Master of Science in Engineering, Youngstown State University, 2020, Department of Civil/Environmental and Chemical Engineering

Concrete structures experience different kinds of mechanical loadings, physical and chemical interactions, and aggressive environmental attacks during their lifetime. It is crucial to perform regular monitoring of these structures to ensure their functionality and to provide public safety. Furthermore, the selection of the most reliable testing methods for the overall condition assessment is also important. Thus, this research is focused on finding the structural condition of a precast deck section in the Lincoln Parking Deck at YSU using a Ground Penetrating Radar (GPR). The main objective of using a GPR is to identify its capability for the condition assessment of concrete structures. A GSSI SIR 4000 mainframe system with a 1.6 GHz antenna was deployed for the radar survey. Small concrete slabs were prepared in the laboratory with fresh and corroded reinforcing bars. Corrosion in reinforcing bars was artificially developed using a Q-Fog cyclic corrosion tester. The GPR response from the slab, having the fresh rebar at varying depth, indicated that the reflection amplitude obtained from the scan of the rebar target decreases with increasing depth. Likewise, comparing GPR B-scan from the fresh and the corroded rebar indicated a qualitative and a quantitative difference in the result. The qualitative difference was observed as the hyperbolas (rebar reflections) showed weakening smoothness, brightness, and visibility with the increase in the amount of corrosion. In the same way, the quantitative difference was observed as there was a decreasing trend in the reflection amplitudes of each point of a hyperbola with an increasing amount of corrosion. The conclusion made from a laboratory experiment was applied for developing the corrosiveness map of a precast deck. The field experiment was performed using a three-wheeled antenna cart setup and following the standard bridge deck survey procedures. Information on rebar size, spacing, and depth was extracted by quantifyin (open full item for complete abstract)

Committee: AKM Anwarul Islam PhD (Advisor); Shakir Husain PhD (Committee Member); Richard Deschenes PhD (Committee Member) Subjects: Civil Engineering; Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2019, Electrical Engineering

This thesis proposes a fast matched-filtered based imaging algorithm to detect and image below ground objects with ground penetrating radar. To image below ground objects, a set of distributed transmitters and receivers are placed above the ground, or slightly buried. The transmitters radiate waveforms into the subsurface. The resulting wave-front impinges upon underground objects, scattering electromagnetic energy in all directions. Receivers collect the reflected electromagnetic signals, retrieve the phase of the scattered signals, and transmit this information to a signal processing system for post-processing. After applying adaptive signal processing algorithms to the collected data, an image of the buried objects can be reconstructed. Reconstructed 2D images of buried objects are computed via numerical discretization and matched filtering techniques. The matched filtering technique requires less computational power and is easier to implement as compared to the matrix inversion technique. Results from simulation analyses and experimental data are used to validate this method. This work includes simulations and experiments with ground penetrating radar calibration techniques to justify the method introduced here.

Committee: Michael Wicks (Advisor) Subjects: Electrical Engineering; Electromagnetics; Environmental Engineering; Environmental Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2016, Electrical Engineering

Radio Frequency (RF) Tomography is a mathematical process of 3D image reconstruction from a measurement using a multistatic distribution of transmitters and receivers. The geometric diversity of these elements increases the information in the measurements. The process of determining the permittivity and conductivity profile in the measurement domain, and, therefore, the shape of the target, from the scattered field measurements, is an inverse problem. To solve this problem, under conventional methods such as the Born approximation, we use the principles of linear scattering to determine a linear relationship between measured returns and target shape. The Born approximation is valid if the scatterer is small and does not interact strongly with other objects. However, strong scatterers within the domain may generate sidelobes masking weaker returns. This masking, in conjunction with multipath effects, may result in loss of features and subsequent failure to identify a target. In this research, a novel method is proposed to increase overall image quality and extend the capabilities of RF tomography by modeling the strong scatterers in the measurement domain as dipoles that behave as secondary sources (transmitters). Unlike conventional methods, the dipole model reduces the effects of the sidelobes from the strong scatterers and exploits the multipath of multiple targets or complex shapes. The multipath phenomena contains more information about the targets permitting illumination in the shadowed region and an increase to the radar aperture length. The electromagnetic characteristics for each modeled dipole are estimated by representing the cells in the measurement domain's image. The eigenvalue and eigenvector from each cell represent the phase and magnitude for the modeled dipole and also the spatial orientation of the target. The process of modeling large scatterers as dipoles can be iterated, addressing one strong scatterer at a time. This method effectively s (open full item for complete abstract)

