Information processing device, information processing method, and program

Abstract

To provide an information processing device, an information processing method and a program, which enable use of seismic motion amplitude values even in channels in which accurate recording of seismic waveforms was not possible due to cycle skipping associated with a DAS method.SOLUTION: An information processing device is provided, comprising an acquisition unit for acquiring time-series data of a phase change of backscattered light, an extraction unit for extracting a first seismic waveform of a channel suffering from cycle skipping and a second seismic waveform of a channel not suffering from cycle skipping, and an estimation unit for estimating a seismic motion waveform of the channel suffering from cycle skipping using an amplitude ratio of the first seismic waveform and the second seismic waveform.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an information processing device, an information processing method, and a program. [Background technology]

[0002] There is an earthquake observation method that uses distributed acoustic sensing (DAS) technology, which uses optical fiber cables as seismometer sensors (see, for example, Non-Patent Document 1). The DAS method measures strain changes along an optical fiber cable and is expected to be a tool that can monitor seismic motion linearly and densely for long periods of time at lower cost than conventional seismometers. Furthermore, the DAS method measures strain by measuring the phase change of backscattered waves emitted by scatterers present in the optical fiber cable. When a light pulse is emitted from a measuring device into the optical fiber cable, the light is scattered by impurities (scatterers) contained in the optical fiber in trace amounts and returns to the measuring device. When the cable is subjected to vibration, the cable expands and contracts, changing the phase of the returning scattered light. By analyzing the change in the phase of this scattered light, it is possible to detect expansion and contraction (strain) at any point along the optical fiber cable. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Satoshi Ide, Eiichiro Araki, et al, “Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan”, Ide et al. Earth, Planets and Space (2021) 73:63,2021 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technique described in Non-Patent Document 1 has a problem in that when an amplitude with a large phase change within a sampling interval is input to an optical fiber cable, cycle skipping occurs and accurate amplitude values ​​are not recorded.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an information processing device, an information processing method, and a program that can utilize seismic motion amplitude values ​​even in channels where cycle skipping occurs in the DAS method and seismic waveforms cannot be accurately recorded. [Means for solving the problem]

[0006] (1) In order to achieve the above object, an information processing device according to one embodiment of the present invention is an information processing device that includes an acquisition unit that acquires time series data of phase changes (phase difference, phase fluctuation) of backscattered light, an extraction unit that extracts a first seismic waveform of a channel in which cycle skipping occurs and a second seismic waveform of a channel in which cycle skipping does not occur, and an estimation unit that estimates a seismic waveform of a channel in which cycle skipping occurs using the amplitude ratio between the first seismic waveform and the second seismic waveform.

[0007] (2) Furthermore, an information processing device according to one aspect of the present invention is the information processing device described in (1) above, in which the estimation unit calculates the amplitude of a predetermined section of the first seismic waveform and the amplitude of a predetermined section of the second seismic waveform, calculates a ratio between the amplitude of a predetermined section of the first seismic waveform and the amplitude of a predetermined section of the second seismic waveform, and multiplies the second seismic waveform by the ratio to estimate the seismic waveform of the channel in which the cycle skipping occurred.

[0008] (3) Furthermore, an information processing device according to one aspect of the present invention is the information processing device described in (2) above, wherein the predetermined section is a coda wave portion of a seismic wave that is twice or more the S wave travel time.

[0009] (4) Furthermore, an information processing device according to one embodiment of the present invention is the information processing device described in (3) above, wherein the estimation unit calculates the amplitude of the coda wave portion of the first seismic waveform using a coda normalized method, and calculates the amplitude of the coda wave portion of the second seismic waveform using the coda normalized method.

[0010] (5) Furthermore, an information processing device according to one embodiment of the present invention is an information processing device described in any one of (1) to (4) above, which converts the signal acquired by the acquisition unit into the frequency domain, and extracts the first seismic waveform and the second seismic waveform based on the ratio of a first frequency component among the components of the converted frequency domain to a second frequency component having a frequency higher than the first frequency of the first frequency component.

[0011] (6) Furthermore, an information processing device according to one aspect of the present invention is the information processing device described in (5) above, in which the extraction unit calculates a ratio between a first frequency component and a second frequency component among the frequency domain components converted to the frequency domain, and determines that the channel is one in which cycle skipping is not occurring if the ratio is greater than or equal to a predetermined value, and determines that the channel is one in which cycle skipping is occurring if the ratio is less than the predetermined value.

[0012] (7) Furthermore, an information processing device according to one embodiment of the present invention is an information processing device described in any one of (1) to (6) above, in which the second seismic waveform is a channel that is within 10 channels of the first seismic waveform.

[0013] (8) Furthermore, an information processing device according to one aspect of the present invention is the information processing device described in (5) or (6) above, wherein the estimation unit calculates a first spectrum of the coda wave portion of the seismic waveform of a channel in which the cycle skipping is occurring, calculates a second spectrum of the coda wave portion of the seismic waveform of a channel in which the cycle skipping is not occurring, calculates a ratio between the calculated first spectrum and the second spectrum, calculates the spectrum of the channel in which the cycle skipping is occurring by multiplying the calculated ratio between the first spectrum and the second spectrum by the second spectrum, and converts the calculated spectrum of the channel in which the cycle skipping is occurring into the time domain to calculate the seismic waveform of the channel in which the cycle skipping is occurring.

