Patent ID: 7628531

Claim:
A method for automatic calibration of temperature measurement during a measurement mode in a system using a fiber optic distributed sensor comprising the steps of: a. in a measurement mode providing a primary light source light pulse energy into a sensing fiber by selection using an optical switch; i. collecting backscattered Raman Stokes and anti-Stokes light components; ii. calculating temperatures using the intensities of the backscattered Raman Stokes and anti-Stokes light components; b. during a correction mode selecting with the optical switch a secondary light source and providing pulses of said secondary light source to the sensing fiber; i. collecting a backscattered Raman Stokes component of that secondary light source; ii. using the Raman Stokes component collected from the secondary light source in said correction mode to correct a Raman anti-Stokes profile collected from the primary light source while in measurement mode; and iii. calculating a corrected temperature from the corrected Raman anti-Stokes profile; c. wherein the primary light source and secondary light source are chosen so that a backscattered anti-Stokes band of said primary light source is substantially the same as a backscattered Stokes band of said secondary light source.