JP2004271326A - Submarine ground behavior measurement system - Google Patents

Abstract

An object of the present invention is to provide a submarine ground behavior measurement system capable of measuring a submarine ground behavior relatively accurately with a simple method.
A plurality of measurement points (2) and a reference point (1) as a reference for a measurement value of the measurement point (2) are provided in the measurement sea area, and the reference points (1) and (2) are re-measured at the reference points (1) and (2). A fixed base 3 is provided, and a seafloor pressure gauge 4 is installed on the fixed base 3 to measure the water depth. The water depth difference between the reference point 1 and the plurality of measurement points 2 and the water depth between the measurement points 2 are measured. By constructing a system that calculates the relative behavior of the submarine ground 6 from the difference, simple and accurate measurement of the submarine ground behavior can be performed.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a submarine ground behavior measurement system for measuring the behavior of a submarine ground.
[0002]
[Prior art]
Development and maintenance of methane hydrate (methane hydrate), which is said to be present in a considerable amount in the seabed surrounding Japan, is being developed and improved, including methods for exploring and mining methane hydrates, and assessing the environmental impact of mining.
By the way, mining of undersea resources is carried out by constructing mining structures on the sea. However, due to the relative displacement of the seabed under the foundation of the mining frame accompanying the mining of underground resources, problems such as tilting and collapse of the mining frame are sufficiently expected. Therefore, it is desirable not only to measure the relative displacement of the seafloor ground at the time of mining in the sea area to be mined, but also to always perform the relative displacement measurement at the planning stage before mining.
In the conventional measurement of the seafloor topography, underwater sound waves and underwater lasers are used. The underwater laser can measure up to a depth of about 50 m with an accuracy of about ± 5 cm in a sea area having a transparency of 5 to 10 m, and the underwater sound wave can measure a depth of about 5000 m.
When measuring the seafloor topography with a survey ship, use a GPS receiver mounted on the survey ship to reach the measurement point and calculate the water depth from the sound wave propagation velocity corrected according to the temperature distribution in the water. ing. At this time, it is necessary to make the coordinates of the GPS measurement point coincide with the water depth data in time.
[0003]
On the other hand, as a method of observing volcanic activity at ridges, three submarine pressure gauges are installed at three places on the seabed, and the relative displacements are calculated by converting the water depth from the seafloor pressure measured by the seafloor pressure gauges. (See Non-Patent Document 1). Attempts have been made to identify the relationship between the change of the seabed ground and the magma decay process, the change in water temperature, the tide, etc. by identifying the behavior of the seabed ground by such a method.
[0004]
[Non-patent document 1]
Hiromi Fujimoto, "Observation of volcanic activity at ridges", International joint research on elucidation of energy and material fluxes at ridges, Science and Technology Agency, Research and Development Bureau, February 2000, Phase II, 1996-1998 results Report [0005]
[Problems to be solved by the invention]
The conventional undersea ground behavior measuring system described above has the following problems.
<B> In the seabed topography such as a continental shelf, it is difficult to ensure high measurement accuracy because the water depth becomes very deep.
<B> When measuring the seafloor topography using underwater sound waves, the sound waves propagate to the seafloor topography with a certain spread, so if the seafloor topography is rich in undulations, a true reflection surface can be obtained due to multiple reflections and other reasons. It is hard to be.
<C> When the ship is rocking, such as pitching, rolling, and yawing, during the measurement of the water depth, it is difficult to detect the rocking and correct the angle of the sound wave in the transmitting direction accurately.
[0006]
[Object of the invention]
The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a seafloor topography measurement system capable of relatively easily performing high-accuracy measurement even when the water depth is deep. It is another object of the present invention to provide a seafloor topography measurement system capable of performing highly accurate measurement even when the seafloor topography is rich in undulations. It is still another object of the present invention to provide a seafloor topography measurement system which does not hinder the measurement of the water depth even when the ship sways such as pitching, rolling, and yawing during the measurement of the water depth.
The present invention achieves at least one of these objects.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the submarine ground behavior measurement system of the present invention is a submarine ground behavior measurement system for measuring the behavior of the submarine ground, and a plurality of measurement points provided in the measurement sea area, A reference point provided in a measurement sea area as a reference of measurement values at a plurality of the measurement points, and a fixed base provided at the reference point and the measurement point to enable re-measurement of the reference point and the measurement point; A seafloor pressure gauge for measuring water depth by being installed on a fixed base, and a relative behavior calculating means for calculating a relative behavior of the seafloor ground from a difference in water depth between the reference point and the plurality of measurement points, A submarine ground behavior measurement system characterized by comprising: Here, the relative behavior calculation means can also calculate the water depth difference between the measurement points.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
