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941.
以新疆艾比湖地区为研究区,通过对现有荒漠化监测指标体系的归纳分析,界定了复合荒漠化概念.利用遥感影像数据提取研究区各类荒漠化的现状与动态变化信息.研究结果表明:单一主导因子荒漠化类型面积占荒漠化土地总面积的82.29%,复合荒漠化面积占17.71%.2002~2005年,艾比湖湖面面积缩小了322.5073 km2,相应的总体土地荒漠化面积增加了7.18%,复合荒漠化面积增加了133%.土地荒漠化的过程同时也发生了变化,风蚀、复合荒漠化增加而土地盐渍化减少,荒漠化程度加重,复合荒漠化类型增加并向其他土地类型扩展. 相似文献
942.
943.
太湖富营养化遥感评价研究 总被引:2,自引:0,他引:2
讨论利用Landsat/TM数据进行太湖富营养化评价的可行性,提出一种与常规湖泊富营养化评价方法(综合营养状态指数法)接轨的遥感评价新方法,建立了太湖富营养化遥感评价模型(中国湖泊营养状态指数模型TSIc),利用Landsat/TM数据定量反演出的太湖Chl - a浓度作为TSIc模型的输入变量,计算出太湖营养状态TSIc值,最后按照湖泊富营养化评价分级标准将太湖营养状态分为贫营养(TSIc<30)、中营养(30≤TSIc≤50)、轻度富营养(50<TSIc≤60)、中度富营养(60<TSIc≤70)和重度富营养(>70)5级. 相似文献
944.
Yang Guohua 《中国地震研究》2007,21(3):269-280
In order to track the space-time variation of regional strain field holistically(in a large scale) and to describe the regional movement field more objectively,the paper uses a nonlinear continuous strain model focused on extracting medium-low frequency strain information on the basis of a region with no rotation.According to the repeated measurements(1999~2001~2004) from GPS monitoring stations in the Sichuan and Yunnan area obtained by the Project of "China Crust Movement Measuring Network",and with the movement of 1999~2001(stage deformation background) as the basic reference,we separated the main influencing factors of the Kunlun Mountain M-S8.1 earthquake in 2001 from the data of 2001 and 2004,and the results indicate:(1) the Kunlun Mountain M-S8.1 earthquake has a discriminating effect on the Sichuan and Yunnan area,moreover,the deformation mode and background had not only certain similitude but also some diversity;(2) The movement field before the earthquake was very ordinal,while after the earthquake,order and disorder existed simultaneously in the displacement field;The displacement quantities of GPS monitoring stations were generally several millimeters;(3) The principal strain field before earthquake was basically tensile in an approximate EW direction and compressive in the SN direction,and tension was predominant.After the earthquake,the principal strain field in the Sichuan area was compressive in the EW direction and tensile in the SN direction,and the compression was predominant.In the Yunnan area,it was tensional in the NE direction and compressive in the NW direction,and tension was predominant;(4) The surficial strain before the earthquake was dominated by superficial expansion,the contractive area being located basically in the east boundary of Sichuan and Yunnan block and its neighborhood.After the earthquake,the Sichuan area was surface contractive(the further north,the greater it was),and south of it was an area of superficial expansion.Generally speaking,the Kunlun Mountain M-S8.1 earthquake played an active role in the accumulation of energy in the Sichuan and Yunnan area.Special attention shall be focused on the segment of Xichang-Dongchuan and its neighborhood. 相似文献
945.
946.
Vector-raster conversion is one of the classic research topics in the field of Geographical Information Systems (GIS). The algorithms commonly used in GIS are devoted to maintaining the vector polygons' shape characteristics, but neglect the gain and loss of a polygon's area, which is another important attribute. This paper proposes an equal-area conversion model based on an area compensation optimization principle. According to the topological relationship among polygons and boundary grids, a neighborhood compensation principle was adopted to assign the attributes of boundary grids and a global optimization algorithm was developed to minimize area distortion in the whole data set. Two experiments were designed and the results indicated that this algorithm not only guaranteed the area error is as small as possible, but also has the advantage as being adaptive to polygon shape and spatial structure. 相似文献
947.
