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Surface deployment of DAS systems: coupling strategies and comparisons to geophone data

Surface deployment of DAS systems: coupling strategies and comparisons to geophone data
Surface deployment of DAS systems: coupling strategies and comparisons to geophone data

Distributed acoustic sensing (DAS) systems are a recent technological development for seismic observations over a broad range of frequencies with a wide variety of applications. Typically, fibre-optic cables are buried underground or cemented into well casings where the cables are well-coupled to the ground. Quick and temporary surface deployment of cables has great potential utility in areas where rapid surveying and minimal disturbance of the subsurface are desired. However, proper mechanical coupling between the fibre and the ground is still a challenge for temporary surface deployments. Here we test four different coupling strategies for a DAS system deployed in a grassy field, including uncoupled, pinned under tension to the ground, weighted down by carpeting, and weighted down by a sandbag. We compare the DAS data to vertical component geophone data and estimated horizontal geophone data to assess the fidelity of DAS ground motion recordings. We find a completely uncoupled fibre is capable of recording seismic energy up to ∼10 m away from the source, while the pinned and weighted fibre record signals over several tens of metres. The DAS recordings compare favourably with the estimated horizontal displacement records from the multi-channel seismic system. There is a good agreement between the phase of the signals acquired by the DAS system with that of the geophones, but there is a mismatch of up to a factor of two in the absolute amplitude at some frequencies. We perform several standard analysis techniques, including refraction and multi-channel analysis of surface waves, on the coupled DAS data. Finally, the instrument response of the coupled DAS data to ground motions is determined using the estimated horizontal component from the multi-channel seismic system. Surface deployments of DAS systems provide a complementary set of observations to standard vertical geophone deployments, for instance, if multi-component geophones are not available. Also, there are some advantages in speed and ease of deployment of DAS in comparison to geophones depending on the coupling strategy used.

DAS, geophone, MASW, surface waves, velocity
1569-4445
465-477
Harmon, Nicholas
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Rychert, Catherine A.
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Davis, John
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Brambilla, Gilberto
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Buffet, William
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Chichester, Ben
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Dai, Yuhang
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Bogiatzis, Petros
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Snook, James
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van Putten, Lieke
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Masoudi, Ali
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Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Rychert, Catherine A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Davis, John
7f762b01-375b-42c8-80cb-65baefffdb97
Brambilla, Gilberto
815d9712-62c7-47d1-8860-9451a363a6c8
Buffet, William
bca7a57f-da49-4f80-9381-0aaa0530f05e
Chichester, Ben
dbeeac38-53e8-4e6c-b7ff-8c8e1e8a3f96
Dai, Yuhang
81b3f9b9-2faa-49d0-97e5-c4907a194810
Bogiatzis, Petros
8fc5767f-51a2-4d3f-aab9-1ee9cfa9272d
Snook, James
2466db53-015e-4c0a-aa6d-589ab1de7e61
van Putten, Lieke
64513739-3d2d-428f-bd09-3c1162f10313
Masoudi, Ali
8073fb9b-2e6c-46c9-89cf-cb8670d76dc0

Harmon, Nicholas, Rychert, Catherine A., Davis, John, Brambilla, Gilberto, Buffet, William, Chichester, Ben, Dai, Yuhang, Bogiatzis, Petros, Snook, James, van Putten, Lieke and Masoudi, Ali (2022) Surface deployment of DAS systems: coupling strategies and comparisons to geophone data. Near Surface Geophysics, 20 (5), 465-477. (doi:10.1002/nsg.12232).

Record type: Article

Abstract

Distributed acoustic sensing (DAS) systems are a recent technological development for seismic observations over a broad range of frequencies with a wide variety of applications. Typically, fibre-optic cables are buried underground or cemented into well casings where the cables are well-coupled to the ground. Quick and temporary surface deployment of cables has great potential utility in areas where rapid surveying and minimal disturbance of the subsurface are desired. However, proper mechanical coupling between the fibre and the ground is still a challenge for temporary surface deployments. Here we test four different coupling strategies for a DAS system deployed in a grassy field, including uncoupled, pinned under tension to the ground, weighted down by carpeting, and weighted down by a sandbag. We compare the DAS data to vertical component geophone data and estimated horizontal geophone data to assess the fidelity of DAS ground motion recordings. We find a completely uncoupled fibre is capable of recording seismic energy up to ∼10 m away from the source, while the pinned and weighted fibre record signals over several tens of metres. The DAS recordings compare favourably with the estimated horizontal displacement records from the multi-channel seismic system. There is a good agreement between the phase of the signals acquired by the DAS system with that of the geophones, but there is a mismatch of up to a factor of two in the absolute amplitude at some frequencies. We perform several standard analysis techniques, including refraction and multi-channel analysis of surface waves, on the coupled DAS data. Finally, the instrument response of the coupled DAS data to ground motions is determined using the estimated horizontal component from the multi-channel seismic system. Surface deployments of DAS systems provide a complementary set of observations to standard vertical geophone deployments, for instance, if multi-component geophones are not available. Also, there are some advantages in speed and ease of deployment of DAS in comparison to geophones depending on the coupling strategy used.

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Near Surface Geophysics - 2022 - Harmon - Surface deployment of DAS systems Coupling strategies and comparisons to - Version of Record
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Accepted/In Press date: 14 July 2022
Published date: 1 August 2022
Additional Information: The authors were partially funded by the Natural Environment Research Council (NE/T005890/1, NE/S012877/1).
Keywords: DAS, geophone, MASW, surface waves, velocity

Identifiers

Local EPrints ID: 471059
URI: http://eprints.soton.ac.uk/id/eprint/471059
ISSN: 1569-4445
PURE UUID: d9adf7e0-0037-4dd3-8a3d-f5e39989df88
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X
ORCID for Gilberto Brambilla: ORCID iD orcid.org/0000-0002-5730-0499
ORCID for Petros Bogiatzis: ORCID iD orcid.org/0000-0003-1902-7476
ORCID for James Snook: ORCID iD orcid.org/0000-0002-4636-6548
ORCID for Lieke van Putten: ORCID iD orcid.org/0000-0002-4428-1727
ORCID for Ali Masoudi: ORCID iD orcid.org/0000-0003-0001-6080

Catalogue record

Date deposited: 25 Oct 2022 16:35
Last modified: 28 Oct 2022 02:01

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Contributors

Author: Nicholas Harmon ORCID iD
Author: John Davis
Author: William Buffet
Author: Ben Chichester
Author: Yuhang Dai
Author: Petros Bogiatzis ORCID iD
Author: James Snook ORCID iD
Author: Lieke van Putten ORCID iD
Author: Ali Masoudi ORCID iD

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