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), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 213-229). / The interpretation of echoes collected by active remote-sensing systems, such as sonar and radar, is often ambiguous due to the complexities in the scattering processes involving the scatterers, the environment, and the sensing system. This thesis addresses this challenge using a combination of laboratory and field experiments, theoretical modeling, and numerical simulations in the context of acoustic scattering by marine organisms. The unifying themes of the thesis are 1) quantitative characterization of the spectral, temporal, and statistical features derived from echoes collected using both broadband and narrowband signals, and 2) the interpretation of echoes by establishing explicit links between echo features and the sources of scattering through physics principles. This physics-based approach is distinct from the subjective descriptions and empirical methods employed in most conventional fisheries acoustic studies. The first part focuses on understanding the dominant backscattering mechanisms of live squid as a function of orientation. The study provides the first broadband backscattering laboratory data set from live squid at all angles of orientation, and conclusively confirms the fluid-like, weakly-scattering material properties of squid through a series of detailed comparisons between data and predictions given by models derived based on the distorted-wave Born approximation. In the second part, an exact analytical narrowband model and a numerical broadband model are developed based on physics principles to describe the probability density function of the amplitudes of echo envelopes (echo pdf) of arbitrary aggregations of scatterers. The narrowband echo pdf model significantly outperforms the conventional mixture models in analyzing simulated mixed assemblages. When applied to analyze fish echoes collected in the ocean, the numerical density of fish estimated using the broadband echo pdf model is comparable to the density estimated using echo integration methods. These results demonstrate the power of the physics-based approach and give a first-order assessment of the performance of echo statistics methods in echo interpretation. The new data, models, and approaches provided here are important for advancing the field of active acoustic observation of the ocean. / by Wu-Jung Lee. / Ph.D.

