Fading Suppression of Φ-OTDR With the New Signal Processing Methodology of Complex Vectors Across Time and Frequency Domains

Interference-Fading-Suppressed Pulse-Coding Φ-OTDR Using Spectrum Extraction and Rotated-Vector-Sum Method

“…Therefore, the influence of Rayleigh interference fading in pulse-coding Φ-OTDR can be almost eliminated, but there may be still some fading points induced by polarization fading. It is possible to be solved by combining SERVS method used here with the polarization diversity detection [17], [29], which is worth further investigations.…”

“…This method reduces the proportion of fading points greatly from 2.98% to 0.33% and reduces the standard deviation of differential phase from 0.6556 rad to 0.2901 rad. It also reduces the minimum level of the averaged power spectral density (PSD) of the differential phase at whole locations along the fiber about 6 dB/Hz [17]. What's more, it achieves a SNR of 43.96 dB for the demodulated vibration signal applied through a piezoelectric transducer (PZT).…”

“…However, sweeping the optical frequency increases the This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ complexity of Φ-OTDR system [17]. In 2019, Zhu Tao et al employed a three-carrier pulse generated by an electro-optic modulator (EOM) to mitigate the interference fading effect greatly in Φ-OTDR [18].…”

Polarization fading mitigation in distributed acoustic sensors based on a high-speed polarization rotator

“…For dual-pulse DAS systems, the phase fading has been eliminated by shifting the phase difference between subsequent pulse-pairs by 2π/3, but at the cost of reduced measurement bandwidth [19]. For coherent DAS systems, a commonly used technique is based on a 90°hybrid [20][21][22].…”

Long Range Raman-Amplified Distributed Acoustic Sensor Based on Spontaneous Brillouin Scattering for Large Strain Sensing

“…High sensitivity and long sensing range of Distributed Acoustic Sensors (DASs) have made them ideal devices for sensing vibrations of elongated structures such as pipelines, railways, and subsea cables [1][2][3][4][5][6]. The sensitivity of DAS systems based on Phase-sensitive Optical Time-domain Reflectometry (φ-OTDR) has seen a continuous improvement over the past decade, reaching levels as low as several tens of pε/ √ Hz [7][8][9][10][11][12][13][14]. Although the lower strain limit of φ-OTDR based DAS (φ-DAS) systems are extended to sub nε levels, the ceiling of the strain range of these systems is limited to several tens of µε due to the trade-off between the maximum sampling rate and the length of the sensing fiber [15,16] (detailed explanation of this trade-off is provided in Section 2).…”