JPH08128869A - Device and system for detecting tsunami - Google Patents

Abstract

PURPOSE: To directly detect a tsunami which occurs in the offing in a moment with an inexpensive simple constitution. CONSTITUTION: One ring fiber 1 composed of three optical fiber loops 1a, 1b, and 1c having different lengths (1a>1b>1c) and a sheath 1d covering the loops 1a, 1b, and 1c is laid on the sea bottom to the offing. Weight measuring sections 2a, 2b, and 2c respectively measure the load of a tsunami from the phase changes of propagated light which occur in their corresponding loops 1a, 1b, and 1c. A tsunami coming a long way applies a load to the loops 1a, 1b, and 1c in this order. Therefore, the load is measured at prescribed time intervals in this order. A tsunami discriminating circuit 5 actuates an alarm 6 and displays the image of the tsunami on a display circuit 7 when the circuit 5 discriminates that the moving speed of the measured load calculated by means of a propagating speed detecting circuit 3 is that of the tsunami.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tsunami detection device for detecting the arrival of a tsunami by detecting the pressure exerted by the tsunami on the sea floor by an optical fiber sensor laid on the sea floor, and a tsunami detection system using the same.

[0002]

2. Description of the Related Art Conventionally, three types of tsunami detection systems are known, including those at the proposal stage. The first method is to record seismometers installed in various places (time-amplitude recording).
To determine the epicenter and epicenter mechanism (the direction and degree of displacement of the seismic fault).
This is a method of predicting the occurrence of a tsunami when fault movement can cause significant topographic changes on the sea floor. This method is
This is the method used by the Japan Meteorological Agency for tsunami forecasts. An example of focusing on only the hypocenter location was shown in
No. 68489.

[0003] The second method is a method of detecting an abnormal change in a measured value of a tide gauge installed on the coast and predicting the arrival of a tsunami. This method is a proposal stage method.

[0004] A third method is a method in which a sensor is installed on the seabed offshore to notify the arrival of a tsunami by underwater ultrasonic communication or the like when pressure due to the tsunami is detected. This method is
For example, it is described in JP-A-63-126097.

[0005]

The above-mentioned conventionally known tsunami detection system has the following problems. That is,
The first method, which analyzes the images of seismometers installed in various places, collects the images of multiple locations once, determines the epicenter, and determines the mechanism. become. Therefore, although all systems are connected by communication lines and the analysis is automated, there is a problem that the transmission to the residents is delayed because it takes several minutes to predict the arrival of the tsunami.

In a second method for detecting a change in a tide gauge,
When an abnormality is detected, a tsunami has already arrived, and there is a problem that the time available for residents to use for evacuation and the like is shorter than in the first method.

[0007] In addition, the third to install a sensor on the seabed offshore
In the method of (1), since power supply for driving and communication of the sensor is required, there is a problem that the weight of the laid cable increases, the construction becomes large, and the installation cost per sensor increases.

Further, the first to third methods have a problem that it is difficult to estimate the spread of the tsunami rushing from the offshore to the coast almost in real time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tsunami detecting device which can instantaneously detect a tsunami rushing from the offshore to the coast by using an optical fiber sensor at the time of the offshore, and which can be installed at a low cost, and communicate a plurality of detection signals thereof. It is an object of the present invention to provide a tsunami detection system capable of estimating in almost real time the spread of a tsunami that collects via a line and rushes from offshore to the coast.

[0010]

In order to achieve the above object, a tsunami detecting device and a tsunami detecting system of the present invention have the following configurations. That is, the tsunami detection device of the first invention is
A plurality of optical fiber loops of different lengths laid on the seabed from the shore to the offshore; a water pressure equal to or higher than a predetermined value received by each optical fiber loop by detecting a phase change of light propagating through the plurality of optical fiber loops; Means for detecting a change in the water pressure; and means for driving an alarm when it is determined from the detected water pressure change and the change time that the tsunami is traveling toward the shore.

According to a second aspect of the present invention, there is provided a tsunami detection apparatus comprising: a plurality of optical fiber loops having different lengths laid on the seabed from the seabed to offshore; and detecting a phase change of light propagating through the plurality of optical fiber loops. Means for detecting a change in water pressure received by each optical fiber loop; and a difference (distance) between the detected water pressure change, the time of the change, and the length of the optical fiber loop.
And means for calculating an advancing speed of the wave from the above; and means for driving an alarm when it is determined that the calculated advancing speed corresponds to the advancing speed of the tsunami.

