This study presents a comprehensive overview of the current state of the Milne Ice Shelf and how it has changed over the last 59 years. The 205 ±1 km2 ice shelf experienced a 28% (82 ±0.8 km2) reduction in area between 1950 – 2009, and a 20% (2.5 ±0.9km3 water equivalent (w.e.)) reduction in volume between 1981 – 2008/2009, suggesting a long-term state of negative mass balance. Comparison of mean annual specific mass balances (up to -0.34 m w.e. yr-1) with surface mass balance measurements for the nearby Ward Hunt Ice Shelf suggest that basal melt is a key contributor to total ice shelf thinning. The development and expansion of new and existing surface cracks, as well as ice-marginal and epishelf lake development, indicate significant ice shelf weakening. Over the next few decades it is likely that the Milne Ice Shelf will continue to deteriorate.

.El georradar es una herramienta cada vez más utilizada en diferentes ámbitos geológicos, medioambientales y de Ingeniería Civil, así como en estudios de caracterización de yacimientos arqueológicos y de diagnóstico de daños en edificios del patrimonio histórico y cultural.En esta tesis se abordan aspectos metodológicos de calibración de la instrumentación y de caracterización de las propiedades electromagnéticas que rigen la propagación y atenuación de ondas electromagnéticas en los suelos. Por otra parte, se estudian aplicaciones en monumentos históricos, yacimientos arqueológicos y diagnóstico de daños.Concretamente, en esta tesis se calibran cuatro antenas, caracterizadas por su frecuencia central de emisión: 200, 500, 900 y 1000 MHz. En cada caso se obtiene la señal sólo con el ruido interno de la antena (sin reflexiones). De dicho ruido, el de mayor amplitud es la señal inicial; su longitud determina la distancia mínima entre la antena y la primera superficie reflectora del medio para que no se produzca acoplamiento entre la reflexión y la señal inicial. Se analiza también el origen de tiempos de la señal para cada antena (cero de la antena) y se estudia la atenuación producida en la señal durante su propagación por el aire (medio no absorbente), que, por lo tanto, se produce por expansión geométrica, siendo la amplitud inversamente proporcional a la distancia. Se ensaya un procedimiento para caracterizar medios electromagnéticamente, relacionando sus propiedades físicas: granulometría, peso específico, porosidad y saturación, con la conductividad, la permitividad y la frecuencia. Se analizan tres medios formados por un mismo material, modificándose tres propiedades: peso específico aparente, compactación y saturación. En cada caso se obtiene la velocidad de propagación, la permitividad dieléctrica, el espectro de frecuencias y la atenuación. Al aumentar la saturación la velocidad es menor, se produce un desplazamiento hacia las bajas frecuencias, se estrecha el ancho de banda y la atenuación por absorción aumenta. Asimismo se analizan y discuten diferentes métodos para obtener la velocidad: tiempos y espesores conocidos, análisis de hipérbolas, comparación de amplitudes, dromocrónicas de un CMP, modelos geotécnicos, contraste de capacitancias y perfiles de estratigrafía conocida. Los mejores resultados obtenidos son los que proporcionan los ensayos de laboratorio con muestras de espesor conocido y el análisis de reflexiones hiperbólicas. De la comparación de los resultados obtenidos con los que proporciona la literatura se deduce la conveniencia de realizar una caracterización en laboratorio en casos que requieran una resolución fina de las anomalías superficiales o de profundidad intermedia.Relacionados con estas investigaciones (caracterización de medios y calibración de antenas), se han ejecutado y estudiado aplicaciones a casos reales que han permitido resolver problemas prácticos y, al mismo tiempo, han permitido también observar las ventajas de la aplicación de los avances de la investigación, así como avanzar en las técnicas de identificación y cancelación de ruidos introducidos por reflexiones externas o múltiples. Los principales casos resueltos hacen referencia a: control de intervenciones de restauración y rehabilitación en monumentos o en construcciones históricas (casos del teatro romano de Sagunto y de los puentes góticos sobre el río Turia), estudio de daños en edificios del patrimonio cultural (casos de la Catedral de Valencia e Iglesia de San Jorge de Paiporta), caracterización de yacimientos arqueológicos (casos del subsuelo de la Catedral de Valencia, de la Iglesia de San Jorge y de la fortaleza romana y convento en Alcántara).Algunos resultados y casos relevantes se sintetizan en fichas monográficas que presentan en forma esquemática las claves referentes al problema estudiado, lugar y herramienta empleada. Estas fichas serán de gran utilidad en el estudio de casos similares y se espera que constituyan el inicio de un catálogo de casos y soluciones. / The Ground-Penetrating Radar (GPR) is a tool more and more used in different geological, Environmental Engineering and Civil Engineering research, as well as in studies of characterisation of archaeological locations and in the diagnosis of the damages in buildings of the historical and cultural heritage. In this thesis, methodological aspects of calibration of the instrumentation are performed. Also, methodological aspects of the soils characterisation by using its electromagnetic properties are analysed. These properties govern the propagation and attenuation of electromagnetic waves in the soils. On the other hand, several applications to the study of historical monuments, archaeological locations and diagnosis of damages are investigated.Particularly, in this thesis four antennae are gauged. These antennae are characterised by their central frequency of emission: 200, 500, 900 and 1000 MHz. For each case, the internal noise of the antenna (radar record without reflections) is obtained;the highest noise is the initial signal (usually the direct wave); its longitude determines the minimum distance between the antenna and the first reflective surface to obtain a radar data where the two events (direct wave and reflected wave) are clearly separated. It is also analysed the time origin of the traces for each antenna (zero of the antenna). The attenuation of the traces during the wave propagation in the air (non-absorbent medium) is also studied. Therefore, in that case, the attenuation is caused by the geometric spreading, and the wave amplitude is inversely proportional to the distance. A procedure is tested to characterise media using its electromagnetic properties: the conductivity, the permitivity and the frequency, relating them with its physical properties: grain size, specific weight, porosity and saturation. Three different media are analysed, formed by the same solid material and modifying three physical properties: the apparent specific weight, the compactation (and, therefore, the porosity) and the saturation. In each case, the wave propagation velocity, the dielectric permitivity, the spectrum of frequencies and the attenuation are obtained. When the saturation increases, the velocity decreases, a displacement takes place toward the low frequencies, the band width is narrowed and the attenuation caused by absorption increases. In addition, different methods to obtain the wave velocity are analysed and discussed: times and well-known thickness, analysis of hyperbolas, comparison of amplitude, radar records obtained in a CMP, geotechnical models, contrast of capacitancy and profiles of well-known stratigraphy. The best results are obtained from the laboratory measurements using samples of well-known thickness and from the analysis of hyperbolic reflections. Comparison of these results and the values provide by the literature is performed. This comparison shows the convenience of carrying out a characterisation of the medium in laboratory in the cases when a fine resolution of the superficial anomalies or of intermediate depth is required. Related with these investigations (characterisation of means and calibration of antennas), several applications to real cases have been performed and studied. These applications have allowed to solve practical problems and, at the same time, to observe the advantages of applying the advances of the investigation, as well as to make progress in the identification techniques and suppression of noise introduced by external or multiple reflections. The main cases resolved make reference to: control of restoration, interventions and rehabilitation in monuments or in historical buildings (cases of the Roman theatre of Sagunto and the Gothic bridges on the river Turia), study of damages in buildings of the cultural heritage (cases of the Cathedral of Valencia and the Church of San Jorge, in Paiporta), characterisation of archaeological locations (cases of the underground of the Cathedral of Valencia, Church of San Jorge and the Roman fortress and the convent in Alcántara). Some results and the best cases cases are synthesised in monographic cards. These cards present, in schematic form, all the information about the studied problem, the emplacement and the used tool. These cards will be very useful in the study of similar cases, and it is expected that they constitute the beginning of a catalogue of cases and solutions.

