Optical fiber sensor and change detection method

Abstract

An optical fiber sensor (1) includes: a setting means (2) that sets an evaluation interval, which is to be set for an optical fiber (11), to either a first interval (L) or a plurality of second intervals (l) which are each shorter than the first interval (L); an extraction means (3) that extracts a change in the condition of a light from the optical fiber (11); and a detection means (4) that detects a change in the surrounding environment on the basis of time series data for the change in the condition of the light during the evaluation interval.

Description

[Technical field]

[0001] The present invention relates to an optical fiber sensor and a method for detecting changes using the optical fiber sensor. [Background technology]

[0002] There are wide-area surveillance systems for monitoring the intrusion of suspicious persons or objects into large-scale important facilities such as airports and military bases. One example of a target monitored by a wide-area surveillance system is a drone. One method for monitoring drones is to use an acoustic sensor such as a microphone (see, for example, Patent Document 1). A drone flies while emitting an acoustic signal specific to the flight state. Therefore, by capturing the acoustic signal emitted by the drone, the presence and direction of the drone can be detected. Patent Document 1 describes how a drone is identified based on the results of matching the acoustic signal of a flying object obtained by an acoustic sensor with previously acquired voice data.

[0003] There is also an estimation device that estimates the direction of a sound source using multiple microphones (see, for example, Patent Document 2). For example, a microphone array (a collection of multiple microphones) is installed at a certain point. The estimation device estimates the direction from the microphone array to the drone using the relationship between the relative position information of each microphone and the acoustic delay time measured from the output of each microphone.

[0004] However, when monitoring a large-scale facility, it is necessary to install a large number of microphone arrays, which results in a large cost for constructing a wide-area monitoring system.

[0005] When constructing a wide-area monitoring system, optical fiber sensing using an optical fiber sensor that can perform continuous monitoring over a long distance is useful from the standpoint of cost, etc. Optical fiber sensing is a technology that uses optical fiber to measure sound, vibration, etc. In optical fiber sensing, the optical fiber itself serves as the sensor. In this specification, a system including an optical fiber and a detector is referred to as an optical fiber sensor. Also, an acoustic sensor based on optical fiber sensing is sometimes referred to as an optical fiber microphone. A collection of multiple optical fiber microphones is sometimes referred to as an optical fiber microphone array.

[0006] One type of optical fiber sensor is a distributed optical fiber sensor. For example, an optical fiber sensor that uses scattered light due to Rayleigh scattering (Rayleigh scattered light) is an example of a distributed optical fiber sensor. Rayleigh scattering is the scattering of light caused by fine particles (impurities) in the optical fiber core. A detection device in an optical fiber sensor that uses Rayleigh scattered light can detect physical changes in the optical fiber caused by sound or vibration based on a signal obtained by detecting backscattered light due to Rayleigh scattering.

[0007] When a section of an optical fiber is affected by an incoming object (for example, incoming sound or vibration), the optical fiber expands or contracts in that section. In other words, the optical fiber is distorted in the longitudinal direction. As a result, the intensity (or amplitude) and phase of the backscattered light generated in that section change. By observing the change in intensity or phase, the influence of the incoming object can be detected. In other words, optical fiber sensors can be used as acoustic sensors or vibration sensors.

[0008] When observing the change in the phase of the backscattered light, the detector may be configured to evaluate the difference (phase difference) between the phase of the backscattered light at the start point of the section and the phase of the backscattered light at the end point of the section. In general, such an evaluation target section is called a gauge length. Hereinafter, the evaluation target section (gauge length) may be simply referred to as a section.

[0009] When optical fiber sensors are installed instead of multiple microphone arrays, a wide-area monitoring system for monitoring a large facility can be constructed at low cost. Furthermore, when a wide-area monitoring system is constructed using optical fiber sensors, it has the advantage of being more resistant to environmental changes and less susceptible to electromagnetic noise than when a microphone array is used. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2017-72557 A [Patent Document 2] International Publication No. 2017 / 216999 [Patent Document 3] JP 2012-68081 A [Non-patent literature]

[0011] [Non-Patent Document 1] RO Schmidt, "Multiple emitter location and signal parameter estimation", IEEE Transactions on Antennas and Propagation, vol. AP-34, NO. 3, pp.276-280, March 1986 Summary of the Invention [Problem to be solved by the invention]

[0012] For example, when the gauge length is set to the total length of an optical fiber, the optical fiber forms one optical fiber microphone. In this case, the sound collection performance of the optical fiber microphone is the performance of a single microphone. With a single microphone, there is a problem that it is difficult to accurately detect the position of a sound source when the level of the acoustic signal is low. This problem is particularly noticeable for acoustic signals that have an amplitude equal to or smaller than the background noise.

[0013] As a result, for example, a wide-area surveillance system configured to monitor the intrusion of suspicious persons or objects using a single optical fiber microphone can monitor a wide area, but has the problem that the surveillance accuracy (for example, the ability to pinpoint the intrusion location of a suspicious person or object) is not high.

[0014] Non-Patent Document 1 describes a method of estimating a direction using the MUSIC (MUltiple SIgnal Classification) method.

[0015] An object of the present invention is to provide an optical fiber sensor and a change detection method that have high detection performance when detecting changes in the surrounding environment using optical fiber sensing. [Means for solving the problem]

[0016] The optical fiber sensor according to the present invention is configured to set an evaluation target section in an optical fiber as follows: When detecting the presence of a sound source First Section Set to , When estimating the direction of a sound source, A plurality of second sections each shorter than the first section. In between A setting means for setting, an extraction means for extracting a change in the state of light from an optical fiber, and a time series data of the change in the state of light in an evaluation target section based on the time series data of the change in the state of light Sound source near the optical fiber installation location and detecting means for detecting the

[0017] The change detection method according to the present invention comprises the steps of: When detecting the presence of a sound source First Section Set to , When estimating the direction of a sound source,A plurality of second sections each shorter than the first section. In between The system extracts changes in the state of light from the optical fiber and calculates the time series data of changes in the state of light in the evaluation section. Sound source near the optical fiber installation location Detect.

[0018] The change detection program according to the present invention causes a computer to: When detecting the presence of a sound source First Section Set to , When estimating the direction of a sound source, A plurality of second sections each shorter than the first section. In between The process involves setting the optical fiber, extracting the changes in the optical state from the optical fiber, and calculating the optical fiber state based on the time series data of the changes in the optical state in the evaluation section. Sound source near the optical fiber installation location and a process of detecting the above. Effect of the Invention

[0019] According to the present invention, the detection performance is improved when optical fiber sensing is used to detect changes in the surrounding environment. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is an explanatory diagram for explaining a configuration example of an optical fiber sensor. [Diagram 2] FIG. 11 is an explanatory diagram for explaining an evaluation target section in a direction estimation mode. [Diagram 3] 1 is a block diagram showing an example of the configuration of an optical fiber sensor according to a first embodiment; [Figure 4] 4 is a block diagram showing an example of the configuration of a determination unit in the first embodiment. FIG. [Diagram 5] 4 is a block diagram showing an example of the configuration of a sound source direction estimation unit. FIG. [Figure 6] 4 is a flowchart showing the operation of the optical fiber sensor according to the first embodiment. [Figure 7] 10 is an explanatory diagram for explaining a process of detecting whether or not a sound source of a suspicious object exists based on sound amplitude data. FIG. [Figure 8]FIG. 11 is a block diagram showing an example of the configuration of a determination unit in the second embodiment. [Figure 9] 10 is a flowchart showing the operation of the optical fiber sensor according to the second embodiment. [Figure 10] FIG. 13 is a block diagram showing an example of the configuration of a determination unit in the third embodiment. [Figure 11] 10 is a flowchart showing the operation of the optical fiber sensor according to the third embodiment. [Figure 12] FIG. 1 is a block diagram showing an example of a computer having a CPU. [Figure 13] FIG. 2 is a block diagram showing a main part of the optical fiber sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] In the following description, the detection target of the change in the surrounding environment of the optical fiber sensor will be mainly the sound of a drone flying and vibrations due to the approach of a suspicious object. However, the embodiment described below can also be applied to the detection of changes in the surrounding environment other than the sound of a drone flying. Examples of other changes in the surrounding environment include temperature changes and changes in the state of buildings near the location where the optical fiber is installed.