<B> Undersea ground behavior measurement system (Fig. 1)
In the submarine ground behavior measurement system according to the present invention, first, for example, one reference point 1 serving as a reference is provided in the measurement sea area 91. Here, the reason for providing the reference point 1 is to determine the measurement value at each measurement point 2 from the same reference before calculating the relative amount of the measurement values at the plurality of measurement points 2. The reference point 1 is preferably provided at a position in the measurement sea area 91 where there is no influence of ground fluctuation due to mining of the seabed ground 6. Then, in the measurement sea area 91, a plurality of measurement points 2 can be provided, for example, in a mesh shape (see FIG. 5). The mesh spacing of the mesh depends on the mining range, but can be set to, for example, about several tens of meters to about 100 meters.
In the present invention, the water depth measurement at the reference point 1 and the measurement point 2 is performed using a seabed pressure gauge 4 described later. The water pressure at the reference point 1 and the water pressure at the measurement point 2 are measured, and the variation of the water pressure difference is determined from the time history of the water pressure data (depth data) at the measurement reference point and the time history of the water pressure data (depth data) at the measurement point. It is calculated (see FIG. 1 (b)).
Here, it can be assumed that the average sea level is substantially the same level in the measurement sea area 91. This is because even if the mining range extends from one to several kilometers square, the seawater level is not expected to fluctuate greatly in such a range, for example, on a still sea surface at approximately the same time. In addition, since the fluctuation of the sea level 5 fluctuates depending on the tide, seawater temperature, and the like, it is preferable that the water depth measurement at the reference point 1 and the arbitrary measurement point 2 be performed continuously or simultaneously. In addition, the average sea level may be determined while performing the geoid correction as appropriate according to the mining range.
[0010]
The water pressure value of the seafloor pressure gauge 4 changes over time due to the influence of a change in water temperature or the like. Although the tendency of such a change is similar to any of the seafloor pressure gauges 4, the amount of change is different. This variation is as large as several cm for one month.
Therefore, when performing long-term simultaneous observation using a plurality of seafloor manometers 4, a plurality of seafloor manometers 4 are mounted on the same fixed base 3 in order to eliminate the influence of the water pressure value change for each seafloor manometer 4. It is preferable to carry out the zero adjustment of the water pressure value (water depth value) by mounting.
[0011]
Here, the three-dimensional coordinates obtained by the GPS positioning based on the GPS mobile station 71 mounted on the survey ship 7 can be used for the determination of the average sea level. However, since the seafloor ground behavior measuring system according to the present invention aims to determine the relative displacement between the measuring points 2, it is not necessary to accurately determine the absolute elevation at the reference point 1 and the measuring point 2. At the reference point 1, the water depth is converted and calculated from the seafloor pressure gauge 4, and at the measurement point 2, the water depth is similarly calculated by the seafloor pressure gauge 4 to obtain the relative ground height and relative displacement between the reference point 1 and each measurement point 2. The quantity can be determined. By using the seafloor pressure gauge 4 in this way, the problems of using underwater sound waves and underwater lasers and the problems of measurement errors caused by fluctuations such as pitching, rolling, and yawing of the ship during depth measurement are eliminated. it can.
[0012]
<B> Fixed base The fixed base 3 is a block body installed on the submarine ground 6 in order to obtain the relative ground height and the relative displacement of the submarine ground 6. FIG. 2 shows an embodiment of the shape of the block body. However, the shape is not limited to the embodiment, and the block body can be manufactured to have any shape and size. Further, the material constituting the block body can be manufactured from, for example, a concrete material or a steel material.
A concave portion 31 (measuring point) is provided on the upper surface of the block body, and an upper lid 32 is always provided on the concave portion 31. When water pressure is measured (when measuring the water depth), the upper lid is opened and the sea bottom pressure is applied to the concave portion 31. A total of 4 can be installed to measure the water depth.
It is preferable that the fixed base 3 be set in advance at the reference point 1 and the measurement point 2. In the measurement of the relative displacement of the seafloor ground using the conventional seafloor pressure gauge, since the fixed base 3 was not used, it was difficult to measure again at the same measurement point. However, by installing the fixed base 3, it is possible to measure the water depth at the same point over a long period from the planning stage to the construction stage of the resource mining work under the seabed 6, which is said to be 10 years or more. At the deep sea floor of about 1000 meters, since waves and storm surges do not occur as on the sea, the fixed base 3 once set can remain at that position.