This Master Thesis examines the possibility to apply a magnetometer developed by the Ångstöm space technology center to a small magnetic ground penetrating radar system with dimension in the order of one dm³. The magnetometer is broadband (DC-1GHz) and miniaturized. Loop antennas are used to transmit the signal.    A series of experiments have been performed in order to characterize the system, mainly examining the ability to determine distance to a target, using continuous sine wave signals and pulse trains. Standing wave patterns are formed between antenna and target and can be used for determining distance in the continuous case. When using a pulse train, the echo from the target could not be resolved using the current experiment set up, distance could therefore not be determined.

The alongshore variability of beach-dune systems and the response and recovery from extreme storms remains poorly understood. The height and extent of foredunes along barrier islands varies over a range of spatial scales, implying that during extreme storms, the beach-dune system should respond in different ways depending on the elevation and volume of the dunes relative to the storm surge. The purpose of this study is to use Ground-Penetrating Radar (GPR) and vibra-cores to investigate the internal structure of small, intermediate and large dunes along a 2.5 km transect of beach in Padre Island National Seashore, TX with particular attention to storm impacts. A series of dune normal and parallel GPR profiles were collected to capture the variation in beach-dune morphology at the three sites. Site locations were chosen along a transition from dissipative to intermediate beach states. Following the Sallenger (2000) storm impact model, the small dune is defined by low-lying topography that is susceptible to overwash and inundation depending on the size of the storm surge. The large dune is characteristic of the “collision regime”, while the intermediate dune represents a transition between “overwash” and “collision regimes”, with the underlying assumption that all three dunes would be impacted by the same level of surge during a single storm event. Results from the GPR survey suggest that each site contains a bright, laterally continuous radar reflector that is interpreted with the aid of the sedimentary data as an erosional layer. Different characteristic radar facies and sequence boundaries provide evidence as to how each dune evolved through and after the storm. Results from XRF scans and grain size analysis show a direct comparison between the GPR reflectors at the storm surface and spikes in calcium counts from XRF scans to distinct changes in grain size parameters at the same depth. It is argued that the location of each shell layer corresponds to a storm surface generated during a single storm, which means it is possible to interpret different recovery mechanisms. The presence of the storm layer across the backbeach and dunes provides evidence for the height and extent of the surge during the storm event. The data suggests that the small dune was overtopped by the surge, experiencing minimal erosion and recovery. The intermediate dune was completely eroded by the surge, but showed the greatest recovery of all the dune sites. The large dune was scoured at the base with marginal impact along its crest and shows minimal recovery after the storm. These results suggest that the evolution (i.e., transgression) of a barrier island varies considerably over short distances.

