OpenUCT :: Browsing by Author "Wilkinson, Andrew John"

Browsing by Author "Wilkinson, Andrew John"

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Open Access
Array-based GPR SAR simulation and image reconstruction
(2002) Desai, Amresh S; Wilkinson, Andrew John
Subsurface object detection has mainly been carried out using conventional ground penetrating radar (OPR) techniques, which use a single receiving antenna from which a number of range profiles (known as ""A Scope"" images) are assembled to form a two-dimensional data field (known as a ""B Scope"" image). These OPR systems have difficulties with high clutter level, surface reflections, limited ground penetration and the required fine resolution. The resolution in the across track and along track directions is limited by the physical aperture in these directions. This project aims at developing a SAR imaging technique, which uses a single transmitting/receiving antenna to synthesize a two-dimensional planar aperture. Thus a three-dimensional reflectivity image of a scene is generated. The resolution in the across track and along track directions is achieved via a SAR aperture synthesis technique. The depth/range resolution is achieved via the transmission of narrowband Stepped Frequency Continuous Wave (SFCW) signals.
Open Access
An automated camera tracking system for single bubble velocity profiling
(2007) Reid, Stewart Charlton; Wilkinson, Andrew John; Harris, Martin
An apparatus has been developed for the automated velocity profiling of single bubbles in aqueous solutions. Using a mobile IEEE 1394 camera and a control algorithm, the apparatus can automatically track a bubble as it rises in a Perspex column. The resulting video footage is then post-processed to obtain the velocity profile of the bubble, amongst other data. This apparatus is to be used in research relevant to the minerals processing industry. The software components were developed in Matlab and Microsoft Visual C++ and implemented in Visual C++. The methodology used to develop the apparatus is presented, and typical examples of velocity profiles are given. An analysis to determine the effect of error of parrallax is also performed.
Open Access
Calibration and image formation in the ABACUS sonar system
(2005) Ng, Ferdinand; Wilkinson, Andrew John
Includes bibliographical references (leaves 138-139).
Open Access
Design and characterization of the measurement electronics for a magnetic induction tomography imaging system
(2008) Wei, Hsin Yu; Wilkinson, Andrew John
A data acquisition transceiver circuit for magnetic induction tomography (MIT) has been developed. MIT is a type of tomography technique that is sensitive to the conductivity of objects, and which can be used in both industrial and biomedical applications. A detailed design process of the MIT transceiver board and the coupling sensor coils are presented in this dissertation. For the purpose of testing the designed hardware, a three channel MIT measuring system was assembled, and various experiments were run on the system. Several different samples with high conductivity (metal sheets) or low conductivity (saline solution) were used to test the performance of the designed transceiver. Its suitability for being applied to the actual MIT system could then be assessed. The noise characteristics and stability of the system were also characterised. A complete eight channel MIT measurement system is presently being assembled based on the prototypes presented in the dissertation. The results obtained from the experiments are very promising. The construction of the multi-channel MIT system and the image reconstruction can confidently be expected in future development.
Open Access
Design and implementation of a parallel registration algorithm for SAR images
(2001) Fadiran, Oladipo O; Inggs, Michael; Wilkinson, Andrew John
Registration of two or more images of the same scene is an important step in image processing that seeks to extract information not obtainable from one of the images in question. This process is required in many Engineering, Scientific and Medical applications. The accuracy of this step is crucial to the reliability of subsequent image processing and or decisions made on its basis. The huge size of the date to be processed, the speed at which the processing is required and the accuracy requirements necessitates a quick, efficient, robust and in some respects automatic program which efficiently harnesses available computing resources. This is the object of this project - the design of an image registration algorithm with a bias for SAR/InSAR applications but also applicable for other registration purposes, implemented on a parallel cluster of computing nodes.
Open Access
The detection and tracking of portable GSM handset using a 5-element circular array
(2005) Lambert-Porter, Jonathan; Wilkinson, Andrew John
Direction Finding (OF) is a process that involves estimating the directions of the arrival for propagating wavefronts impinging on an antenna array from arbitrary directions relative to that antenna array. By understanding how the signals captured relate to the geometry of the OF antenna, one can separate out these signals spatially, and provide their directions of arrival with some degree of certainty. GSM, the Global System for Mobile Communications is a mobile digital communications system which has rapidly gained acceptance on a global scale since the early 1990s. Because the communications standard is made use of throughout the world today, it would be desirable to investigate the feasibility of the detection and tracking of such signals as an extension for OF platforms that are used by monitoring authorities such as the police or service providers. This thesis presents and discusses the implications of detecting and tracking GSM mobile handsets. Because the thesis was commissioned by a company that already manufactures broadband surveillance equipment with a particular OF implementation, the thesis approaches the problem with their specific implementation in mind assessing its competency in detecting and tracking GSM mobile phones. To understand the nature of GSM, a simulator was developed to convey information about the structure of the datasets that would be recorded in the field, and is compared to datasets captured with the OF equipment. Conclusions are drawn from the recordings, and recommendations for future work in this field are discussed.
