JP2018185206A - Submarine geological exploration system, submarine geological exploration method, and submarine geological exploration program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently acquire three-dimensional data on submarine geology by using a single oscillation reception cable.SOLUTION: A submarine geological exploration system includes: a towing body 10; a single oscillation reception cable 20 which is towed by the towing body 10, and to which a plurality of underwater geophones 21 are provided; a plurality of non-blasting type oscillation sources 31, 32, 33, 41, 42, 43 which are arranged in a manner to avoid parallel array to the oscillation reception cable 20 in a planar view, and which output sound waves with waveforms different from each other; and a synthetic wave sorting part 50 for sorting synthetic waves received by the underwater geophones 21 by the waveform into the oscillation sources 31, 32, 33, 41, 42, 43.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a seafloor geological exploration system, a seafloor geological exploration method, and a seafloor geological exploration program. The present invention relates to a geological exploration system, a submarine geological exploration method, and a submarine geological exploration program.

  In conventional submarine geological exploration systems, a plurality of receiving cables (also called streamer cables) are used to increase exploration efficiency. As shown in FIG. 13, the conventional seafloor geological exploration system 100 has a survey ship 110, a plurality of vibration receiving cables 120, an air gun 130, and a wire 140 provided with a parabein 150 at the tip.

  Each vibration receiving cable 120 is provided with an underwater vibration receiver 121 at a predetermined interval. In order to ensure the S / N ratio, the vibration receiving cable 120 is long and has a length of several kilometers, and even a shallow water cable having a depth of about 10 to 20 m has a length of several hundreds of meters. Each of the vibration receiving cables 120 is wound around a winch provided in the survey ship 110 and stored in the ship. When performing seabed geological exploration, the vibration receiving cable 120 is unwound from the winch, put into the water and towed.

  The air gun 130 has an array composed of a plurality of sources, and blasts these sources at the same time (more specifically, instantaneously releases the high-pressure air stored in the chamber). Generate sound waves. In order to adjust the magnitude of the sound wave, a plurality of air guns 130 are provided as shown in FIG. These air guns 130 output sound waves having the same waveform.

  Non-Patent Document 1 describes a land exploration method on land (acoustic tomography ground exploration method) using a piezoelectric element type vibration source that oscillates a pseudo-random wave. In this method, a piezoelectric element type vibration source is disposed at the bottom of one boring hole, and a plurality of geophones are disposed in the other boring hole. Then, while the piezoelectric element type vibration source is moved upward in the borehole, the waveform propagated through the ground is observed by the geophone. According to this method, a waveform reflecting the ground structure can be obtained by calculating the cross-correlation between the oscillation wave and the received wave.

Shinichi Sugawara, “Acoustic tomography ground exploration method (1) Principle and method”, Geophysical Exploration News, Geophysical Exploration News, April 2014, No. 22, P.I. 5-6

  As described above, the conventional submarine geological exploration system uses a plurality of receiving cables in order to increase exploration efficiency. For this reason, there is a problem that the cost of the seafloor geological exploration system becomes high and the maintenance cost for repairing the vibration receiving cable also becomes high.

  In addition, since there are as many winches for storing the receiving cables as there are receiving cables, there is a problem that the survey ship is enlarged.

  Another problem is that the receiving cables are entangled under the influence of tidal currents during seabed geological exploration.

  Another problem is that it is difficult to conduct exploration in shallow water because the receiving cables tend to get entangled when the survey ship turns in shallow water.

  The present invention has been made on the basis of the above recognition, and its purpose is to provide a submarine geological exploration system and a submarine geology capable of efficiently acquiring three-dimensional data relating to the submarine geology using a single receiving cable. To provide exploration methods and submarine geological exploration programs.

The submarine geological exploration system according to the present invention is
A towed body,
A single receiving cable towed by the towed body and provided with a plurality of underwater geophones;
A plurality of non-blasting vibration sources that are arranged so as not to be arranged in parallel with each other in plan view with respect to the vibration receiving cable, and that output sound waves having different waveforms from each other,
A synthesized wave separating unit that separates the synthesized wave received by the underwater geophone into a plurality of reflected waves corresponding to the respective vibration sources;
It is characterized by providing.

