Monitoring device, monitoring system, sound output device, monitoring method, and monitoring program

Abstract

This monitoring device comprises: a waveform information reception unit that receives waveform information of an optical signal that has passed through the inside of an optical fiber cable; a waveform determination unit that determines whether or not an optical signal waveform of interest indicated by the waveform information received by the waveform information reception unit matches a reference waveform; and an event occurrence determination unit that determines that an event to be detected has occurred if it is determined that the optical signal waveform of interest matches the reference waveform. The reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound having the same waveform as an optical signal waveform representing vibrations generated in the optical fiber cable by at least one event to be detected.

Description

Monitoring device, monitoring system, sound output device, monitoring method, and monitoring program

[0001] The present disclosure relates to a monitoring device, a monitoring system, a sound output device, a monitoring method, and a monitoring program that use optical fibers.

[0002] In recent years, technologies have been proposed that use optical fibers to detect the occurrence of a target event. Patent Document 1 discloses an optical fiber sensing system, one example of such technology. A detector detects an abnormality that has occurred in a monitored area based on a vibration pattern contained in an optical signal received from an optical fiber laid in the monitored area, and identifies the location on the optical fiber where the abnormality was detected. A controller then displays on a monitor a map of the monitored area, superimposing on the map the status of the optical fiber laying and a mark indicating the location on the optical fiber where the abnormality was detected, along with information indicating details of the abnormality.

[0003] International Publication No. 2021 / 059507

[0004] However, although the optical fiber sensing system disclosed in Patent Document 1 displays information such as the installation status of the optical fiber, it has the problem that it cannot determine whether or not the event to be detected has occurred using waveforms based on vibrations of the optical fiber cable generated by sound.

[0005] In view of the above-mentioned problems, one of the objectives of the present disclosure is to provide a monitoring device, a monitoring system, a sound output device, a monitoring method, and a monitoring program that are capable of determining whether or not an event to be detected has occurred using a waveform based on vibrations of an optical fiber cable generated by sound.

[0006] The monitoring device according to the present disclosure includes a waveform information receiving unit that receives waveform information of an optical signal that has passed through an optical fiber cable; a waveform determination unit that determines whether or not a target optical signal waveform indicated by the waveform information received by the waveform information receiving unit matches a reference waveform; and an event occurrence determination unit that determines that a detection target event has occurred when it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one detection target event.

[0007] The monitoring system according to the present disclosure includes a monitoring device that monitors the occurrence of a detectable event related to a structure in which an optical fiber cable is installed, and a sound output device that outputs sound, wherein the monitoring device includes a waveform information receiving unit that receives waveform information of an optical signal that has passed through the optical fiber cable, a waveform determination unit that determines whether the target optical signal waveform indicated by the waveform information received by the waveform information receiving unit matches a reference waveform, and an event occurrence determination unit that determines that the target optical signal waveform matches the reference waveform, and that the detectable event has occurred, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one detectable event.

[0008] The sound output device according to the present disclosure outputs sound having the same waveform as an optical signal waveform indicating vibrations caused in an optical fiber cable installed in a structure due to a detectable event related to the structure.

[0009] The monitoring method disclosed herein involves a computer receiving waveform information of an optical signal that has passed through an optical fiber cable, determining whether the target optical signal waveform indicated by the received waveform information matches a reference waveform, and determining that a detection target event has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one detection target event.

[0010] The monitoring program of the present disclosure causes a computer to receive waveform information of an optical signal that has passed through an optical fiber cable, determine whether the target optical signal waveform indicated by the received waveform information matches a reference waveform, and determine that a detection target event has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one detection target event.

[0011] The present disclosure provides a monitoring device, monitoring system, sound output device, monitoring method, and monitoring program that can determine whether or not a target event has occurred using a waveform based on vibrations of an optical fiber cable generated by sound.

[0012] Fig. 1 is a diagram illustrating an example of a monitoring system according to the present disclosure; Fig. 2 is a diagram illustrating an example of a structure in which an optical fiber cable is installed; Fig. 3 is a diagram illustrating an example of a configuration of a monitoring device according to the present disclosure; Fig. 4 is a flowchart illustrating an example of processing executed by the monitoring device according to the present disclosure; and Fig. 5 is a diagram illustrating main components of the monitoring device according to the present disclosure.

