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- Title
Technical Note: Detection of gas bubble leakage via correlation of water column multibeam images.
- Authors
Von Deimling, J. Schneider; Papenberg, C.
- Abstract
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. However, up to the present, the extremely high data rate hampers water column backscatter investigations. More sophisticated visualization and processing techniques for water column backscatter analysis are still under development. We here present such water column backscattering data gathered with a 50 kHz prototype multibeam system. Water column backscattering data is presented in video-frames grabbed over 75 s and a "re-sorted" singlebeam presentation. Thus individual gas bubbles rising from the 24m deep seafloor clearly emerge in the acoustic images and rise velocities can be determined. A sophisticated processing scheme is introduced to identify those rising gas bubbles in the hydroacoustic data. It applies a cross-correlation technique similar to that used in Particle Imaging Velocimetry (PIV) to the acoustic backscatter images. Tempo-spatial drift patterns of the bubbles are assessed and match very well measured and theoretical rise patterns. The application of this processing scheme to our field data gives impressive results with respect to unambiguous bubble detection and remote bubble rise velocimetry. The method can identify and exclude the main driver for misinterpretations, i.e. fish-mediated echoes. Even though image-based cross-correlation techniques are well known in the field of fluid mechanics for high resolution and non-inversive current flow field analysis, this technique was never applied in the proposed sense for an acoustic bubble detector.
- Subjects
UNDERWATER acoustics; NATURAL gas; OCEAN bottom; BACKSCATTERING; PARTICLE image velocimetry
- Publication
Ocean Science Discussions, 2011, Vol 8, Issue 4, p1757
- ISSN
1812-0806
- Publication type
Article
- DOI
10.5194/osd-8-1757-2011