Untersuchungen am Grauen Salzton der Grube „Königshall-Hindenburg”, Reyershausen bei Göttingen

Zusammenfassung Es wurden 15 stratigraphiseh aufeinanderfolgende Proben des Grauen Salztons aus dem Kalisalzbergwerk Königshall-Hindenburg, Reyershausen bei Göttingen, auf ihren Mineralbestand untersueht und ihre chemische Zusammensetzung ermittelt. Die Hauptkomponenten des loslichen Anteils (Salz) sind Anhydrit, Steinsalz und Dolomit, während sick der unlösliche Anteil zum größten Teil aus Illit, Chlorit und Quarz zusammensetzt. Die Korngrößenfraktionen < 6,32 des unlöslichen Anteils bestehen fast aussehlioßlich aus Rlit und Chlorit. Die röntgenographische und mikroskopische Untersuchung ergab eine kontinuierliche Zunahme des Illitgehaltes vom Liegenden zum Hangenden des Profils und eine Abnahme des Chloritgehaltes. Im Zusammenhang mit der Röntgenanalyse konnte der Chemismus dieser beiden Tonminerale bestimmt werden. Es zeigte sich, daß der Chlorit seine Zusammensetzung innerhalb des Profils ändert. Sie entspricht der des Sheridanits (Liegendes), des Klinochlors und des Pennins (Hangendes). Für den Hit muß detritische Herkunft angenommen werden, während der Chlorit sich wahrscheinlich aus der Lösung gebildet hat und damit eine diagenetische Neubildung ist.     

Spatial statistical techniques for aggregating point objects extracted from high spatial resolution remotely sensed imagery

 Using a local maximum filter, individual trees were extracted from a 1 m spatial resolution IKONOS image and represented as points. The spatial pattern of individual trees was determined to represent forest age (a surrogate for forest structure). Point attributes, based on the spatial pattern of trees, were generated via nearest neighbour statistics and used as the basis for aggregating points into forest structure units. The forest structure units allowed for the mapping of a forested area into one of three age categories: young (1–20 years), intermediate (21–120 years), and mature (>120 years). This research indicates a new approach to image processing, where objects generated from the processing of image data (rather than pixels or spectral values) are subjected to spatial statistical analysis to estimate an attribute relating an aspect of forest structure. Received: 22 April 2002 / Accepted: 23 November 2002     

Modeling input errors to improve uncertainty estimates for one-dimensional sediment transport models

Stochastic Environmental Research and Risk Assessment - Bayesian methods have recently been applied to one-dimensional sediment transport models to assess the uncertainty in model predictions due...     

Importance of Spatial Resolution in Global Groundwater Modeling

Global-scale gradient-based groundwater models are a new endeavor for hydrologists who wish to improve global hydrological models (GHMs). In particular, the integration of such groundwater models into GHMs improves the simulation of water flows between surface water and groundwater and of capillary rise and thus evapotranspiration. Currently, these models are not able to simulate water table depth adequately over the entire globe. Unsatisfactory model performance compared to well observations suggests that a higher spatial resolution is required to better represent the high spatial variability of land surface and groundwater elevations. In this study, we use New Zealand as a testbed and analyze the impacts of spatial resolution on the results of global groundwater models. Steady-state hydraulic heads simulated by two versions of the global groundwater model G³M, at spatial resolutions of 5 arc-minutes (9 km) and 30 arc-seconds (900 m), are compared with observations from the Canterbury region. The output of three other groundwater models with different spatial resolutions is analyzed as well. Considering the spatial distribution of residuals, general patterns of unsatisfactory model performance remain at the higher resolutions, suggesting that an increase in model resolution alone does not fix problems such as the systematic overestimation of hydraulic head. We conclude that (1) a new understanding of how low-resolution global groundwater models can be evaluated is required, and (2) merely increasing the spatial resolution of global-scale groundwater models will not improve the simulation of the global freshwater system.     

Single epoch estimation of the Galileo integrity chain sensor station clock offsets

The Galileo integrity chain depends on a number of key factors, one of which is contamination of the signal-in-space errors with residual errors other than imperfect modelling of satellite orbits and clocks. A potential consequence of this is that the user protection limit is driven not by the errors associated with the imperfect orbit and clock modelling, but by the distortions induced by noise and bias in the integrity chain. These distortions increase the minimum bias the integrity chain can guarantee to detect, which is reflected in the user protection limit. A contributor to this distortion is the inaccuracy associated with the estimation of the offset between the Galileo sensor station (GSS) receiver clocks and the Galileo system time (GST). This offset is termed the receiver clock synchronization error (CSE). This paper describes the research carried out to determine both the CSE and its associated error using GPS data as captured with the Galileo System Test Bed Version 1 (GSTB-V1). In the study we simulate open access to a time datum using IGS data. Two methods are compared for determining CSE and the corresponding uncertainty (noise) across a global network of tracking stations. The single-epoch single-station method is an ‘averaging’ technique that uses a single epoch of data, and is carried out at individual sensor stations, without recourse to the data from other stations. The global network solution method is also single epoch based, but uses the inversion of a linearised model of the global system to solve for the CSE simultaneously at all GSS along with a number of other parameters that would otherwise be absorbed into the CSE estimate in the averaging technique. To test the effectiveness of various configurations in the two methods the estimated synchronisation errors across the GSS network (comprising 25 stations) are compared to the same values as estimated by the International GPS Service (IGS) using a global tracking network of around 150 stations, as well as precise orbit and satellite clock models determined by a combination of global analysis centres. The results show that the averaging technique is vulnerable to unmodelled errors in the satellite clock offsets from system time, leading to receiver CSE errors in the region of 12 ns (3.7 m), this value being largely driven by the satellite CSE errors. The global network approach is capable of delivering CSE errors at the level of 1.5 ns (46 cm) depending on the number of parameters in the linearised model. The International GNSS Service (IGS) receiver clock estimates were used as a truth model for comparative assessment.     

