Scleractinian cold-water corals are widely distributed in seaways and basins of the North Atlantic Ocean, including the Straits of Florida. These corals can form extensive biogenic mounds, which are biodiversity hotspots in the deep ocean. The processes that lead to the genesis of such cold-water coral mounds and control their distribution and morphology are poorly understood. This work uses an innovative mapping approach that combines 130 km2 of high resolution geophysical and oceanographic data collected using an Autonomous Underwater Vehicle (AUV) from five cold-water coral habitats in the Straits of Florida. These AUV data, together with ground-truthing observations from eleven submersible dives, are used to investigate fine-scale mound parameters and their relationships with environmental factors. Based on these datasets, automated methods are developed for extracting and analyzing mound morphometrics and coral cover. These analyses reveal that mound density is 14 mound/km2 for the three surveyed sites on the toe-of-slope of Great Bahama Bank (GBB); this density is higher than previously documented (0.3 mound/km2) in nearby mound fields. Morphometric analyses further indicate that mounds vary significantly in size, from a meter to up to 110 m in relief, and 81 to 600,000 m2 in footprint area. In addition to individual mounds, cold-water corals also develop in some areas as elongated low-relief ridges that are up to 25 m high and 2000 m long. These ridges cover approximately 60 and 70% of the mapped seafloor from the sites at the center of the Straits and at the base of the Miami Terrace, respectively. Morphometrics and current data analyses across the five surveyed fields indicate that mounds and ridges are not in alignment with the dominant current directions. These findings contradict previous studies that described streamlined mounds parallel to the northward Florida Current. In contrast, this study shows that the sites dominated by coral ridges are influenced by unidirectional flowing current, whereas the mounds on the GBB slope are influenced by tidal current regime. The GBB mounds also experience higher sedimentation rates relative to the sites away from the GBB slope. Sub-surface data document partially or completely buried mounds on the GBB sites. The sediments burying mounds are off-bank material transported downslope by mass gravity flow. Mass gravity transport creates complex slope architecture on the toe-of-slope of GBB, with canyons, slump scars, and gravity flow deposits. Cold-water corals use all three of these features as location for colonization. Coral mounds growing on such pre-existing topography keep up with off-bank sedimentation. In contrast, away from the GBB slope, off-bank sedimentation is absent and coral ridges grow independently of antecedent topography. In the sediment-starved Miami Terrace site, coral ridge initiation is related to a cemented mid-Miocene unconformity. In the center of the Straits, coral ridges and knobs develop over an unconsolidated sand sheet at the tail of the Pourtales drift. Coral features at the Miami Terrace and center of the Straits have intricate morphologies, including waveform and chevron-like ridges, which result from asymmetrical coral growth. Dense coral frameworks and living coral colonies grow preferentially on the current-facing ridge sides in order to optimize food particle capture, whereas coral rubble and mud-sized sediments accumulate in the ridge leesides. Finally, this study provides a method using solely acoustic data for discriminating habitats in which cold-water corals are actively growing. Results from this method can guide future research on and management of cold-water coral ecosystems. Taken together, spatial quantitative analyses of the large-scale, high-resolution integrated surveys indicate that cold-water coral habitats in the Straits of Florida: (1) are significantly more diverse and abundant than previously thought, and (2) can be influenced in their distribution and development by current regime, sedimentation, and/or antecedent topography.