In the submarine geological exploration system,
The plurality of vibration sources may be provided on an oscillation cable towed by the towing body.

In the submarine geological exploration system,
The plurality of vibration sources may be provided on a pair of oscillation cables that are towed by the towed body and spread away from each other as they move away from the towed body in plan view.

In the submarine geological exploration system,
The towing body is provided so as to project from the towing body, and is provided with an overhanging towing part having rigidity,
The plurality of vibration sources may be provided on a cable suspended from the overhanging towing unit.

In the submarine geological exploration system,
The sound wave oscillated from the vibration source is a non-pulse wave in which at least one of frequency, phase and amplitude changes continuously or randomly,
The oscillation source may oscillate the first non-pulse wave and then oscillate the second non-pulse wave by delaying by a time shorter than the oscillation time of the first non-pulse wave.

In the submarine geological exploration system,
The non-pulse wave may be a pseudo-random wave whose phase changes continuously or a sweep wave whose frequency changes continuously.

In the submarine geological exploration system,
The plurality of vibration sources may be configured by piezoelectric elements, giant magnetostrictive elements, underwater speakers, electromagnetic vibrators, or hydraulic vibrators.

In the submarine geological exploration system,
The towed body may be a ship or an underwater probe.

The seabed geological exploration method according to the present invention is:
A plurality of non-blasting sources arranged so as not to be arranged in parallel in a plan view with respect to a single receiving cable towed by a towed body output sound waves having different waveforms,
A plurality of underwater geophones provided in the geophone cable are output from the respective vibration sources, and receive a synthesized wave obtained by synthesizing a sound wave reflected from the sea bottom or a boundary between the layers,
A combined wave separation unit separates the combined wave into a plurality of reflected waves corresponding to the respective vibration sources;
It is characterized by that.

The seabed geological exploration program according to the present invention is
Computer
Sound waves with different waveforms output from multiple non-blasting sources arranged so as not to be parallel to each other in plan view with respect to a single receiving cable towed by a towed body The combined wave reflected and combined in step 1 is made to function as a combined wave separating means for separating the combined wave into a plurality of reflected waves corresponding to the respective vibration sources.

  The seafloor geological exploration system according to the present invention is provided with a plurality of non-blasting sources that output sound waves having different waveforms and are arranged in parallel with the receiving cable in a plan view, and an underwater receiving device. The combined wave received by the underwater receiver is separated into a plurality of reflected waves corresponding to each source by the combined wave separation unit. Thereby, according to this invention, the three-dimensional data concerning seabed geology can be efficiently acquired using a single receiving cable.

It is a top view which shows the outline of the seabed geological exploration system which concerns on the 1st Embodiment of this invention. 1 is a perspective view showing an outline of a seabed geological exploration system according to a first embodiment of the present invention. It is a flowchart for demonstrating the seabed geological exploration method which concerns on 1st Embodiment. 1 is a simplified diagram of a seafloor geological exploration system according to a first embodiment. (A) is a time waveform diagram of the reflected wave of the sound wave oscillated from the vibration source S1, and (b) is a time waveform diagram of the reflected wave of the sound wave oscillated from the vibration source S2. It is a time waveform figure of the synthetic wave observed with underwater geophone R1, R2, and R3. (A) is a time waveform diagram of a pulse wave corresponding to the vibration source S1, and (b) is a time waveform diagram of a pulse wave corresponding to the vibration source S2. It is a figure which shows an example of the measurement result by the seafloor geological exploration system which concerns on 1st Embodiment. It is a simplified diagram of a seafloor geological exploration system for explaining delayed oscillation. FIG. 4 is a time waveform diagram (left side) of a reflected wave of a sound wave oscillated from the vibration source S1 and a time waveform diagram (right side) of a reflected wave of a sound wave delayed from the vibration source S1. It is a time waveform figure of the synthetic wave observed with underwater geophone R1, R2, and R3. It is a top view which shows the outline of the seabed geological exploration system which concerns on the 2nd Embodiment of this invention. It is a top view which shows the outline of the conventional seabed geological exploration system.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component which has an equivalent function in each figure.

