distance from the bottom of the water (for example, a distance less than or equal to the thickness of the underwater speaker). 【0012】 According to the above configuration, the underwater speaker, which is the source of sound wave vibrations, is placed near the seabed being investigated, thereby improving the accuracy of the seabed structure investigation. 【0013】 The anchoring device includes a weight that is submerged in the water together with the underwater speaker, and a float that provides buoyancy to the underwater speaker. When the weight lands on the bottom of the water, the underwater speaker may float in the water at a predetermined distance from the bottom of the water. 【0014】 According to the above configuration, by floating the underwater speaker in the water, it is possible to prevent the underwater speaker from sinking to the bottom due to its own weight, even if the seabed is soft. In other words, floating the underwater speaker in the water can suppress changes in the depth of the underwater speaker. Therefore, the accuracy of the seabed structure survey is improved. 【0015】 The seabed structure survey system may further include a superposition unit that continuously and repeatedly emits the sound wave vibrations of the same waveform and superimposes the waveforms of the vibrations received by the vibration receiving unit. 【0016】 According to the above configuration, the signal-to-noise ratio (S / N ratio) can be improved by superimposing the waveforms of the vibrations. This makes it possible to investigate, for example, the seabed structure in remote locations (far from the underwater speaker) where only weak vibrations can be received with a single oscillation. As a result, the investigation range can be expanded. [Effects of the Invention] 【0017】 According to the seabed structure survey system of the present invention, the seabed structure can be surveyed efficiently. [Brief explanation of the drawing] 【0018】 [Figure 1] A schematic diagram showing a seabed structure survey system according to the first embodiment of the present invention. [Figure 2] A perspective view showing an underwater speaker and weight according to the first embodiment of the present invention. [Figure 3] A cross-sectional view showing the configuration of an underwater speaker according to the first embodiment of the present invention. [Figure 4]Block diagram showing the configuration of the underwater structure survey system according to the first embodiment of the present invention. [Figure 5] Figure showing an example of the waveform of the sound wave vibration emitted by the underwater speaker according to the first embodiment of the present invention. [Figure 6] Schematic diagram showing the underwater structure survey system according to a modified example of the present invention. [Figure 7] Schematic diagram showing the underwater structure survey system according to another modified example of the present invention. 【Embodiments for Carrying Out the Invention】 【0019】 (First Embodiment) Hereinafter, referring to the accompanying drawings, the submarine structure survey system 100 (an example of an underwater structure survey system) according to an embodiment of the present invention will be described. 【0020】 As shown in FIG. 1, the submarine structure survey system 100 is used to survey the structure of the submarine SF (an example of the underwater). In this embodiment, the submarine structure survey system 100 is used for continuous monitoring of the CO2 storage layer in which CO2 (carbon dioxide) is stored in the submarine SF. By continuously monitoring the CO2 storage layer, for example, the presence or absence of CO2 leakage from the CO2 storage layer can be detected. Note that CO2 is stored in the submarine SF at a depth of, for example, 1 km from the sea floor SB. 【0021】 The submarine structure survey system 100 includes an underwater speaker 1, a vibration receiving device 3, and a control device 4. The submarine structure survey system 100 also includes an anchoring device 2 for fixing the underwater speaker 1 at a fixed point in the sea. 【0022】 (Underwater Speaker) The underwater speaker 1 is arranged in the sea and emits sound wave vibrations toward the submarine SF. In this embodiment, the underwater speaker 1 is transported to the oscillation point by a small ship SH with a gross tonnage of less than 20 tons and submerged in the sea. 【0023】 As shown in Figure 2, the underwater speaker 1 is cylindrical, with a diameter φ of 0.1 to 1 m (for example, 0.4 m) and a thickness D (length in the axial direction DX1) of 0.05 to 0.5 m (for example, 0.1 m), making it a small speaker that can be carried by one person. The underwater speaker 1 is constructed to be water-resistant and pressure-resistant, and is capable of emitting sound wave vibrations in seawater. 【0024】 As shown in Figure 3, the underwater speaker 1 comprises a bottomed cylindrical outer case 11 that is open at one end, a lid 12 that closes the open portion of the outer case 11 and forms a sealed space between itself and the outer case 11, a magnetic circuit section 13 that generates magnetic flux in the sealed space, a voice coil 14 that is movable along the axial direction DX1 of the outer case 11, a connecting member 15 connected to the voice coil 14, and a compression spring 17 positioned between the connecting member 15 and the magnetic circuit section 13. 