Committee: Michael Wicks (Advisor); Keigo Hirakawa (Committee Member); John Loomis (Committee Member); Lorenzo Lo Monte (Committee Member) Subjects: Electrical Engineering

Master of Science in Environmental Science, Youngstown State University, 2024, Department of Physics, Astronomy, Geology and Environmental Sciences

This research project is the establishment of a clandestine grave site, known as the “body farm”, for future geophysical and geochemical studies that will examine the long- term influence of seasons and its relationships between geophysical signatures and volatile organic compound (VOC) emissions from a simulated clandestine grave site that uses buried pig cadavers as human analogues. The objective and motivation of this research is to establish the body farm which will be used in future research that will provide detailed information to government law enforcement agencies that can be used to improve their planning efforts and their ability to locate homicide victims buried in clandestine graves. A simulated clandestine grave site was constructed with 20 graves, five graves were left empty to act as a control, and the other 15 graves contained pig proxies. Given the various scenarios of homicide victims, the different scenarios were simulated at the site involving pigs that are naked, clothed, clothed warped in tarp, and clothed covered in hydrated lime. Future research will conduct seasonal data collection of samples to determine the long term and seasonal relationship between decomposition and geophysical and chemical signatures. Future geophysical data will be collected with geophysical instruments such as ground penetrating radar (GPR), electromagnetic induction (EMI), and high sensitivity magnetic gradiometer. Future chemical analysis will be collected through constructed piezometers and analyzed using Gas Chromatography-Mass Spectrometry (GC-MS) methods. The outcomes from this research will be used by law enforcement agencies and investigators to analyze changes in the long-term seasonal characteristics of VOC emissions and geophysical signatures associated with decomposing pig cadavers. These findings can be used to further improve law enforcement training and their approaches to locate homicide victims located in the subsurface.

Committee: Jeffrey Dick PhD (Advisor); Tom Jordan PhD, PG (Committee Member); Harry Bircher P.E. (Committee Member); Billie Spieler PhD (Committee Member) Subjects: Chemistry; Environmental Geology; Environmental Science

Master of Arts, The Ohio State University, 2024, Geography

Drone-based remote sensing offers a practical platform for studying debris-covered ice and rock glaciers where the surface topography makes fieldwork challenging or prohibitive. Situated between the scale provided by terrestrial or satellite mapping, drones have been widely used over the past decade to construct high resolution maps of surface deformation and flow of glaciers and rock glaciers using structure from motion photogrammetry. However, ground penetrating radar (GPR) is a standard tool for studying ice within debris-covered glaciers and rock glaciers that has not seen widespread deployment in a drone-based capacity. This thesis demonstrates the application of both photogrammetry and GPR as drone-based tools to study buried ice. Fieldwork involved drone photogrammetry of the Lehman Rock Glacier (LRG) at Great Basin National Park (GBNP) in Nevada, USA and drone-based GPR of a debris-covered glacier at Shar Shaw Taga (also called Grizzly Creek) in Kluane National Park and Reserve in southwest Yukon, Canada. Drone photogrammetry of the LRG demonstrated that the upper lobe of the rock glacier is active and flowing at rates of approximately 0.2 – 0.4 m/yr at the center of the upper lobe between 2018 and 2023 with surface elevation loss in the range of 0.75 – 1.5 meters over the same period. The total volume lost is estimated to be 21,000 m3. Drone-based GPR at Shar Shaw Taga demonstrated successful detection and measurement of buried ice along the drone-based transect validated by traditional manual GPR. The inclusion of manual common mid-point (CMP) surveys enabled accurate measurements of depths and layer characteristics along the entire drone radar transect. The limitations and opportunities of the drone-based photogrammetry and GPR are discussed for potential future investigations using these methods.

