Processing device, distributed acoustic sensing system, distributed acoustic sensing method and program

Abstract

A signal acquisition unit (11) acquires a plurality of signal groups acquired on the basis of return light from a plurality of long gauge length sections and a plurality of signal groups acquired on the basis of return light from a plurality of short gauge length sections, the plurality of long gauge length sections and the plurality of short gauge length sections being set for an optical fiber to be used for distributed acoustic sensing. A signal selection unit (12) selects a long gauge length section on the basis of first features of the respective signal groups of the plurality of long gauge length sections, and selects a plurality of short gauge length sections corresponding to the selected long gauge length section. A section estimation unit (13) determines one short gauge length section as a section in which an event has occurred on the basis of second features of the respective signal groups of the selected plurality of short gauge length sections.

Description

[Technical field]

[0001] The present invention relates to a processing device, a distributed acoustic sensing system, a distributed acoustic sensing method, and a non-transitory computer-readable medium having a program stored thereon. [Background technology]

[0002] Distributed acoustic sensing (DAS) is known as one of the optical fiber sensing technologies. In DAS, when sound waves hit an optical fiber, the light passing through the optical fiber is modulated, and by detecting the reflected or transmitted light, sound waves or vibrations in a remote location can be monitored.

[0003] A DAS system generally consists of an optical fiber that senses sound and vibration, and a detection unit called an interrogator. An interrogator is a device that applies a probe light to the optical fiber, receives the reflected light or transmitted light from the optical fiber, and detects the state of sound waves and vibration acting on the optical fiber (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-511491 [Patent Document 2] Special Publication No. 2019-518968 [Patent Document 3] JP 2012-63146 A Summary of the Invention [Problem to be solved by the invention]

[0005] Sensing in a DAS system has a problem that it is difficult to specify the exact location of a phenomenon to be detected (hereinafter referred to as an event). In a DAS system, a section having a predetermined gauge length is set in an optical fiber included in an optical cable laid in a target area, and the state of sound or vibration generated in the section is measured as a signal, and then it is detected in the vicinity of which section an event has occurred. In this case, generally, a signal obtained from a return light from a section with a long gauge length has a high intensity and a high SN (Signal to Noise) ratio. Therefore, although the occurrence of an event can be easily detected, the long gauge length makes it difficult to specify where in the long section the event has occurred. In contrast, a signal obtained from a return light from a section with a short gauge length has a low intensity and a low SN ratio. Therefore, it is difficult to determine whether a signal fluctuation is due to an event occurrence or noise, etc., and the event detection accuracy is poor. Therefore, even if the gauge length is shortened to improve the spatial resolution of event detection, it is difficult to detect an event favorably.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to detect the occurrence of an event with high spatial resolution in a distributed acoustic sensing system. [Means for solving the problem]

[0007] A processing device according to one embodiment of the present invention includes a signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, which are set in an optical fiber used for distributed acoustic sensing; a signal selection unit that selects a long gauge long section based on a first feature value of each of the signal groups of the plurality of long gauge long sections and selects a plurality of short gauge long sections corresponding to the selected long gauge long section; and a section estimation unit that determines one short gauge long section as the section in which an event has occurred based on a second feature value of each of the signal groups of the selected plurality of short gauge long sections.

[0008] A distributed acoustic sensing system according to one embodiment of the present invention comprises an optical fiber used for sensing, a detection unit that outputs an optical pulse to the optical fiber and monitors the return light, and a processing unit that receives the monitoring results of the return light from the detection unit. The processing unit comprises a signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections set in the optical fiber, a signal selection unit that selects a long gauge long section based on a first feature value of each of the signal groups of the plurality of long gauge long sections and selects a plurality of short gauge long sections corresponding to the selected long gauge long section, and a section estimation unit that determines one short gauge long section as the section in which an event has occurred based on a second feature value of each of the signal groups of the selected plurality of short gauge long sections.

[0009] A distributed acoustic sensing method according to one embodiment of the present invention acquires a plurality of signal groups based on return light from a plurality of long gauge long sections and a plurality of signal groups based on return light from a plurality of short gauge long sections, which are set in an optical fiber used for the distributed acoustic sensing, selects a long gauge long section based on a first characteristic value of each of the signal groups of the plurality of long gauge long sections, selects a plurality of short gauge long sections corresponding to the selected long gauge long section, and determines one short gauge long section as the section in which an event occurred based on a second characteristic value of each of the signal groups of the selected plurality of short gauge long sections.

[0010] A non-transitory computer-readable medium having a program stored thereon that is one embodiment of the present invention causes a computer to execute the following processes: acquiring a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections set in an optical fiber used for distributed acoustic sensing; selecting a long gauge long section based on a first feature value of each of the signal groups of the plurality of long gauge long sections and selecting a plurality of short gauge long sections corresponding to the selected long gauge long section; and determining one short gauge long section as the section in which an event occurred based on a second feature value of each of the signal groups of the selected plurality of short gauge long sections. Effect of the Invention

