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101.
Markus Wallner Georg Houben Christoph Lohe Martin Quinger Thomas Himmelsbach 《Hydrogeology Journal》2017,25(8):2303-2321
The identification of potential recharge areas and estimation of recharge rates to the confined semi-fossil Ohangwena II Aquifer (KOH-2) is crucial for its future sustainable use. The KOH-2 is located within the endorheic transboundary Cuvelai-Etosha-Basin (CEB), shared by Angola and Namibia. The main objective was the development of a strategy to tackle the problem of data scarcity, which is a well-known problem in semi-arid regions. In a first step, conceptual geological cross sections were created to illustrate the possible geological setting of the system. Furthermore, groundwater travel times were estimated by simple hydraulic calculations. A two-dimensional numerical groundwater model was set up to analyze flow patterns and potential recharge zones. The model was optimized against local observations of hydraulic heads and groundwater age. The sensitivity of the model against different boundary conditions and internal structures was tested. Parameter uncertainty and recharge rates were estimated. Results indicate that groundwater recharge to the KOH-2 mainly occurs from the Angolan Highlands in the northeastern part of the CEB. The sensitivity of the groundwater model to different internal structures is relatively small in comparison to changing boundary conditions in the form of influent or effluent streams. Uncertainty analysis underlined previous results, indicating groundwater recharge originating from the Angolan Highlands. The estimated recharge rates are less than 1% of mean yearly precipitation, which are reasonable for semi-arid regions. 相似文献
102.
Synchronizing seismic networks with ambient noise 总被引:1,自引:0,他引:1
Christoph Sens-Schönfelder 《Geophysical Journal International》2008,174(3):966-970
The technique of retrieving Green's functions by pairwise correlation of a random wavefield is used to estimate the stability of the timing system of a seismic network. The method is demonstrated with data from a network consisting of stations with four independent clocks and GPS-receivers. For a two years period, daily measurements of the timing error of each of the four systems are obtained. These measurements can be used to correct the timing of the data in periods without GPS reception. The accuracy of this method can exceed the precision of the internal station clocks already after a single day of uncorrected drift. 相似文献
103.
Dirk Enters Hermann Behling Christoph Mayr Lydie Dupont Bernd Zolitschka 《Journal of Paleolimnology》2010,44(1):265-277
Environmental changes of the last 9,300 years were reconstructed by geochemical and pollen analyses of a 14-m-long, laminated
sediment core from Lago Aleixo, south-eastern Brazil. Fossil pollen assemblages indicate open savannah vegetation (campo cerrado)
and gallery forests until approximately 6,900 cal. BP. During that time, siderite laminae were deposited under anoxic conditions
at the lake bottom. Then, increased rainfall and a shorter annual dry period allowed gallery forests and semi-deciduous forests
to expand, leading to more closed cerrado vegetation. High-intensity rainfall events during this period are recorded as peaks
in K and Ti concentrations. The sediment facies during this period consists of alternating layers of diatoms and minerogenic
matter. C/N ratios imply that algae and perhaps soils, too, were the main contributors to sediment organic matter. Biogenic
silica and δ13Corg variations indicate increasing primary productivity, which was related to higher nutrient flux from intensified leaching
of soils, as shown by rising K/Al ratios. Around 800 cal. BP, a closed, semi-deciduous forest developed under present-day
climate conditions. Slope stabilization diminished erosion processes in the catchment and caused reduced input of minerogenic
matter into the basin. Human impact is evident in the topmost homogeneous sediments, as removal of the stabilizing forest
cover amplified soil erosion. The continuous trend to more humid conditions during the Holocene probably reflects increased
influence of the Amazon Basin as a moisture source. We conclude that the Lago Aleixo sediment archive was a sensitive recorder
of environmental dynamics in tropical South America, which were mainly controlled by changes in precipitation patterns. 相似文献
104.
