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51.
本文应用一种基于模糊划分的聚类方法,即模糊ISODATA方法,进行大气环境质量评价。结果表明该方法简单、快速,尤其在待评价的监测点较多时效果甚佳。 相似文献
52.
目前叠加速度的获取主要是通过人工拾取速度谱,存在着效率低、耗时长且易受人为因素影响的缺点.本文提出了一种基于自适应阈值约束的无监督聚类智能速度拾取方法,实现叠加速度的自动拾取,在保证速度拾取精度的同时提高拾取效率.利用时窗方法在速度谱中计算自适应阈值,从而识别出一次反射波速度能量团作为速度拾取的候选区域.然后,根据K均值方法将不同的速度能量团聚类,并将最终的聚类中心作为拾取的叠加速度.最后,依据人工拾取速度的经验,加入了离群速度点的后处理工作,以获得更光滑的速度场.模型和实际地震数据测试结果表明,本文提出的方法总体上与人工拾取叠加速度的精度相当,但明显提升了速度拾取效率,极大缓解了人工拾取负担. 相似文献
53.
Laser scanning systems have been established as leading tools for the collection of high density three-dimensional data over physical surfaces. The collected point cloud does not provide semantic information about the characteristics of the scanned surfaces. Therefore, different processing techniques have been developed for the extraction of useful information from this data which could be applied for diverse civil, industrial, and military applications. Planar and linear/cylindrical features are among the most important primitive information to be extracted from laser scanning data, especially those collected in urban areas. This paper introduces a new approach for the identification, parameterization, and segmentation of these features from laser scanning data while considering the internal characteristics of the utilized point cloud – i.e., local point density variation and noise level in the dataset. In the first step of this approach, a Principal Component Analysis of the local neighborhood of individual points is implemented to identify the points that belong to planar and linear/cylindrical features and select their appropriate representation model. For the detected planar features, the segmentation attributes are then computed through an adaptive cylinder neighborhood definition. Two clustering approaches are then introduced to segment and extract individual planar features in the reconstructed parameter domain. For the linear/cylindrical features, their directional and positional parameters are utilized as the segmentation attributes. A sequential clustering technique is proposed to isolate the points which belong to individual linear/cylindrical features through directional and positional attribute subspaces. Experimental results from simulated and real datasets demonstrate the feasibility of the proposed approach for the extraction of planar and linear/cylindrical features from laser scanning data. 相似文献
54.
Flume experiments were carried out to study the turbulence and its impact on suspension and segregation of grain-sizes under unidirectional flow conditions over the sand-gravel mixture bed. The components of fluid velocity with fluctuations were measured vertically using 3-D Micro-acoustic Doppler velocimeter (ADV). The theoretical models for velocity and sediment suspension have been developed based on the concept of mixing length that includes the damping effect of turbulence due to sediment suspension in the flow over the sand-gravel mixture bed. Statistical analysis of segregation of grain-sizes along downstream of the bed has been performed using the principle of unsupervised learning or clustering problem. Exploratory data analysis suggests that there is a progressive downstream fining of sediment sizes with selective depositions of gravels, sand-gravels and sand materials along the stream, which may be segmented into three regions such as, the upstream, the transitional and the downstream respectively. This contribution is relevant to understand the direction of ancient rivers, the bed material character in the river form, sorting process and its role in controlling the sediment flux through landscape. 相似文献
55.
Identification of regional collision risk in water area is of significance for the safety of navigation. However, traditional risk identification models are subject to the limitations in accuracy, short-term identification and traffic characteristics. Herein, a framework was put forward to identify regional collision risk instantaneously based on AIS data. The vessels were clustered by using the spatial clustering method. Afterwards, the framework was divided into two steps. Firstly, collision risk of each cluster was obtained by collision risk and contribution of the vessels within the cluster. An analytical method was adopted to identify collision risk of each vessel from the perspective of vessel pairs. Contribution of each vessel was determined by using improved Shapley value method in game theory. Secondly, regional collision risk was obtained by collision risk and contribution of each cluster. Case studies were carried out based on the AIS data of Northern Yellow Sea in China to validate the validity of the proposed framework. The results show that the proposed framework can effectively identify collision risk in water area, presenting the potential for collision risk monitoring and collision risk analysis of water area. 相似文献
56.