[0011] According to the present invention, the occurrence of an event can be detected with high spatial resolution in a distributed acoustic sensing system. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a distributed acoustic sensing system according to a first embodiment. [Diagram 2] FIG. 1 is a diagram illustrating a schematic configuration of a processing apparatus according to a first embodiment. [Diagram 3] FIG. 2 is a diagram illustrating in more detail the configuration of the processing device according to the first embodiment. [Figure 4] FIG. 2 is a diagram showing a schematic diagram of a gauge set on an optical fiber. [Diagram 5] FIG. 13 is a diagram illustrating an example of the relationship between a gauge length and a signal. [Figure 6] 4 is a flowchart of an event section determination operation of the distributed acoustic sensing system according to the first embodiment. [Figure 7] FIG. 11 is a diagram illustrating a schematic configuration of a distributed acoustic sensing system according to a second embodiment. [Figure 8] 13 is a flowchart of an event section determination operation of the distributed acoustic sensing system according to the second embodiment. [Figure 9] FIG. 13 is a diagram illustrating a schematic configuration of a distributed acoustic sensing system according to a third embodiment. [Figure 10] 13 is a flowchart of an event section determination operation of the distributed acoustic sensing system according to the third embodiment. [Figure 11] FIG. 13 is a diagram illustrating a schematic configuration of a distributed acoustic sensing system according to a fourth embodiment. [Figure 12] 13 is a flowchart of an event section information update operation of the distributed acoustic sensing system according to the fourth embodiment. [Figure 13] 13 is a flowchart of an event section information update operation of the distributed acoustic sensing system according to the fourth embodiment. [Figure 14] 13 is a flowchart for determining the similarity of events based on the similarity between short gauge long sections corresponding to two adjacent long gauge long sections. [Figure 15] FIG. 13 shows an example in which two adjacent long gauge long sections have a shared short gauge long section. [Figure 16] FIG. 13 shows an example in which two adjacent long gauge long sections do not have a shared short gauge long section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted as necessary.

[0014] First embodiment A DAS system according to a first embodiment will be described. FIG. 1 shows a schematic configuration of a DAS system 100 according to the first embodiment. The DAS system 100 includes detection units 1 and 2, a processing device 10, and an optical fiber F. L and F S The processing device 10 receives the control signal COM L The detection unit 1 is controlled by the control signal COM SThe processing device 10 controls the detection unit 2 based on the detection signal DET indicating the detection result from the detection unit 1. L and receives a detection signal DET indicating the detection result from the detection unit 2. S and performs the signal processing required for acoustic sensing.

[0015] Optical Fiber F L and F S is laid in the same or nearby path in the area targeted for sensing of the acoustic wave AW, and is, for example, a fiber packed in an optical cable C such as a submarine cable.

[0016] The detector 1 is an optical fiber F L and optical fiber F L To Optical Pulse P L and optical fiber F L The backscattered light R L The detector 1 is configured as a so-called interrogator that detects the return light R L The detection signal DET L is output to the processing device 10.

[0017] The detector 2 is an optical fiber F S and optical fiber F S To Optical Pulse P S and optical fiber F S The backscattered light R S The detector 2 is configured as a so-called interrogator that detects the return light R S The detection signal DET S is output to the processing device 10.

[0018] 2 shows a schematic configuration of the processing device 10. FIG. 3 shows a more detailed configuration of the processing device according to the first embodiment. The processing device 10 includes a signal acquisition unit 11, a signal selection unit 12, a section estimation unit 13, and a storage unit 14. The signal acquisition unit 11 receives the detection signals DET output from the detection units 1 and 2, and stores the detection signals DET in a storage unit 14. L and DET SThe signal acquisition unit 11 receives the long gauge long section, performs signal processing to convert the long gauge long section into a data format used for signal processing in the signal selection unit 12, and outputs the processed signal to the signal selection unit 12. The signal selection unit 12 refers to the signal group for the received long gauge long section, selects the long gauge long section estimated to be closest to the sound source, and selects multiple short gauge long sections corresponding to the selected long gauge long section based on the gauge correspondence information TAB described later. The section estimation unit 13 refers to the signal group of the selected multiple short gauge long sections, and determines the short gauge long section estimated to be closest to the sound source as the event section. The storage unit 14 stores the gauge correspondence information TAB, which specifies which short gauge long section corresponds to each long gauge long section, that is, multiple short gauge long sections included in one long gauge long section. Note that the storage unit 14 can also store other information, and the signal acquisition unit 11, the signal selection unit 12, and the section estimation unit 13 can read out necessary information from the storage unit 14 and write necessary information to the storage unit 14 as appropriate.

[0019] In this embodiment, the optical fiber F L and F S The gauges of the optical fibers F are different in length. L and F S In this example, the optical fiber F L Then, in the direction away from the detection unit 1, the gauge length G L (hereinafter referred to as the long gauge length) 1 ~L M (M is an integer of 2 or more) is set. Optical fiber F S Then, the gauge length G is increased in a direction away from the detection unit 2. S (hereinafter also referred to as the short gauge length) 1 ~S N (N is an integer of 2 or greater) is set.

[0020] Long gauge length G L is short gauge length G S In FIG. 4, as an example, the long gauge length G L is short and long gauge length G S 3 times (GL =3G S However, this is only an example, and the long gauge length G L Short gauge length G S As long as the gauge length is longer than G L and short gauge length G S can be any value. For example, the long gauge length G L is several tens of meters, short gauge length G S can be several tens of centimeters to several meters.

[0021] In addition, for two adjacent long gauge long sections, short gauge long sections may be associated with each other so as not to overlap, or short gauge long sections may be associated with each other so as to overlap. For example, in FIG. 4, the long gauge long sections L 1 Short gauge long section S 1 ~S 3 , Long gauge long section L 2 Short gauge long section S 4 ~S 6 , Long gauge long section L 3 Short gauge long section S 7 ~S 9 For example, in FIG. 4, the long gauge long section L 1 and long gauge long section L 2 The short gauge long section S located on the border with 3 may be shared, long gauge long section L 2 and long gauge long section L 3 The short gauge long section S located on the border with 6 In this case, the long gauge long section L 2 Long gauge long section L 1 Short gauge long section shared with S 3 , Short gauge long section S 4 and S 5 , Long gauge long section L 3 Short gauge long section shared with S 6 The number of short gauge long sections shared by two adjacent long gauge long sections is not limited to one, and may be any number.

[0022] As a result, the detection unit 1 is a long gauge long section L 1~L M and outputs the detection results. The detection unit 2 receives the return light from each of the short gauge long section S 1 ~S N The processing device 10 can then appropriately analyze the signals obtained from these detection results.

