Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (M.S.)--University of North Carolina at Wilmington, 2004. / Includes bibliographical references (leaves : 67-72).

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2004. / Includes bibliographical references (leaves 68-69). / Methods which measure seafloor resistivity are uniquely suited to studying hydrothermal circulation in the crust. The magnetometric resistivity (MMR) technique is a galvanic method which uses a bipole current source with a magnetometer receiver. The resistivity of the subsurface can be estimated from the magnetic field read in MMR. In order to analyze and invert MMR data taken near Mid Ocean Ridges, it is important to understand the effects of ridge topography on MMR models. To analyze these effects a 3D MMR forward modeling program MMR3Df̲wd is used to model Mid Ocean Ridges with varying slopes, resistivities, and source/receiver geometries. The modeled magnetic fields are compared with models with a flat seafloor to determine the impact of the ridge topography. Results show that for some of the ridges modeled, the effects of the topography were significant, suggesting that in some instances it is important to include ridge topography in forward models to obtain accurate results from data inversion. / by Lisa A. Lassner. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 206-213. / by John Shai-Fu Shih. / Ph.D.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references (p. 62-63). / The work was motivated by studies of Austin and Lentz (2002) and Pedlosky (2007). The above mentioned works considered two different responses of the stratified flow to a downwelling favorable wind forcing. The first study investigated a time dependent flow with a formation of a constantly expanding relatively well mixed region near the shore and the second considered a steady flow that arises when an offshore varying wind is applied. In my thesis I use ROMS to determine which type of response will take place based on the wind amplitude near the coast. It was demonstrated that if the value of the wind is much smaller than the critical value (determined by the stratification, the rotation rate and the horizontal diffusivity) then the flow is steady (the bbl case) and similar to the one investigated by Pedlosky. If the wind is of the order, or larger than, the critical value then the response is time dependent (the pool case) and similar to the one described by Austin and Lentz. The resulting flow structure of each response was also investigated. I examined the sensitivity of the bbl response to variations in the background vertical diffusivity, the initial stratification and the bottom slope. It was shown that a higher background vertical diffusivity, a higher stratification and a shallower bottom slope correspond to thinner (vertically) and narrower (horizontally) bbl. For the pool case the time dependent structure was also examined, using a number of idealized models. It was shown that the rate of the pool region expansion is a complex function of the local wind stress amplitude and the local depth. / by Evgeny Logvinov. / S.M.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 169-174). / Internal tides are internal waves of tidal period generated by tidal currents flowing over submarine topography. Tall ridges that are nominally two-dimensional (2-D) are sites of particularly strong generation. The subsequent dissipation of internal tides contributes to ocean mixing, thereby playing an important role in the circulation of the ocean. Strong internal tides can also evolve into internal wave solitons, which affect acoustic communication, offshore structures and submarine navigation. This thesis addresses the generation of internal tides by tall submarine ridges using a combined analytical and experimental approach. The first part of the thesis is an experimental investigation of a pre-existing Green function formulation for internal tide generation by a tall symmetric ridge in a uniform density stratification. A modal decomposition technique was developed to characterize the structure of the experimental wave fields generated by 2D model topographies in a specially configured wave tank. The theory accurately predicts the low mode structure of internal tides, and reasonably predicts the conversion rate of internal tides in finite tidal excursion regimes, for which the emergence of non-linearities was notable in the laboratory. In the second part of the thesis, the Green function method is advanced for asymmetric and multiple ridges in weakly non-uniform stratifications akin to realistic ocean situations. / (cont.) A preliminary investigation in uniform stratification with canonical asymmetric and double ridges reveals asymmetry in the internal tide that can be very sensitive to the geometric configuration. This approach is then used with realistic topography and stratification data to predict the internal tide generated by the ridges at Hawaii and at the Luzon Strait. Despite the assumption of two-dimensionality, there is remarkably good agreement between field data, simulations and the new theory for the magnitude, asymmetry and modal content of the internal tide at these sites. The final part of the thesis investigates the possibility of internal wave attractors in the valley of double-ridge configurations. A one-dimensional map is developed to identify the existence and stability of attractors as a function of the ridge geometry. The Green function method is further advanced to include a viscous correction to balance energy focusing and dissipation along an attracting orbit of internal wave rays, and very good agreement is obtained between experiment and theory, even in the presence of an attractor. / by Paula Echeverri Mondragón. / Ph.D.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: p. 333-347. / Ph.D.