[0023] FIG. 1 is an explanatory diagram for explaining a configuration example of an optical fiber sensor. As shown in FIG. 1, the optical fiber sensor includes an optical fiber 11, a detector 12, and an optical fiber microphone array 14 including a plurality of optical fiber microphones 13. Four optical fiber microphones 13 are illustrated in FIG. 1. The number and installation positions of the optical fiber microphones 13 are arbitrary. For example, the optical fiber microphones 13 may be arranged on a single straight line. Furthermore, the optical fiber microphones 13 may be installed at any position on a single plane. Furthermore, the optical fiber microphones 13 may be installed at any position in a three-dimensional space.

[0024] In FIG. 1, the left side shows a usage form in the detection mode. The right side shows a usage form in the orientation estimation mode. The detection mode is a mode for detecting a sound (e.g., a flying sound of a drone) from a sound source (a drone in this embodiment) 10. The orientation estimation mode is a mode for estimating the position of the sound source 10. Therefore, in the orientation estimation mode, the orientation of the sound source 10 is estimated. Note that the evaluation target section in the orientation estimation mode is shorter than the evaluation target section in the detection mode.

[0025] As shown in FIG. 1, a plurality of optical fiber microphones 13 are formed in an optical fiber 11 between a start end (e.g., position Y in the detection mode in FIG. 1) and an end end (e.g., position X in the detection mode in FIG. 1). The optical fiber microphone 13 is formed by winding the optical fiber 11 in a coil shape around a cylindrical resonance medium 15 that resonates with an acoustic signal so that no bending occurs. That is, the optical fiber microphone 13 is formed of the resonance medium 15 and the optical fiber 11. Each optical fiber microphone 13 may be formed of the entire length of the optical fiber 11 wound around the resonance medium 15, or may be formed of a part of the optical fiber 11 wound around the resonance medium 15. When the resonance medium 15 is distorted by an acoustic signal (specifically, sound pressure), the optical fiber 11 expands and contracts according to the magnitude of the acoustic signal. Then, the path length of the light passing through the optical fiber 11 changes. As a result, the amplitude and phase of the backscattered light due to Rayleigh scattering change. The detector 12 can detect a change in the surrounding environment of the optical fiber sensor based on the change in the phase of the backscattered light.

[0026] The optical fiber microphone 13 using the cylindrical resonance medium 15 is disclosed in, for example, Patent Document 3.

[0027] In Fig. 1, L indicates a section to be evaluated in the detection mode. The section to be evaluated may be expressed as a measurement section. In the example shown in Fig. 1, in the detection mode, the section to be evaluated L (first section) is defined as the entire length of the optical fiber 11 between the starting end Y and the ending end X.

[0028] Fig. 2 is an explanatory diagram for explaining the evaluation target section in the orientation estimation mode. As shown in Fig. 2, in the orientation estimation mode, the evaluation target section l (second section) is defined as the entire length of the optical fiber 11 between the start point y and the end point x of the portion where the optical fiber 11 is wound around the resonance medium 15. The section is defined between the start point y and the end point x. Although one optical fiber microphone 13 is shown in Fig. 2, the evaluation target section l is defined similarly for the other optical fiber microphones 13 included in the optical fiber microphone array 14. Four evaluation target sections l are illustrated in Fig. 1.

[0029] 1, in the azimuth estimation mode, the portions of the optical fiber 11 corresponding to the resonant medium 15 are used as the optical fiber microphones 13 (four optical fiber microphones 13 in the example shown in FIG. 1). That is, the evaluation target section is set corresponding to the resonant medium 15. However, the evaluation target section may be set across two or more resonant media 15, and if l≦L / 2 is satisfied, there are two or more portions that can be regarded as optical fiber microphones 13 inside the optical fiber microphone array 14, and it is guaranteed that the optical fiber microphone array 14 has azimuth estimation capability.

[0030] In practice, the evaluation target section is specified by the detector 12 setting a measurement point (e.g., start point y) and a reference point (e.g., end point x) that is separated therefrom by the distance of the measurement section. Setting the measurement point and the reference point by the detector 12 means that the detector 12 calculates the difference in phase information of the backscattered light received from the measurement point and the reference point after a predetermined time has elapsed since the time when light is emitted from the light source built into the detector 12, and regards the phase difference signal acquired by each optical fiber microphone 13 as the acoustic signal acquired when the optical fiber microphone 13 receives the sound. The predetermined time is the time from when light is emitted from the light source to when the backscattered light returns from the measurement point and the reference point. The drone's azimuth detection is performed based on the acoustic arrival time difference of the acoustic signals acquired by each optical fiber microphone 13.

[0031] In the detection mode, the optical fiber sensor operates to detect sounds generated around the optical fiber microphone array 14. In the detection mode, the optical fiber microphone array 14 essentially functions as one omnidirectional microphone. In the orientation estimation mode, each of the optical fiber microphones 13 in the optical fiber sensor functions as a microphone.

[0032] The optical fiber sensor operating in the detection mode has higher sound detection performance than the case where each of the optical fiber microphones 13 is functioning. For example, suppose that the optical fiber microphone array 14 has n optical fiber microphones 13. Also suppose that the noise contained in the acoustic signal is white noise that follows a Gaussian distribution. Based on the principle of synchronous addition, the signal-to-noise ratio of the entire optical fiber microphone array 14 is expected to be √n times the signal-to-noise ratio of each of the optical fiber microphones 13.

[0033] Embodiment 1. (Configuration of the embodiment) Fig. 3 is a block diagram showing a configuration example of the optical fiber sensor of the first embodiment. In the example shown in Fig. 1, the detector 12 in the optical fiber sensor includes a light source 121, a light receiving unit 122, a detection mode signal data collecting unit 126, an orientation estimation mode signal data collecting unit 127, a storage unit 128, and a determination unit 129.

[0034] The light source 121 is, for example, a laser light source that emits laser light. The light source 121 emits pulsed laser light (pulsed light) to the optical fiber 11 in accordance with, for example, an instruction from the determination unit 129. Note that the spatial resolution is determined by the pulse width of the pulsed light.

[0035] The light receiving unit 122 receives backscattered light due to Rayleigh scattering from the optical fiber 11. An optical circulator (not shown in FIG. 1) for separating optical signals is installed between the optical fiber 11 and the light source 121 and the light receiving unit 122. The light receiving unit 122 includes an opto-electrical converter 123, an AD converter 124, and a phase difference signal extractor 125.