【0025】 The outer case 11 and lid 12 are made of a heat-resistant material such as stainless steel that is resistant to deterioration over time. 【0026】 The lid portion 12 has a circular, elastically deformable diaphragm 121 when viewed along the axial direction DX1. The thickness of the diaphragm 121 (length along the axial direction DX1) is set according to the sound pressure emitted by the underwater speaker 1. In this embodiment, the underwater speaker 1 emits sound wave vibrations with a sound pressure of 150 dB to 170 dB, with a median of 160 dB. The size (diameter φ) of the diaphragm 121 is appropriately changed according to the depth of the seabed SF being investigated, the geological conditions, etc. 【0027】 The magnetic circuit section 13 includes an elastic member 130, a first yoke 131 and a second yoke 132 made of magnetic material, and a first magnet 133 and a second magnet 134 made of permanent magnets. The magnetic circuit section 13 is attached to the outer casing 11 via the elastic member 130. The second yoke 132, the first magnet 133, and the second magnet 134 are annular in shape with an axial direction DX1 as the center. 【0028】 The first yoke 131 has a cylindrical portion 131a with an axis in the axial direction DX1. The first yoke 131 also has a first flange 131b extending outward in the radial direction DR at the end of the cylindrical portion 131a furthest from the diaphragm 121, and a second flange 131c extending outward in the radial direction DR at the end closest to the diaphragm 121. 【0029】 The second yoke 132 is positioned on the outer circumference of the second flange 131c of the first yoke 131. A voice coil 14 is positioned between the second flange 131c of the first yoke 131 and the second yoke 132. 【0030】 The first magnet 133 is positioned between the first flange 131b and the second yoke 132 in the axial direction DX1. The first magnet 133 is magnetized all around, and is positioned such that the side closer to the diaphragm 121 is the south pole and the side further away from the diaphragm 121 is the north pole. 【0031】 The second magnet 134 is positioned opposite the first magnet 133 in the axial direction DX1, with the second yoke 132 in between. The second magnet 134 is magnetized all around, with the side closer to the diaphragm 121 being the north pole and the side further away from the diaphragm 121 being the south pole. 【0032】 The voice coil 14 is connected to the diaphragm 121 via a bottomed cylindrical connecting member 15. The voice coil 14 has a coil portion 141 and a bobbin portion 142 connected to the connecting member 15. The coil portion 141 is spirally configured and is positioned within the magnetic flux formed by the first magnet 133 and the second magnet 134. 【0033】 When an electrical signal is input to the underwater speaker 1 via the signal line 16, electricity flows through the voice coil 14. This causes a Lorentz force to act on the voice coil 14, and the connecting member 15 moves along the axial direction DX1 together with the voice coil 14. As a result, the diaphragm 121 vibrates, and sound wave vibrations are emitted. The compression spring 17 is positioned between the connecting member 15 and the first yoke 131 and biases the magnetic circuit section 13 toward the side away from the diaphragm 121. By biasing in this way, the underwater speaker 1 can generate vibrations even when subjected to water pressure. 【0034】 (Anchoring device) The anchoring device 2 shown in Figures 1 and 2 is formed in a frame shape and has a weight 21 that surrounds the underwater speaker 1. Although not shown, the weight 21 has multiple protruding parts that extend from the weight 21 toward the underwater speaker 1, and the underwater speaker 1 is fixed to these parts with bolts. 【0035】 The weight 21 is submerged in the sea along with the underwater speaker 1 when investigating the structure of the seabed SF. When the weight 21 lands (contacts) the seabed surface SB, the underwater speaker 1 is positioned (placed) in the vicinity of the seabed SF. In this embodiment, the underwater speaker 1 is positioned in the vicinity of the seabed SF such that its distance from the seabed SF is less than or equal to the thickness D of the underwater speaker 1, preferably less than or equal to half the thickness D, and more preferably less than or equal to one-quarter of the thickness D. 【0036】 (vibration receiving device) The vibration receiving device 3 receives reflected vibrations (an example of vibrations corresponding to sound wave vibrations) reflected by the seabed SF. As shown in Figure 4, the vibration receiving device 3 has a vibration receiving unit 31, a processing unit 32, and a vibration receiving side communication unit 33. In this embodiment, the vibration receiving device 3 is a distributed acoustic sensing (DAS) that uses an optical fiber as the vibration receiving unit 31. However, the vibration receiving device 3 is not limited to a DAS and may be an ocean bottom seismometer (OBS: Ocean Bottom Observations, OBN: Ocean Bottom Node) as described later. 