Spatial patterns from EOF analysis of soil moisture at a large scale and their dependence on soil,land-use,and topographic properties

We hypothesize that the spatial and temporal variation in large-scale soil moisture patterns can be described by a small number of spatial structures that are related to soil texture, land use, and topography. To test this hypothesis, an empirical orthogonal function (EOF) analysis is conducted using data from the 1997 Southern Great Plains field campaign. When considering the spatial soil moisture anomalies, one spatial structure (EOF) is identified that explains 61% of the variance, and three such structures explain 87% of the variance. The primary EOF is most highly correlated with the percent sand in the soil among the regional characteristics considered, but the correlation with percent clay is largest if only dry days are analyzed. When considering the temporal anomalies, one EOF explains 50% of the variance. This EOF is still most closely related to the percent sand, but the percent clay is unimportant. Characteristics related to land use and topography are less correlated with the spatial and temporal variation of soil moisture in the range of scales considered.     

Do conservative solutes migrate at average pore-water velocity?

According to common understanding, the advective velocity of a conservative solute equals the average linear pore-water velocity. Yet direct monitoring indicates that the two velocities may be different in heterogeneous media. For example, at the Camp Dodge, Iowa, site the advective velocity of discrete Cl- plumes was less than one tenth of the average pore-water velocity calculated from Darcy's law using the measured hydraulic gradient, effective porosity, and hydraulic conductivity (K) from large-scale three-dimensional (3D) techniques, e.g., pumping tests. Possibly, this difference reflects the influence of different pore systems, if the K relevant to transient solute flux is influenced more by lower-K heterogeneity than a steady or quasi-steady water flux. To test this idea, tracer tests were conducted under controlled laboratory conditions. Under one-dimensional flow conditions, the advective velocity of discrete conservative solutes equaled the average pore-water velocity determined from volumetric flow rates and Darcy's law. In a larger 3D flow system, however, the same solutes migrated at approximately 65% of the average pore-water velocity. These results, coupled with direct observation of dye tracers and their velocities as they migrated through both homogeneous and heterogeneous sections of the same model, demonstrate that heterogeneity can slow the advective velocity of discrete solute plumes relative to the average pore-water velocity within heterogeneous 3D flow sytems.     

PRELIMINARY ANALYSIS OF SPATIAL AND TEMPORAL DISTRIBUTION OF SOIL MOISTURE ON A DEFORESTED SLOPE

Soil moisture was measured over a four-month period at 31 sample points on a 1 ha clear-cut site on southern Vancouver Island. At each sample point measurements were collected at 10-cm intervals to the base of the soil profile. The data were used to determine spatial and temporal variations in soil moisture, and to infer the most likely mechanism(s) of soil-water movement vertically through the soil profiles and laterally across the site. All soils showed an increase in moisture content through the monitoring period. There was no strong tendency for moisture content to increase downslope along the topographic gradient. All soils exhibited an increase in soil moisture at depths of 20–30 cm, followed by a decline. This zone of increased soil moisture was correlated with the main root zone, and not with any textural contrasts. Topographic and textural influences on moisture movement through the soil matrix appear to be of minor importance. Moisture appears to follow paths dictated by root systems, which do not necessarily follow the microtopography. [Key words: soil moisture, soil matrix, macropores, topography, southern Vancouver Island, degraded dystric brunisols, dry coastal western hemlock forests.]     

A systematic field-based testing program of hydraulic conductivity and dispersivity over a range in scale

In a small watershed underlain by relatively homogeneous (nonlayered), sandy, glacial outwash, hydraulic conductivity (K) and longitudinal dispersivity (α _L) were systematically measured over a range in scale. Test methods employed in the investigation are conventional and/or based on accepted principles, measurement scales are those typically encountered in applied field problems, and the hydrogeologic setting is typical of large areas within the northern hemisphere and similar to many alluvial environments worldwide. The results show that K measured under radial flow is scale-dependent up to a radius of influence (r _i) of approximately 15 m but reaches an asymptotic value above this threshold. This asymptotic value of K is consistent with results obtained at the regional scale (～10⁴ m) for the same aquifer using non-radial three-dimensional techniques; the initial increase appears to reflect increasing dimensionality of the radial tests with larger r _i. Although α _L was evaluated over a much smaller interval relative to K, α _L proved to be independent of scale over the full range tested, from 2 to 29 m, an unexpected result. The findings support the idea that there is, as yet, no predictable relationship between scale effects in K and α _L at scales normally encountered in applied field hydrogeology.