[0036] The photoelectric converter 123 is, for example, a PD (Photodiode) that converts an optical signal into an electrical signal. The electrical signal converted by the PD includes intensity information and phase information. In this embodiment, the phase information is extracted. The AD converter 124 converts the electrical signal, which is an analog signal, into a digital electrical signal. The phase difference signal extractor 125 extracts phase difference information of an evaluation target section (hereinafter, referred to as a section) from the phase information obtained by the AD converter 124 according to information from the determination unit 129 (information indicating whether the detection mode or the azimuth estimation mode is selected) to obtain a phase difference signal. That is, the phase difference signal extractor 125 recognizes whether the evaluation target section is a first section or a second section according to the information from the determination unit 129. For example, the phase difference at the end point x of the section in FIG. 2 is used as the phase difference. As an example, the phase difference at the end point x of the section is calculated as follows.

[0037] In the detection mode, the phase of the backscattered light at the start point y of the section is P(y), and the phase of the backscattered light at the end point x is P(x). The phase difference is ΔP=P(x)-P(y). The reception time of the backscattered light from the end point x is determined by the emission time of the laser light and the distance from the light source 121 to the end point x. The reception time of the backscattered light from the start point y is determined by the emission time of the laser light and the distance from the light source 121 to the start point y. Therefore, the phase difference signal extractor 125 can determine whether the received backscattered light is backscattered light from the end point x or backscattered light from the start point y based on the time when the backscattered light is received. As a result, the phase difference signal extractor 125 can calculate the phase difference of the section.

[0038] In the direction estimation mode, the phase of the backscattered light at the start point (start end Y) of the section is P(Y), and the phase of the backscattered light at the end point (end end X) is P(X). The phase difference is ΔP=P(X)-P(Y).

[0039] The phase difference signal extractor 125 supplies the phase difference signal to the detection mode signal data collector 126 and the bearing estimation mode signal data collector 127. Hereinafter, the output of the phase difference signal extractor 125 is referred to as acoustic data. The detection mode signal data collector 126 collects acoustic data every moment in the detection mode and stores it in the memory unit 128. Collecting every moment means taking in acoustic data at a predetermined sampling period. The bearing estimation mode signal data collector 127 collects acoustic data every moment in the bearing estimation mode and stores it in the memory unit 128.

[0040] In the detection mode, the determination unit 129 uses the acoustic data (data including information on the phase difference between sections collected by the detection mode signal data collection unit 126 from time to time) stored in the storage unit 128 to determine whether or not an abnormal sound has occurred around the optical fiber microphone array 14. In the direction estimation mode, the determination unit 129 uses the acoustic data (data including information on the phase difference between sections collected by the direction estimation mode signal data collection unit 127 from time to time) stored in the storage unit 128 to generate time series data on the phase difference between sections for each optical fiber microphone 13. The determination unit 129 estimates the direction of the sound source of the abnormal sound using the time series data on the phase difference between each section. Note that in this embodiment and other embodiments, a sound (flying sound of a drone in this embodiment and other embodiments) generated by a suspicious object (a drone (sound source 10) in this embodiment and other embodiments) is called an abnormal sound.

[0041] In this embodiment, when the presence of an abnormal sound source is detected in the detection mode, the determination unit 129 switches the operation mode from the detection mode to the direction estimation mode. Note that, although the direction of the abnormal sound source is estimated in the direction estimation mode, if the determination unit 129 re-determines in the direction estimation mode that the abnormal sound source does not exist, the operation mode is returned from the direction estimation mode to the detection mode.

[0042] Fig. 4 is a block diagram showing an example of the configuration of the determination unit 129. In the example shown in Fig. 4, the determination unit 129 includes an amplitude calculation unit 131, an amplitude comparison unit 132, a section amplitude calculation unit 141, a section amplitude comparison unit 142, and a sound source direction estimation unit 145.

[0043] The amplitude calculation unit 131 and the amplitude comparison unit 132 operate in the detection mode. The section amplitude calculation unit 141, the section amplitude comparison unit 142, and the sound source direction estimation unit 145 operate in the direction estimation mode.

[0044] In this embodiment, the amplitude calculation unit 131 generates time series data of the amplitude of the acoustic data (phase difference signal, i.e., data including the phase difference of the section collected momentarily by the detection mode signal data collection unit 126) stored in the storage unit 128. Hereinafter, the time series data of the amplitude related to the time series data of the phase difference of the section is referred to as acoustic amplitude data.

[0045] When the amplitude comparison unit 132 detects a characteristic difference in the acoustic amplitude data from the time series data of the amplitude when there is no sound-generating object in the vicinity of the optical fiber microphone array 14, the amplitude comparison unit 132 determines that a suspicious object such as a drone is present in the vicinity of the optical fiber microphone array 14. When the determination unit 129 determines that a suspicious object is present, it switches the operation mode to the direction estimation mode. Hereinafter, the time series data of the amplitude when there is no sound-generating object in the vicinity is also referred to as normal time series data. Note that the normal time series data also includes noise in the vicinity of the optical fiber microphone array 14.

[0046] The section amplitude calculation unit 141 generates acoustic amplitude data for each section from the acoustic data (data including information on the phase difference of the section collected every moment by the direction estimation mode signal data collection unit 127) stored in the storage unit 128. When the section amplitude comparison unit 142 determines that there is no characteristic difference between the acoustic amplitude data for each section and the normal time series data, the determination unit 129 switches the operation mode to the detection mode.

[0047] In this embodiment, the determination unit 129 executes processing using the acoustic data stored in the memory unit 128, but the determination unit 129 may also execute processing by directly inputting the outputs (acoustic data) of the detection mode signal data collection unit 126 and the orientation estimation mode signal data collection unit 127.

[0048] 5 is a block diagram showing an example of the configuration of the sound source direction estimation unit 145. In the example shown in FIG. 5, the sound source direction estimation unit 145 includes a cross-correlation calculation unit 151, a sound source direction calculation unit 152, and a sound source direction determination unit 153.

[0049] The cross-correlation calculation unit 151 calculates a cross-correlation function for a plurality of pairs (also pairs for a plurality of sections) of the optical fiber microphone array 14. The sound source direction calculation unit 152 obtains candidates for the direction of the sound source of the abnormal sound using the cross-correlation function. The sound source direction determination unit 153 determines an estimated direction from the candidate directions.

[0050] (Operation of the embodiment) Next, the operation of the optical fiber sensor of the first embodiment will be described with reference to the flow chart of FIG.

[0051] The light source 121 emits a laser beam to the optical fiber 11 (step S1). The emitted laser beam is a pulsed beam. It is preferable that the emission interval (period) of the laser beam (pulsed beam) is longer than the time from when the laser beam is emitted until the backscattered beam is received at the terminal end X. Note that, as an initial state, the operation mode is set to the detection mode. Specifically, the determination unit 129 operates in the detection mode.

[0052] As described above, the backscattered light due to Rayleigh scattering in the optical fiber 11 is received by the light receiving unit 122. Acoustic data is stored in the memory unit 128 via the photoelectric converter 123, the AD converter 124, and the detection mode signal data collecting unit 126.

[0053] In the determination unit 129, the amplitude calculation unit 131 generates acoustic amplitude data from the acoustic data stored in the memory unit 128 (data including information on the phase difference in the section collected momentarily by the detection mode signal data collection unit 126) (step S2). The acoustic amplitude data generated by the processing in step S2 is time-series data of the amplitude for the section extending from the starting point Y to the ending point X of the optical fiber 11. In addition, the amplitude calculation unit 131 calculates the amplitude time average A(t) from the acoustic amplitude data (step S3). The amplitude time average A(t) is calculated as in the following equation (1).

