Verification of ARMA identification for modelling temporal correlations of GNSS observations using the ARMASA toolbox   总被引：1，自引：0，他引：1  

Xiaoguang Luo  Michael Mayer  Bernhard Heck 《Studia Geophysica et Geodaetica》2011,55(3):537-556

The classical least-squares (LS) algorithm is widely applied in practice of processing observations from Global Satellite Navigation Systems (GNSS). However, this approach provides reliable estimates of unknown parameters and realistic accuracy measures only if both the functional and stochastic models are appropriately specified. One essential deficiency of the stochastic model implemented in many available GNSS software products consists in neglecting temporal correlations of GNSS observations. Analysing time series of observation residuals resulting from the LS evaluation, the temporal correlation behaviour of GNSS measurements can be efficiently described by means of socalled autoregressive moving average (ARMA) processes. For a given noise realisation, a well-fitting ARMA model can be automatically estimated and identified using the ARMASA toolbox available free of charge in MATLAB® Central.In the preliminary stage of applying the ARMASA toolbox to residual-based modelling of temporal correlations of GNSS observations, this paper presents an empirical performance analysis of the automatic ARMA estimation tool using a large amount of simulated noise time series with representative temporal correlation properties comparable to the GNSS residuals. The results show that the rate of unbiased model estimates increases with data length and decreases with model complexity. For large samples, more than 80% of the identified ARMA models are unbiased. Additionally, the model error representing the deviation between the true data-generating process and the model estimate converges rapidly to the associated asymptotical value for a sufficiently large sample size with respect to the correlation length.  相似文献   

Cold seeps in Monterey Bay, California: Geochemistry of pore waters and relationship to benthic foraminiferal calcite     

Joris Gieskes  Anthony E. Rathburn  Jonathan B. Martin  M. Elena Prez  Chris Mahn  Joan M. Bernhard  Shelley Day 《Applied Geochemistry》2011,26(5):738-746

An extensive geochemical and biogeochemical examination of CH₄ seeps in the Clam Flats area of Monterey Bay provides insight into the character of relationships between seep geochemistry and benthic foraminiferal geochemistry. The area is characterized by sulfide-rich fluids. Sulfide increases are associated with large increases in alkalinity, as well as small decreases in dissolved Ca and Mg. In addition, only small increases in NH₄ are observed, but values of δ¹³C of dissolved inorganic C are as low as −60‰ at shallow depths (<3 cm). These observations indicate that all these processes are related to the bacterial oxidation of CH₄, which is transported upward by slow seepage of pore fluids. The geochemistry of the pore fluids should be relevant to the geochemistry of the carbonate tests of living and dead foraminifera. However, a profound disequilibrium of approximately an order of magnitude occurs between the δ¹³C values of stained (cytoplasm-containing) foraminiferal carbonate and the C isotope values of ambient pore water dissolved inorganic C. Reasons are unclear for this isotopic disequilibrium, but have important implications for interpretations of foraminiferal carbonate as a paleoenvironmental proxy. Much fine scale work is needed to fully understand the relationships between the biogeochemistry of benthic foraminifera and the geochemistry of the pore waters where they live.  相似文献   

Improving the representation of major landforms in analytical relief shading     

Brooke E. Marston  Bernhard Jenny 《International journal of geographical information science》2013,27(7):1144-1165

Relief shading is the most common type of cartographic relief representation for print and digital maps. Manual relief shading results in informative and visually pleasing representations of terrain, but it is time consuming and expensive to produce. Current analytical relief shading can be created quickly, but the resulting maps are not as aesthetically appealing and do not show landscape features in an explicit manner. This article introduces an automated digital method that produces shaded relief with locally adjusted illumination directions to simulate the techniques and cartographic principles of manual relief shading. Ridgelines and valley lines are derived from a digital terrain model, vectorized, and used in a diffusion curve algorithm. A graph analysis generalizes the lines before using them for diffusion curve shading. The direction of illumination is adjusted based on the spatial orientation of ridgelines and valley lines. The diffusion curve shading is combined with standard analytical relief shading to create a final diffusion relief shading image. Similar to manual relief shading, major landforms and the structure of the terrain are more clearly shown in the diffusion relief shading. The presented method best highlights major landforms in terrain characterized by sharp, clearly defined ridges and valleys.  相似文献   