(First embodiment)
The configuration of the seabed geological exploration system 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  As shown in FIGS. 1 and 2, the seafloor geological exploration system 1 includes a towed body 10, a single receiving cable 20, a pair of oscillation cables 30 and 40, and a plurality of vibration sources 31, 32, 33, and 41. , 42, 43, and a combined wave separation unit 50.

  In this embodiment, the towed body 10 is a ship (also called a survey ship). The type and size of the survey ship are not particularly limited, but a large ship of about 10,000 to 15,000 tons may be used in an oil survey or the like.

  In addition, the towed body 10 may be an underwater probe that navigates underwater. Examples of the underwater probe include an autonomous underwater vehicle (AUV) and a remotely operated unmanned vehicle (Remotely Operated Vehicle).

  The vibration receiving cable 20 is a cable towed by the towed body 10. The vibration receiving cable 20 is provided with a plurality of underwater vibration receivers 21 for receiving sound waves. The underwater geophone 21 is, for example, a hydrophone that converts a sound pressure change into a voltage change. The plurality of underwater geophones 21 may be provided at regular intervals as shown in FIG. 1 or may be provided at irregular intervals. The distance between the underwater geophones 21 is determined in consideration of the desired horizontal resolution.

  Note that a streamer cable or a digital streamer incorporating an A / D converter may be applied as the vibration receiving cable 20 provided with the underwater vibration receiving device 21. The vibration receiving cable 20 is not limited to being directly connected to the towed body 10 but may be connected to the towed body 10 via a relatively high-density cable (lead-in section).

  The oscillation cables 30 and 40 are cables towed by the towed body 10. As shown in FIG. 1, parabein (underwater bottles) 35 and 45 are provided at the ends of the oscillation cables 30 and 40, respectively. When receiving the water flow accompanying the navigation of the towed body 10, the paravines 35 and 45 move away from the towed body 10 outward in the width direction of the towed body 10. For this reason, the pair of oscillating cables 30 and 40 expands so as to be separated from each other as they are separated from the towed body 10 in a plan view while being towed by the towed body 10. Note that the wire 140 described above may be used as the oscillation cables 30 and 40.

  As shown in FIG. 1, the plurality of vibration sources 31, 32, 33, 41, 42, and 43 are provided in a pair of oscillation cables 30 and 40 that spread in a wing shape. More specifically, the vibration sources 31, 32, and 33 are provided in the oscillation cable 30, and the vibration sources 41, 42, and 43 are provided in the oscillation cable 40.

  The arrangement of the vibration sources is not limited to the arrangement shown in FIG.

  Further, the number of vibration sources is not limited to six, and may be any number as long as it is plural. For example, only the vibration source 31 may be provided in the oscillation cable 30, and only the vibration source 41 may be provided in the oscillation cable 40. Further, a spare vibration source may be provided in the oscillation cables 30 and 40.

  Further, the plurality of vibration sources 31, 32, 33, 41, 42, and 43 may be arranged at substantially the same depth from the viewpoint of maintaining the uniformity of the data quality observed by the underwater geophone 21 (FIG. 4). reference). In other words, the depth (towing depth) of each source during towing may be substantially constant.

  The vibration sources 31, 32, 33, 41, 42, and 43 are non-blast type vibration sources, and can generate a continuous wave. These vibration sources include a piezoelectric element (piezo element), a giant magnetostrictive element, an underwater speaker, an electromagnetic vibrator, a hydraulic vibrator, or the like.

  Since the piezoelectric element, the giant magnetostrictive element, and the underwater speaker can easily control the frequency, phase, and amplitude, it is possible to output a non-pulse wave. In the present application, a “non-pulse wave” is a wave in which at least one of frequency, phase, and amplitude changes continuously or randomly. Examples of non-pulse waves include a pseudo-random wave whose phase changes continuously and a sweep wave whose frequency changes continuously. A piezoelectric element or a giant magnetostrictive element can be used as a pseudo-random wave source that oscillates a pseudo-random wave. The non-pulse wave is not limited to a pseudo-random wave or a sweep wave, and for example, music may be oscillated as a non-pulse wave from an underwater speaker.