[0013] An exemplary embodiment will now be described with reference to the drawings. Fig. 1 is a diagram illustrating an example of a monitoring system 1 according to the present disclosure. The monitoring system 1 includes a monitoring device 10, a sensor 20, an optical fiber cable 30, and a sound output device 50. Although Fig. 1 illustrates a single sensor 20, the monitoring system 1 may include multiple sensors 20.

[0014] The monitoring device 10 and the sensor 20 communicate data with each other via a network 40. The network 40 may be configured to include a wide area network such as the Internet and a narrow area network such as a LAN (Local Area Network).

[0015] The monitoring device 10 is a device that monitors the occurrence of a detection target event related to a structure in which an optical fiber cable 30 is installed. A specific example of the monitoring device 10 is an information processing device such as a server. As shown in FIG. 2 , the optical fiber cable 30 is installed on a structure 60 such as a fence. Examples of detection target events include, but are not limited to, events caused by human actions such as climbing the structure 60, shaking the structure 60, leaning a ladder against the structure 60, and destroying the structure 60. Other events that may be detected include events caused by non-human animals, machine operation, and natural phenomena. The machine may be a machine controlled by a person, such as an automobile or an aircraft, or may be remotely controlled or automatically operated by artificial intelligence or the like.

[0016] The sensor 20 is a device that detects an optical signal that has passed through the optical fiber cable 30. A specific example of the sensor 20 is a distributed acoustic sensor (DAS). The sensor 20 can be connected to any position on the optical fiber cable 30. When the sensor 20 detects an optical signal that has passed through the optical fiber cable 30, it transmits waveform information indicating the waveform of the optical signal to the monitoring device 10 via the network 40.

[0017] The sound output device 50 is a device that outputs sound. Specific examples of the sound output device 50 include a directional speaker. The sound output device 50 may be installed on a mobile object such as a drone. The sound output device 50 outputs sound having the same waveform as an optical signal waveform indicating vibrations occurring in the optical fiber cable 30 due to a detection target event related to the structure in which the optical fiber cable 30 is installed. The sound output device 50 can also output sounds obtained by increasing or decreasing the intensity of the sound for each frequency, or by changing the wavelength of the sound. The volume of the sound output by the sound output device 50 may be changed depending on the distance between the sound output device 50 and the optical fiber cable 30. This prevents the vibrations occurring in the optical fiber cable 30 from becoming smaller than the vibrations during learning, even when the distance is large.

[0018] When the sound output device 50 is installed on a mobile body, the sound output device 50 may be configured to output the desired sound after passing the sound through a filter that removes noise generated by the mobile body.

[0019] Here, the waveforms being identical means that at least one of the vibration period or amplitude is identical for a certain period, and does not necessarily mean that the vibration period and amplitude are completely identical for the entire period. Furthermore, if the error between a reference waveform (described later) and the waveform generated in the optical fiber cable 30 by the sound emitted by the sound output device 50 falls within a threshold, the two waveforms may be considered to be identical. Such a threshold may be set manually or by the system depending on the purpose.

[0020] 3 is a schematic diagram showing the configuration of a monitoring device 10 according to the present disclosure. The monitoring device 10 includes a computing device 11, a communication interface (I / F) 12, and a storage device 13.

[0021] The arithmetic device 11 is a device that performs overall control of the monitoring device 10. Specific examples of the arithmetic device 11 include processors such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit). The arithmetic device 11 executes a program stored in the storage device 13 to perform a method defined by the program. Note that in other embodiments, the functions performed by the arithmetic device 11 may also be performed by an integrated circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). These devices correspond to computers.

[0022] The communication interface 12 is an interface for performing data communication between the monitoring device 10 and other devices, such as the sensor 20. The storage device 13 is a storage device in which various data such as programs executed by the arithmetic device 11 and data processed by the arithmetic device 11 are stored.

[0023] The arithmetic unit 11 includes a waveform information receiving unit 110, a waveform determining unit 111, and an event occurrence determining unit 112. These functional units can be realized by a program.

[0024] The waveform information receiving unit 110 receives waveform information of the optical signal transmitted by the sensor 20 and passing through the optical fiber cable 30 .

[0025] The waveform determination unit 111 determines whether the optical signal waveform indicated by the waveform information received by the waveform information receiving unit 110 matches a predetermined reference waveform. The reference waveform is an optical signal waveform indicating vibrations caused in the optical fiber cable 30 due to a detection target event related to the structure in which the optical fiber cable 30 is installed. The reference waveform is obtained by the sound output device 50 irradiating the optical fiber cable 30 with sound having the same waveform as the reference waveform.