【0037】 The vibration receiving unit 31 consists of a light source that emits light, an optical fiber installed on the seabed SF and through which the light emitted from the light source passes, and a light-receiving element that receives light from the optical fiber. The light-receiving element receives scattered light caused by vibrations applied to the optical fiber and outputs a signal (electrical signal). The optical fiber is installed along the seabed surface SB, as well as along the depth direction. 【0038】 The processing unit 32 consists of a CPU (Central Processing Unit) or MPU (Micro Processing Unit) that works in cooperation with the software to realize predetermined functions. The processing unit 32 outputs a signal indicating reflected vibration based on the signal output from the vibration receiving unit 31 (photodetector). The processing unit 32 may also include a storage area such as semiconductor memory and store the aforementioned software, the signal indicating reflected vibration (data indicating reflected vibration), etc. 【0039】 The vibration-receiving communication unit 33 is composed of, for example, a communication circuit and communicates with the control device 4 using a communication standard such as Ethernet or Wi-Fi (registered trademark). The vibration-receiving communication unit 33 transmits a signal indicating reflected vibration acquired by the processing unit 32 to the control device 4. In this embodiment, the vibration-receiving communication unit 33 transmits a signal indicating reflected vibration to the control device 4 in real time. 【0040】 (Control device) The control device 4 has a control-side communication unit 41, a control unit 42, and an output unit 43, and is installed on the ship SH. The output unit 43 is, for example, a display. The control device 4 is an information processing terminal, such as a personal computer, and in addition to the control-side communication unit 41, the control unit 42, and the output unit 43, it has an input unit (not shown) which is a component of an information processing terminal. The input unit consists of a touch sensor, a keyboard, etc., and accepts user input. 【0041】 The control-side communication unit 41 is composed of a communication circuit and communicates with the vibration receiving device 3 using a communication standard that is compatible with the vibration receiving-side communication unit 33. The control-side communication unit 41 receives signals indicating reflected vibrations transmitted from the vibration receiving-side communication unit 33 of the vibration receiving device 3. In this embodiment, the control-side communication unit 41 and the vibration receiving-side communication unit 33 communicate wirelessly. 【0042】 The control unit 42 is composed of a CPU or MPU that works in cooperation with the software to realize predetermined functions, and functions as a speaker control unit 421 and a superposition unit 422. The control unit 42 includes a storage area such as semiconductor memory, and stores the aforementioned software, signals (data) received from the vibration receiving device 3, data necessary to vibrate the underwater speaker 1, etc., in the storage area. 【0043】 The control unit 42 is connected to the underwater speaker 1 by a wire (a linear member 22, such as a rope, as shown in Figure 1). The speaker control unit 421 causes the underwater speaker 1 to oscillate by supplying an electrical signal to it. The speaker control unit 421 supplies the electrical signal to the underwater speaker 1 via the linear member 22 (see Figure 1) connected to the signal line 16 of the underwater speaker 1. 【0044】 The speaker control unit 421 can change the frequency of the sound wave vibrations emitted by the underwater speaker 1. In this embodiment, the speaker control unit 421 causes the underwater speaker 1 to emit sound wave vibrations at a frequency selected from among frequencies between 10 Hz and 10,000 Hz. By setting the frequency in this way, the attenuation of vibrations is suppressed. 【0045】 The speaker control unit 421 causes the underwater speaker 1 to oscillate a chirp signal (sine wave) whose frequency changes over time as a sound wave vibration. In this embodiment, the speaker control unit 421 causes the underwater speaker 1 to oscillate a down chirp signal whose frequency decreases over time. 【0046】 The speaker control unit 421 continuously repeats the same waveform at each chirp period T, causing the underwater speaker 1 to oscillate (see Figure 5). The same waveform refers to a waveform that is substantially identical, meaning that the frequency change per unit time is the same or similar, and the amplitude is the same or similar. The number of oscillations is determined according to the depth and geology of the seabed SF being investigated. 【0047】 The stacking unit 422 stacks the continuously oscillating reflected vibrations based on the signal indicating the reflected vibration received from the vibration receiving device 3. More specifically, the stacking unit 422 adds up multiple waveforms for each chirp period T, aligning their oscillation start times on the time axis. 