WO2012152575A1

WO2012152575A1 - A method for railway monitoring based on fiber optics

Info

Publication number: WO2012152575A1
Application number: PCT/EP2012/057459
Authority: WO
Inventors: Ilya Mokhov; Ivan NIKOLIN
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-05-06
Filing date: 2012-04-24
Publication date: 2012-11-15
Also published as: RU2011118415A

Abstract

The invention refers to a method for railway monitoring based on fiber optics. According to this method, light is fed from an optical source into an optical sensor cable (2) arranged along a railway track (1) and comprising one or more optical fibers, each fiber having a uniform structure along the railway track. The light backscattered in the optical sensor cable (2) is detected and analyzed, resulting in signal patterns comprising signals indicative of different positions along the railway track. Preferably, well-known OTDR- techniques, such as Coherent Ragleigh OTDR and/or Brillouin OTDR, are used in this detecting and analysing step. Finally, the signals in the signal patterns are classified such that the positions along the railway track are assigned to classes out of a number of classes, each class representing a state at the corresponding position along the railway track. This classification step is preferably based on case-based reasoning. The method of the invention enables a reliable detection of the railway condition and of dynamic events, such as third-party intrusions or geo-hazards. Hence, the probability of accidents can be decreased by an early detection of abnormal operation conditions or unpredictable external threats.

Description

A Method for Railway Monitoring Based on Fiber Optics The invention refers to a method for railway monitoring based on fiber optics.

Railways are subjected to external threads, including third- party intrusion, ground movement as well as the ongoing po- tential risk of terrorist attacks and other causes of damage. Although the appropriate use of internal inspection practices and regular surveys provides timely information on any dete^¬ rioration in railway conditions, external threads can be un^¬ predictable .

There are several sensing systems known in the prior art ena^¬ bling the remote sensing of events based on fiber optics. Document WO 2009/148824 Al describes a distributed vibration sensing system using multimode fiber based on the well-known OTDR technique (OTDR = Optical Time Domain Reflectometry) .

Document WO 2010/034986 Al discloses a subsea riser integrity diagnosis system being based on fiber optics. The system is used in order to detect changes in temperature, vibration or strain sensed by a fiber optic strain sensor.

Document DE 10 2004 020 324 Al shows an optical monitoring system for electrical conductors which can be used for moni^¬ toring the power lines of an electrical power supply for trains. The monitoring system is based on fiber Bragg sensors and detects physical parameters like strain.

Document A. P. Strong et al . , "An Integrated System for Pipe^¬ line Condition Monitoring", IPTC Paper Number IPTC-13661-PP describes a monitoring system for pipelines using an optical fiber sensor cable. Events are detected by analyzing the backscattered signals in the cable based on OTDR techniques, particular Brillouin OTDR und Coherent Rayleigh OTDR. It is an object of the invention to provide a method and a system for railway monitoring based on fiber optics enabling a reliable detection of abnormalities along the railway track being monitored.

This object is solved by the method according to claim 1 and the system according to claim 13. Preferred embodiments of the invention are described in the dependent claims.

According to the method of the invention, in a step i) light is fed from an optical source, particularly a laser source, into an optical sensor cable arranged along a railway track and comprising one or more optical fibers, each fiber having a uniform structure along the railway track. Hence, the opti^¬ cal sensor cable forms a continuous sensing element along the railway track. In step ii) of the inventive method, light fed in the cable and being backscattered in this cable is de^¬ tected and analyzed, resulting in signal patterns comprising signals indicative of different positions along the railway track. Hence, a technique for analyzing the backscattered light is used enabling a match of the backscattered signals to different positions along the optical sensor cable and, thus, to different positions along the railway track. In other words, the signal pattern can be resolved spatially, resulting in signals indicative of any position according to the spatial resolution.

In a step iii) of the inventive method, the signals in the signal patterns obtained in step ii) are classified such that the positions along the railway track indicated by the signal patterns are assigned to classes out of a number of classes, each class representing a state at the corresponding position along the railway track.

The invention is based on the idea to use techniques of ana^¬ lyzing backscattered light in optical fibers in order to monitor a railway track based on a classification method. The use of those techniques provides a reliable detection of ab^¬ normalities occurring at any position along the railway track. Hence, a continuous monitoring or the railway track and a detection of unpredictable events are achieved.

In a preferred embodiment of the invention, an OTDR technique is used for analyzing backscattered signals in step ii) . OTDR is a well-known optical fiber sensor technology enabling distributed measurements of parameters along an optical fiber. According to this technique, a series of optical pulses (par^¬ ticularly laser pulses) is injected into a fiber and the strength of the return pulses is measured and integrated as a function of time, thus resulting in a function along the length of the optical fiber.