[0026] The waveform determination unit 111 can use a model trained by machine learning, such as deep learning, to determine whether the optical signal waveform indicated by the waveform information received by the waveform information receiving unit 110 matches a predetermined reference waveform. This model can learn an optical signal waveform that matches the reference waveform as input information, and output information indicating that the input optical signal waveform matches the reference waveform. This model can also learn an optical signal waveform that does not match the reference waveform as input information, and output information indicating that the input optical signal waveform does not match the reference waveform. When an optical signal waveform that matches the reference waveform is input, the trained model outputs information indicating that the input optical signal waveform matches the reference waveform. On the other hand, when an optical signal waveform different from the reference waveform is input, the trained model outputs information indicating that the input optical signal waveform does not match the reference waveform.

[0027] Alternatively, this model can be trained using the feature quantities of a reference waveform as input information, and information indicating that the input optical signal waveform matches the reference waveform as output information. Furthermore, this model can be trained using the feature quantities of an optical signal waveform that differ from the reference waveform as input information, and information indicating that the input optical signal waveform does not match the reference waveform as output information. Waveform feature quantities include the amplitude for each frequency of the waveform, the waveform wavelength, etc. When a trained model is input with feature quantities of an optical signal waveform that match the feature quantities of the reference waveform, it outputs information indicating that the input optical signal waveform matches the reference waveform. On the other hand, when a trained model is input with feature quantities of an optical signal waveform that differ from the feature quantities of the reference waveform, it outputs information indicating that the input optical signal waveform does not match the reference waveform.

[0028] The event occurrence determining unit 112 determines that the event to be detected has occurred when it is determined that the optical signal waveform indicated by the waveform information received by the waveform information receiving unit 110 matches the reference waveform.

[0029] 4 is a sequence diagram showing an example of processing executed by the monitoring device 10. In step S1, the waveform information receiving unit 110 of the monitoring device 10 receives waveform information of the optical signal transmitted by the sensor 20.

[0030] In step S2, the waveform determination unit 111 determines whether the waveform indicated by the waveform information of the optical signal received by the waveform information receiving unit 110 matches the reference waveform. If it is determined that the waveform indicated by the waveform information of the received optical signal does not match the reference waveform (NO), the process returns to step S1. On the other hand, if it is determined that the waveform indicated by the waveform information of the received optical signal matches the reference waveform (YES), the process branches to step S3.

[0031] In step S3, the event occurrence determination unit 112 determines that the event to be detected has occurred, and the processing in FIG. 3 ends.

[0032] 5 is a diagram showing the main components of the monitoring device 10. The waveform information receiving unit 110 receives waveform information of an optical signal that has passed through the optical fiber cable 30. The waveform determining unit 111 determines whether the target optical signal waveform indicated by the waveform information received by the waveform information receiving unit 110 matches a reference waveform, which is a waveform obtained by irradiating the optical fiber cable 30 with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable 30 by an event to be detected. The event occurrence determining unit 112 determines that the event to be detected has occurred when the waveform determining unit 111 determines that the target optical signal waveform matches the reference waveform.

[0033] By employing this configuration, the monitoring device 10 can determine whether or not a detection target event has occurred by using a waveform based on vibrations of the optical fiber cable caused by sound.

[0034] In the above-described embodiment, the waveform determination unit 111 determines whether the target optical signal waveform matches a waveform based on a reference waveform. The waveform based on the reference waveform is an optical signal waveform obtained by irradiating an optical fiber cable with sound obtained by increasing or decreasing the intensity for each frequency of sound having the same waveform as the reference waveform, or sound obtained by changing the wavelength of sound having the same waveform as the reference waveform. The event occurrence determination unit 112 determines that the target event has occurred when it is determined that the target optical signal waveform matches the waveform based on the reference waveform.

[0035] By employing this configuration, the monitoring device 10 can determine whether or not a detection target event has occurred using not only the reference waveform but also a waveform based on the reference waveform.

[0036] Furthermore, in the above-described embodiment, the sound output device 50 outputs a sound having the same waveform as an optical signal waveform indicating vibrations caused in the optical fiber cable installed in the structure due to a detectable event related to the structure. By irradiating this output sound at any position on the optical fiber cable 30, it is possible to simulate the detectable event at any position in the structure. This makes it possible to remotely simulate the detectable event even if the structure is located in a place that is difficult for people to access.

