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Field Mapping (field + mapping)

Distribution by Scientific Domains

Earth and Environmental Science	45%
Humanities and Social Sciences	18%

Selected Abstracts

Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step,pool channel

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2006
Brett L. Vallé
Abstract High-resolution tacheometric field surveying was integrated with computer-assisted drafting to visualize and contrast three-dimensional bed and water surface digital elevation models (DEMs) for submerged and unsubmerged hydraulic jump regions in a bedrock step,pool channel. Measurements were conducted for two discharge conditions. Since previous applica-tions of three-dimensional field mapping and digital elevation modelling of stream channels have been limited to smoothly contiguous gravel-bedded systems, surveying was optimized by topographic setting and scaled to localized bed and water surface discontinuities. Traces and visualizations of the jump regions indicated that dichotomous decimetre shifts in water surface topography occurred for both jump regions from lower to higher discharges. Systematic removal of the survey points and DEM differencing indicated that point densities of ten points per square metre, in conjunction with a survey structure targeting grade breaks of 0·3,0·5 m, were required to capture decimetre form variations of the natural jump regions. The DEMs highlight the importance of recognizing the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Impact of a rock avalanche on a moraine-dammed proglacial lake: Laguna Safuna Alta, Cordillera Blanca, Peru

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2005
Bryn Hubbard
Abstract Moraines that dam proglacial lakes pose an increasing hazard to communities in the Andes and other mountain ranges. The moraines are prone to failure through collapse, overtopping by lake waters or the effect of displacement waves resulting from ice and rock avalanches. Resulting floods have led to the loss of thousands of lives in the Cordillera Blanca mountains of Peru alone in the last 100 years. On 22 April 2002 a rock avalanche occurred immediately to the south-west of Laguna Safuna Alta, in the Cordillera Blanca. The geomorphic evidence for the nature, magnitude and consequences of this event was investigated in August 2002. Field mapping indicated that the avalanche deposited 8,20 × 106 m3 of rock into the lake and onto the surface of the frontal region of Glaciar Pucajirca, which flows into the lake. Repeated bathymetric surveying indicated that ,5 × 106 m3 of this material was deposited directly into the lake. The immediate effect of this event was to create a displacement wave that gained in height as it travelled along the lake basin, overtopping the impounding moraine at the lake's northern end. To achieve overtopping, the maximum wave height must have been greater than 100 m. This, and subsequent seiche waves, caused extensive erosion of both the proximal and distal faces of the impounding terminal moraine. Further deep gullying of the distal face of this moraine resulted from the supply of pressurized water to the face via a relief overflow tunnel constructed in 1978. Two-dimensional, steady-state analysis of the stability of the post-avalanche moraine rampart indicates that its proximal face remains susceptible to major large-scale rotational failure. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Stratigraphic and Morphologic Constraints on the Weichselian Glacial History of Northern Prins Karls Forland, Western Svalbard

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2000
Torbjörn Andersson
Uncertainty remains if ice,free marginal areas existed on the west coast of Svalbard during the Late Weichselian. Field mapping and correlation to well dated raised beach sequences on nearby Brøggerhalvøya reveal the existence of two generations of raised beach deposits on northern Prins Karls Forland. Distinct beach ridges rise up to the inferred Late Weichselian marine limit at 18 m a.s.l. Discontinuous pre,Late Weichselian beach deposits rise from the Late Weichselian marine limit up to approximately 60 m a.s.l. Expansion of local glaciers during the Late Weichselian is indicated by the limited distribution of a till that overlies parts of the older beach sequence. Stratigraphic data and chronological control indicate deposition in a shallow marine environment before 50 ka bp. Correlation to stratigraphic sites on western Svalbard suggests deposition at c. 70 ±10 ka. Glaciotectonic structures disclose expansion of local glaciers into the For,landsundet basin during stage 4 or late stage 5 high relative sea level. Palaeotemperature estimates derived from amino acid ratios indicate that during the time interval c. 70 to 10 ka the area was exposed to cold subaerial temperatures with low rates of racemization. Pedogenesis and frost,shattered clasts at the contact between c. 70 ka deposits and Holocene deposits further indicate a prolonged period of subaerial polar desert conditions during this time interval. The evidence suggests that the Barents Sea ice sheet did not extend across northern Prins Karls Forland during the Weichselian. It is inferred that during the Late Weichselian, ice was drained throughout the major fjords on the west coast of Svalbard and that relatively large marginal areas experienced polar desert conditions and minor expansions of local glaciers. [source]

Slope development reconstruction at two sites in the Bohemian Forest Mountains

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010
Filip Hartvich
Abstract Although the Bohemian Forest is generally considered to be geomorphologically a rather stable region, there are localities which bear proof of a surprisingly high intensity of recent and even present day processes. A multidisciplinary methodology based on the analysis of slope systems was used for researching the present and past dynamics of two hillslopes. Using the results of direct dilatometric monitoring (the slow creep of rock blocks reached a maximum of 1,mm year,1), GPS field mapping, sedimentology, geodetic measurements and DEM analyses, several common rules have been observed for the behaviour of two model localities and a likely polycyclic development established, with recurrence of mass-wasting cycles related to material supply thresholds. Radiometric dating of debris flow activity showed that the cycles span approximately 4000 years. In this area of rather stable bedrock conditions, at least two factors that decrease slope stability need to act together to activate slope processes: i.e. a favourable structural predisposition (dip of major joint or bedding planes) and an increase in relief through either glaciation or river incision. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step,pool channel

Modeling and predicting complex space,time structures and patterns of coastal wind fields

