对数字化过程中数据精度的一些讨论

目前 ,全国各地已经建立了许多地理信息系统。对于地理信息系统中数据精度能否满足人们的要求 ,人们尚没有引起足够的重视。本文分析了数字化过程中数据精度的变化情况 ,并尝试提出具体的解决办法     

边角后方交会的精度分析及布设方案选择

在推出边角后方会简捷精度估算式的基础上,分析并给出了待定点较优的选择区域,还讨论了其解的多值性问题及实质,针对边角后方交会应用中有较严格的布点限制,提出了双边单角后方交会的布设方案;文中给出了其点位与精度计算的固定公式,并附有实例难证。     

Wind-induced baroclinic response of Lake Constance

We present results of various circulation scenarios for the wind-induced three-dimensional currents in Lake Constance, obtained with the aid of a semi-spectral semi-implicit finite difference code developed in Haidvogel et al. and Wang and Hutter. Internal Kelvin and Poincaré-type oscillations are demonstrated in the numerical results, whose periods depend upon the stratification and the geometry of the basin and agree well with measured data. By solving the eigenvalue problem of the linearized shallow water equations in the two-layered stratified Lake Constance, the interpretation of the oscillations as Kelvin and Poincaré-type waves is corroborated.     

Adding Local Accuracy to Direct Sequential Simulation

Geostatistical simulations are globally accurate in the sense that they reproduce global statistics such as variograms and histograms. Kriging is locally accurate in the minimum local error variance sense. Building on the concept of direct sequential simulation, we propose a fast simulation method that can share these opposing objectives. It is shown that the multiple-point entropy of the resulting simulation is related to the univariate entropy of the local conditional distributions used to draw simulated values. Adding local accuracy to conditional simulations does not detract much from variogram reproduction and can be used to increase multiple-point entropy. The methods developed are illustrated using a case study.     

Correcting the Smoothing Effect of Estimators: A Spectral Postprocessor

The postprocessing algorithm introduced by Yao for imposing the spectral amplitudes of a target covariance model is shown to be efficient in correcting the smoothing effect of estimation maps, whether obtained by kriging or any other interpolation technique. As opposed to stochastic simulation, Yao's algorithm yields a unique map starting from an original, typically smooth, estimation map. Most importantly it is shown that reproduction of a covariance/semivariogram model (global accuracy) is necessarily obtained at the cost of local accuracy reduction and increase in conditional bias. When working on one location at a time, kriging remains the most accurate (in the least squared error sense) estimator. However, kriging estimates should only be listed, not mapped, since they do not reflect the correct (target) spatial autocorrelation. This mismatch in spatial autocorrelation can be corrected via stochastic simulation, or can be imposed a posteriori via Yao's algorithm.     

Isotopic equilibration ages for the Miyanohara tonalite from the Higo metamorphic belt in central Kyushu, Southwest Japan: Implications for the tectonic setting during the Triassic

Abstract Miyanohara tonalite occurs in the middle part of the Higo metamorphic belt in the central Kyushu, Southwest Japan. This tonalite intrudes into early Permian Ryuhozan metamorphic rocks in the south and is intruded by Cretaceous Shiraishino granodiorite in the north. The Miyanohara tonalite yielded three mineral ages: (i) 110–100 Ma for Sm–Nd and Rb–Sr internal isochrons and for K–Ar hornblende; (ii) 183 Ma for Sm–Nd internal isochron; and (iii) 211 Ma for Sm–Nd internal isochron. The ages of 110–100 Ma may indicate cooling age due to the thermal effect of the Shiraishino granodiorite intrusion. The ages of 183 Ma and 211 Ma are consistent with timing of intrusion of the Miyanohara tonalite based on geologic constraints. The hornblende in the sample which gave 183 Ma shows discontinuous zoning under microscope, whereas the one which gave 211 Ma does not show zonal structure. These mineralogical features suggest that the 183 Ma sample has suffered severely from later tectonothermal effect compared with the 211 Ma sample. Therefore, the age of 211 Ma is regarded as near crystallization age for the Miyanohara tonalite. The magmatic process, geochronology and initial Sr and Nd isotope ratios for the Miyanohara tonalite are similar to those of early Jurassic granites from the Outer Plutonic Zone of the Hida belt that constitutes a marginal part of east Asia before the opening of the Japan Sea. Intrusion of the Miyanohara tonalite is considered to have taken place in the active continental margin during the late Triassic.     