Committee: Bryan Mark (Advisor); Demián Gómez (Committee Member); Ian Howat (Committee Member); Alvaro Montenegro (Committee Member) Subjects: Geography; Physical Geography

Master of Science, University of Toledo, 2023, Geology

Glacial Lake Agassiz is a paleolake that formed over central North America at the end of the last Ice Age at ~14.3 ka, and its drainage into the North Atlantic likely contributed to the Younger Dryas cooling at ~12,900–11,700 cal yr BP. Drainage events are identified through the chronologic and geomorphic analyses of strandlines, including beach ridges, escarpments, and spits, which record past lake levels. Strandlines in a study area in the southern basin of Lake Agassiz in NW Minnesota warp upward toward the north as a result of glacioisostatic adjustment (GIA). Older strandlines have a steeper north-south gradient than younger strandlines due to differential rates of rebound. The study area contains a series of strandlines that are classified into 11 strandline groups (SGs) rather than named beach ridges previously identified along other sections of the Lake Agassiz coastline. SGs are composed of one or two well-developed beach ridges, or sets of ridges, that branch out and increase in number toward the south, representing many minor drops in lake level up to ~3 m due to a combination of incision of the southern outlet and uplift caused by GIA. A beach ridge formation model developed from littoral sediment sample analyses and GPR data at 100–500 MHz frequencies suggest that strandlines in the study area formed in an overall depositional regressive system with intermittent storm events. The estimated beach ridge rate of formation is ~8.5-17 yrs/ridge based on ~70 Lockhart Phase beach ridges in the study area and the corresponding optically stimulated luminescence (OSL) dates for the Herman through Tintah beaches and meltwater signatures during drainage events. Strandline chronology is also assessed based on eight OSL dating samples. Most of the dates fell within the error margin for published dates from associated strandlines at the southern outlet. However, samples from the Campbell and Tintah beaches are approximately 3,000 years older t (open full item for complete abstract)

Committee: Timothy Fisher (Committee Chair); Richard Becker (Committee Member); Harry Jol (Committee Member) Subjects: Geology; Geomorphology

MS, Kent State University, 2021, College of Arts and Sciences / Department of Earth Sciences

Glacial Lake Maumee (an early ancestor to Lake Erie) developed extensive beach ridges and bars that included an elongate arcuate bar complex at Columbus Grove, OH, that was very similar to the modern Presque Isle flying spit at Erie, PA, in terms of shape, its 10 km length, its shoreline orientation, and its angle from the coast, although it is extremely narrow, distally discontinuous, and extremely thin. The bars consist of relatively fine-grained, poorly sorted, polymodal sediment that has been extensively bioturbated and plowed, although their shapes are well preserved on the modern surface and they retain useful grain size signals regarding depositional processes and settings. Lake floor sediments are primarily very fine to medium silts with secondary clays and minor sands. Bars appear to have accreted in place, locally with lateral expansion but without significant migration or erosion. Vertical successions vary from cryptic upward shoaling and coarsening to quite heterogenous (better seen by extracting peaks rather than using basic descriptive statistics). Bars are thin (commonly <.5 - 1 m), and at least some begin with a marked shift from lake-floor silt to relatively well-developed sands, although rarely as coarse as sand peaks higher in the core. This suggests initiation by extreme waves touching bottom in relatively deep places, and thereby beginning construction of a sand pile that can benefit from progressively weaker waves as it grows upward. The arcuate shape of the bar complex is attributed to waves shoaling against an accretionary bulge in the coastline. However, until the bars start to connect and become continuous, longshore drift is not developed and lateral transport is prohibited, so bar segments grow individually from locally scavenged sand. This lake phase is thought to have been too short-lived to have permitted the bar to mature into a spit and become wide and complicated.

Committee: Neil Wells Dr. (Advisor); Joseph Ortiz Dr. (Committee Member); Anne Jefferson Dr. (Committee Member) Subjects: Geological; Geology; Geomorphology

Master of Sciences (Engineering), Case Western Reserve University, 2020, EECS - Electrical Engineering

Ground-penetrating radar (GPR) is a widely popular sensing method that provides subsurface images in a non-destructive manner. The first part of this work presents a multistatic GPR for vehicle-mounted roadway and utility monitoring applications that employs three methods to improve its performance compared to the state-of-the-art. First of all, the system illuminates the subsurface with pseudo-random codes (m-sequences) that have near-ideal autocorrelation properties. Therefore, the received signal can be matched-filtered to provide pulse compression, which improves both range-resolution and depth of scan compared to traditional impulse-based GPRs. Second of all, the system uses a highly-digital transmit and receive architecture based on direct FPGA-based transmit pulse generation and direct radio frequency (RF) sampling. Last but not least, the analog front-end uses an 8x8 multistatic antenna array design with broadband antipodal Vivaldi elements to provide spatial diversity, leading to improved object localization and reduced drift between scans. Experimental results from indoor and outdoor test-beds confirm the functionality of the proposed GPR system. The second part of this work proposes a proof-of-concept design of a multi-channel broadband low-noise analog front-end (AFE) for multistatic GPR receivers. This custom integrated circuit (IC) design employs the standard TSMC180 CMOS process. The IC includes four amplifier channels; each channel consists of a broadband low-noise amplifier (LNA) employing noise-canceling techniques, a gm-cell-based variable gain amplifier (VGA), and a voltage buffer. This combination allows the IC to achieve low noise figure (NF) and high linearity performance, thus improving the effective resolution and scan depth of the GPR. Measurement results confirm the functionality of the proposed custom multi-channel AFE IC.

