Distinguish measurement of temperature and strain of laid sensing optical fibers based on BOTDR

In order to solve the problems that the initial value of Brillouin peak power in laid sensing optical fibers is hard to be obtained and the measurement error of temperature and strain is large based on Brillouin frequency shift and peak power, the method of distinguish measurement of temperature and strain is proposed. The Brillouin frequency shift and relative peak power coefficients of temperature and strain, as well as initial Brillouin frequency shift, were obtained by calibration experiment. The coefficients in Brillouin power equation were obtained by heuristic method according to the reference fiber in known temperature and strain. Then the initial Brillouin power distribution along the laid fiber was obtained. The measurement error caused by multiplicative noises in sensing system was conquered by normalization. The spikes in the Brillouin peak power profiles at positions of changed temperature or strain were eliminated by using spectral width change. The simulated optical path of optical fiber composite submarine power cable in engineering field was established. The measurement experiment of temperature and strain was performed. The results indicate that the measurement accuracy are 4.3℃ and 110 at 5.6 km. The distinguish measurement of temperature and strain for laid sensing fiber can be realized. The method can provide theoretical and experimental basis for engineering applications.