Geodetic intersection on the ellipsoid     

Lars E. Sjöberg 《Journal of Geodesy》2008,82(9):565-567

Through each of two known points on the ellipsoid a geodesic is passing in a known azimuth. We solve the problem of intersection of the two geodesics. The solution for the latitude is obtained as a closed formula for the sphere plus a small correction, of the order of the eccentricity of the ellipsoid, which is determined by numerical integration. The solution is iterative. Once the latitude is obtained, the longitude is determined without iteration.  相似文献   

Indigenous soil knowledge among the Fulani of northern Burkina Faso: linking soil science and anthropology in analysis of natural resource management     

Lars Krogh  Bjarke Paarup-Laursen 《GeoJournal》1997,43(2):189-197

The indigenous soil knowledge among the Fulani subsistence farmers in two villages of northern Burkina Faso is examined, analysed and assessed with the aim of evaluating its adequacy for sustaining soil fertility and for the appropriateness of tapping indigenous knowledge in development programmes. The analytical framework is a multidisciplinary approach combining soil science and anthropology. The results show a high degree of consistency between the science-based western soil classification and the Fulani soil classification although the routes of generation are different. The farmers are aware of and active in management of soil fertility based on their experience, but express no thorough understanding of the mechanisms of plant growth. The soil knowledge is applied in the farming strategies which, as a primary aim, seek to minimize the risk of harvest failure. However, the analysis also suggests that the knowledge is no part of a free-standing knowledge body which can be separated from the actual agricultural performance. The farmers express a general concern about the present state of the environment and degradation processes; however, there is no motivation to take active control of and manage the bush area. This is in contrast with the way millet cultivators actively manage their fields. An explanation of this is suggested by the division between the two Fulani ethnic subgroups, the FulBe who are the former masters and the RimayBe, the former slaves.  相似文献   

Reservoir description using dynamic parameterisation selection with a combined stochastic and gradient search     

Lars Kristian Nielsen  Sam Subbey  Mike Christie  Trond Mannseth 《Computational Geosciences》2006,10(3):321-342

There is a correspondence between flow in a reservoir and large scale permeability trends. This correspondence can be derived by constraining reservoir models using observed production data. One of the challenges in deriving the permeability distribution of a field using production data involves determination of the scale of resolution of the permeability. The Adaptive Multiscale Estimation (AME) seeks to overcome the problems related to choosing the resolution of the permeability field by a dynamic parameterisation selection. The standard AME uses a gradient algorithm in solving several optimisation problems with increasing permeability resolution. This paper presents a hybrid algorithm which combines a gradient search and a stochastic algorithm to improve the robustness of the dynamic parameterisation selection. At low dimension, we use the stochastic algorithm to generate several optimised models. We use information from all these produced models to find new optimal refinements, and start out new optimisations with several unequally suggested parameterisations. At higher dimensions we change to a gradient-type optimiser, where the initial solution is chosen from the ensemble of models suggested by the stochastic algorithm. The selection is based on a predefined criterion. We demonstrate the robustness of the hybrid algorithm on sample synthetic cases, which most of them were considered insolvable using the standard AME algorithm.  相似文献   

Formation of iron-containing colloids by the weathering of phyllite     

Harald Zänker  Gudrun Hüttig  Thuro Arnold  Heino Nitsche 《Aquatic Geochemistry》2006,12(4):299-325

The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to Milli-Q water. Secondary mineral colloids of 10¹–10² nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)₃ and gibbsite with possible additions of iron silicates and␣iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock–water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity.  相似文献   

Phanerozoic tectonothermal history of the Arabian–Nubian shield in the Eastern Desert of Egypt: evidence from fission track and paleostress data     

Ana-Voica Bojar  Harald Fritz  Sabine Kargl  Wolfgang Unzog 《Journal of African Earth Sciences》2002,34(3-4)

To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously.  相似文献   

Late-Glacial and Early Holocene Environmental and Climatic Change at Lake Tambichozero, Southeastern Russian Karelia     

Barbara Wohlfarth  Ludmila Filimonova  Ole Bennike  Leif Bjrkman  Lars Brunnberg  Nadja Lavrova  Igor Demidov  Gran Possnert 《Quaternary Research》2002,58(3):261

High-resolution lithostratigraphy, mineral magnetic, carbon, pollen, and macrofossil analyses, and accelerator mass spectrometry ¹⁴C measurements were performed in the study of a sediment sequence from Lake Tambichozero, southeastern Russian Karelia, to reconstruct late-glacial and early Holocene aquatic and terrestrial environmental changes. The lake formed ca. 14,000 cal yr B.P. and the area around the lake was subsequently colonized by arctic plants, forming patches of pioneer communities surrounded by areas of exposed soil. A minor rise in lake productivity and the immigration of Betula pubescens occurred ca. 11,500 cal yr B.P. The rise in summer temperatures probably led to increased melting of remnant ice and enhanced erosion. The distinct increase in lake productivity and the development of open Betula-Populus forests, which are reconstructed based on plant macrofossil remains, indicate stable soils from 10,600 cal yr B.P. onward. Pinus and Picea probably became established ca. 9900 cal yr B.P.  相似文献   