Topographic and Satellite Information for Preliminary Route Location

Topographic information from maps and geographical information systems (GIS) has been combined with satellite data (SPOT Panchromatic, SPOT Multispectral and Landsat Thematic Mapper) to derive a product that may be valuable in preliminary route location studies. The objectives of this study were to evaluate the classification accuracy of this combined product, to compare levels of ground detail obtainable from different types of satellite imagery against aerial photography, and to present an example application on the use of the combined product.
The classification accuracy of the combined product was dependent on the type of land cover and was 83 to 100 per cent successful, with accuracy exceeding 95 per cent for most land cover types. The overall accuracy of the product was almost 95 per cent, with accuracy based on KHAT statistics of 92 per cent. Varying levels of ground detail were attainable from different types of satellite imagery. This detail may be adequate for preliminary route selection, especially in the absence of aerial photographs and GIS. The combined product presented in this study was applied successfully in selecting the optimal route for the Greater Amman ring road.     

浅强跃层大振幅内波研究

海洋内波是分析整个海洋中能量的收支和平衡问题时必须研究的一个重要的物理过程 ,对它的研究不仅在整个海洋动力学的研究中占有重要的地位 ,而且对海洋环境与资源的开发和保护、推动其它相关学科的深入研究和发展都具有重要的应用价值。浅强跃层大振幅内波是海洋内波研究中的一个重要组成部分 ,它对人类在浅海中的活动之影响尤其引人注目 :如对海洋石油、天然气等资源的勘探及开采设施的安装施工和正常工作等具有直接的或潜在的破坏性 ;能够改变海水中声传播路线 ,从而影响声通讯设备的正常使用 ,使众多利用声信号进行测量的调查仪器所获取的大量观测资料中带有难以去掉的噪声信号 ;可将富含营养盐底层水带到表层 ,改进了海洋生态环境 ,因而对于海洋生态环境的保护、渔业捕捞及海洋养殖业的发展等具有指导意义 ;还对环流场、物质输运、航道淤积以及深水沉积等有一定的影响。文中主要从浅强跃层大振幅内波的生成机制、传播演变、模型描述以及观测方法等方面介绍了浅强跃层大振幅内波研究的进展状况、存在的问题及其发展趋势。     

南海北部大陆坡区的突发性强流

应用声学多普勒流速剖面仪的定点观测资料 ,分析南海北部东沙群岛西南大陆坡区孤立内波引起的突发性强流。本次观测到的这些强流主要特征为 :( 1 )在 0— 1 50m的观测深度层内 ,流向主要以向岸方向为主 ,每一峰值持续时间约为 1 0— 2 5min。 ( 2 )在大潮期间 ,强流事件出现的次数较多 ,且强度大 ;在小潮期则反之。 ( 3)最强的突发性海流发生于斜压内潮强盛期 ,比天文大潮落后 4— 5d。 ( 4 )突发性强流事件既可呈现多峰型 ,也可呈单峰型。     

U.S. Intercounty Migration in the 1990s: People and Income Move Down the Urban Hierarchy

Internal migration within the United States continues to transform both the magnitude and composition of population at all geographic scales. During 1994 ‐ 1995, the majority of counties gained both people and income, largely as a consequence of net outmigration by higher income migrants from the nation's most populous cities. Regionally, net gainers of both people and income included counties in the West and South as well as other areas renowned for environmental amenities. Spatially, net migration flowed down the urban hierarchy from large central cities to adjacent suburbs which, in turn, exported migrants to exurban areas. Large cities tended to exchange migrants with nearby counties as well as other large cities. Migration patterns such as these are contributing to spatial deconcentration and economic disparity.