Abstract
A phase-sensitive optical time domain reflectometer (Φ-OTDR) can be used for pipeline security. However, the sensing distance (less than 20 km) of traditional Φ-OTDR is too short for the needs of typical oil and gas pipeline monitoring applications (30–50 km). A simple structure Φ-OTDR system utilizing long pulse, balanced amplified detector and heterodyne detection is proposed in this paper and the sensing range is thereby increased to 60 km. Through analyzing the sensing principle of Φ-OTDR, a novel locating strategy is proposed to maintain the locating accuracy at a few meters when a long pulse (5 µs) is used. The increased pulse width deteriorates the time series of each sensing point seriously. In order to eliminate the deterioration, a data processing technique combining wavelet and empirical mode decomposition is applied in this system. The experiment results show that the sensing distance can be increased to 60 km and the locating accuracy is maintained at 6.8 m.
Highlights
Distributed optical fiber sensors are those sensors which simultaneously utilize fiber as transmission medium and sensing medium [1]
The early Φ-OTDR-based distributed optical fiber sensing systems can meet the real-time requirement, but their application is limited in the sensing distance, which is only a few kilometers [2]
We present a long-distance Φ-OTDR sensing system with 60 km sensing distance, 6.8 m locating accuracy, simple structure and low cost, which is suitable for pipeline security monitoring
Summary
Distributed optical fiber sensors are those sensors which simultaneously utilize fiber as transmission medium and sensing medium [1]. Because the phase of the transmission light is sensitive to perturbations, Sensors 2015, 15 the phase-sensitive optical time domain reflectometer (Φ-OTDR) is used for vibration detection application, such as pipeline intrusion and perimeter security. Oil pipeline monitoring is a tough task because of its long distance and real-time requirements. The early Φ-OTDR-based distributed optical fiber sensing systems can meet the real-time requirement, but their application is limited in the sensing distance, which is only a few kilometers [2]. In 2005, Juarez utilized a continuous-wave Er3+ doped fiber Fabry-Perot laser and an electro-optic modulator (EOM) to improve the sensing range to 12 km [3]
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