[0013]
The fixed base 3 can be installed on a predetermined ground using, for example, an underwater transport boat 8. That is, a fixed base is mounted on the underwater transport boat 8, and the underwater transport boat can be guided to the vicinity of the installation location by remote control from the surveying boat 7 at sea (see FIG. 4). A flat part of the terrain is found by an acoustic sounder or a CCD image machine mounted on the underwater transport boat 8, and the wire on which the fixed base 3 is suspended from the underwater transport boat 8 is extended to set the fixed base 3 at a predetermined position.
[0014]
<C> Submarine pressure gauge Conventionally, submarine pressure gauges used in sea areas have been mainly used for tsunami measurement. A number of seafloor pressure gauges are currently installed in the coastal areas of Japan.
An object of the present invention is to realize simple and highly accurate water depth measurement using the seabed pressure gauge 4 in order to identify the relative behavior of the seabed ground 6.
The seafloor pressure measurement (depth measurement) at the reference point 1 and the measurement point 2 is performed, for example, by suspending the seafloor pressure gauge from the submersible while remotely controlling or autonomously guiding the submersible to near the fixed base and stopping underwater. Go (not shown). After removing the upper lid 32 of the fixed base 3 with a hook separately suspended from the submersible and removing dirt in the concave portion 31 with pressurized water, the submarine pressure gauge 4 is installed in the concave portion 31 (measuring point). When installing the seafloor pressure gauge 4, it can be installed using a CCD camera. In addition, the submersible is equipped with an instrument that can detect acceleration in the vertical direction, left and right direction, and front and rear direction, and based on such instrument data, remote control while rotating multiple screws installed in each part of the submarine The submersible can also be stopped underwater near the target.
[0015]
<D> Relative behavior calculation means By converting the water pressure value obtained by the seafloor pressure gauge 4 into a water depth value at each measurement point 2, the relative ground height at each measurement point 2 can be calculated. In this case, for example, by comparing the water depth values at three or more measurement points with each other, the accuracy of the measurement value can be improved while correcting the measurement error. For example, as shown in FIG. 3, L ₃ ≒ L ₁ + ΔL ₂ , L ₃ ≒ L ₁ + ΔL ₁ + ΔL ₃ , and ΔL ₂ ≒ ΔL ₁ + ΔL ₃ . From such a relational expression, the error of the water depth measurement value is corrected from the mutual water depth difference from the reference point 1 to each measurement point 2 (measurement point A, measurement point B, measurement point C) and the water depth difference between each measurement point 2. can do.
Further, the relative ground height and the relative displacement amount of each of the measurement points 2 can be plotted for each mesh provided with the measurement points 2 and the relative behavior observation result can be represented by a contour line 92 (see FIG. 5). Further, by performing such measurement periodically, the relative behavior of the seabed 6 in the measurement sea area 91 and its temporal change can be grasped.
【The invention's effect】
The undersea ground behavior measuring system of the present invention is as described above, so that the following effects can be obtained.
<A> Even when the water depth is deep or the measurement sea area is wide in area, relatively accurate relative ground height and relative displacement of the seafloor ground can be obtained.
<B> Since the measurement method does not require specialty, the relative ground height and relative displacement of the seabed can be obtained by a relatively simple method.
[Brief description of the drawings]
FIG. 1 (a) is an explanatory view illustrating a submarine ground behavior measuring system of the present invention. (B) Explanatory drawing explaining the time series of the water depth difference from each time history of reference point water depth data and measurement point water depth data, and both data.
FIG. 2A is a perspective view showing an embodiment of a fixed base. (B) The perspective view which showed the state which removed the upper lid of the fixed base and installed the seafloor pressure gauge.
FIG. 3 is an explanatory diagram illustrating water depth differences between a reference point and measurement points (A, B, C) and water depth differences between measurement points.
FIG. 4 is an explanatory view showing that a fixed base is transported by an underwater transport boat and is installed on the seabed.
FIG. 5 is an explanatory diagram showing contours of the relative height and relative displacement of the seabed ground created based on the water depth difference from the reference point at each measurement point.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reference point 2 ... Measurement point 3 ... Fixed base 4 ... Submarine pressure gauge 6 ... Submarine ground

Claims (1)

A submarine ground behavior measurement system for measuring the behavior of the submarine ground,
Multiple measurement points provided in the measurement sea area,
Reference points provided in the measurement sea area as a reference of the measurement values at the plurality of measurement points,
Provided at the reference point and the measurement point, a fixed base that allows re-measurement of the reference point and the measurement point,
A seafloor pressure gauge for measuring the water depth installed on the fixed base,
Relative behavior calculation means for calculating the relative behavior of the seabed ground from the respective water depth difference between the reference point and the plurality of measurement points,
Submarine ground behavior measurement system.

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