Christoph Siart Markus Forbriger Erich Nowaczinski Stefan Hecht Bernhard Höfle 《地球表面变化过程与地形》2013,38(10):1135-1147
A multi‐method research design based on terrestrial laser scanning, GIS, geophysical prospecting (electrical resistivity tomography, refraction seismics) and sedimentology is applied for the first time to investigate enclosed karst depressions in an integrated way. Fusing multi‐resolution surface and subsurface geodata provides profound insights into the formation, geometry and geomorphologic processes of dolines. The studied landforms, which are located in the Dikti Mountains of East Crete, are shown to be filled by loose sediments of thicknesses of up to 30 m that mainly consist of fine‐grained material overlying solid bedrock at depths below 35 to 45 m. By combining subsurface observations with geomorphometric calculations, local doline genesis can be traced back to initial collapse of fractured bedrock followed by subsequent infilling with colluvials. In order to define crucial methodological requirements and guidelines for data fusion, both the impact of different elevation models and the influence of data resolution are assessed. Surface volumes of depressions derived by the digital surface model are 7–21% higher than the results obtained from the terrain model due to vegetation. Similarly, estimates of infill volume calculated on the basis of geophysical outcomes and elevation data differ by up to 13%. Calculations of the landforms' current volumes (i.e. total surface and subsurface volume), however, are fairly insensitive to raster resolution. Hence, the distinct geomorphologic properties of landforms (e.g. shape, terrain roughness, slope inclination) substantially determine the geomorphometric analysis of both surface and subsurface data. As shown by the findings, data fusion to integrate digital terrain, geophysical and sedimentological datasets of varied resolutions benefits geomorphologic studies and helps provide a comprehensive image of landforms. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
105.
Yu Zhang Heping Liu Thomas Foken Quinton L. Williams Matthias Mauder Christoph Thomas 《Theoretical and Applied Climatology》2011,103(1-2):119-131
The turbulence data measured at two levels (i.e., 8.7 and 2.7?m) in the Energy Balance Experiment (EBEX), which was conducted in San Joaquin Valley in California during the period from July 20 to August 24, 2000, are used to study the characteristics of coherent structures over an irrigated cotton field. Patch-to-patch irrigation in the field generated the dry-to-wet horizontal advection and the oasis effects, leading to the development of a stably internal boundary layer (SIBL) in the late mornings or the early afternoons. The SIBL persisted in the rest of the afternoons. Under this circumstance, a near-neutral atmospheric surface layer (ASL) developed during the period with a stratification transition from the unstable to stable conditions during the daytime. Therefore, EBEX provides us with unique datasets to investigate the features of coherent structures that were generated over the patches upstream and passed by our site in the unstable ASL, the near-neutral ASL, and the SIBL. We use an objective detection technique and the conditional average method that is developed based on the wavelet analysis. Our data reveal some consistencies and inconsistencies in the characteristics of coherent structures as compared with previous studies. Ramp-like structures and sweep?Cejection cycles under the daytime SIBL have similar patterns to those under the nocturnal stable ASL. However, some features (i.e., intermittence) are different from those under the nocturnal stable ASL. Under the three stratifications, thermal and mechanical factors in the ASL perform differently in affecting the ramp intensity for different quantities (i.e., velocity components, temperature, and specific humidity), leading to coherent structures that modulate turbulence flow and alter turbulent transfer differently. It is also found that coherent structures contribute about 10?C20% to the total fluxes in our case with different flux contributions under three stratifications and with higher transporting efficiency in sensible heat flux than latent heat and momentum fluxes. 相似文献
106.
Hans Romang Massimiliano Zappa Nadine Hilker Matthias Gerber François Dufour Valérie Frede Dominique Bérod Matthias Oplatka Christoph Hegg Jakob Rhyner 《Natural Hazards》2011,56(2):509-527
IFKIS-Hydro is an information and warning system for hydrological hazards in small- and medium-scale catchments. The system
collects data such as weather forecasts, precipitation measurements, water level gauges, discharge simulations and local observations
of event-specific phenomena. In addition, IFKIS-Hydro incorporates a web-based information platform, which serves as a central
hub for the submission and overview of data. Special emphasis is given to local information. This is accomplished particularly
by human observers. In medium-scale catchments, discharge forecast models have an increasing importance in providing valuable
information. IFKIS-Hydro was developed in several test regions in Switzerland and the first results of its application are
available now. The system is constantly extended to additional regions and may become the standard for warning systems in
smaller catchments in Switzerland. 相似文献
107.
