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991.
Changes in forest composition impact ecological services, and are considered important factors driving global climate change. A hybrid sampling method along with a modelling approach to map current and past land cover in Kunming, China is reported. MODIS land cover (2001–2011) data-sets were used to detect pixels with no apparent change. Around 3000 ‘no change points’ were systematically selected and sampled using Google Earth’s high-resolution imagery. Thirty-five per cent of these points were verified and used for training and validation. We used Random forests to classify multi-temporal Landsat imagery. Results show that forest cover has had a net decrease of 14385?ha (1.3% of forest area), which was primary converted to shrublands (11%), urban and barren land (2.7%) and agriculture (2.5%). Our validation indicates an overall accuracy (Kappa) of 82%. Our methodology can be used to consistently map the dynamics of land cover change in similar areas with minimum costs. 相似文献
992.
993.
Alexander T. Lowe Ross Whippo Aaron W. E. Galloway Kevin H. Britton‐Simmons Megan N. Dethier 《Marine Ecology》2015,36(2):129-140
Sea urchins are important ecosystem engineers in subtidal ecosystems worldwide, providing biogenic structure and altering nutrient dynamics through intensive grazing and drift algal capture. The current work evaluates red urchin (Strongylocentrotus franciscanus) density on fixed transects through time, individual displacement, and urchin‐associated benthic community composition using a field‐based approach at multiple depths (in and outside of the macroalgal zone) and replicated across sites in the San Juan Archipelago, Washington. Urchins exhibited no large‐scale, temporal or directional changes in density among depths. Furthermore, 87% of individual urchins observed in repeated small‐scale surveys over 3 weeks exhibited no change in position. Individual displacement was negatively correlated to drift algal capture. Evidence of sedentary behavior from the displacement surveys was supported by the sessile and mobile community composition in areas directly under versus adjacent to (control) urchins. The benthos under urchins had a higher percentage of bare space, crustose coralline algae, and increased density of snails, crabs and shrimp relative to associated control plots. Abundance of mobile organisms associating with urchins increased relative to control plots at the deepest survey depth (30 m), indicating a greater strength of interaction with distance from macroalgal production. This work presents evidence of food availability‐related behavior in red urchins and indicates that even when sedentary, urchins have a strong influence on ecosystem structure through increasing availability of shelter and macroalgal detritus to the benthos. 相似文献
994.
Stefan Hahmann Jakob Miksch Bernd Resch Johannes Lauer Alexander Zipf 《地球空间信息科学学报》2018,21(3):247-256
AbstractFinding the shortest path through open spaces is a well-known challenge for pedestrian routing engines. A common solution is routing on the open space boundary, which causes in most cases an unnecessarily long route. A possible alternative is to create a subgraph within the open space. This paper assesses this approach and investigates its implications for routing engines. A number of algorithms (Grid, Spider-Grid, Visibility, Delaunay, Voronoi, Skeleton) have been evaluated by four different criteria: (i) Number of additional created graph edges, (ii) additional graph creation time, (iii) route computation time, (iv) routing quality. We show that each algorithm has advantages and disadvantages depending on the use case. We identify the algorithms Visibility with a reduced number of edges in the subgraph and Spider-Grid with a large grid size to be a good compromise in many scenarios. 相似文献
995.
Alexander V. Parshin Vladimir A. Morozov Anton V. Blinov Alexey N. Kosterev Alexander E. Budyak 《地球空间信息科学学报》2018,21(1):67-74
AbstractThe prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any ground survey, including magnetic prospecting, difficult and expensive. The current level of geology requires high-precision and large-scale data at the first stages of geological exploration. Since 2012, technologies of aeromagnetic surveying with unmanned aircraft vehicles (UAV) enter the market, but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods. To increase the scale of survey, it is necessary to reduce the altitude and speed of flight, for which the authors develop the methodical and technical solutions described in this article. To obtain data at altitudes of 5 m above the terrain even in a rugged relief, we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions (even a moderate snowfall), and develop a special software to generate flight missions on the basis of digital elevation models. A UAV has special design to reduce magnetic interference of the flight platform; the magnetic sensor is hung below the aircraft. This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016. The results of the comparison between airborne and ground surveys are presented, which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field. An unmanned survey is cheaper and more productive; the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000?1:1000. 相似文献
996.