[0014] (9) In order to achieve the above object, an information processing method according to one embodiment of the present invention is an information processing method in which an information processing device acquires time series data of the phase change (phase difference) of backscattered light, extracts a first seismic waveform of a channel in which cycle skipping occurs and a second seismic waveform of a channel in which cycle skipping does not occur, and estimates the seismic waveform of the channel in which cycle skipping occurs using the amplitude ratio between the first seismic waveform and the second seismic waveform.

[0015] (10) In order to achieve the above object, a program according to one embodiment of the present invention is a program that causes a computer of an information processing device to acquire time series data of the phase change (phase difference) of backscattered light, extract a first seismic waveform of a channel in which cycle skipping is occurring and a second seismic waveform of a channel in which cycle skipping is not occurring, and estimate a seismic waveform of a channel in which cycle skipping is occurring using the amplitude ratio between the first seismic waveform and the second seismic waveform. [Effects of the Invention]

[0016] Even in channels where cycle skipping occurs and seismic waveforms cannot be accurately recorded using the DAS method, seismic amplitude values ​​can be used. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram for explaining an overview of a DAS. [Figure 2] FIG. 10 is a diagram for explaining an example in which a strong amplitude (acceleration) is observed in the DAS. [Figure 3] 1 is a diagram illustrating an example of the configuration of an information processing device according to a first embodiment. [Figure 4] 4 is a flowchart of a processing procedure performed by the information processing device according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing an example of waveforms in which a waveform in which cycle skipping occurs is superimposed on a waveform in the vicinity thereof. [Figure 6] FIG. 6 is a diagram showing an example in which the waveforms in FIG. 5 are superimposed and displayed in the frequency domain. [Figure 7] FIG. 10 is a diagram showing an example of calculating the ratio of the low frequency band to the high frequency band in the frequency domain of each channel using equation (2). [Figure 8] FIG. 10 is a diagram illustrating an example of the configuration of an information processing device according to a second embodiment. [Figure 9] 10 is a flowchart of a processing procedure performed by an information processing device according to a second embodiment. [Figure 10] FIG. 10 shows waveforms of a channel where cycle skipping occurs and a channel where cycle skipping does not occur. [Figure 11] FIG. 11 is a diagram showing a waveform estimated using the waveform of FIG. 10. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of an information processing device according to a third embodiment. [Figure 13] 10 is a flowchart of a processing procedure performed by an information processing device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings used in the following description, the scale of each component is appropriately changed so that each component can be recognized. In all the drawings for explaining the embodiments, the same reference numerals are used for components having the same functions, and repeated explanations will be omitted. Furthermore, in this application, "based on XX" means "based on at least XX," and includes cases where it is based on other elements in addition to XX. Furthermore, "based on XX" is not limited to cases where XX is used directly, but also includes cases where it is based on XX that has been calculated or processed. "XX" is any element (for example, any information).

[0019] [DAS Overview] First, we will provide an overview of DAS (distributed acoustic measurement). Figure 1 is a diagram for explaining the overview of DAS. When an optical pulse is injected from a measuring instrument into an optical fiber cable, the light is scattered by impurities (scatterers) contained in the optical fiber in small amounts and returns to the measuring instrument. When vibrations are applied to the cable, the cable expands and contracts, causing the returning signal to change. By analyzing the change in the phase of this scattered light, it is possible to detect expansion and contraction (strain) at any point in the optical fiber cable. In the following explanation, as shown in Figure 1, the entire length of the cable is divided into predetermined intervals (for example, 10 m), and each predetermined interval is called a channel. For example, if the entire length of the cable is 10 km and the predetermined intervals are 10 m, there are 1,000 channels.

[0020] The seismic waveform St(t,x) recorded by the DAS is described as follows:

[0021]

number

[0022] In equation (1), S(t,x) is the source, P(t,x) is the propagation path, G(t,x) is the shallow sediment layer, C(t,x) is the cable coupling, Res(t,x) is the structural response, and Ori(θ) is the rotation component of the seismic waveform relative to the wavefront. t is the time and x is the position.

[0023] [If a large amplitude (phase difference) is observed] Next, an example in which a large amplitude (phase difference) is observed in the DAS will be described. FIG. 2 is a diagram for explaining an example in which a large amplitude (phase difference) is observed in the DAS. In FIG. 2, the horizontal axis of waveforms g11 to g14 represents time (sec), and the vertical axis represents phase difference. Waveform g11 is an example waveform of a channel in which cycle skipping is not occurring. Waveform g12 is an example waveform of a channel in which cycle skipping is occurring. Waveform g13 is a waveform in which one second from time 40 to 60 seconds of waveform g11 is expanded in the time direction. Waveform g14 is a waveform in which one second from time 40 to 60 seconds of waveform g12 in which cycle skipping is occurring is expanded in the time direction.

