Brillouin-based distributed bend fiber sensor and method for using same

A method for using a Brillouin-based distributed fiber sensor comprising:

• a fiber comprising a first core, a second core, a third core, and a fourth core, wherein the first core, the second core, and the third core are located at three different positions along a circular path within the fiber, wherein the circular path has a radius (r) to a center of the fiber, and wherein the fourth core is located at the center of the fiber;
• and, a Brillouin backscattering sensing mechanism coupled to the first core, the second core, the third core, and the fourth core, the method comprising the steps of:
• obtaining, prior to deployment of the fiber when the fiber has no bend applied thereto, from the Brillouin backscattering mechanism a first Brillouin frequency shift (BFS) baseline measurement (vB1) along the first core, a second BFS baseline measurement (vB2) along the second core, a third BFS baseline measurement (vB3) along the third core, and a fourth BFS baseline measurement (vB4) along the fourth core;
• obtaining, after deployment of the fiber and when there is a bend applied to the fiber, from the Brillouin backscattering mechanism a first BFS bend measurement (v′B1) along the first core, a second BFS bend measurement (v′B2) along the second core, a third BFS bend measurement (v′B3) along the third core, and a fourth BFS bend measurement (v′B4) along the fourth core;
• calculating a change of a first, second, third, and fourth BFS distribution (ΔvB1, ΔvB2, ΔvB3, ΔvB4) respectively along the first, second, third, and fourth cores;
• calculating a temperature distribution (ΔT) along the deployed fiber;
• calculating a first, second, and third bend induced strain distributions (Δε1, Δεe, Δε3,) respectively along the first, second, and third cores;
• calculating a bend angle β along the deployed fiber;
• and
• calculating a bend radius R along the deployed fiber.