Corrections to “A comparison of the tesseroid,prism and point-mass approaches for mass reductions in gravity field modelling” (Heck and Seitz, 2007) and “Optimized formulas for the gravitational field of a tesseroid” (Grombein et al., 2013)     

Xiao-Le Deng  Thomas Grombein  Wen-Bin Shen  Bernhard Heck  Kurt Seitz 《Journal of Geodesy》2016,90(6):585-587

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A method to detect and characterize sub‐daily flow fluctuations          下载免费PDF全文

Franz Greimel  Bernhard Zeiringer  Norbert Höller  Bettina Grün  Reinhold Godina  Stefan Schmutz 《水文研究》2016,30(13):2063-2078

Hydro peaking causes an important environmental impact on running water ecosystems. Many affected rivers have a poor ecological status. In rivers affected by hydro peaking, the flow conditions are highly complex and difficult to grasp. To develop a general framework for detecting and characterizing sub‐daily flow fluctuations, we analysed more than 500 Austrian hydrographs, covering the whole range from unimpacted to heavily impacted rivers. Different fluctuation types could be identified according to the potential source: e.g. sub‐daily flow fluctuations caused by hydro peaking, rainfall or snow and glacier melt. Additionally, the term ‘hydro fibrillation’ was established, to indicate frequently occurring artificial fluctuations with comparably low intensities. An automatic procedure was used to detect frequency and intensity of each flow fluctuation. Using variables based on duration curves of flow fluctuation rates (ramping rates), amplitudes, flow ratios, durations and daily numbers of fluctuations, a predictive model (linear discriminant analysis) was fitted to classify hydrographs into predominant fluctuation regimes. This is the basis for a detailed investigation of present sub‐daily flow regimes and to analyse the differences between the regimes. Based on the results, we finally propose a general framework that enables a standardized assessment of flow fluctuations regarding event intensities and/or event timing. The proposed framework offers a standardized selection of particular flow fluctuations referring to increase and decrease events separately. The selection of specific flow fluctuations can be defined with respect to several research questions (e.g. ecologically relevant fluctuations), which offers a wide range of applications. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Biomarker and compound-specific δ<Superscript>13</Superscript>C evidence for changing environmental conditions and carbon limitation at Lake Koucha,eastern Tibetan Plateau     

Bernhard Aichner  Heinz Wilkes  Ulrike Herzschuh  Steffen Mischke  Chengjun Zhang 《Journal of Paleolimnology》2010,43(4):873-899