[0024] In waveform g14, an accurate waveform cannot be obtained for a period of approximately 0.4 to 0.8 seconds per second due to cycle skipping. Dashed lines g15 and g16 show the expected waveform. In this way, if the difference exceeds ±π within the sampling interval, phase cycle skipping occurs and accurate values ​​are not recorded. As a result, with conventional technology, when estimating damage to structures caused by seismic motion after an earthquake occurs, it is not possible to accurately evaluate the seismic motion amplitude value of a channel where cycle skipping occurred.

[0025] First Embodiment [Configuration example of information processing device] 3 is a diagram showing an example of the configuration of an information processing device according to this embodiment. As shown in FIG. 3, the information processing device 1 includes, for example, a light emitting unit 11, a light receiving unit 12, an extracting unit 13, an output unit 15, and a storage unit 16. The extraction unit 13 includes, for example, an FFT 131 and a determination unit 132 . 3 is merely an example, and the present invention is not limited to this example. For example, the light emitting unit 11 and the light receiving unit 12 may be provided in an external device.

[0026] The light emitting unit 11 emits incident light for measurement that is incident on one end of the optical fiber cable.

[0027] The light receiving unit 12 receives a time series of scattered waves that are returned from the incident measurement light after being scattered by scatterers in the optical fiber cable. That is, the light receiving unit 12 acquires time series data of the phase change (phase difference, phase fluctuation) of the backscattered light. The light receiving unit 12 converts the received signal into an electrical signal by photoelectric conversion and outputs it.

[0028] The extraction unit 13 extracts the seismic waveform (first seismic waveform) of the channel in which cycle skipping occurs.

[0029] The FFT 131 converts the electrical signal output by the light receiving unit 12 into the frequency domain by, for example, fast Fourier transform.

[0030] The determining unit 132 selects, for example, a channel transformed into the frequency domain using the following formula (2) where the ratio of the magnitude of the high frequency domain component to the low frequency domain component is less than a predetermined value as a channel in which cycle skipping is occurring (first seismic waveform).The determining unit 132 then selects, for a channel transformed into the frequency domain using the following formula (2) where the ratio of the magnitude of the high frequency domain component to the low frequency domain component exceeds a predetermined value as a channel in which cycle skipping is not occurring (second seismic waveform).In formula (2), S1=max[|X(f k1 )|] is the maximum value of the low frequency component (e.g., less than 10 Hz) in the frequency domain, S2=max[|X(f k2 )|] is the maximum value of the high frequency components (for example, 10 Hz or higher) in the frequency domain.

[0031]

number

[0032] In addition, the determination unit 132 may select a combination of two channels transformed into frequency domains close to each other, where the difference in magnitude of the high frequency domain components or the low frequency domain components is equal to or greater than a predetermined value, as a channel in which cycle skipping occurs and a channel in which cycle skipping does not occur.

[0033] The output unit 15 outputs the results extracted by the extraction unit 13 to an external device. The external device is, for example, a tablet terminal, a smartphone, a dedicated terminal, a personal computer, a printing device, an image display device, or the like.

[0034] The storage unit 16 stores programs, mathematical expressions, values, values ​​in the middle of calculations, and the like that the information processing device 1 uses for processing.

[0035] [Processing Procedure] Next, a description will be given of an example of a processing procedure performed by the information processing device 1. Fig. 4 is a flowchart of the processing procedure performed by the information processing device according to this embodiment.

[0036] (Step S1) The light emitting unit 11 emits incident light for measurement, and makes it incident on one end of the optical fiber cable.

[0037] (Step S2) The light receiving unit 12 receives the returning scattered wave, converts the received signal into an electrical signal, and outputs it.

[0038] (Step S3) The FFT 131 converts the electrical signal output by the light receiving unit 12 into the frequency domain using fast Fourier transform.

[0039] (Step S4) The determination unit 132 selects, as a channel in which cycle skipping occurs, a channel in which the ratio of the magnitude of the high-frequency domain component to the low-frequency domain component of the channel converted into the frequency domain is less than a predetermined value. The determination unit 132 extracts, as a channel in which cycle skipping does not occur, a channel in which the ratio of the magnitude of the high-frequency domain component to the low-frequency domain component of the channel converted into the frequency domain is greater than a predetermined value.

[0040] [Example of waveform in the time domain and frequency domain] FIG. 5 is a diagram showing an example of waveforms in which a waveform in which cycle skipping occurs and its neighboring waveforms are superimposed. In FIG. 5, the horizontal axis represents time (sec), and the vertical axis represents normalized phase values. Image g51 shows the waveforms of channel 433 in which cycle skipping occurs and its neighboring channel 428 in which cycle skipping does not occur. Image g52 shows the waveforms of channel 2655 in which cycle skipping occurs and its neighboring channel 2662 in which cycle skipping does not occur. Image g53 shows the waveforms of channel 5402 in which cycle skipping occurs and its neighboring channel 5394 in which cycle skipping does not occur. Image g54 shows the waveforms of channel 6143 in which cycle skipping occurs and its neighboring channel 6137 in which cycle skipping does not occur.

