The presence and configuration of subglacial water and sediment maintain the fast flow of arterial ice streams in Antarctica and airborne ice-penetrating radar data represent a potential resource of information about the ice-bed interface. In this thesis an original contribution to the exploration of Antarctic subglacial environments is made through the analysis of airborne surveys from Evans, Institute and Möller Ice Streams, West Antarctica. The primary approach employed is the derivation of bed-returned power (BRP), a proxy for ice-bed reflectivity, which is strongly influenced by the presence of liquid water. Estimating radar englacial attenuation (EA) accurately is a critical part of BRP analysis and a modelled approach is primarily used. BRP is derived across Evans Ice Stream and shows large-scale patterns relating to hypothesised hydrological and geological contrasts at the ice-bed. These results are developed to investigate the influence of: (1) adopted EA correction; (2) the influence of assigned ice dielectric properties in modelled EA; (3) subglacial roughness and (4) the spatial scale over which BRP is derived. Some areas of high basal drag can be detected with BRP analysis, indicating that variations in subglacial hydrology are responsible for their existence. The widely-used empirical method of estimating EA by relating ice thickness to uncorrected BRP is shown to be unreliable where ice properties change along a transect. Monte Carlo error analysis of modelled EA shows that poorly constrained ice dielectric properties also result in significant BRP uncertainty. BRP beneath Institute and Möller Ice Streams is derived on catchment- and local-scales over hypothesised subglacial features. Bungenstock Ice Rise is marked with a clear BRP signal but the locations of "active" lakes, as delineated by satellite altimetry, do not. The sensitivity of idealised flow paths to surface change and grid size are investigated. Potential future research directions regarding BRP analysis are discussed.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 205-213). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 52-62).

Thesis (Ph. D.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains x, 117 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 110-114).

Ground Penetrating Radar (GPR) methods have been used to evaluate the presence, extent, and spatial variability of hydrophobic soils in Southern California Watersheds. It has been shown that high frequency ground penetrating radar equipment, under certain conditions, has the ability to determine the presence, depth, and persistence of post fire hydrophobic soils. As part of this study an extensive investigation was undertaken to not only evaluate the capability of this approach but also to understand under what conditions the method can be applied successfully and what are the limitations of the approach. The investigation includes use of computer simulations and modeling, laboratory investigations in sand boxes with native soils, and multiple field trials spanning a five year time period. Of particular significance is the finding that using GPR it is possible to: locate the interface between the uppermost burnt soil layer, and soil horizons below; quantify the depth at which the hydrophobic layer forms; and quantify the spatial extent of the layer. As part of this study best practice methods for both field and lab experimentation have also been developed and are presented in the body of the thesis. Based on this study it is concluded that the use of GPR can provide a much more accurate and comprehensive method of evaluating the nature of hydrophobic layers in such environments than the current point specific manual methods. As a result the use of GPR has significantly advanced our capacity to assess the potential for increased erosion and the generation of debris flows in such environments after rainfall events.

Ground penetrating radar (GPR) has been used as a railway substructure investigation tool since the late 1990’s and has seen significant development since then. To use GPR as a more effective tool for substructure investigation, a GPR substructure characterization model was developed. This dissertation provides a detailed description of railway track components, track geometry, soil properties and classification and substructure design. The historical background of GPR is discussed together with GPR principles, basic GPR equations, hardware and accessories as well as GPR data collection, processing and interpretation. Other in situ investigation techniques namely the dynamic cone penetrometer (DCP), light weight deflectometer (LWD) , Pencel pressuremeter, surface wave testing, remote video monitoring (RVM), multi-depth deflectometers (MDD) and continuous track modulus measurement techniques are also discussed. A comparison between the different track investigation techniques was also done, with reference to sample rate, cost, effectiveness and value. Two sites in South Africa were selected for the investigation, one with good substructure conditions used for heavy haul coal export close to Vryheid (KN test section) and the other a general freight line with poor substructure conditions near Rustenburg (NT test section). These two sites were selected to develop a GPR substructure characterization model as they provided conditions ranging from poor to very good. This was supported by the analysis of the in situ soil sampling and testing. The calculation of the track substructure modulus from RVM deflection measurements showed three times higher values for the KN test section compared to the NT test section. The subballast and subgrade thickness, the GPR ballast fouling (GBF) index as well as the GPR moisture condition index was used for the classification ranges used in the model. The subballast and subgrade layer roughness values were calculated and used for the substructure classification. The GBF index and the GPR moisture condition roughness were used for the GPR fouling index classification. The GPR deliverables were divided into four classes (i.e. very good, good, moderate and poor). The evaluation of the characterization model showed that a traditional in situ investigation will cost approximately 3.7 times more than that of a GPR investigation. It would also take two thirds of the time to complete the GPR investigation compared to the traditional in situ investigation. The study showed that GPR can be used to develop a substructure characterization model and that it would be more cost effective and efficient than traditional in situ investigation techniques. GPR surveys provide continuous measurements of the track structure condition and can therefore provide a continuous classification unlike the discreet and fragmented nature of in situ investigations. However, in situ tests can be done at certain intervals within the GPR survey or at point where the GPR classification is not clear. The best solution for railway track characterization can therefore be obtained by using GPR and in situ classification in combination. / Dissertation (MEng)--University of Pretoria, 2012. / Civil Engineering / unrestricted

