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991.
小波域尺度积在裂缝检测中的应用 总被引:4,自引:0,他引:4
常规的裂缝检测方法实际是基于道间奇异性的检测,在检测出裂缝发育带的同时也会检测出噪声.若利用大尺度的裂缝检测方法或将一些噪声压制方法与裂缝检测方法配套使用,虽可提高信噪比,但却对裂缝定位不准确.针对这种矛盾,引入小波域尺度积的裂缝检测方法,该方法将相邻尺度上的小波系数相乘,将裂缝在不同尺度间的因果关系隐含在内,在抑制噪音的同时,可有效地提高裂缝检测的精度.通过理论试算和实例应用,证明了该方法的有效性. 相似文献
992.
Yongli Gao 《Environmental Geology》2008,54(5):1017-1027
This paper presents the spatial implementation of the karst feature database (KFD) of Minnesota in a GIS environment. ESRI’s
ArcInfo and ArcView GIS packages were used to analyze and manipulate the spatial operations of the KFD of Minnesota. Spatial
operations were classified into three data manipulation categories: single layer operation, multiple layer operation, and
other spatial transformation in the KFD. Most of the spatial operations discussed in this paper can be conducted using ArcInfo,
ArcView, and ArcGIS. A set of strategies and rules were proposed and used to build the spatial operational module in the KFD
to make the spatial operations more efficient and topographically correct. 相似文献
993.
A sedimentological study of two dimitic lakes in North-Eastern Germany provided a record of anthropogenic impacts and historical
changes of water quality. The upper 50 cm sediment profiles were compared for major nutrients and selected major trace elements.
The sediments were dated by 210Pb and 137Cs measurement. The upper 50 cm sediment profiles represent approximately the last 100 years of history in both lakes. Element
analyses show different characteristic stratigraphic patterns in both lakes. Based on the nutrient and metal stratification,
three characteristic time periods can be documented for both lakes. In addition to agricultural use of the catchment area,
atmospheric pollution greatly influenced the metal concentration in the sediment layers. Variation in the external loading
and redox conditions in the hypolimnion explain the variation in the composition and accumulation of metals in the sediment
stratigraphy. No increases or changes in the trophic level of either lake could be documented based on the accumulation of
the nutrients C, N and P. The ratio of Fe/Mn and Fe/Ca characterized the changing redox conditions. The stratigraphy of Pb
and Zn agrees with the historical variation in atmospheric pollution and confirms literature values for Central and North
Europe. The drop in Pb and Zn over the last 10–15 years is a regional effect in North-Eastern Germany. 相似文献
994.
Deformation-induced polymorphic transformation: experimental deformation of kyanite, andalusite, and sillimanite 总被引:1,自引:0,他引:1
Eric T. Goergen Donna L. Whitney Mark E. Zimmerman Takehiko Hiraga 《Tectonophysics》2008,454(1-4):23-35
Torsion experiments were performed on the Al2SiO5 polymorphs in the sillimanite stability field to determine basic rheological characteristics and the effect of deformation on polymorphic transformation. The experiments resulted in extensive transformation of andalusite and kyanite to sillimanite. No transformation occurred during the hot-press (no deformation) stage of sample preparation, which was carried out at similar P–T conditions and duration as the torsion experiments. Experiments were conducted on fine-grained (< 15 µm) aggregates of natural andalusite, kyanite and sillimanite at 1250 °C, 300 MPa, and a constant shear strain rate of 2 × 10− 4/s to a maximum shear strain of 400%. Electron back-scattered diffraction (EBSD) analysis of the experiments revealed development of lattice-preferred orientations, with alignment of sillimanite and andalusite [001] slightly oblique to the shear plane. The kyanite experiment could not be analyzed using EBSD because of near complete transformation to sillimanite. Very little strain ( 30%) is required to produce widespread transformation in kyanite and andalusite. Polymorphic transformation in andalusite and kyanite experiments occurred primarily along 500 µm wide shear bands oriented slightly oblique and antithetic to the shear plane and dominated by sub-µm (100–150 nm) fibrolitic sillimanite. Shear bands are observed across the entire strain field preserved in the torsion samples. Scanning transmission electron microscope imaging shows evidence for transformation away from shear bands; e.g. fibrolitic rims on relict andalusite or kyanite. Relict grains typically have an asymmetry that is consistent with shear direction. These experimental results show that sillimanite is by far the weakest of the polymorphs, but no distinction can yet be made on the relative strengths of kyanite and andalusite. These observations also suggest that attaining high bulk strain energy in strong materials such as the Al2SiO5 polymorphs is not necessary for triggering transformation. Strain energy is concentrated along grain boundaries, and transformation occurs by a dynamic recrystallization type process. These experiments also illustrate the importance of grain-size sensitive creep at high strains in a system with simultaneous reaction and deformation. 相似文献
995.
基于小波变换的阈值降噪方法在地震资料处理中的应用 总被引:2,自引:0,他引:2
这里主要讨论了小波变换阈值降噪方法的基本原理,并且将广泛使用的通用阈值方法与Birge-Massart阈值方法进行了比较,展现了Birge-Massart阈值选取方法的优越性。通过对模拟数据和实际地震资料的处理结果表明,基于小波变换的Birge-Massart阈值降噪方法对地震信号降噪具有很好的效果。 相似文献
996.
目前国内外许多学者利用沿海GPS站点的高精度坐标时间序列进行海潮特征信息的提取研究,已取得一定成果,但高精度坐标时间序列中不可避免地存在许多噪声,极大影响海潮特征信息的提取。基于日本GMSD站的67d的高精度PPP坐标时间序列,利用小波分析进行去噪实验,经FFT变换后,将提取的结果与FES2004海潮模型的特征值比较。实验结果表明:经小波分析后,GPS站点的时间序列精度得到提高;经小波去噪后的反演精度均有不同程度的提高,最多达到0.14mm,而海潮特征值的量级为厘米级或者亚厘米级,说明小波分析对海潮特征值的提取精度有明显提高。 相似文献
997.
998.
在平面四参数坐标转换模型中,观测向量和误差方程系数矩阵中部分元素都存在误差。提出一种使用整体最小二乘迭代法求解坐标转换四参数的新方法,只改正系数矩阵中含误差的元素,同时使系数矩阵中不同位置的相同元素具有相同改正数,理论上更严谨。设计了平面四参数模型坐标转换实验数据,通过与经典最小二乘、整体最小二乘、混合整体最小二乘3种方法结果对比,验证了新方法的可行性且解算结果更优。 相似文献
999.
在变形监测中获取的观测数据可以看作是时间与空间上的一组变形信号,一般该信号都会呈现趋势性,隐藏其中的周期性不易被发现;利用FFT对其拟合后的残差和小波分解后的高频信号进行变换与分析,通过时间序列分析对其分析结果建模得到短期的预测、预报,效果比较理想。 相似文献
1000.