美国国家级干旱监测业务产品介绍     

王涓力 《干旱气象》2006,24(1):90-94

美国需要改进干旱监测与评估方法。干旱是代价昂贵的自然灾害(联邦应急管理局(FEMA),1995;W ilhite,2000),但经常被评估和预报产品的开发者忽略。相比于其他灾害,干旱表现得更模糊并且不适合用传统的评估或预报方法,它相对缓慢的发生以及其影响的复杂性,需要有一套新的方法来对它进行评估。干旱监测和预报技术的提高会使我们为应对干旱灾害做更好的准备工作,进行更好的应对实践,从而减少社会对干旱及其影响的脆弱性。为追踪和展示全美国干旱的程度、空间范围以及其影响,开发了新的干旱监测工具,研发了每周发布的国家级干旱监测业务产品(th…  相似文献   

藏北多格错仁红层及孢粉组合特征   总被引：6，自引：0，他引：6  

吴珍汉  江万  Doug Nelson  Bill Kidd 《现代地质》2002,16(3):225-230,T001,T002

青藏高原北部羌塘地块广泛出露第三纪陆相红层 ,确定这些红层及其变形的时代对认识青藏高原的形成演化过程具有非常重要的意义。 1998～ 1999年 ,INDEPTH III项目地质课题组人员 2次深入西藏可可西里地区进行科学考察 ,新发现藏北多格错仁红层 ,并在其中发现较多种属的孢粉化石。该孢粉组合反映以温带旱生草原为主体的古植被面貌。通过对青藏高原北部及邻区主要新生代盆地孢粉组合与古环境演化的对比分析 ,结合多格错仁红层上覆弱变形玄武岩 2 5～ 3 2Ma的40 Ar- 3 9Ar高精度测年资料 ,推断多格错仁红层的形成时代为晚中新世 ,多格错仁红层挤压变形所致的约 5 0 %的地壳缩短量发生在中新世末—上新世初。这些资料为建立青藏高原动力学模式提供了新的年代依据  相似文献   

Rural community well-being: models and application to changes in the tobacco-belt in Ontario, Canada     

Doug Ramsey  Barry Smit 《Geoforum》2002,33(3):367-384

In this paper we develop a model of changes in rural community well-being. The model conceptualizes four interrelated dimensions of rural community well-being: physical, psychological, social, and economic. The model recognizes that a range of external forces (political, economic, etc.) exert pressures on rural communities, of which changes in well-being are one outcome. The paper then applies the model to changes which occurred in the tobacco growing region of southern Ontario, Canada. It is argued that this region was impacted by a variety of forces, some general to farming, others specific to tobacco farming, particularly between 1979 and the early 1990s. The empirical application is based on a personally administered farm survey (n=63) conducted between July 1996 and January 1997 and agricultural census data for the years 1981, 1986, 1991, and 1996. The paper concludes by suggesting that the model provides a useful framework for analysing the forces and changing conditions of other rural communities, not only in Canada, but beyond.  相似文献   

Carbon Stores,Sinks, and Sources in Forests of Northwestern Russia: Can We Reconcile Forest Inventories with Remote Sensing Results?     

Krankina  Olga N.  Harmon  Mark E.  Cohen  Warren B.  Oetter  Doug R.  Olga  Zyrina  Duane  Maureen V. 《Climatic change》2004,67(2-3):257-272

Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha^–1 yr^–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha^–1 yr^–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates.  相似文献   

GIS Methodology for Characterizing Historical Conditions of the Willamette River Flood Plain, Oregon     

Doug R Oetter  Linda R Ashkenas  Stanley V Gregory  Paula J Minear 《Transactions in GIS》2004,8(3):367-383