Committee: Soumyajit Mandal (Committee Chair); Kenneth Loparo (Committee Member); Hossein Miri Lavasani (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2020, Electrical and Computer Engineering

The goal of this research was to develop an algorithm to process measured data using an ``optimal'' geometry in order to reconstruct an image of weak targets when strong scatterers are present. This thesis is focused on Weak Target Detection and Imaging in Radio Frequency Tomography (RFT) for Ground Penetrating Radar (GPR). We first start by simplifying the solution of the inversion problem in Radio Frequency Tomography (RFT) based Ground Penetrating Radar (GPR) in order to minimize the compute time for image reconstruction of shallow buried objects. A further goal is to increase the resolution and sharpen the quality of the reconstructed image as we concentrate on weak target detection and imaging in RFT. We propose an accurate, fast method to reconstruct the image of below ground targets using an optimal linear filter, such as matched filter processing. Moreover, a novel method is proposed to improve RFT to detect and imaging weak targets surrounded by strong scatterers in measurement domain. The match filter is the most common approach used to simplify the solution of the inversion problem in GPR model. The proposed method increases the signal-to-noise ratio (SNR) to enhance the quality of the image. Using this technique leads to a decrease in the reconstruction time. Also, it reduces the data acquisition time which is critical in many commercial GPR applications. Compared with other inversion algorithms such as truncated singular value decomposition (TSVD), matched filter algorithms yield a high quality 2D image of shallow buried objects with minimal computational load or noise effect. However, in case of Multi-Target Detection (MTD), RFT has an inherent weakness, especially when strong interfering scatterers and weak targets are present in the same measurement domain. Strong sidelobes from dominant (strong) scatterers can interfere with the echoes from weak targets, thereby leading to missed target detections, and a decrease in the quality of the re (open full item for complete abstract)

Committee: Michael C. Wicks Ph.D (Advisor); Guru Subramanyam Ph.D (Committee Member); Loomis John Ph.D (Committee Member); Youssef Raffoul Ph.D (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Master of Science, University of Akron, 2014, Geology-Geophysics

Ground penetrating radar (GPR), electrical resistivity and seismic refraction surveys were used to image possible buried sinkholes and identify potential areas of subsidence in the shallow paleokarst surface of the Columbus Limestone at Ohio Caverns in Champaign County, Ohio. A buried sinkhole, incipient sinkholes and a possible buried cave passage spatially correlated with orthoimagery and surface evidence of subsidence. Correlations were established by using GIS software overlaying a structure-contour map of the paleokarst, as determined by GPR data, over orthoimagery of the area. Wenner and dipole-dipole electrical resistivity surveys suggest regions of lower resistivity surrounded by higher resistivity are associated with suspected subsidence. Refraction seismic data, collected along the same transect as the resistivity surveys, also correlated with an area of depression in the region of a suspected sinkhole. The seismic velocities from the refraction survey indicated lower depths for the clay soil and Ohio Shale contact and also the boundary between the Ohio Shale and the Columbus Limestone. Remote sensing using electrical resistivity, GPR and seismic refraction techniques successfully imaged the stratigraphy of the area and suggest other areas of incipient sinkhole formation.