[0041] FIG. 6 is a diagram showing an example in which the waveforms in FIG. 5 are superimposed in the frequency domain. The horizontal axis represents frequency (Hz), and the vertical axis represents Fourier amplitude. Image g61 shows the signals in image g51 in FIG. 5 converted into the frequency domain and superimposed. Image g62 shows the signals in image g52 in FIG. 5 converted into the frequency domain and superimposed. Image g63 shows the signals in image g53 in FIG. 5 converted into the frequency domain and superimposed. Image g64 shows the signals in image g54 in FIG. 5 converted into the frequency domain and superimposed. Furthermore, symbols g611, g621, g631, and g641 represent frequency domain components of channels in which cycle skipping does not occur. Symbols g612, g622, g632, and g642 represent frequency domain components of channels in which cycle skipping occurs.

[0042] As shown in FIG. 6, the difference in magnitude of the high frequency band between the frequency domain components of a channel where cycle skipping does not occur and the frequency domain components of a channel where cycle skipping occurs is equal to or greater than a predetermined value.

[0043] 7 is a diagram showing an example of calculating the ratio of the low frequency band to the high frequency band in the frequency domain of each channel using equation (2). The horizontal axis represents the channel, and the vertical axis represents the ratio of the magnitude of the low frequency band to the magnitude of the high frequency band. In this embodiment, if this ratio is equal to or greater than a predetermined value, the channel is determined to be one in which cycle skipping is not occurring, and if this ratio is less than the predetermined value, the channel is determined to be one in which cycle skipping is occurring.

[0044] As described above, in this embodiment, the spectral shape is used to determine the channel in which cycle skipping occurs. As a result, according to this embodiment, it is possible to determine which channels are not experiencing cycle skipping and which channels are experiencing cycle skipping.

[0045] Second Embodiment In this embodiment, the correct value of the waveform of a channel where cycle skipping occurs is estimated using the amplitude ratio in the time domain of the coda wave portion of the waveform of a channel where cycle skipping occurs and the waveform where cycle skipping does not occur.

[0046] 8 is a diagram showing an example of the configuration of an information processing device according to this embodiment. As shown in FIG. 8, the information processing device 1A includes, for example, a light emitting unit 11, a light receiving unit 12 (acquisition unit), an extraction unit 13A, an estimation unit 14, an output unit 15, and a storage unit 16. The extraction unit 13A includes, for example, an FFT 131 and a determination unit 132. The estimation unit 14 includes, for example, an amplitude value calculation unit 141, a ratio calculation unit 142, and a correction calculation unit 143. Note that the configuration example shown in Fig. 8 is an example and is not limited to this. For example, the light emitting unit 11 and the light receiving unit 12 may be included in an external device.

[0047] The extraction unit 13A extracts the seismic waveform St(t, x) of a channel where cycle skipping occurs and the seismic waveform St(t, x+1) of a channel where cycle skipping does not occur. The extraction unit 13A extracts signals from a predetermined section for each channel. Note that the extraction unit 13A extracts channels where cycle skipping occurs using the same processing as the extraction unit 13 in the first embodiment. Note that in this embodiment, in order to reduce the difference between S(t, x) and P(t, x) between channels, the coda wave portion from twice the S-wave travel time onwards in seismic waves that exhibit a constant attenuation waveform regardless of S(t, x) and P(t, x) in the seismic waveform is used as the predetermined section. Note that the predetermined section is not limited to this.

[0048] The estimation unit 14 estimates the seismic waveform of the channel in which cycle skipping has occurred, using the seismic waveform St(t, x) of the channel in which cycle skipping has occurred extracted by the extraction unit 13 and the seismic waveform St(t, x+1) of the channel in which cycle skipping has not occurred.

[0049] The amplitude value calculation unit 141 calculates the amplitude of, for example, the coda wave portion of a predetermined section of the seismic waveform St(t, x) of a channel where cycle skipping occurs. The amplitude value calculation unit 141 calculates the amplitude of, for example, the coda wave portion of a predetermined section of the seismic waveform St(t, x+1) of a channel where cycle skipping does not occur. The amplitude value calculation unit 141 calculates the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St using, for example, the coda normalized method (see, for example, Reference 1). The coda normalized method normalizes the spectral amplitude of the earthquake source by the spectral amplitude of the coda wave at a certain elapsed time, and can measure the attenuation coefficient from data obtained at a single observation point. Note that the calculation method is not limited to this. Furthermore, it is preferable that the channel where cycle skipping does not occur is close to the channel where cycle skipping occurs (for example, within ±10 channels).

[0050] Reference 1; PHILLIPS, WS and K. AKI, “Site amplification of coda waves from local earthquakes in central California”, Bulletin of the Seismological Society of America, Vol.76, No3, p627-648, 1986

[0051] The ratio calculation unit 142 calculates the ratio between the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x) of a channel in which cycle skipping occurs, calculated by the amplitude value calculation unit 141, and the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x+1) of a channel in which cycle skipping does not occur.

[0052] The correction calculation unit 143 calculates the seismic waveform St'(t,x) of the channel in which cycle skipping has occurred by multiplying the ratio calculated by the ratio calculation unit 142 by the seismic waveform St(t,x) of the channel in which cycle skipping has occurred.

