The thesis deals with the detection of the nerve fiber layer disruptions in retina scans. The introduction presents an overview of the human eye fysiology and analyses the input image data. The thesis continues with an investigation of two texture analysis methods. While the method of adapted filters does not produce very good results, the method of brightness assessment is shown to work satisfactorily. The final part of the thesis describes the implemented tool for the detection of the nerve fiber layer disruptions.

Synthetic aperture radar (SAR) was originally designed as an airborne ground-imaging radar technology. But it has long been desired to also be able to use SAR imaging systems to detect, locate, and track moving ground targets, a process called Ground Moving Target Indication (GMTI). Unfortunately, due to the nature of how SAR works, it is inherently poorly suited to the task of GMTI. SAR only focuses targets and image features that remain stationary during the data collection. A moving ground target therefore does not focus in a conventional SAR image, which complicates the process of performing GMTI with SAR systems. This thesis investigates the feasibility of performing GMTI with single-channel, unsquinted, broadside stripmap SAR despite this inherent limitation. This study focuses solely on the idealized case of direct energy returns from point targets on flat ground, where they and the airborne radar platform all move rectilinearly with constant speed. First, the various aspects of how SAR works, the signal processing used to collect the SAR data, and the backprojection image formation algorithm are explained. The effects of target motion are described and illustrated in actual and simulated SAR images. It is shown how the backprojection (BPJ) algorithm, typically used to image a stationary landscape scene, can also focus on moving targets when the target motion is known a priori. A SAR BPJ ambiguity function is also derived and presented. Next, the time-changing geometry between the airborne radar and a ground target is mathematically analyzed, and it is shown that the slant range between the radar and any ground target, moving or stationary, is a hyperbolic function of time. It is then shown that this hyperbolic range history causes the single-channel SAR GMTI problem to be underdetermined. Finally, a method is then presented for resolving the underdetermined nature of the problem. This is done by constraining a target's GMTI solution using contextual information in the SAR image. Using constraining information, a theoretical way is presented to perform limited GMTI with a single-channel SAR system by using a modified form of the BPJ imaging algorithm, and practical considerations are addressed that complicate the process. Instead of focusing on stationary pixels, this GMTI method uses the BPJ ambiguity function to search for moving targets on a straight path, such as a road, by performing matched filtering on a collection of moving pixels in a position-velocity image space. Nevertheless, it is concluded that for moving point targets, general GMTI with no path constraints is infeasible in practice with a single-channel SAR.

No description available.

No description available.

Research investigating the behavioral and physiological responses of bats to echoes typically includes analysis of acoustic signals from microphones and/or microphone arrays, using time difference of arrival (TDOA) between array elements or the microphones to locate flying bats (azimuth and elevation). This has provided insight into transmission adaptations with respect to target distance, clutter, and interference. Microphones recording transmitted signals and echoes near a stationary bat provide sound pressure as a function of time but no directional information. This dissertation introduces spatial audio techniques to bat biosonar studies as a complementary method to the current TDOA based acoustical study methods. This work proposes a couple of feasible methods based on spatial audio techniques, that both track bats in flight and pinpoint the directions of echoes received by a bat. A spatial audio/soundfield microphone array is introduced to measure sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). The custom-built ultrasonic tetrahedral soundfield microphone consists of four capacitive microphones that were calibrated to match magnitude and phase responses using a transfer function approach. Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing and reproduction of the signals measured by the soundfield microphone. Ambisonics provides syntheses and decompositions of a signal containing its directional properties, using the relationship between the spherical harmonics and the directional properties. As the first proposed method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sources since it decomposes a signal into two dominant planewaves. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. It also reconstructed a smooth flight-path of a bat by accurately estimating its direction at each snapshot of pulse measurements in time. The performance of the system was also assessed using statistical analyses of simulations. A signal model was built to generate microphone capsule responses to a virtual source emitting an LFM signal (3 ms, two harmonics: 40-22 kHz and 80-44 kHz) at an angle of 30° in the simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each case represent the accuracy and precision of the estimations, respectively. Results show lower d (distance between a capsule and the soundfield microphone center) or/and higher SNR (signal-to-noise ratio) are required to achieve higher estimator performance. The Cramer-Rao lower bounds (CRLB) of the estimator are also computed with various d and SNR conditions. The CRLB which is for TDOA based methods does not cover the effects of different incident angles to the capsules and signal delays between the capsules due to a non-zero d, on the estimation system. This shows the CRLB is not a proper tool to assess the estimator performance. For the second proposed method, the matched-filter technique is used instead of HARPEx to build another estimation system. The signal processing algorithm based on Ambisonics and the matched-filter approach reproduces a measured signal in various directions, and computes matched-filter responses of the reproduced signals in time-series. The matched-filter result points a target(s) by the highest filter response. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations of imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The echo sound level is determined using the sonar equation. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The simulation results also appear to recommend an echo level over -3 dB for accurate and precise estimations (below 15% RMSE for all parameters). This work proposes two methods to track bats in flight or/and pinpoint the directions of targets using spatial audio techniques. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are believed to be also useful in improving man-made sonar technology. / Doctor of Philosophy / While bats are one of the most intriguing creatures to the general population, they are also a popular subject of study in various disciplines. Their extraordinary ability to navigate and forage irrespective of clutter using echolocation has gotten attention from many scientists and engineers. Research investigating bats typically includes analysis of acoustic signals from microphones and/or microphone arrays. Using time difference of arrival (TDOA) between the array elements or the microphones is probably the most popular method to locate flying bats (azimuth and elevation). Microphone responses to transmitted signals and echoes near a bat provide sound pressure but no directional information. This dissertation proposes a complementary way to the current TDOA methods, that delivers directional information by introducing spatial audio techniques. This work shows a couple of feasible methods based on spatial audio techniques, that can both track bats in flight and pinpoint the directions of echoes received by a bat. An ultrasonic tetrahedral soundfield microphone is introduced as a measurement tool for sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing of the signals measured by the soundfield microphone. Ambisonics also reproduces a measured signal containing its directional properties. As the first method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sound sources. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. The performance of the system was also assessed using statistical analyses of simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each simulation case represent the accuracy and precision of the estimations, respectively. Results show shorter distance between a capsule and the soundfield microphone center, or/and higher SNR (signal-to-noise ratio) are required to achieve higher performance. For the second method, the matched-filter technique is used to build another estimation system. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using matched-filter responses and sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are also believed to be useful in improving sonar technology.