[0054]

number

[0055] In equation (1), T indicates a period for which the time average is calculated. |f(s)| indicates acoustic amplitude data. Note that, although the time average of the amplitude is used in this embodiment, the square mean of the amplitude may also be used.

[0056] Fig. 7 is an explanatory diagram for explaining a process of detecting whether or not a suspicious object (drone (sound source 10)) is present around the optical fiber microphone array 14 based on the acoustic amplitude data. Note that in Fig. 7, the signal is shown in the form of an analog electric signal before being AD converted.

[0057] In the upper part of Fig. 7, an example of acoustic data is shown in black as a vibration waveform. Also, an example of acoustic data after denoising by, for example, a spectral subtraction method is shown in lighter colors as a denoised waveform. In the example shown in the upper part of Fig. 7, three high amplitude sections due to factors other than noise occur in the part where the denoised waveform takes a finite value (see the part surrounded by a rectangle in Fig. 7).

[0058] In the lower part of Fig. 7, an example of acoustic amplitude data is shown in black as an amplitude waveform. Also, an example of the amplitude time average A(t) is shown in light color as an amplitude average. In the example shown in the lower part of Fig. 7, the amplitude time average A(t) is a nearly constant value due to stationary noise, but abrupt changes occur in response to the occurrence of three high amplitude sections different from noise.

[0059] Therefore, by comparing the amplitude time average A(t) with a predetermined threshold value (see the white straight line in the lower part of FIG. 7), it is possible to detect whether or not a suspicious object, i.e., sound source 10, is present. Note that as a suspicious object approaches the optical fiber microphone array 14, the value of the amplitude time average A(t) caused by the sound of the suspicious object increases. Therefore, for example, it is also possible to determine whether or not a suspicious object is approaching by comparing the value of the amplitude time average A(t) with multiple types of threshold values.

[0060] In the determination unit 129, the amplitude comparison unit 132 compares the amplitude time average A(t) with a predetermined threshold value (step S4). The threshold value is a value that allows a sound from a suspicious object to be identified from normal time series data. If the amplitude comparison unit 132 determines in the process of step S4 that the amplitude time average A(t) is equal to or less than the threshold value, it is determined that no suspicious object exists around the optical fiber microphone array 14. In this case, the optical fiber sensor executes the process from step S1 again. If the amplitude comparison unit 132 determines that there is a portion in the amplitude time average A(t) that exceeds the threshold value, the optical fiber sensor performs the process from step S10 onwards. The process from step S10 onwards is a process in the direction estimation mode. That is, the optical fiber sensor switches the operation mode to the direction estimation mode. At this time, the determination unit 129 provides the phase difference signal extractor 125 with information indicating that the mode is the direction estimation mode.

[0061] In the process of step S4, when the amplitude comparing unit 132 determines that the amplitude time average A(t) has one or more portions exceeding the threshold value, the determining unit 129 may switch the operation mode to the orientation estimation mode. However, when the amplitude comparing unit 132 determines that the amplitude time average A(t) has a predetermined number of portions exceeding the threshold value, the determining unit 129 may switch the operation mode to the orientation estimation mode.

[0062] In step S10, the light source 121 emits pulsed light to the optical fiber 11. Note that the width of the pulsed light (pulse width) is defined, for example, by the time interval between the half-value point of the peak power from the rising edge of the pulse signal and the half-value point of the falling edge.

[0063] As described above, the backscattered light due to Rayleigh scattering in the optical fiber 11 is received by the light receiving unit 122. Acoustic data is stored in the memory unit 128 via the photoelectric converter 123, the AD converter 124, and the direction estimation mode signal data collection unit 127.

[0064] The section amplitude calculation unit 141 generates, from the acoustic data, acoustic amplitude data for a section corresponding to each optical fiber microphone 13 (step S11). In addition, the amplitude calculation unit 131 calculates an amplitude time average A s (t) is calculated (step S12). s is a number between 1 and n, and in the example shown in FIG. 1, n=4. s The method for calculating (t) is the same as the method for calculating the amplitude time average A(t) (see equation (1)). The acoustic amplitude data generated in the process of step S12 is time-series data of the amplitude for the section from the start point y to the end point x of each optical fiber microphone 13.

[0065] The section amplitude comparison unit 142 calculates the amplitude time average A s The section amplitude comparison unit 142 compares each of the amplitude time averages A(t) with a predetermined threshold value (step S13). The threshold value is a value that allows a sound from a suspicious object to be identified from normal time series data. In the process of step S13, the section amplitude comparison unit 142 compares all of the amplitude time averages A(t) with a predetermined threshold value (step S14). s If it is determined that (t) is equal to or less than the threshold value, it is determined that no suspicious object is present around the optical fiber microphone array 14. In that case, the optical fiber sensor executes the process from step S1 again. That is, the optical fiber sensor switches the operation mode from the azimuth estimation mode to the detection mode. At this time, the determination unit 129 provides the phase difference signal extractor 125 with information indicating that it is in the detection mode. If the section amplitude comparison unit 142 detects one or more amplitude time averages A s If it is determined that there is a portion exceeding the threshold value at (t), the optical fiber sensor performs the processes in and after step S14.

[0066] By executing the processing of step S13, it is possible to prevent the judgment result of the judgment unit 129 in the detection mode (in this case, the judgment result that a suspicious object is present) from being generated due to an accidental factor, i.e., to prevent a false judgment that a suspicious object is present when a suspicious object is not actually present.

[0067] In the process of steps S14 to S16, the sound source direction estimation unit 145 performs a process of estimating the direction of the sound source 10. In this embodiment, the sound source direction estimation unit 145 performs a process of estimating the direction of the sound source 10 using a time difference of arrival (TDOA) The direction of the sound source 10 (suspicious object) is estimated using the Difference Of Arrival (DDIA).

[0068] TDOA is expressed by the following formula (2): In formula (2), c represents the speed of sound, d represents the distance between the optical fiber microphones 13, and θ represents the azimuth of the sound source 10 (for example, the elevation angle from the optical fiber 11).

[0069] TDOA = d cosθ / c (2)

[0070] Therefore, the direction can be calculated using the following equation (3).

[0071] θ=cos -1 (TDOA·c) / d) ···(3)

[0072] In the sound source direction estimation unit 145, the cross-correlation calculation unit 151 calculates a cross-correlation function of acoustic data in two sections (corresponding to the optical fiber microphones 13) (step S14). If the two sections are expressed as a pair, the cross-correlation calculation unit 151 calculates the cross-correlation function for all pairs that can be selected from the multiple sections. In the example shown in FIG. 1, four optical fiber microphones 13 are formed, so the number of pairs is six. Therefore, the cross-correlation calculation unit 151 calculates six cross-correlation functions.

[0073] The cross-correlation function is expressed as a function of time τ, and the TDOA can be estimated from the time τ that maximizes the value of the cross-correlation function. The sound source direction calculation unit 152 estimates the TDOA for each pair. Then, the sound source direction calculation unit 152 uses each TDOA to calculate the direction of the sound source 10 for each pair (step S15). Each calculated direction is set as a candidate direction of the sound source.

[0074] The sound source direction determining unit 153 determines the sound source direction that is most likely to be correct from among the multiple sound source direction candidates, for example, by performing maximum likelihood estimation (step S16).

