基于边缘图与边缘方向的遥感图像检索     

胡冬芽  任保刚 《测绘科学》2012,37(5):187-189

本文在系统介绍遥感图像检索中边缘特征描述方法的基础上,将边缘特征归纳为边缘图和边缘方向两类特征。通过对遥感目标图像库和纹理图像库上所做实验的分析,揭示了不同算法的特性,并指出综合两类特征可进一步提高算法的检索性能。  相似文献   

南印度洋热带气旋生成频数气候变率对海温异常模响应的研究     

胡派  余锦华  王晨稀 《气象科学》2017,37(6):727-734

基于1980—2014年的哈德莱中心海冰及海温的月平均SST资料,美国联合台风警报中心(JTWC)的best-track资料以及NCEP/NCAR再分析月平均资料,利用广义平衡反馈方法(GEFA)研究南印度洋热带气旋(TC)生成频数对海表温度异常的响应特征。研究表明:(1)南印度TC生成频数对北太平洋第一模态(NP1)和热带大西洋第二模态(TA2)有显著响应,分别通过了置信度为99%和96%的Monte-Carlo检验,对应的响应振幅分别为0.67和0.49。(2)局地环境要素对关键SSTA模的GEFA响应结果显示:当NP1出现类似于太平洋年代际振荡(PDO)的正位相时,850 h Pa相对涡度在15°S附近的印度洋海域上都有一个自西向东的显著正响应带,垂直风切变在马达加斯加以东的大部分海域都表现为显著的负响应,600 h Pa相对湿度在马达加斯加以东的部分海域表现为显著的正响应;当TA2对应的时间系数为正异常时,850 h Pa相对涡度和600 h Pa相对湿度在澳大利亚的西北部印度洋海域表现为显著的正响应,垂直风切变在澳大利亚的西北部印度洋海域表现为显著的负响应。  相似文献   

三种温湿参数下昆明准静止锋锋面位置及锋生函数诊断的对比分析   总被引：3，自引：2，他引：1  

段旭  张亚男  梁红丽 《大气科学》2018,42(2):301-310

针对2008年1~2月昆明准静止锋天气过程,讨论了位温、相当位温和广义位温三个温湿参数及其对应的锋生函数,对比分析结果表明:（1）广义位温因其湿度因子权重过大,不适用于分析以温度梯度定义的昆明准静止锋锋面位置和强度;（2）理想状态下的干大气位温和饱和大气相当位温仅与气压和温度有关,均能较好地反映大气温度场特征,适用于昆明准静止锋的分析,比较而言相当位温对温度锋区的描述更为显著;（3）用位温或相当位温计算锋生函数所得结果直接表达了因温度场变化导致的锋面生消状况,而用广义位温计算锋生函数所得结果同时包含温度锋生（消）和湿度锋生（消）两种情况,不能简洁地判断昆明准静止锋锋面生消状况。  相似文献   

线性最小二乘问题的正则化方法     

刘新国 《中国海洋大学学报(自然科学版)》1989,(3)

本文讨论一类求解线性最小二乘问题的正则化方法的可行性。给出两条较为实用的可行性检验准则,推广了经典的Greville定理。  相似文献   

Application of a data‐based mechanistic modelling (DBM) approach for predicting runoff generation in semi‐arid regions     

S. Mwakalila  P. Campling  J. Feyen  G. Wyseure  K. Beven 《水文研究》2001,15(12):2281-2295

This paper addresses the application of a data‐based mechanistic (DBM) modelling approach using transfer function models (TFMs) with non‐linear rainfall filtering to predict runoff generation from a semi‐arid catchment (795 km²) in Tanzania. With DBM modelling, time series of rainfall and streamflow were allowed to suggest an appropriate model structure compatible with the data available. The model structures were evaluated by looking at how well the model fitted the data, and how well the parameters of the model were estimated. The results indicated that a parallel model structure is appropriate with a proportion of the runoff being routed through a fast flow pathway and the remainder through a slow flow pathway. Finally, the study employed a Generalized Likelihood Uncertainty Estimation (GLUE) methodology to evaluate the parameter sensitivity and predictive uncertainty based on the feasible parameter ranges chosen from the initial analysis of recession curves and calibration of the TFM. Results showed that parameters that control the slow flow pathway are relatively more sensitive than those that control the fast flow pathway of the hydrograph. Within the GLUE framework, it was found that multiple acceptable parameter sets give a range of predictions. This was found to be an advantage, since it allows the possibility of assessing the uncertainty in predictions as conditioned on the calibration data and then using that uncertainty as part of the decision‐making process arising from any rainfall‐runoff modelling project. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

