Comparison of large-area land cover products with national forest inventories and CORINE land cover in the European Alps     

Lars T. Waser  Markus Schwarz 《International Journal of Applied Earth Observation and Geoinformation》2006

Considerable efforts have recently resulted in the development of global land cover data at large spatial scales. The main objective of this study is a comparison of different AVHRR- and MODIS-based forest and land cover products at the scale of the European Alps: a large natural ecosystem that is exposed to both natural environmental threats and human impacts and exploitation. In a first test, the accuracy of land cover products in predicting the overall amount of forest across national boundaries was assessed using national forest inventory statistics. Both variants of forest class combinations resulted in a general overestimation of the forest area. The IGBP 2.0 cover performed best with an overall mean absolute error of 13% and a bias of 0%. In a second test, large-area land cover products were tested for accuracy in predicting 13 aggregated land cover types in a spatially explicit manner using CORINE land cover as reference dataset. Due to data inconsistencies, partly insufficient spatial resolution, steep terrain and land use heterogeneity of the European Alps, only partly satisfactory results were obtained.  相似文献   

Species diversity of the Okavango Delta, Botswana   总被引：4，自引：0，他引：4  

Lars Ramberg  Peter Hancock  Markus Lindholm  Thoralf Meyer  Susan Ringrose  Jan Sliva  Jo Van As  Cornelis Vander Post 《Aquatic Sciences - Research Across Boundaries》2006,68(3):310-337

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High-resolution peat records for Holocene monsoon history in the eastern Tibetan Plateau   总被引：5，自引：1，他引：5  

Lars G. Franzen  A.J.Tim Jull 《中国科学D辑(英文版)》2006,49(6):615-621

Holocene peat sediment has been attached impor-tance to reconstruct the Holocene climatic variations because it can provide much palaeoclimatic informa-tion with high resolution. Analysis on the plant mac-rofossil[1], pollen[2―4], isotope ratio[5―9], element con-tent[10,11], total organic carbon (TOC)[12], humifica-tion[13,14] and grayscale[12] for peat sediment has shown its superiorities as a recorder medium for reconstruct-ing the Holocene climate. Hong et al. have done great fruitful w…  相似文献   

Selection of Streets from a Network Using Self-Organizing Maps   总被引：6，自引：0，他引：6  

Bin Jiang  Lars Harrie 《Transactions in GIS》2004,8(3):335-350

We propose a novel approach to selection of important streets from a network, based on the technique of a self‐organizing map (SOM), an artificial neural network algorithm for data clustering and visualization. Using the SOM training process, the approach derives a set of neurons by considering multiple attributes including topological, geometric and semantic properties of streets. The set of neurons constitutes a SOM, with which each neuron corresponds to a set of streets with similar properties. Our approach creates an exploratory linkage between the SOM and a street network, thus providing a visual tool to cluster streets interactively. The approach is validated with a case study applied to the street network in Munich, Germany.  相似文献   

Displacement properties of landslide masses at the initiation of failure in quick clay deposits and the effects of meteorological and hydrological factors     

Takashi Okamoto  Jan Otto Larsen  Sumio Matsuura  Shiho Asano  Yoshitsugu Takeuchi  Lars Grande 《Engineering Geology》2004,72(3-4):233-251

This study aimed to identify displacement properties of landslide masses at the initiation of failure and factors that affect the landslides activities in areas where quick clay is found. We set up a research site in a quick clay deposit area in Norway and monitored the displacements of landslide masses and meteorological and hydrological factors for a long period of time using an automatic monitoring system. The system collected data for two landslides that occurred at the site from the start of their movement until their ultimate collapse.

The two landslides that were monitored showed definite secondary and tertiary creep stages before they collapsed. One of the landslides moved from the secondary stage to the tertiary creep stage when another landslide occurred nearby. The tertiary stage of this landslide showed reconstruction of short primary, secondary, and tertiary creep stages. These phenomena suggested that (1) the stress at the end of the landslide mass was released during the nearby landslide, and (2) a new stress distribution was formed in the landslide mass. The critical strain differed for 14 times between the two landslide masses we monitored. The difference was likely attributable to the difference in the contents of quick clay, which shows small critical stress against slope failure, as well as topological factors.