[0037] Furthermore, in the above-described embodiment, the sound output device 50 can output a sound obtained by increasing or decreasing the intensity for each frequency of a sound having the same waveform as an optical signal waveform indicating vibrations caused in an optical fiber cable installed in a structure due to a detection target event related to the structure. Also, the sound output device 50 can output a sound obtained by changing the wavelength of a sound having the same waveform as an optical signal waveform indicating vibrations caused in an optical fiber cable installed in a structure due to a detection target event related to the structure.

[0038] This allows the sound output device 50 to output a sound similar to an optical signal waveform that indicates vibrations caused in an optical fiber cable installed in a structure by an event to be detected, thereby simulating various events to be detected.

[0039] <Other Embodiments> In another embodiment, the monitoring device 10 may identify the location where the event to be detected has occurred. In this case, the monitoring device 10 detects the phase and amplitude of emitted light emitted by a laser light source provided in the sensor 20 and the reflected light that is the emitted light reflected at the end point of the optical fiber cable and enters the sensor 20. Next, the monitoring device 10 may identify the location where the event to be detected has occurred based on the difference in phase between the emitted light and the reflected light and the difference in amplitude between the emitted light and the reflected light.

[0040] In another embodiment, the reference waveform may be an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable due to a plurality of events to be detected. In this case, the reference waveform is obtained by combining an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable due to one event to be detected, such as a person climbing a structure, with an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable due to another event to be detected, such as a person destroying a structure.

[0041] This allows the monitoring device 10 to detect multiple events even if they occur simultaneously. In addition, since a reference waveform can be generated by combining optical signal waveforms corresponding to multiple events, it is possible to easily generate an output target sound whose waveform matches the reference waveform.

[0042] In the above examples, the program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray® disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0043] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0044] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate only to one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0045] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes: (Supplementary Note 1) A monitoring device including: a waveform information receiving unit that receives waveform information of an optical signal that has passed through an optical fiber cable; a waveform determining unit that determines whether a target optical signal waveform indicated by the waveform information receiving unit matches a reference waveform; and an event occurrence determining unit that determines that a detection target event has occurred when it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detection target events. (Supplementary Note 2) The monitoring device according to Supplementary Note 1, wherein the waveform determination unit further determines whether or not the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that the event to be detected has occurred if it is determined that the optical signal waveform of the target matches the waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by increasing or decreasing the intensity of the sound for each frequency. (Supplementary Note 3) The monitoring device according to Supplementary Note 1 or 2, wherein the waveform determination unit further determines whether or not the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that the event to be detected has occurred if it is determined that the optical signal waveform of the target matches the waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound.(Supplementary Note 4) A monitoring system comprising: a monitoring device that monitors the occurrence of a detectable event related to a structure in which an optical fiber cable is installed; and a sound output device that outputs sound, wherein the monitoring device comprises: a waveform information receiving unit that receives waveform information of an optical signal that has passed through the optical fiber cable; a waveform determining unit that determines whether the target optical signal waveform indicated by the waveform information receiving unit matches a reference waveform; and an event occurrence determining unit that determines that a detectable event has occurred when it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detectable events. (Supplementary Note 5) A sound output device that outputs sound, wherein the sound output device outputs sound having the same waveform as an optical signal waveform that indicates vibrations caused in an optical fiber cable installed in the structure by a detectable event related to the structure. (Supplementary Note 6) The sound output device according to Supplementary Note 5 outputs sound obtained by increasing or decreasing the intensity of the sound for each frequency, or by changing the wavelength of the sound. (Supplementary Note 7) A monitoring method in which a computer receives waveform information of an optical signal that has passed through an optical fiber cable, determines whether or not a target optical signal waveform indicated by the received waveform information matches a reference waveform, and determines that a detection target event has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one detection target event. (Supplementary Note 8) The monitoring method according to Supplementary Note 7, in which the computer determines whether or not the target optical signal waveform matches a waveform based on the reference waveform, and determines that the detection target event has occurred if it is determined that the target optical signal waveform matches the waveform based on the reference waveform.(Supplementary Note 9) The monitoring method according to Supplementary Note 7 or 8, wherein the computer determines whether the target optical signal waveform matches a waveform based on the reference waveform, and determines that the event to be detected has occurred if it is determined that the target optical signal waveform matches the waveform based on the reference waveform, wherein the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound. (Supplementary Note 10) A monitoring program, wherein the computer receives waveform information of an optical signal that has passed through an optical fiber cable, and determines whether the target optical signal waveform indicated by the received waveform information matches a reference waveform, and determines that the event to be detected has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the events to be detected.