[0075] As described above, in this embodiment, the determination unit 129 substantially forms one omnidirectional microphone by enlarging the evaluation target section, and determines whether or not the sound source 10 exists using the one omnidirectional microphone. If it is determined that the sound source 10 exists, the determination unit 129 can estimate the direction of the sound source 10 with higher accuracy than with an omnidirectional microphone by reducing the evaluation target section, that is, using the multiple optical fiber microphones 13. That is, in this embodiment, the detection performance when detecting a change in the surrounding environment is improved.

[0076] The method of estimating the sound source direction using the multiple optical fiber microphones 13 is not limited to the above method. For example, a whitened cross-correlation function may be used instead of the cross-correlation function to estimate the TDOA. Also, a method of estimating the sound source direction without using TDOA, such as that described in Non-Patent Document 1, may be used.

[0077] Embodiment 2. (Configuration of the embodiment) The overall configuration of the optical fiber sensor of the second embodiment is similar to that of the first embodiment. Fig. 8 is a block diagram showing an example of the configuration of the determination unit 129 in the second embodiment. In the example shown in Fig. 8, the determination unit 129 includes a section amplitude calculation unit 141, a sound source direction estimation unit 145, a feature extraction unit 231, a feature amount determination unit 232, a section feature extraction unit 241, and a section feature amount determination unit 242.

[0078] The feature extraction unit 231 and the feature amount determination unit 232 operate in the detection mode. The section amplitude calculation unit 141, the sound source direction estimation unit 145, the section feature extraction unit 241 and the section feature amount determination unit 242 operate in the direction estimation mode.

[0079] The feature extraction unit 231 extracts features from the acoustic data. Specifically, the feature extraction unit 231 calculates, for example, an acoustic feature amount (hereinafter, referred to as a feature amount) from the acoustic data. The feature amount determination unit 232 determines whether or not the calculated feature amount is based on a sound generated by a suspicious object (in this embodiment, a drone). The section feature extraction unit 241 extracts a feature amount of each section from the acoustic data. The section feature amount determination unit 242 determines whether or not the calculated feature amount is based on a sound generated by a suspicious object.

[0080] The section amplitude calculation unit 141 and the sound source direction estimation unit 145 operate in the same manner as those in the first embodiment.

[0081] (Operation of the embodiment) Next, the operation of the optical fiber sensor of the second embodiment will be described with reference to the flow chart of FIG.

[0082] As in the first embodiment, the light source 121 emits a laser beam to the optical fiber 11 (step S1). Also in this embodiment, the operation mode is set to the detection mode as an initial state. Specifically, the determination unit 129 operates in the detection mode. As in the first embodiment, the light receiving unit 122 receives backscattered light due to Rayleigh scattering in the optical fiber 11. Acoustic data is stored in the memory unit 128 via the photoelectric converter 123, the AD converter 124, and the detection mode signal data collection unit 126.

[0083] In this embodiment, the determination unit 129 determines whether or not a suspicious object, i.e., a sound source 10, is present around the optical fiber microphone array 14 based on features (i.e., feature amounts) extracted from the acoustic data. In the determination unit 129, the feature extraction unit 231 calculates a feature amount B(t) from the acoustic data stored in the storage unit 128 (step S21). There are various indices for the feature amount, and for example, the duration of a feature sound (a sound that deviates from the amplitude of normal time series data) or a frequency derived from the acoustic data is used as the index of the feature amount.

[0084] When frequency is used, the feature extraction unit 231 generates acoustic amplitude data from the acoustic data stored in the storage unit 128. The acoustic amplitude data is time-series data of amplitude for a section extending from the starting point Y to the ending point X of the optical fiber 11. The feature extraction unit 231 then obtains a frequency spectrum by performing, for example, FFT (Fast Fourier transform) on the acoustic data. When the duration of the characteristic sound is used, the feature extraction unit 231 obtains, for example, an envelope of the acoustic data. The frequency spectrum and the duration of the characteristic sound may be used in combination.

[0085] The feature amount determination unit 232 determines whether the calculated feature amount B(t) matches the acoustic feature of a suspicious object (drone) (step S22). In this embodiment, a classifier is created that is trained using acoustic data from a suspicious object that has been actually observed in advance as training data. The classifier is incorporated in the feature amount determination unit 232. The feature amount determination unit 232 inputs the feature amount B(t) to the classifier, and obtains a determination result from the classifier as to whether or not acoustic data exhibiting the feature amount B(t) is acoustic data in the presence of a suspicious object, i.e., whether or not a suspicious object exists.

[0086] If it is determined that no suspicious object is present, the optical fiber sensor executes the processes from step S1 again. If it is determined that a suspicious object is present, the optical fiber sensor executes the processes from step S10 and step S23 onwards. The processes from step S10 and step S23 onwards are processes in the direction estimation mode. That is, the optical fiber sensor switches the operation mode to the direction estimation mode. At this time, the determination unit 129 provides the phase difference signal extractor 125 with information indicating that the mode is the direction estimation mode.

[0087] The feature amount determination unit 232 may compare the calculated feature amount B(t) with a feature amount as a template based on sounds from a suspicious object actually observed in advance. In this case, the feature amount determination unit 232 determines that a suspicious object exists when the difference between the two feature amounts is less than a predetermined threshold value.

[0088] As in the first embodiment, the light source 121 emits a laser beam to the optical fiber 11. The section feature extraction unit 241 generates acoustic amplitude data for the sections corresponding to the optical fiber microphones 13 from the acoustic data (data including information on the phase difference of the sections collected by the direction estimation mode signal data collection unit 127 from time to time) (step S23). The section feature extraction unit 241 also extracts the B s (t) is calculated (step S23). s is a number between 1 and n, and in the example shown in FIG. 1, n=4. s The method of calculating feature quantity B(t) is the same as the method of calculating feature quantity B(t). Note that the acoustic data generated in the process of step S23 is time-series data of phase difference for the section from the start point y to the end point x of each optical fiber microphone 13.

[0089] The section feature amount determination unit 242 calculates the feature amount B s It is determined whether (t) matches the acoustic features of a suspicious object (drone) (step S24). The method of determination by the section feature amount determination unit 242 is similar to the method of determination by the feature amount determination unit 232.

[0090] The section feature amount determination unit 242 determines the feature amount B of all sections. s If it is determined that (t) does not match the acoustic features of the suspicious object, it is determined that there is no suspicious object around the optical fiber microphone array 14. In that case, the optical fiber sensor executes the process from step S1 again. That is, the optical fiber sensor switches the operation mode from the azimuth estimation mode to the detection mode. At this time, the determination unit 129 provides the phase difference signal extractor 125 with information indicating that it is in the detection mode. The section feature determination unit 242 determines one or more feature quantities B s If it is determined that (t) matches the acoustic characteristics of the suspicious object, the optical fiber sensor performs the processes in and after step S14.

[0091] By executing the processing of step S24, it is possible to prevent the judgment result of judgment unit 129 in detection mode (in this case, the judgment result that a suspicious object is present) from being generated due to an accidental factor, i.e., to prevent a suspicious object from being erroneously judged to be present when a suspicious object is not actually present.

[0092] The processes in steps S14 to S16 are the same as those in the first embodiment.

[0093] As described above, in this embodiment, as in the first embodiment, the determination unit 129 determines whether or not the sound source 10 exists by forming a single omnidirectional microphone by enlarging the evaluation target section. If it is determined that the sound source 10 exists, the determination unit 129 can estimate the direction of the sound source 10 with higher accuracy than with an omnidirectional microphone by reducing the evaluation target section, that is, by using multiple optical fiber microphones 13. That is, in this embodiment, the detection performance when detecting a change in the surrounding environment is improved.