[0023] The DAS system 100 of this embodiment is configured to identify the exact location of a sound source by combining a group of signals obtained from return light from multiple long-gauge long sections and a group of signals obtained from return light from multiple short-gauge long sections.

[0024] When analyzing the return light when a sound wave AW reaches an optical fiber in a DAS system, a difference generally occurs between the signal obtained from the return light from a long gauge length section and the signal obtained from the return light from a short gauge length section. Figure 5 shows an example of the relationship between gauge length and signal. Here, as an example, attention is focused on the long gauge length section L and the corresponding short gauge length sections S_1 to S_3, and the waveforms in the frequency domain of the signals SIG_L and SIG_S_1 to SIGS_3 obtained from these are shown. Generally, a signal with high intensity and a high SN (Signal to Noise) ratio is obtained from the return light from the long gauge length section. For this reason, the optical fiber F L When the sound wave AW reaches the long gauge long section, the difference in signal intensity between adjacent long gauge long sections becomes relatively large, so that the long gauge long section close to the sound source can be easily identified.

[0025] In contrast, the return light from the short gauge long section generally produces a signal with low intensity and a low S / N ratio. Therefore, even if the signal intensity of the return light from the short gauge long section is monitored, the fluctuation in the signal intensity is small when sound waves arrive and when the signal intensity fluctuates due to factors other than sound waves, making it difficult to distinguish between these two.

[0026] In the DAS system 100, when a sound wave reaches an optical fiber, the long gauge long section closest to the sound source is first identified by utilizing the characteristics due to the difference in gauge length, and then the signal obtained from the short gauge long section corresponding to the identified long gauge long section, i.e., provided at the same position, is analyzed to determine the short gauge long section closest to the sound source as the event section. This allows the DAS system 100 to determine the position closest to the sound source (event position) with high accuracy.

[0027] The following describes the operation of determining an event position in the DAS system 100. A flowchart of the operation of determining an event section in the DAS system 100 is shown in FIG.

[0028] Step ST11 The detector 1 is an optical fiber F L Light pulse P L and return light R L Then, the return light R L The detection signal DET is obtained by photoelectric conversion of L The detection unit 2 outputs the signal from the optical fiber F S Light pulse P S and the return light R S Then, the return light R S The detection signal DET is obtained by photoelectric conversion of S The data is output to the processing device 10.

[0029] Step ST12 The signal acquisition unit 11 receives a detection signal DET L The signal acquisition unit 11 acquires a signal group of the long gauge long section based on the signal group and outputs the acquired signal group to the signal selection unit 12. The signal acquisition unit 11 also outputs the detection signal DET L and outputs the acquired signal group to the signal selection unit 12.

[0030] Step ST13 The signal selection unit 12 monitors the signal group acquired for each long gauge long section and determines whether there is a long gauge long section in which the first feature amount is greater than a threshold. Here, an example will be described in which the signal intensity of each long gauge long section is used as the first feature amount of each long gauge long section. The signal selection unit 12 monitors the signal group acquired for each long gauge long section and determines whether there is a long gauge long section in which the fluctuation in signal intensity is greater than a threshold.

[0031] Step ST14 When there is a long gauge long section in which the variation in the first feature amount is greater than a threshold, the signal selection unit 12 selects that long gauge long section as a long gauge long section in which an event such as the arrival of a sound wave has occurred.

[0032] Step ST15 The signal selection unit 12 selects a plurality of short gauge long sections corresponding to the selected long gauge long section. Here, a plurality of short gauge long sections corresponding to each of the long gauge long sections are determined in advance, and the gauge correspondence information TAB, which is the correspondence information, may be stored in advance in the storage unit 14 as, for example, a data table. The signal selection unit 12 can select a plurality of short gauge long sections corresponding to the selected long gauge long section by referring to the gauge correspondence information TAB as necessary.

[0033] Step ST16 The section estimation unit 13 selects a short gauge long section (hereinafter referred to as an event section) in which it is estimated that the strongest sound wave has arrived, based on the second feature amount of each of the selected two or more short gauge long sections. Here, an example will be described in which the maximum value of the signal strength of each short gauge long section is used as the second feature amount of each short gauge long section. The processing device 10 obtains the maximum strength value from each of the waveforms of the two or more short gauge long sections, and selects the short gauge long section with the largest maximum value as the event section.

[0034] Although the above describes an example in which an event section is selected using the maximum value of the intensities of the waveforms of the selected multiple short gauge long sections as a feature amount, other feature amounts may be used to select an event section. For example, the feature amount of each short gauge long section may be the similarity of the signal between the selected long gauge long section and each short gauge long section.

[0035] The signal to be used may be a time waveform signal, or a signal obtained by performing a predetermined process on a time waveform signal. For example, the similarity may be calculated using a signal obtained by applying a low-pass filter to a time waveform signal or a signal obtained by performing a process to suppress noise. Also, for example, a time and frequency domain signal obtained by converting a time waveform signal by Fourier transform or CQT (Constant Q Conversion), that is, a so-called spectrogram, may be used. In this case, not only the converted signal itself, but also a signal obtained by performing a predetermined signal process on the converted signal, such as a binarized signal obtained by performing a discrimination process on the intensity of the converted waveform signal using a predetermined threshold value, or a signal obtained by applying an edge enhancement filter to enhance a portion where the intensity changes sharply, may be used. Also, a so-called spectrogram may be used.

[0036] The similarity may be calculated using an index indicating the difference between the waveform signal acquired for the selected long gauge long section and the waveform signal acquired for each short gauge long section. When the feature quantity is a multidimensional quantity such as a distribution of data points or a vector quantity, various indices such as cross-correlation, correlation coefficient, Mahalanobis distance, cosine distance, and Pearson's product moment correlation coefficient can be used as an index indicating the difference. When the feature quantity is a scalar quantity, an index such as the difference between two values ​​or the absolute value of the difference can be used.

