A multi-resolution global land cover dataset through multisource data aggregation     

Le Yu  Jie Wang  XueCao Li  CongCong Li  YuanYuan Zhao  Peng Gong 《中国科学:地球科学(英文版)》2014,57(10):2317-2329

Recent developments of 30 m global land characterization datasets(e.g., land cover, vegetation continues field) represent the finest spatial resolution inputs for global scale studies. Here, we present results from further improvement to land cover mapping and impact analysis of spatial resolution on area estimation for different land cover types. We proposed a set of methods to aggregate two existing 30 m resolution circa 2010 global land cover maps, namely FROM-GLC(Finer Resolution Observation and Monitoring-Global Land Cover) and FROM-GLC-seg(Segmentation), with two coarser resolution global maps on development, i.e., Nighttime Light Impervious Surface Area(NL-ISA) and MODIS urban extent(MODIS-urban), to produce an improved 30 m global land cover map—FROM-GLC-agg(Aggregation). It was post-processed using additional coarse resolution datasets(i.e., MCD12Q1, GlobCover2009, MOD44 W etc.) to reduce land cover type confusion. Around 98.9% pixels remain 30 m resolution after some post-processing to this dataset. Based on this map, majority aggregation and proportion aggregation approaches were employed to create a multi-resolution hierarchy(i.e., 250 m, 500 m, 1 km, 5 km, 10 km, 25 km, 50 km, 100 km) of land cover maps to meet requirements for different resolutions from different applications. Through accuracy assessment, we found that the best overall accuracies for the post-processed base map(at 30 m) and the three maps subsequently aggregated at 250 m, 500 m, 1 km resolutions are 69.50%, 76.65%, 74.65%, and 73.47%, respectively. Our analysis of area-estimation biases for different land cover types at different resolutions suggests that maps at coarser than 5 km resolution contain at least 5% area estimation error for most land cover types. Proportion layers, which contain precise information on land cover percentage, are suggested for use when coarser resolution land cover data are required.  相似文献   

面向分布式服务聚合的“天地图”总体技术架构   总被引：1，自引：0，他引：1  

李志刚  蒋捷  翟永  王茜  黄蔚 《测绘信息与工程》2012,37(5):13-15

介绍了"天地图"面向分布式多节点协同服务的总体架构,以及"天地图"公共地理框架数据体系、在线服务系统、运行支持系统的内容,旨在为同类平台的研究与建设提供参考。  相似文献   

人工合成纳米材料在水环境中的聚沉行为研究进展     

赵晓丽  王珺瑜  方蕾  汤智  吴爱明  赵天慧 《矿物岩石地球化学通报》2019,(3):522-533,439

随着纳米科技的快速发展,纳米材料的种类和数量呈指数增长。人工纳米材料不可避免地进入水环境并发生复杂的环境行为,可能在水中分散悬浮,也可能发生团聚和沉降,从而影响其迁移、转化和归趋。本文综述了近年来有关人工合成纳米材料在水环境中聚沉行为的研究进展,分析了影响纳米材料团聚与沉降的两个主要因素:自身理化性质(材料形态、颗粒尺寸、化学组成、晶体结构、表面修饰等)和水环境要素(pH、离子种类和离子强度、天然有机质等)及相应的作用机理,剖析了当前研究中存在的问题,指出有关纳米材料与无机胶体等物质间的异团聚、各环境要素间的交互作用、以及纳米材料在接近自然环境的低浓度(<1mg/L)条件下的聚沉行为研究仍需进一步完善。  相似文献   

多元聚合分类方案     

吴红光 《大气科学》1996,20(6):767-770

取得对样品（或逆分析中的要素）的客观分类（型），对于提高天气预报的效果有着十分重要的意义，遗憾的是目前尚未见到能够获得合理分类结果的可行客观分类方法。本方案是以聚合为策略，以计算机为工具，通过逐次全面比较所给样本资料各种情况下的分类，试图在这方面进行的一项尝试，方案目前已取得下列成果:① 提供出一种新的分类思路和方法；② 分类客观且有较好的效果；③ 对小样本可确保取得合理分类。  相似文献   

Strategies for Transforming Fine Scale Knowledge to Management Usability     

Kai W. Wirtz 《Marine pollution bulletin》2001,43(7-12):209-214

Simulation tools used for management purposes should fulfill several conditions by being computationally fast, user-friendly, realistic, generic and reliable. These traits are often counteracting since they simultaneously demand for model complexity as well as simplicity. Here we develop a strategy to overcome this general problem of environmental modelling for management use. Major ingredients are model analysis and reduction as new core components of the modelling process. In detail, a set of combined methods is proposed. Within a large class of models the set allows for automatically exploring model behaviour and for aggregating fine scale process knowledge together with spatio temporal resolution. Applications to a huge aquatic European regional seas ecosystem model (ERSEM), a complex photosynthesis model (PGEN) as well as a simple diagenetic model are presented. The analysis and aggregation methods provide first steps towards a new generation of decision support tools able to cope with an increase in scientific knowledge as well as management demands.  相似文献   

Formation of high-grade ignimbrites Part II. A pyroclastic suspension current model with implications also for low-grade ignimbrites   总被引：2，自引：2，他引：0  