[0094] Embodiment 3. The optical fiber sensor can detect the approach of a suspicious object such as a drone to the optical fiber microphone array 14 (the presence of a suspicious object around the optical fiber microphone array 14) as well as the intrusion of a suspicious person or object into a facility in which the optical fiber sensor is installed. The optical fiber sensor of the third embodiment is an optical fiber sensor that can also detect the intrusion of a suspicious person or object. Below, an example will be given in which the optical fiber sensor is installed in a specified facility.

[0095] The optical fiber sensor detects vibrations caused by the intrusion of a suspicious person or object into a facility. The approach of a suspicious object is actually detected as vibrations based on sound pressure. Hereinafter, vibrations based on sound pressure may be referred to as non-contact vibrations, and vibrations caused by the intrusion of a suspicious person or object may be referred to as contact vibrations. In general, an acoustic signal caused by contact vibrations is locally larger than an acoustic signal caused by non-contact vibrations. Therefore, the optical fiber sensor can determine whether an acoustic signal caused by contact vibrations or an acoustic signal caused by non-contact vibrations has been observed based on the intensity (or amplitude) of the observed acoustic signal or the duration of a period in which the intensity (or amplitude) of the audio signal is high. Note that although data related to contact vibrations is essentially vibration data, since acoustic data stored in the storage unit 128 is handled in relation to the detection of contact vibrations, the vibration data is also expressed as generating acoustic amplitude data for a section from the acoustic data.

[0096] (Configuration of the embodiment) The overall configuration of the optical fiber sensor of the third embodiment is similar to that of the first embodiment. Fig. 10 is a block diagram showing an example of the configuration of the determination unit 129 in the second embodiment. In the example shown in Fig. 10, the determination unit 129 includes an amplitude calculation unit 131, an amplitude comparison unit 132, a section amplitude calculation unit 141, a section amplitude comparison unit 142, a sound source direction estimation unit 145, a vibration amplitude calculation unit 161, a vibration amplitude comparison unit 162, and a vibration section identification unit 163. That is, the determination unit 129 in this embodiment has the vibration amplitude calculation unit 161, the vibration amplitude comparison unit 162, and the vibration section identification unit 163 added to the configuration of the first embodiment.

[0097] The vibration amplitude calculation unit 161 generates sound amplitude data for each section from the sound data stored in the storage unit 128. The vibration amplitude comparison unit 162 determines whether or not vibration has occurred in any section based on the sound amplitude data. The vibration section identification unit 163 uses the determination result of the vibration amplitude comparison unit 162 to identify the section into which a suspicious person or object has entered.

[0098] As in the first embodiment, the feature extraction unit 231 and the feature amount determination unit 232 operate in the detection mode. The section amplitude calculation unit 141, the sound source direction estimation unit 145, the section feature extraction unit 241, and the section feature amount determination unit 242 operate in the direction estimation mode.

[0099] In this embodiment, the vibration amplitude calculation unit 161, the vibration amplitude comparison unit 162 and the vibration section identification unit 163 operate in parallel with the feature extraction unit 231 and the feature determination unit 232 related to the detection mode, or the section feature extraction unit 241 and the section feature determination unit 242 related to the orientation estimation mode.

[0100] (Operation of the embodiment) Next, the operation of the optical fiber sensor of the third embodiment will be described with reference to the flowchart of Fig. 11. The process shown in Fig. 11 is performed by the vibration amplitude calculation unit 161 and the vibration amplitude comparison unit 162. In parallel with the process shown in Fig. 11, the process shown in Fig. 6 in the first embodiment is executed.

[0101] The vibration amplitude calculation unit 161 generates acoustic amplitude data for a section corresponding to each optical fiber microphone 13 from the acoustic data stored in the storage unit 128 (step S31). In addition, the vibration amplitude calculation unit 161 calculates an amplitude time average C q (t) is calculated (step S32). q is a number between 1 and n, and in the example shown in FIG. 1, n=4. The amplitude time average C q The method of calculating (t) is the same as the method of calculating the amplitude time average A(t) by the amplitude calculation unit 131 in the first embodiment (see equation (1)). However, here, T in equation (1) is a period corresponding to the length of the section. The acoustic amplitude data generated in the process of step S31 is time-series data of the amplitude of the phase difference signal for the section extending from the start point y to the end point x of each optical fiber microphone 13.

[0102] The vibration amplitude comparison unit 162 compares each of the amplitude time averages Cq(t) with a predetermined vibration amplitude threshold value (step S33). The vibration amplitude threshold value is a value that can identify contact vibration from normal time series data. The vibration amplitude threshold value is a value that the section amplitude comparison unit 142 uses to compare the amplitude time averages A s In the process of step S33, the vibration amplitude comparison unit 162 compares all the amplitude time averages C q If it is determined that (t) is equal to or less than the vibration amplitude threshold, it is determined that no suspicious person or object has entered the facility. In that case, the process is terminated. Note that, for example, when the light source 121 next emits pulsed light to the optical fiber 11, the process from step S31 onward is executed again.

[0103] The vibration amplitude comparison unit 162 compares one or more amplitude time averages C q If it is determined that there is a portion in (t) that exceeds the vibration amplitude threshold, the vibration amplitude calculation unit 161 executes the process of step S34.

[0104] In step S34, the light source 121 emits a laser beam to the optical fiber 11. Backscattered light due to Rayleigh scattering in the optical fiber 11 is received by the light receiving unit 122. Acoustic data is stored in the memory unit 128 via the photoelectric converter 123, the AD converter 124, and a third signal data collecting unit (not shown). Note that, when the detection mode signal data collecting unit 126 is positioned as the first signal data collecting unit and the orientation estimation mode signal data collecting unit 127 is positioned as the second signal data collecting unit, the third signal data collecting unit is a signal data collecting unit different from them. Next, the process of step S35 is executed by the vibration amplitude comparing unit 162.

[0105] When the vibration amplitude comparison unit 162 executes the process of step S35, the evaluation target section is shortened. For example, in the case where i resonant media 15 (i: an integer equal to or greater than 2) are provided, the number of sections is set to (i / 2) when the processes of steps S31 and S32 are executed, and the number of sections is set to i when the process of step S35 is executed. When the number of sections is (i / 2), one section (evaluation target section) is set across two resonant media 15. Specifically, the determination unit 129 provides information indicating the shortening of the section to the phase difference signal extractor 125. The phase difference signal extractor 125 extracts phase difference information of the shortened section (short section) and sets it as a phase difference signal (acoustic data).

[0106] Moreover, when each section is shortened, it is preferable that the length of each section is as short as possible. As an example, the length of each section is set to the minimum value within a range that does not fall below the pulse width of the light emitted to the optical fiber 11.

[0107] The vibration amplitude calculation unit 161 generates acoustic amplitude data for each section from the acoustic data stored in the storage unit 128 (step S35). In addition, the vibration amplitude calculation unit 161 calculates an amplitude time average C r (t) is calculated (step S36). r is 1 to m (m>n). m corresponds to i in the above example. Also, n corresponds to (i / 2) in the above example. The amplitude time average C r The method of calculating (t) is the same as the method of calculating the amplitude time average A(t) by the amplitude calculation unit 131 in the first embodiment (see formula (1)). However, here, T in formula (1) is a period corresponding to the length of the section.

[0108] The vibration section identification unit 163 detects a plurality of amplitude time averages C r (t) The maximum amplitude time average C r The section corresponding to (t) is identified as the section where vibration occurred, that is, the section where a suspicious person or object has entered (step S37).

