A review on missing hydrological data processing     

Yongbo Gao  Christoph Merz  Gunnar Lischeid  Michael Schneider 《Environmental Earth Sciences》2018,77(2):47

Like almost all fields of science, hydrology has benefited to a large extent from the tremendous improvements in scientific instruments that are able to collect long-time data series and an increase in available computational power and storage capabilities over the last decades. Many model applications and statistical analyses (e.g., extreme value analysis) are based on these time series. Consequently, the quality and the completeness of these time series are essential. Preprocessing of raw data sets by filling data gaps is thus a necessary procedure. Several interpolation techniques with different complexity are available ranging from rather simple to extremely challenging approaches. In this paper, various imputation methods available to the hydrological researchers are reviewed with regard to their suitability for filling gaps in the context of solving hydrological questions. The methodological approaches include arithmetic mean imputation, principal component analysis, regression-based methods and multiple imputation methods. In particular, autoregressive conditional heteroscedasticity (ARCH) models which originate from finance and econometrics will be discussed regarding their applicability to data series characterized by non-constant volatility and heteroscedasticity in hydrological contexts. The review shows that methodological advances driven by other fields of research bear relevance for a more intensive use of these methods in hydrology. Up to now, the hydrological community has paid little attention to the imputation ability of time series models in general and ARCH models in particular.  相似文献   

Statistical analyses of Global U-Pb Database 2017     

Stephen J.Puetz  Carlos E.Ganade  Udo Zimmermann  Glenn Borchardt 《地学前缘(英文版)》2018,9(1):121-145

The method of obtaining zircon samples affects estimation of the global U-Pb age distribution.Researchers typically collect zircons via convenience sampling and cluster sampling.When using these techniques,weight adjustments proportional to the areas of the sampled regions improve upon unweighted estimates.Here,grid-area and modern sediment methods are used to weight the samples from a new database of 418,967 U-Pb ages.Preliminary tests involve two age models.Model-1 uses the most precise U-Pb ages as the best ages.Model-2 uses the~(206)Pb/~(238)U age as the best age if it is less than a1000 Ma cutoff,otherwise it uses the~(207)Pb/~(206)Pb age as the best age.A correlation analysis between the Model-1 and Model-2 ages indicates nearly identical distributions for both models.However,after applying acceptance criteria to include only the most precise analyses with minimal discordance,a histogram of the rejected samples shows excessive rejection of the Model-2 analyses around the1000 Ma cutoff point.Because of the excessive rejection rate for Model-2,we select Model-1 as the preferred model.After eliminating all rejected samples,the remaining analyses use only Model-1 ages for five rock-type subsets of the database:igneous,meta-igneous,sedimentary,meta-sedimentary,and modern sediments.Next,time-series plots,cross-correlation analyses,and spectral analyses determine the degree of alignment among the time-series and their periodicity.For all rock types,the U-Pb age distributions are similar for ages older than 500 Ma,but align poorly for ages younger than 500 Ma.The similarities(500 Ma)and differences(500 Ma)highlight how reductionism from a detailed database enhances understanding of time-dependent sequences,such as erosion,detrital transport mechanisms,lithification,and metamorphism.Time-series analyses and spectral analyses of the age distributions predominantly indicate a synchronous period-tripling sequence of~91-Myr,~273-Myr,and~819-Myr among the various rock types.  相似文献   

Monotone nonlinear finite-volume method for challenging grids     

M. Schneider  B. Flemisch  R. Helmig  K. Terekhov  H. Tchelepi 《Computational Geosciences》2018,22(2):565-586

This article presents a new positivity-preserving finite-volume scheme with a nonlinear two-point flux approximation, which uses optimization techniques for the face stencil calculation. The gradient is reconstructed using harmonic averaging points with the constraint that the sum of the coefficients included in the face stencils must be positive. We compare the proposed scheme to a nonlinear two-point scheme available in literature and a few linear schemes. Using two test cases, taken from the FVCA6 benchmarks, the accuracy of the scheme is investigated. Furthermore, it is shown that the scheme is linearity-preserving on highly complex corner-point grids. Moreover, a two-phase flow problem on the Norne formation, a geological formation in the Norwegian Sea, is simulated. It is demonstrated that the proposed scheme is consistent in contrast to the linear Two-Point Flux Approximation scheme, which is industry standard for simulating subsurface flow on corner-point grids.  相似文献   