Our analyses of the effects of hydrological and meteorological factors on landslides showed that the precipitation of 3 and 10 days before six slope failures as the final stages of the landslides that had occurred in the research area was no different from the mean precipitation of periods that showed no slope failure, suggesting that precipitation had no direct effects on the collapse of the landslide masses. On the other hand, the traveling velocities of the landslide masses during the secondary creep stage, which was prior to their collapse, were affected by the water content of the soil and precipitation (and the amount of snowmelt water), but was little correlated with the pore-water pressure of the quick clay layer. We also found that the presence of snow cover scarcely affected landslide movements.  相似文献   

The 9th-Generation International Geomagnetic Reference Field   总被引：5，自引：0，他引：5  

International Association of Geomagnetism  Aeronomy  Division V  Working Group Participating members: S. Macmillan  S. Maus  T. Bondar  A. Chambodut  V. Golovkov  R. Holme  B. Langlais  V. Lesur  F. Lowes  H. Lühr  W. Mai  M. Mandea  N. Olsen  M. Rother  T. Sabaka  A. Thomson  I. Wardinski 《Geophysical Journal International》2003,155(3):1051-1056

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Formation of turbid ice during autumn freeze-up in the Kara Sea   总被引：1，自引：0，他引：1  

Lars H. Smedsrud 《Polar research》2003,22(2):267-286

A one-dimensional (vertical) model is used to estimate the mass of ice-rafted sediment in turbid sea ice on the shallow Kara Sea shelf during autumn freeze-up. Sediment is entrained into the ice through aggregation with frazil ice crystals that are diffused downwards by wind-generated turbulence. Data from local meteorological stations are used to force the model, while water stratification and sediment concentrations from the area are used to initiate the model. Model results indicate a 0.2 m thick layer of slush ice created during 48 h with a mean wind of 6 m/s and an air temperature of −10°C. This ice contains ca. 20 mg/1 of sediment, or in total ca. 2% of the annual sediment discharge by nearby rivers. In shallow areas (<20 m depth) the process is very effective with winds of ca. 12 m/s, and the process can incorporate many years of sediment discharge. In the deeper areas (>20 m depth), the strong salinity stratification implies that winds above 18 m/s are needed for the process to be effective. For the rest of the winter months the same process may lead to additional sediment incorporated in a coastal polynya, but the freeze-up alone has the capacity to incorporate the total summer discharge of sediment into the surface ice. Calculated sediment concentrations in the surface ice cover are in the range 3 mg/1-19 g/1, in good agreement with available field data.  相似文献   

Spatial Transgression and the BYU Jerusalem Center Controversy*     

Daniel H. Olsen  Jeanne Kay Guelke 《The Professional geographer》2004,56(4):503-515

Dominant groups tend to construct the meaning of places to justify and sustain their ideology and orthodoxy in order to solidify power and to maintain their control over others. New outsider groups whose ideology disrupts the established order and sovereignty of the dominant group can be labeled transgressive ( Sibley 1995; Cresswell 1996 ). Transgressions of hegemonic spaces force dominant groups to reexamine themselves and to reaffirm or to modify their position. This concept of transgression is used to examine the controversy surrounding the building of the Brigham Young University Jerusalem Center in the mid‐1980s in Jerusalem. The public outcry among some Israelis over the building of this educational edifice concerned the potential use of the Jerusalem Center as a focal point for Mormon (Latter‐day Saints) proselytizing efforts. We examine the way the Jerusalem Center was viewed and depicted by its opponents, suggesting how basic geographic concepts such as scale and site further refine the concept of spatial transgression for buildings and urban redevelopment.  相似文献   

Integral formulas for heterogeneous data in physical geodesy     

Lars Sjoberg 《Journal of Geodesy》1979,53(4):297-315

The least squares estimator is derived for a random stochastic process implied by one or two heterogeneous random stochastic processes on a sphere. The solution can be regarded as least squares collocation in the continuous case. When the method is applied in physical geodesy the statistical expectation is usually substituted by the global average and the method will then give the minimum mean squares errors of the estimated quantities. The solutions can also be considered as generalizations of the classical integral formulas in physical geodesy for heterogeneous data information.  相似文献   