Armin Freundt 《Bulletin of Volcanology》1999,60(7):545-567

 Analogue experiments in part I led to the conclusion that pyroclastic flows depositing very high-grade ignimbrite move as dilute suspension currents. In the thermo–fluid–dynamical model developed, the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation. Initial conditions of the currents are derived from column-collapse modeling for magmas with an initial H₂O content of 1–3 wt.% erupting through circular vents and caldera ring-fissures. The flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content, temperature, bottom slope and coarser initial grain size. Progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance. The ash plumes reach stratospheric heights and distribute 30–80% of the erupted material as widespread co-ignimbrite ash. Pyroclastic suspension currents with initial mass fluxes of 10⁷-10¹² kg/s can spread for tens of kilometers with only limited cooling, although they move as supercritical, strongly entraining currents for the eruption conditions considered here. With increasing eruption mass flux, cooling during passage through the fountain diminishes while cooling during flow transport increases. The net effect is that eruption temperature exerts the prime control on emplacement temperature. Pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is T_o>1.3^.T_mw, the minimum welding temperature. High eruption rates, a large fraction of fine ash, and a ring-fissure vent favor the formation of extensive high-grade ignimbrite. For very hot eruptions producing sticky, partially molten pyroclasts, analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation, which reduces runout. As a result, very high-grade ignimbrites cannot spread more than a few tens of kilometers from their source. In cooler pyroclastic currents, particles do not aggregate, and the sedimentation process may involve re-entrainment of particles, which potentially leads to more extensive cooling and longer runout; such effects, however, are only significant when net erosion of substrate occurs. Model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios. The model also provides an alternative explanation of the observed decrease in H/Lratios with ignimbrite mass. Received: 10 May 1998 / Accepted: 21 October 1998  相似文献   

复合目标的赋值──聚合操作     

李霖 《武汉大学学报(信息科学版)》1995,(3)

介绍了有关目标聚合的一般特征，在ＧＩＳ软件Ｓｍａｌｌｗｏｒｌｄ上讨论了聚合操作的一般过程。按目标属性本身的特点，将数值聚合归为三个基本类，以实例形式介绍了这些属性值的聚合方法。并根据Ｓｍａｌｌｗｏｒｌｄ支持的面向对象语言ｍａｇｉｋ，利用面向对象的数据模型实现其聚合操作过程。  相似文献   

Hierarchical aggregation in percolation model     

Ilya Zaliapin  Henry Wong  Andrei Gabrielov   《Tectonophysics》2006,413(1-2):93

There is a growing belief that the complex dynamics of seismicity can be better understood by studying the collective behavior of numerous lithosphere instability sources rather than focusing on the details of each of them. Classical site-percolation is a simple and tractable model which exhibits such important general features of complex systems as criticality and phase transitions of second kind. It also illustrates the mechanism of hierarchical aggregation, which is very important for explaining collective phenomena in material fracture and earthquake nucleation processes. We study the dynamics of a 2D site percolation model on a square lattice using the hierarchical approach introduced by Gabrielov et al., Phys. Rev. E., 5293–5300, 1999. The key elements of the approach are the tree representation of clusters and the Horton–Strahler scheme for cluster ranking. Accordingly, the evolution of percolation model is considered as a hierarchical inverse cascade of cluster aggregation. We analyzed the growth of the percolation cluster and established the time-dependent rank distribution of its subclusters, as well as corresponding laws for its mass, rank, and their relationship. We report several phenomena premonitory to the onset of percolation that complement the traditional power-law increase of the model's observables. In addition, we have shown that the Tokunaga side-branching constraint uniquely determines the mass–rank relationship for a general aggregation process (not necessarily originated from the percolation model). The results can be used for development and improvement of earthquake prediction techniques.  相似文献   

Tourmaline nodules from Capo Bianco aplite (Elba Island,Italy): an example of diffusion limited aggregation growth in a magmatic system   总被引：1，自引：0，他引：1  

Diego Perugini  Giampiero Poli 《Contributions to Mineralogy and Petrology》2007,153(5):493-508

The morphology of tourmaline nodules occurring in the Capo Bianco aplite (Elba Island, Italy) is studied. Outcrop features indicate that tourmaline nodules are the product of magmatic crystallization, as they are aligned along flow fields developed within the magmatic hosting mass. Mesoscopic observations indicate that nodule morphologies are very variable, from rounded to dendritic. Morphometric analyses show that tourmaline nodules are fractals and that fractal dimension quantifies their degree of irregularity. Numerical simulations of nodule growth are performed by using a Diffusion-Limited Aggregation process. The presence in natural samples of nodules with different morphologies is explained by considering a chaotic magmatic system characterized by a complex interplay between growth rate in different dynamical regions, latent heat of crystallization, and local convection dynamics. It is suggested that higher growth rates correspond to growth of tourmaline nodules in dynamical regions where the transfer of nutrients is very efficient. In such conditions, the latent heat released by the growing nodule is high, inducing strong local convection dynamics, destabilizing the nodule interface, and promoting the formation of dendritic morphologies. On the contrary, the growth of nodules in dynamical regions characterized by weak transfer of nutrients is inhibited leading to weak local convection dynamics and, consequently, to the formation of rounded morphologies.  相似文献   

Spatial organization of a shredder guild of caddisflies (Trichoptera) in a riffle - Searching for the effect of competition     

Dénes Schmera  Tibor Ero?s 《Limnologica》2007,37(2):129-136

The shredder guild plays an outstanding role in the functioning of headwater stream ecosystems by processing allochthonous leaf litter. Traditionally, the abiotic habitat template is regarded as the major determinant of its organization, and only a limited number of studies support the importance of biotic interactions. The aim of the present study was to examine whether competition plays a significant role in organizing the shredder guild of caddisflies in a riffle. Null-model based co-occurrence, co-existence and guild variation analyses were used in the study of guild organization. In addition, the traditional variance to mean ratio was applied for measuring the intraspecific aggregation of guild members. The non-significant metric values of co-occurrence and co-existence analyses predicted that competition was of limited importance in structuring the spatial organization of the shredder guild. The observed aggregated spatial distribution of species, suggests that besides stochastic events, deterministic forces should also contribute to the organization of the shredder guild of caddisflies.  相似文献