Thesis (Ph. D.)--Joint Program in 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 (p. 239-252). / The challenges of directly observing active turbidity currents necessitates the consideration of preserved deposits for deciphering the behavior of these systems. In this thesis, I take advantage 3-D subsurface seismic data and outcrop exposures to study turbidites at scales ranging from bed to basin. At the basin scale, I develop a method to estimate the time-frame over which sedimentation and subsidence come into equilibrium. Using seismic data from the Fisk Basin, Gulf of Mexico, I find that, during periods of broadly distributed, sheet-like deposition, equilibrium time is on the order of 4.6 x 105 years. In contrast, during periods of confined channel development, that time drops to 2.0 x 105 years. Identifying these equilibrium times is critical because, at times below equilibrium, autogenic and allogenic stratigraphic signals cannot be distinguished. At the scale of turbidite beds, detailed grainsize analyses of sediment samples from the Capistrano Formation, San Clemente, California reveal the potential for misinterpretation that arises when deposits are studied without consideration for the dynamics of sedimentation. Previously interpreted as the result of anomalous sandy turbidites, using simple bed shear calculation and Froude scaling, I show that these coarse sediments are consistent with classical muddy, low-density turbidity cur- rents. Finally, at the scale of amalgamated turbidite beds, I use outcrop mapping and aerial photography of the Zerrissene Turbidite System, Namibia to provide a measure of lateral and vertical continuity of a deepwater turbidite system. / (cont.) Previous studies have been hampered by limited exposure while the extensive continuous exposure of the Zerissenne show that correlation lengths of these systems can exceed 1.5 km. / by William J. Lyons, III. / Ph.D.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), 2001. / Includes bibliographical references (leaves 207-215). / Matched-field methods concern estimation of source location and/or ocean environmental parameters by exploiting full wave modeling of acoustic waveguide propagation. Typical estimation performance demonstrates two fundamental limitations. first, sidelobe ambiguities dominate the estimation at low signal-to-noise ratio (SNR), leading to a threshold performance behavior. Second, most matched-field algorithms show a strong sensitivity to environmental/system mismatch, introducing some biased estimates at high SNR. In this thesis, a quantitative approach for ambiguity analysis is developed so that different mainlobe and sidelobe error contributions can be compared at different SNR levels. Two large-error performance bounds, the Weiss-Weinstein bound (WWB) and Ziv-Zakai bound (ZZB), are derived for the attainable accuracy of matched-field methods. To include mismatch effects, a modified version of the ZZB is proposed. Performance analyses are implemented for source localization under a typical shallow water environment chosen from the Shallow Water Evaluation Cell Experiments (SWellEX). The performance predictions describe the simulations of the maximum likelihood estimator (MLE) well, including the mean square error in all SNR regions as well as the bias at high SNR. The threshold SNR and bias predictions are also verified by the SWellEX experimental data processing. These developments provide tools to better understand some fundamental behaviors in matched-field performance and provide benchmarks to which various ad hoc algorithms can be compared. / by Wen Xu. / Ph.D.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, the Woods Hole Oceanographic Institution), 2003. / Includes bibliographical references (p. 118-120). / by Christopher George Bohner. / S.M.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 181-201). / Real-time cooperation between autonomous vehicles can enable time-critical missions such as tracking and pursuit of a dynamic target or environmental feature, but relies on wireless communications. Underwater, communication over distances beyond about one hundred meters is almost exclusively accomplished through acoustics, which bring challenges such as propagation delays, low data rates, packet loss, and scheduling constraints due to interference and limited bandwidth. These limitations make underwater pursuit missions preeminent applications of networked control. Motivated by such applications, this thesis presents contributions towards multi-vehicle feedback control in the presence of severe communication constraints. The first major area of work considers the formulation and solution of new underwater multi-vehicle tracking and pursuit problems using closed-loop control. We begin with a centralized robust optimization approach for multicast routing and power control which is suitable for integration with vehicle control. Next, we describe field experiments in range-based target pursuit at high tracking bandwidths in a challenging shallow-water environment. Finally, we present a methodology for pursuit of dynamic ocean features such as fronts, which we validate using hindcast ocean model data. The primary innovation is a projection algorithm which carries out linearization of ocean model forecast dynamics and uncertainty directly in vehicle coordinates via a forward model technique. The resulting coupled linear stochastic system is suitable for networked control. The second area of work presents a unified formalism for multi-vehicle control and estimation with measurement, control, and acknowledgment packets all subject to scheduling, delays and packet loss. The modular framework we develop is built around a jump linear system description incorporating receding horizon optimization and buffering at actuators. Integration of these elements enables synthesis of a novel technique for estimation using delayed and lossy control acknowledgments-a desirable and practical capability of fielded systems that has not been considered to date. Simulations and field experiments demonstrate the effectiveness of our approach. / by Brooks Louis-Kiguchi Reed. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Many species of whales migrate annually between high-latitude feeding grounds and low-latitude breeding grounds. Yet, very little is known about how these animals navigate during these migrations. This thesis takes a first look at the roles of geomagnetic and acoustic cues in humpback whale navigation and orientation, in addition to documenting some effects of human-produced sound on beaked whales. The tracks of satellite-tagged humpback whales migrating from Hawaii to Alaska were found to have systematic deviations from the most direct route to their destination. For each whale, a migration track was modeled using only geomagnetic inclination and intensity as navigation cues. The directions in which the observed and modeled tracks deviated from the direct route were compared and found to match for 7 out of 9 tracks, which suggests that migrating humpback whales may use geomagnetic cues for navigation. Additionally, in all cases the observed tracks followed a more direct route to the destination than the modeled tracks, indicating that the whales are likely using additional navigational cues to improve their routes. There is a significant amount of sound available in the ocean to aid in navigation and orientation of a migrating whale. This research investigates the possibility that humpback whales migrating near-shore listen to sounds of snapping shrimp to detect the presence of obstacles, such as rocky islands. A visual tracking study was used, together with hydrophone recordings near a rocky island, to determine whether the whales initiated an avoidance reaction at distances that varied with the acoustic detection range of the island. No avoidance reaction was found. Propagation modeling of the snapping shrimp sounds suggested that the detection range of the island was beyond the visual limit of the survey, indicating that snapping shrimp sounds may be suited as a long-range indicator of a rocky island. Lastly, this thesis identifies a prolonged avoidance reaction of a Blainville's beaked whale to playbacks of Navy mid-frequency active sonar and orca predation calls. Navy sonar exercises have been linked to beaked whale strandings, and identifying whether these are the result of a mistaken predator avoidance reaction may help prevent future strandings. / by Ann Nichole Allen. / Ph.D.

Thesis: S.M. in Oceanographic Engineering, Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 83-87). / Recent advances in acoustic navigation methodologies are enabling the way for AUVs to extend their submerged mission time and maintain a bounded XY position error. Additionally, advances in inertial sensor technology have drastically lowered the size, power consumption, and cost of these sensors. Nonetheless, these sensors are still noisy and accrue error over time. This thesis builds on the research and recent developments in single beacon one-way-travel- time (OWTT) acoustic navigation and investigates the degree of bounding position error for small AUVs with a minimal navigation strap-down sensor suite, relying mostly on a consumer grade microelectromechanical system (MEMS) inertial measurement unit (IMU) and a vehicle's dynamic model velocity. An implementation of an Extended Kalman Filter (EKF) that includes IMU bias estimation and coupled with a range filter, is obtained in the field on two OceanServer Technology, Inc. Iver2 AUVs and one Bluefin Robotics SandShark [mu]AUV. Results from these field trials on Ashumet Pond of Falmouth, Massachusetts, the Charles River of Cambridge, Massachusetts, and Monterey Bay near Santa Cruz, California show a navigation solution accuracy comparable to current standard navigation techniques. / by James H. Kepper, IV. / S.M. in Oceanographic Engineering

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), 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 185-193). / This thesis describes the physics of fully three-dimensional low frequency acoustic interaction with internal waves, bottom sediment waves and surface swell waves that are often observed in shallow waters and on continental slopes. A simple idealized model of the ocean waveguide is used to analytically study the properties of acoustic normal modes and their perturbations due to waves of each type. The combined approach of a semi-quantitative study based on the geometrical acoustics approximation and on fully three-dimensional coupled mode numerical modeling is used to examine the azimuthal dependence of sound wave horizontal reflection from, transmission through and ducting between straight parallel waves of each type. The impact of the natural crossings of nonlinear internal waves on horizontally ducted sound energy is studied theoretically and modeled numerically using a three-dimensional parabolic equation acoustic propagation code. A realistic sea surface elevation is synthesized from the directional spectrum of long swells and used for three-dimensional numerical modeling of acoustic propagation. As a result, considerable normal mode amplitude scintillations were observed and shown to be strongly dependent on horizontal azimuth, range and mode number. Full field numerical modeling of low frequency sound propagation through large sand waves located on a sloped bottom was performed using the high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic ducting is shown to steer acoustic energy beams along the sand wave's curved crests. / by Alexey Alexandrovich Shmelev. / Ph.D.