A. M. F. Lagmay K. S. Rodolfo F. P. Siringan H. Uy C. Remotigue P. Zamora M. Lapus R. Rodolfo J. Ong 《Bulletin of Volcanology》2007,69(7):797-809
The 1991 Pinatubo eruption left 5–6 km3 of debris on the volcano slopes, much of which has been mobilized into large lahars in the following rainy seasons. Also
during the eruption, collapse, localized in part along preexisting faults, left a caldera 2.5 km in diameter that almost immediately
began to accumulate a 1.6 × 108 m3 lake. By 2001, the water had risen to the fault-controlled Maraunot Notch, the lowest, northwestern portion of the caldera
rim comprising the physiographic sill of the Caldera Lake. That year, a narrow artificial canal dug into an old volcanic breccia
underlying the outlet channel failed to induce a deliberate lake breakout, but discharge from heavy rains in July 2002 rapidly
deepened the notch by 23 m, releasing an estimated 6.5 × 107 m3 of lake water that bulked up into lahars with a volume well in excess of 1.6 × 108 m3. Lakes in other volcanoes have experienced multiple breakouts, providing practical motivation for this study. Fieldwork and
high-resolution digital elevation models reveal andesites and ancient lacustrine deposits, strongly fractured and deformed
along a segment of the Maraunot Fault, a prominent, steeply dipping, left-lateral fault zone that trends N35°–40°W within
and parallel to the notch. Seismicity in 1991 demonstrated that the Maraunot Fault is still active. The fault zone appears
to have previously been the erosional locus for a large channel, filled with avalanche or landslide deposits of an earlier
eruption that were exhumed by the 2002 breakout floods. The deformed lacustrine sediments, with an uncalibrated 14C age of 14,760 ± 40 year BP from a single charcoal sample, attest to the existence of an earlier lake, possibly within the
Tayawan Caldera, rim remnants of which survive as arcuate escarpments. That lake may well have experienced one or more ancient
breakouts as well. The 2002 event greatly reduced the possibility of another such event by scouring away the erodible breccia,
leaving less erodible fractured andesites and lacustrine rocks, and by enlarging the outlet channel and its discharge capacity.
Several lines of evidence indicate, however, that future lahar-generating lake breakouts at the notch may keep populations
of Botolan municipality downstream at risk: (1) a volume of 9.5 × 107 m3 of lake water remains perched 0.8 km above sea level; (2) seismicity in 1991 demonstrated that the Maraunot Fault is still
active and movements of sufficient magnitude could enlarge the outlet and the discharge through it; (3) more likely, however,
with or without earthquake activity, landslides from the steep to overhanging channel walls could block the channel again,
and a major rainstorm could then cause a rise in lake level and sudden breakouts; (4) intrusion of a new dome into the bottom
of the lake, possibly accompanied by phreatic explosions, could expel large volumes of lahar-generating water. 相似文献
948.
CHEN QuanHong LI WenHou GAO YongXiang GUO YanQin FENG JuanPing ZHANG DaoFeng CAO HongXia LIANG JiWei 《中国科学D辑(英文版)》2007,50(Z2):47-58
The deep-lake facies of the Yanchang Formation represents a large outflowing lake basin in the Ordos area. Its deposition can be divided into four stages lake genetic and expanding stage, peak stage, inversion stage and dying stage. All the stages are obviously consistent with the evolution of depositional environment and the paleoclimate in the region. The study indicates that the lake basin has evolution fluctuations from highstand to lowstand for four times in its evolution history, and the deposition center of the lake has not obviously moved, staying along the Huachi-Yijun belt. The deep lake sedimentary system mainly consists of deep water deltas and turbidite fans during the entire evolution course of the lake basin in the Late Triassic. The former mainly developed on the slope of steep shore of the delta in the early period of the deep-water expansion and gradually experienced a big shift from deep-water deltas to shallow-water platform delta. And the latter appeared almost in all the above stages and had two types of turbidite fans, slope-moving turbidite fans and slump turbidite fans. The slope-moving turbidite fans have relatively complete facies belts overlapping one another vertically and consist of the slope channel of inter fans, the turbidite channel, inter turbidite channel and turbidite channel front of middle fans and outer fans (or lakebottom plain). However, the slide-moving turbidity fans are formed in the deep lake with their microfacies difficult to be distinguished, and only the center microfacies and edge microfacies can be determined. The two types of the turbidity fans are similarly distributing in the near-root-slope and far-root-slope regions. The deep-lake deposition governs the distribution of the hydrocarbon and reservoir, while the slope-moving turbidite fans are excellent reservoirs for oil-gas exploration due to their great thickness, widespread distribution and accumulation properties. 相似文献
949.
950.
GIS中地籍宗地面积的方差分量估计 总被引:2,自引:0,他引:2
探讨在地籍宗地数字化的面积处理问题中,把已知面积数据和数字化坐标同时作为观测值的面积处理方法.采用方差分量估计,解决已知面积数据参与平差时的权的确定.通过实例分析,认为采用条件平差方差分量估计方法来对宗地面积处理,能够更加合理地调整已有面积与由数字化坐标得到的面积值之间的差异. 相似文献