  In addition, since the piezoelectric element, the giant magnetostrictive element, the underwater speaker, and the like oscillate sound waves having a higher frequency than the air gun, the vertical resolution (resolution in the depth direction) can be improved as compared with the air gun. For example, when the frequency of the vibration source is 200 Hz and the average speed of sound waves in the formation is 2000 m / sec, the wavelength of sound waves is 10 m. In general, the vertical resolution is ¼ of the wavelength, so the vertical resolution in this case is 2.5 m. Therefore, it is possible to identify up to 2.5 m thick formation.

  The plurality of vibration sources 31, 32, 33, 41, 42, and 43 oscillate sound waves having different waveforms. Sound waves output from each source propagate in parallel toward the seabed. For example, pseudo-random waves are used as different waveforms. This pseudo-random wave is a continuous wave generated by phase modulation based on a single-frequency sine wave. In the case of a pseudo-random wave, it has a wavelength that depends on the frequency of the sine wave by a process (cross-correlation process) that calculates the cross-correlation between the oscillation wave oscillated from the oscillation source and the oscillation wave received by the underwater geophone. A pulse wave is obtained.

  Note that the sound waves oscillated from the vibration sources 31, 32, 33, 41, 42, and 43 are not limited to pseudo-random waves as long as they have different waveforms, and non-pulse waves other than pseudo-random waves may be used.

  The sound waves having different waveforms may be oscillated simultaneously from the vibration sources 31, 32, 33, 41, 42, 43, or may be oscillated with a time difference.

  As described above, the plurality of vibration sources 31, 32, 33, 41, 42, 43 are provided on the oscillation cables 30, 40 that spread in a wing shape. For this reason, as shown in FIG. 1, a line (virtual line) connecting adjacent vibration sources is not parallel to the vibration receiving cable 20 in plan view. That is, the plurality of vibration sources 31, 32, 33, 41, 42, 43 are arranged so as not to be arranged in parallel with the vibration receiving cable 20 in plan view. Thereby, the seabed geological data can be acquired in a plane.

  From the viewpoint of the exploration area, it is most advantageous that the line connecting the vibration sources is orthogonal to the vibration receiving cable 20. On the other hand, from the viewpoint of spatial high resolution exploration, the angle at which the line connecting the vibration sources and the vibration receiving cable 20 intersect is preferably small.

  The synthesized wave separation unit 50 separates the synthesized wave received by the underwater geophone 21 into a plurality of reflected waves corresponding to the respective vibration sources 31, 32, 33, 41, 42, and 43. Here, the “synthetic wave” is a wave obtained by synthesizing the sound wave output from each source and reflected by the sea bottom or the boundary of the stratum. Since six vibration sources are provided in this embodiment, the combined wave is a wave obtained by combining six reflected waves. The synthesized wave separation unit 50 separates the synthesized wave received by the underwater geophone 21 into six reflected waves.

  More specifically, when the synthesized wave separation unit 50 receives a waveform signal of a synthesized wave received by the underwater geophone 21, the synthesized wave received by the underwater geophone 21 and the oscillation output from the source 31. A cross-correlation process for calculating a cross-correlation with the wave is performed, and a reflected wave of the oscillation wave is acquired. The cross-correlation process is similarly performed for the other sources (sources 32, 33, 41, 42, and 43). By these processes, the synthesized wave is separated into a plurality of reflected waves corresponding to each vibration source. The synthesized wave separation unit 50 performs such synthesized wave separation processing on each underwater geophone 21.

  In the present embodiment, the synthesized wave separation unit 50 is realized by a program that operates on a computer provided in the towed body 10. This computer is connected to each vibration source 31, 32, 33, 41, 42, 43 and each underwater geophone 21 and transmits a control signal to each oscillation source or waveform data received by each underwater geophone. Receive.