[0053] The output unit 15 outputs the seismic waveform St'(t, x) of the channel in which cycle skipping occurred, estimated by the estimation unit 14, to an external device. The external device is, for example, a tablet terminal, a smartphone, a dedicated terminal, a personal computer, a printer, an image display device, etc.

[0054] The storage unit 16 stores programs, mathematical expressions, values, values ​​in the middle of calculations, and the like that the information processing device 1 uses for processing.

[0055] [Estimation principle] Next, we explain the principle of estimating the seismic waveform St'(t,x) of the channel where cycle skipping occurs. The seismic waveform St(t,x) of a channel where cycle skipping occurs can be expressed as in equation (1) above. The seismic waveform St(t,x+1) of a nearby channel where cycle skipping does not occur can be expressed as in equation (3) below. * indicates waveform convolution.

[0056]

number

[0057] In the case of signals between nearby channels, S(t,x) and P(t,x) do not change significantly within a few tens of meters, so it can be assumed that approximately the same waveforms are recorded. That is, in equations (1) and (3), S(t,x) = S(t,x+1) and P(t,x) = P(t,x+1). As a result, the ratio β of St(t,x) to St(t,x+1) is given by the following equation (4).

[0058]

number

[0059] Therefore, the difference between the seismic waveforms recorded by DAS between a channel where cycle skipping occurs and a nearby channel where cycle skipping does not occur can be clarified by taking the ratio of the amplitude values, limited to the same seismic waveform. This allows the waveform of a cycle-skipped channel to be estimated from the waveform of a non-cycle-skipped channel, or the waveform of a cycle-skipped channel can be estimated from the waveform of a non-cycle-skipped channel using the ratio between channels, G(t,x)*C(t,x)*Res(t,x).

[0060] [Processing Procedure] Next, a description will be given of an example of a processing procedure performed by the information processing device 1. Fig. 9 is a flowchart of a processing procedure performed by the information processing device according to this embodiment.

[0061] (Step S11) The light emitting unit 11 emits incident light for measurement, and makes it incident on one end of the optical fiber cable.

[0062] (Step S12) The light receiving unit 12 receives the returning scattered wave, converts the received signal into an electrical signal, and outputs it.

[0063] (Step S13) The extraction unit 13A extracts a signal in a predetermined section for each channel. The extraction unit 13A converts the electrical signal output by the light receiving unit 12 into the frequency domain using a fast Fourier transform. The extraction unit 13A selects, as a channel in which cycle skipping is occurring, a channel in which the ratio of the magnitude of the high-frequency region component to the low-frequency region component of the channel converted into the frequency domain is less than a predetermined value. The extraction unit 13A selects, as a channel in which cycle skipping is occurring, a channel in which the ratio of the magnitude of the high-frequency region component to the low-frequency region component of the channel converted into the frequency domain exceeds a predetermined value.

[0064] (Step S14) The amplitude value calculation unit 141 calculates the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x) of a channel in which cycle skipping occurs, and the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x+1) of a channel in which cycle skipping does not occur.

[0065] (Step S15) The ratio calculation unit 142 calculates the ratio between the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x) of a channel in which cycle skipping occurs and the amplitude of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t, x+1) of a channel in which cycle skipping does not occur.

[0066] (Step S16) The correction calculation unit 143 multiplies the seismic waveform St(t, x+1) of the channel in which cycle skipping did not occur by the ratio calculated by the ratio calculation unit 142 to calculate the seismic waveform St'(t, x) of the channel in which cycle skipping occurred.

[0067] (Step S17) The output unit 15 outputs the corrected seismic waveform St'(t, x) of the channel in which cycle skipping occurred to an external device.

[0068] [confirmation result] Next, examples of the results of estimating earthquake motion waveforms using the above-described method will be described with reference to FIGS. FIG. 10 shows waveforms of a channel where cycle skipping occurs and a channel where it does not occur. Waveform g21 is the waveform of a channel where cycle skipping occurs. Waveform g101 in FIG. 10 is the waveform of a channel where cycle skipping does not occur. The horizontal axis of waveforms g101 and g111 represents time (sec), and the vertical axis represents a normalized phase value. For example, in waveform g111, 32768 (2^15) corresponds to π, and -32768 (2^15) corresponds to -π.

[0069] Fig. 11 is a diagram showing a waveform estimated using the waveform of Fig. 10. In Fig. 10, the horizontal axis represents time (sec) and the vertical axis represents a normalized value of the phase. Image g120 is a waveform estimated using the result of calculating the amplitude ratio between waveform g101 of a channel where cycle skipping occurs and waveform g111 of a channel where cycle skipping does not occur in Figure 10. Waveform g121 is the waveform of a channel where cycle skipping occurs, and is waveform g111 in Figure 10 (the vertical axis scale is different between waveform g111 and image g120). Waveform g122 is an estimated waveform. Moreover, images g130 and g140 are enlarged images of a portion of image g120. As with images g130 and g140, the phase and amplitude match except for the cycle skipping portion.

[0070] In the above-described embodiment, for example, an optical fiber cable may already be installed, or a new optical fiber cable may be installed. The above-described embodiment can be used in a railway where an optical fiber cable has already been installed, for example, along the tracks.