Recent environmental developments have stimulated an interest in conservation and restoration of the historical Willamette River flood plain, both to protect against flooding and to provide wildlife habitat. In order to best utilize scarce resources, we characterized historical and modern river channel and flood‐plain conditions to evaluate changes and help prioritize restoration sites. Using cartographic and photographic data sources, we developed a Geographic Information System (GIS) to map active channels, side channels, islands and tributaries for four separate dates, as well as riparian and flood‐plain vegetation characteristics for pre‐European settlement and modern time periods. Coverages based on flood records and other boundaries were used to partition the flood plain into spatial subsets for analysis. The GIS allowed comparisons between historical and present conditions for a variety of environmental factors. Much of the pre‐settlement channel complexity has been removed. Total channel length in 1995 was 26% less than in 1850, with almost 58% of the river's side channels disconnected from the system. In addition, we found a 72% loss of flood‐plain forest from 1850 to 1995, since it was converted to agricultural and urban land uses. Selected river and flood‐plain variables were made available for a spatial model to prioritize potential locations for flood‐plain restoration.  相似文献   

Subspace inversion of electromagnetic data: application to mid-ocean-ridge exploration   总被引：2，自引：0，他引：2  

Martyn Unsworth  Doug Oldenburg 《Geophysical Journal International》1995,123(1):161-168

Controlled-source electromagnetic (CSEM) surveys have the ability to provide tomo-graphic images of electrical conductivity within the Earth. the interpretation of such data sets has long been hampered by inadequate modelling and inversion techniques. In this paper, a subspace inversion technique is described that allows electric dipole-dipole data to be inverted for a 2-D electrical conductivity model more efficiently than with existing techniques. the subspace technique is validated by comparison with conventional inversion methods and by inverting data collected over the East Pacific Rise in 1989. A model study indicates that, with adequate data, a variety of possible mid-ocean-ridge conductivity models could be distinguished on the basis of a CSEM survey.  相似文献   

Can bottom-up procedures improve the performance of stream classifications?     

Ton Snelder  José Barquín Ortiz  Doug Booker  Nicolas Lamouroux  Hervé Pella  Ude Shankar 《Aquatic Sciences - Research Across Boundaries》2012,74(1):45-59

Top-down methods for defining stream classifications are based on a conceptual model or expert-defined rules, whereas bottom-up methods use biological training data and statistical modelling. We compared the performance of six classification methods for explaining the taxonomic composition of invertebrate and fish assemblages recorded at 327 and 511 sites, respectively, distributed throughout France. Classification 1 and 2 were top-down classifications; The European Water Framework System A (WFDa,) and the French Hydro-ecoregions (HER 2). Four bottom-up classification procedures of increasing complexity were defined based on 11 variables that included watershed characteristics describing climate, topography, and geology, and site characteristics including elevation, bed slope and temperature. Classification 3 was defined using matrix correlation (MC) to select a combination of variable categories that produced the best discrimination of the observed taxonomic composition. Classification 4 and 5 were defined by clustering the sites based on their taxonomic data and then using linear discriminant analysis (LDA) and Random forests (RF) to discriminate the clusters based on the environmental variables. Classification 6 was defined using generalized dissimilarity modelling (GDM). Our hypothesis was that the bottom-up classifications would perform better because they flexibly accommodate complex relationships between compositional and environmental variation. We tested the classifications using the classification strength statistic (CS). The RF-based classification fitted the taxonomic patterns better than GDM or LDA and these latter classifications generally fitted better than the MC, WFDa or HER classifications. Cross validation analysis showed that differences in predictive CS (i.e. the CS statistics produced from sites not used in defining the classifications) were often significant. However, these differences were generally small. Gains in predictive performance of classifications appear to be small relative to the increase in complexity in the manner in which environmental variables are combined to define classes.  相似文献   

Measurement of persistent organic pollutants (POPs) in plastic resin pellets from remote islands: toward establishment of background concentrations for International Pellet Watch   总被引：1，自引：0，他引：1  

Heskett M  Takada H  Yamashita R  Yuyama M  Ito M  Geok YB  Ogata Y  Kwan C  Heckhausen A  Taylor H  Powell T  Morishige C  Young D  Patterson H  Robertson B  Bailey E  Mermoz J 《Marine pollution bulletin》2012,64(2):445-448