The increasing reliance on oceans, rivers and waterways in a spectrum of human activities have demonstrated the large demand for advanced marine technologies that facilitate multifarious in-water services and tasks. The autonomous underwater vehicle (AUV) is a representative marine technology which has been contributing continuously to many ocean-related fields. An elaborate control system is essential to AUVs. However, AUVs present difficult control system design problems due to their nonlinear dynamics, the unpredictable environment and the poor knowledge about the hydrodynamic coupling of the vehicle degrees of freedom. When designing the motion controller, the practical constraints on the AUV system such as limited perceiving, computing and actuating capabilities should also be respected. The model predictive control (MPC) is an advanced control technology that leverages optimization to calculate the control command. Thanks to the optimization nature, MPC can conveniently handle the complex nonlinearity in system dynamics as well as the state and control constraints. MPC takes the receding horizon control paradigm which gains satisfactory robustness against model uncertainties and external disturbances. Therefore, MPC is an ideal candidate for solving the AUV motion control problems. On the other hand, since the optimization is solved by iterative numerical algorithms, the obtained control signal is an implicit function of the system state, which complicates the characterization of the closed-loop properties. Moreover, the nonlinear system dynamics makes the online optimization nonlinear programming (NLP) problems. The high computational complexity may cause an issue on the real-time control for embedded platforms with limited computing resources. In order to push the advanced MPC technology towards real-world AUV applications, this PhD dissertation is concerned with fundamental AUV motion control problems and attempts to address the aforementioned challenges and provide novel solutions. This dissertation proceeds with Chapter 1 by providing state-of-the-art introductions to related research areas. The mathematical model used for the AUV motion control is elaborated in Chapter 2. In Chapter 3, we consider the AUV navigation and control problem in constrained workspace. A unified receding horizon optimization framework consisting of the dynamic path planning and the nonlinear model predictive control (NMPC) tracking control is developed. Although the NMPC tracking controller well accommodates the practical constraints on the AUV system, it presents a brand new design philosophy compared with the existing control systems that are implemented on real AUVs. Since the existing AUV control systems are reliable controllers, AUV practitioners tend not to fully replace them but to improve the control performance by adding features. By considering this, in Chapter 4, we develop the Lyapunov-based model predictive control (LMPC) scheme which builds on the existing AUV control system and invoke online optimization to improve the control performance. Chapter 5 focuses on the path following (PF) problem. Unlike the trajectory tracking control which equally emphasizes the spatial and temporal control objectives, the PF control often prioritizes the path convergence over the speed assignment. To incorporate this objective prioritization into the controller design, a novel multi-objective model predictive control (MOMPC) scheme is developed. While the MPC technique provides several salient features (e.g., optimality, constraints handling, objective prioritization, robustness, etc.), those features come at a price: a computational bottleneck is formed by the heavy burden of solving online optimizations in real time. To explicitly address this issue, in Chapter 6, the computational complexity of the MPC algorithms is particularly emphasized. Two novel strategies which potentially alleviate the computational burden of the MPC-based AUV tracking control are proposed. In Chapter 7, some conclusive remarks are provided and a few avenues for future research are identified. / Graduate

Este trabalho trata do controle dos movimentos de um Veículo Submersível Autônomo (VSA). Veículos submersíveis são difíceis de controlar devido à alta não linearidade de seus modelos, ao forte acoplamento de movimentos, ao desconhecimento de certas dinâmicas, às incertezas do próprio modelo, devido a distúrbios externos impostos pelo ambiente e devido ao ruído de sensores. A dificuldade de controle pode ser exacerbada quando o veículo é subatuado. Para realização deste trabalho foi escolhido um VSA do tipo torpedo, cujo modelo matemático disponível na literatura foi devidamente modificado para garantir uma melhor descrição de seus movimentos em seis graus de liberdade (6-GL). O modelo foi então validado através de simulações numéricas. Para a síntese dos controladores utilizou-se uma técnica de controle avançada. Mais especificamente, utilizou-se a abordagem do controle H1 para sistemas multivariáveis. Assim foram obtidos controladores centralizados capazes de superar o problema do forte acoplamento de movimentos. Técnicas de controle avançado permitem também considerar as informações disponíveis sobre perturbações, incertezas, ruídos e diferentes tipos de entrada já na fase de síntese, o que permite obter controladores com desempenho adequado numa ampla faixa de operação. Neste trabalho, em particular, a técnica da Sensibilidade Mista foi escolhida para a síntese de controladores robustos. Nesta abordagem, formatam-se algumas funções de malha fechada ligadas a sensibilidade do sistema buscando garantir estabilidade e desempenho robusto para o sistema controlado. Usando a mesma técnica de controle desenvolveu-se ainda um controlador de dois graus de liberdade (2-GL), apropriado para aplicação no problema de guiagem, onde procura-se seguir trajetórias tridimensionais. Os controladores desenvolvidos foram testados em simulações numéricas, produzindo-se uma grande quantidade de resultados. A análise destes resultados revela o poder e flexibilidade das técnicas escolhidas. / This work focuses the motion control of an Autonomous Underwater Vehicle (AUV). Underwater vehicles are difficult to control due to high non-linearities of its model, coupling between dynamics, unknown dynamics, model uncertainties, disturbances and sensor noises. Difficulty is greater, when the system is subactuated. In this work, a mathematical model of a torpedo-like AUV available in the bibliography was chosen and refined, leading to a six degree of freedom (6-DOF) model. The model was further analyzed and validated by a number of numerical simulations. Advanced approaches were used for the synthesis of controllers. Speciffically, a H1 approach for multivariable systems was used. Thus, a centralized controller was developed, able to avoid the problem of high coupling between the variables. This advanced approach is also able to use informations about perturbations, uncertainties, noises and different types of input signals in the synthesis stage, leading to controllers with better performance in a large operation bandwidth. In this work, a Mixed Sensitivity approach was employed. This control approach is based on the shapping of well known closed-loop sensitivity functions, seeking to achieve stability and performance robustness. Using a similar technique, a controller with two degree of freedom (2-DOF) was also synthesised, to tackle the guidance problem tracking of 3-D trajectories was then fully achieved. The controllers developed were tested in a number of numerical simulations. Analyses of results reveals the power and flexibility of the employed techniques.

