Patent ID: 7646944

Claim:
A system for monitoring a structure and for locating a position of a disturbance event, comprising: a transceiver producing a first, a second and a third optical signals entering a first, a second and a third optical fibers; the first, second and third fibers encompassing the monitored structure; the first, second and third fibers forming different density of fibers in different parts of the monitored structure; wherein the density is determined as a total length of all fibers within the structure element; the first, second and third fibers having a returning point; the returning point being a coupler operating in both directions; the coupler having a first, a second, a third input-outputs; the first, second and third input-outputs being connected to the first, second and third fibers respectively; the first, second and third signal becoming a fourth, a fifth and a sixth optical signals after passing the returning point; the fourth, fifth and sixth optical signals propagating from the returning point towards the transceiver along the first, second and third fibers respectively; the first, second and third fibers being capable of having some characteristic of the first, second, third, fourth, fifth and sixth signals modified or affected by the disturbance event; and detector means for detecting the modified fourth, fifth and sixth optical signals and for determining a difference between the receiving times of the modified signals in order to locate the disturbance event, wherein the detection is being performed with different sensitivity in different parts of the monitored structure.