Open Access
DSSS detection and direction finding methods for a DSP-based small aperture DF system
(2005) Durrett, David; Wilkinson, Andrew John
This dissertation discusses an investigation into methods for detection and direction finding of direct-sequence spread-spectrum signals (DSSS), appropriate for a particular DSP-based direction finding platform. Relevant details on DSSS and radio direction finding are presented. These are used as the theorectical basis for the developemtn of a software-bases simulator fo the direction finding platform, which in turn is used to develop and investigate various algorithms. The algorithms included use a least-squares model-based approach. The results of experiments run on simulated data indicate that this approach has merit for the automated detection and direction finding of DSSS signals. the least-squares algorithm applied to a single capture of power-spectrum data is shown to perform comparably with human experts.
Open Access
Eddy current detection of fatigue cracks in drill pipes
(2012) Molteno, Matthew Robert; Tait, Robert B; Wilkinson, Andrew John; Becker, TH
The Vertical Marine Mining technique is a lucrative method used by De Beers to recover bottom lying diamonds from the seabed, mainly off the coast of Namibia. The method employs a 200m length pipe-drilling structure rotated from the surface and acting as a conduit through which the disturbed sediment is transported to the surface for processing. However, cyclic operating stresses combined with corrosion have tended to cause circumferential fatigue cracks to develop on the outside surface of the drill pipe and propagate inwards. As no early warning system exists, these cracks propagate undetected until failure occurs. High operational costs and losses associated with down time, provide a strong motivation for a system to detect fatigue cracking prior to failure, especially given that fatigue crack growth rate and fatigue lifetimes can be estimated using Fracture Mechanics principles. Therefore what is required is an early warning of fatigue crack initiation with non-destructive testing (NOT). The eddy current method is an ideal NDT technique as it does not require contact with the test surface and is highly sensitive to fatigue cracks .. However, this method is generally only sensitive to surface and near surface defects. This proves to be a major limitation - the external drill pipe surface is obstructed by flanges and fittings such that continuous inspection of the external surface would be impossible. Therefore two specialised eddy current methods to allow the detection of external fatigue cracks from inside the drill pipe were reviewed, namely: Pulsed Eddy Current (PEC) and Remote Field Eddy Current (RFEC). It was found that unlike PEC, RFEC is highly sensitive to external circumferential planar defects in ferrous pipes. This, above all, highlighted the suitability of RFEC for drill pipe inspection.
Open Access
Finite element method using vector finite elements applied to eddy current problems
(2011) Adams, Leila; Reddy, B Daya; Wilkinson, Andrew John
Vector fields found in electromagnetics are fundamentally different to vector fields found in other research areas such as structural mechanics. Electromagnetic vector fields possess different physical behaviour patterns and different properties in comparison to the other vector fields and therein lies the necessity of the development of a finite element which would be able to cater for these differences . The vector finite element was then developed and used within the finite element method specifically for the approximation of electromagnetic problems. This dissertation investigates the partial differential equation that governs eddy current behaviour. A finite element algorithm is coded and used to solve this partial differential equation and produce vector field simulations for fundamental eddy current problems.
Open Access
Imaging and counting of targets with a high resolution multibeam sonar
(2010) Mussai, Kushwant; Wilkinson, Andrew John
This dissertation pertains to the development of an imaging and counting system for a high resolution multibeam sonar. A mathematical model for the operation of the multibeam sonar is derived. The computational model is developed into a simulator for the multibeam sonar in MATLAB.
Open Access
Implementation and analysis of a bayesian approach to topographic reconstruction with multiple antenna synthetic aperture radar interferometry
(2001) Ashok, Amit; Wilkinson, Andrew John
Multiple-antenna synthetic aperture radar (SAR) interferometry is a single-pass interferometry technique for topographic mapping. A Bayesian model-base approach to topographic recontruction with multiple-antenna SAR interferomety, proposed by Dr. A. J. Wilkinson, is implemented and analysed in this dissertation.