[0037] Furthermore, as the feature amount, principal components obtained by performing principal component analysis on a time waveform signal or a signal in the time and frequency domain, or Mel-frequency cepstral coefficients of a signal in the time and frequency domain may be used.

[0038] As described above, according to this configuration, the general location where an event occurred is specified in a long gauge long section, and the event section is determined from a short gauge long section corresponding to the specified long gauge long section, thereby narrowing down the detailed location of the event section. In other words, the event section can be determined with high spatial resolution.

[0039] As described above, in a short gauge long section, the signal-to-noise ratio of a signal obtained by the occurrence of an event is low, and it is generally difficult to determine whether a signal fluctuation is due to an event or the influence of noise or the like. However, according to this configuration, the general position where an event occurred is identified by using a long gauge long section where a signal with a high signal-to-noise ratio is obtained. As a result, it is possible to determine with high accuracy the short gauge long section where the event occurred, since the intensity fluctuation appearing in the signal in the short gauge long section corresponding to the identified long gauge long section can be determined to be due to an event.

[0040] Embodiment 2 In the first embodiment, an example is described in which a long gauge long section is set in one of two optical fibers and a short gauge long section is set in the other, but other configurations are possible as long as a signal group of the long gauge long section and a signal group of the short gauge long section can be obtained. Below, other configurations of a DAS system that can obtain a signal group of the long gauge long section and a signal group of the short gauge long section will be described.

[0041] 7 shows a schematic configuration of a DAS system 200 according to the second embodiment. The DAS system 200 includes a processing device 2, a detection unit 1, and an optical fiber F. The detection unit 1 is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0042] In the DAS system 200, similarly to the DAS system 100, the detection unit 1 outputs an optical pulse P to the optical fiber F and can monitor the return light R from a gauge section of a predetermined gauge length set in the optical fiber F. This makes it possible to obtain a group of signals obtained for a plurality of gauge sections.

[0043] The processing device 2 is configured to be able to convert the acquired signal group into signals of different gauge length intervals by performing a predetermined signal processing. The signal acquisition unit 21, the signal selection unit 22, the interval estimation unit 23, and the storage unit 24 of the processing device 2 correspond to the signal acquisition unit 11, the signal selection unit 12, the interval estimation unit 13, and the storage unit 14 of the processing device 1, respectively.

[0044] In this configuration, a long-gauge long section is set in the optical fiber F, and a signal group obtained for the long-gauge long section by signal processing can be converted into a signal group for a short-gauge long section.

[0045] The following describes the operation of the DAS system 200. Fig. 8 shows a flowchart of the event section determination operation of the DAS system 200 according to the second embodiment. In Fig. 8, step ST12 in Fig. 6 is replaced with steps ST21 and ST22.

[0046] Step ST21 The signal acquiring unit 21 acquires a group of signals corresponding to the long gauge long section.

[0047] Step ST22 The signal acquiring unit 21 performs signal processing on the signal group corresponding to the long gauge long section based on the signal processing condition INF read from the storage unit 24, and acquires a signal group corresponding to the short gauge long section.

[0048] The other steps ST11, and ST13 to ST16 are similar to those in FIG. 6, and therefore the description thereof will be omitted.

[0049] The signal processing conditions in this configuration can be determined by performing an initial setting process as follows. First, a known sound source is set in advance near the optical fiber F, and the optical fiber F is irradiated with known sound waves to obtain a signal group for the long gauge long section. Then, a short gauge long section is set in the optical fiber, and the known sound waves are irradiated again to obtain a signal group for the short gauge long section. Then, the two obtained signal groups are compared, and initial setting process is performed to set conditions for converting the signal of the long gauge long section to obtain a signal of the short gauge long section, thereby obtaining signal processing conditions and storing them in the storage unit 24 as signal processing conditions INF.

[0050] Also, a short-gauge long section may be set in the optical fiber F, and a signal group obtained for the short-gauge long section by signal processing may be converted into a signal group for the long-gauge long section. In this case, the signal processing conditions can be obtained in the same manner as described above.

[0051] As a modified example of the DAS system 200, it is possible to obtain a signal group for the long gauge long section and a signal group for the short gauge long section by changing the detection of the return light in the detection unit. For example, two light receiving units may be provided in the detection unit, and the return light from the optical fiber F may be distributed to the two light receiving units. In this case, it is possible to obtain a signal group for the long gauge long section from the signal output from one light receiving unit and a signal group for the short gauge long section from the signal output from the other light receiving unit by physically dividing the return light in two without using signal processing. Thus, similarly, each time an optical pulse is output, it is possible to simultaneously obtain a signal group for the long gauge long section and a signal group for the short gauge long section from the signal output from the other light receiving unit.

[0052] As described above, according to the DAS system of the second embodiment, it is possible to determine an event interval with high spatial resolution, similarly to the first embodiment.

[0053] Third embodiment A DAS system according to the third embodiment will be described. The DAS system 300 according to the third embodiment is configured as a modified example of the DAS system 200. Fig. 9 shows a schematic configuration of the DAS system 300 according to the third embodiment. The DAS system 300 has a processing device 3, a detection unit 1, and an optical fiber F. The detection unit 1 and the optical fiber F are similar to those of the DAS system 200, and therefore description thereof will be omitted.

[0054] The processing device 3 is configured to be able to acquire a signal group of a long gauge length section and a signal group of a short gauge length section by switching the gauge length as described later. The signal acquisition unit 31, the signal selection unit 32, the section estimation unit 33, and the storage unit 34 of the processing device 3 correspond to the signal acquisition unit 11, the signal selection unit 12, the section estimation unit 13, and the storage unit 14 of the processing device 1, respectively.

