Distributed Vibration Sensor Research Articles

Detecting microseismicity using distributed vibration

Distributed acoustic sensing (DAS) and, more generally, distributed vibration sensing (DVS) offer new approaches to the detection of seismic waves, based on interrogation of a fibre-optic cable. We investigated the detection of microseismic events using a heterodyne distributed vibration sensor (hDVS), comparing to a pair of borehole geophone arrays co-located in the monitoring well. The aim was to establish the current performance level of hDVS for microseismic monitoring and to understand any differences between geophone and hDVS responses. We compared the microseismic events detected simultaneously on both systems. Under the assumption that hDVS measures strain in the fibre, the comparison to geophone particle velocity was made in the strain-rate domain. We supported these observations with modelling work. We found the hDVS measurements directly comparable to the geophones, indicating a potentially true amplitude response from hDVS. An anomaly in the hDVS frequency response was a function of apparent phase velocity. Modelling verified the observed effect as consistent with the filtering effect of the light pulse used in fibre interrogation. We find that hDVS detects microseismicity but is not yet a replacement for the borehole array. However, improved microseismic response might be achieved with shorter pulse-length systems in the next generation of fibre interrogators. The heterodyne distributed vibration sensor (hDVS), together with other forms of distributed acoustic sensing (DAS), have been reported as observation techniques for microseismic monitoring (Webster et al., 2013; Li et al., 2015; Molteni et al., 2016). We present further results from the study described by Molteni et al. (2016) and extend the discussion on the differences between observation with a borehole array of geophones and observation on a laser-interrogated fibre-optic cable that is cemented behind casing.

Real-Time Distributed Vibration Monitoring System Using $\Phi$ -OTDR

The purpose of this paper is to theoretically analyze and experimentally demonstrate the investigation on a distributed optical fiber sensor based on phase-sensitive optical time domain reflectometry ( $\Phi $ -OTDR) for real-time vibration monitoring with different signal processing methods. The $\Phi $ -OTDR system is investigated in two aspects: the hardware parameter and the interrogation scheme. The effect of pulsed light power that enters into the sensing fiber on $\Phi $ -OTDR is first discussed. Then, two systems based on the differential method and the Prewitt edge detection method applied for $\Phi $ -OTDR are presented for 1-D and 2-D vibration location, respectively. Finally, a high-speed acquisition system based on FPGA is applied to realize the 3-D real-time vibration monitoring. This new distributed vibration sensor can be used as an ideal source for the third-party intrusion identification, pipeline monitoring, and ultrasonic wave detection in explosive environment.

Practical investigation of suitable decoding techniques for spectral amplitude coding optical code division multiple access‐based vibration sensing

A suitable decoding technique for spectral amplitude coding optical code division multiple access (SAC-OCDMA)-based secured distributed vibration sensor is investigated. The study is carried out to identify the most appropriate techniques for receiving the transmitted vibration signal in SAC-OCDMA-based system. The techniques which are direct decoding, complementary and logical AND decoding are compared based on the level of crosstalk, number of components used and supported transmission distance in multiplexed vibration sensing using both simulation and experiment. The results show direct decoding capable of supporting 55 km unlike the other two which are 44 and 38 km, respectively. Aside that, direct decoding techniques could be implemented with less number of components and has optimal signal-to-noise ratio while still preventing the system again the ‘man in the middle’ attack.

A Fading-Discrimination Method for Distributed Vibration Sensor Using Coherent Detection of $\varphi $ -OTDR

We have proposed an effective method to discriminate the false alarm peaks induced by fading effect in distributed fiber-optic vibration sensing systems based on coherent heterodyne detection of phase-sensitive optical time-domain reflectometer ( $\varphi $ -OTDR). By comparison of the demodulated phase of backscattered light returned from the location of the sensing fiber before and behind the alarm peaks, the false alarm peaks can be distinguished from real vibration alarm peaks. We have demonstrated a fiber-optic distributed vibration sensor with efficient fading discrimination based on $\varphi $ -OTDR system that has a measurement range of 2.5 km, a spatial resolution of 2.5 m, and a signal-to-noise ratio of 16 dB. The results provide a simple and low-cost approach for the false alarm discrimination in all-fiber $\varphi $ -OTDR systems.

Distributed vibration sensing for seismic acquisition

Distributed vibration sensing (DVS), also known as distributed acoustic sensing (DAS), is a relatively new method for recording seismic data using a standard fiber-optic cable as the sensor. Although the dynamic range and noise floor of DVS systems are currently below those of industry-standard seismic sensors, usable seismic data can be obtained in downhole configurations, as this is the source and receiver configuration at which DVS is most sensitive. The use of DVS for more conventional land and marine seismic acquisition is still some way off. However, the potential benefits of simple, lightweight fiber-optic cables, with fine spatial sampling and the ability to instrument all offsets of any spread, suggest it is worth pursuing these new applications. Permanent reservoir monitoring, particularly for marine environments, represents another application where the simplicity of fiber-optic sensors is attractive. Advances in laser interrogation techniques and signal processing continue to improve the quality of DVS data, increasing its potential applications across the seismic industry.