非轴对称条件下用三维模式匹配法计算电阻率测井响应   总被引：9，自引：3，他引：9       下载免费PDF全文

谭茂金  张庚骥  运华云  赵文杰 《地球物理学报》2007,50(3):939-945

采用模式匹配法研究了非轴对称条件下普通电阻率测井响应.根据非轴对称的地层模型，建立了新型的坐标系，确定在井轴与地层法线所形成的XOY平面上用数值方法，与此面垂直的方向上用解析方法.在XOY平面上的数值分析中，构建了广义特征值问题；在Z轴方向的解析部分中，人为地划分了一些介质层，并根据电磁场在层界面的连续性条件，推导出了各层之间场量的传递关系，从而摒弃了传统上二维模式匹配法中的复杂的反射阵和透射阵理论，完成了三维模式匹配理论.多种地层模型的数值结果对比表明，该方法在轴对称条件下的计算结果和二维模式匹配法的计算结果具有很好的一致性.此外，应用此算法还研究了倾斜地层等各种非轴对称的地层模型电阻率测井响应，系统地考察了井斜角对普通电阻率测井响应的影响.  相似文献   

基于广义塑性力学的土体次加载面循环塑性模型(Ⅰ): 理论与模型   总被引：4，自引：1，他引：4  

孔亮  郑颖人  姚仰平 《岩土力学》2003,24(2):141-145

简要地介绍了次加载面理论的基本思想、假设及其物理解释。在广义塑性力学的框架内，引入次加载面的思想，把常规的椭圆-抛物线双屈服面模型，扩展为次加载面循环塑性模型，以反映循环荷载作用下土体的曼辛效应与棘轮效应。模型能考虑塑性应变增量对应力增量的相关性，既能反映土体的循环加载特性，又能反映正常固结土和超固结土的单调加载特性。  相似文献   

Spatial-temporal rainfall modelling for flood risk estimation   总被引：4，自引：6，他引：4  

H. S. Wheater  R. E. Chandler  C. J. Onof  V. S. Isham  E. Bellone  C. Yang  D. Lekkas  G. Lourmas  M.-L. Segond 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(6):403-416

Some recent developments in the stochastic modelling of single site and spatial rainfall are summarised. Alternative single site models based on Poisson cluster processes are introduced, fitting methods are discussed, and performance is compared for representative UK hourly data. The representation of sub-hourly rainfall is discussed, and results from a temporal disaggregation scheme are presented. Extension of the Poisson process methods to spatial-temporal rainfall, using radar data, is reported. Current methods assume spatial and temporal stationarity; work in progress seeks to relax these restrictions. Unlike radar data, long sequences of daily raingauge data are commonly available, and the use of generalized linear models (GLMs) (which can represent both temporal and spatial non-stationarity) to represent the spatial structure of daily rainfall based on raingauge data is illustrated for a network in the North of England. For flood simulation, disaggregation of daily rainfall is required. A relatively simple methodology is described, in which a single site Poisson process model provides hourly sequences, conditioned on the observed or GLM-simulated daily data. As a first step, complete spatial dependence is assumed. Results from the River Lee catchment, near London, are promising. A relatively comprehensive set of methodologies is thus provided for hydrological application.  相似文献   

利用广义反射-透射系数方法求解含低速层水平层状介质模型中面波频散曲线问题   总被引：11，自引：6，他引：11       下载免费PDF全文

何耀锋  陈蔚天  陈晓非 《地球物理学报》2006,49(4):1074-1081

在计算面波频散问题的广义反射-透射系数方法基础上研究了含有低速层的均匀平层固体地球模型的面波的频散曲线以及简正振型的计算问题. 当不存在低速层时，仅利用陈晓非1993年提出的单一的久期函数对求解这两个问题已经足够. 但是当模型中存在低速层时，该单一久期函数在数值求解较低阶模式很困难. 本文提出用久期函数族代替该单一久期函数、对不同的简正振型模式采用对应的久期函数来求解的方法，从而更加容易有效地求解较低阶的模式，完善了利用广义反射-透射系数方法求解面波频散问题的理论和算法.  相似文献   

Historical and pooled flood frequency analysis for the River Tay at Perth, Scotland   总被引：1，自引：0，他引：1  

N Macdonald  A Werritty  A R Black  L J McEwen† 《Area》2006,38(1):34-46

Improved estimates of UK flood risk during a period of increased climatic variability place challenges on existing methods that rely on short instrumental records. This paper examines the value of using historical data (both documentary and epigraphic) to augment existing gauged records for the River Tay at Perth as part of a multi-method approach to assessing flood risk. Single station and pooled methods are compared with flood risk estimates based on an augmented historical series (1815–2000) using the Generalized Logistic and Generalized Pareto distributions. The value of using an even longer, but less reliable, extended historical series (1210–2000) is also examined. It is recommended that modelling flood risk for return periods >100 years should incorporate historical data, where available, and that a multi-method approach using a high threshold Generalized Pareto distribution can also add confidence in flood risk estimates for return periods <100 years based on standard methods.  相似文献