[0055] In the DAS system 300, a long gauge long section and a short gauge long section are alternately set in a time-division manner in the optical fiber F. That is, a process of acquiring a signal group in a state where a long gauge long section is set and a process of acquiring a signal group in a state where a short gauge long section is set can be alternately performed.

[0056] The following describes the operation of the DAS system 300. Fig. 10 shows a flowchart of the event section determination operation of the DAS system 300 according to the third embodiment. In Fig. 10, steps ST11 and ST12 in Fig. 6 are replaced with steps ST31 to ST36.

[0057] Step ST31 The signal acquiring unit 31 first sets a plurality of long gauge long sections in the optical fiber F.

[0058] Step ST32 The detection unit 1 outputs an optical pulse P to an optical fiber F and monitors the return light R. Then, the detection unit 1 outputs a detection signal DET obtained by photoelectrically converting the return light R to the processing device 10.

[0059] Step ST33 The signal acquisition unit 31 acquires a signal group of the long gauge long section based on the detection signal DET, and stores the acquired signal group in, for example, a storage unit 34 as long gauge long section signal group information SIG L Store as .

[0060] Step ST34 The signal acquiring unit 31 sets a plurality of short gauge long sections in the optical fiber F by switching the gauge length.

[0061] Step ST35 The detection unit 1 outputs an optical pulse P to an optical fiber F and monitors the return light R. Then, the detection unit 1 outputs a detection signal DET obtained by photoelectrically converting the return light R to the processing device 10.

[0062] Step ST36 The signal acquisition unit 31 acquires a signal group of the short gauge long section based on the detection signal DET, and stores the acquired signal group in, for example, a storage unit 34 as short gauge long section signal group information SIG S Store as .

[0063] The other steps ST13 to ST16 are the same as those in FIG. 6, and therefore the description will be omitted.

[0064] In this configuration, for example, when sound waves are emitted continuously or intermittently from a sound source, sound waves from the same sound source can be sampled multiple times. This makes it possible to obtain a signal group for a long gauge long section and a signal group for a short gauge long section for similar or similar sound waves, even if they are not simultaneous in time, by setting the timing of switching the gauge length to be sufficiently short.

[0065] As described above, according to the DAS system of the third embodiment, like the first and second embodiments, it is possible to determine an event interval with high spatial resolution.

[0066] Fourth embodiment In the first embodiment, only one long gauge long section is selected, and multiple short gauge long sections close to the sound source are determined from multiple short gauge long sections corresponding to the selected one long gauge long section. However, when an event occurs in two long gauge long sections, it may be better to determine multiple short gauge long sections close to the sound source from short gauge long sections corresponding to these two long gauge long sections. In this embodiment, a DAS system that determines multiple short gauge long sections close to the sound source from short gauge long sections corresponding to two long gauge long sections in this manner will be described.

[0067] FIG. 11 is a schematic diagram showing a configuration of a DAS system 400 according to the fourth embodiment. The DAS system 400 has a configuration in which the processing device 1 of the DAS system 100 is replaced with a processing device 4. The detecting units 1 and 2, the optical fiber F L and F S is similar to that of the DAS system 100, so the explanation will be omitted.

[0068] The signal acquisition unit 41, the signal selection unit 42, the section estimation unit 43, and the storage unit 44 of the processing device 4 correspond to the signal acquisition unit 11, the signal selection unit 12, the section estimation unit 13, and the storage unit 14 of the processing device 1, respectively.

[0069] The following describes the operation of the DAS system 400. After performing the event section determination operation shown in Fig. 6, if an event section exists in an adjacent long gauge long section, the DAS system 400 determines whether the event sections are the same event, i.e., whether they are caused by the same sound wave, and updates the event section information as necessary.

[0070] 12 and 13 show flowcharts of the event section information update operation of the DAS system 400 according to the fourth embodiment. The steps in Fig. 12 and Fig. 13 are performed after the completion of steps ST11 to ST16 in Fig. 6.

[0071] In this configuration, steps ST11 to ST16 in FIG. 6 are performed to obtain the long-gauge long-section signal group information SIG L, Short Gauge Long Section Signal Group Information SIG S , and event section information EVT, which is information indicating a short gauge long section that is an event section, is stored.

[0072] Step ST41 The signal acquisition unit 41 refers to the event section information EVT and the gauge correspondence information TAB, and searches for a location where an event section exists in each of two adjacent long gauge long sections, starting from the detection unit 1. If there is no location where an event section exists in each of two adjacent long gauge long sections, the process ends.

[0073] Step ST42 If there is a location where an event section exists in each of two adjacent long gauge long sections, the signal selection unit 42 selects the two adjacent long gauge long sections LA and LB that it has found, and passes the selection result to the section estimation unit 43.

[0074] Step ST43 As described in the first embodiment, the section estimation unit 43 calculates the similarity between the long gauge long sections LA and LB, and judges whether the calculated similarity is greater than a predetermined threshold. If the similarity between the long gauge long sections LA and LB is equal to or less than the predetermined threshold, the process returns to step ST41. From this, it can be understood that if the similarity is small, the signal groups of the long gauge long sections LA and LB are dissimilar, and each has been judged to be a different event.

[0075] Step ST44 If the similarity calculated in step ST43 is greater than a predetermined threshold, the section estimation unit 43 deletes the event sections of the long gauge long sections LA and LB. Specifically, the section estimation unit 43 accesses the storage unit 44 and performs a process of deleting the event sections of the long gauge long sections LA and LB from the event section information EVT.

[0076] Step ST45 The signal selection unit 42 selects a plurality of short gauge long sections corresponding to the long gauge long section LA.