Distributed fiber-optic vibration sensing based on phase extraction from time-gated digital OFDR.

A novel distributed fiber vibration sensing technique based on phase extraction from time-gated digital optical frequency domain reflectometry (TGD-OFDR) which can achieve quantitative vibration measurement with high spatial resolution and long measurement range is proposed. A 90 degree optical hybrid is used to extract phase information. By increasing frequency sweeping speed, the influence of environmental phase disturbance on TGD-OFDR is mitigated significantly, which makes phase extraction in our new scheme more reliable than that in conventional OFDR-based method, leading to the realization of long distance quantitative vibration measurement. By using the proposed technique, a distributed vibration sensor that has a measurement range of 40 km, a spatial resolution of 3.5 m, a measurable vibration frequency up to 600 Hz, and a minimal measurable vibration acceleration of 0.08g is demonstrated.

Influences of pulse on phase-sensitivity optical time domain reflectometer based distributed vibration sensor

The influences of pulse, including the pulse width Tp and the peak pulse power Ipeak, on phase-sensitivity optical time-domain reflectometer (φ-OTDR) based distributed vibration sensor are investigated in this paper. A numerical simulation is performed to illustrate the relationships between pulse and temporal response trace as well as the visibility of interferential Rayleigh backscattering light. The simulation results show that the method of amplifying Ipeak is benefit for increasing the amplitude of temporal response trace, while it is useless for improving the visibility. In contrast, the method of broadening Tp is useful for increasing the amplitude of temporal response trace by improving the visibility. Laboratory experiments are implemented by using a φ-OTDR prototype with an electro-dynamic vibration table producing stable vibration signals. The good agreement of experimental with simulated results validates the theoretical analysis.

Fiber-Optic Distributed Vibration Sensor for Pipeline Pre-Alarm

Pipeline security is very important in oil and gas transportation. Traditional technology such as negative pressure wave detection, acoustic detection doesn’t match the need of pre-alarm. A fiber-optic distributed vibration sensor (FDVS) is proposed and investigated. It is found that the FDVS has the advantages of long sensing distance, high spatial resolution, high sensitivity, high reliability, etc. According to calculating the time delay of the two MZIs , the vibration can be located.

Phase-sensitive Optical Time Domain Reflectometer Assisted by First-order Raman Amplification for Distributed Vibration Sensing Over >100 km

In this study, the authors present an experimental and theoretical description of the use of first order Raman amplification to improve the performance of a Phase-sensitive optical time domain reflectometer (φOTDR) when used for vibration measurements over very long distances. A special emphasis is given to the noise which is carefully characterized and minimized along the setup. A semiconductor optical amplifier and an optical switch are used to greatly decrease the intra-band coherent noise of the setup and balanced detection is used to minimize the effects of RIN transferred from the Raman pumps. The sensor was able to detect vibrations of up to 250 Hz (close to the limits set by the time of flight of light pulses) with a resolution of 10 m in a range of 125 km. To achieve the above performance, no post-processing was required in the φOTDR signal. The evolution of the φOTDR signal along the fiber is also shown to have a good agreement with the theoretical model.

All Fiber Distributed Vibration Sensing Using Modulated Time-Difference Pulses

An optical fiber distributed sensing system merging Mach-Zehnder interferometer (MZI) and phase-sensitive optical time domain reflectometer for vibration measurement with wide frequency response and spatial resolution is proposed and demonstrated. Two acoustic optical modulators are adopted to generate narrow and wide pulses, respectively, on both ends of sensing fiber with a time difference. Narrow pulses are used to generate Rayleigh backscattering light, which locates the vibration point, while wide pulses interfere with reference light as an MZI to obtain frequency response. To simulate the high frequency responses of crack in civil structures, the sudden break of pencils adjacent to the fiber loop has been measured. The experimental results show 5 m spatial resolution and up to 6.3 MHz frequency response with 50 ns pulse width are achieved in 1150 m sensing distance.