[0071] As described above, according to this embodiment, seismic motion amplitude values ​​can be used even in channels where cycle skipping has occurred and seismic waveforms cannot be accurately recorded, making it possible to build a very high-density linear seismic observation network along optical fiber cables. Optical fiber cables are laid along railway tracks. According to this embodiment, applying DAS to these cables makes it possible to quickly detect seismic motion along railway tracks, leading to the prevention of derailments. It also makes it possible to identify structural damage locations within a few meters during an earthquake, enabling the rapid resumption of service.

[0072] The length of the interval between sampling for each channel may be set depending on the environment, etc. The sampling intervals may or may not be equal.

[0073] Third Embodiment In this embodiment, the correct value of the waveform of a channel where cycle skipping occurs is estimated using the amplitude ratio in the frequency domain of the coda wave portion of the waveform of a channel where cycle skipping occurs and the waveform where cycle skipping does not occur.

[0074] 12 is a diagram showing an example of the configuration of an information processing device according to this embodiment. As shown in FIG. 12, the information processing device 1B includes, for example, a light emitting unit 11, a light receiving unit 12 (acquisition unit), an extraction unit 13B, an estimation unit 14B, an output unit 15, and a storage unit 16. The extraction unit 13B includes, for example, an FFT 131 and a determination unit 132. The estimation unit 14B includes, for example, an amplitude value calculation unit 141B, a ratio calculation unit 142B, and a correction calculation unit 143B. Note that the configuration example shown in Fig. 12 is an example and is not limited to this. For example, the light emitting unit 11 and the light receiving unit 12 may be included in an external device.

[0075] The extraction unit 13B extracts the seismic waveform St(t, x) of a channel where cycle skipping occurs and the seismic waveform St(t, x+1) of a channel where cycle skipping does not occur, using processing similar to that of the first embodiment. The extraction unit 13B extracts signals within a predetermined section for each channel. Specifically, the extraction unit 13B converts the signals acquired by the light-receiving unit 12 (acquisition unit) into the frequency domain and extracts a first seismic waveform and a second seismic waveform based on the ratio of a first frequency component to a second frequency component, which is higher than the first frequency of the first frequency component, among the components in the converted frequency domain. The extraction unit 13B also calculates the ratio of the first frequency component to the second frequency component among the components in the converted frequency domain, and determines that a channel does not experience cycle skipping if the ratio is equal to or greater than a predetermined value, and determines that a channel experiences cycle skipping if the ratio is less than the predetermined value. In the embodiment, in order to reduce the difference between the S(t, x) and P(t, x) channels, the coda wave portion of the seismic waveform, which shows a constant attenuation waveform regardless of S(t, x) and P(t, x), is used as the predetermined section. However, the predetermined section is not limited to this.

[0076] The estimation unit 14B estimates the seismic waveform of the channel in which cycle skipping has occurred, using the seismic waveform St(t, x) of the channel in which cycle skipping has occurred extracted by the extraction unit 13B and the seismic waveform St(t, x+1) of the channel in which cycle skipping has not occurred.

[0077] The amplitude calculation unit 141B calculates a first spectrum St(f,x) of, for example, the coda wave portion of a predetermined section of the seismic waveform St(t,x) of a channel where cycle skipping occurs. The amplitude calculation unit 141B calculates a second spectrum St(f,x+1) of, for example, the coda wave portion of a predetermined section of the seismic waveform St(t,x+1) of a channel where cycle skipping does not occur. The amplitude calculation unit 141B calculates the amplitude of the predetermined section (e.g., the coda wave portion) of the seismic waveform St using, for example, the coda normalized method (see, for example, Reference 2). The coda normalized method normalizes the spectral amplitude of the earthquake source by the spectral amplitude of the coda wave at a certain elapsed time, allowing the attenuation coefficient to be measured from data obtained at a single observation point. Note that the calculation method is not limited to this. Furthermore, it is preferable that the channel where cycle skipping does not occur is close to the channel where cycle skipping occurs (e.g., within ±10 channels).

[0078] Reference 2; Kazuo Yoshimoto, Haruo Sato, “Frequency-dependent attenuation of P and S waves in the Kanto area, Japan, based on the coda-normalization method”, Geophysical Journal International Vol. 114, Issue 1, 165-174, 1993

[0079] The ratio calculation unit 142B calculates the ratio between the first spectrum St(f,x) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x) of a channel in which cycle skipping occurs as calculated by the amplitude value calculation unit 141B, and the second spectrum St(f,x+1) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x+1) of a channel in which cycle skipping does not occur.

[0080] The correction calculation unit 143B calculates the spectrum St'(f,x) of the channel where cycle skipping occurred by multiplying the second spectrum St(f,x+1) of the seismic waveform St(t,x+1) of the channel where cycle skipping did not occur by the ratio calculated by the ratio calculation unit 142B, and performs an inverse FFT on this to calculate the seismic waveform St'(t,x) of the channel where cycle skipping occurred, which is the correction value.