Plastic resin pellets collected from remote islands in the Pacific, Atlantic, and Indian Oceans and the Caribbean Sea were analyzed for polychlorinated biphenyls (PCBs), dichloro-diphenyltrichloroethane and its degradation products (DDTs), and hexachlorocyclohexanes (HCHs). Concentrations of PCBs (sum of 13 congeners) in the pellets were 0.1-9.9 ng/g-pellet. These were 1-3 orders of magnitude smaller than those observed in pellets from industrialized coastal shores. Concentrations of DDTs in the pellets were 0.8-4.1 ng/g-pellet. HCH concentrations were 0.6-1.7 ng/g-pellet, except for 19.3 ng/g-pellet on St. Helena, where current use of lindane is likely influence. This study provides background levels of POPs (PCBs<10 ng/g-pellet, DDTs <4 ng/g-pellet, HCHs <2 ng/g-pellet) for International Pellet Watch. Sporadic large concentrations of POPs were found in some pellet samples from remote islands and should be considered in future assessments of pollutants on plastic debris.  相似文献   

Geomechanical property estimation of unconventional reservoirs using seismic data and rock physics          下载免费PDF全文

Andrea Cortis  Jinsong Chen  Doug Sassen  Howard Rael 《Geophysical Prospecting》2015,63(5):1224-1245

An extension of a previously developed rock physics model is made that quantifies the relationship between the ductile fraction of a brittle/ductile binary mixture and the isotropic seismic reflection response. By making a weak scattering (Born) approximation and plane wave (eikonal) approximation, with a subsequent ordering according to the angles of incidence, singular value decomposition analyses are performed to understand the stack weightings, number of stacks, and the type of stacks that will optimally estimate two fundamental rock physics parameters – the ductile fraction and the compaction and/or diagenesis. It is concluded that the full PP stack, i.e., sum of all PP offset traces, and the “full” PS stack, i.e., linear weighted sum of PS offset traces, are the two optimal stacks needed to estimate the two rock physics parameters. They dominate over both the second‐order amplitude variation offset “gradient” stack, which is a quadratically weighted sum of PP offset traces that is effectively the far offset traces minus the near offset traces, and the higher order fourth order PP stack (even at large angles of incidence). Using this result and model‐based Bayesian inversion, the seismic detectability of the ductile fraction (shown by others to be the important rock property for the geomechanical response of unconventional reservoir fracking) is demonstrated on a model characteristic of the Marcellus shale play.  相似文献   

Characterization of complex fluvial systems using remote sensing of spatial and temporal water level variations in the Amazon,Congo, and Brahmaputra Rivers   总被引：1，自引：0，他引：1  

Hahn Chul Jung  James Hamski  Michael Durand  Doug Alsdorf  Faisal Hossain  Hyongki Lee  A. K. M. Azad Hossain  Khaled Hasan  Abu Saleh Khan  A.K.M. Zeaul Hoque 《地球表面变化过程与地形》2010,35(3):294-304

The Surface Water and Ocean Topography (SWOT) satellite mission will provide global, space‐based estimates of water elevation, its temporal change, and its spatial slope in fluvial environments, as well as across lakes, reservoirs, wetlands, and floodplains. This paper illustrates the utility of existing remote sensing measurements of water temporal changes and spatial slope to characterize two complex fluvial environments. First, repeat‐pass interferometric SAR measurements from the Japanese Earth Resources Satellite are used to compare and contrast floodplain processes in the Amazon and Congo River basins. Measurements of temporal water level changes over the two areas reveal clearly different hydraulic processes at work. The Amazon is highly interconnected by floodplain channels, resulting in complex flow patterns. In contrast, the Congo does not show similar floodplain channels and the flow patterns are not well defined and have diffuse boundaries. During inundation, the Amazon floodplain often shows sharp hydraulic changes across floodplain channels. The Congo, however, does not show similar sharp changes during either infilling or evacuation. Second, Shuttle Radar Topography Mission measurements of water elevation are used to derive water slope over the braided Brahmaputra river system. In combination with in situ bathymetry measurements, water elevation and slope allow one to calculate discharge estimates within 2.3% accuracy. These two studies illustrate the utility of satellite‐based measurements of water elevation for characterizing complex fluvial environments, and highlight the potential of SWOT measurements for fluvial hydrology. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献