Combination of spatial networks using an estimated covariance matrix     

Klaus-Peter Schwarz 《Journal of Geodesy》1974,48(2):171-186

When combining satellite and terrestrial networks, covariance matrices are used which have been estimated from previous data. It can be shown that the least-squares estimator of the unknown parameters using such an estimated covariance matrix is not necessarily the best. There are a number of cases where a more efficient estimator can be obtained in a different way. The problem occurs frequently in geodesy, since in least-squares adjustment of correlated observations estimated covariance matrices are often used. If the general structure of the covariance matrix is known, results can often be improved by a method called covariance adjustment. The statistical model used in least-squares collocation leads to a type of covariance matrix which fits into this framework. It is shown in which way improvements can be made using a modified approach of principal component analysis. As a numerical example the combination of a satellite and a terrestrial network has been computed with varying assumptions on the covariance matrix. It is shown which types of matrices are critical and where the usual least-squares approach can be applied without hesitation. Finally, a simplified representation of covariances for spatial networks by means of a suitable covariance function is suggested. Paper presented at the International Symposium on Computational Methods in Geometrical Geodesy-Oxford, 2–8 September, 1973.  相似文献   

Hydrogeological properties of fault zones in a karstified carbonate aquifer (Northern Calcareous Alps,Austria)     

H. Bauer  T. C. Schröckenfuchs  K. Decker 《Hydrogeology Journal》2016,24(5):1147-1170

This study presents a comparative, field-based hydrogeological characterization of exhumed, inactive fault zones in low-porosity Triassic dolostones and limestones of the Hochschwab massif, a carbonate unit of high economic importance supplying 60 % of the drinking water of Austria’s capital, Vienna. Cataclastic rocks and sheared, strongly cemented breccias form low-permeability (<1 mD) domains along faults. Fractured rocks with fracture densities varying by a factor of 10 and fracture porosities varying by a factor of 3, and dilation breccias with average porosities >3 % and permeabilities >1,000 mD form high-permeability domains. With respect to fault-zone architecture and rock content, which is demonstrated to be different for dolostone and limestone, four types of faults are presented. Faults with single-stranded minor fault cores, faults with single-stranded permeable fault cores, and faults with multiple-stranded fault cores are seen as conduits. Faults with single-stranded impermeable fault cores are seen as conduit-barrier systems. Karstic carbonate dissolution occurs along fault cores in limestones and, to a lesser degree, dolostones and creates superposed high-permeability conduits. On a regional scale, faults of a particular deformation event have to be viewed as forming a network of flow conduits directing recharge more or less rapidly towards the water table and the springs. Sections of impermeable fault cores only very locally have the potential to create barriers.  相似文献   

A numerical investigation on height anomaly prediction in mountainous areas     

Ye Cai Li  Michael G. Sideris  Klaus-Peter Schwarz 《Journal of Geodesy》1995,69(3):143-156

This paper provides numerical examples for the prediction of height anomalies by the solution of Molodensky's boundary value problem. Computations are done within two areas in the Canadian Rockies. The data used are on a grid with various grid spacings from 100 m to 5 arc-minutes. Numerical results indicate that the Bouguer or the topographicisostatic gravity anomalies should be used in gravity interpolation. It is feasible to predict height anomalies in mountainous areas with an accuracy of 10 cm (1) if sufficiently dense data grids are used. After removing the systematic bias, the differences between the geoid undulations converted from height anomalies and those derived from GPS/levelling on 50 benchmarks is 12 cm (1) when the grid spacing is 1km, and 50 cm (1) when the grid spacing is 5. It is not necessary, in most cases, to require a grid spacing finer than 1 km, because the height anomaly changes only by 3 cm (1) when the grid spacing is increased from 100 m to 1000 m. Numerical results also indicate that, only the first two terms of the Molodensky series have to be evaluated in all but the extreme cases, since the contributions of the higher order terms are negligible compared to the objective accuracy.  相似文献   

Measurements of Volatile Organic Compounds (VOC) During POPCORN 1994: Applying a New On-Line GC–MS-Technique     

Arno Wedel  Klaus-Peter Müller  Monika Ratte  Jochen Rudolph 《Journal of Atmospheric Chemistry》1998,31(1-2):73-103

