Digital image processing techniques can be used to correct the distortions produced on a ship's sonar display that are caused by some of the components of the rotational movement of the ship.

Master of Science

Synthetic Aperture Sonar (SAS) provides the best opportunity for side-looking sonar mounted on underwater platforms to achieve high-resolution images. However, SAS processing requires strict constraints on resolvable platform motion. The most common approach to estimate this motion is to use the Redundant Phase Center (RPC) technique. Here the ping interval is set, such that a portion of the sonar array overlaps as the sensor moves forward. The time delay between the pings received on these overlapping elements is estimated using cross-correlation. These time delays are then used to infer the pingto-ping vehicle motion. Given the stochastic nature of the operational environment, some level of decorrelation between these two signals is likely. In this research, two iterative signal decomposition methods well suited for nonlinear and non-stationary signals, are investigated for their potential to improve the Time Delay Estimation (TDE). The first of this type, the Empirical Mode Decomposition (EMD) was introduced by Huang in the seminal paper, The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis and is the foundation for the algorithms used in this research. This method decomposes a signal into a finite sequence of simple components termed Intrinsic Mode Functions (IMFs). The Iterative Filter (IF) approach, developed by Lin, Wang and Zhou, builds on the EMD framework. The sonar signals considered in this research are complex baseband signals. Both the IF and EMD algorithms were designed to decompose real signals. However, the IF variant, the Multivariate Fast Iterative Filtering (MFIF) Algorithm, developed by Cicone, and the EMD variant, the Fast and Adaptive Multivariate Empirical Mode Decomposition (FAMVEMD) algorithm, developed by Thirumalaisamy and Ansell, preserve both the magnitude and phase in the decomposition and hence were chosen for this analysis. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

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Across species, bats exhibit wildly disparate differences in their noseleaf and pinnae shapes. Within Rhinolophid and Hipposiderid families, bats actively deform their pinnae and noseleaf during biosonar operation. Both the pinnae and noseleaf act as acoustic baffles which interact with the outgoing and incoming sound; thus, they form an important interface between the bat and its environment. Beampatterns describe this interface as joint time-frequency transfer functions which vary across spatial direction. This dissertation considers bat biosonar shape diversity and shape dynamics manifest as beampatterns. In the first part, the seemingly disparate set of functional properties resulting from diverse pinnae and noseleaf shape adaptations are considered. The question posed in this part is as follows: (i) what are the common properties between species beampatterns? and (ii) how are beampatterns aligned to a common direction for meaningful analysis? Hence, a quantitative interspecific analysis of the beampattern biodiversity was taken wherein: (i) unit[267]{} different pinnae and noseleaf beampatterns were rotationally aligned to a common direction and (ii) decomposed using principal component analysis, PCA. The first three principal components termed eigenbeams affect beamwidth around the single lobe, symmetric mean beampattern. Dynamic shape adaptations to the pinnae and noseleaf of the greater horseshoe bat (textit{Rhinolophus ferrumequinum}) are also considered. However, the underlying dynamic sensing principles in use are not clear. Hence, this work developed a biomimetic substrate to explore the emission and reception dynamics of the horseshoe bat as a sonar device. The question posed in this part was as follows: how do local features on the noseleaf and pinnae interact individually and when combined together to generate peak dynamic change to the incoming sonar information? Flexible noseleaf and pinnae baffles with different combinations of local shape features were developed. These baffles were then mounted to platforms to biomimetically actuate the noseleaf and pinnae during pulse emission and reception. Motions of the baffle surfaces were synchronized to the incoming and outgoing sonar waveform, and the time-frequency properties of the emission and reception baffles were characterized across spatial direction. Different feature combinations of the noseleaf and pinnae local shape features were ranked for overall dynamic effect. / Ph. D.

No / The Shetland Islands are well known for their archaeology, with many features from later prehistory surviving to an exceptional degree, with brochs being an excellent example. Less is known of submerged prehistoric sites, though the offshore profile of the islands means that ancient occupation of the current submerged zone was likely, and also that the sites are likely preserved. One such archaeological site, previously identified, occurs near Semblister. The site has been known locally, and is recorded as a broch in the local Historic Environment Records, however, its dimensions and location do not strongly suggest that it is a broch. Combining satellite imagery – the site is in relatively shallow water and visible – with targeted side-scan sonar survey and data processing, will aid the development of a process approach to the re-classification / confirmation of historically recorded sites, and archaeological prospection in the shallow water zone. / University of Bradford

This thesis investigates the improvements that can be made to Bayesian passive sonar tracking in the context of active-passive sonar data fusion. Performance improvements are achieved by exploiting the prior information available within a typical Bayesian data fusion framework. The algorithms developed are tested against both simulated data and data measured during the SEABAR 07 sea trial. Results show that the proposed approaches achieve improved detection, decreased estimation error, and the ability to track quiet targets in the presence of loud interferers. / text

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