基于小波特征融合的Hyperion影像降维方法     

孙小芳 《测绘工程》2015,(8):11-15

根据影像中地物光谱曲线的小波特征点确定地物识别的合适光谱分辨率,通过融合原先若干窄波段生成具有适合地物识别光谱分辨率的宽波段数据,达到降维高光谱数据的目的。文中对hyperion影像进行坏线和Smile效应去除,经过FLAASH大气校正,得到155个波段。对提取的八类地物的样本平均光谱进行DB4小波分解,计算小波细节系数方差;以小波细节系数信息熵作为特征点,得出不可渗透表面、居民地、水田、裸土4类地物识别适宜光谱分辨率为80nm,其余地物识别适宜光谱分辨率为160nm。以窄波段间的活跃度为指标进行融合,生成降维后的宽波段分别是21个波段和11个波段。8类地物在3尺度和4尺度下的分类结果说明降维影像能满足应用需求,提出的降维方法可行。  相似文献   

一种面向异常检测的高光谱图像降维算法     

马丽  鞠才  朱菲 《测绘科学》2015,40(7):29-33

针对高光谱数据预处理中传统降维算法的不足,文章提出采用线性局部切空间排列(LLTSA)算法进行降维,并在低维空间中,以数据点到背景流形的最小距离为度量进行异常目标检测。面向异常目标检测问题的降维算法,需要考虑计算量和异常污染两个问题:为减少计算量,选择图像中一部分具有代表性的训练数据进行LLTSA降维并求取用于泛化的投影矩阵;为避免异常信息对背景特性的影响,应该选择不含异常的背景训练数据建立背景流形。背景训练点的选择基于递归多层分割算法,结合分割块的大小和分割块被近邻点重构的误差,去除分割结果中可能包含异常的区域并尽可能多地保留背景信息。实验结果表明LLTSA可以利用少数特征有效区分背景和异常,基于LLTSA的检测算法比经典RX和核RX算法具有更好的异常检测性能。  相似文献   

植被分布对小流域产流影响的数值实验          下载免费PDF全文

李妍敏  安翼  刘青泉 《水科学进展》2015,26(2):187-195

基于二维运动波模型,建立了一个适用于小流域场次降雨产汇流过程的动力学模型。通过对典型小流域内不同区域(坡顶、坡中及坡底区域及距离流域出口的远近)种植植被时产流过程的数值模拟,分析了小流域内植被分布对产流过程的影响。结果表明:植被分布及其特性对小流域场次降雨产流有较明显的影响;下游区域种植植被的减水效果和延滞洪峰作用优于上游区域,陡坡区域减水效果优于缓坡区域,且郁闭度越大,这种差别越明显;在该研究条件下,下游区的减水效果可达到上游区的3倍;30%郁闭度条件下减水效果可达10%和20%郁闭度条件下的3倍和1.4倍。  相似文献   

淮河流域洪涝灾害时间对称性研究     

王云  延军平  马卫 《地球物理学进展》2020,(1):358-366

准确判断重大自然灾害发生趋势对于防灾减灾意义重大.基于时间对称性理论,本文构建“可公度降噪—对称性趋势判断—信息结构系稳定性检验”研究模式,判断了淮河流域(HRB)洪涝灾害发生趋势.结果表明:(1)通过可公度降噪处理去除了噪声元素,提高了预测的精确性;(2)运用三元可公度、蝴蝶结构图、信息结构系等方法判断,2019年HRB发生洪涝灾害的信号较强,该年发生洪涝灾害的随机性概率为66.7%,不漏报置信水平为57.1%;(3)通过洪涝灾害与太阳黑子活动的相关性分析可知,HRB在太阳黑子活动谷年附近易发生洪涝灾害,进一步提高了预测结果的可信度.“可公度降噪—对称性趋势判断—信息结构系稳定性检验”研究模式是对现有时间对称性方法的补充和完善,以期为中国灾害预测起到一定的推动作用.  相似文献   

Direct numerical simulation of flow over a slotted cylinder at low Reynolds number     