[0081] [Estimation principle] Next, we will explain the principle of calculating the seismic waveform St'(t,x) of a channel where cycle skipping occurs. The seismic waveform St(t,x) of a channel where cycle skipping occurs can be expressed as in the above equation (1), and the frequency components can be expressed as in the following equation (5). × indicates multiplication, and in the frequency domain, each element can be expressed by multiplication.

[0082]

number

[0083] The seismic waveform St(t,x+1) of a nearby channel where cycle skipping does not occur can be expressed as in the above equation (5), and the frequency components can be expressed as in the following equation (6).

[0084]

number

[0085] In the case of signals between nearby channels, S(f,x) and P(f,x) do not change significantly within a few tens of meters, so it can be assumed that approximately the same waveforms are recorded. That is, in equations (5) and (6), S(f,x) = S(f,x+1) and P(f,x) = P(f,x+1). As a result, the ratio of St(f,x) to St(f,x+1) is given by the following equation (7).

[0086]

number

[0087] Therefore, the difference between the seismic waveforms recorded by DAS between a channel with cycle skipping and a nearby channel without cycle skipping can be clarified by taking the spectral ratio, limited to the same seismic waveform. This allows the waveform of a cycle-skipped channel to be estimated from the waveform of a non-cycle-skipped channel. Alternatively, the waveform of a cycle-skipped channel can be estimated from the waveform of a non-cycle-skipped channel using the inter-channel ratio G(f,x) × C(f,x) × Res(f,x).

[0088] [Processing Procedure] Next, an example of the processing procedure performed by the information processing device 1B will be described with reference to Fig. 13, which is a flowchart of the processing procedure performed by the information processing device according to this embodiment.

[0089] (Step S21) The light emitting unit 11 emits incident light for measurement, and makes it incident on one end of the optical fiber cable.

[0090] (Step S22) The light receiving unit 12 receives the returning scattered wave, converts the received signal into an electrical signal, and outputs it.

[0091] (Step S23) The extraction unit 13B extracts a signal in a predetermined section for each channel. The extraction unit 13B converts the electrical signal output by the light receiving unit 12 into the frequency domain using a fast Fourier transform. The extraction unit 13B selects, among the channels converted into the frequency domain, channels in which the ratio of the magnitude of the high-frequency region component to the low-frequency region component is less than a predetermined value as channels in which cycle skipping is occurring, and extracts, among channels in which the ratio of the magnitude of the high-frequency region component to the low-frequency region component is equal to or greater than the predetermined value as channels in which cycle skipping is not occurring.

[0092] (Step S24) The amplitude value calculation unit 141B calculates the spectrum St_cоda(f,x) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x) of a channel in which cycle skipping occurs, and the spectrum St_cоda(f,x+1) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x+1) of a channel in which cycle skipping does not occur.

[0093] (Step S25) The ratio calculation unit 142B calculates the ratio β' between the spectrum St_cоda(f,x) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x) of a channel in which cycle skipping occurs and the spectrum St_cоda(f,x+1) of a predetermined section (e.g., the coda wave portion) of the seismic waveform St(t,x+1) of a channel in which cycle skipping does not occur, using the following equation (8):

[0094]

number

[0095] (Step S26) The correction calculation unit 143B multiplies the spectrum St(f, x+1) of the seismic waveform St(t, x+1) of the channel where cycle skipping did not occur by the ratio calculated by the ratio calculation unit 142B to calculate the spectrum St'(f, x) of the channel where cycle skipping occurred, performs an inverse FFT on it, and calculates the corrected value, the seismic waveform St'(t, x) of the channel where cycle skipping occurred, using the following equation (9).

[0096]

number

[0097] (Step S27) The output unit 15 outputs the corrected seismic waveform St'(t, x) of the channel in which cycle skipping occurred to an external device.

[0098] [confirmation result] Next, examples of the results of estimating earthquake motion waveforms using the above-described method are similar to the estimation results of the second embodiment, and are shown in, for example, FIGS. 10 to 11.

[0099] In the above-described embodiment, for example, an optical fiber cable may already be installed, or a new optical fiber cable may be installed. The above-described embodiment can be used in a railway where an optical fiber cable has already been installed, for example, along the tracks.

[0100] As described above, according to this embodiment, seismic motion amplitude values ​​can be used even in channels where cycle skipping has occurred and seismic waveforms cannot be accurately recorded, making it possible to build a very high-density linear seismic observation network along optical fiber cables. Optical fiber cables are laid along railway tracks. According to this embodiment, applying DAS to these cables makes it possible to quickly detect seismic motion along the railway line, leading to the prevention of derailment by promptly stopping trains. It also makes it possible to identify structural damage locations within a few meters during an earthquake, enabling the rapid resumption of service.

[0101] The length of the interval between sampling for each channel may be set depending on the environment, etc. The sampling intervals may or may not be equal.

[0102] As a result, according to this embodiment, it is possible to accurately and efficiently select channels in which cycle skipping has occurred and channels in which cycle skipping has not occurred.

[0103] In the above-described embodiments, examples have been described in which acquired data is processed to estimate and present an appropriate value for the channel in which cycle skipping occurred, but this is not limiting. The information processing device 1 (or 1A, 1B) may use the estimated data to present information indicating the possibility of an earthquake or tremor occurring when the phase difference value is equal to or greater than a threshold, along with the corresponding channel or a location corresponding to the channel. In this case, the storage unit 16 stores information indicating a location (e.g., latitude and longitude) in advance, associating the channel with the information.