Micro-feature-motivated numerical analysis of the coupled bio-chemo-hydro-mechanical behaviour in MICP     

Wang  Xuerui  Nackenhorst  Udo 《Acta Geotechnica》2022,17(10):4537-4553

Acta Geotechnica - A coupled bio-chemo-hydro-mechanical model (BCHM) is developed to investigate the permeability reduction and stiffness improvement in soil by microbially induced calcite...  相似文献   

Reconstructing deep‐time histories from integrated thermochronology: An example from southern Baffin Island,Canada     

Kalin T. McDannell  David A. Schneider  Peter K. Zeitler  Paul B. O'Sullivan  Dale R. Issler 《地学学报》2019,31(3):189-204

We present a multi‐chronometric approach for reconstructing deep‐time thermal histories using southern Baffin Island as a case study. This continuous thermal history begins with the Palaeoproterozoic Trans‐Hudson Orogeny and is derived from inverse and forward models that integrate thermochronometers spanning some 500°C: new apatite U–Pb ages and K‐feldspar ⁴⁰Ar/³⁹Ar multi‐diffusion domain data, published (U–Th)/He zircon ages and new multi‐kinetic fission‐track results. Integration of data from a wider temperature range reduces ambiguities in thermal‐history modelling and permits us to constrain the timing of geological processes including, extended post‐orogenic cooling, enhanced later Proterozoic cooling, and then episodic burial and exhumation in the Palaeozoic–Mesozoic.  相似文献   

A 3D gravity and magnetic model for the Entenschnabel area (German North Sea)     

Dressel  Ingo  Barckhausen  Udo  Heyde  Ingo 《International Journal of Earth Sciences》2018,107(1):177-190

International Journal of Earth Sciences - In this study, we focus on structural configuration of the Entenschnabel area, a part of the German exclusive economic zone within the North Sea, by means...  相似文献   

Identification of the uranium speciation in an underground acid mine drainage environment     

Thuro Arnold  Nils Baumann  Sina Brockmann  Udo Zimmermann  Stephan Weiß 《Geochimica et cosmochimica acta》2011,75(8):2200-3065

The subsurface acid mine drainage (AMD) environment of an abandoned underground uranium mine in Königstein/Saxony/Germany, currently in the process of remediation, is characterized by low pH, high sulfate concentrations and elevated concentrations of heavy metals, in particular uranium. Acid streamers thrive in the mine drainage channels and are heavily coated with iron precipitates. These precipitates are biologically mediated iron precipitates and related to the presence of Fe-oxidizing microorganisms forming copious biofilms in and on the Fe-precipitates. Similar biomineralisations were also observed in stalactite-like dripstones, called snottites, growing on the gallery ceilings.The uranium speciation in these solutions of underground AMD waters flowing in mine galleries as well as dripping from the ceiling and forming stalactite-like dripstones were studied by time resolved laser-induced fluorescence spectroscopy (TRLFS). The fluorescence lifetime of uranium species in both AMD water environments were best described with a mono-exponential decay, indicating the presence of one major species. The detected positions of the emission bands and by comparing it in a fingerprinting procedure with spectra obtained for acid sulfate reference solutions, in particular Fe(III) - SO₄²⁻ - UO₂²⁺ reference solutions, indicated that the uranium speciation in the AMD environment of Königstein is dominated in the pH range of 2.5-3.0 by the highly mobile aquatic uranium sulfate species UO₂SO_4(aq) and formation of uranium precipitates is rather unlikely as is retardation by sorption processes. The presence of iron in the AMD reduces the fluorescence lifetime of the UO₂SO_4(aq) species from 4.3 μs, found in iron-free uranium sulfate reference solutions, to 0.7 μs observed in both AMD waters of Königstein and also in the iron containing uranium sulfate reference solutions.Colloids were not observed in both drainage water and dripping snottite water as photon correlation spectroscopy analyses and centrifugation experiments at different centrifugal accelerations between 500g and 46000g revealed. Thus transport and uranium speciation at the investigated AMD sites is neither influenced by U(IV) or U(VI) eigencolloids nor by uranium adsorbed on colloidal particles.This study shows that TRLFS is a suitable spectroscopic technique to identify the uranium speciation in bulk solutions of AMD environments.  相似文献   

