层间滑移隔震结构地震作用有限元分析

将二硫化钼作为摩擦材料设计出一种带限位器的滑移隔震支座。根据多层框架结构变形的特点,给出适用于滑移框架隔震结构的计算模型,推导出层间滑移隔震结构的运动方程。运用SAP2000有限元软件建立一层间滑移框架隔震结构的有限元模型,对比分析El Centro地震波下摩擦系数和隔震层位置不同时隔震结构的地震反应。结果表明,上部结构的动力反应随摩擦系数的增加而不断增大,滑移隔震结构的减震效果逐渐减弱,但隔震层的滑移量却在不断减小;摩擦系数的选取应综合考虑减震效果和隔震层滑移量两个因素。随着隔震层的增高,结构的加速度反应和层间位移反应整体上呈增大趋势,隔震效果不断减弱,且隔震层的加速度值下部层比上部层要大得多,一层隔震和三层隔震时的变形主要集中于隔震层,而五层隔震时结构层间位移并未出现突变,说明隔震层设置在较高位置处对结构体系的影响较小。     

水准面精化成果在公路勘测中的应用

通过在玉树西南高海拔、无控制点区域公路工程的生产作业中,利用常规方法和玉树似大地水准面精化成果在基础控制测量中的应用,互相校核,通过相关应用数据统计,为西部困难地区取代低等级水准测量和精化成果的推广应用进行了有益的探讨.     

一种顾及异常控制点的坐标转换方法

坐标转换中如果有异常控制点参与转换参数的求解,会导致转换参数的可靠性差,最终使得转换精度降低。为了有效抵抗异常控制点对坐标转换的影响,在最小二乘中融入了异常点搜索算法,搜索完成后自动生成定位矩阵,通过定位矩阵直接求得经过异常值修正后的转换参数。实验结果表明,该方法对中小异常值的定位和估值较为有效,转换残差显著减小,修正后的控制点保证数量和空间分布不变,对转换精度有益。     

2008年攀枝花6.1级地震序列精定位

利用四川和云南区域数字地震台网震相到时资料,并结合Hypo2000+Hypo DD对2008年8月30日攀枝花MS6.1地震序列进行了定位。定位结果表明,地震序列的震中在空间上呈近SN向展布,余震密集区长度约为30km,主震震源深度约为14km。序列深度的分布范围主要为0~4、5~20km,而4~5km范围显示为明显的少震层。沿序列长轴的深度剖面显示,余震区中段存在1个不规则的少震的"空区",为1955年634级地震的破裂区,该地震发生在空区的南端。分析认为,2008年8月30日攀枝花MS6.1地震是因汶川8.0级地震后的应力调整造成未破裂的小凹凸体发生破裂所致。余震密集分布区沿垂直于破裂长轴的两个剖面则显示了在其北端地震震源分布更深,且断层面向NW倾斜,与已知的红格断裂的倾向一致。     

Classification of vegetation in an open landscape using full-waveform airborne laser scanner data

Airborne laser scanning (ALS) is increasingly being used for the mapping of vegetation, although the focus so far has been on woody vegetation, and ALS data have only rarely been used for the classification of grassland vegetation. In this study, we classified the vegetation of an open alkali landscape, characterized by two Natura 2000 habitat types: Pannonic salt steppes and salt marshes and Pannonic loess steppic grasslands. We generated 18 variables from an ALS dataset collected in the growing (leaf-on) season. Elevation is a key factor determining the patterns of vegetation types in the landscape, and hence 3 additional variables were based on a digital terrain model (DTM) generated from an ALS dataset collected in the dormant (leaf-off) season. We classified the vegetation into 24 classes based on these 21 variables, at a pixel size of 1 m. Two groups of variables with and without the DTM-based variables were used in a Random Forest classifier, to estimate the influence of elevation, on the accuracy of the classification. The resulting classes at Level 4, based on associations, were aggregated at three levels — Level 3 (11 classes), Level 2 (8 classes) and Level 1 (5 classes) — based on species pool, site conditions and structure, and the accuracies were assessed. The classes were also aggregated based on Natura 2000 habitat types to assess the accuracy of the classification, and its usefulness for the monitoring of habitat quality. The vegetation could be classified into dry grasslands, wetlands, weeds, woody species and man-made features, at Level 1, with an accuracy of 0.79 (Cohen’s kappa coefficient, κ). The accuracies at Levels 2–4 and the classification based on the Natura 2000 habitat types were κ: 0.76, 0.61, 0.51 and 0.69, respectively. Levels 1 and 2 provide suitable information for nature conservationists and land managers, while Levels 3 and 4 are especially useful for ecologists, geologists and soil scientists as they provide high resolution data on species distribution, vegetation patterns, soil properties and on their correlations. Including the DTM-based variables increased the accuracy (κ) from 0.73 to 0.79 for Level 1. These findings show that the structural and spectral attributes of ALS echoes can be used for the classification of open landscapes, especially those where vegetation is influenced by elevation, such as coastal salt marshes, sand dunes, karst or alluvial areas; in these cases, ALS has a distinct advantage over other remotely sensed data.     

求取小区域GPS网CGCS2000坐标的方法研究

本文通过联测IGS跟踪站获取南宁地区若干控制点的ITRF框架瞬时历元坐标,并根据IGS跟踪站速度内插出南宁地区地壳板块运动速度,从而将控制点ITRF坐标进行历元转换与框架转换;同时根据南宁某CORS站观测值所求板块运动速度,对相关结论进行验算。结果表明:基于准确的板块运动速度场,采用历元与框架转换方式求取CGCS2000坐标能够满足小区域GPS控制测量的精度要求。     

基于非线性运动分析的CGCS2000下我国CORS站运动特征

CGCS2000(中国地心坐标系统2000)下CORS(全球导航卫星系统连续运行参考站)站的非线性运动主要受到地壳非构造形变信息、框架点公共误差信息和观测误差信息的组合影响,分析我国CORS站坐标时间序列中包含的非线性运动信息是维护CGCS2000坐标框架精确性、可靠性的基础.本文研究方法首先采用国际卫星对地观测数据及相关地球物理模型,计算了由质量负荷效应造成的地壳非构造形变, 并以此修正了这些非构造形变对国家CORS站坐标时间序列的影响.其次采用主成分空间滤波算法(PCA)提取质量负荷改正后的CGCS2000坐标框架公共误差(Common Mode Errors, CME)的时空特性.最后采用最大似然法定量估计了负荷改正和滤波后的国家CORS网坐标时间序列的噪声特性,采用加权最小二乘法评定了考虑不同噪声影响的CGCS2000框架下的国家CORS网年速度估值和实际精度.     

A HIGH-RESOLUTION, GRIDDED DATASET FOR MONTHLY TEMPERATURE NORMALS (1971-2000) IN SWEDEN

A baseline climatology is required in evaluating climate variability and changes on regional and local scales. Gridded climate normals, i.e. averages over a 30‐year period, are of special interest since they can be readily used for validation of climate models. This study is aimed at creating an updated gridded dataset for Swedish monthly temperature normals over the period 1971–2000, based on standard 2‐m air temperature records at 510 stations in mainland Sweden. Spatial trends of the normal temperatures were modelled as functions of latitude, longitude and elevation by multiple linear regression. The study shows that the temperature normals are strongly correlated with latitude throughout the year and especially in cold months, while elevation was a more important factor in June and July. Longitude played a minor role and was only significant in April and May. Regression equations linking temperature to latitude, longitude and elevation were set up for each month. Monthly temperature normals were detrended by subtracting spatial trends given by the regressions. Ordinary kriging was then applied to both original data (simple method) and de‐trended data (composite method) to model the spatial variability and to perform spatial gridding. The multiple regressions showed that between 82% (summer) and 96% (winter) of the variance in monthly temperature normals could be explained by latitude and elevation. Unexplained variances, i.e. the residuals, were modelled with ordinary kriging with exponential semivariograms. The composite grid estimates were calculated by adding the multiple linear trends back to the interpolated residuals at each grid point. Kriged original temperature normals provided a performance benchmark. The cross–validation shows that the interpolation errors of the normals are significantly reduced if the composite method rather than the simple one was used. A gridded monthly dataset with 30‐arcsecond spacing was created using the established trends, the kriging model and a digital topographic dataset.     

过去2000年亚洲气候变化(PAGES-Asia2k)集成研究进展及展望

介绍了国际过去全球变化研究计划(PAGES)过去2000年气候变化研究网络的设立背景、研究目的及亚洲在其中的独特性;总结了过去2000年亚洲气候变化(PAGES-Asia2k)集成研究的主要进展及中国的贡献,分析了当前在亚洲区域开展该项研究的主要问题及难点,并对未来研究进行了展望。亚洲历史悠久,高分辨率的代用资料丰富,是开展过去2000年气候变化研究的理想区域,但目前尚处于起步阶段。已有进展表明:在过去1200年中,亚洲830-1220年相对温暖,1340-1880年明显寒冷,20世纪则快速增暖;但亚洲气候类型多、变化过程复杂、区域差异大。因此,发展气候序列重建的新技术方法,提高重建序列的时、空分辨率、空间覆盖度和重建结果的精度,建立亚洲过去2000年气候代用资料数据库,集成重建过去2000年区域温度变化序列及干湿变化空间型,进而开展区域气候变化驱动机制与气候变化影响及适应研究,是该计划下一步的研究重点。     

基于模糊综合评判方法的遥感影像压缩主观质量评价

介绍遥感影像压缩的主观评价方法及其分类,并应用模糊综合评判方法对采用JPEG2000标准和SPIHT改进算法压缩后的重建影像进行质量评价。评价结果表明:随着压缩比增加,两种压缩算法压缩后的影像质量均逐渐下降;当压缩比不超过4∶1时,两种压缩算法得到的影像效果均较好,与原始影像差别不大;当压缩比相同时,JPEG2000算法的压缩效果略好于SPIHT算法;在地形较复杂的丘陵和山地,两种压缩算法压缩后的影像质量下降,影像失真较严重。