Coral reef ecosystems are the most diverse on earth, and their subsistence is being threatened by natural and adverse anthropogenic patterns and processes. In an effort to understand and protect these marine environments, several programs have outlined strategies and initiatives. For example, the United States Coral Reef Task Force���s Mapping and Information Working Group has outlined a specific goal to map all coral reefs below 30 m depth by 2009. This study contributes to achieving that goal for three sites around the island of Tutuila, American Samoa, lying in the heart of the South Pacific. American Samoa, a U.S. territory, is home to the Fagatele Bay National Marine Sanctuary, the smallest and most remote in the United States, and to the National Park of American Samoa. Extensive modern scientific surveys were implemented around the territory in 2001 and have since continued and increased. The presence of protected areas and the existence of scientific data collected with state of the art technology have made the site a priority for the Coral Reef Task Force. In this study, methods for classifying surficial seafloor characteristics as bathymetric position index (BPI) zones and structures were developed and applied to the study sites. BPI zones and structures were classified by using algorithms that combine high-resolution (1 m) multibeam bathymetry and its derivatives: bathymetric position index at multiple scales and slope. The development of algorithms and the classification scheme involved the use of historical and current classification studies and three-dimensional visualization. In addition, the BPI zones and structures were compared to limited biological, geological, and physical attributes recorded during accuracy assessment surveys (photos) and towed diver surveys (video). A rugosity (surface ratio) analysis was added to the study to give a picture of the seafloor roughness. The BPI zone and structure classifications overlap and extend existing classifications from Ikonos satellite imagery for water depths shallower than 30 m. Methods, data and classifications developed and applied in this study will be available to the public as a benthic habitat mapping tool (ArcGIS extension), in an online GIS data archive, and on a compact disc attached to this thesis. They contribute to a broader understanding of the marine and coastal environment and will serve as a baseline of information for benthic habitat mapping and future biological, ecological, and geological surveys. The baseline gives a good indication of characteristics that may indicate areas of high biodiversity. The final maps presented here are especially useful to managers, researchers and scientists that seek to establish and monitor a wider and more effective network of marine and coastal protection. / Graduation date: 2005

Video based remote sensing techniques are well suited to collect spatially resolved wave images in the surf zone with breaking waves and dynamic bathymetric changes. An advanced video-based depth inversion method is developed to remotely survey bathymetry in the surf zone. The present method involves image processing of original wave image sequences, wave property estimation based on linear feature extraction from the processed image sequences, and is combined with a nonlinear depth inversion model. The original wave image sequences are processed through video image frame differencing and directional low-pass filtering schemes to remove wave-breaking-induced foam noise having high frequencies in the surf zone. The features of individual crest trajectories are extracted from the processed and rectified image sequences, i.e. processed image cross-shore timestacks, by tracking pixels of high intensity within an interrogation window of a Radon-transform-based line-detection algorithm. The wave celerity is computed using space-time information of the extracted trajectories of individual wave crests in the cross-shore timestack domain. The presented retrieval of nearshore bathymetry from video image sequences is based on a nonlinear depth inversion using the nonlinear shallow water wave theory. The nonlinear wave amplitude dispersion effects at the breaker points are determined by combining the nonlinear shallow water celerity equation with a wave breaker criterion, thereby computing water depths iteratively from the celerity measured from the video data. The water depths estimated at the breaker points present initial bathymetric anchor points. Bathymetric profiles in the surf zone are inverted by calculating wave heights dissipated after wave breaking with a wave dissipation model and wave heights shoaled before wave breaking with a wave shoaling model. The continuous wave amplitude dispersion effects are subtracted from the measured celerity profiles, resulting in nearshore bathymetric profiles. The nonlinear depth inversion derived bathymetric estimates from nearshore imagery match the measured values with a biased mean depth error of about +0.06m in the depth range of 0.1 to 3m. In addition, the wave height estimates by the depth inversion model are comparable to the in-situ measured wave heights with a biased mean wave height error of about +0.14m. The present depth inversion method based on optical remote-sensing supports coastal management, navigation, and amphibious operations.

A benthic environments classification system is devised from digital interpretations of multi-spectral IKONOS satellite imagery for 1,360 km2 of the carbonate platform and presented in a comprehensive digitized map. The classification scheme is designed as a 7th order hierarchical structure that integrates 5 Physiographic Realms, 24 Morphodynamic Zones, 11 Geoforms, 39 Landforms, 6 dominant surface sediment types, 9 dominant biological covers and 3 densities of biological covers for the description of benthic environments. Digital analysis of the high-resolution (4 m) IKONOS imagery employed ESRI's ArcMap to manually digitize 412 mapping units at a scale of 1:6,000 differentiated by spectral reflectance, color tones, and textures of seafloor topologies. The context of each morphodynamic zone is characterized by the content and areal distribution (in km2) of geomorphic forms and biological covers. Over 58% of the mapping area is occupied by sediment flats, and seagrasses are colonized in almost 80% of the topologies. / by Jacob Thomas Steinle. / Thesis (M.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.