In the ocean, internal gravity waves are generated by tidal flow over sea floor topography. An internal gravity wave is only able to freely propagate if the buoyancy frequency is greater than the driving frequency, where the buoyancy frequency is proportional to the square root of the density gradient. A turning depth is defined as a height below which the buoyancy frequency is less than the driving frequency. King et al. showed that turning depths for internal waves generated by lunar tidal flow exist in the ocean, at varying heights from the sea floor [11]. The present study is the first to examine the generation and propagation of internal waves by tidal flow over topography that lies below a turning depth. I use laboratory experiments and numerical simulations to examine the effect of these turning depths on energy flux of the internal waves generated by tidal flow over topography. I find excellent agreement between numerical and laboratory work, and I show that the internal wave energy is strongly damped by the presence of a turning depth above the topography. Further, this has strong implications for ocean energy budget calculations. / text

A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

A parameterization is presented for turbulence dissipation due to baroclinic tide impacting on abrupt shelf topography that is supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcing velocity. Upon impact, the tide cascades to higher vertical modes. Vertical internal modes that are arrested at the crest of the topography in the form of lee waves are assumed to dissipate, while faster modes are assumed to propagate away. The energy flux in each mode is predicted with topography that allows linear numer- ical solutions. The parameterization is tested using high-resolution two-dimensional numerical models of baroclinic tides impinging on an isolated shelf of various heights approximated as a step-function. The recipe is seen to work well compared to numeri- cal simulations of isolated shelves, although it consistently underestimates model flux divergence. Despite low forcing velocities having a more accurate numerical linear solution, the recipe does poorly because it does not accurately predict the modes that become trapped and dissipate. Maximum dissipation occurs when flow is on-shelf and lee waves form, indicating lee waves are the mechanism by which dissipation occurs. / Graduate / 0415

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 255-264). / by Jason I. Gobat. / Ph.D.

The shoaling of horizontally propagating internal waves may provide an important source of mixing and transport in estuaries and coastal seas. Parameterizing such effects in numerical models demands better understanding of several aspects of wave energetics, especially relating to horizontal energy flux and turbulence generation. Observations are needed to build this understanding. To address some of these issues in the estuarine context, an intensive field program was undertaken in Summer 2008 in the St. Lawrence Estuary, involving shore-based photogrammetry, ship-based surveys, and moorings that held conventional and turbulence-resolving sensors. The measurements reveal that waves generally arrived during the rising phase of the M2 tide. Shoreward of the 40m isobath, waves traversed the field site perpendicular to bathymetry, a pattern that continued as the waves transformed nonlinearly. A tight temperature-salinity relationship permits the estimation of the time-varying density field from a moored chain of temperature-depth recorders. A new method for inferring the heaved internal wave density field is developed, using a relaxation solver to determine the wave streamfunction. The method is applied to discrete events measured with acoustic Doppler profilers to estimate the kinetic and available potential energy, as well as the nonlinear horizontal energy flux. Acoustic Doppler velocimeters were used to infer near-bottom turbulent energetics, revealing two main features. First, a period of wave incidence had turbulence dissipation rates that exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event indicate that the turbulence is at least partly locally generated. A simple model for wave-induced turbulence is proposed based on the energy flux measurements. Generally, the results suggest that during the rising phase of the tide, energy input from shoaling waves is required to explain the observed levels of dissipation. Estimates of vertical diffusivity during times of wave shoaling are on average 3 times larger than values predicted by tidal shear alone.

Thesis (S.M. in Mechanical Engineering)--Joint Program in Ocean Engineering/Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2007. / Includes bibliographical references (p. 91-92). / Reducing the deleterious effect of Vortex Induced Vibrations (VIV) in marine risers is an important task for ocean engineers; and many competing factors exist in the design of VIV suppression devices. This thesis explores the experimental minimization of the drag force and the disruption of vortex formation by utilizing VIV suppression devices. Two series of tests are conducted-both utilizing separate testing designs. The first tests are the flexible cylinder experiments, detailed in Chapter 2, which determine the drag force and vibration amplitude of numerous, original testing configurations. The second series of tests are the rigid cylinder, PIV experiments, detailed in Chapter 3. These tests measure both the drag force on the cylinder and the oscillating component of the lift force, the latter of which is a good indication of vortex formation. The Chapter 3 tests also image the test section wake-providing helpful insight into the physical process of vortex formation. In brief, this thesis presents a detailed description and results of the two series of original VIV suppression tests. Many original configurations are tested, and the results are contained herein. / by David Emmanuel Farrell. / S.M.

