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Acoustic and optical determination of bubble size distributions - quantification of seabed gas emissions

Acoustic and optical determination of bubble size distributions - quantification of seabed gas emissions
Acoustic and optical determination of bubble size distributions - quantification of seabed gas emissions
Passive acoustic techniques can be used to identify and quantify underwater gas release at natural sites, or at locations related to anthropogenic activities. There are still signifcant issues in extracting bubble signals from background noise, particularly for bubble counting and sizing techniques relying on inversion of the time-averaged acoustic spectrum. In this work we propose an adaptive single bubble identifcation technique, which incorporates bubble acoustic characteristics including pulsation time interval, frequency bandwidth and radiation strength. The methods applies a cross-spectrogram, enabling an increase in signal-to-noise ratio resulting in a reduction of the false alarm rate on bubble identifcation. We demonstrate this technique using an array of hydrophones to determine the bubble size distribution and gas flux at a controlled CO2 release site, 4 m beneath the seabed, at 120 m water depth in the central North Sea. The results show that the bubble radius, as estimated using acoustics has a distribution with a peak in the 0.15-0.3 cm range, while an estimate based on optical method suggests a range of 0.2-0.5 cm. The gas
flux is acoustically estimated as 32-88 kg/day in response to a known gas injection flow rate 143 kg/day, indicating 22-62% of the injected CO2 is emitted from the seabed in gaseous form, with the remainder being trapped, or dissolved.
1750-5836
Li, Jianghui
9c589194-00fa-4d42-abaf-53a32789cc5e
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba
Roche, Ben
2746ee9e-1b87-4d2f-b4e1-dcdc0ca7a719
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Leighton, namrip
3e5262ce-1d7d-42eb-b013-fcc5c286bbae
Davis, John
7f762b01-375b-42c8-80cb-65baefffdb97
Fone, Joseph
59875008-8272-4f3a-a5c8-66b616d95977
Li, Jianghui
9c589194-00fa-4d42-abaf-53a32789cc5e
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba
Roche, Ben
2746ee9e-1b87-4d2f-b4e1-dcdc0ca7a719
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Leighton, namrip
3e5262ce-1d7d-42eb-b013-fcc5c286bbae
Davis, John
7f762b01-375b-42c8-80cb-65baefffdb97
Fone, Joseph
59875008-8272-4f3a-a5c8-66b616d95977

Li, Jianghui, White, Paul, Roche, Ben, Bull, Jonathan, Leighton, namrip, Davis, John and Fone, Joseph (2021) Acoustic and optical determination of bubble size distributions - quantification of seabed gas emissions. International Journal of Greenhouse Gas Control. (doi:10.1016/j.ijggc.2021.103313).

Record type: Article

Abstract

Passive acoustic techniques can be used to identify and quantify underwater gas release at natural sites, or at locations related to anthropogenic activities. There are still signifcant issues in extracting bubble signals from background noise, particularly for bubble counting and sizing techniques relying on inversion of the time-averaged acoustic spectrum. In this work we propose an adaptive single bubble identifcation technique, which incorporates bubble acoustic characteristics including pulsation time interval, frequency bandwidth and radiation strength. The methods applies a cross-spectrogram, enabling an increase in signal-to-noise ratio resulting in a reduction of the false alarm rate on bubble identifcation. We demonstrate this technique using an array of hydrophones to determine the bubble size distribution and gas flux at a controlled CO2 release site, 4 m beneath the seabed, at 120 m water depth in the central North Sea. The results show that the bubble radius, as estimated using acoustics has a distribution with a peak in the 0.15-0.3 cm range, while an estimate based on optical method suggests a range of 0.2-0.5 cm. The gas
flux is acoustically estimated as 32-88 kg/day in response to a known gas injection flow rate 143 kg/day, indicating 22-62% of the injected CO2 is emitted from the seabed in gaseous form, with the remainder being trapped, or dissolved.

Text
BubbleIdentification20210131reviewnomark - Accepted Manuscript
Restricted to Repository staff only until 7 April 2022.
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Accepted/In Press date: 19 March 2021
e-pub ahead of print date: 7 April 2021

Identifiers

Local EPrints ID: 448012
URI: http://eprints.soton.ac.uk/id/eprint/448012
ISSN: 1750-5836
PURE UUID: 854d5a86-2061-4edb-a28c-f2af84467f2d
ORCID for Jianghui Li: ORCID iD orcid.org/0000-0002-2956-5940
ORCID for Paul White: ORCID iD orcid.org/0000-0002-4787-8713
ORCID for namrip Leighton: ORCID iD orcid.org/0000-0002-1649-8750

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Date deposited: 30 Mar 2021 16:33
Last modified: 29 Apr 2021 01:52

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