Thesis: S.M., 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), 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 163-168). / Recent advances in autonomous underwater vehicle (AUV) technology have led to their wide- spread acceptance and adoption for use in scientific, commercial, and defence applications in the underwater domain. At the same time, research progress in swarm robotics has seen swarm intelligence algorithms in use with greater eect on real-world robots in the field. A group of AUVs utilizing swarm intelligence concepts has the potential to address issues more effectively than a single AUV, and such a group can potentially open up new areas of application. Examples include the monitoring and tracking of highly dynamic oceanographic phenomena such as phytoplankton blooms and the use of an AUV swarm as a virtual acoustic receiver for sea-bottom seismic surveying or the monitoring of naturally occurring acoustic radiation from cracking ice. However, the limitations of the undersea environment places unique constraints on the use of existing swarm robotics approaches with AUVs. In particular, algorithms must be distributed and robust in the face of localization error and degraded communications. This work presents an investigation into one particular swarm strategy for a group of AUVs, termed formation control, with consideration to the constraints of the underwater domain. Four formation control algorithms, each developed and tested within the MOOS-IvP framework, are presented. In addition, a 'formation quality' metric is introduced. This metric is used in conjunction with a measure of formation energy expenditure to compare the efficacy of each behaviour during construction of a desired formation, and formation maintenance while it drifts in ocean currents. This metric is also used to compare robustness of each algorithm in the presence of vehicle failure and changing communication rate. / by Nicholas Rahardiyan Rypkema. / S.M.

Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 77). / Due to the costs involved and time required to perform experiments at sea, it is important to provide accurate simulations of the ocean environment. Using the ray tracing code, BELLHOP, the Mission Oriented Operating Suite (MOOS), methods outlined by the Naval Research Laboratory (NRL) for bottom reverberation, and MATLAB, a model will be developed to incorporate the effects of bottom reverberation into the BELLHOP suite of code. This will be accomplished by using BELLHOP to generate a ray trace and eigen ray file. Then a MATLAB script will take the BELLHOP information and calculate the reverberation level using the NRL model by measuring the amplitude and reverberation at a receiver array simulated on the ocean floor. These reverberation values will then be used to determine the reverberation level at the source due to these bottom interactions. Testing of the simulation will include deep and shallow ocean profiles and multiple sound speed profiles (SSP). Following this testing, the goal is to implement the model in existing C++ code used for the testing of AUV systems. The ability to accurately model the ocean will not only allow for testing of autonomy code in the laboratory, but also make it possible to refine and calibrate code making ship time more efficient. / by Thomas Edward Miller. / S.M.

Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 97-103). / The presence of superimposed bedforms, where smaller bedforms exist on larger bedforms, is ubiquitous to energetic tidal environments. Due to their wide range in scale, it is difficult to simultaneously observe these features over tidal timescales. This thesis examines the morphological response of superimposed bedforms to a tidally reversing flow using novel instrumentation and platform systems. A method is outlined in chapter 2 to expand the functionality of low-mounted sidescan sonars by utilizing sonar shadows to estimate bedform height and asymmetry. Empirical models are generated to account for realistic variability in the seabed and the method is validated with bathymetric observations of wave-orbital ripples and tidally reversing megaripples. Given the high temporal and spatial resolution of seafloor frame mounted rotary sidescan sonars, the dynamics and evolution of the bedforms over an approximately 40 m x 40 m area can be resolved. In chapter 3 the method is applied to data of superimposed bedforms at Wasque Shoals, an ebb delta off the southeast corner of Martha's Vineyard, MA. These data reveal the small, superimposed bedforms reversing their asymmetry with the flow while the larger bedforms on which they reside remain oriented in the direction of the dominant flow. Similar bedform dynamics are observed at Nauset Inlet, a dynamic inlet system, on Cape Cod, MA using an autonomous jet-powered kayak, the Jetyak, equipped with a bathymetric swath sonar. The time needed for bedform asymmetry to reverse in the presence of a tidal flow was estimated with a geometric bedform model that incorporates an empirical sediment transport rate. The morphological lag time from the observations agree well with the geometric model with larger bedforms and slower flows resulting in a longer lag time. Finally, the migration of these superimposed bedforms is considered in chapter 4. Data from the rotary sidescan sonar at Wasque Shoals capture the interaction of smaller bedforms, or megaripples, with a dune. The net convergence of megaripples on the tidally dominate lee face of the dune suggests that the smaller bedforms serve as an intermediate step between grain-scale transport processes and larger scale dune migration. / by Katie Renae Jones. / S.M.

Thesis (M.S.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 1994. / Includes bibliographical references (p. 57-58). / by Denis Peregrym. / M.S.