Committee: David Steer Dr. (Advisor); John Peck Dr. (Committee Member); Ira Sasowsky Dr. (Committee Member) Subjects: Environmental Geology; Geographic Information Science; Geological; Geology; Geophysical; Geophysics

Master of Science (MS), Wright State University, 2013, Earth and Environmental Sciences

Abstract Shank, Jared W., M.S. Department of Earth and Environmental Sciences, Wright State University, 2013, A geophysical investigation to locate missing graves utilizing ground penetrating radar, electromagnetic, and magnetic methods. Old cemeteries often have graves that are unmarked because gravestones are missing or degraded and the graves are in areas for which maps or other historical documents are incomplete. This is the case for one cemetery in southwestern Ohio, known as Stevenson Cemetery, which contains graves of Revolutionary War and War of 1812 veterans. The immediate goal of this study is to locate unmarked graves in this cemetery using geophysical techniques. The broader goal is to evaluate three geophysical techniques to determine the effectiveness of each. The three geophysical techniques evaluated in this study are magnetics, electro-magnetics, and ground-penetrating radar. Magnetic surveys were accomplished using a Geometrics 858 Cesium Magnetometer (gradiometer configuration). Electromagnetic surveys were accomplished using a GSSI EMP 400 Profiler (16 kHz, 9 kHz, & 5 kHz) and a Minelab E-Trac metal detector (1.5-100 kHz, using 28 simultaneous frequencies). Ground-penetrating radar surveys were accomplished using a GSSI SIR-3000 GPR with a 400 MHz antenna. For a portion of the Stevenson Cemetery, a survey grid was established and utilized with each instrument. The ground-penetrating radar survey yielded a linear pattern of anomalies, which could represent graves. The electromagnetic method produced anomalies at each of the frequencies used. These anomalies appear to correspond to the magnetic anomalies. The ground-penetrating radar results were poor in 3D due to the presence of tree roots. However, individual 2D radargrams revealed some anomalies that coincide with the magnetic and electromagnetic anomalies. Overall, the magnetometer data yielded the best results. These were not definitive on their own and the best approach is to c (open full item for complete abstract)

Committee: Ernest Hauser Ph.D. (Committee Chair); Doyle Watts Ph.D. (Committee Member); David Dominic Ph.D. (Committee Member) Subjects: Electromagnetics; Geophysical; Geophysics

PHD, Kent State University, 2014, College of Arts and Sciences / Department of Geography

In this study, ground-penetrating radar (GPR) was utilized as a tool to apply form analogy related to the formation of a suite of modern landforms on Skeidararsandur, Iceland, and the same, although ancient, landforms found in the Chautauqua Drumlin Field in northwestern Pennsylvania. These landforms, which consist of valleys/channels, drumlins, eskers and deltas, are considered to be part of a continuum involving subglacial meltwater, but questions have arisen as to whether the conditions of its release were catastrophic or steady-state. GPR data from Pennsylvania could not confirm the conditions that resulted in the formation of the large valleys that dissect the Pennsylvania drumlin field due to the expanse of the area and the considerable amount of anthropogenic interferences in the predominantly urban setting. However, form analogy did prove to be useful when comparing features at Skeidararsandur with smaller-scale landforms at Glover quarry in Pennsylvania, although the quarry was most likely a subset of a much larger feature. Foreset beds were the most-readily identifiable feature found in several cross sections at Skeidararsandur and in the quarry, along with similar sedimentological assemblages that were revealed in GPR surveys and surficial observations. Based on this information, landforms within the quarry and those found at Skeidararsandur have been identified as deltas and kames, and indicate that they were formed near the glacial margin by the deposition of sediment via glacial meltwater as the ice became stagnant or receded. It is known that tunnel valleys and eskers also form near the ice margin, therefore allowing for the conclusion based on form analogy that features in both areas were created by similar process, although on considerable differences in scale.

Committee: Mandy Munro-Stasiuk PhD (Advisor); Scott Sheridan PhD (Committee Member); Thomas Schmidlin PhD (Committee Member); Neil Wells PhD (Committee Member); Abdul Shakoor PhD (Committee Chair) Subjects: Geology; Physical Geography

MA, Kent State University, 2013, College of Arts and Sciences / Department of Geography

