Diffuse flow at hydrothermal vents: A new technique for measuring fluid velocity by tracking of apparent background deformation
Abstract
Current estimates of the heat flux from hydrothermal vent fields are based primarily on measurements at individual vents. Although likely a large fraction of the total heat flux, these measurements do not account for the widespread diffuse fluid flow observed throughout vent fields. However, measurement of the heat flux due to diffuse flow is difficult because the flow is often transparent without particulate matter, and does not originate from a single source location, negating most methods for opaque fluids and individual plumes. To overcome these difficulties, a new, two-step digital image analysis technique is used to calculate the average fluid velocity. We use images of a motionless, random medium (e.g. rocks) obtained through the lens of a moving refraction index anomaly (e.g. a hot upwelling). First, the apparent background displacements are calculated using Particle Image Velocimetry (PIV); displacements are determined by a cross-correlation of pixel intensities across consecutive images. Second, the average fluid velocity is calculated by cross-correlating the second-derivative of the apparent background displacements between consecutive PIV calculations. Verification of the method is performed using laboratory and numerical experiments of a rising plume in a constant viscosity fluid and a fluid with temperature dependent viscosity. The method determines a 2D average velocity field due to the 3D fluid motion between each image. Results indicate that calculations are sensitive to image resolution, image capture rate, thermal noise of the camera CCD, and individual parameters of the calculation such as interrogation window size. This method will be used on data from the Bathyluck2009 cruise (September, 2009) to estimate the diffuse heat flux for portions of the Lucky Strike hydrothermal field. Results of these estimates will be presented and compared to the estimates from individual vents and as well as to the heat flux of the entire Lucky Strike field.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T13A1855M
- Keywords:
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- 0540 COMPUTATIONAL GEOPHYSICS / Image processing;
- 3015 MARINE GEOLOGY AND GEOPHYSICS / Heat flow;
- 3080 MARINE GEOLOGY AND GEOPHYSICS / Submergence instruments: ROV;
- AUV;
- submersibles;
- 3094 MARINE GEOLOGY AND GEOPHYSICS / Instruments and techniques