This thesis examines the barotropic M2 tidal circulation and associated oceanographic properties in the Kyuquot Sound. The main contribution of this thesis is the development of a simple analytical model based on results from a Finite-Volume Coastal Ocean Model (FVCOM), describing a two-channel system. The simple analytical model allows us to estimate the energy dissipation rate in Crowther Channel and recognizes that friction is responsible for phase difference (between currents and elevation) variations as we move along the channel. This is done without running complex numerical models or collecting extensive observation data. We found a difference in velocity phases between a dominant channel (Kyuquot Channel) and a secondary channel (Crowther Channel) in Kyuquot Sound. The velocity phase response in the secondary channel is out of phase with the dominant channel, and varies when we move along the channel, while the elevation phases are consistent between the two channels. This result has a potentially significant impact on future biological and navigation decisions. Our research is also focused on getting a general understanding of the circulation in Kyuquot Sound, and offers an energy budget comparison between the analytical and numerical model results. These results allow the contrast between the simple analytical and the numerical model to be clarified, as the advantages and limitations of both are discussed in detail. / Graduate / 0415 / 0759 / 0547 / diwan@uvic.ca

Thesis: Ph. D., Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Department of Aeronautics and Astronautics; and the Woods Hole Oceanographic Institution), 2020 / Cataloged from student-submitted PDF of thesis. / Includes bibliographical references (pages 181-198). / Sea ice thickness has long been an under-measured quantity, even in the satellite era. The snow surface elevation, which is far easier to measure, cannot be directly converted into sea ice thickness estimates without knowledge or assumption of what proportion of the snow surface consists of snow and ice. We do not fully understand how snow is distributed upon sea ice, in particular around areas with surface deformation. Here, we show that deep learning methods can be used to directly predict snow depth, as well as sea ice thickness, from measurements of surface topography obtained from laser altimetry. We also show that snow surfaces can be texturally distinguished, and that texturally-similar segments have similar snow depths. This can be used to predict snow depth at both local (sub-kilometer) and satellite (25 km) scales with much lower error and bias, and with greater ability to distinguish inter-annual and regional variability than current methods using linear regressions. We find that sea ice thickness can be estimated to <20% error at the kilometer scale. The success of deep learning methods to predict snow depth and sea ice thickness suggests that such methods may be also applied to temporally/spatially larger datasets like ICESat-2. / by M. Jeffrey Mei. / Ph. D. / Ph.D. Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Department of Aeronautics and Astronautics; and the Woods Hole Oceanographic Institution)

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), 2002. / Includes bibliographical references (leaves 140-148). / This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically efficient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animal. / (cont.) Imaging technologies used to exactly measure the morphology of the scattering features of fish include very high-resolution Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which are used for morphological evaluation and incorporation into the scattering model. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean. / by D. Benjamin Reeder. / Ph.D.

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references (leaves 184-189). / In the ocean, low frequency acoustic waves propagate with low attenuation and cylindrical spreading loss over long-ranges, making them an effective tool for underwater source localization, tomography, and communications. Underwater mountains, or seamounts, are ubiquitous throughout the world's oceans and can absorb and scatter acoustic energy, offering many interesting acoustic modeling challenges. The goal of the research performed in support of this thesis is to measure the acoustic scattered field of a large, conical seamount at long-range, and reconcile observations with 2-D range-dependent acoustic models, for the purpose of understanding the effects of highly range-dependent bathymetry. The Basin Acoustic Seamount Scattering Experiment (BASSEX) was conducted to measure the scattered fields of the two seamounts which form the Kermit-Roosevelt Seamount Complex in the Northeast Pacific Ocean during September and October of 2004. The experiment used fixed and ship-deployed acoustic sources transmitting m-sequence signals at 68.2 and 250 Hz carrier frequencies, with 35 and 83 Hz bandwidth, respectively. The receiver was a towed hydrophone array with 3 m sensor spacing, cut for 250 Hz. BASSEX is the first experiment to measure acoustic arrival patterns in the scattered field of a seamount at many locations at sound path ranges of order 500 km, utilizing a rich bathymetry and sound velocity database. Convergence zones in the forward-scattered field of seamounts at long-range are observed, created by higher order mode coupling and blockage. Acoustic ray arrival angles, travel times, and amplitudes show good agreement with parabolic equation (PE) acoustic modeling results inside the forward-scattered fields; in particular, simulated results are fairly accurate for weak surface-reflected-bottom-reflected acoustic rays. The width of the forward-scattered field is shown to span the projected width of a seamount. / (cont.) Temporal coherence of ray amplitude inside a seamount scattered field could not be determined due to array movement issues, and should be the focus of future research to determine the stability of scattered acoustic rays for applications such as acoustic tomography. Robust adaptive beamforming methods are used to process hydrophone array data gathered in the BASSEX experiment. Non-stationarity in the observed noise field caused by array fluctuations and data acquisition system malfunctions motivate the use of a time varying Capon adaptive beam former, and strong acoustic harmonics from ship operations motivate the use of a frequency and steering angle dependent white noise gain constraint. In an effort to process snap-shot deficient data sets, the novel physically constrained maximum likelihood (PCML) beamformer was further developed and applied. By using orthonormal trigonometric eigenvector bases to determine the maximum likelihood spectral covariance matrix, the PCML beamformer computational efficiency is significantly increased. / by Joseph J. Sikora, III. / Ph.D.