Researchers have studied the subglacial and proglacial impacts of glacial outburst floods through observation and measurements during flooding events and through analysis of the landscape and sediments after flooding events. While both erosion and sediment deposition dynamics have been studied extensively (eg. Sharp, 1985; Rijsdijk et al., 1999; Van Der Meer, 1999; Overgaard and Jakobsen, 2001; Glasser et al., 2003; Russell et al., 2006;); the routing and effects of pressurized groundwater during glacial outburst flooding are currently poorly understood. The objectives of this research are; 1) to test whether or not Ground Penetrating Radar (GPR) can can effectively image nearly vertical subsurface sedimentary structures thought to result from hydrofracturing of consolidated and confined glacial outwash sediments; 2) to determine if these subsurface sedimentary structures are in fact derived from pressurized groundwater. The site of this study is on western Skeidararsandur, Iceland, near the Sula river. Skeidararsandur is the largest glacial outwash plain on Earth encompassing an area of approximately 1300 km2 (Klimek, 1973). Because it is subject to frequent glacial outburst floods (Roberts et al., 2002) it makes an excellent laboratory to study glacial outwash structures. There are many surface ridges that have been interpreted as groundwater escape structures and correlated to previous outburst floods (Russell et al., 2006; Munro-Stasiuk et al., 2009). In addition, clastic dykes appear to represent groundwater escape pathways through the sands and gravels of the sandur (Munro-Stasiuk et al., 2009). GPR was able to detect steeply dipping clastic dykes and direction of flow at the study site. In addition, GPR can detect sinuous subsurface linear geologic features using proper scan orientation. The results of this study will lead to a better understanding of the dynamics of pressurized groundwater escape mechanisms resulting from sudden glacial outburst (open full item for complete abstract)

Committee: Mandy Munro-Stasiuk (Advisor) Subjects: Geography; Geology; Geomorphology; Physical Geography; Remote Sensing

Master of Science (MS), Wright State University, 2012, Earth and Environmental Sciences

A near-surface geophysical survey was conducted at SunWatch Indian Village in Dayton, Ohio. The main motivations for this investigation were to evaluate geophysical methods to locate, map, and identify features associated with the SunWatch Indian Village archaeological site and to expand the area surveyed. Previous studies (Houston, 2002; Miller, 2004) have determined that burials covered with limestone slabs are relatively easy to detect and map geophysically with GPR and electrical resistivity. This was reconfirmed in this study by collecting 3D GPR data over a ‘control' location previously surveyed by Houston (2002) and Miller (2004). However, similar anomalies were not observed in the other areas surveyed in this study suggesting that they are absent there. The GPR data were collected at 6 inch line spacing for 3D surveys. A comparison of 3D GPR analysis of 6 inch line spacing and 12 inch line spacing (by removing alternate lines) indicates that a 6 inch line spacing was better at defining the subtleties of limestone slabs but that the 12 inch line spacing was adequate for mapping the slab-covered burial site. Electromagnetic (EM) surveys were also conducted across the control as well as new areas but the EM did not show an anomaly at the known limestone slab-covered burial in the control area. This suggests that EM is not able to detect small, thin, resistive bodies (limestone slabs) in these conductive soils. On the other hand electrical resistivity is useful in detecting limestone slabs (Houston, 2002; Miller, 2004) but may be unable to detect more subtle conductivity contrasts likely associated with storage/ trash pits. The magnetic gradiometer surveys were successful in identifying local magnetic anomalies that correlated with an EM inphase anomaly. An interesting find was that the EM unit was able to detect in several unexcavated areas anomalies of high conductivity and low magnetic susceptibly that are believed to be associated with clusters of storage/tr (open full item for complete abstract)

Committee: Ernest Hauser PhD (Committee Chair); Doyle Watts PhD (Committee Member); David Dominic PhD (Committee Member) Subjects: Archaeology; Environmental Science; Geophysics

Doctor of Philosophy, The Ohio State University, 2005, Electrical Engineering

Due to high demand for wide bandwidth applications, UWB antennas have received significant attention in many commercial and military application areas. They can provide very wide bandwidth information with a single antenna configuration. However, designing UWB antennas have very strict requirement such as broadband matching, broad beamwidth, and good efficiency throughout the operational frequency band which is generally difficult to obtain. In this work, the finite different time domain (FDTD) method was selected for the design and optimization of UWB antennas in many different application areas. They include ground penetrating radar (GPR), anechoic chamber feed antenna, near field probe antenna and tapered chamber feed. All these antennas require UWB operation, dual linear polarization, and broad beamwidth. For each application area, they have their own detail operation requirements. With the help of the FDTD code and through understanding, the antennas are deeply studied and analyzed for the final design. This process saves time and cost compared to the repeated prototyping. For the verification of the numerical result, prototype antennas are built, measured and compared to its numerical model result. The measurement and the simulations agree due to the realistic modeling of the geometry.