《Applied Ocean Research》2019

Direct numerical simulation was conducted to investigate the flow past a slotted cylinder at low Reynolds number (Re) of 100. The slotting of cylinder affects the boundary layer separation, vortex formation position, recirculation region length and wake width, which are determined by the type of slit. The streamwise slit (SS1), T-shaped slit (SS3) and Y-shaped slit (SS4) act as passive jets, while the transverse slit (SS2) achieves an alternate self-organized boundary layer suction and blowing. The flow rate in slits fluctuates over time due to the alternate vortex shedding and fluctuating pressure distribution around the cylinder surface. One fluctuation cycle of flow rate is caused by a pair of vortices shedding for SS2, SS3 and SS4, while it is created by each vortex shedding for SS1. The wall shear stress and flow impact on the slit wall partly contribute to the hydrodynamic forces acting on the slotted cylinder. Taking into account the internal wall of slit, the transverse slit plays the best role in suppressing the fluid forces with drag reduction of 1.7% and lift reduction of 17%.  相似文献   

软土场地基础隔震建筑减震性能研究     

罗翔  戴靠山  吕洋  张世明  周光鑫  魏明宇 《地震工程与工程振动》2020,(1):213-222

本文研究土与结构相互作用(SSI)对多层及中高层基础隔震建筑地震需求及隔震效率的影响规律,隔震层采用LRB铅芯橡胶与LNR普通橡胶隔震支座组合,就我国现行《建筑抗震设计规范》(GB50011-2010)中软土场地设置隔震层问题做探讨。提出土与基础隔震结构相互作用的简化计算模型,对不同场地及隔震设计目标下的多层及中高层基础隔震结构进行时程分析。研究表明:软土场地基础隔震建筑隔震层的有效隔震效率相对于硬土场地有所下降,必须通过设置具有一定规格的LRB支座来满足隔震目标。本文给出了铅芯橡胶支座极限变形需求随建筑层高及隔震目标变化的规律。  相似文献   

超高沥青混凝土心墙高应力水平的降低措施研究     

高俊  党发宁  马宗源 《岩土力学》2020,41(5):1730-1739

随着沥青混凝土心墙堆石坝的快速发展，超高沥青混凝土心墙堆石坝建设迎来了前所未有的机遇，但随着坝高的增加，心墙的安全挑战也变得异常突出。基于应力水平的定义，提出降低超高沥青混凝土心墙高应力水平的措施，依托心墙应力水平的敏感性研究，推算了独立满足和综合满足心墙屈服剪切破坏控制标准的心墙材料强度参数（最敏感材料参数）取值范围。研究表明，心墙应力水平随坝高和河谷岸坡坡比的增加而显著增大；心墙破坏比 、黏聚力 和内摩擦角 属于高敏感性参数；增大心墙破坏比 、黏聚力 和内摩擦角 能够显著地降低心墙应力水平；推荐适宜建设超高沥青混凝土心墙堆石坝的心墙破坏比 、黏聚力 和内摩擦角 取值范围： 0.8、 0.4 MPa和 31.5°（坝高 200 m），且随坝高的增长梯度按5%/25 m、15%/25 m和5%/25 m进行调整。  相似文献   