[0077] Step ST46 The section estimation unit 43 selects a candidate event section SA, which is a short-gauge long section estimated to have been reached by a sound wave with the strongest intensity, based on the feature amounts of each of a plurality of short-gauge long sections corresponding to the long-gauge long section LA.

[0078] Step ST47 The signal selection unit 42 selects a plurality of short gauge long sections corresponding to the long gauge long section LB.

[0079] Step ST48 The section estimation unit 43 selects a potential event section SB, which is a short-gauge long section estimated to have been reached by a sound wave with the strongest intensity, based on the feature amounts of each of a plurality of short-gauge long sections corresponding to the long-gauge long section LB.

[0080] Step ST49 The section estimation unit 43 calculates the similarity between the long gauge long section LA and the event section candidate SA, and the similarity between the long gauge long section LB and the event section candidate SB, and then determines whether the similarity between the long gauge long section LA and the event section candidate SA is equal to or greater than the similarity between the long gauge long section LB and the event section candidate SB.

[0081] Step ST50 If the similarity between the long gauge long section LA and the event section candidate SA is equal to or greater than the similarity between the long gauge long section LB and the event section candidate SB, the event section candidate SA is determined as the event section, and the event section information EVT is updated. Then, the process returns to step ST41.

[0082] Step ST51 If the similarity between the long gauge long section LA and the event section candidate SA is smaller than the similarity between the long gauge long section LB and the event section candidate SB, the event section candidate SB is determined as the event section, and the event section information EVT is updated. Then, the process returns to step ST41.

[0083] By performing the above steps ST41 to ST51, when event sections resulting from the same event exist in multiple long gauge sections, it is possible to delete the overlapping event sections and consolidate them into event sections resulting from a single event.

[0084] Furthermore, since dissimilar event sections can be left as they are, it is possible to suitably store information about event sections caused by different events.

[0085] 12 and 13, the similarity of the events is determined based on the similarity of the waveform signals of two adjacent long gauge long sections, but it may be determined based on the similarity of the short gauge long sections corresponding to the two adjacent long gauge long sections. A specific description will be given below.

[0086] Fig. 14 shows a flowchart for determining the similarity of events based on the similarity between short gauge long sections corresponding to two adjacent long gauge long sections. In Fig. 14, step ST43 in Fig. 12 is replaced with steps ST61 to ST64.

[0087] Step ST61 The section estimation unit 43 judges whether there is a short gauge long section shared by the long gauge long sections LA and LB. Here, sharing of a short gauge long section will be explained. FIG. 15 shows an example in which the long gauge long sections LA and LB have a short gauge long section shared by them. In this example, a short gauge long section S that exists across the boundary BND between the long gauge long sections LA and LB is SH is a short gauge long section corresponding to both the long gauge long sections LA and LB. Fig. 16 shows an example in which the long gauge long sections LA and LB do not have a shared short gauge long section. In this example, the long gauge long sections LA and LB each correspond to their own short gauge long section, and there is no short gauge long section that overlaps with both.

[0088] Step ST62 When there is a short gauge long section shared between the long gauge long sections LA and LB, the section estimation unit 43 estimates the shared short gauge long section S SH The similarity between the short gauge long section Sa corresponding to the long gauge long section LA and the short gauge long section Sb corresponding to the long gauge long section LB, which are adjacent to each other, is calculated. In other words, the short gauge long section Sa is a similarity between the short gauge long section Sb and the short gauge long section Sb, which are adjacent to each other, among the multiple short gauge long sections corresponding to the long gauge long section LA. SH The short gauge long section Sb is the short gauge long section that is closest to the long gauge long section LB other than the long gauge long section LB. The short gauge long section Sb is the short gauge long section S that is shared among the multiple short gauge long sections corresponding to the long gauge long section LB. SH This is the short-gauge long section that is closest to the long-gauge long section LA other than the long-gauge long section LA.

[0089] Step ST63 When there is no short gauge long section shared by the long gauge long sections LA and LB, the section estimation unit 43 estimates a short gauge long section Sa adjacent to the long gauge long section LB among the multiple short gauge long sections corresponding to the long gauge long section LA, and a short gauge long section Sa adjacent to the long gauge long section LA among the multiple short gauge long sections corresponding to the long gauge long section LB. Sb The similarity between and is calculated.

[0090] Step ST64 The section estimation unit 43 judges whether the similarity between the short gauge long section Sa and the short gauge long section Sb is greater than a predetermined threshold value. If the similarity is greater than the predetermined threshold value, the process proceeds to step ST44, and if the similarity is equal to or less than the predetermined threshold value, the process returns to step ST41.

[0091] The other steps are similar to those in FIG. 12 and FIG. 13, and therefore the description will be omitted.

[0092] Therefore, in this case as well, similarly to FIG. 12 and FIG. 13, short gauge long sections based on the same event can be consolidated into one.

[0093] Although the above description is given as a modified example of the DAS system 100 according to the first embodiment, this is merely an example. It goes without saying that the present invention can be applied to the DAS systems according to the second and third embodiments as long as the signal group of the long gauge long section and the signal group of the short gauge long section can be used.

[0094] Other embodiments The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above-described embodiment, the similarity has been described, but the similarity may be an index indicating similarity when it is large and dissimilarity when it is small, or an index indicating dissimilarity when it is large and similarity when it is small.

[0095] In the above embodiment, the step of determining which of the two values ​​a and b is larger has been described, but when the values ​​a and b are equal, it may be determined that the value a is larger, or the value b is larger, as necessary. In other words, it may be determined whether the value a is larger than the value b (i.e., whether the value b is equal to or smaller than the value a), or whether the value a is equal to or larger than the value b (i.e., whether the value b is smaller than the value a).