  The combined wave separation unit 50 may be provided in the vibration receiving cable 20 or may be provided in a land analysis station. In the former case, the synthesized wave separation unit 50 is realized by, for example, a program that operates on an IC chip constituting an A / D converter of a digital streamer. In the latter case, the synthesized wave separation unit 50 is realized by, for example, a program that operates on a computer provided in the analysis station. Note that the land computer and the towed body 10 may be connected by wireless communication to perform cross-correlation processing in real time.

<Submarine geological exploration method>
Next, the operation of the seafloor geological exploration system 1 according to the present embodiment will be described with reference to the flowchart of FIG. 3 and FIGS. In the following, for the sake of simplicity, a case where there are two vibration sources (S1, S2) and three underwater geophones (R1, R2, R3) will be described as shown in FIG. In FIG. 4, the vibration source S1 and the vibration source S2 are arranged at different positions in the direction perpendicular to the paper surface.

  The plurality of vibration sources S1 and S2 output sound waves having different waveforms (step S11). As described above, the vibration sources S1 and S2 are non-blasting sources that are arranged so as not to be parallel to the single receiving cable 20 towed by the towed body 10 in plan view.

  As shown in FIG. 4, the sound waves oscillated from the vibration sources S1 and S2 propagate toward the seabed and are reflected at the seabed and the boundary between the strata. FIG. 5A is a time waveform diagram of the reflected wave of the sound wave oscillated from the vibration source S1, and FIG. 5B is a time waveform diagram of the reflected wave of the sound wave oscillated from the vibration source S2. Fig.5 (a) and FIG.5 (b) have shown the waveform for every underwater geophone R1, R2, R3. 5 (a) and 5 (b), the t-axis of the vertical axis indicates the time (ie, depth) from when the sound wave is output from the vibration source to when it is received by the underwater receiver. The same applies to the time waveform diagrams described below for the t-axis.

  A plurality of underwater geophones R1, R2, and R3 receive a synthesized wave that is output from each of the sources S1 and S2, and is synthesized with a sound wave that is reflected on the sea floor or the boundary between the layers (step S12). In this step, the underwater geophones R1, R2, and R3 do not receive the waveforms shown in FIGS. 5A and 5B, but actually receive the synthesized wave shown in FIG. In other words, the underwater geophones R1, R2, and R3 receive waves to which the sound waves oscillated from the vibration sources S1 and S2 are added.

  Thereafter, the combined wave separation unit 50 separates the combined wave into a plurality of reflected waves corresponding to the vibration sources S1 and S2 (step S13). Specifically, the waveform signal of the synthesized wave is transmitted to the synthesized wave separation unit 50, and the synthesized wave separation unit 50 executes cross-correlation processing. As a result, the synthesized wave is separated into two reflected waves (shot recording) respectively corresponding to the vibration source S1 and the vibration source S2, as shown in FIGS. 7 (a) and 7 (b). FIG. 7A shows a time waveform diagram of a pulse wave corresponding to the vibration source S1, and FIG. 7B shows a time waveform diagram of a pulse wave corresponding to the vibration source S2.

  FIG. 8 shows an example of measurement results obtained by the seabed geological exploration system 1 according to the present embodiment. More specifically, the results obtained by navigating in the Uchiura Bay of Suruga Bay almost in the east-west direction (WE) are shown. Here, a piezoelectric element was used as the vibration source. As shown in FIG. 8, changes in the layer thickness among the sea bottom surface F1, the formation boundary surface F2, and the formation boundary surface F3 are clearly observed with high vertical resolution. In addition, the reflected wave group (region G) in the Kamo-oki group and the reflected wave (region H) at the top of the Toi-oki group are clearly observed.

  In the present embodiment, two oscillation cables 30 and 40 are provided as the oscillation cables, but the number of oscillation cables is not limited to this. The oscillation cables 30 and 40 may be towed by a towing body different from the towed body 10.