Galaxy clustering properties have been studied for decades to constrain cosmological parameters and have today, with large datasets of high-redshift sources piling up, become a powerful tool to discriminate and characterize primeval galaxies. In the last years, several Lyman-Alpha Emitter (LAE) galaxy samples have been gathered, which are big, uniform and compact enough to allow clustering analysis. Here we present a summary of the discussion session on the clustering properties of LAEs at the “Understanding Lyman-Alpha Emitters” conference. 相似文献
57.
The intermittent structure of turbulence within the canopy sublayer (CSL) is sensitive to the presence of foliage and to the
atmospheric stability regime. How much of this intermittency originates from amplitude variability or clustering properties
remains a vexing research problem for CSL flows. Using a five-level set of measurements collected within a dense hardwood
canopy, the clustering properties of CSL turbulence and their dependence on atmospheric stability are explored using the telegraphic
approximation (TA). The binary structure of the TA removes any amplitude variability from turbulent excursions but retains
their zero-crossing behaviour, and thereby isolating the role of clustering in intermittency. A relationship between the spectral
exponents of the actual and the TA series is derived across a wide range of atmospheric stability regimes and for several
flow variables. This relationship is shown to be consistent with a relationship derived for long-memory and monofractal processes
such as fractional Brownian motion (fBm). Moreover, it is demonstrated that for the longitudinal and vertical velocity components,
the vegetation does not appreciably alter fine-scale clustering but atmospheric stability does. Stable atmospheric stability
conditions is characterized by more fine scale clustering when compared to other atmospheric stability regimes. For scalars,
fine-scale clustering above the canopy is similar to its velocity counterpart but is significantly increased inside the canopy,
especially under stable stratification. Using simplified scaling analysis, it is demonstrated that clustering is much more
connected to space than to time within the CSL. When comparing intermittency for flow variables and their TA series, it is
shown that for velocity, amplitude variations modulate intermittency for all stability regimes. However, amplitude variations
play only a minor role in scalar intermittency. Within the crown region of the canopy, a ‘double regime’ emerges in the inter-pulse
duration probability distributions not observed in classical turbulence studies away from boundaries. The double regime is
characterized by a power-law distribution for shorter inter-pulse periods and a log-normal distribution for large inter-pulse
periods. The co-existence of these two regimes is shown to be consistent with near-field/far-field scaling arguments. In the
near-field, short inter-pulse periods are controlled by the source strength, while in the far-field long inter-pulse periods
are less affected by the precise source strength details and more affected by the transport properties of the background turbulence. 相似文献
58.
北京地区热岛效应及日较差特征 总被引：4，自引：3，他引：1
通过对2007～2010年北京地区经质量控制后的123个自动气象站气温数据采用K均值聚类方法分类, 得到城区、郊区、西部和北部山区、西南和东北部山区4个温度分区, 分析了4个分区气温的年变化、日变化和日较差变化特征, 并对北京地区热岛效应的时间变化特征进行了细致分析。结果表明:聚类分析方法可对北京地区温度很好地进行分区, 分区结果与站点的地形和下垫面情况较为吻合;不同分区温度日较差在西部和北部山区最大, 在西南部和东北部山区次之, 郊区再次之, 在城区的日较差最小;在一年中, 各温度分区以2月、5月与10月日较差较大, 其中以5月的日较差为最大;北京地区热岛效应在冬季和夜间较强, 而3～8月热岛较弱, 在夏季的白天比其它季节白天强。 相似文献
59.
图像分割是SAR溢油检测中的关键步骤,但由于SAR影像中存在斑点噪声,使得一般的图像分割算法难以收到理想的效果,严重影响溢油检测的精度.发展一种基于凝聚层次聚类(Hierarchical Agglomerative Clustering,HAC)的溢油SAR图像分割算法.该算法利用多尺度分割的思想,能够有效保持SAR影像中溢油斑块的形状特征,并能减少细碎斑块的产生.利用2010年墨西哥湾的Envisat ASAR影像开展了溢油SAR图像分割实验,并将该算法和Canny边缘检测、OTSU阈值分割、FCM分割、水平集分割等方法进行了对比.结果显示,HAC方法可以有效减少细碎斑块的产生,有助于提高SAR溢油检测的精度. 相似文献
60.