Atmospheric concentrations of ca. 250 C6–C15 hydrocarb on and C4–C12 oxygenated volatile organic compounds (VOC) including alkanes, benzene and alkyl benzenes, monoterpenes and aldehydes were measured in August 1994 during the POPCORN campaign (POPCORN = Photo-Oxidant formation by Plant emitted Compounds and OH Radicals in North-Eastern Germany). About 80 substances together contributed 90% of the atmospheric carbon in this range of molecular weight. During this field campaign VOC-emissions from several crop and tree species and the ambient concentrations of CO, C2–C7 non-methane hydrocarbons (NMHC), C1 and C2 aldehydes, nitrogen oxides, ozone and hydroxyl-radicals (OH) were also measured. These data were used to interpret the VOC measurements presented here. The on-line GC–MS used for the VOC measurements combines adsorptive sampling with thermal desorption and GC–MS analysis in an automated system. Internal standards were used to quantify the measurements. Ozone was destroyed prior to the sample preconcentration through the gas phase reaction with NO. Aromatic compounds like benzene, toluene and xylenes were the most abundant compound class among the measured substances, -pinene and 3-carene, most probably originating from pineforests ca. 1 km away from the measuring site, were the most abundant monoterpenes. The highest mixing ratios of most compounds were measured in nights with strong inversion situations. The toluene mixing ratios then reached 630 pptv; -pinene mixing ratios went up to 430 pptv. The median of all toluene and -pinene measurements during the campaign was 125 pptv or 22 pptv, respectively. These values are on the lower end of ambient measurements reported for continental sites. In most samples also n-pentanal, n-hexananl, n-nonanal and n-undecanal were present. Median mixing ratios were 9, 16, 14 and 8 pptv, respectively. Emission studies indicate that these highly reactive compounds are most probably emitted from maize. It is shown by a simple first order approach that the potential for ozone formation during the POPCORN campaign was roughly equal for anthropogenic and biogenic VOC. From measured concentrations of ozone, OH-radicals, methane, CO, C2–C15 nonmethane hydrocarbons (NMHC) and C5–C11 aldehydes a photochemical production of ozone in the order of 3.5 ppb/h can be estimated. Apart from formaldehyde and acetaldehyde, which are at least partly products of VOC oxidation, the substance group with the largest contribution to the VOC turnover are the monoterpenes. They contribute ca. 30%. However, the mechanism of terpene oxidation is very complex and presently only partly understood. Thus the actual contribution of monoterpenes to ozone formation is very uncertain. Other measured compound classes such as light alkenes, alkanes, aromatics, and C5–C11 aldehydes contribute each between 10% and 15% to ozone formation. The measuring site was not influenced directly from strong biogenic or anthropogenic sources, and the results obtained during the POPCORN campaign can be regarded as a typical picture of a remote rural central European environment.  相似文献   

Element partitioning in calcite as a function of solution flow rate: a study on vein calcites from the Harz Mountains     

P. Möller  V. Lüders  J. Schröder  J. Luck 《Mineralium Deposita》1991,26(3):175-179

A semi-empirical treatment of isothermal element partitioning caused by flow rate-dependent calcite growth from hydrothermal solutions yields element/Ca ratios that are qualitatively similar to those observed in calcite bands of the Pb-Zn banded ores from the Harz Mountains, Germany. The comparison of the calculations with the analytical results suggests that flow rates varied between episodes of calcite precipitation as well as during formation of individual bands. Based on a flow rate-dependent element partition coefficient, changing element/Ca ratios in precipitates from a hydrotherm are therefore not necessarily indicative of changing compositions of the fluid. The variations in element/Ca ratios to be envisaged could be as much as a factor of three.Notation A defined by Eq. 8 - a, b individual values of any element in Eq. 1 - c concentration in moles/m³ - C ₀ initial concentration moles/m³ - i running parameter - F area of precipitation in m² - k _p rate constant of pth order reaction in s · m³/moles^p - R linear (one-dimensional) growth rate in moles/m² · s - p order of growth reaction - s distance from entry of solution in m - s ₀ vertical extension of a vein in m - t time in s - v flow rate of hydrothermal solution in m/s - v₀ standard flow rate in m/s - _r relative flow rate in multiple of v₀ - fraction of total precipitation - ₀ fraction of precipitation under reference conditions when the hydrothermal solution leaves the vein - defining the sign in Eq. 1 for elements that are en riched (= +1) or impoverished (= -1) - logarithmic partition coefficient in Eq. 10 - (R) logarithmic partition coefficient as a function of variable growth rate - [ ], { } concentration ratios of fluids and solids, respectively - EL/Ca calculated ratio of El/Ca in the calcite surface zone after Eq. 11  相似文献   

Water-budget of Upper Lake Constance: An estimation of total supply based on runoff and water level variations     

Gustav Wagner  Barbara Mahmoudian  Heinz Gerd Schröder 《Aquatic Sciences - Research Across Boundaries》1994,56(2):179-189

An inflow-outflow model of the Upper Lake Constance has been adapted to fit the discharge data from the outletSeerhein at Constance. In order to perform mass balances the supplies and runoffs of the lake were calculated from 1961 at 1991.Three decades worth of results show no trend in annual supply patterns, aside from annual and seasonal fluctuations. When compared to earlier results, one finds slightly greater annual runoffs into the Seerhein of approximately 5%.  相似文献   

