Characterization of Internal Waves and Tides Over a Caldera in the New England Seamount Chain and Their Impact on Short-Term Acoustic Path Availability
Abstract
In pursuit of understanding the relationship between oceanography and acoustics, this thesis characterizes sound-speed fluctuations from moored Conductivity, Temperature, and Depth (CTD) observations in the New England Seamount Chain (NESC) and estimates their impact on acoustic path availability using normal mode andray theory. A single vertical mooring with oceanographic instruments was deployed in the summer of 2022 over a3000 m tall caldera in the NESC to quantify the vertical and temporal scales of the fluctuating water column in the Sargasso and Slope seas. Dominant oceanographic processes in the NESC include the Gulf Stream current, eddies,and internal waves (IWs). Isotherm displacements are analyzed with visual and spectral techniques to quantify impacts from these phenomena. Isotherm displacements are greater in the Slope Sea than the Sargasso Sea, which is evident from filtered high pass isotherms and IW spectral variances. Isotherm spectra indicate the presence of a semidiurnal internal tide, tidal harmonics, and random high-frequency IWs above the caldera. The frequency-dependent normal mode structure of a subsurface duct in the Sargasso Sea is strongly impacted by eddies and IWs.Acoustic path availability near the Atlantis II seamount is investigated using ray theory, which identifies exploitable acoustic paths with minimal boundary interactions. A ray simulation with IW sound speed perturbations demonstrates an increase in exploitable acoustic paths.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2023
- Accession Number
- AD1213294
Entities
People
- Braydon M. Hammond
Organizations
- Naval Postgraduate School