Monitoring volcanic hazard using eddy covariance at Solfatara volcano, Naples, Italy     

C Werner  G Chiodini  D Voigt  S Caliro  R Avino  M Russo  T Brombach  J Wyngaard  S Brantley 《Earth and Planetary Science Letters》2003,210(3-4):561-577

An eddy covariance (EC) station was deployed at Solfatara crater, Italy, June 8–25, 2001 to assess if EC could reliably monitor CO₂ fluxes continuously at this site. Deployment at six different locations within the crater allowed areas of focused gas venting to be variably included in the measured flux. Turbulent (EC) fluxes calculated in 30-min averages varied between 950 and 4460 g CO₂ m⁻² d⁻¹; the highest measurements were made downwind of degassing pools. Comparing turbulent fluxes with chamber measurements of surface fluxes using footprint models in diffuse degassing regions yielded an average difference of 0% (±4%), indicating that EC measurements are representative of surface fluxes at this volcanic site. Similar comparisons made downwind of degassing pools yielded emission rates from 12 to 27 t CO₂ d⁻¹ for these features. Reliable EC measurements (i.e. measurements with sufficient and stationary turbulence) were obtained primarily during daytime hours (08:00 and 20:00 local time) when the wind speed exceeded 2 m s⁻¹. Daily average EC fluxes varied by ±50% and variations were likely correlated to changes in atmospheric pressure. Variations in CO₂ emissions due to volcanic processes at depth would have to be on the same order of magnitude as the measured diurnal variability in order to be useful in predicting volcanic hazard. First-order models of magma emplacement suggest that emissions could exceed this rate for reasonable assumptions of magma movement. EC therefore provides a useful method of monitoring volcanic hazard at Solfatara. Further, EC can monitor significantly larger areas than can be monitored by previous methods.  相似文献   

The measurement of sulfate mineral solubilities in the Na-K-Ca-Cl-SO₄-H₂O system at temperatures of 100, 150 and 200°C     

Daniela Freyer  Wolfgang Voigt 《Geochimica et cosmochimica acta》2004,68(2):307-318

At T > 100°C development of thermodynamic models suffers from missing experimental data, particularly for solubilities of sulfate minerals in mixed solutions. Solubilities in Na⁺-K⁺-Ca²⁺-Cl⁻-SO₄²⁻/H₂O subsystems were investigated at 150, 200°C and at selected compositions at 100°C. The apparatus used to examine solid-liquid phase equilibria under hydrothermal conditions has been described.In the system NaCl-CaSO₄-H₂O the missing anhydrite (CaSO₄) solubilities at high NaCl concentrations up to halite saturation have been determined. In the system Na₂SO₄-CaSO₄-H₂O the observed glauberite (Na₂SO₄ · CaSO₄) solubility is higher than that predicted by the high temperature model of Greenberg and Møller (1989), especially at 200°C. At high salt concentrations, solubilities of both anhydrite and glauberite increase with increasing temperature. Stability fields of the minerals syngenite (K₂SO₄ · CaSO₄ · H₂O) and goergeyite (K₂SO₄ · 5 CaSO₄ · H₂O) were determined, and a new phase was found at 200°C in the K₂SO₄-CaSO₄-H₂O system. Chemical and single crystal structure analysis give the formula K₂SO₄ · CaSO₄. The structure is isostructural with palmierite (K₂SO₄ · PbSO₄). The glaserite (“3 K₂SO₄ · Na₂SO₄”) appears as solid solution in the system Na₂SO₄-K₂SO₄-H₂O. Its solubility and stoichiometry was determined as a function of solution composition.  相似文献   

"Exploration for Hidden Water" by Mohammad Karaji—The Oldest Textbook on Hydrology?     

Mehdi Nadji  Rudolf Voigt 《Ground water》1972,10(5):43-46

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Über Hiatus-Konkretionen (dargestellt an Beispielen aus dem Lias)     

Prof. Dr. Ehrhard Voigt 《International Journal of Earth Sciences》1968,58(1):281-296

Zusammenfassung Als Hiatus-Konkretionen werden Kalk-Konkretionen aus dem nord- und süddeutschen Lias (Domerien) beschrieben, welche ein durch Sedimentationsunterbrechungen bedingtes mehrphasiges Wachstum erkennen lassen oder durch das Zusammenwachsen verschieden alter, durch Diskontinuitätsflächen getrennter Konkretionen entstanden sind.Der Hiatus wird dadurch bewiesen, daß die frühdiagenetisch im Sediment gebildeten Konkretionen ausgewaschen, korrodiert, angebohrt oder von Austern, Serpuliden, Bryozoen oder anderen sessilen Organismen besiedelt wurden. Nach erneuter Einbettung setzt die Konkretionsbildung wieder ein, wobei sich die jüngeren Toneisensteine um die älteren, die ihnen als Ansatzstellen dienten, herum gebildet haben.

