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结合Landsat TM影像、Envisat ASAR的C波段雷达影像和地形辅助数据,采用决策树方法,包括分类回归树(C1assification and Regression Tree,CART)和随机森林(Random Forest,RF)算法,对扎龙湿地进行遥感分类。用实测GPS样本点对分类结果进行精度验证,并与最大似然监督分类方法(Maximum Likelihood Classification,MLC)对比。结果表明,地形辅助数据和雷达后向散射系数对湿地分类精度的提高起重要作用。基于RF算法分类结果的总精度和Kappa系数分别为92.6%和0.901,沼泽湿地的分类精度达到96.3%,较CART算法和MLC监督分类方法有明显提高。该研究提供了一种快速、高效的内陆淡水沼泽湿地遥感分类技术。 相似文献
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The mollusc Watsonella crosbyi was studied on the basis of material from the lower Cambrian Dahai Member of the Zhujiaqing Formation in eastern Yunnan, China and the Pestrotsvet Formation of the Aldan River region in the Siberian Platform. This fossil had been excessively described under different names in the literature, such as Heraultia varensalensis Cobbold, 1935, H. sibirica Missarzhevsky, 1974, Heraultipegma yunnanensis He and Yang, 1982, H. yannanese He and Yang, 1982, Watsonella yunnanensis, W. crosbyi Grabau, 1900, etc. Taxonomic revision shows that other species are junior synonyms of W. crosbyi. Analysis of functional morphology implies that W. crosbyi may be rather a helcionelloid than a rostroconch since its univalved conch is untorted endogastric and lacks a rostrum and a true internal pegma. Replicas of the original microstructures preserved on the surfaces of phosphatic internal moulds confirm that the shell consists of two layers. The inner layer is lamello-fibrillar, and the outer layer is spherulitic prismatic. The widespread geographical occurrences in both siliciclastic and carbonate rocks of the late Terreneuvian indicate that W. crosbyi is an important index fossil for global correlations and subdivision of the Cambrian Series 1 (Terreneuvian). The first appearance datum (FAD) of W. crosbyi is suggested to be a potential GSSP (Global Boundary Stratotype Section and Point) candidate marker for defining the base of the Cambrian Stage 2. 相似文献
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Quantifying Barrovian metamorphism in the Danba Structural Culmination of eastern Tibet 总被引:3,自引:0,他引:3
O. M. Weller M. R. St‐Onge D. J. Waters N. Rayner M. P. Searle S.‐L. Chung R. M. Palin Y.‐H. Lee X. Xu 《Journal of Metamorphic Geology》2013,31(9):909-935
The Danba Structural Culmination is a tectonic window into the late Triassic to early Jurassic Songpan‐Garzê Fold Belt of eastern Tibet, which exposes an oblique section through a complete Barrovian‐type metamorphic sequence. Systematic analysis of a suite of metapelites from this locality has enabled a general study of Barrovian metamorphism, and provided new insights into the early thermotectonic history of the Tibetan plateau. The suite was used to create a detailed petrographic framework, from which four samples ranging from staurolite to sillimanite grade were selected for thermobarometry and geochronology. Pseudosection analysis was applied to calculate P–T path segments and determine peak conditions between staurolite grade at ~5.2 kbar and 580 °C and sillimanite grade at ~6.0 kbar and 670 °C. In situ U–Pb monazite geochronology reveals that staurolite‐grade conditions were reached at 191.5 ± 2.4 Ma, kyanite‐grade conditions were attained at 184.2 ± 1.5 Ma, and sillimanite‐grade conditions continued until 179.4 ± 1.6 Ma. Integration of the results has provided constraints on the evolution of metamorphism in the region, including a partial reconstruction of the regional metamorphic field gradient. Several key features of Barrovian metamorphism are documented, including nested P–T paths and a polychronic field gradient. In addition, several atypical features are noted, such as P–T path segments having similar slopes to the metamorphic field gradient, and Tmax and Pmax being reached simultaneously in some samples. These features are attributed to the effects of slow tectonic burial, which allows for thermal relaxation during compression. While nested, clockwise P–T–t loops provide a useful framework for Barrovian metamorphism, this study shows that the effects of slow burial can telescope this model in P–T space. Finally, the study demonstrates that eastern Tibet experienced a significant phase of crustal thickening during the Mesozoic, reinforcing the notion that the plateau may have a long history of uplift and growth. 相似文献
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20 世纪科尔沁的人口变化及其特征分析 总被引:3,自引:0,他引:3
利用蒙、汉、日语多种文献资料就科尔沁近百年的人口变化进行了分析,结果发现: 一个世纪以来科尔沁人口增加很快,平均人口密度从民国初期的2.40 人/km2 增加到2000 年 的39.72 人/km2,约为世纪初的17 倍;新增人口主要为1949 年前的关内流民、1949 年中华人民共和国成立后的移民以及移民生育;人口增加最高峰出现在1949 年后的计划移民时期, 伪满时期的流民则构成了研究区近百年另一个显著的移民高潮;移入人口在科尔沁的分布受 距离农区的空间间隔、科尔沁自然环境条件及其变化、城镇化等因素影响,人口密度呈现从 科尔沁外围到腹地、从农耕区到农牧交错区和牧区、从城镇到农村牧区逐渐降低的空间分布特征,移入人口成为20 世纪科尔沁的农耕主力军。 相似文献
38.
宁夏地表湿润状况及极端干湿事件演变规律 总被引:11,自引:5,他引:6
利用宁夏1961—2004年月平均气温、月降水量资料,计算了地表湿润指数,以此为基础对宁夏地表湿润状况及极端干湿事件的分布特征进行了较为深入的研究。结果表明:近40多年来,宁夏大致经历了冷湿期、冷干期、暖干期;自20世纪60年代以来,宁夏年极端干旱频率有增加的趋势,极端湿年高频区逐渐缩小; 80年代以来,宁夏极端干旱年事件高频区明显扩大;不同气候型态下,极端干湿事件频率具有明显差异,冷干期极端干旱事件最多,极端湿润事件最少,冷湿期极端干旱频率最小,极端湿润频率最大。 相似文献
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Evaluating an Analytical Model to Predict Subsurface LNAPL Distributions and Transmissivity from Current and Historic Fluid Levels in Groundwater Wells: Comparing Results to Numerical Simulations 下载免费PDF全文
Robert J. Lenhard Kaveh Sookhak Lari John L. Rayner Greg B. Davis 《Ground Water Monitoring & Remediation》2018,38(1):75-84
A recent analytical model predicts free, entrapped, and residual LNAPL saturations and the LNAPL transmissivity in the subsurface from current and historic fluid levels in groundwater wells. As such, the model accounts for effects of fluid level fluctuations in a well. The model was developed to predict LNAPL specific volumes and transmissivities from current fluid level measurements in wells and either recorded historic fluid level fluctuations in wells or estimates. An assumption is made in the model that the predictions are not dependent on whether the historic highest or lowest fluid level elevations in a well occur first. To test the assumption, we conduct two simulations with a modified multiphase flow numerical code TMVOC that incorporates relative permeability‐saturation‐capillary head relations employed in the model. In one simulation, the initial condition is for fluid levels in a well at the historic highest elevations. In the other simulation, the initial condition is for fluid levels in a well at the historic lowest elevations. We change the boundary conditions so both historical conditions occur followed by generating the current condition. Results from the numerical simulations are compared to model predictions and show the assumption in the analytical model is reasonable. The analytical model can be used to develop/refine conceptual site models and for assessing potential LNAPL recovery endpoints, especially on sites with fluctuating fluid levels in wells. 相似文献