Committee: Robert Lee (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2004, Geological Sciences

Ground Penetrating Radar (GPR) is a common technique for locating buried objects in the near surface. The near surface is never perfectly homogeneous due to different moisture levels, grain packing, and types of material that influence the properties in the subsurface. This dissertation examines the influence of heterogeneity on GPR measurements, its influence on spatial dispersion, and defining the GPR response from a range of standard deviations of different numerical models. Most modeling in GPR concentrates on antenna patterns or dispersion caused by complex permittivity in homogeneous blocks of material. The forward model developed in this dissertation incorporates heterogeneity by replacing the traditional homogenous spatial regions with a distribution of physical properties. The models in this dissertation maintain the major spatial model boundaries, but the physical model values within each boundary are determined by a statistical distribution. Statistical approximations of heterogeneity of the physical property distributions can provide an approximation of the geologic noise that influences GPR measurements. This dissertation presents a numerical modeling analysis of random property variation, where the variations occur in one, two, and three directions. The models are developed for a half space and a two layered earth model where the input is a Ricker wavelet. Most of the visible spatial dispersion of the electrical field in both the half space and the layered earth models studied in this dissertation, occurred in the near region of the electromagnetic field. However, the largest average dispersion occurred in the far field at 1.0 m distance from a dipole source. The presence of horizontal layers increased the dispersive effects of the random distribution of electrical property values. There was also a measurable change in the dispersed field when the layers were vertical. There was more change with thin horizontal layers than with tubes or three dimension (open full item for complete abstract)

Committee: Jeffrey Daniels (Advisor) Subjects: Geophysics

Master of Science (MS), Bowling Green State University, 2010, Geology

Karst, near surface bedrock cavity, fracture, or cave (solution) features, are present near the Crystal Rock Cave system in Erie County, north-central Ohio. Previously, a capacitively-coupled electrical resistivity study of the area was completed to evaluate the methodology for detecting karst features in the subsurface. Resistivity traverses were completed over known subsurface features using different transmitter-receiver spacing, varying the penetration depth of the resistivity survey. The study found that the larger electrode spacing distances and thin, low-clay soils at the Crystal Rock Cave site provided data that clearly identify known sinkhole and cavity features. However, the durability and maneuverability of the towed resistivity array posed problems and resulted in somewhat unreliable datasets in several instances. To evaluate the findings of the previous resistivity study and assess the ability of ground-penetrating radar (GPR) to identify the same features, a GPR survey was also completed along the same resistivity transects over the Crystal Rock Cave system. The use of GPR is a well-established method of not only detecting subsurface cavities but also mapping the subsurface. The cart-mounted, 400-MHz antenna, GSSI GPR system identified the karst features by detecting the adequately contrasting dielectric properties of the soils, bedrock, and associated air-filled cavities within the shallow subsurface. The shallow (5 m) transects resulted in higher resolution datasets and profiles that clearly show more detail. Deeper (10 m) transects required significant processing and manipulation in order to enhance deeper reflections and to retain detailed, shallow reflections. During GPR data interpretation and comparison to resistivity pseudosections, similar solution features were discernable and comparable within the subsurface profiles generated by the two methods at numerous locations along transects. Comparison of resistivity pseudosections and GPR profile s (open full item for complete abstract)

Committee: Jeffrey Snyder (Advisor); Charles Onasch (Committee Member); Sheila Roberts (Committee Member) Subjects: Geology; Geophysics

Master of Science, University of Akron, 2008, Geology

Analyses of multiple, coincident electrical resistivity and ground penetrating radar surveys successfully imaged a collapse zone and other areas of concern in the vicinity of a previously undocumented, shallow coal mine in Summit County, Ohio. Analyses and inverse modeling of resistivity profiles collected using a Wenner array illustrated that high resistivity regions were associated with collapse of structurally weak sandy shale overlying an excavated coal seam at ~ 10 m depth. Analyses of ~80 radar profiles indicated that such data were more successful at imaging potential near-surface collapse areas than the resistivity method. Futhermore, those data appeared to provide evidence that such collapses propagated from deeper within the section by successive failure of multiple units rather than as a complete structural collapse. The combination of these two techniques illustrated that the spatial extent of actual and potential mine collapse areas can be successfully mapped despite site limitations imposed by property boundaries in an urban setting.

Committee: David Steer PhD (Advisor) Subjects: Geophysics