【0048】 For example, the superposition unit 422 superimposes multiple waveforms such that the oscillation start time P1 of the first waveform V1, which shows reflected vibration as shown in Figure 5, matches the oscillation start time P2 of the second waveform V2, thereby superimposing the first waveform V1 and the second waveform V2. The superposition unit 422 outputs the result of superimposing the multiple waveforms via the output unit 43. The control unit 42 cross-correlates the signal from the vibration receiving device 3 (superimposed waveform) with the emitted waveform from the speaker control unit 421. This makes it possible to obtain a record similar to that obtained when an impulsive waveform is emitted from the underwater speaker 1. The control unit 42 may also analyze the structure of the seabed SF based on the superimposed result and output the result of the analysis of the seabed SF structure via the output unit 43. 【0049】 (Methods for conducting seabed surveys) The investigation of the structure of the seabed SF using the aforementioned seabed structure investigation system 100 is carried out as follows. First, the ship SH equipped with the underwater speaker 1 heads toward a predetermined oscillation point (CO2 reservoir), and the underwater speaker 1, which is fitted with an anchoring device 2, is positioned underwater with controlled location. 【0050】 After the underwater speaker 1 is positioned, it is made to perform an oscillation operation, which involves repeatedly emitting sound wave vibrations of the same waveform. The oscillation operation is started when the operator inputs an operation to the control device 4 to instruct it to perform the oscillation operation. The number of oscillations is determined according to the depth, geology, etc. of the area being investigated, as described above. 【0051】 After the oscillation operation is completed, the underwater speaker 1 is retrieved by the ship SH, which then moves the underwater speaker 1 to the next oscillation point. At the next oscillation point, the underwater speaker 1 is made to perform the oscillation operation again. In this way, the underwater speaker 1 is repeatedly made to perform the oscillation operation in the area covering the CO2 reservoir. By analyzing the reflected waves (superimposed reflected waves) obtained from the repeated oscillation operations of the underwater speaker 1 in the area covering the CO2 reservoir, the CO2 reservoir can be continuously monitored. 【0052】 (Effects of the first embodiment) Air guns used in marine surveys require large-scale equipment such as compressors. On the other hand, when investigating the structure of seabed SF using the underwater speaker 1 according to the above embodiment, equipment such as compressors attached to the air gun is unnecessary. Therefore, the structure of seabed SF can be investigated without operating relatively large vessels, allowing for efficient investigation of the seabed structure. 【0053】 Furthermore, as mentioned above, air guns require a compressor, and towing a hydrophone array several kilometers long necessitates the use of large vessels for oceanographic surveys, resulting in high costs and making them unsuitable for continuous (high-frequency) surveys of seabed structures. On the other hand, as mentioned above, underwater speaker 1 is small, eliminating the need for large vessels and keeping costs down, thus making it applicable to continuous (high-frequency) surveys of seabed structures. 【0054】 Furthermore, because air guns emit sound wave vibrations with high energy instantaneously (for example, sound pressure exceeding 200 dB), there are concerns about their impact on the environment, such as fisheries and marine life (environmental burden). On the other hand, the underwater speaker 1 according to this embodiment emits sound wave vibrations with a sound pressure of about 160 dB, thus suppressing the impact on the environment, such as fisheries and marine life, and reducing the environmental burden. Moreover, the underwater speaker 1 according to this embodiment is small and consumes less power than when using an air gun, thus contributing to energy saving. 【0055】 Furthermore, because the diaphragm 121 (vibrating surface) of the underwater speaker 1 vibrates, vibrations can be efficiently generated in seawater, and vibrations (sound wave vibrations) from the underwater speaker 1 are transmitted to the seabed SF more reliably. 【0056】 According to the above embodiment, the underwater speaker 1 is fixed to the seabed SF (fixed point) by the anchoring device 2. In other words, since the underwater speaker 1, which is the source of sound wave vibrations, is fixed in place underwater, the accuracy of the investigation of the structure of the seabed SF is improved. In particular, in the above embodiment, the position of the underwater speaker 1, which is the source of sound wave vibrations, is placed near the seabed SF that is the target of the investigation, so the accuracy of the investigation of the structure of the seabed SF is improved. 