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  • 1
    Description / Table of Contents: Ground penetrating radar (GPR) is transforming the way earth scientists and engineers describe and interpret near-surface sedimentary environments in the field. Because of recent advances in equipment, GPR now provides continuous, high-resolution data that other geophysical investigative tools cannot achieve. GPR has proven useful in a wide array of environmental, geological, and engineering applications. Included in this book are practical guidelines for data collection and interpretation, from antennae configurations to sequence stratigraphy, together with new advances such as vertical radar profiles and 3-D GPR imaging for hydrocarbon reservoir modelling, designed to assist new and veteran users get the most from GPR. Case studies in this book detail GPR investigations in a wide array of sedimentary environments including alluvial fans, braided rivers, spits, beaches, sand dunes, lakes, bogs, and floodplains. Examples of GPR investigation applied to stratigraphic correlation problems in Holocene, Pleistocene, and ancient sediments; hydrocarbon reservoir modelling; and detection and mapping of contaminants, reservoir infilling, land mines, and fault displacements are included.
    Pages: Online-Ressource (VII, 330 Seiten)
    ISBN: 1862391319
    Language: English
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  • 2
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The internal structure of coastal foredunes from three sites along the north Norfolk coast has been investigated using ground-penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non-destructive or geophysical technique. Combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, roll-over and beach deposits. Foredune ridges contain large sets of low-angle cross-stratification from dune foreslope accretion with trough-shaped structures from cut and fill on the crest and rearslope. Foreslope accretion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore winds. Bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement. Radar sequence boundaries within dunes have been traced below the water-table passing into beach erosion surfaces. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion surface may be correlated with erosion in the 1950s, possibly the 1953 storm. Results suggest that dune ridge development is intimately linked to changes in the shoreline, with dune development associated with coastal progradation while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which illustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is directed along the coast and offshore, which reduces the landward migration of sand dunes.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2003-01-01
    Description: The Maputaland area of northeastern South Africa is characterized by extensive dunefields which developed during polyphase reworking of regional aeolian cover sand from the Mid-Pleistocene to the Holocene. Extended parabolic dunes, many preserved only as wind-rift trailing limbs, as well as areas of sinuous crested dunes, hummocky dune systems and the high, composite, accretionary coastal barrier dune cordon are the dominant dune forms. There are few natural sections exposing the stratigraphic succession and unequivocal relative age relationships between dune systems are uncommon. A ground penetrating radar (GPR) survey of dunes and representative aeolian sand stratigraphic units was undertaken in order to investigate the internal structure of the different dune forms and identify stratigraphic relationships between buried sedimentary units. The GPR profiles revealed that the trailing limbs of almost all the parabolic dunes that were surveyed comprise stacked sand units, separated by low-angle reflections interpreted as bounding surfaces, which accumulated through polyphase vertical accretion. Most extended parabolic dunes are aligned north-south and the upper parts of the dunes are characterized by inclined reflections in GPR profile interpreted as large-scale sets of cross-stratification with apparent dips toward the west. A hummocky dune revealed cross-stratified aeolian sand superimposed on a truncated dune form and probably formed through deflation of pre-existing dunes. Using 100 MHz and 200 MHz antennae, it is clear that GPR is capable of imaging very fine sedimentary structures and buried erosional surfaces in the homogeneous aeolian sand of Maputaland. At some of the sites investigated, the buried sand units identified were sampled by hand-augering for infrared-stimulated luminescence dating. The age determinations on these samples suggest that vertical accretion of up to 7 m of sand occurred intermittently over variable time scales up to 25 000 years on some parabolic dune limbs during the Late Pleistocene. In some complex dunefields, adjacent dunes were mobilized at different times, suggesting that remobilization was localized. The implications of the complex internal structure and vertical accretion of extended parabolic dunes are discussed in the context of changes in vegetation cover and water table due to seasonal and short-term cyclical climate variations as well as long-term climate change patterns during the last glacial cycle and the Holocene.
