EGU2020-7343
https://doi.org/10.5194/egusphere-egu2020-7343
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Distributed Acoustic Sensing from mHz to kHz: Empirical Investigations of DAS Instrument Response

Patrick Paitz1, Pascal Edme1, Cédric Schmelzbach1, Joesph Doetsch1, Dominik Gräff1, Fabian Walter1, Nathaniel Lindsey2, Athena Chalari3, and Andreas Fichtner1
Patrick Paitz et al.
  • 1ETH Zürich, Zürich, Switzerland (patrick.paitz@erdw.ethz.ch)
  • 2Stanford University, Stanford, United States
  • 3Silixa Ltd, Elstree, United Kingdom

With the upside of high spatial and temporal sampling even in remote or urban areas using existing fiber-optic infrastructure, Distributed Acoustic Sensing (DAS) is in the process of revolutionising the way we look at seismological data acquisition. However, recent publications show variations of the quality of DAS measurements along a single cable. In addition to site- and orientation effects, data quality is strongly affected by the transfer function between the deforming medium and the fiber, which in turn depends on the fiber-ground coupling and the cable properties. Analyses of the DAS instrument response functions in a limited part of the seismological frequency band are typically based on comparisons with well-coupled conventional seismometers for which the instrument response is sufficiently well known to be removed from the signal.

In this study, we extend the common narrow-band analyses to DAS response analyses covering a frequency range of five orders of magnitude ranging from ~4000 s period to frequencies up to ~100 Hz. This is based on a series of experiments in Switzerland, including (1) active controlled-source experiments with co-located seismometers and geophones, (2) low-frequency strain induced by hydraulic injection in a borehole with co-located Fiber-Bragg-Grating (FBG) strain-meters, and (3) local to teleseismic ice- and earthquake recordings with  co-located broadband stations.

Initial results show a site-unspecific, approximately flat instrument response for all experiments.

The initial results suggest that the amplitude and phase information of DAS recordings are sufficient for conventional geophysical methods such as event localisation, full-waveform inversion, ambient noise tomography and even event magnitude estimation. Despite the promising initial results, further engagement by the DAS community is required to evaluate the DAS performance and repeatability among different interrogation units and study sites.

How to cite: Paitz, P., Edme, P., Schmelzbach, C., Doetsch, J., Gräff, D., Walter, F., Lindsey, N., Chalari, A., and Fichtner, A.: Distributed Acoustic Sensing from mHz to kHz: Empirical Investigations of DAS Instrument Response, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7343, https://doi.org/10.5194/egusphere-egu2020-7343, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-7343, Luis Matias, 06 May 2020

    Is DAS sensitive only to strain along the cable or is it sensitive also to pressure? Pressure I believe would be a second order effect. Can the cable sense pressure also? How can you separate both effects?

    • AC1: Sensitivity to pressure, Patrick Paitz, 06 May 2020

      Hi Luis, thank you for the comment. There is a pressure sensitivity due to the Poisson Effect. But there are papers around that show that this effect is quite small. If I remember correctly, this is also discussed in: "Interaction of helically wound fibre-optic cables with plane seismic waves" by Kuvshinov (Geophysical Prospecting). The author discusses the potential of helical fibers for broadside sensitivity as well.

  • CC2: Comment on EGU2020-7343, Björn Lund, 06 May 2020

    Hi,

    It would be interesting to see how the solution/transfer function degrades away from the place of determination. You could probably show that by comparing to the next determination, an the next and so on?

    /Björn

    • AC2: Distance vs. response, Patrick Paitz, 06 May 2020

      Hi Björn, 

      thank you very much for the comment! This is indeed something that can be done, and indeed should be done! I will write it on my To-Do-List :)