泰国水稻种植面积月变化的遥感监测

介绍了光学和微波遥感影像相结合进行泰国水稻种植面积监测方法。泰国雨季雨量充足 ,气温适合 ,同一时间耕地上水稻的物候多样 ,每月水稻种植面积都发生变化。利用旱季的TM影像 ,获得耕地信息。同时利用TM影像覆盖的雷达区域进行非耕地去除 ,进行非监督分类 ,提取反映水稻种植不同生长期的雷达影像后向反射系数特征 ,建立各种类型的分类模型 ,采用监督分类的方法对全景雷达数据进行水稻种植情况调查 ,并分别予以识别和统计 ,反映研究区水稻月种植情况。分类结果通过类别检验和面积量算检验进行精度评价和分析。     

Discussion on the dynamic mechanism of Great North China area based on the observed stress data

Introduction The Great North China, located at longitude 106E to 124E and latitude 31N to 42N, in-cludes three secondary active tectonic blocks, Ordos, Yanshan and North China plain (Figure 1). The geological tectonics of these three secondary blocks is much different from each other. As a stable block with high rigidity, the Ordos block is mostly surrounded by down-faulted basins with an inactive interior since Cenozoic, although the fault zones along its boundary are strongly active wi…     

Stability and accuracy analysis of the central difference method for real‐time substructure testing

The central difference method (CDM) that is explicit for pseudo‐dynamic testing is also believed to be explicit for real‐time substructure testing (RST). However, to obtain the correct velocity dependent restoring force of the physical substructure being tested, the target velocity is required to be calculated as well as the displacement. The standard CDM provides only explicit target displacement but not explicit target velocity. This paper investigates the required modification of the standard central difference method when applied to RST and analyzes the stability and accuracy of the modified CDM for RST. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrogeochemistry of karst underground waters at shallow depth in Guiyang City, Guizhou Province

The aim of this study is to shed light on the hydrogeochemical characteristics of karst underground waters at shallow depth in Guiyang City, Guizhou Province with an emphasis on the geochemistry of major elements. Guiyang City bears abundant underground waters and it is also an important representative of the karst areas throughout the world. Ca^2 and Mg^2 are the dominant cations, accounting for 81% -99.7% of the total, and HCO3^- and SO4^2- are the dominant anions. Weathering of limestones and dolostones is the most important factor controlling the hydrogeochemistry of underground waters, and weathering of sulfate and evaporite rocks is less important. Moreover, the precipitation and human activities also have a definite influence on the hydrogeoehemistry of underground waters in the region studied.     

云南东北部拱王山末次冰期

1 Introduction The Gongwang mountains constitute one of the few high m ountains of irrefutable late Pleistocene glaciation in eastern China. This area is one of the m ost extensively studied Quaternary geologicallocationsin eastern China and the interpret…     

Land degradation in the source region of the Yellow River, northeast Qinghai-Xizang Plateau: classification and evaluation

Land degradation imposes a great threat to the world. It is not merely an environmental issue, but also a social and economic problem. Land desertification is among the main aspects of environment changes in the source region of the Yellow River. Previous studies focused on water resource utilization and soil erosion, but land degradation in the source region of the Yellow River even the whole Qinghai-Xizang Plateau received little attention. Based on the data obtained by field investigation and TM satellite images of 2000, this study provides the classification and evaluation information of the land degradation in the source region of the Yellow River. There are six types of land degradation in this region: water erosion in the northern mountains around the Gonghe Basin, sandy desertification in the Gonghe Basin and Upland Plain Area, aridization in the lower reaches, salinization in the Gonghe Basin, vegetation degradation in the intramontance basin and freezing and thawing erosion in the high mountains. The total degraded area is 34,429.6 km², making up 37.5% of the land in the study area. Finally, land degradation in the source region of the Yellow River was evaluated according to changes in the physical structure and chemical component of soils, land productivity, secondary soil salt and water conditions.     

Impact of human activity on the estuary of the Qiantang River and the reclamation of tidal flats and river regulation

The swing of the main channel of the Qiantang River is controlled by the high-water and low-water changes in the river, as well as the impact of large-scale reclamation of tidal flats. Its evolution in modern times is the result of the combined functions of natural and man-made factors. This paper analyzes the cause of the formation of the South Channel and Xisan Tidal Furrow and proposes the regulation principle of “To regulate the river and reclaim tidal flats by taking the advantage of local topography”. It is suggested to cut off the South Channel and Xisan Tidal Furrow completely to restrict the swing of the main channel and to increase the reclamation area of the tidal flat at the same time.     