Triassic lacustrine red-beds and palaeoclimate: The „Buntsandstein“ of Helgoland and the malmros Klint member of East Greenland     

Lars B. Clemmensen 《International Journal of Earth Sciences》1979,68(2):748-774

The playa-lake origin of the Lower Triassic Buntsandstein of Helgoland and the Upper Triassic Malmros Klint Member of East Greenland is suggested by: the continental setting; absence of marine fossils and occurrence of fresh-water trace fossils; evidence of shallow water, fluctuations in water level, frequent subaerial exposure and oxidizing depositional conditions; evidence of low-energy wave-action and absence of evidence for tidal influence. The Buntsandstein contains aeolian dunes and evaporites, but only rare fluvial sandstones and very rare fresh-water trace fossils. In contrast the Malmros Klint Member contains no aeolian sandstones and evaporites, but common fluvial sandstones and numerous fresh-water trace fossils. Wave ripple crest orientation suggests that both sequences were deposited during the influence of alternating NE and SE trade winds. The Buntsandstein appears to have been deposited in a central trade wind region with dominant winds from SE and short rainy seasons; the Malmros Klint Member was apparently deposited in a marginal trade wind region with dominant NE winds and longer rainy seasons.

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Zusammenfassung Der Buntsandstein auf Helgoland und der Malmros Klint Member (Obere Trias) in Ostgrönland werden als Playaseebildungen interpretiert auf Grund von: Vorkommen von Süßwasser-Lebenspuren und Mangel an marinen Fossilien; Beweise für Seichtwasser, Schwankungen in Wassertiefen, häufige Trockenlegung und oxydierende Ablagerungsverhältnisse; Beweise für schwachen Wellenschlag aber Mangel an Gezeiten; der stratigraphischen Einfügung in einer kontinentalen Schichtenfolge. Der Buntsandstein enthält Winddünen und Evaporite, aber nur wenige fluviatile Sandsteine und einzelne Süßwasser-Lebenspuren. Im Gegensatz dazu enthält der Malmros Klint Member keine äolische Sandsteine und keine Evaporite, sondern viele fluviatile Sandsteine und zahlreiche Süßwasser-Lebenspuren. Die Orientierung der Oszillationsrippelkämme beweist vermutlich, daß die beiden Schichtenfolgen während des Einflusses umlaufender Nordost- und Südostpassatwinde abgelagert wurden. Der Buntsandstein wurde wahrscheinlich in einer zentralen Passatwindregion mit vorherrschenden Südostwinden und kurzen Regenperioden abgelagert; der Malmros Klint Member wurde wahrscheinlich in einer Randpassatwindregion mit vorherrschenden Nordostwinden und längeren Regenperioden abgelagert.

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Résumé Le Grès bigarré (Trias inférieur) de Héligoland et le Malmros Klint Member (Trias supérieur) du Groenland oriental sont interprétés comme des formations lacustres éphémères à cause de: présence d'ichnofossiles d'eau douce et l'absence de fossiles marins; évidence d'eau peu profonde, variation de la profondeur d'eau fréquentes dessiccations et conditions sédimentaires oxydantes; évidence d'action calme des vagues, mais absence de marée; 1'emplacement stratigraphique dans une séquence continentale. Le Grès bigarré contient des dépôts éoliens et des évaporites, mais peu de grès fluviatiles et des ichnofossiles rares d'eau douce. Par contre le Malmos Klint Member ne contient ni de grès éoliens, ni d'évaporites, mais plusieurs grès fluviatiles et de nombreux ichnofossiles d'eau douce. L'orientation des crêtes ripplemarks semble prouver que les deux séquences ont été déposées sous l'influence des alizés du nord-est et du sud-est. Le Grès bigarré de Héligoland semble s'être déposé dans une région centrale des alizés avec des vents dominants du sud-est et de brèves saisons pluvieuses. Evidemment le Malmros Klint Member s'est déposé dans une région marginale des alizés avec des vents dominants du nord-est et des saisons pluvieuses plus longues.

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