Quantification of Diffuse Hydrothermal Flows Using Multibeam Sonar

Tuesday, 16 December 2014
Anatoliy N. Ivakin1, Darrell R. Jackson1, Karen G Bemis2 and Guangyu Xu2, (1)University of Washington, Applied Physics Laboratory, Seattle, WA, United States, (2)Rutgers University, Institute of Marine and Coastal Sciences, New Brunswick, NJ, United States
The Cabled Observatory Vent Imaging Sonar (COVIS) deployed at the Main Endeavour node of the NEPTUNE Canada observatory has provided acoustic time series extending over 2 years. This includes 3D images of plume scattering strength and Doppler velocity measurements as well as 2D images showing regions of diffuse flow. The diffuse-flow images display the level of decorrelation between sonar echos with transmissions separated by 0.2 s. The present work aims to provide further information on the strength of diffuse flows. Two approaches are used: Measurement of the dependence of decorrelation on lag and measurement of phase shift of sonar echos, with lags in 3-hour increments up to several days. The phase shifts and decorrelation are linked to variations of temperature above the seabed, which allows quantification of those variations, their magnitudes, spatial and temporal scales, and energy spectra. These techniques are illustrated using COVIS data obtained near the Grotto vent complex.