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Calcareous concretions from the middle Lias (Domerian) of Northern and Southern Germany revealing growth in several phases conditioned by interruptions of sedimentation or by coalescence of concretions of different age are called Hiatus Concretions. The hiatuses are proved by the fact that these concretions, which were formed in the sediment by early diagenetic processes, were washed out and are corroded or bored on the surface and encrusted by oysters, serpulids, bryozoans or other sessile benthonic organisms.After a new beginning of sedimentation the growth of the concretions started again. By this process the younger concretions included the older ones which often were the starting point for a new generation of concretions.In section the ancient surfaces with incrusting shells can be observed.

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Résumé Des concrétions de CaCO₃ du lias moyen (Domérien) de l'Allemagne du Nord et de Sud laissant reconnaître une croissance en plusieurs phases conditionnées par des interruptions de la sédimentation ou qui sont formées par une fusion des concrétions separées par des surfaces de discontinuité sont appelées des «concrétions à hiatus».Le hiatus est reconnu par le fait que les concrétions formées dans le sédiment pendant la première phase d'une diagénèse sont erodées, corrodées, envahies par des organismes perforants, ou recouvertes en partie par des Huîtres, Serpulides, Bryozoaires ou autres animaux sessiles. Après une sédimentation nouvelle la croissance des concrétions s'est poursuivie. Les concrétions nouvelles ont enveloppées les anciennes qui leur ont servi de noyaux. On peut observer sur les sections des surfaces de discontinuité marquées par des organismes encroûtants.

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Airborne near-real-time monitoring of assembly and parking areas in case of large-scale public events and natural disasters     

Hannes Römer  Jens Kersten  Ralph Kiefl  Stefan Plattner  Alexander Mager  Stefan Voigt 《International journal of geographical information science》2014,28(4):682-699

A critical requirement for an effective and coordinated response by public entities tasked with management, security, and relief during large-scale public events or natural disasters is the availability of current situational information. However, today there is a lack of comprehensive operational systems allowing a near-real-time (NRT) collection, visualization, and provision of situational information for larger areas. In this study a methodological framework is proposed, which allows an NRT extraction and visualization of situational information based on aerial image acquisition. The framework combines digital image analysis using a generic supervised information extraction approach based on statistical modeling with a downstream web-based visualization component realized through an automatic update of web services. Even though being applicable for different scenarios, the workflow will be demonstrated for the specific use-case of a NRT monitoring of open spaces including assembly and parking areas. Compared to other approaches, image analysis results indicate a high robustness and a low demand for computational power sources (7 seconds per image). Due to a high degree of automation, the proposed workflow contributes to a NRT ‘end-to-end’ monitoring system, which was developed within the VABENE (German acronym for ‘traffic management under large-scale public events and disaster conditions’) project covering all parts from the acquisition of raw aerial imagery to the dissemination of information products to end-users.  相似文献   

Galaxy cluster mass profiles     

L. M. Voigt  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2006,368(2):518-533

Accurate measurements of the mass distribution in galaxy and cluster haloes are essential to test the cold dark matter (CDM) paradigm. The cosmological model predicts a universal shape for the density profile in all haloes, independent of halo mass. Its profile has a 'cuspy' centre, with no evidence for the constant density core. In this paper, we carry out a careful analysis of 12 galaxy clusters, using Chandra data to compute the mass distribution in each system under the assumption of hydrostatic equilibrium. Due to their low concentration, clusters provide ideal objects for studying the central cusps in dark matter haloes. The majority of the systems are consistent with the CDM model, but four objects exhibit flat inner density profiles. We suggest that the flat inner profile found for these clusters is due to an underestimation of the mass in the cluster centre (rather than any problem with the CDM model), since these objects also have a centrally peaked gas mass fraction. We discuss possible causes for erroneously low-mass measurements in the cores of some systems.  相似文献   

