New VLBI2010 scheduling strategies and implications on the terrestrial reference frames   总被引：1，自引：1，他引：0  

Jing Sun  Johannes Böhm  Tobias Nilsson  Hana Krásná  Sigrid Böhm  Harald Schuh 《Journal of Geodesy》2014,88(5):449-461

In connection with the work for the next generation VLBI2010 Global Observing System (VGOS) of the International VLBI Service for Geodesy and Astrometry, a new scheduling package (Vie_Sched) has been developed at the Vienna University of Technology as a part of the Vienna VLBI Software. In addition to the classical station-based approach it is equipped with a new scheduling strategy based on the radio sources to be observed. We introduce different configurations of source-based scheduling options and investigate the implications on present and future VLBI2010 geodetic schedules. By comparison to existing VLBI schedules of the continuous campaign CONT11, we find that the source-based approach with two sources has a performance similar to the station-based approach in terms of number of observations, sky coverage, and geodetic parameters. For an artificial 16 station VLBI2010 network, the source-based approach with four sources provides an improved distribution of source observations on the celestial sphere. Monte Carlo simulations yield slightly better repeatabilities of station coordinates with the source-based approach with two sources or four sources than the classical strategy. The new VLBI scheduling software with its alternative scheduling strategy offers a promising option with respect to applications of the VGOS.  相似文献   

Combining the Arc Marine Framework with Geographic Metadata to Support Ocean Acoustic Modeling     

Anthony W. Isenor  Tobias W. Spears 《Transactions in GIS》2014,18(2):183-200

A data model for use in a rapid environmental assessment system is constructed. The data model is used in an information layer that supports acoustic assessments of the ocean environment. Such an assessment requires use of both historic and real‐time oceanographic data. The foundation of the data model is Arc Marine, a framework specification for geospatial oceanographic databases that provides structures for containing the basic data types used in oceanographic research. Arc Marine also allows design extensions to account for application specific data structures as demonstrated through incorporation of aspects of the International Organization for Standardization (ISO) 19115 Geographic Information–Metadata standard. The ISO 19115 standard provides structures for recording the historic processing of the data sets. The data model is used to construct a database in the open source database management system (DBMS) PostgreSQL. The resulting system also incorporates the concept of user exits, the seamless extension of the DBMS through inclusion of application‐specific software.  相似文献   

Decoding the complex internal chemical structure of garnet porphyroblasts from the Zermatt area,Western Alps   总被引：1，自引：0，他引：1  

Kurt Bucher  Tobias Bjrn Weisenberger  Oliver Klemm  Sebastian Weber 《Journal of Metamorphic Geology》2019,37(9):1151-1169

Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and textural features that can be used for untangling its metamorphic development. Large garnet porphyroblasts may show extremely complex internal structures as a result of a polycyclic growth history, deformation, and modification of growth structures by intra‐ and intercrystalline diffusion. The complex internal structure of garnet porphyroblasts from garnet–phengite schists (GPS) of the Zermatt area (Western Alps) has been successfully decoded. The centimetre‐sized garnet porphyroblasts are composed of granulite facies garnet fragments overgrown by a younger generation of grossular‐rich eclogite facies garnet. The early granulite facies garnet (G‐Grt) formed from low‐P, high‐T metamorphism during a pre‐Alpine orogenic event. The late garnet (E‐Grt) is typical of high‐pressure, low‐temperature (HPLT) metamorphism and can be related to Alpine subduction of the schists. Thus, the garnet of the GPS are polycyclic (polymetamorphic). G‐Grt formation occurred at ~670 MPa and 780°C, E‐Grt formed at ~1.7 GPa and 530°C. The G‐Grt is relatively rich in Prp and poor in Grs, while E‐Grt is rich in Grs and poor in Prp. The Alm content (mol.%) of G‐Grt is 68 of E‐Grt 55. After formation of E‐Grt between and around fragmented G‐Grt at 530°C, the GPS have been further subducted and reached a maximum temperature of 580°C before exhumation started. Garnet composition profiles indicate that the initially very sharp contacts between the granulite facies fragments of G‐Grt and fracture seals of HPLT garnet (E‐Grt) have been modified by cation diffusion. The profiles suggest that Ca did not exchange at the scale of 1 µm, whereas Fe and Mg did efficiently diffuse at the derived maximum temperature of 580°C for the GPS at the scale of 7–8 µm. The Grt–Grt diffusion profiles resulted from spending c. 10 Ma at 530–580°C along the P–T–t path. The measured Grt composition profiles are consistent with diffusivities of log D_MgFe = ?25.8 m²/s from modelled diffusion profiles. Mg loss by diffusion from G‐Grt is compensated by Fe gain by diffusion from E‐Grt to maintain charge balance. This leads to a distinctive Fe concentration profile typical of uphill diffusion.  相似文献   