  As described above, in the seafloor geological exploration system 1 according to the present embodiment, sound waves having different waveforms oscillated from a plurality of vibration sources 31, 32, 33, 41, 42, 43 are applied to one vibration receiving cable 20. The vibration is received by the provided underwater receiver 21. Thereafter, cross-correlation processing is performed to separate the synthesized wave received by the underwater geophone 21 into a plurality of reflected waves corresponding to each source. As a result, even with only one receiving cable, it is possible to obtain three-dimensional data equivalent to the case where the number of receiving cables equal to the number of the vibration sources is used. In this embodiment, since six vibration sources are used, three-dimensional data equivalent to the seafloor geological exploration system 100 using six vibration receiving cables can be acquired.

  Therefore, according to the present embodiment, it is possible to efficiently acquire the three-dimensional data relating to the seabed geology using a single receiving cable. In other words, according to the present embodiment, it is possible to acquire the three-dimensional data related to the seabed geology with the same efficiency as the conventional seabed geological exploration system using a plurality of receiving cables.

  Further, as shown in FIG. 8, according to the present embodiment, it is possible to perform seabed geological exploration with high vertical resolution. Therefore, the seafloor geological exploration system 1 is also effective for site surveys for investigation of seafloor active faults and preparation for well drilling.

  Furthermore, according to this embodiment, since only one vibration receiving cable is required, the following effects can be obtained.

  The cost of the seafloor geological exploration system can be reduced, and maintenance such as repair of the receiving cable can be facilitated.

  Further, it is not necessary to install a plurality of winches for storing the vibration receiving cables, and the towing body such as a research ship can be downsized.

  In addition, when conducting submarine geological surveys, it is possible to easily deploy the receiving cable and store it in the winch.

  Further, in a sea area where there are many vessels such as fishing boats, the number of guard vessels deployed near the tip of the vibration receiving cable can be reduced.

  In addition, the receiving cable can be prevented from being tangled. Therefore, it is possible to perform seabed geological exploration even when affected by tidal currents or in shallow water areas (especially extremely shallow water areas with a water depth of 10 m or less).

  Furthermore, according to this embodiment, since the vibration source is not a blast type (impulse wave type) such as an air gun, but a non-blast type (continuous wave type), the following effects can be obtained.

  There is no need to provide a compressor on a towing body such as a survey ship, and the towing body can be downsized.

  In addition, the influence on marine mammals and fish can be reduced, and submarine geological exploration considering the living environment of marine organisms can be performed.

  Also, unlike air guns, no air bubbles are generated, so the S / N ratio of the received wave can be improved.

<About delayed oscillation>
Here, a delayed oscillation method for improving the horizontal resolution will be described with reference to FIGS. FIG. 9 is a simplified diagram of a seafloor geological exploration system for explaining delayed oscillation. For simplicity, FIG. 9 shows a case where there is one vibration source (only S1) and three underwater geophones (R1, R2, R3). The left waveform diagram of FIG. 10 shows the time waveform of the reflected wave of the sound wave (non-pulse wave W1) oscillated from the vibration source S1, and the right waveform diagram of FIG. 10 shows the sound wave delayed from the vibration source S1. It is a time waveform figure of the reflected wave of (non-pulse wave W2).

  When a non-destructive type vibration source (piezo element, giant magnetostrictive element, underwater speaker, etc.) that oscillates a non-pulse wave is used, the oscillation time (non-pulse wave oscillation time) is 15-30, for example, depending on the depth of exploration. About seconds. As the exploration depth becomes deeper, larger oscillation energy is required, so the oscillation time needs to be lengthened.

  For example, when the moving speed of the towed body 10 is 2 m / second and the oscillation time is 20 seconds, waveform data is obtained every 40 m. Therefore, when the number of underwater geophones is one, the horizontal resolution is 40 m, and the horizontal structure is low, so there is a possibility that an accurate geological structure cannot be grasped. Therefore, as described below, the sound source S1 may be caused to delay and oscillate the sound wave.