Open Access
Low frequency, in-situ vibrating sample magnetometer : electrical systems and control software design
(2006) Kelly, Simon Gilbert Daneel; Claeys, Michael; Wilkinson, Andrew John
A low frequency vibrating sample magnetometer has been built to measure the in-situ properties of ferromagnetic catalysts. The instrument allows measurements to be taken during an experimental catalyst test run (in-situ). The vibration is performed by a motor crank arrangement frequency of 2 Hz. The software designed to control the instrument and the reaction was written in Lab View which enabled a rapid prototyping approach. This thesis focuses on the software and electrical systems of the setup. Results of research conducted using this system are published separately however this document shows the relationship between the magnetic saturation and remnance and the mass of ferromagnetic material present in the reference material as well as the effect of temperature on this material.
Open Access
A micropower ultra-wideband RADAR profiling system
(2006) Chang, Yu-Ming Alvin; Wilkinson, Andrew John
Ultra-wideband (UWB) technology can be used in many applications, including radar, communications, and geo-location. In this dissertation, UWB technology is utilized to directly generate sub-nanosecond pulses with more than 1 GHz bandwidth to implement radio detection and ranging (RADAR) for distances up to 5 or 10 metres. This low-cost, rnicropower radiation, short-range radar profiling system consists of the radar circuitry, the data-acquisition subsystem, the signal processing subsystem and the graphical user interface. Additional modules such as a front-end RF amplifier can be integrated into the complete system. The performance was analysed, particularly the circuitry performance and system performance. The capability for detecting metal objects was demonstrated, along with discussion of preliminary "seeing-through-wall" experiments.
Open Access
Multiple transducer synthetic aperture sonar interferometry for emulating SAR interferometry
(2007) Lewitton, Neil; Wilkinson, Andrew John
Multiple transducer single-pass synthetic aperture sonar interferometry in air is a technique that can emulate topographic mapping techniques that have not been implemented using radar or that are relatively expensive and difficult to obtain in practice for the radar engineer who wishes to test algorithms using suitable data. This dissertation describes the implementation of a 40 kHz synthetic aperture sonar for acquiring radar-like data. Investigations into beamformed synthetic aperture sonar images as well as multiple-baseline sonar interferons resulting from imaging a variety of scenes are presented in this thesis.
Open Access
On a wildlife tracking and telemetry system : a wireless network approach
(2008) Markham, Andrew; Wilkinson, Andrew John
Motivated by the diversity of animals, a hybrid wildlife tracking system, EcoLocate, is proposed, with lightweight VHF-like tags and high performance GPS enabled tags, bound by a common wireless network design. Tags transfer information amongst one another in a multi-hop store-and-forward fashion, and can also monitor the presence of one another, enabling social behaviour studies to be conducted. Information can be gathered from any sensor variable of interest (such as temperature, water level, activity and so on) and forwarded through the network, thus leading to more effective game reserve monitoring. Six classes of tracking tags are presented, varying in weight and functionality, but derived from a common set of code, which facilitates modular tag design and deployment. The link between the tags means that tags can dynamically choose their class based on their remaining energy, prolonging lifetime in the network at the cost of a reduction in function. Lightweight, low functionality tags (that can be placed on small animals) use the capabilities of heavier, high functionality devices (placed on larger animals) to transfer their information. EcoLocate is a modular approach to animal tracking and sensing and it is shown how the same common technology can be used for diverse studies, from simple VHF-like activity research to full social and behavioural research using wireless networks to relay data to the end user. The network is not restricted to only tracking animals – environmental variables, people and vehicles can all be monitored, allowing for rich wildlife tracking studies.
Open Access
Rot detection in wooden poles using electrical impedance tomography
(2006) Sattar, Fayaaz Ali; Wilkinson, Andrew John
The proposal for this dissertation was to develop a nondestructive method of testing wooden utility poles for rot and termite damage. The nondestructive method that was chosen for this project was that of electrical impedance tomography in which an image of the permittivity in a cross section would be created from impedance measurements made between electrodes attached to the boundary of the pole.
Open Access
Signal and image processing for electrical resistance tomography
(2002) Naidoo, Thoneshan; Wilkinson, Andrew John
Electrical Resistance Tomography (ERT) is in essence an imaging technique.In ERT current is injected into and removed from a vessel via paired electrodes. The resulting voltage measurements are captured between the remaining electrode pairs. The principle behind ERT is to map these boundary voltages into a conductivity distribution that represents the domain of the vessel. The author has coded a versatile reconstruction algorithm based on the Newton-Raphson algorithm. The knowledge gained by implementing the algorithm is documented in this thesis. The literature covers the basic aspects of two-dimensional and three-dimensional ERT. It is hoped that this thesis will create a greater interest in ERT at the University of Cape Town (UCT) and also act as a building block for further developments. The thesis starts by presenting the basic concepts of ERT such as the underlying equations, the various boundary measurement strategies and a global perspective of ERT. The nature of this thesis is on software reconstruction and in so doing information on the incorporation of the Finite Element Method in ERT is provided. The thesis goes on to provide information about the reconstruction algorithms, which incorporate regularization. A novel aspect of this thesis involves the calibration and pre-processing of boundary voltages. These concepts were conceptualised and developed during formal communications with Dr. Wilkinson (2002) and Randal (2002). The calibration schemes try to eliminate the potential errors that can arise inthe captured data thus allowing for a clearer image to be reconstructed, Electrical Resistance Tomography. This thesis further develops the idea of parallelizing the Newton-Raphson algorithm to increase the speed of the algorithm. Various schemes on how this parallelization is achievable are put forward.
