The aim of this study was to develop and examine the use of backscatter data collected with multibeam sonar (MBS) systems for benthic habitat mapping. Backscatter data were collected from six sites around the Australian coastal zone using the Reson SeaBat 8125 MBS system operating at 455 kHz. Benthic habitats surveyed in this study included: seagrass meadows, rhodolith beds, coral reef, rock, gravel, sand, muddy sand, and mixtures of those habitats. Methods for processing MBS backscatter data were developed for the Coastal Water Habitat Mapping (CWHM) project by a team from the Centre for Marine Science and Technology (CMST). The CMST algorithm calculates the seafloor backscatter strength derived from the peak and integral (or average) intensity of backscattered signals for each beam. The seafloor backscatter strength estimated from the mean value of the integral backscatter intensity was shown in this study to provide an accurate measurement of the actual backscatter strength of the seafloor and its angular dependence. However, the seafloor backscatter strength derived from the peak intensity was found to be overestimated when the sonar insonification area is significantly smaller than the footprint of receive beams, which occurs primarily at oblique angles. The angular dependence of the mean backscatter strength showed distinct differences between hard rough substrates (such as rock and coral reef), seagrass, coarse sediments and fine sediments. The highest backscatter strength was observed not only for the hard and rough substrate, but also for marine vegetation, such as rhodolith and seagrass. The main difference in acoustic backscatter from the different habitats was the mean level, or angle-average backscatter strength. However, additional information can also be obtained from the slope of the angular dependence of backscatter strength. / It was shown that the distribution of the backscatter. The shape parameter was shown to relate to the ratio of the insonification area (which can be interpreted as an elementary scattering cell) to the footprint size rather than to the angular dependence of backscatter strength. When this ratio is less than 5, the gamma shape parameter is very similar for different habitats and is nearly linearly proportional to the ratio. Above a ratio of 5, the gamma shape parameter is not significantly dependent on the ratio and there is a noticeable difference in this parameter between different seafloor types. A new approach to producing images of backscatter properties, introduced and referred to as the angle cube method, was developed. The angle cube method uses spatial interpolation to construct a three-dimensional array of backscatter data that is a function of X-Y coordinates and the incidence angle. This allows the spatial visualisation of backscatter properties to be free from artefacts of the angular dependence and provides satisfactory estimates of the backscatter characteristics. / Using the angle-average backscatter strength and slope of the angular dependence, derived by the angle cube method, in addition to seafloor terrain parameters, habitat probability and classification maps were produced to show distributions of sand, marine vegetation (e.g. seagrass and rhodolith) and hard substrate (e.g. coral and bedrock) for five different survey areas. Ultimately, this study demonstrated that the combination of high-resolution bathymetry and backscatter strength data, as collected by MBS, is an efficient and cost-effective tool for benthic habitat mapping in costal zones.

Le réseau REBENT constitue un nouveau réseau de surveillance des habitats benthiques dont la vocation est d'établir un état de référence et un suivi régulier de la faune et de la flore littorales. Ce réseau entre en phase opérationnelle sur la région Bretagne. L'approche sectorielle est caractérisée par un ensemble d'études de sites (20) sur lesquels une cartographie détaillée des habitats est réalisée au 1/10 000 ou 1/25 000ème. Pour identifier en domaine subtidal les unités morpho-sédimentaires et/ou biologiques, elle s'appuie sur la combinaison de plusieurs systèmes acoustiques (sonar à balayage latéral, sondeurs mono et multifaisceaux, système RoxAnn), calibrés par des observations du fond (prélèvements, vidéo sous-marine, plongée). Les baies de Concarneau et de Quiberon, et l'archipel de Glénan, ont été les premiers secteurs ainsi reconnus en 2003. Ces travaux montrent l'intérêt de combiner plusieurs sources acoustiques et différentes embarcations pour caractériser préalablement les habitats par petits fonds. Certaines biocénoses semblent répondre directement aux ondes acoustiques (maërl, crépidule, lanice, étoiles de mer, ophiures, maldanes) alors que d'autres, comme les fonds à Haploops, se distinguent par la morphologie du substrat sur lequel les colonies se fixent (fonds vaseux à cratères). La précision des levés (positionnement et résolution sur le fond) et la gestion sous SIG des résultats permettent de mieux comprendre la distribution spatiale de ces habitats et de suivre leur évolution.

