HR: 1340h
AN: OS43B-0552    [Abstracts]
TI: Optical sensing for characterization of bubble plumes from methane seeps
AU: * Pizarro, O
EM: opizarro@whoi.edu
AF: Woods Hole Oceanographic Institution, DSL MS 7, Woods Hole, MA 02543 United States
AU: Camilli, R
EM: rcamilli@whoi.edu
AF: Woods Hole Oceanographic Institution, DSL MS 7, Woods Hole, MA 02543 United States
AU: Whelan, J
EM: jwhelan@whoi.edu
AF: Woods Hole Oceanographic Institution, DSL MS 7, Woods Hole, MA 02543 United States
AB: Methane seeps are potentially a key contributor to atmospheric methane and to the global greenhouse gas budget. Improved estimates of methane flux from ocean floor seeps is required to understand the magnitude and characteristics of this contribution to the carbon cycle. % State of the art In steady, slow seeps a large portion of the gas is dissolved and oxidized before reaching the surface. However, in high-intensity methane seeps the bubble density, speed and size are such that a significant fraction of the gas can reach the atmosphere. Dissolved methane can be measured fairly reliably at the sea surface with traditional equilibration techniques. New types of in-situ chemical sensors can quantify dissolved methane deeper in the water column. Quantifying methane within the water column in the free gas phase (\emph{i.e.}, in the form of bubbles) remains a challenging problem. Current approaches rely either on indirect acoustic methods or direct collection of bubbles. Acoustic methods have the disadvantage of requiring extensive calibration, and can fail to distinguish the bubble signal from other sources of acoustic noise. Gas-capture techniques are mechanically complex, have a surface expression that introduces some noise, and can potentially alias episodic events. %how slow ? In both cases the fine scale structure such as herogeneity of the bubbling plume is lost. % Proposed We propose a vision-based system to detect and track bubble plumes. High speed optical imagery is propenables precise measurements of the motion of bubbles through a process involving identification of the individual bubbles (and rejection of other particles). Additional image processing steps are then used to estimate each bubble's volume and velocity. These are then integrated to produce an estimate of volumetric flux rate. This technique can also reveal fine scale variabilities in the spatial and temporal structure within the plume. %We discuss sensing configurations based on a stereo setup and based on a camera and a laser sheet. We are currently developing an imaging package that will be deployed on fixed moorings in parallel with an array of conventional chemical sensors. When deployed close to the ocean floor this system will also be able to recover cm-level bathymetry around the source of the plume. Preliminary results from a flume test with ground truth and a field test suggest that vision-based sensing can complement other sensing modalities.
DE: 4820 Gases
DE: 4894 Instruments and techniques
DE: 4294 Instruments and techniques
DE: 1694 Instruments and techniques
DE: 1635 Oceans (4203)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting