Web上的GIS资源分析与典型网站介绍

Web上蕴藏着巨大的资源，有效地利用这些资源将会给我们的学习和工作带来很大的帮助。文中分析了目前Web上的GIS资源，介绍了典型的GIS网站及如何在网上搜寻GIS资源。     

A simple yet more accurate model to calculate solar radiative flux in the inhomogeneous atmosphere

A simple yet more accurate semiempirical model is developed to calculate solar radiative flux in the optically inhomogeneous atmosphere. In the model a parameterized expression of spherical reflectance and transmitance of the atmosphere is confirmed, and the weighted single scatter albedo and weighted asymmetric factor are introduced to fit four empirical correction factors responsible for radiative fluxes in the inhomogeneous atmosphere. For both clean and turbid models, there are 120060 sets of radiative flux simulations for accuracy checks of the model, which cover 0-50 cloud optical depths, 0-0.8 surface reflectance, Junge and Log-normal aerosol size distributions, and 0-0.05 imaginary parts of aerosol refractive indexes. In case of the homogeneous atmosphere, standard errors of the 120060 upward fluxes from the present model are 1.08% and 1.04% for clean and turbid aerosol models, respectively; and those of the downward fluxes are 4.12% and 3.31%. In case of the inhomogeneous atmosphere, standard errors of the upw ard fluxes from the present model are 3.01% and 3.48% for clean and turbid aerosol models.respectively; and those of the downward fluxes are 4.54% and 4.89%, showing a much better accuracy than the results calculated by using an assumption of the homogeneous atmosphere.     

长江中游新石器时代遗址规模的分布特征

运用ArcGIS软件建立了长江中游地区9.0~4.0 ka BP文化遗址的空间数据库,采用叠加分析和统计学方法,对文化遗址的规模、海拔分布、坡度、距河流远近等特征进行了系统分析。结果表明：① 由新石器时代早期到晚期,遗址的数量、规模和分布范围等均呈现增长或扩大趋势,叠置型遗址个数增加;② 遗址一般具有低海拔、平缓地形和距河流较近的选址倾向,晚期的文化遗址大体保持该倾向,但对海拔、坡度及距河流远近等的选择开始出现分化。③ 新石器时代晚期不同规模的文化遗址在选址上存在一定分异。小型遗址多分布在坡度为6°~15°的缓坡地,中型及以上规模的遗址更倾向于坡度为2°~6°平缓地;中小型至大型遗址的海拔分布均以30~50 m为主,特大型遗址的海拔分布以50~100 m为主;特大型遗址在距河流1000 m以内的分布比例高于其他规模遗址;④ 新石器文化在早中期受气候、水源、地形等自然环境因素影响较大,晚期文化的适应能力有所增强。     

鄂尔多斯高原秦汉遗址空间分布及环境指示意义

人类活动遗址是反映过去人类生产、生活环境的重要指标。基于野外调查、文献资料整理和城市地理学相关理论,分析了鄂尔多斯高原168处秦汉聚落遗址的空间分布特征。结果表明,遗址空间结构呈典型的十字模式分布,其中心为今东胜区、伊金霍洛旗所在。秦汉遗址的分布密集区,以鄂尔多斯高原东部的黄土丘陵山地、毛乌素沙地和库布齐沙漠的中间地带为主。库布齐沙漠流动沙丘区没有遗址分布,毛乌素沙地内部尽管分布有不少遗址,但规模相对较小,不存在大型遗址,可能只是区域连接的中转站,不具备区域中心功能。这一分布模式或表明毛乌素沙地在秦汉时期的环境并不宜居,该研究为长期以来鄂尔多斯高原秦汉时期人类活动的环境影响争论提供了新视角。     

多层接地框架土-结构共同作用分析

多层接地框架是山地、丘陵地区多见的一种结构形式,但以往对其抗震性能研究不足很多。利用二次开发后的ANSYS对多层接地框架抗震性能进行了上下部共同作用分析,发现多层接地框架的抗震性能受到地基情况的明显影响。     

非均匀电磁波在导电媒质界面反射的横向偏移

由电磁场边值关系给出了非均匀电磁波在导电媒质界面反射时反射系数所产生的附加相角. 利用这一附加相角导出了非均匀电磁波在导电介质界面的横向偏移,并进行了横向偏移的相关计算,绘出了横向偏移随入射角的变化曲线. 结果表明：在导电媒质界面反射电磁波的横向偏移随入射角的增大而增大,当入射角接近90°时,电磁波在界面要传播较长时间后才返回第一种媒质. 在同一入射角电场偏振化方向在入射面的电磁波要比电场偏振化方向垂直于入射面的电磁波的横向偏移大,随着电磁波频率的增加横向偏移变小.     