The transition from the present-day climate to a modern Snowball Earth     

Aiko Voigt  Jochem Marotzke 《Climate Dynamics》2010,35(5):887-905

We use the coupled atmosphere–ocean general circulation model ECHAM5/MPI-OM to investigate the transition from the present-day climate to a modern Snowball Earth, defined as the Earth in modern geography with complete sea-ice cover. Starting from the present-day climate and applying an abrupt decrease of total solar irradiance (TSI) we find that the critical TSI marking the Snowball Earth bifurcation point is between 91 and 94% of the present-day TSI. The Snowball Earth bifurcation point as well as the transition times are well reproduced by a zero-dimensional energy balance model of the mean ocean potential temperature. During the transition, the asymmetric distribution of continents between the Northern and Southern Hemisphere causes heat transports toward the more water-covered Southern Hemisphere. This is accompanied by an intensification of the southern Hadley cell and the wind-driven subtropical ocean cells by a factor of 4. If we set back TSI to 100% shortly before the transition to a modern Snowball Earth is completed, a narrow band of open equatorial water is sufficient for rapid melting. This implies that for 100% TSI the point of unstoppable glaciation separating partial from complete sea-ice cover is much closer to complete sea-ice cover than in classical energy balance models. Stable states can have no greater than 56.6% sea-ice cover implying that ECHAM5/MPI-OM does not exhibit stable states with near-complete sea-ice cover but open equatorial waters.  相似文献   

Biocalcification in the Eastern Oyster (<Emphasis Type="Italic">Crassostrea virginica)</Emphasis> in Relation to Long-term Trends in Chesapeake Bay pH     

George G. Waldbusser  Erin P. Voigt  Heather Bergschneider  Mark A. Green  Roger I. E. Newell 《Estuaries and Coasts》2011,34(2):221-231

Anthropogenic carbon dioxide (CO₂) emissions reduce pH of marine waters due to the absorption of atmospheric CO₂ and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed 23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures. Biocalcification declined significantly with a reduction of ∼0.5 pH units and higher temperature and salinity mitigated the decrease in biocalcification.  相似文献   

The use of tracers to assess drill-mud penetration depth into sandstone cores during deep drilling: method development and application     

Linda Pellizzari  Dominik Neumann  Mashal Alawi  Dieter Voigt  Ben Norden  Hilke Würdemann 《Environmental Earth Sciences》2013,70(8):3727-3738

For the utilization of deep saline aquifers in the frame of geotechnical use, such as geological sequestration of CO₂, H₂ or energy storage, a baseline characterization of pristine reservoir rock cores is required to monitor changes in the indigenous microbial communities and pore fluids, and to study alterations in rock characteristics resulting from interaction with geological storage technologies. However, drilling procedures and technical fluids, particularly drill mud, are sources of core contamination. To measure the penetration of drill mud into the cores, three tracers (fluorescein, microspheres, and 4′,6-diamidino-2-phenylindole stained bacteria) were tested under laboratory conditions. The flow of drill mud into core samples was induced by applying uniaxial pressure differentials to the core, and the penetration depth was microscopically determined for each tracer. Fluorescein was extracted from the rock samples and quantified fluorometrically. The results indicate that all tested tracers are suitable for tracking drill-mud penetration. The actual penetration depth seems to be related to differences in mineral composition and texture as well as microfractures. Among all tested tracers, fluorescein labelling is the simplest, cheapest and most accurate method for analyzing the contamination of rock cores by technical fluids. The application of this tracer was successfully applied during two deep drilling campaigns at the CO₂ storage pilot site in Ketzin, Germany. The results highlight that the use of tracers is indispensable to ensure the quality of core samples for microbiological and biogeochemical analysis.  相似文献   

Utility of the 2-D Multi-Electrode Resistivity Imaging Technique in Groundwater Exploration in the Voltaian Sedimentary Basin, Northern Ghana   总被引：2，自引：0，他引：2  

Anthony Ewusi  Jerry S. Kuma  Hans J. Voigt 《Natural Resources Research》2009,18(4):267-275

Guinea worm and other water borne diseases associated with untreated surface water use have necessitated that communities are supplied with groundwater in the Northern Region of Ghana. The Electrical Resistivity Survey (ERS) method is one of the common geophysical survey techniques used for borehole siting in Ghana. Various groundwater exploration programs have utilized it by employing the four electrode system. However, the ERS has not been able to locate potential borehole sites successfully in the Voltaian Sedimentary Basin (VSB) in the Northern Region of Ghana although it has been successful in other geological formations. Unsatisfactory results obtained from the employment of the ERS system in the VSB therefore necessitated an experiment with the 2-D Multi-Electrode Resistivity Imaging (2-D MERI) technique. Field results show that the 2-D MERI is a robust and efficient technique: an improvement on the four electrode ERS system in terms of amount and quality of data obtained. The 2-D MERI interpretations were confirmed with a much improved borehole drilling success rate of 60% compared to 38% obtained using the ERS within the mudstone and shale formations. The 2-D MERI also indicated that very low resistivity layers in the VSB may not necessarily be good targets for borehole drilling and the generally held notion that groundwater cannot be found at depths more than 25 m is no longer tenable.  相似文献