【0057】 Furthermore, according to the above embodiment, the superposition unit 422 of the control device 4 superimposes the waveforms of vibrations received by the vibration receiving unit 31. In other words, it can amplify the vibrations received from the vibration receiving device 3. This makes it possible to improve the signal-to-noise ratio (S / N ratio). For example, it becomes possible to investigate the structure of seabed SFs in distant locations (far from the underwater speaker 1) where only weak vibrations can be received with a single oscillation. As a result, the investigation range can be expanded. 【0058】 Furthermore, as described in the above embodiment, since the seabed structure survey system 100 uses optical fibers as the vibration receiving unit 31, reflected vibrations from multiple locations can be acquired in real time, and spatial resolution can also be improved. In addition, since the optical fibers used as the vibration receiving unit 31 are part of existing infrastructure, the installation work of the vibration receiving device 3 and the collection of data showing the acquired reflected vibrations are easier compared to, for example, using a seabed seismometer, and costs can be reduced. 【0059】 (modified version) In the above embodiment, the control device 4 was mounted on the ship SH, but it may be located on land. If such a change is made, the control device 4 may wirelessly control the underwater speaker 1. 【0060】 In the above embodiment, the vibration receiving device 3 was fixed in place by a weight 21 placed on the seabed SB, but the method of fixing the underwater speaker 1 can be appropriately changed depending on the seabed environment (for example, the degree of softness of the seabed ground). For example, as shown in Figure 6, the anchoring device 2 may further have a float 23 that provides buoyancy to the underwater speaker 1. In this case, when the weight 21 lands (contacts) the seabed SB, the underwater speaker 1 will have a distance from the seabed SB and float in the sea. The float 23 may be connected indirectly (for example, via a linear member 22) or directly to the underwater speaker 1. Furthermore, when the underwater speaker 1 is to float in the water, the weight 21 and the ship SH may be directly connected by a linear member 22, as shown in Figure 7. By making the underwater speaker 1 float in the water, it is possible to avoid the underwater speaker 1 sinking to the seabed SF by its own weight even if the seabed SB is soft. In other words, the depth change of underwater speaker 1 can be suppressed. Therefore, the accuracy of investigating the structure of the seabed SF is improved. 【0061】 Furthermore, the vessel SH described in the above embodiment may have a solar panel P that generates electricity from sunlight, and the vessel SH may supply the power generated by the solar panel P to the underwater speaker 1 via the linear member 22. As described above, since the power consumption of the underwater speaker 1 is small, long-term monitoring becomes possible with the power generated by the solar panel P. The vessel SH may also have a battery system B (secondary battery) that stores the power generated by the solar panel P, and the power (signal) stored in the battery system B may be supplied to the underwater speaker 1. This makes it possible for the underwater speaker 1 to continuously emit sound wave vibrations for a long period of time. 【0062】 Furthermore, the vessel SH may also have a GPS time server G (GPS antenna) for acquiring the time, and the speaker control unit 421 may determine a trigger for emitting sound wave vibrations from the underwater speaker 1 by referring to the time on the GPS time server G. 【0063】 Furthermore, the vessel SH described in the above embodiment may be a manned vessel or an unmanned submersible. If the vessel SH is an unmanned submersible, the underwater speaker 1 can continuously emit sound wave vibrations at the same location for a long period of time. 【0064】 Furthermore, although the above embodiment described a case where the vibration receiving device 3 (processing unit 32) is an optical fiber distributed vibration sensor, the vibration receiving device 3 may be a seismometer other than an optical fiber distributed vibration sensor (a seabed seismometer). If the vibration receiving device 3 is composed of the aforementioned seismometer, the seabed structure survey system 100 may be equipped with multiple vibration receiving devices 3, and each of the multiple vibration receiving devices 3 may receive reflected vibrations at multiple locations. This makes it possible to construct a three-dimensional geological model. In addition, reflected vibrations at multiple locations may be received by moving one vibration receiving device 3. Furthermore, the vibration receiving device 3 may be an ocean bottom cable seismometer (OBC). 【0065】 In this embodiment, a case was described in which one underwater speaker 1 moves sequentially to multiple locations and emits sound wave vibrations at each location. However, multiple underwater speakers 1 may be placed at multiple locations to emit sound wave vibrations. In addition, the underwater speaker 1 may emit sound wave vibrations at only one location, rather than at multiple locations. 