La classification sur ombre de mines marines peut être effectuée à partir d'images sonar haute résolution. Cependant, la classification mono-vue admet des limites du fait de leur forme géométrique parfois complexe. Une manière de s'affranchir des ambiguïtés consiste à effectuer une classification multi-vues. Dans un premier temps, il convient d'assimiler les spécificités de l'imagerie sonar. D'un côté, les propriétés statistiques des pixels et le principe d'acquisition des images sont des connaissances avantageusement prises en compte lors de l'étape de segmentation. D'un autre côté, les distorsions géométriques qui affectent l'ombre portée du fait des performances du sonar et de la prise de vue doivent être considérées. En matière de reconnaissance de formes, les données sonar segmentées peuvent être diversement résumées suivant qu'on s'attache à définir des grandeurs indépendantes des positions relatives objet-sonar et/ou de la résolution du sonar ou bien, autorisant une reconstruction du contour et la conservation de l'orientation de la forme associée. Ces considérations du problème mono-vue ont préparé l'élaboration de processus plus complexes de classification multi-vues. D'une part, on manipule les attributs issus d'un traitement image par image. Deux cas se présentent : en exploitant l'évolution de la forme de l'ombre en fonction du trajet du sonar ou, au contraire, en s'affranchissant des transformations du plan. Dans le premier cas, on caractérise de manière globale l'ensemble des valeurs successives prises par des attributs sensibles aux diverses formes de l'ombre. Dans le second cas, sans connaissance précise des conditions d'acquisition, les attributs extraits sont fusionnés et présentés à l'opérateur sous forme de mesures pour l'aide à la décision. Par la logique floue d'autre part, les outils de reconnaissance de formes calculés sur des données binaires ont été étendus au cas de données en niveaux de gris d'une nouvelle image pour sa caractérisation.

QC 20100621

<p>Manatees (Mammalia: Sirenia), along with the closely related dugongs, are the only herbivorous marine mammals. Manatees consume a wide variety of vascular plants and algae in both marine and freshwater habitats. However, little is known about what characteristics influence diet and food selectivity, especially in freshwater habitats, which represent a large portion of the available habitat for the endangered Antillean manatee, <italic>Trichechus manatus manatus</italic>, in Central and South America. Understanding foraging ecology is an important element of effective conservation strategies.</p><p>This dissertation investigated various aspects of the foraging ecology of the Antillean manatee in a freshwater habitat, specifically: 1) how plant availability (i.e. species richness, diversity, and abundance) varied seasonally with changes in water depths, 2) manatee food selectivity from a representative set of plant species from that freshwater habitat, and 3) the relationship of plant nutritive compounds and availability with manatee food selectivity. In addition, this dissertation describes the multiple uses of sonar technology for studying manatees and habitat characteristics in freshwater.</p><p>Plant availability to manatees was evaluated by conducting monthly plant surveys from July 2010-July 2011 in four contact lakes in the wetlands of Tabasco, Mexico. Manatee food selectivity was examined by conducting food selection experiments on a wild adult manatee during the low water season with 54 plant species representing 25+ genera. The nutritive components (i.e. crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HC), and ash) and plant availability values for selected and non-selected plants species were evaluated to determine their relationship with manatee food selectivity. The applicability of using side-scan sonar for manatee research was tested in various freshwater and estuarine habitats in Honduras, Costa Rica, Panama, and the wetlands of Tabasco, Mexico between 2006-2011.</p><p>The major findings of this dissertation are as follows. Plant species richness, diversity, and abundance were greatest during the rising water season (July-August) and lowest during the low water season (March-June). No plants were available in April-June, which represented the majority of the low water season. The wild manatee</p><p>selected 27 (11+ genera) of the 54 species examined during the feeding experiments. Of the plant characteristics tested (i.e. nutritive components and plant availability), only digestible fiber (HC) was significantly related to manatee food selection, with manatees</p><p>selecting plants with higher HC content. Four unique applications were identified for the use of side-scan sonar to facilitate manatee research in freshwater habitats: 1) confirmation of visual sightings and determination of group size, 2) determination of mother-calf pairs, 3) habitat characterization, and 4) assisting manatee captures.</p><p>Results from this study reveal that manatees living in the freshwater wetlands of Tabasco, Mexico have to cope with a highly seasonal availability of plants and that while manatees consume plants from a wide variety of genera, they are highly selective. Unlike other herbivorous mammals, manatee food selectivity was not influenced by CP, NDF, or ADF, but rather by digestible fiber. A unique suit of anatomical and physiological characteristics suggests that manatees may be fiber digestion specialists. Both seasonal plant availability and the manatee's large dietary breadth must be considered when developing 1) conservation strategies for wild manatees in freshwater habitats and 2) protocols for captive rehabilitation of orphaned and stranded manatees that will be reintroduced into the wild.</p> / Dissertation