Jashar?ArfaiEmail author Dieter?Franke Christoph?Gaedicke Rüdiger?Lutz Michael?Schnabel Stefan?Ladage Kai?Berglar Mario?Aurelio Jennie?Montano Nicole?Pellejera 《Marine Geophysical Researches》2011,32(3):349-362
Interpretation of deep 2-D multi-channel seismic data sheds insights into the geological evolution of the West Luzon Basin,
Philippines. This basin is a sediment-filled trough that is located between the island of Luzon and the outer arc high of
the west Luzon subduction zone. High-amplitude, low-frequency reflection bands mark the acoustic basement. The basement, at
about 6 s (TWT), is dissected by normal faults with some of them being inverted in a later phase of deformation. The sedimentary
successions, overlying the basement are stratified with partly chaotic structures and discontinuous reflectors. Five regional
unconformities separate major stratigraphic units. Grid calculations of our seismic data reveal variations in the sedimentation
pattern of the basin with a shift of the deposition centre from east to west and backwards during formation. A distinct bottom-simulating
reflector is commonly observed. Because the northern boundary of the continental fragments to the South of the West Luzon
Basin is unclear we speculate that the basin may be (partly) underlain by continental crust. The continental crust was affected
by rifting prior to and during the opening of the South China Sea and the basin was overprinted at a later stage by a forearc
structural setting when subduction was initiated. 相似文献
108.
Safe pipeline transportation of carbon dioxide is a critical issue in the developing field of carbon capture and storage technology. Inadequate fluid thermo- and regimes for on- and offshore transport through high-pressurized pipelines can induce pipe material obsolescence or even pipeline rupture. In such cases, CO2 (Carbon dioxide) will be released and dispersed in the ambient medium. The dispersion is influenced by the total amount of released fluid, jet pressure and direction, the released concentrations, leakage hole size, ambient material properties and is also affected by the dynamical conditions of the environmental medium. The goal of this study is the hydrodynamical characterization of carbon dioxide jet expansion and dispersion in the ambient atmosphere in case of onshore pipeline accidental leaks. Numerical simulations were carried out by means of a 3D turbulent CFD (computational fluid dynamics) code which includes multi-component flow treatment. The influence of the jet release pressure and size of the leakage hole on harmful CO2 concentration distances will be analyzed. 相似文献
109.
Christoph Clauser 《Surveys in Geophysics》2009,30(3):163-191
The heat of the Earth derives from internal and external sources. A heat balance shows that most of the heat provided by external
sources is re-emitted by long-wavelength heat radiation and that the dominant internal sources are original heat and heat
generated by decay of unstable radioactive isotopes. Understanding of the thermal regime of the Earth requires appreciation
of properties and mechanisms for heat generation, storage, and transport. Both experimental and indirect methods are available
for inferring the corresponding rock properties. Heat conduction is the dominant transport process in the Earth’s crust, except
for settings where appreciable fluid flow provides a mechanism for heat advection. For most crustal and mantle rocks, heat
radiation becomes significant only at temperatures above 1200°C.
相似文献
Christoph ClauserEmail: |
110.
Claire L. Smith Ian J. Fairchild Christoph Spötl Silvia Frisia Andrea Borsato Steven G. Moreton Peter M. Wynn 《Quaternary Geochronology》2009,4(1):11-21
Determination of annual lamination provides important additional constraints to radiometric dates on speleothems, both for dating the duration of specific growth intervals and optimizing growth models. In the absence of visible laminae, however, speleothem age models are reliant upon curve fitting through discretely dated points and are therefore inherently more uncertain than annual chronologies from laminae. Given that the impact of seasonality on speleothems is expected to be strong enough to generate an annual pulse in trace element chemistry regardless of whether or not visible or fluorescent growth laminae are visible, we demonstrate the potential for deriving high-resolution stalagmite chronologies from non-laminated samples using annual chemical variations in stalagmites from two Alpine caves (Obir, Austria and Ernesto, NE Italy). Trace element data were obtained by ion microprobe analyses for H, P, Mg, Na, Sr and Ba and the annual signal was sought using spectral and wavelet analysis. An automated chemical peak-counting software tool was developed in MATLAB©. It counts significant annual peaks using criteria of minimum amplitude in relation to the local standard deviation of signal variation and minimum separation between peaks determined by the thickness of the preceding layers. Verification of the tool using visibly laminated samples suggests the software is a reliable and accurate method of chronology building, with hit ratios greater than 0.93 and less than 0.75% false alarm occurrences. Used in conjunction with other dating methods such as radiocarbon, U–Th and sulphur peak dating, the automated chemical laminae chronology-building approach provides a more meaningful alternative to simple age-depth curve fitting for non-laminated samples. 相似文献