In this dissertation, we develop a new framework for 3D trajectory planning of Autonomous Underwater Vehicles (AUVs) in realistic ocean scenarios. The work is divided into three parts. In the first part, we provide a new approach for deterministic trajectory planning in steady current, described using Ocean General Circulation Model (OGCM) data. We apply a Non-Linear Programming (NLP) to the optimal-time trajectory planning problem. To demonstrate the effectivity of the resulting model, we consider the optimal time trajectory planning of an AUV operating in the Red Sea and the Gulf of Aden. In the second part, we generalize our 3D trajectory planning framework to time-dependent ocean currents. We also extend the framework to accommodate multi-objective criteria, focusing specifically on the Pareto front curve between time and energy. To assess the effectiveness of the extended framework, we initially test the methodology in idealized settings. The scheme is then demonstrated for time-energy trajectory planning problems in the Gulf of Aden. In the last part, we account for uncertainty in the ocean current field, is described by an ensemble of flow realizations. The proposed approach is based on a non-linear stochastic programming methodology that uses a risk-aware objective function, accounting for the full variability of the flow ensemble. We formulate stochastic problems that aim to minimize a risk measure of the travel time or energy consumption, using a flexible methodology that enables the user to explore various objectives, ranging seamlessly from risk-neutral to risk-averse. The capabilities of the approach are demonstrated using steady and transient currents. Advanced visualization tools have been further designed to simulate results.

This thesis examines two methods for monocular visual odometry, FAST + KLT and ORBSLAM2, in the case of underwater environments.This is done by implementing and testing the methods on different underwater datasets. The results for the FAST + KLT provide no evidence that this method is effective in underwater settings. However, results for the ORBSLAM2 indicate that good performance is possible whenproperly tuned and provided with good camera calibration. Still, thereremain challenges related to, for example, sand bottom environments and scale estimation in monocular setups. The conclusion is therefore that the ORBSLAM2 is the most promising method of the two tested for underwater monocular visual odometry. / Denna uppsats undersöker två metoder för monokulär visuell odometri, FAST + KLT och ORBSLAM2, i det särskilda fallet av miljöer under vatten. Detta görs genom att implementera och testa metoderna på olika undervattensdataset. Resultaten för FAST + KLT ger inget stöd för att metoden skulle vara effektiv i undervattensmiljöer. Resultaten för ORBSLAM2, däremot, indikerar att denna metod kan prestera bra om den justeras på rätt sätt och får bra kamerakalibrering. Samtidigt återstår dock utmaningar relaterade till exempelvis miljöer med sandbottnar och uppskattning av skala i monokulära setups. Slutsatsen är därför att ORBSLAM2 är den mest lovande metoden av de två testade för monokulär visuell odometri under vatten.

The presented work focuses on the theoretical and practical aspects concerning the design and development of a formal method to build a mission control system for autonomous underwater vehicles bringing systematic design principles for the formal description of missions using Petri nets. The proposed methodology compounds Petri net building blocks within it to de_ne a mission plan for which it is proved that formal properties, such as reachability and reusability, hold as long as these same properties are also guaranteed by each Petri net building block. To simplify the de_nition of these Petri net blocks as well as their composition, a high level language called Mission Control Language has been developed. Moreover, a methodology to ensure coordination constraints for teams of multiple robots as well as the de_nition of an interface between the proposed system and an on-board planner able to plan/replan sequences of prede_ned mission plans is included as well. Results of experiments with several real underwater vehicles and simulations involving an autonomous surface craft and an autonomous underwater vehicles are presented to show the system's capabilities. / El treball presentat en aquesta tesi està centrat en el disseny i desenvolupament d'un mètode formal per a construir un sistema de control de missió per a vehicles submarins autònoms, que aporta principis sistemàtics de disseny per a la descripció formal de missions. La metodologia proposada parteix d'uns blocs elementals de construcció, descrits mitjançant xarxes de Petri. La composició d'aquests blocs entre si genera un pla de missió per el qual diverses propietats, com ara accessibilitat o reutilització, són garantides sempre i quan aquestes mateixes propietats siguin també garantides per a cada un dels blocs elementals de construcció. Per simplificar la definició d'aquests blocs, així com per simplificar-ne la seva composició, s'ha desenvolupat un llenguatge d'alt nivell anomenat Mission Control Language. A més, s'ha inclòs una metodologia per assegurar la coordinació de restriccions entre equips de múltiples robots. També s'ha establert una interfície entre el sistema proposat i un planificador a bord del vehicle capaç de planificar/replanificar seqü_encies de plans de missió prèviament definits. Per tal de demostrar les capacitats del sistema, s'han presentat resultats d'experiments amb diversos vehicles submarins reals, així com simulacions amb vehicles autònoms submarins i en superfície.

