Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. Title from title screen (viewed Sept. 24, 2007). Includes bibliographical references (leaves 77-78). Online version of the print original.

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The objective of the research is to achieve a systematic combination of acoustic echo reduction components that together achieve a robust performance of the MCAEC system as a whole. Conventional approaches to the acoustic echo reduction system typically assume that individual components would perform ideally. For example, the adaptive algorithm for AEC is often developed in the absence of strong near-end signal, the algorithm for RES is often an added module that is developed as a separate noise reduction component, and the decorrelation procedure for MCAEC is yet another add-on module that simply introduces some form of distortion to the reference signal. The main challenge is in designing a consistent criterion across all modules that can be jointly optimized to form a more consistent framework for acoustic echo reduction. The decorrelation procedure can potentially benefit from the system approach as well if it is designed by taking the near-end listener into account. The MCAEC system should be optimized not only for the echo cancellation and suppression performance, but also for the reference signal quality after the added distortion from the decorrelation procedure. Finally, a tuning strategy is presented to jointly optimize the parameters across all modules using object criteria.

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Achieving autonomous in complex natural environments has the potential to transform society by bringing the benefits of automation from the confines of the factory floor to the outdoors. There, it could benefit areas such as environmental monitoring and clean-up, precision agriculture, delivery of goods. A fundamental requirement for achieving these goals are sensors that can provide reliable support for navigation, e.g., a drone, in natural environments. In this thesis, sonar-based navigation has been investigated as an approach to parsimonious autonomous sensing for drones. Bats living in dense vegetation have demonstrated that autonomous navigation in a complex, natural environment based on two one-dimensional ultrasonic echo streams is feasible. Here, a biomimetic sonar head has been used to collect echo data from recreations of natural foliage in the lab under controlled conditions. This data was used to address the research question whether the grazing angle at which the sonar is looking at a surface can be estimated from the echoes -- despite the random three-dimensional nature of the scatter from the foliage. To investigate this, the echoes have been subjected to statistical analysis such as spectral coherence and cross-correlation. Most importantly, the foliage data was compared against predictions made by the Endura method (energy, duration, and range method) that has been devices for two-dimension random scatterers. The results of this analysis shows that -- despite their profoundly random nature -- echoes can be used to estimate the sonar grazing angle directly, i.e., without the need to resort to reconstructions of the foliage geometry. This opens the possibility of developing simple devices for navigation control in natural environments that can control the direction of motion at a very little computational cost. / Master of Science / Autonomously flying drones is a potential technology that could bring benefits to the society and improve the quality of life for humans[22]. Therefore, a study of autonomously flying in a natural environment is necessary, and this thesis will focus on drone that could recognize objects with different grazing angle and acoustic signal by collecting data from near foliage surface. For example, when a bush wall is in front of the drone, a on board computer could inform drone whether the drone airline will collide with the bush wall or the bush wall is safely out of drone’s path[5]. If on board computer reads that there will be a collision with bush wall, then drone needs to make decision (change direction or stop immediately) to avoid crush on to bush wall. A sonar based navigation system has been investigated as an approach to achieve autonomous sensing for drones, which is inspired by bats. Bats use their natural sonar system to navigate in cave or forest, hence, it is hardly to see bats slam into any obstacles while flying. Bats navigation behaviours could be reconstructed as a sonar based autonomy. Hence, this thesis is inspired by bats to determine if there is a computational way to illustrate that sonar based sensor could be a solution to achieve reactive autonomy by using different grazing angle of the surface’s acoustic signals.

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Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 3, 2007) Includes bibliographical references (p. 65-66).

Much work is presently being done concerning small scale heterogeneities in the earth's crust. These heterogeneities range from pores in sedimentary rocks up to fluctuations in the density and seismic constants of the earth's crust with scale lengths of kilometers. The ability to study and quantify these heterogeneities using seismic methods would be a major advance in the earth sciences. Physical modeling has been shown to be a useful technique for investigating various aspects of wave propagation. In this thesis, two physical modeling experiments (one three-dimensional and one two-dimensional) are used to investigate the scattering of seismic waves from small scale heterogeneities and the changes in seismic velocity and apparent attenuation resulting from this scattering. The effects of both isotropic and anisotropic scattering on velocity and apparent attenuation are calculated. These experimental results are compared to theoretical results. The theory used for isotropic scattering for the three-dimensional experiment is a modified version of Wu's single scattering theory, where instead of calculating the scattering for a single scatterer using the Born approximation, the exact results for scattering from a cylindrical shape are used. While the results for compressional waves and both components of shear waves compare reasonably well for small scatterer volume fractions, at larger scatterer volume fractions, where the need for multiple scattering is more likely, the results for all waves do not compare as well. Many theories used to test anisotropic scattering predict changes in velocity rather than changes in apparent attenuation. The velocity changes are used primarily in this work due to geometrical focusing by a seismic lens that biases the amplitudes (and hence the estimates of apparent attenuation) at low frequencies where most theories predict apparent attenuation. Velocities are calculated from the data using travel times and low frequency phase shifts for the compressional waves and for one component of the shear waves measured in this two-dimensional experiment. Theories that are used to predict compressional and shear wave velocities for both isotropic and anisotropic scatterers are based on a fractional volume method (isotropic), two crack methods (isotropic and anisotropic), and a finely layered method (anisotropic). The isotropic experimental results have much larger, non-linear changes in the velocities than do the isotropic theoretical results. The anisotropic experimental results have similar shapes to both theoretical anisotropic methods for compressional waves and to the theoretical anisotropic crack method for shear waves. Attenuation is computed using log spectral ratios and compares as well with the theoretical results as can be expected within the limits set. A method using anisotropic apparent attenuation to help quantify the scatterers is developed for use with field data. / Graduation date: 1987