In a preferred embodiment, Rayleigh OTDR, particularly Coherent Rayleigh OTDR, and/or Brillouin OTDR are used as OTDR techniques in step ii) . A brief description of those tech^¬ niques can be found in the above mentioned IPTC paper from A. P. Strong et al .. As described in this paper, Rayleigh OTDR is a technique for characterization of distributions of pa^¬ rameters in optical fibers and is widely used in the optical telecommunications industry for quality control of optical fibers, both after manufacture and during installation and splicing. According to Rayleigh OTDR, brief pulses of light with a typical length between 10 ns to 100 ns are launched into the fiber. As the light propagates along the fiber, a fraction of the light is scattered due to inhomogeneities in the glass (so-called Rayleigh scattering) . A fraction of this light is re-captured in the fiber and propagates back in the opposite direction to the incident beam. The resulting signal is continuous as opposed to being made up from discrete re^¬ flection. This backscattered signal is detected and analyzed as a function of time. Thus, it is possible to determine the attenuation coefficient of the fiber, the length of the fi^¬ ber, and the position of any non-linearities or defects in the fiber. The Rayleigh OTDR technique and in general any OTDR technique can be adapted to perform distributed sensing in a sensor cable along a railway track because the signals of backscattered light also depend on external influences and events acting upon the sensor cable. As mentioned above, Coherent Rayleigh OTDR may also be used in a preferred embodiment of the invention. Coherent Rayleigh OTDR is based on the same principle as standard Rayleigh OTDR, i.e. it operates on the same Rayleigh backscatter principle. However, in commercial OTDR instruments, care is taken to select laser sources with a short coherence length much smaller than the instrument spatial resolution, so that co^¬ herent noise caused by interferometric effects is minimized. This results in a system that becomes extremely sensitive to variations in fiber propagation conditions caused by external influences, such as vibrations caused by third-party inter^¬ vention, with the additional and desirable ability to resolve position. Hence, this technique is particularly suitable to monitor the positions along a railway track in order to de^¬ tect external events.

Instead of or additionally to the above mentioned Rayleigh OTDR technique, the Brillouin OTDR technique may also be used for monitoring a railway track. This technique relies on the detection of Brillouin scattering which arises from the in- teraction between the incident photons and thermally gener^¬ ated lattice vibrations (phonons) in the sensing optical fi^¬ ber. In essence, the lattice vibration forms a temporary and transitory grating which interacts with the light fed to the sensing optical fiber. If the acoustic wavelength of the pho- ton matches the optical wavelength of the incident photons, scattering can occur which redirects the light in the return direction. Brillouin OTDR thus operates in a very similar manner as Rayleigh OTDR, but measures the spatial distribu^¬ tion of wavelength shift and/or intensity of the spontaneous Brillouin scattering, which in turn yields information about the local temperature and the strain conditions in the sens^¬ ing fibers which are also parameters which can be monitored along a railway track. The optical sensor cable used in the method of the invention can be arranged at different positions along the railway track. In a preferred embodiment, the optical sensor cable is arranged on the ground or under the ground along the railway track, particularly beside the railway track or between the rails of the railway track. This enables a very good detec^¬ tion of different and unpredictable events, like geo-hazards or third-party intrusion.

In another preferred embodiment of the invention, the optical sensor cable is included in a power cable. Hence, power ca^¬ bles which are conventionally used to supply power to trains along the railway track may be adapted to include the optical sensor cable.

In another embodiment of the invention, the signals in the signal patterns are changed by acoustic signals or strain or temperature changes occurring at the corresponding position along the railway track. In this embodiment, vibrations re^¬ sulting in acoustic signals can be detected in step ii) and classified in step iii) .

The number of classes used in step iii) can be defined on different criteria. In a preferred embodiment, the number of classes corresponds to one or more of the following states:

A railway train is running on the railway track;

a human or animal is walking near or on the railway track;

- the ground under the railway track is moving;

a heavy object is contacting the railway track;

a car is driving near or on the railway track.

Other states may be classified according to the invention. Particularly, the classification can be more general such that a class refers to a state where a hazard exists on or near the railway track, particularly a geo-hazard and/or a third-party intrusion. The classification can also be used to distinguish between geo-hazards and third-party intrusions. According to the above classification, dynamic external events which may cause a disturbance of the operation of the railway can be detected.

In another embodiment, the classification may also be used in order to monitor the condition of the railway track. To do so, the above mentioned state where a railway train is run^¬ ning on the railway track is further classified in subclasses comprising a normal operation condition of the railway track and an abnormal operation condition of the railway track. Hence, by analysing the signal when a train is running on the railway track, internal abnormalities, e.g. cracks in the rails or sweepers, may be detected.

In another embodiment of the invention, the state where the railway train is running and the railway track is recorded over time, resulting in a tracking of the railway train.