Erratum to: “A collaborative study on temperature diurnal tide in the midlatitude mesopause region (41°N, 105°W) with Na lidar and TIMED/SABER observations” [J. Atmos. Sol.–Terres. Phys. 72 (2010) 541–549]     

Tao Yuan  Chiao-Yao She  David Krueger  Steven C. Reising  Xiaoli Zhang  Jeffrey M. Forbes 《Journal of Atmospheric and Solar》2010,72(14-15):1067

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Influence of glacier advance on the development of the multipart Riffeltal rock glacier,Central Austrian Alps          下载免费PDF全文

Jana‐Marie Dusik  Matthias Leopold  Tobias Heckmann  Florian Haas  Ludwig Hilger  David Morche  Fabian Neugirg  Michael Becht 《地球表面变化过程与地形》2015,40(7):965-980

The multipart Riffeltal rock glacier, located in a tributary valley of the Kaunertal, Tyrol, Austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of pro‐glacial areas and to get a better understanding of glacier–rock glacier interactions. The subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages, origin and root zones, and therefore diverse development. To determine the reasons for their diverging development, the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping, geophysical methods and measurement of the basal temperature of the winter snow cover (BTS). Permafrost modelling was performed on the basis of BTS data and land surface parameters derived from a high resolution airborne laser scanning (ALS) digital elevation model (DEM). Additionally, the ALS data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012. Glacier–rock glacier interactions during and since the Little Ice Age (LIA) are evident for the development of the studied rock glacier. A geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence. The combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Authigenic carbonates from active methane seeps offshore southwest Africa   总被引：2，自引：1，他引：1  

Catherine Pierre  Marie-Madeleine Blanc-Valleron  Jér?me Demange  Omar Boudouma  Jean-Paul Foucher  Thomas Pape  Tobias Himmler  Noemi Fekete  Volkhard Spiess 《Geo-Marine Letters》2012,32(5-6):501-513

The southwest African continental margin is well known for occurrences of active methane-rich fluid seeps associated with seafloor pockmarks at water depths ranging broadly from the shelf to the deep basins, as well as with high gas flares in the water column, gas hydrate accumulations, diagenetic carbonate crusts and highly diverse benthic faunal communities. During the M76/3a expedition of R/V METEOR in 2008, gravity cores recovered abundant authigenic carbonate concretions from three known pockmark sites—Hydrate Hole, Worm Hole, the Regab pockmark—and two sites newly discovered during that cruise, the so-called Deep Hole and Baboon Cluster. The carbonate concretions were commonly associated with seep-benthic macrofauna and occurred within sediments bearing shallow gas hydrates. This study presents selected results from a comprehensive analysis of the mineralogy and isotope geochemistry of diagenetic carbonates sampled at these five pockmark sites. The oxygen isotope stratigraphy obtained from three cores of 2–5?m length indicates a maximum age of about 60,000–80,000?years for these sediments. The authigenic carbonates comprise mostly magnesian calcite and aragonite, associated occasionally with dolomite. Their very low carbon isotopic compositions (–61.0?<?δ¹³C ‰ V-PDB?<?–40.1) suggest anaerobic oxidation of methane (AOM) as the main process controlling carbonate precipitation. The oxygen isotopic signatures (+2.4?<?δ¹⁸O ‰ V-PDB?<?+6.2) lie within the range in equilibrium under present-day/interglacial to glacial conditions of bottom seawater; alternatively, the most positive δ¹⁸O values might reflect the contribution of ¹⁸O-rich water from gas hydrate decomposition. The frequent occurrence of diagenetic gypsum crystals suggests that reduced sulphur (hydrogen sulphide, pyrite) from sub-seafloor sediments has been oxidized by oxygenated bottom water. The acidity released during this process can potentially induce the dissolution of carbonate, thereby providing enough Ca²⁺ ions for pore solutions to reach gypsum saturation; this is thought to be promoted by the bio-irrigation and burrowing activity of benthic fauna. The δ¹⁸O–δ¹³C patterns identified in the authigenic carbonates are interpreted to reflect variations in the rate of AOM during the last glacial–interglacial cycle, in turn controlled by variably strong methane fluxes through the pockmarks. These results complement the conclusions of Kasten et al. in this special issue, based on authigenic barite trends at the Hydrate Hole and Worm Hole pockmarks which were interpreted to reflect spatiotemporal variations in AOM related to subsurface gas hydrate formation–decomposition.  相似文献   

