On the sensitivity of distributed acoustic sensing

Gabai, Haniel; Eyal, Avishay

doi:10.1364/ol.41.005648

Cited by 144 publications

(58 citation statements)

References 12 publications

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“…A third type of optical noise manifests as a reduced amplitude pattern that is quasi‐random in space but time invariant. This common problem in phase‐sensitive Optical Time‐Domain Reflectometery measurements is called optical fading (Gabai & Eyal, ). Generally speaking, fading results from destructive interference, which can happen when the random electric fields from scatterers within the fiber sum to a very small total magnitude (Hecht, ).…”

Section: The Das Measurement Principlementioning

confidence: 99%

On the Broadband Instrument Response of Fiber‐Optic DAS Arrays

2020

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Distributed Acoustic Sensing (DAS) is a novel tool in array seismology that measures the phase of backscattered laser pulses traveling in a fiber‐optic cable, and relates this measurement to the axial strain induced on the cable by a propagating seismic wavefield. Combining DAS with telecommunications optical fiber networks has begun to address a range of earth science questions where cost and field logistics have historically hindered observations. Unlike classic inertial seismometers, DAS instrument response is presently unquantified. This topic includes a variable sensing element—the fiber, including packaging and installation—which changes between experiments. Ignoring this element, one DAS record should approximate a fixed‐length strain gauge, which exactly measures Earth's motion down to quasi‐static frequencies relevant to geodesy. In this paper, we test this hypothesis using seismological observations of teleseismic earthquakes and microseism noise spanning the 1 to 120 s period range. We use a commercial DAS interrogator unit connected to an optical fiber previously used for telecommunication and a colocated broadband seismometer to estimate the DAS transfer function. We find a 1:1 correspondence with actual ground motion from 10–120 s. At shorter periods (1–10 s), DAS amplitude response is enhanced by 3–11 dB. Phase response is flat over this range of periods. We interpret the recovered DAS response function in terms of hypothesized fiber coupling and photonic effects. We propose this calibration methodology for future DAS experiments where seismic amplitude information is desired.

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Section: The Das Measurement Principlementioning

confidence: 99%

On the Broadband Instrument Response of Fiber‐Optic DAS Arrays

2020

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“…The comparisons are performed between the mathematically reconstructed results of the FISTA and OMP methods and the experimental results obtained with f-OTDR conventional processing. The conventional processing of the f-OTDR raw-data is envelope detection to obtain the fiber profile and calculation of differential phase along the 'fast' time axis (namely, spatial phase difference) to obtain a linear measurement of the dynamic excitation signal of interest [38][39][40]. FISTA and OMP are mathematical methods which were developed to solve equations such as equation (2) for a sparse vector of unknowns.…”

Section: Resultsmentioning

confidence: 99%

Sparse recovery methodologies for quasi-distributed dynamic strain sensing

Shiloh¹,

Shen-Tzur²,

Eyal³

et al. 2020

J. Phys. Photonics

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Quasi-distributed measurement of strain and/or temperature is often implemented using arrays of weakly reflecting fiber Bragg gratings (FBGs) whose reflection peaks are centered at the same nominal wavelength. The signals are obtained by measuring the phase difference between the reflections of consecutive FBGs. Typically, in such a system, the spatial resolution of the interrogator must be compatible with the spatial separation between consecutive FBGs. Insufficient resolution leads to an overlap of reflection peaks, a decrease in the differential-phase signal and poor sensitivity. In this paper, we study the use of two different sparsity based methodologies for improving the sensitivity of such quasi distributed acoustic sensing systems in the case where traditional signal processing approaches do not provide sufficient spatial resolution. These methods enable relaxing the requirements regarding the interrogator or, alternatively, reducing the needed separation between reflectors. Experimentally, these techniques were used to measure 1 kHz dynamic strain induced in a fiber segment between two discrete reflectors, located at the end of a 4 km long fiber. The separation between the reflectors was 18 m while the pulse (spatial) width was intentionally chosen bigger than that. It yielded approximately 5 dB increase in the measured signal compared to the traditional processing approach and an order of magnitude improvement in the sensitivity,~m 0.9 rad Hz .

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“…This is reasonable since the relative PSD at heterodyne frequency is the difference between the PSD at ∆ f and the noise floor. In Gabai's work [22], it has been found that the SNR of the demodulated phase was directly proportional to the SNR of the backscattered trace. According to Equation (2), the higher the noise floor, the lower the SNR of the demodulated phase, explaining the negative relation between the relative PSD at heterodyne frequency and the noise floor.…”

Section: Relation Between Psd and Noise Floormentioning

confidence: 97%

Performance Improvement of Dual-Pulse Heterodyne Distributed Acoustic Sensor for Sound Detection

Zhang

et al. 2020

Sensors

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Phase fading is fatal to the performance of distributed acoustic sensors (DASs) influencing its capability of distributed measurement as well as its noise level. Here, we report the experimental observation of a strong negative correlation between the relative power spectrum density (PSD) at the heterodyne frequency and the noise floor of the detected phase for the heterodyne demodulated distributed acoustic sensor (HD-DAS) system. We further propose a weighted-channel stack algorithm (WCSA) to alleviate the phase fading noise via an enhancement of the relative PSD at the heterodyne frequency. Experimental results show that the phase noise of the demodulated signal can be suppressed by 13.7 dB under optimal condition. As a potential application, we exploited the improved HD-DAS system to retrieve a piece of music lasted for 205 s, demonstrating the reliability of detecting wideband sound signal without distortion.

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On the sensitivity of distributed acoustic sensing

Cited by 144 publications

References 12 publications

On the Broadband Instrument Response of Fiber‐Optic DAS Arrays

On the Broadband Instrument Response of Fiber‐Optic DAS Arrays

Sparse recovery methodologies for quasi-distributed dynamic strain sensing

Performance Improvement of Dual-Pulse Heterodyne Distributed Acoustic Sensor for Sound Detection

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