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High accurate global navigation satellite systems (GNSS) require to correct a signal delay caused by the troposphere. The delay can be estimated along with other unknowns or introduced from external models. We assess the impact of the recently developed augmentation tropospheric model on real-time kinematic precise point positioning (PPP). The model is based on numerical weather forecast and thus reflects the actual state of weather conditions. Using the G-Nut/Geb software, we processed GNSS and meteorological data collected during the experiment using a hot-air balloon flying up to an altitude of 2000 m. We studied the impacts of random walk noise setting of zenith total delay (ZTD) on estimated parameters and the mutual correlations, the use of external tropospheric corrections, the use of data from a single or dual GNSS constellation and the use of Kalman filter and backward smoothing processing methods. We observed a significant negative correlation of the estimated rover height and ZTD which depends on constraining ZTD estimates. Such correlation caused a degraded performance of both parameters when estimated simultaneously, in particular for a single GNSS constellation. The impact of ZTD constraining reached up to 50-cm differences in the rover height. Introducing external tropospheric corrections improved the PPP solution regarding: (1) shortened convergence, (2) better overall robustness, particularly, in case of degraded satellite geometry, (3) less adjusted parameters with lower correlations. The numerical weather model-driven PPP resulted in 9–12- and 5–6-cm uncertainties in the rover altitude using the Kalman filter and the backward smoothing, respectively. Compared to standard PPP, it indicates better performance by a factor of 1–2 depending on the availability of GNSS constellations, the troposphere constraining and the processing strategy. 相似文献
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This paper studies aspects that influence the de‐ghosting performance of marine multi‐level sources based on a modified Johnson model. The normalized squared error between actual signature and its corresponding ghost‐free signature is introduced to evaluate the multi‐level source design. The results show that optimum depth combinations and volume combinations exist in the design. However, there is also some flexibility in the volume combination which makes it possible to optimize with respect to residual bubble oscillation. By considering both operational aspects and performance, we propose that three or four levels in a multi‐level source are reasonable. Compared to a horizontal source, a multi‐level source can be designed to reduce the notch effect, strengthen the down‐going energy and improve the energy transmission directivity. Studies of the influence of depth and firing time deviations indicate that a multi‐level source is more stable than a normal horizontal source in an operational environment. 相似文献
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Tree radial growth is influenced by individual tree abilities, climate, competition, disturbance regimes, as well as biogeomorphic processes – including biomechanical interactions between trees and soil. Trees are actively involved in hillslope dynamics, both responding to and affecting many (bio)geomorphic processes. Using dendrochronology, we studied feedbacks associated with tree–soil–landscape formation, specifically relationships between hillslope processes, biomechanical effects of trees in soils, tree microhabitat conditions and their morphological adaptations, in the flysch zone of the Carpathians. We visually evaluated stem shape, microhabitat conditions and the biomechanical effects of 1663 trees. Cores were taken in four growing directions from 224 individuals of European beech (Fagus sylvatica L.). In a set of 193 cross-dated beeches, average tree-ring widths and tree eccentricities in all directions were calculated and analysed in relation to the biogeomorphic impacts of trees. Some significant drivers of tree radial growth and sources of stem eccentricity were detected. The radial growth of trees on which deadwood was leaning was markedly limited. In contrast, trees with exposed roots expressed the highest growth rates. This clearly suggests that root exposure may not be an effect of ‘exogenous’ soil creep, but may rather result from individually intensifying tree growth due to fine-scale disturbance dynamics. The response of biomechanical tree–soil interactions in tree radial growth weakened with increasing stem diameter, reflecting the stabilizing role of larger trees. The significance of calendar year on radial growth suggests seasonality in the dynamic component of soil creep. Tree eccentricity was observed mainly in the downslope direction, which suggests a relatively complex effect of biomechanics on stem tilting. © 2020 John Wiley & Sons, Ltd. 相似文献
