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

TitleBroadband Acoustic Measurements of a Controlled Seep with Multiple Gases for Verification of Flux Estimates Through Bubble Dissolution and Target Strength Models
Publication TypeThesis
Year2018
AuthorsRychert, K
Degree and ProgramMaster of Science
DegreeOcean Engineering/Ocean Mapping
Number of Pages74
Date PublishedSeptember 1
UniversityUniversity of New Hampshire
LocationDurham, NH

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. 

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