Replacing humans with underwater robots for accomplishing marine tasks such as oceanic supervision and undersea operations have been an endeavour from long time ago. Hence, a number of underwater robots have been developed. Among those underwater robots, developing biomimetic swimming robots has been appealing for many researchers and institutes since these robots have shown superior performance. Biomimetic swimming robots have higher swimming efficiency, manoeuvrability and noiseless performance. However, the existing biomimetic swimming robots are specialised for a single gait of locomotion like cruising, manoeuvrability and accelerating while for efficient accomplishment of marine tasks, an underwater robot needs to have multiple gaits of locomotion. In order to develop multiple-gaited swimming robots, the optimal characteristics of each gait of swimming must be combined together, whereas the combination is not usually possible. The problem needs to be addressed during the design process. Moreover, the optimality of the actuation mechanism of robots - that do not utilise any artificial muscle - could be assured using the mathematical model employed for simulation of their swimming behaviour. However, the existing models are incomplete and, accordingly, not reliable since their assumptions like the constant speed of flow around the fish robot could be used when the average speed of the flow is determined during experiment while before development of robots, the flow speed is not known. In addition to that, the simulation results must be optimised using the experimental observations in nature and analytical results while the optimisation algorithms are based on one fitness function. The aforementioned problems as well as the fabrication challenges of free-swimming biomimetic robots are addressed in a development process of multiple-gaited fish-mimetic robots introduced by the author in this thesis. This development method engages the improvement of all development steps of fish robots including design, mathematical modelling, optimisation and fabrication steps. In this thesis, the aforementioned steps are discussed and the contributions of the method for each step are introduced. As an outcome of the project, two prototypes of fish robots called UC-Ika 1 & 2 are built.

Approved for public release; distribution is unlimited / Unmanned vehicle technology has matured significantly over the last two decades. This is evidenced by its widespread use in industrial and military applications ranging from deep-ocean exploration to anti-submarine warefare. Indeed, the feasiblity of short-range, special-purpose vehicles (whether aunonomous or remotely operated) is no longer in question. The research efforts have now begun to shift their focus on development of reliable, longer-range, high-endurance and fully autonomous systems. One of the major underlying technologies required to realize this goal is Artificial Intelligence (AI). The latter offers great potential to endow vehicles with the intelligence needed for full autonomy and extended range capability; this involves the increased application of AI technologies to support mission planning and execution, navigation and contingency planning. This thesis addresses two issues associated with the above goal for Autonomous Underwater Vehicles (AUV's). Firstly, a new approach is proposed for path planning in underwater environments that is capable of dealing with uncharted obstacles and which requires significantly less planning time and computer memory. Secondly, it explores the use of expert system technology in the planning of AUV missions.