  As shown in FIGS. 9 and 10, the oscillation source S1 oscillates the non-pulse wave W1 (first non-pulse wave) and then delays by a time (delay time D) shorter than the oscillation time of the non-pulse wave W1. Thus, the non-pulse wave W2 (second non-pulse wave) is oscillated. That is, the non-pulse wave W2 is oscillated so as to overlap the non-pulse wave W1 in time.

  The non-pulse wave W2 may have the same waveform as the non-pulse wave W1 or a different waveform. Even in the case of different waveforms, it is necessary not to be the same as waveforms oscillated from other sources. In order to keep the quality of the observation data constant, it is preferable that the non-pulse wave W1 and the non-pulse wave W2 have the same oscillation time.

  The shorter the delay time, the higher the horizontal resolution. On the other hand, the shorter the delay time, the more power needs to be supplied to the source. Therefore, it is preferable to determine the delay time in consideration of necessary horizontal resolution, power that the towed body 10 can supply to the vibration source, durability of the vibration source, and the like.

  As shown in FIG. 11, the underwater geophones R1, R2, and R3 receive a combined wave in which the non-pulse wave W1 and the non-pulse wave W2 are added. The synthesized wave separation unit 50 executes the cross-correlation process, so that the received synthesized wave is separated into pulse waves for the non-pulse waves W1 and W2. More specifically, the reflected wave data of the non-pulse wave W1 can be obtained by calculating the cross-correlation between the non-pulse wave W1 and the synthesized wave. Further, by calculating the cross-correlation between the non-pulse wave W2 and the synthesized wave, the reflected wave data of the non-pulse wave W2 can be obtained. In the cross-correlation process between the non-pulse wave W2 and the synthesized wave, only waveform data after the delay time td (see FIG. 11) is used as the synthesized wave.

  As described above, the horizontal resolution can be improved by oscillating the non-pulse wave W2 with a predetermined delay time from the non-pulse wave W1. For example, when the moving speed of the towed body 10 is 2 m / second, the oscillation time is 20 seconds, and the delay time is 10 seconds, the waveform data is obtained every 10 seconds, so that the horizontal resolution can be improved to 20 m.

  Thus, even when using a non-blast type source with a relatively long oscillation time compared to a blast type source such as an air gun, the horizontal resolution can be improved by using the delayed oscillation method described above. it can. As a result, it is possible to obtain data having a horizontal resolution equivalent to or greater than that of the blasting source.

(Second Embodiment)
Next, a seafloor geological exploration system 1A according to a second embodiment of the present invention will be described with reference to FIG. The difference of the second embodiment from the first embodiment is the place where the vibration source is provided. Hereinafter, the second embodiment will be described focusing on the differences.

  As shown in FIG. 12, the seafloor geological exploration system 1A includes a towed body 10, an overhanging towing unit 11, a single vibration receiving cable 20, a plurality of vibration sources 31, 32, 33, 41, 42, 43, And a combined wave separation unit 50.

  The towing body 10 is provided with an overhanging towing portion 11 which is provided so as to project from the towing body 10 and has rigidity. In this embodiment, as shown in FIG. 12, the overhanging towing unit 11 is provided so as to extend along the width direction of the towing body 10. The overhanging towing unit 11 is configured using, for example, a ladder.

  The plurality of vibration sources 31, 32, 33, 41, 42, 43 are provided on the cable 12 suspended from the overhanging towing unit 11 as shown in FIG. 12. In the present embodiment, the line connecting the vibration sources intersects with the vibration receiving cable 20 at a substantially right angle. Thereby, the exploration area can be maximized.

  When the towing body 10 is a ship as in the present embodiment, the overhanging towing unit 11 may be disposed above the water surface (that is, in the air). Thereby, seawater resistance by the overhanging towing part 11 can be avoided.

  Further, the overhanging towing unit 11 may be configured such that the angle (intersection angle) at which the line connecting the vibration sources intersects the vibration receiving cable 20 is not a right angle. For example, the overhanging towing unit 11 may extend obliquely backward from the side surface of the towing body 10. Moreover, you may adjust an intersection angle by changing the length of the cable 12 for every vibration source.