[0109] In addition to the effects of the first embodiment, the present embodiment can provide an effect of being able to estimate the intrusion point of a suspicious person or object into a facility or the like in which an optical fiber sensor is installed.

[0110] In this embodiment, when the processes of steps S1, S21, and S22 are executed, the manner in which the sections are set is the same as the manner in which the sections are set in the detection mode, but the manner in which the sections are set may be the same as the manner in which the sections are set in the orientation estimation mode.

[0111] In addition, in this embodiment, the vibration amplitude calculation unit 161, the vibration amplitude comparison unit 162, and the vibration section identification unit 163 are added to the determination unit 129 in the first embodiment, but the vibration amplitude calculation unit 161, the vibration amplitude comparison unit 162, and the vibration section identification unit 163 may be added to the determination unit 129 in the second embodiment. That is, a function of estimating an intrusion point of a suspicious person or object may be added to the optical fiber sensor of the second embodiment.

[0112] Furthermore, the optical fiber sensor of this embodiment is configured to execute the processing shown in FIG. 6 in the first embodiment in parallel with the processing shown in FIG. 11, but the processing shown in FIG. 11 and the processing shown in FIG. 6 may be configured to be executed with a time lag.

[0113] Furthermore, the optical fiber sensor of this embodiment estimates the intrusion point of a suspicious person or object based on the amplitude obtained from the vibration data (acoustic data stored in the memory unit 128). However, the intrusion point of a suspicious person or object may also be estimated based on features obtained from the vibration data (the duration of vibration that deviates from the amplitude of normal time series data or the frequency derived from the vibration data).

[0114] In each of the above embodiments, the use of the optical fiber 11 including one fiber (core + cladding) or the use of one fiber in an optical fiber including multiple fibers is assumed. However, the optical fiber sensor of each of the above embodiments can also use multiple fibers in an optical fiber including multiple fibers. Also, for example, when an optical fiber including multiple fibers is used, the optical fiber sensor can use any one fiber in the detection mode and another fiber in the orientation estimation mode.

[0115] The optical fiber sensor in each of the above-mentioned embodiments, which selectively uses the detection mode and the azimuth estimation mode, is an optical fiber sensor based on an OTDR (Optical Time Domain Reflectometer) that uses backscattered light due to Rayleigh scattering. It is also possible to apply this to an optical fiber sensor using the OFDR (Optical Frequency Domain Reflectometry) method.

[0116] In addition, the above-described embodiments may be applied to Raman scattering for detecting temperature, etc. The above-described embodiments may be applied to an optical fiber sensor based on an R-OTDR that uses backscattered light due to a change in the state of polarization (SoP) of the backscattered light. The present invention may be applied to an optical fiber sensor based on a P-OTDR that detects vibrations and the like using a polarization-domain optical fiber (P-OTDR).

[0117] In other words, the ideas of the above embodiments can be effectively applied to a method that can achieve high detection performance by selectively using a case in which sensor sensitivity is prioritized over spatial resolution and a case in which spatial resolution is prioritized over sensor sensitivity (in each of the above embodiments, a first section and multiple second sections are selectively used).

[0118] Each of the above embodiments can be configured by hardware, but can also be realized by a computer program.

[0119] FIG. 12 is a block diagram showing an example of a computer having a CPU (Central Processing Unit). 1 is a block diagram of a computer implemented in the detector 12 in the optical fiber sensor of each of the above-mentioned embodiments. The CPU 1000 executes processing in accordance with a program (software element: code) stored in the storage device 1001 to realize each function in the above-mentioned embodiments. That is, it realizes the functions of the detection mode signal data collector 126, the orientation estimation mode signal data collector 127, and the determination unit 129 in the first to third embodiments. Note that instead of the CPU 1000, a GPU (Graphics Processing Unit) or a combination of a CPU and a GPU can also be used.

[0120] The storage device 1001 is, for example, a non-transitory computer readable medium. The non-transitory computer readable medium includes various types of tangible storage media. Specific examples of the non-transitory computer readable medium include a magnetic recording medium (for example, a hard disk), a magneto-optical recording medium (for example, a magneto-optical disk), a compact disc-read only memory (CD-ROM), a compact disc-recordable (CD-R), a compact disc-rewritable (CD-R / W), and a semiconductor memory (for example, a mask ROM, a programmable ROM (PROM), an erasable PROM (EPROM), and a flash ROM). In addition, when a rewritable storage medium is used as the storage device 1001, the storage device 1001 can be used as the storage unit 128.

[0121] The program may also be stored in various types of transitory computer readable media, to which the program is supplied, for example, via a wired or wireless communication path, i.e., via an electrical signal, an optical signal, or an electromagnetic wave.

[0122] The memory 1002 is realized by, for example, a random access memory (RAM), and is a storage means for temporarily storing data when the CPU 1000 executes processing. A configuration is also conceivable in which a program held in the storage device 1001 or a temporary computer-readable medium is transferred to the memory 1002, and the CPU 1000 executes processing based on the program in the memory 1002.

[0123] Fig. 13 is a block diagram showing the main parts of the optical fiber sensor. The optical fiber sensor 1 shown in Fig. 13 includes a setting means (setting unit) 2 (in the embodiment, this is realized by the phase difference signal extractor 125 and the judgment unit 129. In particular, for example, this is realized by the phase difference signal extractor 125 extracting the phase difference signal of the evaluation target section according to the information from the judgment unit 129.) that sets the evaluation target section set in the optical fiber to either a first section or a plurality of second sections each shorter than the first section, an extraction means (extraction unit) 3 (in the embodiment, this is realized by the phase difference signal extractor 125.) that extracts a state change of light from the optical fiber (for example, the phase difference of the backscattered light), and a detection means (detection unit) 4 (in the first embodiment, this is realized by the section amplitude comparison unit 142 and the sound source direction estimation unit 145. In the second embodiment, this is realized by the section feature amount judgment unit 242 and the sound source direction estimation unit 145.) that detects a change in the surrounding environment based on time-series data of the state change of light in the evaluation target section.

[0124] The setting means 2 may be configured to switch the evaluation section between the first section and the second section when it is determined that the time average of the amplitude of the time series data of the phase difference in the evaluation section exceeds a predetermined value.

[0125] The optical fiber sensor 1 may include a feature determination means (feature determination unit: in the embodiment, realized by a feature extraction unit 231 and a feature amount determination unit 232) for determining the features of a signal based on the signal including information on the phase difference, and the setting means 2 may be configured to switch the evaluation target section between the first section and the second section when it is determined that the features match the predetermined acoustic features of a suspicious object.

[0126] The optical fiber sensor 1 may include a second setting means (second setting unit: in the third embodiment, realized by the phase difference signal extractor 125 and the judgment unit 129) for setting the evaluation target section to a plurality of short sections, each of which is shorter than the second section. In particular, for example, the phase difference signal extractor 125 is realized by extracting a phase difference signal of the evaluation target section according to information from the judgment unit 129.) and an identification means (identification unit: in the third embodiment, realized by the vibration section identification unit 163) for identifying a short section that exhibits the maximum value of the time average of the amplitude of the time series data of the phase difference of each of the plurality of short sections.

[0127] Although a part or all of the above-described embodiments can be described as follows, the present invention is not limited to the following configurations.

