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| Titel |
Technical Note: Detection of gas bubble leakage via correlation of water column multibeam images |
| VerfasserIn |
J. Schneider von Deimling, C. Papenberg |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 8, no. 2 ; Nr. 8, no. 2 (2012-03-14), S.175-181 |
| Datensatznummer |
250005506
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| Publikation (Nr.) |
 copernicus.org/os-8-175-2012.pdf |
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| Zusammenfassung |
| Hydroacoustic detection of natural gas release from the seafloor has been
conducted in the past by using singlebeam echosounders. In contrast, modern
multibeam swath mapping systems allow much wider coverage, higher
resolution, and offer 3-D spatial correlation. Up to the present, the
extremely high data rate hampers water column backscatter investigations and
more sophisticated visualization and processing techniques are needed. Here,
we present water column backscatter data acquired with a 50 kHz prototype
multibeam system over a period of 75 seconds. Display types are of
swath-images as well as of a "re-sorted" singlebeam presentation. Thus,
individual and/or groups of gas bubbles rising from the 24 m deep seafloor clearly emerge in
the acoustic images, making it possible to estimate rise velocities. A
sophisticated processing scheme is introduced to identify those rising gas
bubbles in the hydroacoustic data. We apply a cross-correlation technique
adapted from particle imaging velocimetry (PIV) to the acoustic backscatter
images. Temporal and spatial drift patterns of the bubbles are assessed and
are shown to match very well to measured and theoretical rise patterns. The
application of this processing to our field data gives clear results with
respect to unambiguous bubble detection and remote bubble rise velocimetry.
The method can identify and exclude the main source of misinterpretations,
i.e. fish-mediated echoes. Although image-based cross-correlation techniques
are well known in the field of fluid mechanics for high resolution and
non-inversive current flow field analysis, we present the first application
of this technique as an acoustic bubble detector. |
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