Sha Luo

Spatial Resolution Improvement of Distributed Raman Temperature Measurement System

Ensuring the synchronization of backscattered Raman light and improving the sampling rate are of great importance to improve the spatial resolution of a distributed Raman temperature measurement system. To keep the synchronization of the Anti-Stokes and Stokes light and improve the sampling rate, four effective methods are proposed in this paper. First, the asynchrony caused by the difference in the hardware is eliminated by attaching a fiber to the pigtail of APD, which detects the earlier arriving signal. Next, the data acquisition card chooses different sampling rates for the Anti-Stokes and Stokes light according to the velocity of propagation. Then, a new algorithm is adopted to decrease the difference in the fiber position between the Anti-Stokes and Stokes signals. Finally, the optical switch with different length of pigtails is applied to improve the sampling rate without upgrading the hardware of data acquisition card. By theoretical analysis and experimental simulation, the proposed measures in this paper can improve the spatial resolution effectively.

An Improved Denoising Method in RDTS Based on Wavelet Transform Modulus Maxima

This paper proposed and demonstrated an improved wavelet transform modulus maxima (WTMM) denoising method to decrease the temperature error without decreasing spatial resolution in Raman distributed temperature sensors. In this scheme, the WTMM were obtained by combining those on the high and low decomposition scales, and the temperature signal was reconstructed using the WTMM. Experimental results show that the new proposed method has better denoising effect than the conventional one, allowing for the temperature error reduction of ~2 °C at 30 °C and 60 °C without decreasing spatial resolution comparing to original data.

Theoretical analysis of the impact of Rayleigh noise on the performance of distributed Raman temperature sensors

We present a theoretical model to analyze the impact of Rayleigh noise on Raman distributed temperature sensors (RDTS), which use the anti-Stokes and Stokes light or anti-Stokes component only as the demodulation signals. Based on this model, the effects of Rayleigh noise on temperature accuracy, sensitivity, and resolution are investigated both at only one point and in a section of the fiber. The analysis indicates that for RDTS demodulated by anti-Stokes light only, the temperature accuracy, sensitivity, and resolution decrease by about 1°C, 10%, and 0.25°C on the assumption that the Rayleigh noise accounts for 10% of the anti-Stokes intensity. Moreover, for RDTS demodulated by Stokes and anti-Stokes light, the temperature accuracy, sensitivity, and resolution decrease by about 1°C, 10%, and 0.2°C assuming that the Rayleigh noise in two paths is equal to 10% of the intensity of anti-Stokes and Stokes light. The analysis demonstrates that the impact of Rayleigh noise on sensing capacities of RDTS is non-negligible, thus providing a major contribution to the elimination of Rayleigh noise in RDTS.

Novel demodulation method for eliminating Rayleigh scattering in Raman distributed temperature sensors using anti-Stokes light only

A novel temperature demodulation method which eliminates the impact of Rayleigh scattering on Raman distributed temperature sensors (RDTS) using anti-Stokes light only is presented. This method utilizes two sections of reference fiber which are placed into temperature control chambers with different temperatures, such that the impact caused by the variation of laser’ power and the Rayleigh scattering is eliminated by the two reference temperatures. In the experiment, the temperature error caused by the Rayleigh scattering was decreased by 0.6℃ and 1.7℃ at 30℃ and 50℃compared with conventional method respectively.