中国地质灾害防治成效与问题对策     

刘传正  陈春利 《工程地质学报》2020,28(2):375-383

文章回顾了中国地质灾害调查评价、监测预警、综合防治、应急响应、信息化建设、技术装备、技术标准、学术研究、行业进步和法治化建设等工作业绩。中国地质灾害造成的遇难人数1995~2000年年均死亡失踪1205人,2001~2005年均死亡失踪884人,2006~2010年均死亡失踪776人(2010年数据不含甘肃舟曲县城山洪泥石流造成的1765人死亡失踪),2011~2017年均死亡失踪395人,2018年死亡失踪112人。2001~2010年发生地质灾害总数量194702处,平均1.947万处/年;直接经济损失385.3亿元,平均38.5亿元/年,平均19.8万元/处。2011~2018年发生地质灾害总数量为84718处,平均1.06万处/年;直接经济损失355.7亿元,平均44.5亿元/年,平均41.9万元/处。2001年以来城乡社区直接经济损失占国家GDP的比例不断下降,平均年降率为0.016‰。地质灾害成功预报数量占地质灾害总数的比例从2003的5%上升到2018年的20%左右。经过采取各种减灾措施,城乡社区需要应急避险人数逐渐减少。总结了存在的问题和面临的形势,如防灾文化建设薄弱、法制不健全和直接经济损失统计局限于城乡社区而未覆盖工程建设行业的地质灾害等。提出了地质灾害防治要建立政府、企业、个人、社会(包括保险业)和科技界五位一体的防灾减灾“伙伴”关系等对策。  相似文献   

Nitrogen fixation driven by mesoscale eddies and the Kuroshio Current in the northern South China Sea and the East China Sea     

Liuyang Li  Chao Wu  Jun Sun  Shuqun Song  Changling Ding  Danyue Huang  Laxman Pujari 《海洋学报(英文版)》2020,39(12):30-41

N₂ fixation rates (NFR, in terms of N) in the northern South China Sea (nSCS) and the East China Sea (ECS) were measured using the acetylene reduction assay in summer and winter, 2009. NFR of the surface water ranged from 1.14 nmol/(L·d) to 10.40 nmol/(L·d) (average at (4.89±3.46) nmol/(L·d), n=11) in summer and 0.74 nmol/(L·d) to 29.45 nmol/(L·d) (average at (7.81±8.50) nmol/(L·d), n=15) in winter. Significant spatio-temporal heterogeneity emerged in our study: the anticyclonic eddies (AE) (P<0.01) and the Kuroshio Current (KC) (P<0.05) performed significantly higher NFR than that in the cyclonic eddies or no-eddy area (CEONE), indicating NFR was profoundly influenced by the physical process of the Kuroshio and mesoscale eddies. The depth-integrated N₂ fixation rates (INF, in terms of N) ranged from 52.4 μmol/(m2·d) to 905.2 μmol/(m2·d) (average at (428.9±305.5) μmol/(m2·d), n=15) in the winter. The contribution of surface NFR to primary production (PP) ranged from 1.7% to 18.5% in the summer, and the mean contribution of INF to new primary production (NPP) in the nSCS and ECS were estimated to be 11.0% and 36.7% in the winter. The contribution of INF to NPP (3.0%–93.9%) also decreased from oligotrophic sea toward the eutrophic waters affected by runoffs or the CEONE. Furthermore, we observed higher contributions compared to previous studies, revealing the vital roles of nitrogen fixation in sustaining the carbon pump of the nSCS and ECS.  相似文献   

Effect of connecting rain barrels on the storage size reduction     

Yongwon Seo  Nam‐Jeong Choi  Daeryong Park 《水文研究》2012,26(23):3538-3551

In this article, the possibility of sharing rain barrels and the potential benefit of reducing storage size through physical and non‐physical connections of rain barrels in a community are investigated. Using the concepts of homogeneous/heterogeneous users in rainwater harvesting systems (RWHS), two simple cases of a community composed of four prospective users are examined. The first is performed with the users who have the same mean and variance in water demands (homogeneous users), and the second is with the users with different means and variances (heterogeneous users). To take account for the rainfall characteristics in different places, historical records from six cities in the USA are used for storage–reliability–yield analysis. The result indicates that required total storage can be reduced by connecting multiple rain barrels. In addition, a significant difference is found between homogeneous and heterogeneous user groups. Homogeneous users do not achieve a substantial benefit from connecting their rain barrels; these users may even be disadvantaged by sharing. In contrast, heterogeneous users receive benefit by reducing the total required storage. Most benefit is expected between users with maximum difference in mean water demands. The reduction in storage size was as considerable as 37% in this study. The quantity of storage reduction depends on locations and target reliabilities. Knowledge of the benefits and limitations of rain barrel connections can improve RWHS performance through ability to customize a network plan for individual users. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献