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  • 4
    Publication Date: 2003-01-01
    Description: Within sedimentological studies, ground penetrating radar (GPR) is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non-destructive method. The purpose of this paper is to provide an introduction to the collection, processing and interpretation of GPR data so that future sedimentary studies can be improved. With GPR equipment now being lightweight, robust and portable, proper data collection and survey design methods need to be followed in order to acquire high resolution, subsurface digital data. Various factors are discussed including: reflection profiling, velocity soundings, test surveys, topography, logistics, data quality and extreme environments. Basic data processing and visualization are then reviewed, followed by a discussion on GPR interpretation strategies including a background to radar stratigraphy. For the sedimentary geologist or geomorphologist, GPR offers unique data of the shallow subsurface including stratigraphy, geometry, architecture and structure.
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  • 5
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    In:  Geological Society Special Publication 211: 1-7.
    Publication Date: 2003-01-01
    Description: In sedimentary geology, ground penetrating radar (GPR) is used primarily for stratigraphic studies where near-continuous, high-resolution profiles aid in determining: (1) stratigraphic architecture, (2) sand-body geometry, and (3) correlation and quantification of sedimentary structures. In the past, to investigate lateral continuity and variability of sediments, we had to infer the correlation between boreholes, outcrops or shallow trenches. Nowadays, with suitable ground conditions (sediment with high resistivity, e.g. sands and gravels), we can collect GPR profiles that show the subsurface stratigraphy. In addition, 3-D GPR can provide much greater appreciation of sand-body geometry and architecture. GPR is, however, not a universal panacea; in some cases, ground truth is still required because lithological determination is by no means unequivocal, therefore borehole or outcrop data may be required to corroborate the results of a GPR survey. Indeed, the latest GPR survey data, including 3-D depth migration, required both boreholes and outcrop data to generate a 3-D velocity model (e.g. Corbeanu et al. 2001). In addition, fine-grained sediments (low resistivity) and areas with saline groundwaters cause rapid attenuation of the radar signal, leading to poor signal penetration. This book begins with an introductory paper (Jol & Bristow 2003) aimed at those with little or no experience of GPR and including the basics of data collection, processing and interpretation. The book is then divided into sections on sedimentary environments, including aeolian and coastal, fluvial and alluvial fan, glacial, and lakes; ancient sediments (reservoir analogues); tectonics; and engineering and environmental applications. The final section looks at various aspects of GPR methodology. ... This 250-word extract was created in the absence of an abstract.
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  • 6
    Publication Date: 2015-06-29
    Description: From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world’s greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2011-09-01
    Description: Antarctica is the coldest, driest, and windiest continent on Earth, and contains sand dunes, like deserts elsewhere. The structure and age of the cold climate dunes found in the Victoria Valley, Antarctica, are described in the light of changing climate in the Ross Sea region of Antarctica during the late Holocene. Ground penetrating radar (GPR) was used to image sand dune stratigraphy, and optically stimulated luminescence (OSL) was used to determine when the sands were deposited. The timing of sand dune accretion identified from the GPR stratigraphy ranges from the present day to ca. 1.3 kyr B.P. The OSL ages were used to calculate end-point migration rates of 0.05-1.5 m/yr, lower than migration rates from photogrammetry and field surveys undertaken over the past 50 yr. The earliest recorded dune development, ca. 1.3 kyr B.P., was probably controlled by intensification of circumpolar westerlies at that time as well as by drier conditions and lower temperatures that promoted dune stabilization. The dune reactivation ca. 300 yr ago coincides with cooling ca. A.D. 1700-1850, and strengthening of southern circumpolar westerlies. The increase in rate of dune migration after this period and especially the past 200 yr may coincide with the modern rise in CO2 and the warmest temperatures in Antarctica during the past 800 kyr.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 8
    Publication Date: 2020-06-24
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 9
    Publication Date: 2003-05-01
    Print ISSN: 0037-0738
    Electronic ISSN: 1879-0968
    Topics: Geosciences
    Published by Elsevier
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  • 10
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