According to the first or second aspect of the present invention, there is provided means for displaying an image of a tsunami on a display from a change in water pressure received by each of the plurality of optical fiber loops. Covered as a cable laid.

A tsunami detection system according to a third aspect of the present invention includes a plurality of tsunami detection apparatuses according to the first or second aspect of the invention, which are arranged along a coastline and connected to a communication line; Means for receiving detection signals from a plurality of tsunami detection devices and displaying an estimated image of a tsunami wave front on a display device.

[0014]

Next, the operation of the tsunami detection device and the tsunami detection system of the present invention configured as described above will be described. Regarding the principle of pressure detection using an optical fiber, JNField's experiment is known (Reference 1: JNField, CKAsawa, OGRa).
mer and MKBarnoski “Fiber opticsensor” J. Acoust.
Soc. Am., 67, 816-818 (1979)). Also, many application examples of using an optical fiber as a pressure sensor have been introduced (for example, {Reference 2: Toba, "optical fiber sensor",
Research on Machinery, Vol. 38, No. 1, 184-190 (1986)},
｛Reference 3: Takahashi, Kikuchi, “Optical Fiber Hydrophone”, Electronic Ceramics, '84 Spring, Special Issue on Light and Thin Films, 51-56 (1984)｝, ｛Reference 4: Fujii, “Optical Fiber Interferometer Development and practical issues ", Optronics,
No. 3, 43-49 (1983)｝).

Therefore, in the tsunami detecting apparatus of the present invention, the known optical fiber is used as a pressure sensor, paying attention to the fact that the pressure exerted on the seabed when a tsunami occurs becomes large. A plurality of optical fiber loops are prepared. By doing so, it is possible to grasp the progress of the wave from the pressure change time at each turning point of each optical fiber loop.

Specifically, in the first invention, it is assumed that there is accumulation of data in the range of pressure values received on the sea floor when a tsunami occurs. If a pressure change is detected, that is, a tsunami is detected, and a similar pressure change is detected at the next turnaround point of the long optical fiber loop, it can be determined that the tsunami is traveling toward the shore, and an alarm is issued. Emit.

In the second aspect of the present invention, data on the range of pressure values applied to the sea floor at the time of the occurrence of a tsunami is insufficient at present, but data on the traveling speed of the tsunami is considerably accumulated. The traveling speed of the wave is calculated from the pressure change at each loop turning point, the change time, and the difference between the lengths of the optical fiber loops, and the alarm can be activated when the traveling speed corresponds to the traveling speed of the tsunami.

As described above, in the tsunami detection device of the present invention,
The occurrence of tsunami offshore can be detected almost instantly only at the landing point of the sensor cable without collating the observation records at multiple points. The looped optical fiber also serves as a communication circuit and sensor, eliminating the need for power supply to the offshore area.
Since the weight of the sensor is reduced, the installation cost can be significantly reduced.

In the third invention, the above-described tsunami detecting device of the present invention is connected by a communication line, receives detection signals of a plurality of tsunami detecting devices, and displays a pressure at a turning point of each optical fiber loop on a display. An estimated image of the tsunami wavefront, which connects lines of equal change with a line, is displayed. This shows the spread of the tsunami coming from offshore, and the tsunami spread can be estimated in almost real time.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a tsunami detector according to an embodiment of the present invention. In FIG. 1, the tsunami detection device includes a ring fiber 1, a weight measuring unit 2 (2a, 2b, 2c), a propagation velocity detection circuit 3, a clock 4, a tsunami determination circuit 5, an alarm 6, It is basically composed of the display circuit 7.

In this embodiment, the ring fiber 1 has three optical fiber loops (1a, 1b, 1c) having different lengths.
Is coated with a coating 1d to form a single cable.
Specifically, the optical fiber loop 1a is offshore 1500 km
It reciprocates up to and is connected to the weight measuring unit 2a. The optical fiber loop 1b reciprocates up to 1000km offshore and is connected to the weight measuring unit 2b. The optical fiber loop 1c reciprocates up to 500km offshore and is connected to the weight measuring unit 2c.