The role of precursory structures on Tertiary deformation in the Black Forest—Hegau region     

Egli  Daniel  Mosar  Jon  Ibele  Tobias  Madritsch  Herfried 《International Journal of Earth Sciences》2017,106(7):2297-2318

International Journal of Earth Sciences - Structural inheritance of preexisting crustal discontinuities is widely accepted to have played a crucial role during the Cenozoic tectonic evolution of...  相似文献   

From geotechnical analysis to quantification and modelling using LiDAR data: a study on rockfall in the Reintal catchment,Bavarian Alps,Germany     

Tobias Heckmann  Martin Bimböse  Michael Krautblatter  Florian Haas  Michael Becht  David Morche 《地球表面变化过程与地形》2012,37(1):119-133

In the year 2007, enhanced rockfall activity was observed within the scarp of a 500 BP rockslide in the Reintal catchment (Northern Calcareous Alps, Germany); the largest of a series of events took place in August, when almost 50000 m³ of rock were detached from the subvertical rock face and deposited on a talus cone. In this case study, we focus on three aspects of rockfall research: first, we compile detailed geomorphological and geotechnical findings to explain the causes of the recent events. The results of laboratory tests and stability estimations suggest that rockfall activity will persist in the future as the old rockslide scarp still contains unstable rock masses. Second, we use digital elevation data from a pre‐event airborne LiDAR survey (ALS) and post‐event terrestrial laserscanning (TLS) to quantify landform changes and the mass balance of the rockfall event(s). The widespread availability of ALS elevation data provides a good opportunity to quantify fresh events using a comparatively inexpensive TLS survey; this approach is complicated by uncertainties resulting from the difficult coregistration of ALS and TLS data and the specific geometric problems in steep (ALS) and flat (TLS) terrain; it is therefore limited to at least medium‐sized events. Third, the event(s) is simulated using the results of the LiDAR surveys and a modified GIS‐based rockfall model in order to test its capability of predicting the extent and the spatial distribution of deposition on the talus cone. Results show that the model generally reproduces the process domain and the spatial distribution of topographic changes but frequently under‐ and over‐estimates deposition heights. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Perspectives in Modelling Climate–Hydrology Interactions     

Stefan Hagemann  Tanja Blome  Fahad Saeed  Tobias Stacke 《Surveys in Geophysics》2014,35(3):739-764

Various land–atmosphere coupling mechanisms exist that may lead to large-scale impacts on climate and hydrology. Some of them are still less understood and not adequately represented in state-of-the-art climate modelling. But, as the current generation of climate models enables consideration and implementation of important coupling processes, the present study provides perspectives for the modelling of relevant climate–hydrology interactions. On a more short-term perspective, these comprise anthropogenic land use and especially irrigation, which has been shown that it may even affect remote regions. On a long-term perspective, the coupling of hydrology to carbon cycle and vegetation becomes important, specifically the dynamics of permafrost and wetlands. Here, we present a review of current knowledge combined with some exemplary studies from a large-scale point of view. Therefore, we focus on climate–hydrology interactions that are relevant on scales utilized in the current or forthcoming global and regional climate modelling exercises.  相似文献   

Effect of ice sheet growth and melting on the slip evolution of thrust faults     

Heidi Turpeinen  Andrea Hampel  Tobias Karow  Georgios Maniatis 《Earth and Planetary Science Letters》2008,269(1-2):230-241

Field investigations suggest that postglacial unloading and rebound led to the formation or re-activation of reverse faults even in continental shields like Scandinavia. Here we use finite-element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading. The model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation. The magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet, the viscosity of the lithospheric layers and the long-term shortening rate. In contrast, the width of the ice sheet, the rate of deglaciation or the fault dip have an only minor influence on the slip evolution. In all experiments, the slip rate variations are caused by changes in the differential stress. The modelled deglaciation-induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the Fennoscandian ice sheet, which led to the formation of spectacular fault scarps in particular in the Lapland Fault Province. Furthermore, our model results support the idea that the low level of seismicity in currently glaciated regions like Greenland and Antarctica is caused by the presence of the ice sheets. Based on our models we expect that the decay of the Greenland and Antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions.  相似文献