655 research outputs found

    Applications of Ground Penetrating Radar to Structural Analysis of Carbonate Terraces on the Island of Bonaire, Caribbean Netherlands

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    This thesis utilized the method of ground penetrating radar to investigate the structural geology of carbonate units in relation to the evolution of the island of Bonaire, Caribbean Netherlands. Two surveys were completed on the island for this purpose: a long continuous cross-island transect, as well as a smaller set of lines that facilitated three-dimensional interpretation at an outcrop known as Seru Grandi. In the detailed processing workflow implemented for the collected datasets, steps were taken to remove unwanted signal noise, and advanced imaging techniques where then applied to generate interpretable subsurface cross-sections. A novel numerical interpretation tool was developed for use on the cross-island transect, which adapted a traditional k-means clustering algorithm for use with structure-parallel vectors derived from structure tensors. The results of this method were utilized in defining a set of radar facies for the cross-island transect. Mapping of these radar facies identified subsurface features related to subtidal-to-foreshore depositional sequences in the southern part of the transect, a potential lagoon system in the south-central portion, eolianites within the center of the transect, and clinoforms related to platform slope deposits in the northeast portions of the survey. Using the small-scale dataset at the Seru Grandi outcrop, subsurface geometries of a previously identified geologic unconformity were described. This unconformity was identified here to be the remnants of a wave cut-platform occurring at the site. The specific geometry of this feature was related to external controls on wave cut-platform development. In addition, the data collected at Seru Grandi identified a set of clinoform surfaces in the subsurface below the mapped unconformity. These observations were compared to previously identified clinoforms observed on the face of the outcrop. Observations and interpretations from both surveys in this study were used to provide additional information relating to the geologic evolution of Bonaire

    Structural Investigation of the Odessa Meteorite Crater Using High Resolution Geophysics in a Complex Environment

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    From its discovery in 1921, the Odessa Meteorite Crater has interested researchers and mining companies who had initially hoped to locate a buried mass of meteoric iron. To find the impactor, a major geologic study of the crater was conducted in 1941. Even though the impactor has not been found, the thorough geologic constraints make the crater an excellent location to test the application of near-surface geophysical methods to complex environments. Recently, researchers have focused on determining the age of the crater, the environmental effects of the impact, and the size, incident angle, and direction of the impactor responsible for the crater. However, the heavily eroded and anthropogenically modified state of the exposed crater presents several challenges to impactor attribute estimation. The exposed rim is irregular in shape such that the original size and shape of the crater is indeterminate, only ~3 m of the estimated 30 m of original crater depth remain unfilled by post impact sediment, and previous geologic studies have left the remains of several large trenches transecting the crater rim. To more accurately determine the original size of the crater, ERT and GPR geophysical methods were used to image the exposed and unexposed rim strata. However, the geologic complexity of the crater and the presence of anthropogenic or “cultural” noise posed problems to both ERT and GPR data acquisition and processing. Geophysical results point to a main crater of ~120 m in diameter and ~35 m depth. Additionally, the eastern non-circular portion of the expose crater rim is hypothesized to have form from the simultaneous impact of a small meteorite broken from the main meteorite during atmospheric entry. Further ERT study is recommended to investigate the secondary crater further

    An optimization of the work disruption by 3D cavity mapping using GPR: A new sewerage Project in Torrente (Valencia, Spain)

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    [EN] This paper describes the inspection for cavity detection in an urban area in Torrente (Valencia, Spain). A shallow cave was found during the excavation work for a new sewerage project. Digging activities were stopped immediately and a GPR survey (400 MHZ antenna) was required to reorganise the sewerage planning. The 3D GPR-mapping pinpointed most of the detected cavities on one side of the street. As a result, the sewerage system layout was moved to the side of the street where less evidence of cavities was detected. Therefore, GPR technique is a helpful tool for minimizing costs, time, work safety risks and inconveniences to people living in the neighbourhood during civl engineering works, especially in urbanised areas.Garcia-Garcia, F.; Valls-Ayuso, A.; Benlloch Marco, J.; Valcuende Payá, MO. (2017). An optimization of the work disruption by 3D cavity mapping using GPR: A new sewerage Project in Torrente (Valencia, Spain). Construction and Building Materials. 154:1226-1233. doi:10.1016/j.conbuildmat.2017.06.116S1226123315

    Using Ground Penetrating Radar and attribute analysis for identifying depositional units in a fluvial-aeolian interaction environment: The Guandacol Valley, northwest Argentina