For Autonomous Underwater Vehicles (AUVs) to be able to conduct longterm surveys, the ability to return to a docking station for maintenance and recharging is crucial. A dynamic docking system where a slowly moving submarine acts as the docking station provides increased hydrodynamic control and reduces the impact of environmental disturbances. A vision-based relative positioning system using a camera, mounted on the AUV, and light sources, mounted on the docking station, is investigated as a suitable high-resolution and high-frequency solution for a short-range relative positioning system. Detection and identification of the true light sources in the presence of reflections, ambient light, and other luminaries, requires a robust tracking pipeline that can reject false positives. In this thesis, we present a complete tracking pipeline, from image processing to pose estimation, specifically for a soft docking scenario. We highlight the issues of light source detectors based on finding a unique global threshold and detectors based on gradient information and propose a novel method, based on using a suitable threshold for each light source. Rejection of false positives is handled systematically by rejecting pose estimates resulting in large re-projection errors, and a configuration of the light sources is proposed that enhances the pose estimation performance. The performance of the proposed light source detector is evaluated on the D-recovery dataset. Results show that the proposed method outperforms other methods in identifying the light sources. The tracking pipeline is evaluated with experiments as well as a simulation based on the Stonefish simulator. / För att autonoma undervattensfordon ska kunna utföra långsiktiga undersökningar är möjligheten att återvända till en dockningsstation för underhåll och laddning avgörande. Ett dynamiskt dockningssystem där en långsamtgående ubåt agerar som dockningsstation ger en ökad hydrodynamisk kontroll och minskar påverkan av omgivande miljöstörningar. Ett synbaserat, relativt positioneringssystem som använder en kamera, monterad på farkosten, och ljuskällor, monterad på dockningsstationen, undersöks som en lämplig högupplöst och högfrekvent lösning för ett relativt positioneringssystem med kort räckvidd. Detektering och identifiering av de verkliga ljuskällorna i närvaro av reflektioner, omgivande ljus och andra störande ljuskällor kräver ett robust spårningssystem som kan särskilja de sanna ljuskällorna från de omgivande störningarna. I denna uppsats presenteras ett komplett spårningssystem, från bildbehandling till positionsestimering, specifikt för ett soft docking scenario. Vi lyfter fram problem med detektorer baserat på att hitta ett unikt globalt tröskelvärde och detektorer baserade på gradientinformation. Vi föreslår en ny metod baserad på att använda ett lämpligt tröskelvärde för varje ljuskälla. Omgivande störningar hanteras systematiskt genom att avvisa positionestimeringar som resulterar i stora projektionsfel, och en konfiguration av ljuskällorna föreslås som förbättrar positionsestimeringens prestanda. Prestandan hos den föreslagna ljuskällsdetektorn utvärderas på datasetet D-recovery. Resultaten visar att den föreslagna metoden överträffar andra metoder i att identifiera ljuskällorna. Spårningsystemet utvärderas med experiment samt en simulering baserad på Stonefish-simulatorn.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In recent years Autonomous Underwater Vehicles (AUVs) have become interesting for harbor mapping and protection. AUVs require a SONAR sensor for observing their surroundings, thus enabling them to perform collision avoidance manoeuvres and scanning their operating environment for intruders or foreign objects, e.g. mines. To perform such actions the SONAR sensor is required to supply very fine range resolution for target imaging, as well as providing information about possible target velocity. Basic SONAR theory is discussed, as well as different approaches to signal design and processing techniques, for achieving the required resolution in range and target velocity. Two of the discussed approaches are selected for processing range and target velocity, respectively. Both approaches are simulated for their validity before being tested by using a custom-built platform. The platform is highly configurable and designed for capacity of testing a variety of SONAR signals and set ups. Furthermore, the platform is built by using off-the-shelf components to minimize development costs. The results of simulations and practical tests are presented. A high correlation between theory and practice is achieved. The knowledge and the platform presented form the stepping stone for further SONAR sensor developments. / AFRIKAANSE OPSOMMING: In die laaste jare het outonome onderwater voertuie (OOV) toenemend belangrik geword vir die kartografie en beskerming van hawens. OOV’s vereis SONAR sensore wat hulle in staat stel, om hulle omgewing waar te neem en sodoende botsing vermydings take te verrig en ook om hul werksomgewing noukeurig te skandeer om indringers of vreemde voorwerpe, bv. myne, op te spoor. Om sulke werk te verrig, word van die SONAR sensor vereis, om baie fyn afstand oplossings vir teiken te verskaf, insluitend die moontlike snelheid van die teiken. Basiese SONAR teorie word bespreek, en dan verskeie benaderings van sein ontwerp en verwerkings tegnieke. Twee van die bespreekte benaderings word gekies om afstand en teiken snelheid onderskeidelik te verwerk. Altwee benaderings word gesimuleer om hul geldigheid vas te stel, voor dat hulle getoets word op ’n pasmaat vervaardigde platform. Die platform is hoogs aanpasbaar en is ontwerp vir sy vermoë om ’n verskeidenheid SONAR seine en verwerkings te hanteer. Verder is die platform vervaardig met standard rakonderdele om ontwikkelingskoste so laag as moontlik te hou. Die uitslae van die simulerings en praktiese toetse word voorgestel. ’n Hoë mate aan korrelasie is bereik tussen teorie en praktyk. Die kennis en die platvorm, wat hier voorgestel word, vorm die eerste trappie vir toekomstige SONAR sensor ontwikkeling.