Comparison of gas with liquid chromatography for the determination of benzenepolycarboxylic acids as molecular tracers of black carbon     

Maximilian P.W. Schneider  Rienk H. Smittenberg  Thorsten Dittmar  Michael W.I. Schmidt   《Organic Geochemistry》2011,42(3):275-282

Existing methods for black carbon (BC) quantification measure different parts of the BC continuum, which complicates the calculation of a global BC budget. Benzenepolycarboxylic acids (BPCA) are used as molecular markers to quantify and characterize BC in soils and sediments using gas chromatography for BPCA separation (GC-BPCA). Recently, this method was refined for BC analysis in seawater using high performance liquid chromatography (LC-BPCA), which omits the cleaning steps and derivatization necessary in GC analysis. As yet it is not clear whether the two analytical methods yield similar results. Here we apply both methods to a suite of laboratory produced charcoals derived from wood and grass. We found systematically lower total BPCA-C contents and larger analytical variability for all tested charcoals when using GC-BPCA compared to LC-BPCA, the latter giving 1.5 ± 0.3 times higher yields for the charcoal samples formed at 275-700 °C. At lower and higher pyrolysis temperatures the differences between the two analytical methods were larger. The main reason for the differences between the two methods is the loss of BPCA during sample preparation for GC analysis. We propose a correction factor of 1.5 to account for at least part of these losses. No qualitative biases, i.e. towards more or less functionalized BPCAs, were observed between the two methods. The relative contribution of mellitic acid C to total BPCA-C, a measure for the degree of condensation of BC, was the same in the two analytical techniques. Qualitative differences between wood and grass charcoals as detected by both methods were small.  相似文献   

Highly gravity-driven flow of a NAPL in water-saturated porous media using the discontinuous Galerkin finite-element method with a generalised Godunov scheme     

Lauriane Schneider  Raphaël di Chiara Roupert  Gerhard Schäfer  Philippe Helluy 《Computational Geosciences》2015,19(4):855-876

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Centennial-scale climate change from decadally-paced explosive volcanism: a coupled sea ice-ocean mechanism   总被引：1，自引：1，他引：0  

Y. Zhong  G. H. Miller  B. L. Otto-Bliesner  M. M. Holland  D. A. Bailey  D. P. Schneider  A. Geirsdottir 《Climate Dynamics》2011,37(11-12):2373-2387

Northern Hemisphere summer cooling through the Holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes. However, centennial-scale climate departures, such as the Little Ice Age, must be caused by other forcings, most likely explosive volcanism and changes in solar irradiance. Stratospheric volcanic aerosols have the stronger forcing, but their short residence time likely precludes a lasting climate impact from a single eruption. Decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea-surface temperatures that exceeds that of any single eruption. Here we use a global climate model to evaluate the potential long-term climate impacts from four decadally paced large tropical eruptions. Direct forcing results in a rapid expansion of Arctic Ocean sea ice that persists throughout the eruption period. The expanded sea ice increases the flux of sea ice exported to the northern North Atlantic long enough that it reduces the convective warming of surface waters in the subpolar North Atlantic. In two of our four simulations the cooler surface waters being advected into the Arctic Ocean reduced the rate of basal sea-ice melt in the Atlantic sector of the Arctic Ocean, allowing sea ice to remain in an expanded state for?>?100 model years after volcanic aerosols were removed from the stratosphere. In these simulations the coupled sea ice-ocean mechanism maintains the strong positive feedbacks of an expanded Arctic Ocean sea ice cover, allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated, potentially resulting in a centennial-scale or longer change of state in Arctic climate. The fact that the sea ice-ocean mechanism was not established in two of our four simulations suggests that a long-term sea ice response to volcanic forcing is sensitive to the stability of the seawater column, wind, and ocean currents in the North Atlantic during the eruptions.  相似文献