Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / Ground penetrating radar is currently proving itself as an invaluable tool for the prediction of geological structures in the mining environment. Borehole radar is a specific application of this technology, useful in the prediction of the course of rock layers between boreholes ahead of mining. Establishing borehole radar as an industrial tool requires a system that is more userfriendly and easier to deploy than the bi-static radar systems currently available. The development of a monostatic radar system is discussed. It is an ultra wide band, pulse radar system that operates at VHF (10-100 MHz). The system is required to detect reflections from objects 5 m away and further. This translates to a total electromagnetic propagation time of approximately 100 ns or more in the rock medium. The complete design process - from fundamental requirements, through a conceptual design, to a final electronic circuit - is discussed. The design is also built, measured in the laboratory and taken for initial field trails. The following aspects are considered: • Pulse generation by means of an original circuit based on power MOSFETs. • Routing of the transmitted- and received signal between transmitter, receiver and antenna. This is done using a novel, active quasi circulator topology. • Methods of increasing isolation (actively and passively) between transmitter and receiver. • Interfacing with a specific receiver, antenna and data acquisition system.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2001. / Over the last decade, as the mining industry of South Africa is moving to ever deeper mines, the borehole radar is becoming an increasingly important field of research. In December 2000, Burger completed his thesis on Electromagnetic Modelling of a Borehole Radar Environment with the FDTD Method. The goal of this thesis is to extend the research presented in Burger's thesis, considering how more advanced modelling techniques can be applied to the FDTD analysis of the borehole radar environment. Some of these techniques include implementation of dispersive and conductive material models, and developing Uniaxial Perfectly Matched Layer boundary conditions for matching these model. Simulations were run to measure the performance of these boundary condition for matching dispersive and conductive materials. The thesis also includes the implementation of a parallel version of the FDTD algorithm using the Message Passing Interface library. Finally several realistic borehole models where simulated to test the accuracy of the code and to show how the code can be used to model real world problems.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2002. / An efficient radiating strucllire was needed for borehole pulsed radar applications in the 10-100 MHz frequency band. Both resistively loaded and insulated wire antennas were investigated and an active antenna is proposed as a fmal solution. The study proceeded from the characterization of the origin of radiation on a conductive dipole wire antenna when excited with a transient. Different radiation mechanisms were identified when the antenna was excited with a current or voltage source. The wire antenna in insulated surroundings was modelled using transmission line theory to simulate the antenna in the borehole environment. The transmission line model proved to be useful for investigating conducting and resistively loaded antennas for the dimensions associated with borehole surveys. From the modelling results, it became apparent that the asymmetric resistively loaded antenna might provide the best practical solution. This antenna displays reasonably stable input impedance and low far-field variations for different theta angles across the desired frequency band. Different percentage Wu-King resistive profiles were studied to show that a 50% reduction in the normal Wu-King resistor values will add only a little ringing but have better amplitude response than the 100% Wu-King loading. The asymmetric resistively loaded antenna has better sensitivity to receiving transients when combined with a high impedance source load than when symmetrically loading the antenna. An active antenna incorporating the asymmetric resistively loaded antenna and a low noise current feedback front end amplifier was built and measured in an air environment. The results show that the active antenna has a flat transfer function and reacts as a wide band electric field probe with better resolution than in the conventional 50 Q loaded case

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / Modern technology is reducing the cost of electronic devices. The speed of these devices and their reliability is improving. They can be used to implement low cost systems without compromising performance. The design of two linear FM-CW radars using direct digital synthesis (DDS) is discussed. The use of the DDS simplifies the generation of the linear frequency sweep that is required. The systems are analysed mathematically and by computer simulation, before being implemented in hardware. The first system is to be used to measure the position of pedestrians, at short range. The other system is to be used as a ground penetrating radar to measure the depth of objects located close to the surface. The design of a micro-strip patch array with a corporate feed network is also discussed. The antenna is constructed, measured and used in the pedestrian measurement system. Both systems are tested and used for initial radar measurements and the results obtained are presented.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The successful operation of a pulsed monostatic borehole radar system requires that cur- rent on the antenna due to transmitter pulses subsides quickly. Deterioration of the radar antenna feed-point current settling times when deployed in water-¯lled boreholes showed that the radar system's performance is highly environmentally sensitive. Electromagnetic models are used to investigate this e®ect, since measuring the feed-point and radiative characteristics of an insulated antenna deployed in a borehole is practically impossible at present. A transmission line model for insulated antennas is utilized to model the borehole radar antenna in electrically dense media. Predicted input impedance values however do not correspond well to those from numerical ¯eld simulation software and the model is shown to be inadequate for modelling insulated antennas in environments of low conductivity. Radiated ¯eld results are however found to be accurate. A study of the feed-point and radiative characteristics of the borehole radar antenna in a range of di®erent borehole environment is performed using electromagnetic ¯eld simulation software. Results con¯rm that the borehole radar antenna has longer feed- point current settling times and degraded radiated pulse waveforms when deployed in water-¯lled boreholes. Simple lumped element networks with driving-port impedances approximately equal to antenna input impedances are synthesized from simulated input impedance results for a range of borehole environments. This allows diagnostics on the radar system to be performed in the laboratory, with the antenna load appearing as if the system were deployed in a borehole. The use of an antenna with distributed resistive and capacitive loading is proposed as a modi¯cation that would result in improved feed-point characteristics in water-¯lled boreholes. Results from simulations and experiments are presented that con¯rm that the new antenna design substantially reduces feed-point current settling times after the transmitter ¯res.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2000. / South Africa has an immensely rich reserve of minerals which still has to be exploited. The problem with these reserves is that they exist in reefs where the mining environment is extremely hazardous, and where mining is very expensive. These are only two of the reasons why borehole radar has recently become a very important field of research in the South African mining industry. These radars have to operate in rock, which has a number of electromagnetically problematic characteristics, which greatly complicate modelling and design of suitable radars. The goal of this project is to demonstrate how the Finite Difference Time Domain (FDTD) method may be used to electromagnetically model and simulate borehole radars and subterranean environments.