[0104] The above-described method can be applied to facilities other than railway facilities, such as submarine cables.

[0105] The information processing device 1 (or 1A, 1B) of the present invention may be implemented by recording a program for realizing all or part of the functions of the information processing device 1 (or 1A, 1B) on a computer-readable recording medium, and loading and executing the program recorded on the recording medium into a computer system. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. The term "computer system" also includes a WWW system equipped with a homepage provision environment (or display environment). The term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. The term "computer-readable recording medium" also refers to devices that retain a program for a certain period of time, such as volatile memory (RAM) within a computer system that serves as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line.

[0106] The program may also be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by transmission waves in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be a program that realizes part of the above-mentioned functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the above-mentioned functions in combination with a program already recorded in the computer system.

[0107] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention. [Explanation of symbols]

[0108] 1, 1A, 1B... information processing device, 11... light emitting unit, 12... light receiving unit, 13, 13A, 13B... extraction unit, 14, 14A, 14B... estimation unit, 15... output unit, 16... storage unit, 141, 141B... amplitude value calculation unit, 142, 142B... ratio calculation unit, 143, 143B... correction calculation unit, 131... FFT, 132... determination unit

Claims

1. An acquisition unit that acquires time-series data of phase changes of backscattered light emitted from scatterers present in an optical fiber cable; an extracting unit that extracts a first seismic waveform of a channel in which cycle skipping occurs and a second seismic waveform of a channel in which cycle skipping does not occur, from among the channels at predetermined intervals of the optical fiber cable; an estimation unit that estimates a seismic waveform of a channel in which cycle skipping occurs by using an amplitude ratio between the first seismic waveform and the second seismic waveform; An information processing device comprising:

2. The estimation unit Calculating the amplitude of a predetermined section of the first seismic waveform and the amplitude of a predetermined section of the second seismic waveform; Calculating a ratio between the amplitude of a predetermined section of the first seismic waveform and the amplitude of a predetermined section of the second seismic waveform; multiplying the second seismic waveform by a ratio between the amplitude of a predetermined section of the first seismic waveform and the amplitude of a predetermined section of the second seismic waveform to estimate a seismic waveform of the channel in which the cycle skipping occurred; The information processing device according to claim 1 .

3. The predetermined section is a coda wave portion of the seismic wave after twice the S wave travel time. The information processing device according to claim 2 .

4. The estimation unit calculates an amplitude of a coda wave portion of the first seismic waveform using a coda normalized method, and calculates an amplitude of a coda wave portion of the second seismic waveform using the coda normalized method. The information processing device according to claim 3 .

5. the extraction unit converts the signal acquired by the acquisition unit into a frequency domain, and extracts the first seismic waveform and the second seismic waveform based on a ratio of a first frequency component to a second frequency component having a frequency higher than a first frequency of the first frequency component among the components of the converted frequency domain.

3. The information processing device according to claim 1.

6. the extraction unit calculates a ratio between the first frequency component and the second frequency component among the frequency domain components converted into the frequency domain, and determines that the channel is one in which the cycle skipping is not occurring when the ratio between the first frequency component and the second frequency component is equal to or greater than a predetermined value, and determines that the channel is one in which the cycle skipping is occurring when the ratio between the first frequency component and the second frequency component is less than a predetermined value. The information processing device according to claim 5 .

7. The second seismic waveform is a channel that is within 10 channels of the first seismic waveform.

3. The information processing device according to claim 1.

8. The estimation unit Calculating a first spectrum of a coda wave portion of a seismic waveform of a channel where the cycle skipping occurs, and calculating a second spectrum of a coda wave portion of a seismic waveform of a channel where the cycle skipping does not occur; Calculating a ratio between the calculated first spectrum and the calculated second spectrum; calculating a spectrum of the channel in which the cycle skipping occurs by multiplying the second spectrum by the calculated ratio between the first spectrum and the second spectrum; Transforming the calculated spectrum of the channel in which the cycle skipping occurred into the time domain to calculate the seismic waveform of the channel in which the cycle skipping occurred. The information processing device according to claim 6 .

9. The information processing device Obtain time-series data of the phase change of backscattered light emitted from scatterers present in the optical fiber cable, extracting a first seismic waveform from a channel where cycle skipping occurs and a second seismic waveform from a channel where cycle skipping does not occur from among channels at predetermined intervals of the optical fiber cable; using an amplitude ratio between the first seismic waveform and the second seismic waveform, to estimate a seismic waveform of a channel in which cycle skipping occurred; Information processing methods.

10. The computer of the information processing device Obtaining time-series data of the phase change of backscattered light emitted from a scatterer present in the optical fiber cable, extracting a first seismic waveform from a channel where cycle skipping occurs and a second seismic waveform from a channel where cycle skipping does not occur from among channels at predetermined intervals of the optical fiber cable; using an amplitude ratio between the first seismic waveform and the second seismic waveform to estimate a seismic waveform of a channel in which cycle skipping occurred; program.

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