This thesis presents an analysis of the behavior of an equiangular spiral antenna using a mixture of numerical and measurement techniques. The antenna is studied as an isolated element and as a part of a spiral-based ground-penetrating radar (GPR) detection system. The numerical modeling was based on the parallelized finite-difference time-domain method and the model was validated by comparison with a prototype antenna and detection system. The intention is to isolate the effect of varying different geometrical parameters that define the spiral element or the spiral GPR system. With some notion of each parameter's effect, systems that use the spiral antenna can be designed more easily. The analysis of the spiral antenna in isolation provides a set of design graphs for the antenna. A set of design graphs are constructed that allow one to better understand the effect of the chosen dielectric substrate on the characteristic impedance of the antennas. A second set of design graphs give very specific data about the lower cut-off frequency possible for the antennas given a requirement on its minimum boresight gain, axial ratio, or voltage standing-wave ratio when matched with an appropriate transmission line. The analysis of the spiral antenna in the context of a detection system provides information on the effect of the ground on the GPR system and to what extent the circular polarization properties of the spiral antenna play a role in GPR. It is shown that a spiral antenna used in a monostatic radar configuration will reject a symmetric scatterer well into the near-field. The importance of a resistive loading to the spiral arms is demonstrated for this rejection to be optimal. In addition, it is shown that increasing the dielectric constant of the ground narrows the pattern and polarization properties, making the antenna more directive towards boresight when the spiral antennas radiate into a flat ground. In addition to this work, a method for reducing the truncation error when calculating the planewave spectrum of an antenna is described.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 114-121). Also available on the Internet.

Thesis (M.A.)--Portland State University, 2002. / Computer-produced typeface. Includes bibliographical references (leaves 119-123).

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 114-121). Also available on the Internet.

Measuring the relative apparent dielectric permittivity of the subsurface is an easy and inexpensive way to indirectly obtain the volumetric water content. Many of the instruments that measure the dielectric, specifically borehole ground penetrating radar, rely on the travel time of an electromagnetic wave through a moist soil. Through inversion of the travel time, the water content can be calculated provided the path over which the wave travels is known exactly. In traditional interpretations of water content, the travel path of the electromagnetic wave is assumed to be direct from the transmitting antenna to the receiving antenna, irregardless of the propagation velocity structure. A new analysis is presented for the interpretation of first arrival travel time measurements from borehole ground penetrating radar during zero-offset profiling that considers critically refracted ray paths. By considering critical refraction at interfaces between contrasting propagation velocities, the travel path becomes dependent upon the velocity structure. Several infiltration experiments were performed to test whether critical refraction occurs in the subsurface. The infiltrating water will change the velocity structure of the subsurface in a predictable manner The interpretations of travel time were then compared to predictions made with an unsaturated flow model and supporting instrumentation. It was found that when critical refraction was not considered, the volumetric water content was underestimated by up to 30%. Correcting for critical refractions, therefore, becomes an important step in properly characterizing the subsurface. The new analysis presented herein may improve our ability to use direct measurements in water resource management practices to assess water availability in semi arid regions.

High latitude soils are estimated to store a considerable part of the global pool of soil organic carbon (SOC). Studies of global and regional SOC pools have estimated total inventories in northern Sweden’s subarctic region to fall within 10-50 kg m-2. However, correction factors for stone and boulder content of soils are often overlooked in SOC-studies and soil profiles are commonly normalized to a depth of 1 m, which can result in substantial overestimates of the SOC pool if a large part of the soil volume is occupied by stones/boulders or if the soil depth is shallower than 1 m. This study was performed to quantify SOC in soils of the Torneträsk catchment area using detailed measures of soil depth and stone/boulder contents. Two non-destructive sampling methods, ground penetrating radar (GPR) and rod penetration, were used to measure soil depth and stone and boulder content in the catchment area. Results show that average soil depth (n = 52344) varied between 0.95 – 2.14 m depending on elevation and the average mire depth was 0.63 m. Stone and boulder content of the soil was estimated to 49 – 68 % depending on elevation. The results were added to existing carbon and soil density data from the Torneträsk catchment area and total SOC inventories were calculated to 6.8 – 13.1 kg m-2. The results of this study indicate that previous studies on regional and global scale may have overestimated the SOC pools in the subarctic regions of northern Sweden.