FIG. 2 shows the structure of one weight measuring unit 2 and the relationship with one optical fiber loop (ring fiber 11) connected to it, that is, the structure of a pressure sensor. In FIG. 2, the He-Ne laser light emitting section 20 has a wavelength of 0.1 nm.
A 6238 μm laser beam is continuously emitted. The emitted laser beam is split by the semi-transparent mirror 21 in two directions without shifting the phase.

One of the split beams is formed by the slit 22 and the lens 2.
3 and the waveform is adjusted and applied to the input end of the ring fiber 11 laid on the sea floor. The laser beam sent to the ring fiber 11 reciprocates offshore, and is emitted from the output end thereof toward the light receiving surface of the photodiode 27.

The other branch light is formed by the slit 24 and the lens 2
5 and the waveform is adjusted and applied to the input end of the ring optical fiber 11 and the reference optical fiber 26 having the same length. The laser beam sent to the reference optical fiber 26 is emitted from the output end thereof toward the light receiving surface of the photodiode 27.

Here, when pressure changes in seawater around the ring fiber 11, physical properties of the optical fiber change, and the phase of the propagating laser beam changes. Since the light emitted from the ring fiber 11 and the light emitted from the reference optical fiber 26 are input to the photodiode 27 in a superimposed manner, if a phase change occurs in the light propagated through the ring fiber 11, the photodiode 27 becomes a young interference fringe 28. Is converted into a voltage signal and output. Every time the phase changes by 2π, one interference fringe is shifted and one light and dark occurs.

The counter circuit 29 counts the number of light and dark occurrences, and the weight conversion circuit 30 multiplies the counted value by a predetermined conversion value to calculate the tsunami weight newly added to the ring fiber 11, and the propagation velocity detection circuit Output to 3.

At present, no relationship has been obtained between the change in the weight of seawater on the seabed and the number of moving interference fringes. However, in an indoor experiment relating to the measurement of strain, about 200 interference fringes have been reported to be transferred for a load of 100 g in a section of several tens of cm using the same wavelength as in this example (Reference 2).

FIG. 3 is a conceptual diagram of a tsunami. The tsunami research literature (Hatori, "Aspects of Tsunami Propagating from the Tsugaru Strait to the Sea of Japan", Earthquake, Vol. 2, Vol. 45, pp. 169- 17
6 (1992)), the tsunami wavelength is about 1000 km, and the wave height is 1
At 0 cm, the propagation speed can be estimated to be 1000 km / h, and the weight of a 1 cm thick half-wavelength (hatched portion) tsunami can be estimated to be 250 tons, assuming a seawater density of 1 g / cm ³ .

Then, assuming that the section of the laboratory experiment is 50 cm, the section 500 km shown in FIG. 3 corresponds to a scale of 10 ⁶ times. The load of 250 tons is 2.5 × 10 ⁶ times the load of 100 g. The scale ratio of this example and the indoor experiment regarding the load and the sensor section is 1 in both cases.
Since 0 ⁶ times of the order, S / N to a sensor also comparable. Therefore, it should be possible to observe the movement of the interference fringe in the counter circuit 29 when a tsunami actually occurs.

Now, in FIG. 1, the tsunami coming from far away first reaches the turning position of the optical fiber loop 1a extending up to 1500 km offshore. The tsunami
The load on the optical fiber loop 1a increases with the progress,
After 0 minute, the weight measuring section 2a detects the load (250 tons) of the “push” portion.

During the next 30 minutes, the tsunami applies a load of "push" to the optical fiber loop 1b, so that the weight measuring unit 2b detects a load of 250 tons. At this time, since the "pull" portion of the tsunami is applied to the optical fiber loop 1a, the weight measuring unit 2a detects the load of the "pull" portion, and the designated weight of the weight measuring unit 2a eventually returns to zero. . The three weight measuring units measure the weight in this way.

The propagation speed detection circuit 3 reads from the clock 4 the time at which the weight measuring units 2a and 2b instruct 250 tons and stores the time. Then, based on a time difference of 30 minutes between the two and a distance difference of 500 km between the two optical fiber loops (1a, 1b), the moving speed of this load is calculated, and the calculation result is given to the tsunami determination circuit 5. It is calculated that the possibility that the load is moving at 1000 km / h is high.