[0096] In the above embodiment, the present invention has been described as a hardware configuration, but the present invention is not limited to this. The present invention can also be realized by making a CPU (Central Processing Unit) execute a computer program to perform processing in a processing device. The above-mentioned program can be stored using various types of non-transitory computer readable media and supplied to a computer. The non-transitory computer readable media includes various types of tangible storage media. Examples of the non-transitory computer readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R / W, and semiconductor memories (e.g., mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, and RAM (Random Access Memory)). The program may also be supplied to a computer by various types of transitory computer readable media. Examples of the transitory computer readable media include electric signals, optical signals, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire or an optical fiber, or via a wireless communication path.

[0097] The present invention has been described above, but it can also be described as follows.

[0098] (Supplementary Note 1) A processing device having: a signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, both of which are set in an optical fiber used for distributed acoustic sensing; a signal selection unit that selects a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections and selects a plurality of short gauge long sections corresponding to the selected long gauge long section; and a section estimation unit that determines one short gauge long section as a section in which an event has occurred based on a second feature amount of each of the signal groups of the selected plurality of short gauge long sections.

[0099] (Supplementary Note 2) The processing device described in Supplementary Note 1, wherein the signal selection unit compares the signals of each of the selected multiple short gauge long sections with the signal of the selected long gauge long section, and determines the short gauge long section having a signal that is most similar to the signal of the selected long gauge long section as the section in which the event occurred.

[0100] (Supplementary Note 3) The processing device according to Supplementary Note 2, wherein the signal selection unit uses, as the signal, any one of a time waveform signal, a waveform signal obtained by applying a frequency filter to the time waveform signal, a waveform signal that has been processed to suppress noise in the time waveform signal, a signal obtained by Fourier transforming the time waveform signal, a signal obtained by transforming the time waveform signal using Constant Q Conversion (CQT), and a spectrogram obtained from the time waveform signal.

[0101] (Supplementary Note 4) The processing device described in Supplementary Note 1, wherein the signal selection unit determines the section in which the event occurred based on principal components obtained by performing principal component analysis on the time waveform signals of each of the selected multiple short gauge long sections or the waveform signals obtained by converting the time waveform signals, or based on Mel frequency cepstrum coefficients of the time waveform signals of each of the selected multiple short gauge long sections or the waveform signals obtained by converting the time waveform signals.

[0102] (Supplementary Note 5) The processing device according to any one of Supplementary Notes 1 to 4, wherein the signal selection unit selects a long gauge long section in which a first feature amount is greater than a first threshold value.

[0103] (Supplementary Note 6) The processing device according to any one of Supplementary Notes 1 to 5, wherein the signal selection unit determines, among the selected plurality of short gauge long sections, the section having the maximum first feature value as the section in which the event occurred.

[0104] (Supplementary Note 7) The processing device described in Supplementary Note 1, wherein the signal selection unit selects a long-gauge long section in which a first feature is greater than a first threshold, and determines, among the selected plurality of short-gauge long sections, the one in which the first feature is maximum as the section in which the event occurred.

[0105] (Appendix 8) A processing device as described in any one of appendices 1 to 7, wherein the multiple long gauge long sections are set on a first optical fiber, and the multiple short gauge long sections are set on a second optical fiber in the same or adjacent path as the first optical fiber.

[0106] (Appendix 9) The processing device described in any one of Appendices 1 to 7, wherein the signal acquisition unit acquires a signal group by setting one of the multiple long gauge long sections and the multiple short gauge long sections in a single optical fiber, and acquires a signal group of the other of the multiple long gauge long sections and the multiple short gauge long sections by performing a predetermined signal processing on the acquired signal group.

[0107] (Supplementary Note 10) The processing device described in any one of Supplementary Notes 1 to 7, wherein the signal acquisition unit alternately performs a process of setting the multiple long gauge long sections in a single optical fiber and acquiring a signal group of the multiple long gauge long sections, and a process of setting the multiple short gauge long sections in the single optical fiber and acquiring a signal group of the multiple short gauge long sections.

[0108] (Supplementary Note 11) A processing device as described in any one of Supplementary Notes 1 to 10, wherein after determining the section in which the event occurred, two adjacent long gauge long sections including the section in which the event occurred are searched for, and if the signals of the two adjacent long gauge long sections are similar, a plurality of corresponding short gauge long sections are selected for each of the two adjacent long gauge long sections, and one short gauge long section is selected as an event section candidate based on a second feature amount of each of the signal groups of the selected plurality of short gauge long sections, and a similarity indicating the degree of similarity between a signal of a first long gauge long section that is one of the two adjacent long gauge long sections and a signal of an event candidate of the first long gauge long section is compared with a similarity indicating the degree of similarity between a signal of a second long gauge long section that is the other of the two adjacent long gauge long sections and a signal of an event candidate of the second long gauge long section, and the event candidate of the long gauge section with the greater similarity is determined as a new section in which the event occurred, instead of the section in which the event occurred in the first and second long gauge long sections.

[0109] (Supplementary Note 12) After determining the section in which the event occurred, search for two adjacent long gauge long sections including the section in which the event occurred, select one short gauge long section from each of the two adjacent long gauge long sections that is adjacent to the other long gauge long section, and if the signals of the two short gauge long sections selected from the two adjacent long gauge long sections are similar, select a corresponding number of short gauge long sections for each of the two adjacent sections, and select one short gauge long section as a candidate event section based on the feature amounts of each of the signals of the selected number of short gauge long sections; A processing device as described in any one of Appendix 1 to 10, which compares a similarity indicating the degree of similarity between a signal of a first long gauge long section, which is one of the two adjacent long gauge long sections, and a signal of an event candidate in the first long gauge long section, with a similarity indicating the degree of similarity between a signal of a second long gauge long section, which is the other of the two adjacent long gauge long sections, and a signal of an event candidate in the second long gauge long section, and determines the event candidate in the long gauge section with the greater similarity as a new section in which an event has occurred, instead of the event occurrence section of the first and second long gauge long sections.