The study of the spatial aspects of multipath in wireless communications environments is an increasingly important addition to the study of the temporal aspects in the search for ways to increase the utilization of the available wireless channel capacity. Traditionally, multipath has been viewed as an encumbrance in wireless communications, two of the major impairments being signal fading and intersymbol interference. However, recently the potential advantages of the diversity offered by multipath rich environments in multiuser communications have been recognised. Space time coding, for example, is a recent technique which relies on a rich scattering environment to create many practically uncorrelated signal transmission channels. Most often, statistical models have been used to describe the multipath environments in such applications. This approach has met with reasonable success but is limited when the statistical nature of a field is not easily determined or is not readily described by a known distribution.¶ Our primary aim in this thesis is to probe further into the nature of multipath environments in order to gain a greater understanding of their characteristics and diversity potential. We highlight the shortcomings of beamforming in a multipath multiuser access environment. We show that the ability of a beamformer to resolve two or more signals in angle directly limits its achievable capacity.¶ We test the probity of multipath as a source of spatial diversity, the limiting case of which is co-located users. We introduce the concept of separability to define the fundamental limits of a receiver to extract the signal of a desired user from interfering users’ signals and noise. We consider the separability performances of the minimum mean square error (MMSE), decorrelating (DEC) and matched filter (MF) detectors as we bring the positions of a desired and an interfering user closer together. We show that both the MMSE and DEC detectors are able to achieve acceptable levels of separability with the users as close as λ/10.¶ In seeking a better understanding of the nature of multipath fields themselves, we take two approaches. In the first we take a path oriented approach. The effects on the variation of the field power of the relative values of parameters such as amplitude and propagation direction are considered for a two path field. The results are applied to a theoretical analysis of the behaviour of linear detectors in multipath fields. This approach is insightful for fields with small numbers of multipaths, but quickly becomes mathematically complex.¶ In a more general approach, we take a field oriented view, seeking to quantify the complexity of arbitrary fields. We find that a multipath field has an intrinsic dimensionality of (πe)R/λ≈8.54R/λ, for a field in a two dimensional circular region, increasing only linearly with the radius R of the region. This result implies that there is no such thing as an arbitrarily complicated multipath field. That is, a field generated by any number of nearfield and farfield, specular and diffuse multipath reflections is no more complicated than a field generated by a limited number of plane waves. As such, there are limits on how rich multipath can be. This result has significant implications including means: i) to determine a parsimonious parameterization for arbitrary multipath fields and ii) of synthesizing arbitrary multipath fields with arbitrarily located nearfield or farfield, spatially discrete or continuous sources. The theoretical results are corroborated by examples of multipath field analysis and synthesis.

Ocular fundus image can provide information on pathological changes caused by local ocular diseases and early signs of certain systemic diseases. Automated analysis and interpretation of fundus images has become a necessary and important diagnostic procedure in ophthalmology. Among the features in ocular fundus image are the optic disc, fovea (central vision area), lesions, and retinal vessels. These features are useful in revealing the states of diseases in the form of measurable abnormalities such as length of diameter, change in color, and degree of tortuosity in the vessels. In addition, retinal vessels can also serve as landmarks for image-guided laser treatment of choroidal neovascularization. Thus, reliable methods for blood vessel detection that preserve various vessel measurements are needed. In this paper, we will examine the pathological issues in the analysis of retinal vessels in digital fundus images and give a survey of current image processing methods for extracting vessels in retinal images with a view to categorize them and highlight their differences and similarities. We have also implemented two major approaches using matched filter and mathematical morphology respectively and compared their performances. Some prospective research directions are identified. / Singapore-MIT Alliance (SMA)

