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1.
Severe weather affecting European transport systems: the identification,classification and frequencies of events 总被引：1，自引：0，他引：1
Andrea Vajda Heikki Tuomenvirta Ilkka Juga Pertti Nurmi Pauli Jokinen Jenni Rauhala 《Natural Hazards》2014,72(1):169-188
Severe weather can have serious repercussions in the transport sector as a whole by increasing the number of accidents, injuries and other damage, as well as leading to highly increased travel times. This study, a component of the EU FP7 Project EWENT, delineates a Europe-wide climatology of adverse and extreme weather events that can be expected to affect the transport network. We first define and classify the relevant severe weather events by investigating the effects of hazardous conditions on different transportation modes and the infrastructure. Consideration is given to individual phenomena such as snowfall, heavy precipitation, heat waves, cold spells, wind gusts; a combined phenomenon, the blizzard, is also considered. The frequency of severe weather events, together with the changes in their spatial extension and intensity, is analyzed based on the E-OBS dataset (1971–2000) and the ERA-Interim reanalysis dataset (1989–2010). Northern Europe and the Alpine region are the areas most impacted by winter extremes, such as snowfall, cold spells and winter storms, the frequency of heavy snowfall. The frequency of hot days is highest in Southern Europe. Severe winds and blizzards are the most common over the Atlantic and along its shores. Although heavy rainfall may affect the whole continent on an annual basis, extreme precipitation events are relative sparse, affecting particularly the Alps and the Atlantic coastline. A European regionalization covering similar impacts on the transport network is performed. 相似文献
2.
Conflating Privilege and Vulnerability: A Reflexive Analysis of Emotions and Positionality in Postgraduate Fieldwork 总被引：1，自引：0，他引：1
Grounded in a self-reflexive, intersectional analysis of positionality, we examine emotions in fieldwork through the autobiographical accounts that we gathered during our postgraduate ethnographic research in the Global South. We show how we, two female early-career geographers, emotionally coped with instances that put us in a vulnerable position due to loneliness, commitment to the field, insistent questioning, violence, and violent threats. We argue that a culture of silence surrounding fieldwork difficulties and their emotional consequences tend to permeate our discipline. We contend that geography departments ought to provide mentorship that takes into account doctoral candidates' different positionalities, conflated vulnerability and privilege, and embodied intersectional axes. This renewed awareness will help not only to reveal possible risks and challenges connected with fieldwork but also ultimately to enrich the overall academic discussions within our discipline. 相似文献
3.
Manuel Nitsche Jens M. Turowski Alexandre Badoux Dieter Rickenmann Tobias K. Kohoutek Michael Pauli James W. Kirchner 《地球表面变化过程与地形》2013,38(8):810-825
Topographic measurements are essential for the study of earth surface processes. Three‐dimensional data have been conventionally obtained through terrestrial laser scanning or photogrammetric methods. However, particularly in steep and rough terrain, high‐resolution field measurements remain challenging and often require new creative approaches. In this paper, range imaging is evaluated as an alternative method for obtaining surface data in such complex environments. Range imaging is an emerging time‐of‐flight technology, using phase shift measurements on a multi‐pixel sensor to generate a distance image of a surface. Its suitability for field measurements has yet not been tested. We found ambient light and surface reflectivity to be the main factors affecting error in distance measurements. Low‐reflectivity surfaces and strong illumination contrasts under direct exposure to sunlight lead to noisy distance measurements. However, regardless of lighting conditions, the accuracy of range imaging was markedly improved by averaging multiple images of the same scene. For medium ambient lighting (shade) and a light‐coloured surface the measurement uncertainty was approximately 9 mm. To further test the suitability of range imaging for field applications we measured a reach of a steep mountain stream with a horizontal resolution of approximately 1 cm (in the focal plane of the camera), allowing for the interpolation of a digital elevation model on a 2 cm grid. Comparison with an elevation model obtained from terrestrial laser scanning for the same site revealed that both models show similar degrees of topographic detail. Despite limitations in measurement range and accuracy, particularly at bright ambient lighting, range imaging offers three‐dimensional data in real time and video mode without the need of post‐processing. Therefore, range imaging is a useful complement or alternative to existing methods for high‐resolution measurements in small‐ to medium‐scale field sites. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Diatom communities and assemblages are widely used as indicators of ecological change in aquatic environments and for reconstructing palaeo-environments. Good calibration data sets, directly linking changes in diatom composition to environmental factors, are needed for building reliable gradient models with high indicative value. Such models have a broad applicability because most diatom species have cosmopolitan distributions. This paper presents community analyses of brackish-water diatoms living on submerged stones in four areas of the Baltic Sea proper along the Swedish coast. The communities on the stones were composed of epilithic, epiphytic, epipelic, epipsammic and occasionally some pelagic species. Altogether, 158 quantitative samples were taken at 41 sites between 23 April and 11 May, 1990, and the data set contained 300 diatom taxa belonging to 75 genera. Species data were analysed with principal components analysis (PCA) and environmental factors were fitted passively by multiple regression analysis on the ordination results. Differences in community composition could be explained by variation in salinity (which was correlated with N:P and Si:P ratios and the occurrence of macroalgae on the stones), nutrient concentrations and variation in exposure to wave action (which was correlated to the occurrence of soft bottoms around the stones, water temperature and the occurrence of sand grains and macroalgae on the stones). Separate analyses for small taxa (cell biovolume <1000 μm3), for large taxa (cell biovolume ≥1000 μm3) and for small and large diatom taxa together showed that diatoms of different size classes respond differently to environmental variation. 相似文献
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GPS Solutions - Carrier phase observations are required for high-accuracy positioning with Global Navigation Satellite Systems. This requires that the correct number of whole carrier cycles in each... 相似文献
7.