Hence, it can be determined at any time where the train is located on the railway track.

In order to implement the classification step according to step iii) , any computer-implemented method may be used. Par^¬ ticularly, machine learning techniques are applied to provide an appropriate classification. In a preferred embodiment, the classification in step iii) is based on the well-known technique of case-based reasoning using training data of states classified in known classes. The states classified in known classes form the case-base of the case-based reasoning, said cases being collected in the training phase. With known techniques, e.g. the method of k nearest neighbours, unknown cases represented by the signals detected and analysed in step ii) are mapped to states of known cases, thus resulting in a classification of the states obtained in step ii) .

As the classification in step iii) is usually based on stan^¬ dard training data not considering the special environment where the railway track is located, the signals of the signal patterns are preferably filtered in step ii) based on one or more parameters referring to the environment where the rail^¬ way track is located, said filtered signals be classified in step iii) .

In another preferred embodiment of the invention, the posi^¬ tions along the railway track and the assigned classes ob^¬ tained in step iii) are output on a user interface, particu^¬ larly a user interface in a central monitoring station. This enables an efficient remote monitoring of a railway track. Particularly, alarms may be output on the user interface in case that special events, like third-party intrusions or geo- hazards, are determined in step iii) of the inventive method. Besides the above method, the invention also comprises a sys^¬ tem for railway monitoring based on fiber optics. The system comprises a light source, particularly a laser source, for feeding light into an optical sensor cable, which is also a part of the system. The sensor cable is arranged along a railway track and comprises one or more optical fibres, each fiber having a uniform structure along the railway track. The system further comprises a detecting and analysing means for detecting and analysing the light backscattered in the opti^¬ cal sensor cable, resulting in signal patterns comprising signals indicative of different positions along the railway track. Moreover, the system includes a classifying means for classifying the signals in the signal patterns such that the positions along the railway track are assigned to classes out of a number of classes, each class representing a state at the corresponding position along the railway track. Any of the above described variants of the method according to the invention may be implemented in this monitoring system.

The classifying means of the system is preferably implemented as a software module running on a corresponding hardware. In another preferred embodiment, the detecting and analysing means as well as the classifying means are included in one single processing unit. Optionally, the light source may also be part of this processing unit.

In the following, a preferred embodiment of the invention is described in detail with respect to the accompanying Fig. 1. This figure shows schematically the components used in a sys^¬ tem for railway monitoring according to the invention.

The system shown in Fig. 1 is used for monitoring a railway track 1 including two rails la as well as sleepers lb. This is evident from the upper sectional view and the lower per^¬ spective view in Fig. 1. The system includes a fiber optical cable 2. A detailed view of this cable is shown in the right part of Fig. 1. The optical fibers of this cable are inside a power cable, i.e. the cable also includes power transmission lines and thus forms a combined sensing and power cable. The position of this cable in relation to the railway track is indicated by arrows P pointing to the sectional and the per^¬ spective view of Fig. 1. As can be seen from the perspective view, the cable is located beside the railway track on the ground, thus enabling a detection of events occurring near the railway track.

The structure of the ground under the railway track is indi- cated in the sectional view of Fig. 1. The ground includes several layers. The lowermost layer LI corresponds to the subsoil or natural ground. A subgrade layer L2 is formed on layer LI being followed by an optional blanket in the form of layer L3. Layers L2 and L3 are the formation of the railway track. On layer L3, there is a ballast and sub-ballast layer L4 on which the railway track including rails la and sleepers lb is formed. In the embodiment as shown in Fig. 1, the cable 2 is located on the ballast layer. However, the cable may also be buried in another layer shown in Fig. 1. Furthermore, the cable may also be positioned between the rails of the railway track. The system as shown in Fig. 1 is based on OTDR in order to obtain signals backscattered in the sensor cable and repre^¬ senting corresponding positions along the railway track. In a preferred embodiment, Coherent Ragleigh OTDR technique is used which enables a good detection of acoustic signals which are usually caused by external events. However, other OTDR techniques like Brillouin OTDR may also be used in the system as shown in Fig. 1. In order to implement the OTDR technique, a laser source (not shown) is used which launches laser pulses into the fibers of the optical sensor cable 2. The backscattered laser light is detected and analysed by a sig^¬ nal processing unit which is schematically shown in Fig. 1 and designated by reference numeral 3. The signal processing unit includes a case-based reasoner which is trained by training data of known events. Examples of such events have been described in the foregoing. Particularly, the case-based reasoner enables the detection of third-party intrusions and geo-hazards which are severe disturbances which shall be de^¬ tected when monitoring a railway track.