Thesis: Ph. D., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 283-314). / Animal movement is motivated in part by energetic constraints, where fitness is maximized by minimizing energy consumption. The energetic cost of movement depends on the resistive forces acting on an animal; changes in this force balance can occur naturally or unnaturally. Fishing gear that entangles large whales adds drag, often altering energy balance to the point of terminal emaciation. An analog to this is drag from tags attached to cetaceans for research and monitoring. This thesis quantifies the effects of drag loading from these two scenarios on fine-scale movements, behaviors and energy consumption. I measured drag forces on fishing gear that entangled endangered North Atlantic right whales and combined these measurements with theoretical estimates of drag on whales' bodies. Entanglement in fishing gear increased drag forces by up to 3 fold. Bio-logging tags deployed on two entangled right whales recorded changes in the diving and fine-scale movement patterns of these whales in response to relative changes in drag and buoyancy from fishing gear and through disentanglement: some swimming patterns were consistently modulated in response. Disentanglement significantly altered dive behavior, and can affect thrust production. Changes in the force balance and swimming behaviors have implications for the survival of chronically entangled whales. I developed two bioenergetics approaches to estimate that chronic, lethal entanglements cost approximately the same amount as the cost of pregnancy and supporting a calf to near-weaning. I then developed a method to estimate drag, energy burden and survival of an entangled whale at detection. This application is essential for disentanglement response and protected species management. Experiments with tagged bottlenose dolphins suggest similar responses to added drag: I determined that instrumented animals slow down to avoid additional energetic costs associated with drag from small bio-logging tags, and incrementally decrease swim speed as drag increases. Metabolic impacts are measurable when speed is constrained. I measured the drag forces on these tags and developed guidelines depending on the relative size of instruments to study-species. Together, these studies quantify the magnitude of added drag in complementary systems, and demonstrate how animals alter their movement to navigate changes in their energy landscape associated with increased drag. / by Julie M. van der Hoop. / Ph. D.

Thesis (Ph.D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 171-181). / Mobile robotic systems operating over long durations require algorithms that are robust and scale efficiently over time as sensor information is continually collected. For mobile robots one of the fundamental problems is navigation; which requires the robot to have a map of its environment, so it can plan its path and execute it. Having the robot use its perception sensors to do simultaneous localization and mapping (SLAM) is beneficial for a fully autonomous system. Extending the time horizon of operations poses problems to current SLAM algorithms, both in terms of robustness and temporal scalability. To address this problem we propose a reduced pose graph model that significantly reduces the complexity of the full pose graph model. Additionally we develop a SLAM system using two different sensor modalities: imaging sonars for underwater navigation and vision based SLAM for terrestrial applications. Underwater navigation is one application domain that benefits from SLAM, where access to a global positioning system (GPS) is not possible. In this thesis we present SLAM systems for two underwater applications. First, we describe our implementation of real-time imaging-sonar aided navigation applied to in-situ autonomous ship hull inspection using the hovering autonomous underwater vehicle (HAUV). In addition we present an architecture that enables the fusion of information from both a sonar and a camera system. The system is evaluated using data collected during experiments on SS Curtiss and USCGC Seneca. Second, we develop a feature-based navigation system supporting multi-session mapping, and provide an algorithm for re-localizing the vehicle between missions. In addition we present a method for managing the complexity of the estimation problem as new information is received. The system is demonstrated using data collected with a REMUS vehicle equipped with a BlueView forward-looking sonar. The model we use for mapping builds on the pose graph representation which has been shown to be an efficient and accurate approach to SLAM. One of the problems with the pose graph formulation is that the state space continuously grows as more information is acquired. To address this problem we propose the reduced pose graph (RPG) model which partitions the space to be mapped and uses the partitions to reduce the number of poses used for estimation. To evaluate our approach, we present results using an online binocular and RGB-Depth visual SLAM system that uses place recognition both for robustness and multi-session operation. Additionally, to enable large-scale indoor mapping, our system automatically detects elevator rides based on accelerometer data. We demonstrate long-term mapping using approximately nine hours of data collected in the MIT Stata Center over the course of six months. Ground truth, derived by aligning laser scans to existing floor plans, is used to evaluate the global accuracy of the system. Our results illustrate the capability of our visual SLAM system to map a large scale environment over an extended period of time. / by Hordur Johannsson. / Ph.D.