Apparatus and method for monitoring a structure using a counter-propagating signal method for locating events

A method for monitoring a structure to locate the position of an event, including the steps of;

• launching light into a waveguide so that the light is caused to propagate in both directions along the waveguide to thereby provide counter-propagating optical signals in the waveguide, the waveguide being capable of having the counter-propagating optical signals or some characteristic of the signals modified or effected by an external parameter caused by the event, to provide modified counter-propagating optical signals;
• and
• detecting the modified counter-propagating optical signals effected by the parameter and for determining the time delay or difference between the modified signals in order to determine the location of the event.

An apparatus for monitoring an optic fibre communication link into which data signals are launched and from which the data signals are received, and for locating the position of a disturbance to the link including;

• a light source for launching light into the link so that the light is caused to propagate in both directions along the link to thereby provide counter-propagating optical signals in the link, the link being capable of having the counter-propagating optical signals or some characteristic of the signals modified or effected by the disturbance to provide modified counter-propagating optical signals;
• and
• detector means for detecting the modified counter-propagating optical signals and for determining the time delay or difference between the modified counter-propagating optical signals in order to determine the location of the disturbance.

A method for monitoring an optical fibre communication link into which data signals are launched and from which the data signals are received, to locate the position of a disturbance to the link, including the steps of;

• launching light into the link so that the light is caused to propagate in both directions along the link to thereby provide counter-propagating optical signals in the link, the link being capable of having the counter-propagating optical signals or some characteristic of the signals modified or effected by the disturbance to provide modified counter-propagating optical signals;
• and
• detecting the modified counter-propagating optical signals effected by the disturbance and for determining the time delay or difference between the modified signals in order to determine the location of the disturbance.