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1.
Tilo Usbeck Peter Waldner Matthias Dobbertin Christian Ginzler Christian Hoffmann Flurin Sutter Charlotte Steinmeier Richard Volz Gustav Schneiter Martine Rebetez 《Theoretical and Applied Climatology》2012,108(3-4):451-462
This study compares the surface wind speed and forest damage data of two exceptionally severe winter storms, Vivian 1990 and Lothar 1999. The study area comprises the region that suffered damage in Switzerland. The wind speed data were derived from simulations of MeteoSwiss (Federal Office of Meteorology and Climatology), measurements during the storm periods and expert analyses of the data. The remotely sensed forest damage data were provided by the Federal Office for the Environment and the forest cover data by Swiss Federal Statistical Office. We compared data on the peak gust and maximum average wind speed, with data on the spatially related forest area and forest damage area, and found some clear differences in the correlations between the different wind data and forest damage. Our results point generally to the damage-causing role of near-surface gusts at maximum wind speeds during the storm. These tended to be spatially distributed on a fine scale. In only a few cases were the results statistically significant. However, these results could probably be improved with better wind data. For example, gust measurements spatially closer to forests or simulations of gusts at maximum wind speed could be produced with a spatially higher resolution. 相似文献
2.
Comparing seven candidate mission configurations for temporal gravity field retrieval through full-scale numerical simulation 总被引：3，自引：2，他引：1
Basem Elsaka Jean-Claude Raimondo Phillip Brieden Tilo Reubelt Jürgen Kusche Frank Flechtner Siavash Iran Pour Nico Sneeuw Jürgen Müller 《Journal of Geodesy》2014,88(1):31-43
The goal of this contribution is to focus on improving the quality of gravity field models in the form of spherical harmonic representation via alternative configuration scenarios applied in future gravimetric satellite missions. We performed full-scale simulations of various mission scenarios within the frame work of the German joint research project “Concepts for future gravity field satellite missions” as part of the Geotechnologies Program, funded by the German Federal Ministry of Education and Research and the German Research Foundation. In contrast to most previous simulation studies including our own previous work, we extended the simulated time span from one to three consecutive months to improve the robustness of the assessed performance. New is that we performed simulations for seven dedicated satellite configurations in addition to the GRACE scenario, serving as a reference baseline. These scenarios include a “GRACE Follow-on” mission (with some modifications to the currently implemented GRACE-FO mission), and an in-line “Bender” mission, in addition to five mission scenarios that include additional cross-track and radial information. Our results clearly confirm the benefit of radial and cross-track measurement information compared to the GRACE along-track observable: the gravity fields recovered from the related alternative mission scenarios are superior in terms of error level and error isotropy. In fact, one of our main findings is that although the noise levels achievable with the particular configurations do vary between the simulated months, their order of performance remains the same. Our findings show also that the advanced pendulums provide the best performance of the investigated single formations, however an accuracy reduced by about 2–4 times in the important long-wavelength part of the spectrum (for spherical harmonic degrees ${<}50$ ), compared to the Bender mission, can be observed. Concerning state-of-the-art mission constraints, in particular the severe restriction of heterodyne lasers on maximum range-rates, only the moderate Pendulum and the Bender-mission are beneficial options, of course in addition to GRACE and GRACE-FO. Furthermore, a Bender-type constellation would result in the most accurate gravity field solution by a factor of about 12 at long wavelengths (up to degree/order 40) and by a factor of about 200 at short wavelengths (up to degree/order 120) compared to the present GRACE solution. Finally, we suggest the Pendulum and the Bender missions as candidate mission configurations depending on the available budget and technological progress. 相似文献
3.
Near-surface electromagnetic, rock magnetic, and geochemical fingerprinting of submarine freshwater seepage at Eckernf?rde Bay (SW Baltic Sea) 总被引：1，自引：1，他引：0
Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor.
Resulting local anomalies in the morphology and physical properties of surface sediments are usually explored with seismo-acoustic
imaging techniques. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization
by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility,
hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for a first time with a high-resolution survey of freshwater seeps in Eckernf?rde Bay
(SW Baltic Sea). We demonstrate that EM profiling, complemented and validated by acoustic as well as sample-based rock magnetic
and geochemical methods, can create a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration
of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both
diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud
thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite,
is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater
advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction
(depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations. 相似文献
4.
O. Baur H. Bock E. Höck A. Jäggi S. Krauss T. Mayer-Gürr T. Reubelt C. Siemes N. Zehentner 《Journal of Geodesy》2014,88(10):959-973
Several techniques have been proposed to exploit GNSS-derived kinematic orbit information for the determination of long-wavelength gravity field features. These methods include the (i) celestial mechanics approach, (ii) short-arc approach, (iii) point-wise acceleration approach, (iv) averaged acceleration approach, and (v) energy balance approach. Although there is a general consensus that—except for energy balance—these methods theoretically provide equivalent results, real data gravity field solutions from kinematic orbit analysis have never been evaluated against each other within a consistent data processing environment. This contribution strives to close this gap. Target consistency criteria for our study are the input data sets, period of investigation, spherical harmonic resolution, a priori gravity field information, etc. We compare GOCE gravity field estimates based on the aforementioned approaches as computed at the Graz University of Technology, the University of Bern, the University of Stuttgart/Austrian Academy of Sciences, and by RHEA Systems for the European Space Agency. The involved research groups complied with most of the consistency criterions. Deviations only occur where technical unfeasibility exists. Performance measures include formal errors, differences with respect to a state-of-the-art GRACE gravity field, (cumulative) geoid height differences, and SLR residuals from precise orbit determination of geodetic satellites. We found that for the approaches (i) to (iv), the cumulative geoid height differences at spherical harmonic degree 100 differ by only \({\approx }10~\%\) ; in the absence of the polar data gap, SLR residuals agree by \({\approx }96~\%\) . From our investigations, we conclude that real data analysis results are in agreement with the theoretical considerations concerning the (relative) performance of the different approaches. 相似文献
5.