  According to the present embodiment, as in the case of the first embodiment, it is possible to efficiently acquire the three-dimensional data relating to the seabed geology using a single receiving cable. Further, the other effects described in the first embodiment can be obtained similarly.

  Furthermore, in the second embodiment, since the vibration source is suspended from the overhanging towing unit 11 having rigidity, the speed and tidal current of the towed body 10 are higher than those in the first embodiment in which the vibration source is provided in the cable. The influence on the arrangement of the vibration source can be reduced. Thereby, the intersection angle between the line connecting the vibration sources and the receiving cable 20 can be easily adjusted to a predetermined angle, and the intersection angle can be stably maintained. As a result, according to the present embodiment, the three-dimensional data related to the seabed geology can be acquired more efficiently and stably.

  Based on the above description, those skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the above-described embodiments. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

1,1A, 100 Undersea geological exploration system 10 Towing body 11 Overhanging towing part 12 Cable 20, 120 Vibration receiving cable 21, 121 Underwater geophone 30, 40 Oscillation cable 35, 45, 150 Parabein (underwater dredging)
31, 32, 33, 41, 42, 43 Source 50 Synthetic wave separation unit 110 Survey ship 130 Air gun 140 Wire
D Delay time F1 Sea bottom F2, F3 Formation boundary R1, R2, R3 Underwater geophone S1, S2 Source W1, W2 Non-pulse wave

Claims (10)

A towed body,
A single receiving cable towed by the towed body and provided with a plurality of underwater geophones;
A plurality of non-blasting vibration sources that are arranged so as not to be arranged in parallel with each other in plan view with respect to the vibration receiving cable, and that output sound waves having different waveforms from each other,
A synthesized wave separating unit that separates the synthesized wave received by the underwater geophone into a plurality of reflected waves corresponding to the respective vibration sources;
A submarine geological exploration system characterized by comprising:   The submarine geological exploration system according to claim 1, wherein the plurality of vibration sources are provided on an oscillation cable towed by the towing body.   2. The seabed geology according to claim 1, wherein the plurality of vibration sources are provided on a pair of oscillation cables that are towed by the towed body and spread away from each other in plan view. Exploration system. The towing body is provided so as to project from the towing body, and is provided with an overhanging towing part having rigidity,
The submarine geological exploration system according to claim 1, wherein the plurality of vibration sources are provided on a cable suspended from the overhanging towing unit. The sound wave oscillated from the vibration source is a non-pulse wave in which at least one of frequency, phase and amplitude changes continuously or randomly,
The oscillation source oscillates a first non-pulse wave and then oscillates a second non-pulse wave with a delay of a time shorter than an oscillation time of the first non-pulse wave. The seafloor geological exploration system according to any one of 1 to 4.   The seafloor geological exploration system according to claim 5, wherein the non-pulse wave is a pseudo-random wave whose phase changes continuously or a sweep wave whose frequency changes continuously.   The submarine geological exploration system according to any one of claims 1 to 6, wherein the plurality of vibration sources are configured by piezoelectric elements, giant magnetostrictive elements, underwater speakers, electromagnetic vibrators, or hydraulic vibrators.   The submarine geological exploration system according to any one of claims 1 to 7, wherein the towed body is a ship or an underwater explorer. A plurality of non-blasting sources arranged so as not to be arranged in parallel in a plan view with respect to a single receiving cable towed by a towed body output sound waves having different waveforms,
A plurality of underwater geophones provided in the geophone cable are output from the respective vibration sources, and receive a synthesized wave obtained by synthesizing a sound wave reflected from the sea bottom or a boundary between the layers,
A combined wave separation unit separates the combined wave into a plurality of reflected waves corresponding to the respective vibration sources;
Submarine geological exploration method characterized by this. Computer
Sound waves with different waveforms output from multiple non-blasting sources arranged so as not to be parallel to each other in plan view with respect to a single receiving cable towed by a towed body A submarine geological exploration program for functioning as a combined wave separation means for separating a combined wave reflected and combined by a plurality of reflected waves corresponding to each source.

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