中国西部退耕还林(草)和沙漠化土地绿化的区域性气候效应

中国正在实施的西部大开发必将导致较大规模的土地利用和地表覆盖(LULC)变化,其中最重要的两类LULC变化是退耕还林(草)和沙漠化土地绿化工程。利用最新的全球地表特征资料数据库(GLCCD)识别以上两项生态建设工程的实施规模与范围,并以此更新了目前比较流行的区域气候模式的下边界条件,利用修正了的区域气候模式研究上述大规模LULC变化可能对中国区域性气候造成的影响。使用的卫星资源数据库是由美国地质测绘局(USGS)和Nebraska-Lincoln大学牵头,根据NOAA卫星的AVHRR资料、USGS掌握的高分辨率数字化地图,以及生态区划和植被分布等资料组建的。     

热带森林生态系统气象观测铁塔的设计

讨论了西双版纳地区原始热带雨林和人工林气象观测铁塔的选择与设计，扼要地介绍了气象观测铁塔的塔形，结构及春功能，并提出了在高湿多雷热带雨林地区设计，安装铁塔应注意的事项及解决途径。     

RELATIONSHIP OF ECO-ENVIONMENTAL CHANGE WITH NATURAL EROSION AND ARTIFICIALLY ACCELERATED EROSION

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重庆市云阳县开发荒山资源,发展经济林木

根据县内荒山资源特点,通过因地制宜,树立生态经济学观点,把开发荒山资源与保护生态环境密切结合,加以发展经济林木,促进了当地经济发展。     

Dynamic stochastic estimation of physical variables

A fundamental problem facing the physical sciences today is analysis of natural variations and mapping of spatiotemporal processes. Detailed maps describing the space/time distribution of groundwater contaminants, atmospheric pollutant deposition processes, rainfall intensity variables, external intermittency functions, etc. are tools whose importance in practical applications cannot be overestimated. Such maps are valuable inputs for numerous applications including, for example, solute transport, storm modeling, turbulent-nonturbulent flow characterization, weather prediction, and human exposure to hazardous substances. The approach considered here uses the spatiotemporal random field theory to study natural space/time variations and derive dynamic stochastic estimates of physical variables. The random field model is constructed in a space/time continuum that explicitly involves both spatial and temporal aspects and provides a rigorous representation of spatiotemporal variabilities and uncertainties. This has considerable advantages as regards analytical investigations of natural processes. The model is used to study natural space/time variations of springwater calcium ion data from the Dyle River catchment area, Belgium. This dataset is characterized by a spatially nonhomogeneous and temporally nonstationary variability that is quantified by random field parameters, such as orders of space/time continuity and random field increments. A rich class of covariance models is determined from the properties of the random field increments. The analysis leads to maps of continuity orders and covariances reflecting space/time calcium ion correlations and trends. Calcium ion estimates and the associated statistical errors are calculated at unmeasured locations/instants over the Dyle region using a space/time kriging algorithm. In practice, the interpretation of the results of the dynamic stochastic analysis should take into consideration the scale effects.     

随机地震荷载作用下饱和粉土的液化特性

为了考虑随机地震荷载作用下饱和粉土的液化特性，研究了如何通过合理的地震响应分析确定饱和粉土层受到的随机地震荷载，进一步探讨了随机地震荷载作用下的动三轴试验技术，以及利用此种试验分析饱和粉土液化特性的方法。研究结果为形成判别饱和粉土层地震液化可能性的新方法提供了依据。     

Flexible spectral methods for the generation of random fields with power-law semivariograms

Random field generators serve as a tool to model heterogeneous media for applications in hydrocarbon recovery and groundwater flow. Random fields with a power-law variogram structure, also termed fractional Brownian motion (fBm) fields, are of interest to study scale dependent heterogeneity effects on one-phase and two-phase flow. We show that such fields generated by the spectral method and the Inverse Fast Fourier Transform (IFFT) have an incorrect variogram structure and variance. To illustrate this we derive the prefactor of the fBm spectral density function, which is required to generate the fBm fields. We propose a new method to generate fBm fields that introduces weighting functions into the spectral method. It leads to a flexible and efficient algorithm. The flexibility permits an optimal choice of summation points (that is points in frequency space at which the weighting function is calculated) specific for the autocovariance structure of the field. As an illustration of the method, comparisons between estimated and expected statistics of fields with an exponential variogram and of fBm fields are presented. For power-law semivariograms, the proposed spectral method with a cylindrical distribution of the summation points gives optimal results.     

对近年来地震危险区预测效果的评估

采用R值评分方法，对中国地震局地球物理研究所2001—2004年度划定的全国地震危险区进行了评估，2001—2004年度的R值分别为0．265、0．182、0．293、0．404。近两年的R值相对高些，为了排除随机成分，做了相应的随机预报试验检验，并对地震落入危险区的随机概率作了估计。结果表明，4个年度的R值明显高于随机预报，除2002年度外，地震随机落入危险区的概率很低，不到2％。这说明中国地震局地球物理研究所实际地震危险区划分取得了一定的效果，且逐年提高。     

Determination of S-wave velocity structure using microtremors and spac method applied in Thessaloniki (Greece)

Array measurements of microtremors at 16 sites in the city of Thessaloniki were performed to estimate the V_s velocity of soil formations for site effect analysis. The spatial autocorrelation method was used to determine phase velocity dispersion curves in the frequency range from 0.8–1.5 to 6–7 Hz. A Rayleigh wave inversion technique (stochastic method) was subsequently applied to determine the Vs profiles at all the examined sites. The determination of V_s profiles reached a depth of 320 m. Comparisons with V_s values from cross-hole tests at the same sites proved the reliability of the SPAC method. The accuracy of the V_s profiles, the ability to reach large penetration depths in densely populated urban areas and its low cost compared to conventional geophysical prospecting, make Mictrotremor Exploration Method very attractive and useful for microzonation and site effects studies. An example of its application for the site characterization in Thessaloniki is presented herein.     

具有空间分布裂缝岩石的随机介质模型

利用随机过程的谱展开理论以及Hudson等人的裂纹介质模型构造一种裂纹数密度是空间平稳随机过程的随机介质模型。这个模型可以将裂纹的微观参数(裂纹数密度)与裂纹介质的宏观性质(弹性常数)联系起来,能灵活、有效地描述实际非均匀裂纹介质。模型算例表明,弹性常数的空问分布特征与裂纹数密度的有差别,而且对不同的弹性常数影响不同。通过改编自相关长度的大小,可以模拟裂缝在两个坐标轴方向上具有不同分布尺度的情况。最后,利用高阶的交错网格有限差分方法,我们模拟了地震波在具有随机分布裂缝岩石中的传播特征。