The development of low-frequency SONAR systems, using a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated, thus allowing multiple viewpoints of a target). Furthermore, time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution of the time dependent echo spectrum to differentiate a man-made target (e.g. an elastic spherical shell, or cylinder) from a natural one of the similar shape (e.g. a rock). Indeed, key energetic features of man-made objects can aid in identification and classification in the presence of clutter and noise. For example, in a fluid-loaded thin spherical shell, an energetic feature is the mid-frequency enhancement echoes (MFE) that result from antisymmetric Lamb waves propagating around the circumference of the shell, which have been shown to be an acoustic feature useful in this pursuit. This research investigates the enhancement and benefits of bistatic measurements using the Wigner-Ville analysis along with acoustic imaging methods. Additionally, the advantage of joint space-time-frequency coherent processing is investigated for optimal array processing to enhance the detection of non-stationary signals across an array. The proposed methodology is tested using both numerical simulations and experimental data for spherical shells and solid cylinders. This research was conducted as part of the Shallow Water Autonomous Mine Sensing Initiative (SWAMSI) sponsored by ONR.

The aim of this thesis work has been to investigate how miniaturization, such as microsystems technology, can potentially increase the scientific throughput in exploration of hard-to-reach underwater environments, such as the subglacial lakes of Antarctica, or other challenging environments, including cave systems and wrecks. A number of instruments and subsystems applicable to miniature submersibles have been developed and studied, and their potential to provide a high functionality density for size-restricted exploration platforms has been assessed. To provide an onboard camera system with measurement capabilities, simulation and design tools for diffractive optics were developed, and microoptics realized to project reference patterns onto objects to reveal their topography. The influence of murky water on the measurement accuracy was also studied. For longer-range mapping of the surroundings, and under conditions with even less visibility, the performance of a very small, high-frequency side-scanning sonar was investigated using extensive modeling and physical testing. In particular, the interference on the acoustic beam from tight mounting in a hull was investigated. A range in excess of 30 m and centimeter resolution were obtained. Besides these systems, which can be used to navigate and map environments, a two-dimensional, thermal sensor for minute flows was developed. Measuring speed and direction of water flows, this sensor can aid in the general classification of the environment and also monitor the submersible’s movement. As the flow of waters in subglacial lakes is estimated to be minute, the detection limit and sensitivity were investigated. Measurements of water properties are facilitated by the chip-based conductivity, temperature, and depth sensor system developed. Macroscopically, this is an essential oceanographic instrument with which salinity is determined. Contrary to what was expected, MHz frequencies proved to be advantageous for conductivity measurements. Finally, sampling of water using an acoustically enriching microdevice, and even enabling return of pristine samples via the use of integrated latchable, high-pressure valves, was realized and evaluated. Particularly, investigations of the device’s ability to capture and hold on to microorganisms, were conducted. Further developed and studied, these devices – as subsystems to miniature submersibles, or as stand-alone instruments – should enable exploration of previously unreachable submerged environments. / Deeper Access, Deeper Understanding (DADU)

