Long Term Strain and Temperature Measurements on a Railway using Brillouin OTDR

A distributed temperature and strain sensing (DTSS) system based on Brillouin backscatter was used to measure changes during a 5 month period on an 9km length of fibre optic cable deployed next to a railway line, including on an embankment and a bridge. By measuring the amplitude and frequency of the Brillouin backscatter it was possible to determine both temperature and strain changes. Most of the strain changes occurred slowly over many weeks, however some rapid strain changes occurred on part of the embankment on one particular day. Temperature effects were dominated by the diurnal and seasonal variations of the air temperature. At a number of points along the cable there were small optical losses that varied with time, but the ability of the system to also carry out regular Rayleigh OTDR measurements meant that these losses could be accounted for, so they had minimal effect on the data.