Broadband Acoustic Measurements of a Controlled Seep with Multiple Gases for Verification of Flux Estimates Through Bubble Dissolution and Target Strength Models

Kevin Rychert
M.S. in OE/Ocean Mapping
Friday, May. 4, 2018, 1:00pm
Chase 130
Abstract

To verify existing models for conversion of acoustic target strength to estimates for the total volume of methane gas released from the seafloor through the water column, a synthetic seep system was designed and fabricated. This system creates individual bubbles of a specific sizes most commonly found in gaseous methane seeps, <1 to 5[mm] radii, which can be released at any interval at depths up to 200[m]. The synthetic seep system was deployed off the coast of New Hampshire adjacent to the Isles of Shoals to a depth of 55[m]. Acoustic backscatter from 16-24 [kHz] was collected by steaming over the synthetic seep multiple times with a suite of broadband splitbeam sonar systems. Each iteration ensonified a predetermined and calibrated bubble size created by the system at depth. These data represent a direct field measurement which tested models describing bubble evolution and acoustic scattering during the ascent through the water column for bubbles of different sizes and gasses. Validating these models directly tests the ability of broadband sonar systems to estimate the transport of gas from the seabed to the ocean and atmosphere. 

Bio

Kevin Rychert received his B.S. in physics from the University of New Hampshire. During his undergraduate education, he researched pulsating aurora through work at the Magnetosphere-Ionosphere Research Laboratory (MIRL). After graduation while employed at the Electron Paramagnetic Resonance (EPR) Center at Dartmouth College, he researched dosimetry and oximetry. He is now pursuing an M.S. in Ocean Engineering/Ocean Mapping at the Center for Coastal and Ocean Mapping (CCOM), specifically working on the development of a broadband acoustic system for quantifying the flux of free gas in methane seeps.