A sediment core from Lake Koucha (eastern Tibetan Plateau) was investigated using organic biomarkers and their stable carbon isotope signatures. The correlation between TOC content, total amount of aquatic macrophyte-derived n-alkanes (e.g. nC₂₃) and δ¹³C values of TOC and nC₂₃ indicates that Lake Koucha was macrophyte-dominated before 8 cal ka BP. Shortly after the lake turned from a saline to a freshwater system at 7.2 cal ka BP, a variety of algal and bacterial markers such as hopanoids and isoprenoids emerged, of which phytane, pentamethylicosene (PMI), moretene and diploptene are particularly abundant. Phytane and PMI show different isotopic signals (≈−18 and ≈−28‰, respectively), which indicates that they originated from different sources. Phytane may have been derived from cyanobacteria, while methanogenic archaea may be the source of PMI. The isotopic depletion of diploptene and moretene (≈−60‰) indicates the presence of methanotrophs. After 6.1 cal ka BP, the saturated C₂₀ highly branched isoprenoid (HBI) became the dominant constituent of the aliphatic hydrocarbon fraction. Such dominance has rarely been reported in lacustrine environments, and indicates a strong presence of algae (most likely diatoms) or cyanobacteria. At 4.7 cal ka BP, the appearance of an unsaturated C₂₅ HBI, which is a specific biomarker for diatoms, was noted. Furthermore, the level of nC₁₇-alkane was observed to increase in abundance in the uppermost two samples. These results suggest that the lake was phytoplankton-dominated during the last 6.1 ka. Relatively low biomarker concentrations and δ¹³C values at 6.0, 3.1 and 1.8 cal ka BP indicate the occurrence of cool periods, which is in agreement with inferences from other locations on the Tibetan Plateau. The δ¹³C values of nC₂₃ range from −23.5 to −12.6‰, with high values at the peak of macrophyte abundance at ca. 11 cal ka BP and at the phytoplankton maximum between ca 6.1 and 2.8 cal ka BP. Thus, aquatic macrophyte-derived mid-chain n-alkanes have been found to be excellent indicators of carbon-limiting conditions, which lead to the assimilation of isotopically-enriched carbon species. The limitation of carbon sources could be a localized phenomenon occurring in dense plant stands (as in the older section of the core), or it may be induced by high primary productivity (as in the younger section). Since the δ¹³C value of the inorganic carbon source may vary, the offset between the δ¹³C values of nC₂₃ and TIC could serve as a more precise proxy for carbon-limiting conditions in lacustrine environments, which could in turn be interpreted with respect to lacustrine paleo-productivity.  相似文献   

Strain rotation coupling and its implications on the measurement of rotational ground motions     

Martin van Driel  Joachim Wassermann  Maria Fernanda Nader  Bernhard S. A. Schuberth  Heiner Igel 《Journal of Seismology》2012,16(4):657-668

Spatial derivatives of the seismic wave field are known to be sensitive to various site effects (e.g., cavity effects, topography, and geological inhomogeneities). In this study, the focus is on strain rotation coupling that can cause significant differences between point measurements compared to array-derived rotational motions. The strain rotation coupling constants are estimated based on finite element simulations for inhomogeneous media as well as for the 3D topography around Wettzell, Germany (the location of the G ring laser). Using collocated array and ring laser data, the coupling constants of the ring laser itself are shown to be small. Several examples are shown to illustrate the order of magnitude that strain-induced rotation might have on the seismograms in the near field of volcanoes as well as in the far field and in the low-frequency spectrum (free oscillations).  相似文献   

Screening of Microalgae for Feasible Mass Production in Industrial Hypersaline Wastewater Using Disposable Bioreactors     

Sebastian Menke  Anne Sennhenn  Jörg‐H. Sachse  Elke Majewski  Bernhard Huchzermeyer  Thomas Rath 《洁净——土壤、空气、水》2012,40(12):1401-1407

Ten algae species were analyzed by comparing their growth in specific hypersaline industrial wastewater. It was a by‐product of fertilizer production which was released by K + S Aktiengesellschaft, Germany. Due to processing, brine water contains a high amount of salts ( 200 g L^?1). A successful algal biotechnology mainly depends on choosing and screening the adequate algae for a specific application along with the design of optimal culture conditions with comparable photo bioreactor technologies. Therefore, a high throughput screening technology was developed. In comparison to glass flasks or flat panel reactors this system was eligible for screening applications because of disposable characteristics and the equability of each culture tube. Dunaliella salina, Tetraselmis tetrathele, and Nannochloropsis salina grew in the presence of hypersaline wastewater where T. tetrathele grew best to a wastewater concentration of 75% by salt shock experiments. D. salina tolerates a wastewater level up to 80% by gradual increase. Intracellular ion contents of lyophilized algae samples were measured. They feature special transporter to either exclude ions, i.e., sodium from the cell, or to include ions like potassium and magnesium in order to secure functionality of sensitive enzymes. Under saline stress conditions these transport systems as well as metabolic pathways leading to the production of compatible osmolytes could be induced. Stress tolerance mechanisms developed in initially unstressed culture either by stepwise adaptation or by shock exposure to harsh salt condition. For this reason a feasible mass production in industrial hypersaline wastewater was possible.  相似文献   