The Nicoya Peninsula of Costa Rica is unusually close to the Middle America Trench (MAT), such that interface locking along the megathrust is observable under land. Here, rapid convergence between the downgoing Cocos and the over-riding Caribbean plates at ~85mm/yr allows for observable high strain rates, frequent large earthquakes and ongoing micro-seismicity. By taking advantage of this ideal location, a network of 20 on-land broadband seismometers was established in cooperation between UC Santa Cruz, Georgia Tech, and OVSICORI, with most stations operating since 2008. To evaluate what seismicity tells us about the ongoing state of coupling along the interface, we must consistently evaluate the location and magnitude of ongoing micro- seismicity. Because of large levels of anthropogenic, biologic, and coastal noise, automatic detection of earthquakes remains problematic in this region. Thus, we resorted to detailed manual investigation of earthquake phases. So far, we have detected nearly 7,000 earthquakes below or near Nicoya between February and August 2009. From these events we evaluate the fine-scale frequency-magnitude distribution (FMD) along the subduction megathrust. The results from this b-value mapping‟ are compared with an earlier study of the seismicity 9 years prior. In addition, we evaluate them relative to the latest geodetically derived locking. Preliminary comparisons of spatial and temporal variations of the b-values will be reported here. Because ongoing manual detection of earthquakes is extremely laborious and some events might be easily neglected, we are implementing a match-filter detection algorithm to search for new events from the continuous seismic data. This new approach has been previously successful in identifying aftershocks of the 2004 Parkfield earthquake. To do so, we use the waveforms of 858 analyst-detected events as templates to search for similarly repeating events during the same periods that have been manually detected. Preliminary results on the effectiveness of this technique are reported. The overall goal of this research is to evaluate the evolution of stress along the megathrust that may indicate the location and magnitude of potentially large future earthquakes. To do so, I make the comparison between the FMD and the interface locking. Only positive correlations are observed in the Nicoya region. The result is different from the one derived from the seismic data set that was recorded 9 years before our data. Therefore, to substantiate the causes for the different relationships between the b-value and the coupling degree, we need additional data with more reliable magnitudes.

Spectrum sensing is an important aspect of cognitive radio systems. In order to efficiently utilize the spectrum, the role of spectrum sensing is essential in cognitive radio networks. The transmitter detection based techniques: energy detection, cyclostationary feature detection, and matched filter detection, is most commonly used for the spectrum sensing. The Energy detection technique is implemented in the 2-hop cooperative cognitive radio network in which Orthogonal Space Time Block Coding (OSTBC) is applied with the Decode and Forward (DF) protocol at the cognitive relays. The Energy detection technique is simplest and gives good results at the higher Signal to Noise Ratio (SNR) values. However, at the low SNR values its performance degrades. Moreover, each transmitter detection technique has a SNR threshold, below which it fails to work robustly. This thesis aims to find the most reliable and accurate spectrum sensing technique in the 2-hop cooperative cognitive radio network. Using Matlab simulations, a comparative analysis of three transmitter detection techniques has been made in terms of higher probability of detection. In order to remove the shortcomings faced by all the three techniques, the Fuzzy-combined logic sensing approach is also implemented and compared with transmitter detection techniques. / Atti Ur Rehman (atti.rehmman@gmail.com) ph: +358-440458080

This thesis studies the design and implementation of an ultra-sonic water depth sounder. The depth sounder is implemented in a hand-held smart console used by divers. Since the idea of echo sounding is to measure the flight time between transmitting the signal and receiving the echo, the main challenge of this task is to find a time-of-flight (ToF) estimation for a signal in noise. It should be suitable for this specific application and robust when implemented in the device. The thesis contains an investigation of suitable ToF methods. More detailed evaluations of the matched filter, also known as the correlation method, and the linear phase approach are done. Aspects like pulse frequency and duration, speed of sound in water and underwater noise are taken into account. The ToF-methods are evaluated through simulation and experiments. The matched filter approach is found suitable based on these simulations and tests with signals recorded by the console. This verification leads to the implementation of the algorithm on the device. The algorithm is tested in real time, the results are evaluated and improvements suggested. / Denna rapport behandlar skattning av vattendjup med hjälp av ultraljudspulser och implementation av detta. Djupmätaren implementeras i en handhållen dykarkonsoll. Eftersom grundidén i ekolodning är att mäta tiden mellan att pulsen skickas iväg och att ekot tas emot är en stor del av utmaningen att hitta en lämplig metod för att skatta flykttiden för en signal i brus. Metoden ska passa för detta användingsområde och vara robust. Rapporten tar upp tidigare forskning gjord inom flykttidsestimering. De metoder som utvärderas för implementation är det matchade filtret, också kallad korrelationsmetoden, och linjär fas-metoden. Andra aspekter som avvägs och utreds är pulsfrekvens och pulsvaraktighet, ljudets hastighet och brus under vattnet. Metoderna för att skatta flykttid utvärderas genom simuleringar. Det matchade filtret bedöms vara lämpligt baserat på dessa simuleringar och experiment med data inspelad med konsollen. Denna verifikation leder till att algoritmen implementeras på konsollen. Den implementerade algoritmen testas i realtid, resultaten utvärderas och förbättringar föreslås.