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); and, (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2001. / Includes bibliographical references (p. 125-127). / mproving the performance of modular, low-cost autonomous underwater vehicles (AUVs) in such applications as long-range oceanographic survey, autonomous docking, and shallow-water mine countermeasures requires improving the vehicles' maneuvering precision and battery life. These goals can be achieved through the improvement of the vehicle control system. A vehicle dynamics model based on a combination of theory and empirical data would provide an efficient platform for vehicle control system development, and an alternative to the typical trial-and-error method of vehicle control system field tuning. As there exists no standard procedure for vehicle modeling in industry, the simulation of each vehicle system represents a new challenge. Developed by von Alt and associates at the Woods Hole Oceanographic Institute, the REMUS AUV is a small, low-cost platform serving in a range of oceanographic applications. This thesis describes the development and verification of a six degree of freedom, non-linear simulation model for the REMUS vehicle, the first such model for this platform. In this model, the external forces and moments resulting from hydrostatics, hydrodynamic lift and drag, added mass, and the control inputs of the vehicle propeller and fins are all defined in terms of vehicle coefficients. This thesis describes the derivation of these coefficients in detail. The equations determining the coefficients, as well as those describing the vehicle rigid-body dynamics, are left in non-linear form to better simulate the inherently non-linear behavior of the vehicle. Simulation of the vehicle motion is achieved through numeric integration of the equations of motion. The simulator output is then checked against vehicle dynamics data collected in experiments performed at sea. The simulator is shown to accurately model the motion of the vehicle. / by Timothy Prestero. / 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), 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 223-232). / The lateral line is a critical component of the fish sensory system, found to affect numerous aspects of behavior including maneuvering in complex fluid environments, schooling, prey tracking, and environment mapping. This sensory organ has no analog in modem ocean vehicles, despite its utility and ubiquity in nature, and could fill the gap left by sonar and vision systems in turbid cluttered environments. Yet, while the biological sensory system suggests the broad possibilities associated with such a sensor array, nearly nothing is known of the input processing and what information is available via the real lateral line. This thesis demonstrates and characterizes the ability of lateral-line-inspired linear pressure sensor arrays to perform two sensory tasks of relevance to biological and man-made underwater navigation systems, namely shape identification and vortex tracking. The ability of pressure sensor arrays to emulate the "touch at a distance" feature of the lateral line, corresponding to the latter's capability of identifying the shape of objects remotely, is examined with respect to moving cylinders of different cross sections. Using the pressure distribution on a small linear array, the position and size of a cylinder is tracked at various distances. The classification of cylinder shape is considered separately, using a large database of trials to identify two classification approaches: One based on differences in the mean flow, and one trained on a subset which utilizes information from the wake. The results indicate that it is in general possible to extract specific shape information from measurements on a linear pressure sensor array, and characterize the classes of shapes which are not distinguishable via this method. Identifying the vortices in a flow makes it possible to predict and optimize the performance of flapping foils, and to identify imminent stall in a control surface. Vortices in wakes also provide information about the object that generated the wake at distances much larger than the near-field pressure perturbations. Experimental studies in tracking a vortex pair and an individual vortex interacting with a flat plate demonstrate the ability to track vortices with a linear pressure sensor array from both small streamlined bodies and large flat bodies. Based on a theoretical analysis, the relationship between the necessary array parameters and the range of vortices of interest is established. / by Vicente I. Fernandez. / Ph.D.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 49-50). / The focus of this thesis is the design and development of a system for rapid extraction of dissolved inorganic carbon from seawater and groundwater samples for radiocarbon dating. The Rapid Extraction of Dissolved Inorganic Carbon System (REDICS) consists of two subsystems - one for sample introduction, acidification, and carbon dioxide extraction, and one for carbon dioxide quantification and storing. The first subsystem efficiently extracts the dissolved inorganic carbon from the water sample in the form of carbon dioxide by utilizing a gas-permeable polymer membrane contractor. The second subsystem traps, quantifies and stores the extracted gas using cryogenics. The extracted carbon dioxide is further processed for stable and radiocarbon isotope analysis at the National Ocean Sciences Accelerator Mass Spectrometer Facility at the Woods Hole Oceanographic Institution. The REDICS system was tested using seawater standards collected at 470m and 4000m depth in the Atlantic Ocean and analyzing the extracted CO₂. The results were compared to the results for the same standards processed on the current NOSAMS water stripping line. The results demonstrate that the system successfully extracts more than 99% of the dissolved inorganic carbon in less than 20 minutes. Stable isotope and radiocarbon isotope analyses demonstrated system precision of 0.02%c and 3.5% respectively. / by Kalina Doneva Gospodinova. / 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), 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.