利用主成分分析法分析GNSS坐标时间序列

利用主成分分析法对陆态网224个GNSS基准站坐标时间序列进行分析.首先对基准站原始坐标序列进行突变项拟合、粗差剔除、缺失数据插值补齐等预处理;然后对预处理后的站点残差坐标时间序列分N、E、U方向组建时间序列矩阵进行主成分分析,根据各方向主分量及其相应的空间特征向量分析站点空间响应分布特征、共模误差以及异常站点的影响....     

Evaluation of seismic displacement demands from the September 19, 2017 Puebla‐Morelos (Mw = 7.1) earthquake in Mexico City

This short communication presents the assessment of seismic inelastic and elastic displacement demands computed from earthquake ground motions (EQGMs) recorded in Mexico City during the intermediate‐depth intraslab Puebla‐Morelos earthquake on 19 September 2017 (Mw = 7.1). Evaluation is conducted by means of peak elastic and inelastic displacement demand spectra, inelastic displacement ratio, C_R, spectra, and generalized interstory drift spectra computed for selected recording stations located in different soil sites of Mexico City, including those located in areas of reported collapsed buildings. Results of this study confirm previous observations made from interplate (subduction) EQGMs that peak inelastic displacement demands are greater than corresponding elastic counterparts for short‐to‐medium period structures, while the opposite is true for medium‐to‐long period structures. Possible basin site effects were identified from generalized interstory drift spectra. It is also shown that an equation introduced in the literature to obtain estimates of C_R developed from interplate EQGMs provides also a good estimate for mean C_R computed from the intermediate‐depth intraslab EQGMs.     

硬场地实测记录下几种土层地震反应分析程序可靠性对比

以日本KiK-net强震观测台网中硬场地井下记录为样本,对传统等效线性化方法LSSRLI-1（频域）、SHAKE2000,时域非线性方法DEEPSOIL和频域一致等效线性化方法SOILQUAKE等几种计算程序在硬土场地地震反应分析中的可靠性进行对比检验。检验工况包括KiK-net井下台网中地表峰值加速度不小于0.05g的水平硬场地的总计344台次的加速度记录,涉及5个台站,土层厚度6~50m,地表峰值加速度范围0.050~0.805g。结果表明:认为硬土场地以往计算方法能够体现土层放大的认识是片面的,在中强地震动情况下,现有流行方法计算出的地表响应会偏小,强地震动下会严重偏小,会给工程抗震设计提供偏于危险的输入;硬场地中烈度8度以下（地表PGA在0.19g以下）,SHAKE2000和DEEPSOIL、LSSRLI-1（频域）计算结果与实际记录差距可以接受,但烈度8度以上,计算出地表响应均较实际记录明显偏小,且随地震动强度增加差距急剧增大;硬场地中,无论何种烈度,SOILQUAKE16计算的地表加速度响应与实测相当,可体现出土层放大作用。     

Changes in carbon and nutrient fluxes from headwaters to ocean in a mountainous temperate to subtropical basin

Water erosion provides major links in global cycles of carbon (C), nitrogen (N) and phosphorus (P). Although significant research on erosion mechanisms has been done, there is still little knowledge on C, N and P fluxes across landscapes to the ocean and their controlling factors in subtropical climates. A four‐year study quantifying and comparing particulate and dissolved C, N and P from multiple scales (microplot, plot, microcatchment, subcatchment, catchment, sub‐basin and basin) was performed in Thukela basin (≈30 000 km²), South Africa. The basin climate was largely subtropical‐humid [mean annual precipitation (MAP) > 980 mm yr^‐1], but temperate (MAP >2000 mm yr^‐1) on the highlands. Open grassland, cropland and bushland were the major land uses. On average, 65, 24 and 4 g m^‐2 yr^‐1 C, N and P were displaced from original topsoil positions, but only 0.33, 0.005 and 0.002 mg m^‐2 yr^‐1 were, respectively, exported to the ocean. The fluxes decreased by 95, 97 and 84%, respectively, from plot to microcatchment outlet; and decreased further in downstream direction by >99% from microcatchment to basin outlet. The hillslope (microplot to microcatchment) fluxes correlated strongly with rainfall parameters. Particulate contributions dominated hillslope fluxes at 73, 81 and 76% of total annual C, N and P, respectively. Although particulate C dominated in the microcatchment‐catchment reach (55%), N (54%) and P (69%) were dominated by dissolved forms. The lower basin zone was dominated by dissolved flux contributions at 93, 81 and 78% for C, N and P for the sub‐basin outlet. These results suggested spatially varying drivers of C, N and P losses from the landscape to the ocean, via the river network. Deposition was envisaged the dominant hillslope level loss process, which gradually gave way to mineralization and biotic uptake in the river network as flux contributions shifted from being predominantly particulate to dissolved forms. Copyright © 2017 John Wiley & Sons, Ltd.