干涉型分布式光纤振动传感技术的研究进展

干涉型分布式光纤振动传感技术的研究进展

基于小波信息熵的分布式振动传感系统的扰动评价方法

基于小波信息熵的分布式振动传感系统的扰动评价方法

Positioning Error Reduction Technique Using Spectrum Reshaping for Distributed Fiber Interferometric Vibration Sensor

A novel positioning error reduction technique is proposed for dual Mach-Zehnder fiber interferometric distributed vibration sensor. The 3 dB bandwidth of the power spectrum of interference signal is broadened to reduce the mean square error (MSE) of the cross-correlation based positioning algorithm. A high-pass filter (HPF) whose cutoff frequency is larger than the upper frequency of signal 3 dB bandwidth is applied to reshape the original power spectrum by attenuating the magnitude of low-frequency mainlobe to the same order as that of the small high-frequency components. The usage of HPF can cause bandwidth broadening and signal to noise ratio (SNR) reduction, the influence of both effects on ultimate positioning MSE are analyzed in detail. Theoretical analysis shows that there exists a valid region for the cutoff frequency of the HPF within which the contribution of bandwidth broadening dominates the process. The technique is also experimentally verified and analyzed by field test on an installed submarine cable between two islands of Zhejiang Province, China. Field test results coincide with the theoretical predictions and show that a maximum of 7 dB reduction of positioning MSE can be achieved when optimal cutoff frequency of HPF is used.

Continuous wavelet transform for non-stationary vibration detection with phase-OTDR

We propose the continuous wavelet transform for non-stationary vibration measurement by distributed vibration sensor based on phase optical time-domain reflectometry (OTDR). The continuous wavelet transform approach can give simultaneously the frequency and time information of the vibration event. Frequency evolution is obtained by the wavelet ridge detection method from the scalogram of the continuous wavelet transform. In addition, a novel signal processing algorithm based on the global wavelet spectrum is used to determine the location of vibration. Distributed vibration measurements of 500 Hz and 500 Hz to 1 kHz sweep events over 20 cm fiber length are demonstrated using a single mode fiber.

Development of Distributed Vibration Sensing System Based on Polarization Optical Time Domain Reflectometry

Development of Distributed Vibration Sensing System Based on Polarization Optical Time Domain Reflectometry

One Frequency Component Dependency Based Distributed Vibration Sensor Applying a Modified Sagnac Interferometer with a Delay Fiber Loop

One Frequency Component Dependency Based Distributed Vibration Sensor Applying a Modified Sagnac Interferometer with a Delay Fiber Loop

Wavelet Denoising Method for Improving Detection Performance of Distributed Vibration Sensor

This letter proposed and demonstrated a wavelet technique to reduce the time domain noise to get submeter spatial resolution in the distributed vibration sensor based on phase optical time domain reflectometry. A new wavelet shrinkage approach allows the distributed vibration measurement of 20-Hz and 8-kHz events to be detected over 1-km sensing length with a 5-ns optical pulse, which is equivalent to 50-cm spatial resolution using the single-mode sensing fiber.

High Sensitivity Distributed Vibration Sensor Based on Polarization-Maintaining Configurations of Phase-OTDR

A system based on all-polarization-maintaining configurations of the phase-sensitive optical time-domain reflectometry (OTDR) is presented for vibration sensing. Both polarization-induced signal fading and noise are mitigated via polarization-maintaining components. The detectable frequency response is increased to ~2.25 kHz. Moreover, only a straight sensing fiber segment of ~0.13 m instead of several closed fiber loops is needed to sense the vibration event with a spatial resolution of 1 m, which makes it convenient for vibration monitoring in practical applications. The maximum distance between the sensing fiber and vibration event can be 18 cm.

Distributed Vibration Sensor Based on Coherent Detection of Phase-OTDR

We developed a distributed vibration sensor by using heterodyne detection and signal processing of moving averaging and moving differential for the phase optical time domain reflectometry system. The broadband acoustic frequency components generated by pencil-break vibration have been measured and identified in location by our distributed vibration sensor for the first time. Pencil break measurement is a standard technique to emulate the acoustic emission of cracks in concrete or steel bridges for early crack identification. The spatial resolution is 5m and the highest frequency response is 1 kHz, which is limited by the trigger frequency of data acquisition card. This new sensing system can be used for vibration detection of health monitoring of various civil structures as well as any dynamic monitoring requirement.

A SVM-based pipeline leakage detection and pre-warning system

A SVM-based pipeline leakage detection and pre-warning system is presented in this paper. In the system an optical cable is laid in parallel with a pipeline in the same ditch and three single mode optical fibers inside constitute the distributed vibration sensor. The sensor is based on Mach–Zehnder optical fiber interferometer and can detect the vibration signals along a pipeline in real time. Then the eigenvectors of vibration signals are extracted by “energy-pattern” method based on wavelet packet decomposition. Subsequently the vibration signals are recognized by support vector machine (SVM) through the features so that it can judge whether any abnormal event is taking place. If any abnormal event is found along a pipeline, the location is thus calculated. A series of trials in situ have been done, showing that the system is of good accuracy and real time performance both in recognition and locating.