Ground sensing utilizing active sources
Apparatus and methods for determining ground stability measurements utilizing active sources are disclosed. In one example implementation, a distributed optical sensor detects strains along a length of a railway line. Here, for example, one or more trains provide active sources. The static strain before and after passage of the active source is utilized to determine ground stability. According to other aspects, measurements may be normalized based on characteristics of the active source.
1 . A method of determining ground stability utilizing a distributed optical sensor, the method comprising:
transmitting, along an optical fibre, optical signals, wherein the optical signals are transmitted as outbound pulses and returned as returning pulses along the optical fibre;
determining, via an interrogator device coupled to the distributed optical sensor, a first static strain at at least one location along a length of the distributed optical sensor;
detecting, via processing of the returning pulse by the interrogator device, variation in strain at the at least one location caused by an active source which is a moving vehicle travelling along a route with which the optical fibre is associated, such that variation in strain generated by the vehicle can be detected by the distributed optical sensor;
determining a second static strain at the at least one location after the variation in strain caused by the active source has ended; and
determining a difference between the first static strain and the second static strain.
2 . A method according to claim 1 wherein the detection of variation in strain is performed by detecting higher frequency variations in strain at the location.
3 . A method according to claim 1 wherein a relative strength of the active source is determined based on higher frequency variations in strain.
4 . A method according to claim 1 , further comprising normalizing the difference between first and second static strains based on strength of the active source.
5 . A method according to claim 1 , further comprising determining an indication of ground stability at the location based on the difference between first and second strains.
6 . A method according to claim 5 , wherein the indication of ground stability is also based on a plurality of differences between the first and second strains.
7 . A method according to claim 1 wherein the active source is a train and the distributed optical sensor is associated with train tracks on which the train runs.
8 . A method according to claim 1 , further comprising performing the method at a plurality of locations along the length of the distributed optical sensor.
9 . A method according to claim 8 , wherein the method further comprises:
sampling the returning pulse at particular times to determine backscatter from particular locations of the plurality of locations along a length of the distributed optical sensor; and
averaging measurements from the plurality of locations.
10 . An optical sensing system for determining ground stability along a route that an active source travels, the system comprising:
a distributed optical sensor;
an optical fibre of the distributed optical sensor, the optical fibre mounted in ground along the route that the active source travels; and
an interrogator optically connected to the optical fibre and configured to transmit an optical signal into the optical fibre as an outbound pulse and to detect returning optical signals output from the optical fibre, the returning optical signals being backscatter from the output pulse, wherein the interrogator is configured to:
determine a first static strain at at least one location along a length of the distributed optical sensor based on the returning optical signals;
detect, via sampling of the returning pulse at particular times to determine backscatter from particular locations of the plurality of locations along a length of the distributed optical sensor, variation in strain at the at least one location by measuring the backscatter that results from physical disturbance of the optical fibre caused by travel of the active source along the route;
determine a second static strain at the at least one location after the variation in strain caused by presence of the active source has ended; and
determine a difference between the first static strain and the second static strain.
11 . The method according to claim 2 , wherein the relative strength of the active source is determined based on higher frequency variations in strain.
12 . The method according to claim 11 , further comprising normalizing the difference between first and second static strains based on strength of the active source.
13 . The method according to claim 12 , further comprising determining an indication of ground stability at the location based on the difference between first and second strains.
14 . The method according to claim 13 , wherein the indication of ground stability is also based on a plurality of differences between first and second strains.
15 . The method according to claim 13 , wherein the active source is a train and the distributed optical sensor is associated with train tracks on which the train runs.
16 . The method according to claim 15 , wherein the indication of ground stability is also based on a plurality of differences between first and second strains.
17 . The method according to claim 15 , further comprising performing the method at a plurality of locations along the length of the distributed optical sensor.
18 . The method according to claim 17 , wherein the indication of ground stability is also based on a plurality of differences between first and second strains.
19 . The method according to claim 17 , wherein the method comprises averaging measurements from the plurality of locations.
20 . The method according to claim 19 , wherein the indication of ground stability is also based on a plurality of differences between first and second strains.