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    This paper deals with the application of the Ground Penetrating Radar (GPR) method and the analysis of attributes of the GPR data to characterize and interpret a fluvial-aeolian interaction field located in the Guandacol Valley, northwest Argentina. Several profiles over dunes, interdunes, aeolian mesoforms, and fluvial channels have been acquired. Each data section is analyzed by using standard images of the amplitude of the electric field, as well as representations of different attributes of the reflections such as contrast, dip, curvature, parallelism, and RMS frequency. The analysis of attributes improves the interpretation of the subsurface, by quantifying and making evident properties of the reflection patterns that characterize the sedimentary units. The information obtained using the GPR profiles allows defining seven radar packages, which are useful for reconstructing the internal structure of the fluvial-aeolian succession. Packages 1, 2 and 3 illustrate the stratification of different types of low-sinuosity and high-sinuosity aeolian dunes, as well as aeolian mesoforms. Package 4 corresponds to horizontal or low-angle inclined reflectors obtained in both sandy interdunes and upper parts of several aeolian dunes. A muddy bed that covers most of the area (package 5) probably indicates a period of climate amelioration linked to a high level of the water table. The fluvial component of the fluvial-aeolian succession exhibits two different packages; package 6 represents the infill of partially incised fluvial channels with frequent incisions (concave-up bounding surfaces) and bars (convex-up surfaces). Package 7 is composed of the stacking of parallel to subparallel horizontal reflectors, without concave-up surfaces that indicate deep channels. Finally, we propose a conceptual model that relates the principal radar packages with the temporal evolution of the fluvial-aeolian interaction field of Guandacol Valley.Fil: Zabala Medina, Peter. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Limarino, Carlos Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Bonomo, Nestor Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Salvó Bernárdez, Salomé Candela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Osella, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

    A Hidden Spider Web of Roots: Utilizing Ground Penetrating Radar to Uncover Laterally Expansive Roots of an Oak Tree

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    Roots are critical to understanding tree health, subsurface biomass, and overall tree root stability. However, accessing tree roots is difficult and traditional methods used to quantify roots harm or kill the tree. Ground penetrating radar (GPR) provides a non-invasive way to characterize subsurface roots without harming the tree. GPR provides high-resolution data and the ability to collect data with high spatial coverage, making it an ideal tool for characterizing roots. GPR works by detecting contrasts in dielectric permittivity or electromagnetic (EM) velocity at interfaces between materials. Small scattering objects, like roots, generate predictable artifacts called diffraction hyperbolas. Diffraction hyperbolas will obscure subsurface structure but contain valuable information about the EM velocity of the soil because their shape depends on the mean root square of the velocity and the depth of the diffractor. We used diffraction hyperbolas to determine an average EM velocity and then used this velocity to apply a migration to remove the hyperbolas and clean up the image. We collected over 258 GPR lines at 10 cm spacing using a 500 MHz antenna. We set up the lines in three triangular grids remaining perpendicular to the radial direction centered over a large White Oak (Quercus alba) on Clemson’s campus. We hand fit ~1800 diffraction hyperbolas to show that the soil velocity was 0.091 m/ns, much faster than the commonly assumed 0.065 m/ns for soil. We used the average velocity to apply a F-K migration to every individual profile. On each profile, we calculated the instantaneous amplitude by taking the magnitude of the Hilbert Transform because roots show up as positive bulls-eye anomalies in this domain. We build depth sections where individual roots can be seen as deep as 1.36 m and extending as far as 8.6 m away from the trunk. These profiles can then be extracted and compiled at specific depths to create depth sections. Our data support two key observations: 1) obtaining an accurate migration velocity is critical to image roots, 2) Although improvements can still be made, GPR can be used to characterize root networks of trees with shallow (\u3c 1.5 m) dendritic root networks. Using the methods presented in this thesis it is possible to estimate the subsurface biomass of the largest roots surrounding a given tree

    Delineation of a produced water plume in Pointe Coupee Parish, Louisiana

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    Three pits were excavated in the 1960’s at the Fordoche Oil Field in Lottie, Louisiana, as evaporation pits for oil well produced brines. The pits were closed and completed in the 1980’s. Previous studies indicate that produced water has leached into the subsurface within the area to the south and southeast of the pits. Ground penetrating radar (GPR) was utilized in an attempt to delineate the present location of the plume as well as test the feasibility of GPR within a clayey soil in south Louisiana. In addition to collection of GPR data, electrical conductivity logs and soil cores (including core sampling for sediment classification and chloride analysis) were collected. Electrical logs confirmed the presence of permeable zones interlaying impermeable zones. Core sampling for chloride confirmed the presence of the produced water within the study area. GPR was unsuccessful in delineating the plume at the site because of the high conductivity of the shallow sediments which inhibited penetration of radar waves. Calibration GPR studies were completed at grave sites in north and south Louisiana which proved successful due to favorable conditions

    Hydrogeologic Investigation of a Covered Karst Terrain

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    Increasing demand for water for agricultural use within the Dougherty Plain of the Southeastern United States has depleted surface water bodies. In karstic landscapes, such as the Dougherty Plain in southwest Georgia where the linkages between surface and ground waters are close, there is a need to understand the physical characteristics of the subsurface that allow these close linkages. Having a better understanding of the subsurface characteristics will aid numerical modeling efforts that underpin policy decisions and economic analyses. Two common features on this karstic landscape are draws and geographically isolated wetlands. Using LiDAR, aerial imagery, and ground-penetrating radar, this study investigates the subsurface characteristics of a draw and a series of geographically isolated wetlands. GPR reflections indicative of karst features are laterally-continuous and connect the landscape to nearby Ichawaynochaway Creek. The identification of the size and scale of the laterally continuous karstic features will guide the implementation of groundwater models used to determine irrigation and forest restoration programs while minimizing the impacts of water use on surface streams and the ecosystems
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