The tsunami judging circuit 5 judges whether the moving load is like a tsunami according to the judging rules shown in Table 1, and if it judges that the moving load is like a tsunami, immediately drives the alarm 6 to sound and simultaneously Observed tsunami image (wavefront)
Is displayed on the display circuit 7. The display circuit 7 displays the observation contents for each distance between the turning points of the optical fiber loop.

[0034]

[Table 1]

Although the above is the case of three optical fiber loops, it is clear that the tsunami can be detected in the same manner even if the number is increased. Since a load of 250 tons in a section of 500 km cannot be considered other than a tsunami, if observation data is accumulated and confirmation is obtained, the alarm will sound when the weight is detected, that is, when the movement of the load is detected. It is also possible to make it.

Next, as shown in FIG. 4, a plurality (three in the illustrated example) of the tsunami detectors 41 of the present invention described above are arranged along the coastline, and they are connected to a communication line 42. The detection signals of the three tsunami detectors taken through the communication lines (each of the return points 4 of each ring fiber 43)
4) The wavefront of the tsunami that is spreading (tsunami wavefront) by smoothly connecting the outermost “push” turning points of the “push” to the display in response to the tsunami “push” and “pull” information (Estimated image) 46 can be displayed. In addition, 47 is the epicenter of the tsunami earthquake estimated from the earthquake observation.

[0037]

As described above, in the tsunami detecting apparatus of the present invention, a well-known optical fiber is used as a pressure sensor, paying attention to the fact that the pressure applied to the seabed when a tsunami occurs is considerably large. Since a plurality of optical fiber loops with different lengths are prepared and the progress of the wave can be grasped from the pressure change time at each turning point of each optical fiber loop, there is no need to collate observation records at multiple points In addition, the offshore tsunami occurrence can be detected almost instantaneously only at the point where the sensor cable is landed. In addition, the looped optical fiber serves as both the communication circuit and the sensor, eliminating the need to supply power to the offshore area and reducing the weight of the sensor. Further, the tsunami detection system of the present invention has an effect that the spread of a tsunami rushing from offshore can be estimated almost in real time.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a tsunami detection device according to one embodiment of the present invention.

FIG. 2 is a configuration block diagram of a pressure (weight) sensor of the present invention.

FIG. 3 is a conceptual diagram of a tsunami.

FIG. 4 is a diagram showing a configuration example and a display example of a tsunami detection system of the present invention.

[Explanation of symbols]

 1,11,43 Ring fiber 1a, 1b, 1c Optical fiber loop 1d Coating 2, 2a, 2b, 2c Weight measuring unit 3 Propagation velocity detection circuit 4 Clock 5 Tsunami judgment circuit 6 Alarm device 7 Display circuit 20 He-Ne laser emission Part 21 Semi-transparent mirror 22,24 Slit 23,25 Lens 26 Reference optical fiber 27 Photodiode 28 Interference fringe 29 Counter circuit 30 Weight conversion circuit 41 Tsunami detector 42 Communication line 44 Turning point 45 Indicator 46 Tsunami wavefront 47 Seismic source

Claims (5)

[Claims] 1. A plurality of optical fiber loops having different lengths laid on a seabed from a coast to an offshore; detecting a phase change of light propagating through the plurality of optical fiber loops and receiving each of the optical fiber loops. Means for detecting a change in water pressure greater than or equal to a predetermined value; means for driving an alarm when it is determined from the detected change in water pressure and the time of change that the tsunami is traveling toward the shore. Tsunami detector. 2. A plurality of optical fiber loops having different lengths laid on the seabed from the seabed to the offshore; detecting a phase change of light propagating through the plurality of optical fiber loops and receiving each of the optical fiber loops. Means for detecting a change in the water pressure that has occurred; means for calculating the traveling speed of the wave from the detected change in the water pressure, the time of the change, and the difference (distance) between the lengths of the optical fiber loops; Means for driving an alarm when it is determined that the speed corresponds to the speed. 3. The tsunami detection device according to claim 1, further comprising: means for displaying an image of a tsunami on a display based on a change in water pressure received by each of the plurality of optical fiber loops. 4. The tsunami detection device according to claim 1, wherein the plurality of optical fiber loops are covered as one laid cable. 5. A plurality of tsunami detection devices according to claim 1 arranged along a shoreline and connected to a communication line; and a plurality of tsunami detection devices captured via a communication line. Means for receiving a detection signal and displaying an estimated image of a tsunami wave front on a display device.