[0110] (Supplementary Note 13) A distributed acoustic sensing system comprising: an optical fiber used for sensing; a detection unit that outputs an optical pulse to the optical fiber and monitors the return light; and a processing unit that receives the monitoring results of the return light from the detection unit, wherein the processing unit comprises: a signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections set in the optical fiber; a signal selection unit that selects a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections and selects a plurality of short gauge long sections corresponding to the selected long gauge long section; and a section estimation unit that determines one short gauge long section as a section in which an event has occurred based on a second feature amount of each of the signal groups of the selected plurality of short gauge long sections.

[0111] (Supplementary Note 14) A distributed acoustic sensing method comprising: acquiring a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, both of which are set in an optical fiber used for distributed acoustic sensing; selecting a long gauge long section based on a first feature value of each of the signal groups of the plurality of long gauge long sections; selecting a plurality of short gauge long sections corresponding to the selected long gauge long section; and determining one short gauge long section as the section in which an event has occurred based on a second feature value of each of the signal groups of the selected plurality of short gauge long sections.

[0112] (Appendix 15) A non-transitory computer-readable medium having stored thereon a program that causes a computer to execute the following processes: acquiring a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, both of which are set in an optical fiber used for distributed acoustic sensing; selecting a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections and selecting a plurality of short gauge long sections corresponding to the selected long gauge long section; and determining one short gauge long section as a section in which an event occurred based on a second feature amount of each of the signal groups of the selected plurality of short gauge long sections. [Explanation of symbols]

[0113] 100, 200, 300, 400 DAS Systems 1, 2 Detector 10, 20, 30, 40 Processing device 11, 21, 31, 41 Signal acquisition section 12, 22, 32, 42 Signal selection section 13, 23, 33, 43 Interval Estimation Section 14, 24, 34, 44 storage section EVT Event Section Information F, F L , F S Optical Fiber INF signal processing conditions SIG LLong gauge long section signal group information SIG S Short Gauge Long Section Signal Group Information TAB Gauge Compatibility Information

Claims

1. A signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, both of which are set in an optical fiber used for distributed acoustic sensing; a signal selection unit that selects a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections, and selects a plurality of short gauge long sections corresponding to the selected long gauge long section; and a section estimation unit that determines one short gauge long section as a section in which an event has occurred based on the second feature amounts of each of the signal groups in the selected plurality of short gauge long sections. Processing unit.

2. the signal selection unit compares the signals of each of the selected short gauge long sections with the signal of the selected long gauge long section, and determines the short gauge long section having a signal that is most similar to the signal of the selected long gauge long section as the section in which the event occurred. The processing device of claim 1 .

3. the signal selection unit uses, as the signal, any one of a time waveform signal, a waveform signal obtained by applying a frequency filter to the time waveform signal, a waveform signal obtained by performing processing to suppress noise of the time waveform signal, a signal obtained by Fourier transforming the time waveform signal, a signal obtained by transforming the time waveform signal by CQT (Constant Q Conversion), and a spectrogram obtained from the time waveform signal. The processing device according to claim 2 .

4. the signal selection unit determines the section in which the event occurred based on principal components obtained by performing principal component analysis on the time waveform signals of the selected plurality of short gauge long sections or the waveform signals obtained by converting the time waveform signals, or based on Mel frequency cepstrum coefficients of the time waveform signals of the selected plurality of short gauge long sections or the waveform signals obtained by converting the time waveform signals. The processing device of claim 1 .

5. the signal selection unit selects a long gauge long section in which a first feature amount is greater than a first threshold value; The processing device according to any one of claims 1 to 4.

6. the signal selection unit determines, from among the selected plurality of short gauge long sections, the section in which the first feature amount is maximum as the section in which the event has occurred; The processing device according to any one of claims 1 to 5.

7. The signal selection unit is selecting a long gauge long section in which the first feature amount is greater than a first threshold value; determining, from among the selected plurality of short gauge long sections, the section in which the first feature amount is maximum as the section in which the event occurs; The processing device of claim 1 .

8. An optical fiber used for sensing; a detection unit that outputs an optical pulse to the optical fiber and monitors the return light; a processing device that receives a monitoring result of the return light from the detection unit, The processing device includes: a signal acquisition unit that acquires a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections set in the optical fiber; a signal selection unit that selects a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections, and selects a plurality of short gauge long sections corresponding to the selected long gauge long section; and a section estimation unit that determines one short gauge long section as a section in which an event has occurred based on the second feature amounts of each of the signal groups in the selected plurality of short gauge long sections. Distributed acoustic sensing system.

9. Acquire a plurality of signal groups based on return light from a plurality of long gauge long sections and a plurality of signal groups based on return light from a plurality of short gauge long sections, which are set in an optical fiber used in distributed acoustic sensing; selecting a long gauge long section based on a first characteristic amount of each of the signal groups of the plurality of long gauge long sections, and selecting a plurality of short gauge long sections corresponding to the selected long gauge long section; determining one short gauge long section as a section in which an event has occurred based on second feature amounts of each of the signal groups in the selected plurality of short gauge long sections; Distributed acoustic sensing methods.

10. A process of acquiring a plurality of signal groups acquired based on return light from a plurality of long gauge long sections and a plurality of signal groups acquired based on return light from a plurality of short gauge long sections, both of which are set in an optical fiber used for distributed acoustic sensing; selecting a long gauge long section based on a first feature amount of each of the signal groups of the plurality of long gauge long sections, and selecting a plurality of short gauge long sections corresponding to the selected long gauge long section; determining, based on the second feature amounts of each of the signal groups in the selected plurality of short gauge long sections, one short gauge long section as a section in which an event has occurred; program.

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