Altti Jokinen Shaojun Feng Wolfgang Schuster Washington Ochieng Chris Hide Terry Moore 《地球空间信息科学学报》2013,16(3):141-148
Traditional positioning methods, such as conventional Real Time Kinematic (cRTK) rely upon local reference networks to enable users to achieve high-accuracy positioning. The need for such relatively dense networks has significant cost implications. Precise Point Positioning (PPP) on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks, hence providing significant cost benefits especially in remote areas. This paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer ambiguities. Integrity monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method. A new method to detect and exclude GPS base-satellite failures is developed. A base-satellite is a satellite whose measurements are differenced from other satellite’s measurements when using between-satellite-differenced measurements to estimate position. The failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing modes. The results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static cases. In the kinematic processing cases, failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites. 相似文献
8.
Laura Borgnino Carlos P. De Pauli Pedro J. Depetris 《Environmental Earth Sciences》2012,65(2):441-451
Arsenate adsorption was studied in three clastic sediments, as a function of solution pH (4.0–9.0) and arsenate concentration.
Using known mineral values, protolytic constants obtained from the literature and K
ads values (obtained by fitting experimental adsorption data with empirical adsorption model), the constant capacitance surface
complexation model was used to explain the adsorption behavior. The experimental and modelling approaches indicate that arsenate
adsorption increases with increased pH, exhibiting a maximum adsorption value before decreasing at higher pH. Per unit mass,
sample S3 (smectite–quartz/muscovite–illite sample) adsorbs more arsenate in the pH range 5–8.5, with 98% of sites occupied at pH 6.
S1 and S2 have less adsorption capacity with maxima adsorption in the pH ranges of 6–8.5 and 4–6, respectively. The calculation of
saturation indices by PHREEQC at different pH reveals that the solution was undersaturated with respect to aluminum arsenate
(AlAsO42H2O), scorodite (FeAsO42H2O), brucite and silica, and supersaturated with respect to gibbsite, kaolinite, illite and montmorillonite (for S3 sample). Increased arsenate concentration (in isotherm experiments) may not produce new solid phases, such as AlAsO42H2O and/or FeAsO42H2O. 相似文献
9.
L. Borgnino M. G. Garcia M. V. del Hidalgo M. Avena C. P. De Pauli M. A. Blesa P. J. Depetris 《Aquatic Geochemistry》2010,16(2):279-291
We propose a model that explains the acid–base surface properties of clastic sediments from two Argentinean reservoir lakes.
The model uses potentiometric titration data sets and fixed parameters such as the apparent stability constants and reaction
stoichiometries of acid–base equilibriums involving known mineral phases. The model considers that sediments act as a set
of independent sorption surfaces, such as organic matter, clay silicate, and iron (hydr)oxides, thus the acid–base equilibrium
and the correspondent protolytic constants are represented by a humic acid, a Na-illite, and a poor crystalline Fe-hydr(oxide).
In agreement with experimental data, the model predicts that all sediment samples show a similar charging behavior, increasing
the negative charge as the pH increases. The net charge of sediments is controlled by the presence of negatively charged minerals
and/or organic matter coatings. This reveals the great influence of clays and organic matter functional groups on the acid–base
surface properties of sediments, and consequently on the surface reactivity toward contaminant transport. 相似文献
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