Target tracking is one the most fundamental elements of a radar system. The aim of target tracking is the reliable estimation of a target&#039 / s true state based on a time history of noisy sensor observations. In real life, the sensor data may include substantial noise. This noise can render the raw sensor data unsuitable to be used directly. Instead, we must filter the noise, preferably in an optimal manner. For land, air and surface marine vehicles, very successful filtering methods are developed. However, because of the significant differences in the underwater propagation environment and the associated differences in the corresponding sensors, the successful use of similar principles and techniques in an underwater scenario is still an active topic of research. A comparative study of the effects of the underwater environment on a number of tracking algorithms is the focus of the present thesis. The tracking algorithms inspected are: the Kalman Filter, the Extended Kalman Filter and the Particle Filter. We also investigate in particular the IMM extension to KF and EKF filters. These algorithms are tested under several underwater environment scenarios.

Marine search and rescue activities have been plagued with the problem of risking the lives of rescuers in rescue operations. With increasing developments in sensor technologies, it became a necessity in the marine search and rescue community to develop an autonomous marine craft to assist in rescue operations. Autonomy of marine craft requires a robust localization technique and process. To apply robust localization to marine craft, GPS technology was used to determine the position of the marine craft at any given point in time. Given that the operational environment of the marine was at open air, river, sea etc. GPS signal was always available to the marine craft as there are no obstructions to GPS signal. Adequate cognizance of the current position and states of an unmanned marine craft was a critical requirement for navigation of an unmanned surface vehicle (USV). The unmanned surface vehicle uses GPS in conjunction with state estimated solution provided by inertial sensors. In the absence of the GPS signal, navigation is resumed with a digital compass and inertial sensors to such a time when the GPS signal becomes accessible. GPS based navigation can be used for an unmanned marine craft with the mathematical modelling of the craft meeting the functional requirements of an unmanned marine craft. A low cost GPS unit was used in conjunction with a low cost inertial measurement unit (IMU) with sonar for obstacle detection. The use of sonar in navigation algorithm of marine craft was aimed at surveillance of the operational environment of the marine craft to detect obstacles on its path of motion. Inertial sensors were used to determine the attitude of the marine craft in motion. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

For synthetic aperture imaging, position and orientation deviation is of great concern. Unknown motions of a Synthetic Aperture Sonar (SAS) can blur the reconstructed images and degrade image quality considerably. Considering the high sensitivity of synthetic aperture imaging technique to sonar deviation, this research aims at providing a thorough navigation solution for a free-towed synthetic aperture sonar (SAS) comprising aspects from the design and construction of the navigation card through to data postprocessing to produce position, velocity, and attitude information of the sonar. The sensor configuration of the designed navigation card is low-cost Micro-Electro-Mechanical-Systems (MEMS) Magnetic, Angular Rate, and Gravity (MARG) sensors including three angular rate gyroscopes, three dual-axial accelerometers, and a triaxial magnetic hybrid. These MARG sensors are mounted orthogonally on a standard 180mm Eurocard PCB to monitor the motions of the sonar in six degrees of freedom. Sensor calibration algorithms are presented for each individual sensor according to its characteristics to precisely determine sensor parameters. The nonlinear least square method and two-step estimator are particularly used for the calibration of accelerometers and magnetometers. A quaternion-based extended Kalman filter is developed based on a total state space model to fuse the calibrated navigation data. In the model, the frame transformations are described using quaternions instead of other attitude representations. The simulations and experimental results are demonstrated in this thesis to verify the capability of the sensor fusion strategy.