Simulated Airborne Flux Measurements in a LES generated Convective Boundary Layer     

M. Schröter  J. Bange  S. Raasch 《Boundary-Layer Meteorology》2000,95(3):437-456

One aim of past boundary-layer experiments with aircraft was the determination of areally averaged heat fluxes. In spite ofsophisticated instrumentation the measured fluxes extrapolated to the ground differed significantly from fluxes measured directly at ground stations. This studypresents simulated sensible heat flux measurements with aircraft flightsthrough a synthetic convective boundary layer created by a401 × 401 × 42 cubic-grid large eddy simulation (LES) with agrid spacing of 50 m. After some considerations with respect to necessary measurement lengths using results ofLenschow and Stankov (1986 – J. Atmos. Sci. 43, 1198–1209), simulated measurementcampaigns were carried out in three modelruns. During each model run five sets ofmeasurement runs were carried out successively.During each set of runs 10 aircraftflew at 10 altitudes with a ground speedof 100 m s^-1 simultaneously throughtime and space. In total, 150 legs were carried out, 15 at each flight level. The resulting`measured' heat fluxes were compared withthose of the `true' flux profiles obtaineddirectly from the ensemble-averagedLES-generated data. No significant systematic error between `measured' and `true' profiles was observed. Furthermore, the comparison of the resulting relative error with the theory ofLenschow and Stankov showed a good agreement at allmeasurement levels.  相似文献   

Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: Theocamoebians as paleolimnological indicators     

Audrey Dallimore  Claudia J. Schröder-Adams  Scott R. Dallimore 《Journal of Paleolimnology》2000,23(3):261-283

Richards Island, Northwest Territories, Canada, is characterized by thermokarst lakes which record Holocene limnological change. This study is the first report of thecamoebian assemblages and continuous annual lake water temperatures from these Arctic lakes. Ecological environments on Richards Island are influenced by a climatic gradient resulting from the contrasting influences of the cold Beaufort Sea to the north and the warm waters of the Mackenzie Delta to the east and west. This climatic gradient in turn influences modern thecamoebian assemblages, and is an indication of the complexity involved in interpreting past conditions from core material in this area.Population abundance and species diversity of thecamoebian assemblages on Richards Island are not significantly different from those reported from temperate and semi-tropical latitudes. However, certain assemblage characteristics, such as large and coarse agglutinated tests, dominance of assemblages by one or two species and low morphological variation are interpreted to be diagnostic of Arctic conditions. Thecamoebian assemblages in core material from the area indicate that the local paleolimnological conditions may have changed within the last 3 ka, and this is unrecorded in previously reported pollen data.Paleoenvironmental interpretations in a permafrost landscape have to take into account morphological instability of thermokarst lakes, which can be the cause of paleolimnological and consequently faunal change. In this area ecosystem development is clearly related to geomorphology and local climatic effects and is not exclusively controlled by regional climate change.  相似文献   

Geologic constraints on the origin of red organic‐rich material on Ceres          下载免费PDF全文

C. M. Pieters  A. Nathues  G. Thangjam  M. Hoffmann  T. Platz  M. C. de Sanctis  E. Ammannito  F. Tosi  F. Zambon  J. H. Pasckert  H. Hiesinger  S. E. Schröder  R. Jaumann  K.‐D. Matz  J. C. Castillo‐Rogez  O. Ruesch  L. A. McFadden  D. P. O'Brien  M. Sykes  C. A. Raymond  C. T. Russell 《Meteoritics & planetary science》2018,53(9):1983-1998

The geologic context of red organic‐rich materials (ROR) found across an elongated 200 km region on Ceres is evaluated with spectral information from the multispectral framing camera (FC) and the visible and near‐infrared mapping spectrometer (VIR) of Dawn. Discrete areas of ROR materials are found to be associated with small fresh craters less than a few hundred meters in diameter. Regions with the highest concentration of discrete ROR areas exhibit a weaker diffuse background of ROR materials. The observed pattern could be consistent with a field of secondary impacts, but no appropriate primary crater has been found. Both endogenic and exogenic sources are being considered for these distinctive organic materials.  相似文献   

Towards multi-resolution global climate modeling with ECHAM6–FESOM. Part I: model formulation and mean climate     

D. Sidorenko  T. Rackow  T. Jung  T. Semmler  D. Barbi  S. Danilov  K. Dethloff  W. Dorn  K. Fieg  H. F. Goessling  D. Handorf  S. Harig  W. Hiller  S. Juricke  M. Losch  J. Schröter  D. V. Sein  Q. Wang 《Climate Dynamics》2015,44(3-4):757-780

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