The signal processing unit is preferably located in a central monitoring station so that personnel in this monitoring station is informed about particular events and may initiate countermeasures to avoid railway accidents caused by those events. Furthermore, the signals generated by trains running along the track may be analysed by the signal processing unit in order to distinguish between a normal operation and an abnormal operation. Thus, the condition of the railway may be monitored .

The invention as described in the foregoing has several ad^¬ vantages. Particularly, the well-known technique of Optical Time Domain Reflectometry is used for railway condition monitoring and for detecting unwanted events near railway tracks. This solution provides a unique and proactive approach to railway monitoring. It performs an analysis of a combination of measurements to provide the railway owner/operator with an event recognition and location capability, in effect provid^¬ ing a hazard warning system and offering the operator the po- tential to take early action to prevent damage. By using a remote optical detection system, optionally with an optically powered amplification, a detection range up to and above 100 km is possible without the need for any electronics and re^¬ mote power along the railway.

An important element of the invention is the optical sensor cable. This may be adapted to enable distributed strain meas^¬ urements so that ground movements, e.g. caused by an earth^¬ quake, can be monitored, whilst withstanding the rigors of the railway environment. The system can also be configured for detecting third-party interference and railway conditions with the majority of existing optical sensor cables. Further^¬ more, the tracking of a train position during its movement can be implemented in the monitoring system.

Claims

Patent Claims

1. A method for railway monitoring based on fiber optics, wherein

i) light is fed from an optical source into an optical

sensor cable (2) arranged along a railway track (1) and comprising one or more optical fibers, each fiber having a uniform structure along the railway track (1); ii) the light backscattered in the optical sensor cable (2) is detected and analysed, resulting in signal patterns comprising signals indicative of different positions along the railway track (1);

iii) the signals in the signal patterns are classified such that the positions along the railway track (1) are as- signed to classes out of a number of classes, each class representing a state at the corresponding position along the railway track (1) .

2. The method according to claim 1, wherein in step ii) an OTDR technique (OTDR = Optical Time Domain Reflectometry) is used for analysing the backscattered light.

3. The method according to claim 2, wherein the OTDR technique comprises Rayleigh OTDR, particularly Coherent Rayleigh OTDR, and/or Brillouin OTDR.

4. The method according to one of the preceding claims, wherein the optical sensor cable (2) in arranged on the ground or under the ground along the railway track (1), par- ticularly beside the railway track (1) or between the rails (la) of the railway track (1) .

5. The method according to one of the preceding claims, wherein the optical sensor cable (2) is included in a power cable.

6. The method according to one of the preceding claims, wherein the signals in the signal patterns are changed by acoustic signals or strain or temperature changes occurring at the corresponding position along the railway track (1) .

7. The method according to one of the preceding claims, wherein the number of classes used in step iii) correspond to one or more of the following states:

a railway train is running on the railway track (1); a human or animal is walking near or on the railway track ( 1 ) ;

- the ground under the railway track (1) is moving;

a heavy object is contacting the railway track (1);

a car is driving near or on the railway track (1);

a hazard exists on or near the railway track (1), par^¬ ticularly a geo-hazard and/or a third-party intrusion.

8. The method according to claim 7, wherein the state where a railway train is running on the railway track (1) is further classified in subclasses comprising a normal operation condi^¬ tion of the railway track (1) and an abnormal operation con- dition of the railway track (1) .

9. The method according to claim 7 or 8, wherein the state where a railway train is running on the railway track (1) is recorded over time resulting in a tracking of the railway train.

10. The method according to one of the preceding claims, wherein the classification in step iii) is based on case- based reasoning using training data of states classified in known classes.

11. The method according to one of the preceding claims, wherein the signals of the signal patterns are filtered in step ii) based on one or more parameters referring to the en- vironment where the railway track (1) is located, the fil^¬ tered signals being classified in step iii) .

12. The method according to one of the preceding claims, wherein the positions along the railway track (1) and the as^¬ signed classes obtained in step iii) are output on a user in^¬ terface, particularly a user interface in a central monitor^¬ ing station.

13. A system for railway monitoring based on fiber optics, comprising :

a light source for feeding light into an optical sensor cable (2) which is arranged along a railway track (1) and comprising one or more optical fibers, each fiber having a uniform structure along the railway track (1); a detecting and analysing means for detecting and analysing the light backscattered in the optical sensor cable (2), resulting in signal patterns comprising signals indicative of different positions along the rail^¬ way track ( 1 ) ;

a classifying means for classifying the signals in the signal patterns such that the positions along the rail^¬ way track (1) are assigned to classes out of a number of classes, each class representing a state at the cor^¬ responding position along the railway track (1) .

14. The system according to claim 13, wherein the system is arranged such that it can perform a method according to one of claims 2 to 12.

15. The method according to claim 13 or 14, wherein the tecting- and analysing means and the classifying means included in one processing unit (3) .