Petrology and geochemistry of the shoshonite-hosted Skouries porphyry Cu–Au deposit, Chalkidiki, Greece 总被引：2，自引：0，他引：2
Tilo Kroll Daniel Müller Thomas Seifert Peter M. Herzig Albrecht Schneider 《Mineralium Deposita》2002,37(1):137-144
The Skouries porphyry Cu-Au deposit, containing an indicated reserve of 206 Mt at 0.54% Cu and 0.80 g/t Au, is hosted by at least four hypabyssal monzonite-porphyry phases. In decreasing age, they are: (1) pink monzonite, (2) main monzonite, (3) intra-mineral monzonite, and (4) late-stage porphyry. High-grade ore is directly associated with the main and intra-mineral monzonite phases. All intrusive phases are cut by late-stage monzonite dykes that are barren. The monzonites have porphyritic textures with phenocrysts of plagioclase, alkali feldspar and amphibole as well as apatite and titanite microphenocrysts in a fine-grained feldspar-dominated groundmass. Mineralized samples are affected to varying degrees by potassic alteration, ranging from weak biotite-magnetite disseminations, through cross-cutting veinlets of hydrothermal orthoclase, to zones with pervasive orthoclase flooding. The high halogen contents of the Skouries intrusions are reflected in the high Cl and F concentrations of mica phases (up to 0.19 and 2.48 wt% respectively). The presence of magmatic magnetite in all intrusive phases implies high oxygen fugacities of the parental melts. All four monzonite phases have relatively evolved compositions, as reflected by their high SiO2, low MgO and low mg#, and variable but low contents of mantle-compatible elements such as V, Ni and Co. However, their mg# suggests increasing degrees of fractionation of the parental melts with decreasing age. Their high K2O (up to 5.8 wt%) and K2O/Na2O ratios (>1), as well as their high Ce/Yb and Th/Yb ratios (>34 and >21 respectively), which are believed to have been unaffected by alteration processes, are typical of alkaline rocks of the shoshonite association. Importantly, the Skouries intrusions are characterized by very high U and Th contents (up to 18.9 ppm and 62 ppm, respectively) that are consistent with accessory thorite and rare allanite in several samples. The high initial 87Sr/86Sr ratios (0.7082) for the Skouries intrusions suggest crustal contamination during emplacement. The use of geochemical discrimination diagrams assigns the rocks to a continental arc setting in accord with the interpretation of previous workers. 相似文献
6.
This paper aims at a comparative study of several measures to compensate for gross errors in kinematic orbit data. It starts with a simulation study on the influence of a single outlier in the orbit data on the gravity field solution. It is shown that even a single outlier can degrade the resulting gravity field solution considerably. To compensate for outliers, two different strategies are investigated: wavelet filters, which detect and eliminate gross errors, and robust estimators, which due to an iterative downweighting gradually ignore those observations that lead to large residuals. Both methods are applied in the scope of the analysis of a 2-year kinematic CHAMP (challenging minisatellite payload) orbit data set. In various real data studies, robust estimators outperform wavelet filters in terms of resolution of the derived gravity field solution. This superior performance is at the cost of computational load, as robust estimators are implemented iteratively and require the solution of large sets of linear equations several times. 相似文献
7.
8.
We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905‐4 at 2° 30′ N off Cameroon and GeoB 4906‐3 at 0° 44′ N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine‐grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial‐scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high‐frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial‐scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
The establishment of a long-term stable global reference frame is important for studying sea level records for, e.g., climate-related studies. GPS stations connected to the tide gauge benchmarks provide the necessary technique. However, the analysis of existing GPS solutions showed inconsistencies within the time series especially for the height component. To solve related issues, in 2001 the IGS Tide Gauge Benchmark Monitoring Pilot Project was established. The aim is the processing and re-processing of GPS data of stations at or near tide gauges in order to provide homogeneous and high-quality estimates of the vertical motion. A second objective is the establishment, maintenance and expansion of existing network of GPS stations at tide gauges. During the recent years six different analysis centers have processed overlapping GPS at tide gauge networks and are providing individual solutions allowing now to provide a combined solution. The ansatz for the combination is explained and quality measures are given. In addition, on the basis of the reconstruction of sea level anomalies, the benefit of using the combined TIGA solution is demonstrated. 相似文献
10.
Tilo Felgenhauer 《GeoJournal》2018,83(4):871-884
Volunteered geographic information (VGI) has fundamentally changed the way in which geoinformation is generated, distributed and handled. It entails manifold practices and discourses which are currently investigated from both affirmative and critical perspectives. Expanding on the range of theoretical approaches to VGI, this article explores the condition and the limits of VGI from a social theory perspective to explore the following questions: what is the basic structure of VGI both as a form of practice and a form of knowledge? What are aspects of integration and aspects of divergence with regard to VGI practices? Are there inherent limitations to VGI practices especially with regard to its emancipatory and educational potential? To approach these issues several established analytical frameworks are discussed, and a specific categorization of VGI’s symbolic geographies as interaction content will be introduced. Based on this categorization two opposed types of interaction practice can be distinguished: While information on VGI gathering and processing as a part of interaction content is vital to a competent use and deeper understanding of the system (“self-explanatory”) many interface designs have a very limited output in order to promote user-friendliness (“easy-to-use”). While the latter may increase the popularity of VGI it also limits interaction language to everyday language, to familiar spatial vocabularies of place, city, region, landscape or nation—instead of mediating technology’s spatialities or exploring more innovative ways of spatial representation. 相似文献