REDUCTION OF COHERENT NOISE IN THE LANDAU PLACZEK RATIO METHOD FOR DISTRIBUTED FIBER OPTIC TEMPERATURE SENSING

The Landau Placzek ratio method for distributed fibre optic temperatur e sensing is based on the ratio of the Rayleigh and Brillouin backscat tered light. However, because of the coherent nature of Rayleigh scatt ering, use of the same narrow bandwidth source as required for the Bri llouin signal, results in significant coherent noise in the Rayleigh s ignal. A novel technique is demonstrated whereby the amplified spontan eous emission noise and amplifying properties of an erbium doped fibre amplifier may be exploited to reduce the coherent noise on the Raylei gh backscatter signal. This results in a significant improvement in bo th temperature and spatial resolution over previously reported results .