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Abstract Distributed Acoustic Sensing (DAS) is an emerging technology that converts optical fibers into dense arrays of strainmeters, significantly enhancing our understanding of earthquake physics and Earth's structure. While most past DAS studies have focused primarily on seismic wave phase information, accurate measurements of true ground motion amplitudes are crucial for comprehensive future analyses. However, amplitudes in DAS recordings, especially for pre‐existing telecommunication cables with uncertain fiber‐ground coupling, have not been fully quantified. By calibrating three DAS arrays with co‐located seismometers, we systematically evaluate DAS amplitudes. Our results indicate that the average DAS amplitude of earthquake signals closely matches that of co‐located seismometer data across frequencies from 0.01 to 10 Hz. The noise floor of DAS is comparable to that of strong‐motion stations but higher than that of broadband stations. The saturation amplitude of DAS is adjustable by modifying the pulse repetition rate and gauge length. We also demonstrate how our findings enhance the understanding of fiber‐optic seismology and its implications for natural hazard mitigation and Earth structure imaging and monitoring. Specifically, our results suggest that with proper settings, DAS can detectP‐waves from an M6+ earthquake occurring 10 km from the cable without saturation, indicating its viability for earthquake early warning. Through quantitative comparison and analysis, we also find that local ambient traffic noise levels strongly affect the quality of seismic interferometry measurement, which is a powerful tool for near‐surface imaging and monitoring. Our methodology and findings are valuable for future DAS experiments that require precise seismic amplitude measurements.
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Field trial of coexistence and simultaneous switching of real-time fiber sensing and 400GbE supporting DCI and 5G mobile services
Coexistence of real-time constant-amplitude distributed acoustic sensing (DAS) and 400GbE signals is verified by field trial over metro fibers, demonstrating no QoT impact during co-propagation and supporting preemptive DAS-informed optical path switching before link failure.
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- Award ID(s):
- 2029295
- PAR ID:
- 10457281
- Date Published:
- Journal Name:
- in Proc. IEEE/OPTICA Optical Fiber Communication Conference (OFC’23
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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SUMMARY Distributed acoustic sensing (DAS) networks promise to revolutionize observational seismology by providing cost-effective, highly dense spatial sampling of the seismic wavefield, especially by utilizing pre-deployed telecomm fibre in urban settings for which dense seismic network deployments are difficult to construct. However, each DAS channel is sensitive only to one projection of the horizontal strain tensor and therefore gives an incomplete picture of the horizontal seismic wavefield, limiting our ability to make a holistic analysis of instrument response. This analysis has therefore been largely restricted to pointwise comparisons where a fortuitious coincidence of reference three-component seismometers and colocated DAS cable allows. We evaluate DAS instrument response by comparing DAS measurements from the PoroTomo experiment with strain-rate wavefield reconstructed from the nodal seismic array deployed in the same experiment, allowing us to treat the entire DAS array in a systematic fashion irrespective of cable geometry relative to the location of nodes. We found that, while the phase differences are in general small, the amplitude differences between predicted and observed DAS strain rates average a factor of 2 across the array and correlate with near-surface geology, suggesting that careful assessment of DAS deployments is essential for applications that require reliable assessments of amplitude. We further discuss strategies for empirical gain corrections and optimal placement of point sensor deployments to generate the best combined sensitivity with an already deployed DAS cable, from a wavefield reconstruction perspective.more » « less
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Abstract Significant interest has developed in using optical fibers for seismology through Distributed Acoustic Sensing (DAS). However, converting DAS strain measurements to actual ground motions can result in errors and uncertainties due to imperfect coupling of the fiber to the earth and instrument response functions. To address this, we conducted a comparative analysis of strain data recorded by DAS, Optical Fiber Strainmeters (OFSs), and estimates derived from seismic data. This study used dark fibers in a commercial cable connecting two islands in Puget Sound, Washington, USA. The cable extends from a telecommunication substation on Whidbey Island, through an underground conduit, and across Saratoga Passage to Camano Island. The strain along the cable was recorded using OFS Michelson interferometers and a DAS interrogator, with a broadband seismometer positioned at one end. Comparing a teleseismic earthquake recording showed that summed DAS channels agreed well with OFS recordings. The amplitude discrepancies between the measurements and the seismometer's estimated strain indicated poor coupling between the cable and the earth. We also evaluated DAS amplitude response using a piezoelectric cylinder (PZT) to generate ground truth strain. The findings revealed a notable amplitude decrease in DAS recordings at lower frequencies, highlighting the need for amplitude calibration. Moreover, some underwater signals in the study area were strongly correlated with the velocity of the tidal current. These signals can be localized through coherence calculations between the DAS and OFS recordings.more » « less
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