【0066】 Furthermore, although the above embodiment described a case in which a down chirp signal is emitted as the sound wave vibration emitted from the underwater speaker 1, the underwater speaker 1 may also emit an up chirp signal whose frequency increases over time. In addition, the underwater speaker 1 may emit sound wave vibrations that exclude frequencies that are averse to marine organisms (fish, mammals, etc.) living in water. Moreover, the underwater speaker 1 may emit sound wave vibrations other than chirp signals, such as pseudo-random waves. 【0067】 In the above embodiment, the overlapping section 422 overlapped the signal indicating reflected vibration received from the vibration receiving device 3, that is, the reflected wave. However, the overlapping section 422 may also overlap refracted waves, surface waves, etc., other than reflected waves. 【0068】 In the above embodiment, the waveforms of reflected vibrations were superimposed, but for example, in investigations at locations close to the underwater speaker 1, it is not necessary to superimpose the waveforms of reflected vibrations. 【0069】 In the above embodiment, the polymerization unit 422 output the result of polymerization of multiple waveforms via an output unit 43 such as a display, but the control unit 42 may output the polymerization result to an external device via a control-side communication unit 41. Alternatively, the control unit 42 may analyze the structure of the seabed SF based on the polymerization result and output the result of the analysis of the seabed SF structure. 【0070】 In the above embodiment, the speaker control unit 421 and the overlapping unit 422 were implemented by the control device 4, but the speaker control unit 421 and the overlapping unit 422 may be implemented by different devices. Also, the processing unit 32 of the vibration receiving device 3, the speaker control unit 421 and the overlapping unit 422 may be implemented by a single control device 4, or they may each be implemented by different devices. 【0071】 In the above embodiment, a weight 21 was described as an example of the anchoring device 2, but the anchoring device 2 may be a submersible equipped with an underwater speaker 1. 【0072】 In the above embodiment, the underwater speaker 1 was placed in seawater, but the underwater speaker 1 may also be placed in water other than seawater, such as a lake or river, and the underwater speaker 1 may be placed at the bottom of a lake or the bottom of a river. 【0073】 In the above embodiment, a case in which the seabed structure survey system 100 is used for monitoring CO2 reservoirs was described, but the seabed structure survey system 100 can also be used to survey seabed structures other than CO2 reservoirs. [Explanation of Symbols] 【0074】 1. Underwater speaker 2. Anchoring device 3 Vibration receiver 4. Control device 11 Outer case 12 Lid 13 Magnetic circuit section 14 Voice coil 15 Connecting Members 16 signal lines 21 Weight 22 Linear members 23 Floats 31 Receiver section 32 Processing Units 33 Receiving side communication section 41 Control side communication unit 42 Control Unit 43 Output section 100 Seabed Structure Survey System 121 Diaphragm 130 Elastic member 131 First York 131a Cylindrical part 131b First flange 131c Second flange 132 Second York 133 First Magnet 134 Second Magnet 141 Coil section 142 Bobbin section 421 Speaker Control Unit 422 Polymerization section B Battery System DR Radial direction DX1 Axial direction G GPS Time Server P Solar Panel SB Seabed surface science fiction undersea SH Ship

Claims

[Claim 1] An underwater speaker is placed in the water and emits sound wave vibrations towards the bottom of the water, A vibration receiving unit that receives vibrations corresponding to sound wave vibrations from the seabed, A speaker control unit that controls the underwater speaker and A seabed structure survey system equipped with the following features. [Claim 2] The seabed structure survey system according to claim 1, further comprising an anchoring device for fixing the underwater speaker at a fixed point underwater. [Claim 3] The anchoring device has a weight that is submerged in the water together with the underwater speaker. The seabed structure survey system according to claim 2, wherein when the weight lands on the seabed, the underwater speaker is positioned near the seabed. [Claim 4] The anchoring device includes a weight that is submerged in the water together with the underwater speaker, and a float that provides buoyancy to the underwater speaker. The seabed structure survey system according to claim 2, wherein when the weight lands on the seabed, the underwater speaker floats in the water at a predetermined distance from the seabed. [Claim 5] The underwater speaker continuously and repeatedly emits the sound wave vibrations of the same waveform. The seabed structure survey system according to claim 1 or 2, further comprising a polymerization unit that polymerizes the waveforms of reflected vibrations received by the vibration receiving unit.

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