三峡库区巴东县城附近主要滑坡边界轨迹分形分维特征与滑坡稳定性关系

为了探索复杂滑坡轨迹结构演化及其稳定性定量分析计算的新途径，本文利用分形分维理论，分析三峡库区巴东县城附近滑坡边界轨迹的几何分形结构，并采用盒维数法分别求得巴东县城附近11个滑坡边界轨迹的分维值，计算结果表明：每个滑坡的轨迹结构具有其特征性的分维值，轨迹结构越复杂，结构层次越清楚，分维值越高；其中，榨房坪滑坡和黄腊石滑坡的分维值最高，分别为1.50和1.483，西壤口和谭家湾滑坡的分维值最低，分别为0.925和0.732；而黄土坡和赵树岭滑坡的分维值介于二者之间，分别为1.111和1.091。结合典型滑坡边界轨迹结构演化与滑坡稳定性关系的定性分析及前期滑坡稳定性定量计算和模拟分析，初步揭示：滑坡边界轨迹结构与稳定性是密切相关的，滑坡边界轨迹宏观扩展增值越明显，轨迹结构越复杂，分维值越高，其稳定性条件也越差，因此，分数维可作为衡量滑坡轨迹结构复杂性和稳定性的重要标志；滑坡边界轨迹宏观扩展变形存在一个极限，超过这个极限滑坡的局部失稳就转化为整体滑动；而滑坡边界轨迹则记录了滑坡变形扩展现象和信息，因此，相对应地滑坡轨迹分形结构的分维值也应存在一个极值，在极值点滑坡体处于临滑状态；滑坡边界轨迹结构的极限分维值大致为1.4～1.5，此时滑坡接近于整体极限失稳状态，而分维值在1.1～1.3之间则表示滑坡处于整体稳定，局部存在潜在失稳状态，分维值小于1则表示滑坡处于相对稳定状态。     

Fluid generation and evolution during exhumation of deeply subducted UHP continental crust: Petrogenesis of composite granite–quartz veins in the Sulu belt,China

Composite granite–quartz veins occur in retrogressed ultrahigh pressure (UHP) eclogite enclosed in gneiss at General's Hill in the central Sulu belt, eastern China. The granite in the veins has a high‐pressure (HP) mineral assemblage of dominantly quartz+phengite+allanite/epidote+garnet that yields pressures of 2.5–2.1 GPa (Si‐in‐phengite barometry) and temperatures of 850–780°C (Ti‐in‐zircon thermometry) at 2.5 GPa (~20°C lower at 2.1 GPa). Zircon overgrowths on inherited cores and new grains of zircon from both components of the composite veins crystallized at c. 221 Ma. This age overlaps the timing of HP retrograde recrystallization dated at 225–215 Ma from multiple localities in the Sulu belt, consistent with the HP conditions retrieved from the granite. The ε_Hf(t) values of new zircon from both components of the composite veins and the Sr–Nd isotope compositions of the granite consistently lie between values for gneiss and eclogite, whereas δ¹⁸O values of new zircon are similar in the veins and the crustal rocks. These data are consistent with zircon growth from a blended fluid generated internally within the gneiss and the eclogite, without any ingress of fluid from an external source. However, at the peak metamorphic pressure, which could have reached 7 GPa, the rocks were likely fluid absent. During initial exhumation under UHP conditions, exsolution of H₂O from nominally anhydrous minerals generated a grain boundary supercritical fluid in both gneiss and eclogite. As exhumation progressed, the volume of fluid increased allowing it to migrate by diffusing porous flow from grain boundaries into channels and drain from the dominant gneiss through the subordinate eclogite. This produced a blended fluid intermediate in its isotope composition between the two end‐members, as recorded by the composite veins. During exhumation from UHP (coesite) eclogite to HP (quartz) eclogite facies conditions, the supercritical fluid evolved by dissolution of the silicate mineral matrix, becoming increasingly solute‐rich, more ‘granitic’ and more viscous until it became trapped. As crystallization began by diffusive loss of H₂O to the host eclogite concomitant with ongoing exhumation of the crust, the trapped supercritical fluid intersected the solvus for the granite–H₂O system, allowing phase separation and formation of the composite granite–quartz veins. Subsequently, during the transition from HP eclogite to amphibolite facies conditions, minor phengite breakdown melting is recorded in both the granite and the gneiss by K‐feldspar+plagioclase+biotite aggregates located around phengite and by K‐feldspar veinlets along grain boundaries. Phase equilibria modelling of the granite indicates that this late‐stage melting records P–T conditions towards the end of the exhumation, with the subsolidus assemblage yielding 0.7–1.1 GPa at <670°C. Thus, the composite granite–quartz veins represent a rare example of a natural system recording how the fluid phase evolved during exhumation of continental crust. The successive availability of different fluid phases attending retrograde metamorphism from UHP eclogite to amphibolite facies conditions will affect the transport of trace elements through the continental crust and the role of these fluids as metasomatic agents interacting with the mantle wedge in the subduction channel.