[0128] (Appendix 1) An optical fiber sensor that detects changes in the surrounding environment of an optical fiber, a setting means for setting an evaluation section of the optical fiber to one of a first section and a plurality of second sections each shorter than the first section; an extracting means for extracting a change in state of light from the optical fiber; a detection means for detecting a change in the surrounding environment based on time-series data of a change in the state of the light in the evaluation section; An optical fiber sensor comprising:

[0129] (Note 2) The change in the state of light is the phase difference of the backscattered light from the optical fiber. Appendix 1 Optical fiber sensor.

[0130] (Note 3) When it is determined that the time average of the amplitude of the time series data of the phase difference in the evaluation section exceeds a predetermined value, the setting means switches the evaluation section between the first section and the second section. Appendix 2 Optical fiber sensor.

[0131] (Note 4) A feature determining means for determining a feature of the signal based on the signal including the phase difference information, The setting means switches the evaluation target section between the first section and the second section when the feature determining means determines that the determined feature matches a predetermined acoustic feature. A fibre optic sensor according to appendix 2 or appendix 3.

[0132] (Additional Note 5) A second setting means for setting the evaluation target section to a plurality of short sections each shorter than the second section; a means for identifying a short section that exhibits a maximum value of a time average of the amplitude of time-series data of the phase difference of each of the plurality of short sections; 5. The optical fiber sensor of any one of claims 2 to 4, comprising:

[0133] (Note 6) The setting means sets the second section to a length shorter than half the length of the first section. 1. An optical fiber sensor according to any of claims 1 to 5.

[0134] (Appendix 7) An optical fiber microphone is formed by the entire length or part of the optical fiber wound around a cylindrical resonant medium that resonates with an acoustic signal. 10. The optical fibre sensor of any of Annexes 1 to 6.

[0135] (Appendix 8) A method for detecting a change in the surrounding environment of an optical fiber, comprising: setting an evaluation section of the optical fiber to be one of a first section and a plurality of second sections each shorter than the first section; Extracting a change in state of light from the optical fiber; A change in the surrounding environment is detected based on time series data of the change in the state of the light in the evaluation section. Change detection methods.

[0136] (Note 9) The change in the state of light is the phase difference of the backscattered light from the optical fiber. Change detection method of appendix 8.

[0137] (Appendix 10) When it is determined that the time average of the amplitude of the time series data of the phase difference in the evaluation target section exceeds a predetermined value, the evaluation target section is switched between the first section and the second section. The change detection method of appendix 9.

[0138] (Appendix 11) A feature of the signal is determined based on the signal including the phase difference information, When it is determined that the determined characteristic matches a predetermined acoustic characteristic, the evaluation target section is switched between the first section and the second section. 11. The change detection method of claim 9 or 10.

[0139] (Appendix 12) A plurality of short sections are set, each of which is shorter than the second section; Identifying a short section that exhibits a maximum value of the time average of the amplitude of the time series data of the phase difference for each of the plurality of short sections 12. The change detection method of any of claims 8 to 11.

[0140] (Appendix 13) A computer-readable recording medium storing a change detection program, The change detection program is configured to: A process of setting an evaluation target section of the optical fiber to one of a first section and a plurality of second sections each shorter than the first section; extracting a change in state of light from the optical fiber; and detecting a change in the surrounding environment based on time-series data of a change in the state of the light in the evaluation section. Recording medium.

[0141] (Appendix 14) The change in the state of light is the phase difference of the backscattered light from the optical fiber. The recording medium of Appendix 13.

[0142] (Appendix 15) To the computer, A process of setting an evaluation section of an optical fiber to one of a first section and a plurality of second sections each shorter than the first section; extracting a change in state of light from the optical fiber; and detecting a change in the surrounding environment based on time-series data of a change in the state of the light in the evaluation section. A change detection program for.

[0143] (Appendix 16) The change detection program of Appendix 15, wherein the change in the state of light is a phase difference of backscattered light from the optical fiber.

[0144] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. [Explanation of symbols]

[0145] 1. Optical fiber sensor 2 Setting method 3 Extraction means 4. Detection Methods 10. Sound Source 11 Optical Fiber 12 Detector 13 Fiber Optic Microphone 14 Fiber optic microphone array 15 Resonant medium 121 Light source 122 Light receiving part 123 Photoelectric converter 124 A / D converter 125 Phase difference signal extractor 126 Detection mode signal data collection unit 127 Heading Estimation Mode Signal Data Collection Unit 128 Storage section 129 Judgment section 131 Amplitude calculation section 132 Amplitude comparison section 141 Section amplitude calculation unit 142 Section Amplitude Comparison Unit 145 Sound source direction estimation section 151 Cross-correlation calculation unit 152 Sound source direction calculation section 153 Sound source direction determination unit 161 Vibration amplitude calculation unit 162 Vibration Amplitude Comparison Unit 163 Vibration section identification unit 231 Feature Extraction Unit 232 Feature determination unit 241 Section Feature Extraction Unit 242 Section feature determination unit 1000 CPU 1001 Storage device 1002 Memory

Claims

1. An optical fiber sensor for detecting a sound source in the vicinity of an installation position of an optical fiber, a setting means for setting an evaluation section in the optical fiber to a first section when detecting the presence of a sound source, and for setting the evaluation section to a plurality of second sections, each of which is shorter than the first section, when estimating the direction of the sound source; an extracting means for extracting a change in state of light from the optical fiber; a detection means for detecting a sound source in the vicinity of a position where the optical fiber is laid based on time-series data of changes in the state of the light in the evaluation target section; An optical fiber sensor comprising:

2. The change in the state of light is the phase difference of the backscattered light from the optical fiber.

2. The optical fiber sensor according to claim 1.

3. The setting means switches the evaluation section between the first section and the second section when it is determined that a time average of the amplitude of the time series data of the phase difference in the evaluation section exceeds a predetermined value.

3. The optical fiber sensor according to claim 2.

4. a characteristic determining means for determining a characteristic of the signal based on the signal including the information of the phase difference, The setting means switches the evaluation target section between the first section and the second section when the feature determining means determines that the determined feature matches a predetermined acoustic feature.

4. The optical fiber sensor according to claim 2.

5. a second setting means for setting the evaluation target section to a plurality of short sections each shorter than the second section; a means for identifying a short section that exhibits a maximum value of a time average of the amplitude of time-series data of the phase difference of each of the plurality of short sections; The optical fiber sensor according to claim 2 , further comprising:

6. The setting means sets the second section to a length shorter than half the length of the first section. The optical fiber sensor according to any one of claims 1 to 5.

7. A fiber optic microphone is formed by wrapping the entire length or a portion of the optical fiber around a cylindrical resonant medium that resonates with an acoustic signal. The optical fiber sensor according to any one of claims 1 to 6.

8. A change detection method for detecting a sound source in the vicinity of an installed position of an optical fiber, comprising the steps of: an evaluation target section set in the optical fiber is set to a first section when detecting the presence of a sound source, and is set to a plurality of second sections, each of which is shorter than the first section, when estimating the direction of the sound source; Extracting a change in state of light from the optical fiber; Detecting a sound source near a position where the optical fiber is laid based on time-series data of changes in the state of the light in the evaluation target section. Change detection methods.

9. The change in the state of light is the phase difference of the backscattered light from the optical fiber. The method of claim 8.

10. On the computer, A process of setting an evaluation target section in an optical fiber to a first section when detecting the presence of a sound source, and setting it to a plurality of second sections, each of which is shorter than the first section, when estimating the direction of the sound source; extracting a change in state of light from the optical fiber; and detecting a sound source in the vicinity of the installation position of the optical fiber based on time-series data of the change in the state of the light in the evaluation target section. A change detection program for.

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