ENVIRONMETRICS, Issue 5 2005
Montserrat Fuentes
Abstract A statistical technique is developed for wind field mapping that can be used to improve either the assimilation of surface wind observations into a model initial field or the accuracy of post-processing algorithms run on meteorological model output. The observed wind field at any particular location is treated as a function of the true (but unknown) wind and measurement error. The wind field from numerical weather prediction models is treated as a function of a linear and multiplicative bias and a term which represents random deviations with respect to the true wind process. A Bayesian approach is taken to provide information about the true underlying wind field, which is modeled as a stochastic process with a non-stationary and non-separable covariance. The method is applied to forecast wind fields from a widely used mesoscale numerical weather prediction (NWP) model (MM5). The statistical model tests are carried out for the wind speed over the Chesapeake Bay and the surrounding region for 21 July 2002. Coastal wind observations that have not been used in the MM5 initial conditions or forecasts are used in conjunction with the MM5 forecast wind field (valid at the same time that the observations were available) in a post-processing technique that combined these two sources of information to predict the true wind field. Based on the mean square error, this procedure provides a substantial correction to the MM5 wind field forecast over the Chesapeake Bay region. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Tectonics and quaternary evolution of the Northern Apennines watershed area (upper course of Arno and Tiber rivers, Italy)

GEOLOGICAL JOURNAL, Issue 1 2009
Marco Bonini
Abstract This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary Tuscan-Romagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1,Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle,Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Formation and reorientation of structure in the surge-type glacier Kongsvegen, Svalbard

JOURNAL OF QUATERNARY SCIENCE, Issue 3 2002
John Woodward
Abstract Kongsvegen, a surge-type glacier in Spitsbergen, Svalbard, shares a tide-water margin with the glacier Kronebreen. The complex has been in retreat since a surge advance of Kongsvegen around 1948. The surface of Kongsvegen displays suites of deformational structures highlighted by debris-rich folia. These structures are melting out to form a network of sediment ridges in the grounded terminal area. The structures are also visible in a marginal, 1 km long, 5,20 m high cliff-face at the terminus. Current models for the evolution of deformational structures at Kongsvegen divide the structures into suites based on their orientation and dip, before assigning a mechanism for genesis based on structure geometry. Interpretation of aerial photographs and field mapping of surface structures suggest that many structures were reorientated or advected during the surge. We suggest that many of the deformational structures highlighted by debris-rich folia represent reorientated, sediment-filled crevasses. Some evidence of thrusting is apparent but the process is not as ubiquitous as previously suggested. Many deformational structures also appear to have been offset by more recent structures. Mechanisms of structural development must, therefore, be considered within the context of distinct stages of glacier flow dynamics and multiple surge episodes. Furthermore, evidence for thrusting and folding within the glacier systems of Svalbard has been used as the basis for interpreting Quaternary glacial landforms in the UK. The findings of this paper, therefore, have implications for interpretations of the Quaternary record. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Simultaneous echo refocusing in EPI

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2002
David A. Feinberg
Abstract A method to encode multiple two-dimensional Fourier transform (2D FT) images within a single echo train is presented. This new method, simultaneous echo refocusing (SER), is a departure from prior echo planar image (EPI) sequences which use repeated single-shot echo trains for multislice imaging. SER simultaneously acquires multiple slices in a single-shot echo train utilizing a shared refocusing process. The SER technique acquires data faster than conventional multislice EPI since it uses fewer gradient switchings and fewer preparation pulses such as diffusion gradients. SER introduces a new capability to simultaneously record multiple spatially separated sources of physiologic information in subsecond image acquisitions, which enables several applications that are dependent on temporal coherence in MRI data including velocity vector field mapping and brain activation mapping. Magn Reson Med 48:1,5, 2002. © 2002 Wiley-Liss, Inc. [source]

Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties ,

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2001
Marcello Alecci
Abstract The RF B1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B1 distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B1 uniformity was 9 cm with phantoms and 7 cm in the head. Magn Reson Med 46:379,385, 2001. © 2001 Wiley-Liss, Inc. [source]

Trabecular bone volume fraction mapping by low-resolution MRI

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2001
M.A. Fernández-Seara
Abstract Trabecular bone volume fraction (TBVF) is highly associated with the mechanical competence of trabecular bone. TBVF is ordinarily measured by histomorphometry from bone biopsies or, noninvasively, by means of high-resolution microcomputed tomography and, more recently, by micro-MRI. The latter methods require spatial resolution sufficient to resolve trabeculae, along with segmentation techniques that allow unambiguous assignment of the signal to bone or bone marrow. In this article it is shown that TBVF can be measured under low-resolution conditions by exploiting the attenuation of the MR signal resulting from fractional occupancy of the imaging voxel by bone and bone marrow, provided that a reference signal is available from a marrow volume devoid of trabeculation. The method requires accurate measurement of apparent proton density, which entails correction for various sources of error. Key among these are the spatial nonuniformity in the RF field amplitude and effects of the slice profile, which are determined by B1 field mapping and numerical integration of the Bloch equations, respectively. By contrast, errors from variations in bone marrow composition (hematopoietic vs. fatty) between trabecular and reference site are predicted to be small and usually negligible. The method was evaluated in phantoms and in vivo in the distal radius and found to be accurate to 1% in marrow volume fraction. Finally, in a group of 12 patients of varying skeletal status, TBVF in the calcaneus was found to strongly correlate with integral bone mineral density of the lumbar vertebrae (r2 = 0.83, p < 0.0001). The method may fail in large imaging objects such as the human trunk at high magnetic field where standing wave and RF penetration effects cause intensity variations that cannot be corrected. Magn Reson Med 46:103,113, 2001. © 2001 Wiley-Liss, Inc. [source]