[0046] Some or all of the elements described in Supplementary Notes 2 and 3 that are dependent on Supplementary Note 1 may also be dependent on Supplementary Note 4 and Supplementary Note 10 in the same dependent relationship as Supplementary Note 2 and Supplementary Note 3. Some or all of the elements described in any Supplementary Note may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0047] This application claims priority based on Japanese Patent Application No. 2024-154467, filed September 9, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0048] 1: Monitoring system 10: Monitoring device 11: Arithmetic unit 110: Waveform information receiving unit 111: Waveform determining unit 112: Event occurrence determining unit 12: Communication interface 13: Storage device 20: Sensor 30: Optical fiber cable 40: Network 50: Sound output device 60: Structure

Claims

1. A monitoring device comprising: a waveform information receiving unit that receives waveform information of an optical signal that has passed through an optical fiber cable; a waveform determining unit that determines whether a target optical signal waveform indicated by the waveform information received by the waveform information receiving unit matches a reference waveform; and an event occurrence determining unit that determines that a detection target event has occurred when it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detection target events.

2. The monitoring device of claim 1, wherein the waveform determination unit further determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that an event of the detection target has occurred if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by increasing or decreasing the intensity of each frequency of the sound.

3. The monitoring device of claim 1 or 2, wherein the waveform determination unit further determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that an event of the detection target has occurred if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound.

4. A monitoring system comprising: a monitoring device that monitors the occurrence of a detectable event related to a structure in which an optical fiber cable is installed; and a sound output device that outputs sound, wherein the monitoring device comprises: a waveform information receiving unit that receives waveform information of an optical signal that has passed through the optical fiber cable; a waveform determining unit that determines whether the target optical signal waveform indicated by the waveform information received by the waveform information receiving unit matches a reference waveform; and an event occurrence determining unit that determines that a detectable event has occurred when it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detectable events.

5. The monitoring system of claim 4, wherein the waveform determination unit further determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that an event to be detected has occurred if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by increasing or decreasing the intensity of each frequency of the sound.

6. The monitoring system of claim 4 or 5, wherein the waveform determination unit further determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and the event occurrence determination unit determines that an event of the detection target has occurred if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound.

7. A sound output device that outputs sound, the sound output device having the same waveform as an optical signal waveform that indicates vibrations caused in an optical fiber cable installed in a structure due to a detectable event related to the structure.

8. The sound output device according to claim 7, which outputs a sound obtained by increasing or decreasing the intensity of each frequency of the sound, or by changing the wavelength of the sound.

9. A monitoring method in which a computer receives waveform information of an optical signal that has passed through an optical fiber cable, determines whether the target optical signal waveform indicated by the received waveform information matches a reference waveform, and determines that a detection target event has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detection target events.

10. A monitoring method as described in claim 9, wherein the computer determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and if it is determined that the optical signal waveform of the target matches the waveform based on the reference waveform, determines that the event to be detected has occurred, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by increasing or decreasing the intensity of each frequency of the sound.

11. A monitoring method as described in claim 9 or 10, wherein the computer determines whether the optical signal waveform of the target matches a waveform based on the reference waveform, and if it is determined that the optical signal waveform of the target matches the waveform based on the reference waveform, determines that the event to be detected has occurred, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound.

12. A monitoring program that causes a computer to receive waveform information of an optical signal that has passed through an optical fiber cable, determine whether the target optical signal waveform indicated by the received waveform information matches a reference waveform, and determine that a detection target event has occurred if it is determined that the target optical signal waveform matches the reference waveform, wherein the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with a sound having the same waveform as an optical signal waveform that indicates vibrations caused in the optical fiber cable by at least one of the detection target events.

13. The monitoring program of claim 12, which causes the computer to determine whether the optical signal waveform of the target matches a waveform based on the reference waveform, and if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, determines that the event to be detected has occurred, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by increasing or decreasing the intensity of each frequency of the sound.

14. A monitoring program as described in claim 12 or 13, which causes the computer to determine whether the optical signal waveform of the target matches a waveform based on the reference waveform, and if it is determined that the optical signal waveform of the target matches a waveform based on the reference waveform, determines that the event to be detected has occurred, and the waveform based on the reference waveform is an optical signal waveform obtained by irradiating the optical fiber cable with sound obtained by changing the wavelength of the sound.

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