Open Access
Super-resolution phased array sonar imaging
(2005) Eccles, Etienne Frederick; Wilkinson, Andrew John
This dissertation applies super-resolution signal processing alogrithms to image reconstruction for a multibeam phased array sonar. A generic data model for phased array sonars is first developed and is used to derive conventional signal processing concepts for image reconstruction which are necessary for the implementation of the super-resolution algorithms. The most well studied super-resolution algorithms in the literature are reviewed and evaluated for their application to sonar imaging with a focus on rubustness to additive noise and model errors and to their computaitonal efficiency. The algorithms are evaluated on borht by simulation and real data from the ABACUS sonar, an example of a phased array sonar. An efficienct sub-imaging algorithm for implementing super-resuolution imaging for the ABAcus is developed and is compared to the conventional image reconstruction algorithm. Super-resolution inter-ferometric imaging is also developed and evaluated. The Minimum Variance filter is found to be the most suitable algorithm for super-resolution imaging for this type of sonar.
Open Access
Synthetic aperture sonar imaging using compressive sensing and an ultrasound transducer array
(2013) Jideani, Josiah Chimnanu; Wilkinson, Andrew John
Compressive sensing (CS) also known as compressive sampling is a technique used to reconstruct or recover the full-length of a signal with only a few non-adaptive measurements. It is a model-based framework for data acquisition and signal recovery that is based on the principles of sparsity and incoherence. Sparsity refers to the fact that a signal of interest is sparse and compressible and can be represented concisely in a given basis. Incoherence refers to the idea that a sparse signal is spread out in the basis in which it is acquired. A prominent area of application of this technique is tomography such as magnetic resonance imaging (MRI), X-ray CT, and in 3D synthetic aperture radar (SAR) imaging for reconstructing the elevation reflectivity profile. This dissertation describes the investigation into three-dimensional (3D) synthetic aperture sonar (SAS) imaging in air using compressive sampling. In the work, a 3D SAS simulator using compressive sampling was implemented in MATLAB. The effect of the number of baselines as well as the super-resolution factor on the final image was also investigated. A real 3D SAS imaging system was designed and the results were compared with the results of the simulated system. In the system, the SAS data was captured in a multiple transducer (baseline), single-pass configuration with 15 ultrasonic receivers and a single ultrasonic transmitter that operate at about 40 kHz. Signal conditioning circuits for the transmit and receive signals were built on pieces of veroboard. A PC which ran a custom designed LabVIEW virtual instrument (VI) was used for the synchronous transmission and reception of ultrasonic signals, and the control of the SAS platform via the NI PCI-6070E data acquisition card. The received 2D SAS signal from each transducer was focused using the accelerated chirp scaling algorithm. Compressive sensing was applied to a stack of focused 2D SAS images to achieve focusing in the elevation direction. 3D scenes containing point targets were successfully reconstructed in 3D SAS images using this technique with 9 baselines and a super-resolution factor of 3. The results confirm that CS is an effective technique in super-resolution tomographic reconstructions provided the baseline span is small compared to the imaging range. Also for reliable reconstructions, the appropriate super-resolution factor and number of acquisitions must be chosen.
Open Access
Three applications of satellite borne repeat pass SAR interferometry in Southern Africa
(2000) Doyle, Gavin S; Wilkinson, Andrew John; Hartnady, Chris; Inggs, Michael
Synthetic Aperture Rada Interferometry (InSAR) is a relatively new remote sensing technique, which can be used to derive precise topographic height change information over large areas. It is a technique which has been used in a great variety of situations, from the topographic mapping of Venus to the detection of subtle ground deformations due to earthquakes and mining subsidence. The InSAR technique involves using the phase information inherent in radar images to extract elevation and elevation change information. The process requires very careful co-registration of a pair of complex images of the same scene, followed by the multiplication of the one image by the complex conjugate of the other. In this manner, a phase difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface. An extension to the InSAR technique, is that of difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface.