Temperature and Acoustic Field Reconstruction in Fiber Optic DAS System Based on Variational Mode Decomposition

Although numerous efforts have been dedicated toward developing fiber optic distributed acoustic sensing (DAS) system with high performances, challenges still remain in achieving DAS under high-temperature condition. This study thoroughly evaluates the influential mechanism of high temperature (
$\sim 300~^{\circ }$
C) on the
$\emptyset $
-OTDR-based DAS system. Experimental results demonstrate that phase shifts of the interferometric signal are linearly proportional to the temperature variations. Temperature-induced thermal strain shows as a wide-spectrum low-frequency signal, and the center frequency component approaches zero. Since the generated thermal strain can lead to the signal-to-noise ratio (SNR) deterioration and the false alarms of DAS system, in this study, variational mode decomposition (VMD) is first proposed to separate the temperature-induced thermal strain from the effective acoustic signal, and the SNR of DAS system for detecting audio acoustic signal in high temperature has been improved to 21.2 dB. Furthermore, dual-parameter measurement of relative temperature and acoustic sensing can also be realized using VMD method. When compared with the previously reported dual-parameter measurement methods based on the combination of DAS/DTS, single back Rayleigh signal is acquired, and back Raman signal is no longer needed, which largely reduces the system volume and demodulation complexity.