<p>Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing.</p><p>A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates.</p><p>The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären.</p><p>Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.</p>

The Wanganui-Wilberg landslide lies between Hokitika and Franz Josef townships, at the entrance of Harihari, on the true left bank of the Wanganui River, by State Highway 6. This apparently co-seismic landslide belongs to the class of events called rock avalanches - powerful destructive agents (Keefer, 1984) in the landscape. Other rock avalanches are numerous (Whitehouse, 1983), and widespread over the Southern Alps of New Zealand, and many appear to be co-seismic. De Mets et al. (1994) used the model NUVEL-1A to characterize the motion of the Alpine fault: 37 mm/year at an azimuth of 071° for the strike-slip and a dip-slip of 10 mm/year normal to the strike direction. Although linear when seen from the sky, the detailed morphology of the fault is more complex, called en échelon (Norris and Cooper, 1997). It exhibits metamorphosed schists (mylonite series) in its hanging wall (McCahon, 2007; Korup, 2004). Earthquakes on the Alpine fault have a recurrence time of c. 200-300 years and a probability of occurrence within 100 years of 88% (Rhoades and Van Dissen, 2002). Thought to have been triggered by the AD1220 event (determined by dendrochronology), the Wanganui-Wilberg rock avalanche deposit represents only 20% of its original volume, which was c. 33 million cubic metres. The deposit probably dammed the Wanganui River and, as a result, created a small and short-lived lake upstream. The next earthquake capable of triggering such events is likely to occur fairly soon (Yetton, 1998). Knowledge of historic catastrophic events such as the Wanganui-Wilberg rock avalanche is of crucial importance in the development of future hazard and management plans.

The “green agenda” combined with highway congestion has accelerated the demand for increased freight and passenger travel on the world’s railways. These increases have driven demand for more efficient and rapid investigation of trackbed ballast. Network Rail and other rail infrastructure operators spend significant financial sums on inspecting, tamping, adjusting, cleaning, and replacing trackbed ballast. Such maintenance is often to the detriment of normal network operation. Industry requires a method of ballast evaluation that is non-intrusive, cheap, can appraise long stretches of track in a short period of time, and give a fingerprinting result from which time-to-maintenance can be calculated and planned. Thus, the aim was to develop evaluation methods using non-destructive testing techniques. A 10-year old full-scale trackbed composed of variously fouled ballast was re-visited and used for experimentation. The condition of the ballast was calculated using the Ionescu Fouling Index. Earlier research at the University of Edinburgh enabled researchers worldwide to characterise ballast using ground penetrating radar (GPR). This research was repeated, validated and taken forward in a series of GPR experiments on the trackbed using a range of antennas from 500MHz to 2.6GHz. New "scatter" metrics were developed to determine ballast condition from the GPR waveforms. These metrics were then used to predict the Ionescu Fouling Index with a correlation coefficient greater than 0.9. One of the current approaches to evaluating the stiffness of railway ballast is to use a Falling Weight Deflectometer (FWD). The viability of using a Prima 100 mini-FWD on railways to measure stiffness was determined and deemed to be ineffective on ballast. The applicability of the impulse response technique on railways was determined. An instrumented hammer was used to excite the ballast, with a geophone measuring the response. The Frequency Response Function of this was successfully correlated with the Ionescu Fouling Index with a correlation coefficient also greater than 0.9. Finally, using GPR data and measured stiffness data collected by Banverket, Sweden, a numerical model to successfully relate radar responses to stiffness was developed.

This thesis presents a novel antenna structure that satisfies the challenging requirements of an air coupled high speed ground penetrating radar (GPR). The desired GPR system is to achieve high spatial resolution and accurate inspection results while scanning at relatively high speed for highway pavement and bridge deck inspection. This work utilizes the Ultra Wide Band (UWB) antenna design to achieve both physical and electrical requirements imposed. The design procedure starts with a short survey to discuss typical UWB antennas used for GPR applications, and various tradeoffs of each type specifically when used for Air Coupled GPR applications. Our structure anatomy is presented, followed by a theory introduction that mainly focuses on achieving good impedance matching throughout the proposed antenna structure. A proof-of-concept MATLAB model is created to evaluate the preliminary physical dimensions that can achieve minimum reflections at antenna's feed point. These dimensions are then used in SolidWorks to create a 3D model that is imported later in HFSS to obtain accurate electromagnetic characteristics. Furthermore, fine tunings are performed to the antenna structure to optimize both gain and impedance matching. The SolidWorks 3-D structural model is finally used for antenna fabrication. The measurements recorded from the field experiments using the prototypes manufactured are compared to the simulation results confirming our initial findings. Both measurements and simulation results demonstrated very small reflection loss across the 700 MHz ~ 6 GHz frequency band with a very high directed gain and radiation efficiency.