A noninvasive method for measuring the velocity of diffuse hydrothermal flow by tracking moving refractive index anomalies

作者：Mittelstaedt Eric^*; Davaille Anne; van Keken Peter E; Gracias Nuno; Escartin Javier

来源：Geochemistry Geophysics Geosystems, 2010, 11: Q10005.

DOI：10.1029/2010GC003227

• hydrothermal vents
• diffuse flow
• cross-correlation techniques
• particle image velocimetry

Diffuse flow velocimetry (DFV) is introduced as a new, noninvasive, optical technique for measuring the velocity of diffuse hydrothermal flow. The technique uses images of a motionless, random medium (e. g., rocks) obtained through the lens of a moving refraction index anomaly (e. g., a hot upwelling). The method works in two stages. First, the changes in apparent background deformation are calculated using particle image velocimetry (PIV). The deformation vectors are determined by a cross correlation of pixel intensities across consecutive images. Second, the 2-D velocity field is calculated by cross correlating the deformation vectors between consecutive PIV calculations. The accuracy of the method is tested with laboratory and numerical experiments of a laminar, axisymmetric plume in fluids with both constant and temperature-dependent viscosity. Results show that average RMS errors are similar to 5%-7% and are most accurate in regions of pervasive apparent background deformation which is commonly encountered in regions of diffuse hydrothermal flow. The method is applied to a 25 s video sequence of diffuse flow from a small fracture captured during the Bathyluck' 09 cruise to the Lucky Strike hydrothermal field (September 2009). The velocities of the similar to 10 degrees C-15 degrees C effluent reach similar to 5.5 cm/s, in strong agreement with previous measurements of diffuse flow. DFV is found to be most accurate for approximately 2-D flows where background objects have a small spatial scale, such as sand or gravel.

• 出版日期2010-10-8