Oxygen fugacity and geochemical variations in the martian basalts: implications for martian basalt petrogenesis and the oxidation state of the upper mantle of Mars     

Christopher D.K Herd  Lars E BorgJohn H Jones  James J Papike 《Geochimica et cosmochimica acta》2002,66(11):2025-2036

The oxygen fugacity of the Dar al Gani 476 martian basalt is determined to be quartz-fayalite-magnetite (QFM) −2.3 ± 0.4 through analysis of olivine, low-Ca pyroxene, and Cr-spinel and is in good agreement with revised results from Fe-Ti oxides that yield QFM −2.5 ± 0.7. This estimate falls within the range of oxygen fugacity for the other martian basalts, QFM −3 to QFM −1. Oxygen fugacity in martian basalts correlates with ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, and La/Yb ratios, indicating that the mantle source of the basalts is reduced and that assimilation of crust-like material controls the oxygen fugacity. This allows constraints to be placed on the oxidation state of the martian mantle and on the nature of assimilated crustal material. The assimilated material may be the product of early and extensive hydrothermal alteration of the martian crust, or it may be amphibole- or phlogopite-bearing basaltic rock within the crust. In either case, water may play a significant role in the oxidation of basaltic magmas on Mars, although it may be secondary to assimilation of ferric iron-rich material.  相似文献   

Accessibility Measures in Spatial Mismatch Models     

Eugene D. Perle  Harald Bauder  Nancy Beckett 《The Professional geographer》2002,54(1):106-110

Implicit in all spatial mismatch models is the concept of accessibility. However, there is an immense variety of measures utilized in the literature to index the concept, and it is not clear how much of the disparity in findings between studies is attributable to alternative measures. This research note attempts to provide some evidence on the impact of alternative measures of accessibility in employment probability models.  相似文献   

Methodology for construction, calibration and validation of a national hydrological model for Denmark   总被引：13，自引：0，他引：13  

Hans Jrgen Henriksen  Lars Troldborg  Per Nyegaard  Torben Obel Sonnenborg  Jens Christian Refsgaard  Bjarne Madsen 《Journal of Hydrology》2003,280(1-4):52-71

An integrated groundwater/surface water hydrological model with a 1 km² grid has been constructed for Denmark covering 43,000 km². The model is composed of a relatively simple root zone component for estimating the net precipitation, a comprehensive three-dimensional groundwater component for estimating recharge to and hydraulic heads in different geological layers, and a river component for streamflow routing and calculating stream–aquifer interaction. The model was constructed on the basis of the MIKE SHE code and by utilising comprehensive national databases on geology, soil, topography, river systems, climate and hydrology. The present paper describes the modelling process for the 7330 km² island of Sjælland with emphasis on the problems experienced in combining the classical paradigms of groundwater modelling, such as inverse modelling of steady-state conditions, and catchment modelling, focussing on dynamic conditions and discharge simulation. Three model versions with different assumptions on input data and parameter values were required until the performance of the final, according to pre-defined accuracy criteria, model was evaluated as being satisfactory. The paper highlights the methodological issues related to establishment of performance criteria, parameterisation and assessment of parameter values from field data, calibration and validation test schemes. Most of the parameter values were assessed directly from field data, while about 10 ‘free’ parameters were subject to calibration using a combination of inverse steady-state groundwater modelling and manual trial-and-error dynamic groundwater/surface water modelling. Emphasising the importance of tests against independent data, the validation schemes included combinations of split-sample tests (another period) and proxy-basin tests (another area).  相似文献   

Stochastic Structural Modeling   总被引：3，自引：0，他引：3  

Lars Holden  Petter Mostad  Bjørn Fredrik Nielsen  Jon Gjerde  Chris Townsend  Signe Ottesen 《Mathematical Geology》2003,35(8):899-914

A consistent stochastic model for faults and horizons is described. The faults are represented as a parametric invertible deformation operator. The faults may truncate each other. The horizons are modeled as correlated Gaussian fields and are represented in a grid. Petrophysical variables may be modeled in a reservoir before faulting in order to describe the juxtaposition effect of the faulting. It is possible to condition the realization on petrophysics, horizons, and fault plane observations in wells in addition to seismic data. The transmissibility in the fault plane may also be included in the model. Four different methods to integrate the fault and horizon models in a common model is described. The method is illustrated on an example from a real petroleum field with 18 interpreted faults that are handled stochastically.  相似文献