ABSTRACTNowadays, several research projects show interest in employing volunteered geographic information (VGI) to improve their systems through using up-to-date and detailed data. The European project CAP4Access is one of the successful examples of such international-wide research projects that aims to improve the accessibility of people with restricted mobility using crowdsourced data. In this project, OpenStreetMap (OSM) is used to extend OpenRouteService, a well-known routing platform. However, a basic challenge that this project tackled was the incompleteness of OSM data with regards to certain information that is required for wheelchair accessibility (e.g. sidewalk information, kerb data, etc.). In this article, we present the results of initial assessment of sidewalk data in OSM at the beginning of the project as well as our approach in awareness raising and using tools for tagging accessibility data into OSM database for enriching the sidewalk data completeness. Several experiments have been carried out in different European cities, and discussion on the results of the experiments as well as the lessons learned are provided. The lessons learned provide recommendations that help in organizing better mapping party events in the future. We conclude by reporting on how and to what extent the OSM sidewalk data completeness in these study areas have benefited from the mapping parties by the end of the project. 相似文献
997.
998.
Dmitri?A.?IonovEmail author Vladimir?S.?Prikhodko Jean-Louis?Bodinier Alexander?V.?Sobolev Dominique?Weis 《Contributions to Mineralogy and Petrology》2005,149(6):647-665
We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of the Siberian craton, which formed in the Mesoproterozoic. High equilibration temperatures (870–1,010°C) of the xenoliths and the absence of garnet-bearing peridotites indicate a much thinner lithosphere than in the central craton. Most common among the xenoliths are clinopyroxene-poor lherzolites and harzburgites with Al2O3 and CaO contents nearly as low as in refractory xenoliths from kimberlite pipes (Mir, Udachnaya) in the central and northern Siberian craton. By contrast, the Tok peridotites have higher FeO, lower Mg-numbers and lower modal orthopyroxene and are apparently formed by shallow partial melting (3 GPa). Nearly all Tok xenoliths yield petrographic and chemical evidence for metasomatism: accessory phlogopite, amphibole, phosphates, feldspar and Ti-rich oxides, very high Na2O (2–3.1%) in clinopyroxene, LREE enrichments in whole-rocks.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
999.
Vyacheslav?V.?AkininEmail author Alexander?V.?Sobolev Theodoros?Ntaflos Wolfram.?Richter 《Contributions to Mineralogy and Petrology》2005,150(1):85-101
Clinopyroxene megacrysts from young melanephelinitic lavas were divided into Cr-rich and Cr-poor suites. Sr, Nd, and Pb isotopic
ratios of leached megacrysts and host lava are indistinguishable from each other and indicate a depleted source. Host lavas
do not display chemical evidence for significant fractional crystallization, which is required to explain the compositional
range of the megacrysts. This rules out a simple cognate genetic relationship between the two, and strictly defines megacrysts
as xenocrysts. The well-defined correlations of trace elements with the Mg-numbers in the megacrysts are interpreted as the
result of extensive fractional/equilibrium crystallization of magma over a large temperature range at near isobaric condition
in the upper mantle. Trace element variations in megacrysts are consistent with fractional crystallization of clinopyroxene
alone for the Cr-rich suite, and clinopyroxene + garnet for the Cr-poor suite from at least two bathes of related melts. Megacrysts
parent magma might represent mantle melts, which were never erupted in their initial composition. 相似文献
1000.
Kristina?B.?KatsarosEmail author Alexander?V.?Soloviev Robert?H.?Weisberg Mark?E.?Luther 《Boundary-Layer Meteorology》2005,116(2):175-185
Consideration of the dependence of various components of the sea-surface heat and momentum fluxes on sea surface temperature
(SST) leads to an explanation for the observed reduction in the horizontal temperature gradients in the uppermost layer of
the ocean (a few to 10 m in depth). Horizontal temperature gradients within the mixed layer can be masked by a near-surface
layer of warm water. This camouflage of horizontal temperature gradients has importance for the remote sensing of SST used
by the fishing industry, for the estimation of acoustic transmission, and for the forecasting of hurricane development, among
many uses of SST data. Diurnal warming conditions in the Straits of Florida are examined by a simulation calculation and by
analysis of observations obtained on moorings deployed on the south-east Florida shelf. When there is net heating (i.e., the
solar input is stronger than the combined latent, sensible and longwave radiative heat losses) the originally warmer water
experiences less heating than the colder water, leading to a weakening of the horizontal SST gradients as seen by surface
buoys or satellites. The warmer water also experiences more mixing and therefore less increase in temperature. The strongest
effect of the diurnal heating on wind stress occurs when the SST starts out cooler than the air temperature and the atmosphere
is stably stratified. Diurnal warming can then rapidly increase the SST above the air temperature because of reduced wind
stress and reduced upper-ocean mixing. After that the wind stress increases as convectively driven turbulence contributes
to the atmospheric exchange. 相似文献