Advanced nondestructive inspection techniques like stress wave timing and resistance microdrilling have been used to successfully inspection timber bridges, but it is most effective on girder style bridges. There is a noted need to develop additional inspection techniques for longitudinal deck/slab timber bridges, which comprise about 20% of the national bridge inventory. One technique that holds potential is ground penetrating radar, a recognized nondestructive testing technique that has been used effectively for many different environmental and transportation applications. It has been utilized successfully to identify buried objects, internal defects and material changes. The objective of this research was to assess the potential for using GPR to identify and assess simulated deterioration in longitudinal timber deck timber bridges. GPR scans were completed in the longitudinal and transverse directions of a screwlaminated timber bridge deck before and after a bituminous layer was added to assess embedded defects that simulated voids, decay, insect damage and horizontal shear splitting. Assessment of the GPR wave energy signal was completed using visualization software that was provided with the commercial GPR unit used for the testing. The radar signal was analyzed in both the longitudinal direction (antenna front to back) and the transverse direction (antenna side to side). Interpretation of the radar signals allowed for the identification of various internal defects present in the deck. Based on the results, GPR has the potential to identify internal defects in timber bridge decks before and after a bituminous layer was added. Large, rectangular void defects (at least 6? by 12? by 5 in. (15.2? by 30.4? by 12.7 cm)) that were hollow, filled with foam, or filled with sawdust/adhesive were most easily identified under all scanning conditions. The addition of a bituminous layer, common to slab bridge construction, damped the signal response and made it more difficult to identify defects. Several smaller defects that were found in the deck without a bituminous layer were not identified in scanning completed after the bituminous layer was added.

The use of geophysical tools to locate clandestine burials involving bodies has seen increasing popularity among forensic personnel. Often, these search methods are important to highlight certain areas where a body may or may not be located prior to utilizing invasive search techniques. Because of the success of these tools within real-life forensic searches, the use of controlled studies that monitor and detect cadavers over certain lengths of time have been increasingly utilized. However, these controlled studies have not monitored various burial scenarios that mimic real-life situations. This study focused on detecting and monitoring six burials containing pig carcasses used as proxies for human bodies and two control burials with a conductivity meter and ground-penetrating radar (GPR) with a 500-MHz and a 250-MHz antenna over a twelve month period. Each burial within this study represented a different forensic scenario that mimicked a real-life situation. Further, forensic use of GPR in both controlled settings as well as real-life searches have mainly focused on the use of a 500-MHz antenna. Therefore, this research also compared the use of a 250-MHz antenna with a 500-MHz antenna. Lastly, a number of GPR imagery options were utilized including reflection profiles and horizontal slices with various GPR software programs to compare the results obtained. Results obtained from the conductivity meter were compared to the results obtained by both antennae of the GPR. Overall, the use of multiple GPR imagery options provided increased resolution of the burial scenarios. Results showed that the conductivity meter was not a beneficial geophysical tool because none of the burial scenarios were detected. On the other hand, the use of GPR showed that the graves with objects added to the pig carcasses provided iv increased resolution compared to the graves containing only pig carcasses. Lastly, the 250-MHz antenna provided better resolution of the burial scenarios than the 500-MHz antenna due to easier discrimination of the forensic targets. Therefore, the use of a 250-MHz antenna would be a viable option to search for clandestine burials containing adult-sized bodies

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In this paper, the research prototype of a high-performance GPR imaging system is presented. The system is equipped with the capability of synthetic-aperture scan, stepfrequency FMCW illumination, and high-resolution tomographic image reconstruction.