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The Stubenberg meteorite—An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field 
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下载免费PDF全文 Addi Bischoff Jean‐Alix Barrat Kerstin Bauer Christoph Burkhardt Henner Busemann Samuel Ebert Michael Gonsior Janina Hakenmüller Jakub Haloda Dennis Harries Dieter Heinlein Harald Hiesinger Rupert Hochleitner Viktor Hoffmann Melanie Kaliwoda Matthias Laubenstein Colin Maden Matthias M. M. Meier Andreas Morlok Andreas Pack Alexander Ruf Philippe Schmitt‐Kopplin Maria Schönbächler Robert C. J. Steele Pavel Spurný Karl Wimmer 《Meteoritics & planetary science》2017,52(8):1683-1703
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Marián Jakubík Tomáš Paulech Luboš Neslušan Piotr A. Dybczyński Giuseppe Leto 《Earth, Moon, and Planets》2009,105(2-4):379-383
Considering the model of the initial disc of planetesimals consisting of 10,038 test particles, we simulated the formation of small-body reservoirs in the outer Solar System for the 2-Gyr period. We present the results from the simulation, which concern the part of the scattered disc with objects that have the semi-major axes larger than 50 AU and do not cross the Neptune’s orbit. A suitable border between the scattered disc and the inner Oort cloud, in terms of semi-major axis, appears to be no more than 2,500 AU. The simulated and observed values of perihelion distance and inclination to the Ecliptic typically cover the range between 30 and 40 AU and from 0° to 30°, respectively. No simulated or observed values of the inclination exceed 45°. The distributions of eccentricity and inclination in the simulation are more consistent with their observed counterparts, if the primary observational selection effects are imitated in the simulated distributions. 相似文献
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Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm. 相似文献
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Snow Accumulation on a Small High‐Arctic Glacier Svenbreen: Variability and Topographic Controls 下载免费PDF全文
下载免费PDF全文 Jakub Małecki 《Geografiska Annaler: Series A, Physical Geography》2015,97(4):809-817
One of the main controls on the net mass change of land‐terminating Arctic glaciers is the magnitude and distribution of snow accumulation. In Dickson Land, region of Svalbard with the greatest distance to the sea, the issue has not been receiving much scientific attention for decades. In this paper, new snow accumulation data are presented from Svenbreen in Dickson Land from end‐of‐winter surveys. The measured winter balance was 0.42 ± 0.15 m w.e. in 2010, 0.50 ± 0.10 m w.e. in 2011 and 0.62 ± 0.10 cm w.e. in 2012. Snow depth and water equivalent have been analysed in the background of altitude, slope and aspect extracted from the digital elevation model of the glacier. On steep northern slopes (>15°) accumulation was the highest, whereas it was decreased on southern slopes with moderate inclination (9–12°). Elevation, which on many glaciers proved to be highly correlated with snow depth, explained only 17–34% of snow depth variability due to complex interplay between local climate and geometry of a small valley. 相似文献
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Analysis of the relationship between the stream regulations and the geomorphologic effects of floods 总被引：1，自引：0，他引：1
Jakub Langhammer 《Natural Hazards》2010,54(1):121-139
This article presents the results of analysis of relationships between stream regulations and the geomorphic effects of floods
for the case of the Blanice river basin in the Czech Republic, which was at the center of an extreme flooding event that impacted
Central Europe in August 2002. The assessment is based on a geostatistical analysis of data on the distribution of flood effects
and stream modifications acquired by field survey and completed by historical maps and digital cartography. Using the cluster
analysis and regression tree classification, relationships between the occurrence of erosion and deposition forms, and the
parameters of stream modification and general physiography were tested. The results indicate a limited relationship between
stream modifications and the occurrence of geomorphic effects of the flood. The cluster analysis detected different sets of
parameters linked to erosion and accumulation. The accumulation was related to physiographic properties of stream, while erosion
was related to the presence of weirs in the stream segment. The regression tree classification demonstrates the potentially
critical combinations of stream modifications related to the occurrence of flood effects. 相似文献