Crayfish and fish as bioturbators of streambed sediments: Assessing joint effects of species with different mechanistic abilities     

Bernhard Statzner  Pierre Sagnes 《Geomorphology》2008,93(3-4):267-287

Many studies illustrate that bioturbating animal species individually affect aquatic sediments through diverse mechanistic abilities, whereas assessments of joint effects of such species on sediments are relatively rare. Such joint effects have implications for real systems, in which different bioturbators coexist, but are difficult to predict for two reasons. First, they can be additive (being the sum of the individual effects of each species) or they can be positive or negative interactive (being greater or smaller than the sum of the individual effects). Second, if interactive, they can depend on biotic interactions that affect the bioturbating activities of the species and/or they can depend on physical interactions among bioturbator-induced sediment modifications. Using experimental streams, we assessed such joint effects on gravel–sand sediments for flow and sediment conditions preferred by barbel (Barbus barbus) but also used by gudgeon (Gobio gobio) and, in a second experiment, for flow and sediment conditions preferred by both male crayfish (Orconectes limosus) and gudgeon. These species have different mechanistic abilities to affect gravel and/or sand in stream beds. In each experiment, we measured (i) the transport of gravel and sand at baseflow (during 12 experimental days); (ii) four sediment surface characteristics (after 12 d); and (iii) the critical shear stress (τ_c) causing incipient gravel and sand motion during experimental floods (after 12 d). Gudgeon contributed differently to the joint effects in the two experiments, which related to its individual weight, prevailing baseflow shear stress, sediment particle weight, and sediment mixture (availability of surface sand). Overall, the species pairs had predominantly negative interactive joint effects on the sediment variables assessed by us. Both a literature survey and observations during the experiments provided no evidence for direct biotic interactions between barbel and gudgeon or crayfish and gudgeon, so one would reasonably associate their negative interactive effects on the sediments with physical interactions among bioturbator-induced sediment surface modifications. Individually, each species reduced the percentage of sand in the surface layer and the surface algal cover to relatively low values so that the species pairs could not accomplish much greater joint effects on these variables, explaining their negative interactive effects on them. As algal cover particularly affected the τ_c for gravel and sand, the negative interactive effects of the animals on this surface variable chained toward the τ_c for the sediments, on which the species pairs also had negative interactive effects. Such chained negative interactive effects on sediment variables are seemingly a general pattern of joint bioturbator effects on aquatic sediments, i.e., the many so far described single-species effects should be smaller than their sum if the species coexists in nature.  相似文献   

The loss of K,REE, Th,and U from a Martian and a terrestrial basalt by acidic leaching     

Gerlind DREIBUS  Reinhard HAUBOLD  Wolfgang HUISL  Bernhard SPETTEL 《Meteoritics & planetary science》2008,43(11):1895-1908

Abstract— The mobilization of K, rare earth elements (REE), Th, and U from Martian surface material upon contact with acidic solutions probably occurred extensively on Mars about 4 to 3.5 Ga ago and seems to have occurred locally in more recent times. We have studied the dissolution of these elements by leaching the basaltic shergottite Zagami and the terrestrial basalt BE‐N at constant pH values ranging from 5 to 1 in the absence and presence of added salts. Potassium is nearly immobile in Zagami and mobilized readily from BE‐N. The REE reside mostly in calcium phosphates and dissolve readily, with those in whitlockite of Zagami reacting slightly better than those in apatite of BE‐N. Thorium and U also reside mostly in calcium phosphates. Both dissolve similarly for both basalts and less readily than the REE. The experiments indicate the extent of the mobilization of K, REE, Th, and U, when acidic water leached the surface of Mars. Potassium was released slowly and in a small relative amount. The REE, and particularly the LREE, became mobile readily and were possibly distributed over large areas before immobilization. Thorium and U dissolved more slowly than the REE and were distributed less widely.  相似文献