Abstract
We propose a novel denoising method based on empirical mode decomposition (EMD) to improve the signal-to-noise ratio (SNR) for vibration sensing in phase-sensitive optical time domain reflectometry (φ-OTDR) systems. Raw Rayleigh backscattering traces are decomposed into a series of intrinsic mode functions (IMFs) and a residual component using an EMD algorithm. High frequency noise is eliminated by removing several IMFs at the position without vibration selected by the Pearson correlation coefficient (PCC). When the pulse width is 50 ns, the SNR of location information for the vibration events of 100 Hz and 1.2 kHz is increased to as high as 42.52 dB and 39.58 dB, respectively, with a 2 km sensing fiber, which demonstrates the excellent performance of this new method.
Highlights
Distributed fiber optical sensors are an effective technology for measurement of physical quantities such as strain, temperature and vibration
Distributed fiber sensors based on backscattering light along the fiber include polarization-OTDR, phase-sensitive OTDR (φ-OTDR) and Brillouin OTDR [5,6,7,8,9] devices are proposed to locate the position of disturbances with a satisfactory spatial resolution
Ultra-long sensing distance of 131.5 km was realized in φ-OTDR with high spatial resolution by combining heterodyne detection and Raman amplification [10]
Summary
Distributed fiber optical sensors are an effective technology for measurement of physical quantities such as strain, temperature and vibration. Distributed fiber sensors based on backscattering light along the fiber include polarization-OTDR, phase-sensitive OTDR (φ-OTDR) and Brillouin OTDR [5,6,7,8,9] devices are proposed to locate the position of disturbances with a satisfactory spatial resolution. Sensors 2017, 17, 1870 fiber as long as the scattering points do not change Disturbances such as strains or vibrations can affect the refractive index of the sensing fiber, the amplitude of Rayleigh backscattering curves corresponding to the disturbance position will be changed. A high-performance way based on power spectrum analysis is introduced to eliminate undesirable effects resulting from frequency drifts of the lasers and this improves the SNR of φ-OTDR systems [17]. Vibration events of 100 Hz and 1.2 kHz are experimentally demonstrated and the SNR of location information is improved to 42.52 dB and 39.58 dB, respectively, with a pulse width of 50 ns and an optical fiber length of 2 km
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