虚拟参考站技术（VRS）在城市控制网应用中的精度分析     

黄凯  吕华新 《东北测绘》2007,30(6):144-147

介绍了VRS技术的概念、工作原理、技术方法以及影响VRS测量精度的几大关键因素，通过对试验数据大量的比测与研究，将影响测量精度的因素进行了深入的探讨与分析。  相似文献   

基于纠错编码的小波域自适应盲水印算法     

耿迅  龚志辉  张春美  黄艳 《测绘学院学报》2007,(3)

提出了一种小波域自适应盲水印算法,并采用(7,4)汉明码技术进行纠错编码。以伪随机二值序列作为水印,采用中值系数抖动的方法将水印嵌入到小波变换后的低频分量,并且根据小波域系数间隔的大小自适应地确定水印量化步长,水印检测过程不需要原始图像的参与。实验结果表明,算法的自适应性强,具有较好的不可见性,且可以有效地抵抗JPEG压缩、锐化、加噪、模糊和缩放等攻击。  相似文献   

Long-Term Trend and Abrupt Change for Major Climate Variables in the Upper Yellow River Basin   总被引：7，自引：0，他引：7  

ZHAO Fangfang  XU Zongxue  HUANG Junxiong 《Acta Meteorologica Sinica》2007,21(2):204-214

On the basis of the mean air temperature, precipitation, sunshine duration, and pan evaporation from 23 meteorological stations in the upper Yellow River Basin from 1960 to 2001, the feasibility of using hypothesis test techniques to detect the long-term trend for major climate variables has been investigated. Parametric tests are limited by the assumptions such as the normality and constant variance of the error terms. Nonparametric tests have not these additional assumptions and are better adapted to the trend test for hydro-meteorological time series. The possible trends of annual and monthly climatic time series are detected by using a non-parametric method and the abrupt changes have been examined in terms of 5-yr moving averaged seasonal and annual series by using moving T-test (MTT) method, Yamamoto method, and Mann-Kendall method. The results show that the annual mean temperature has increased by 0.8℃in the upper Yellow River Basin during the past 42 years. The warmest center was located in the northern part of the basin. The nonlinear tendency for annual precipitation was negative during the same period. The declining center for annual precipitation was located in the eastern part and the center of the basin. The variation of annual precipitation in the upper Yellow River Basin during the past 42 years exhibited an increasing tendency from 1972 to 1989 and a decreasing tendency from 1990 to 2001. The nonlinear tendencies for annual sunshine duration and pan evaporation were also negative. They have decreased by 125.6 h and 161.3 mm during the past 42 years, respectively. The test for abrupt changes by using MTT method shows that an abrupt wanning occurred in the late 1980s. An abrupt change of the annual mean precipitation occurred in the middle 1980s and an abrupt change of the mean sunshine duration took place in the early 1980s. For the annual mean pan evaporation, two abrupt changes took place in the 1980s and the early 1990s. The test results of the Yamamoto method show that the abrupt changes mostly occurred in the 1980s, and two acute abrupt changes were tested for the spring pan evaporation in 1981 and for the annual mean temperature in 1985. According to the Mann-Kendall method, the abrupt changes of the temperature mainly occurred in the 1990s, the pan evaporation abrupt changes mostly occurred in the 1960s, and the abrupt changes of the sunshine duration primarily took place in the 1980s. Although the results obtained by using three methods are different, it is undoubted that jumps have indeed occurred in the last four decades.  相似文献   

Effect of Atmospheric Haze on the Deterioration of Visibility over the Pearl River Delta   总被引：14，自引：0，他引：14  

WU Dui  BI Xueyan  DENG Xuejiao  LI Fei  TAN Haobo  LIAO Guolian  HUANG Jian 《Acta Meteorologica Sinica》2007,21(2):215-223

The studies on the effect of atmospheric aerosol on climate and environment are hot issues in the current circle of international science and technology. In recent years the pollution of aerosol is getting worse and worse over the Pearl River Delta. The clouds of aerosol occur all year round, with heavy pollution area located at the western side at the mouth of Pearl River. The haze weather mainly occurs from October to April next year, resulting in visibility deterioration. From the beginning of 1980s, visibility dramatically deteriorated, obviously increasing haze weather, in which there are three big fluctuations, showing the periods of pollutions of dust, sulphate and dust, fine particle from photochemical process and sulphate and dust accompanying with the development of economy respectively. The long-term tendency of visibility caused by fog and light fog does not show a tendency due to human activities or economic development, which mainly shows the interannual and interdecadal variation of climate. The deterioration of visibility has close relation to the fine particles over Pearl River Delta, with half of PM10 overpass the limited value set by national second graded standard (150μg m-3), meanwhile, all values of PM2.5 overpass the day-mean limited value of American national standard (65μg m-3), especially from October to January next year, monthly mean values of PM2.5 almost reach two times of standard value, indicating the fine particle concentration is very high. The ratio of PM2.5 to PM10 is also very high, reaching 58%-77%, higher especially in dry season than in rainy season. Thus it is the fine particle pollution in aerosol pollution over the Pearl River Delta. Compared with the data of 15 years ago, the ratio of fine particle to aerosol has obviously increased.  相似文献   

陕西省2006年气候影响评价     

田武文  雷向杰  黄祖英 《陕西气象》2007,(3):26-29

2006年陕西年平均气温全省大部异常偏高,根据全省29个气象站的资料统计,有20站突破了建站以来的历史最高记录。年降水量全省大部属正常年份,降水时空分布不均,北部和南部偏少,中部接近常年或略偏多;冬季偏多,春季偏少,夏季大部接近常年同期,秋季偏少;暴雨日数及强度接近常年,全省无大面积洪涝事件发生。苹果花期冻害强度大、范围广、危害重,为严重花期冻害级别;盛夏陕南中西部遭遇严重干旱,干旱程度居50 a以来第3位;10—11月气候异常偏暖使部分地区的冬小麦出现冬前旺长现象。2006年属一般年景。  相似文献   

亚澳季风各子系统气候学特征的异同研究 II. 夏季风水汽输送   总被引：5，自引：1，他引：5       下载免费PDF全文

陈际龙  黄荣辉 《大气科学》2007,31(5):766-778

利用1979~2002年的ERA-40和NCEP/NCAR逐日再分析资料以及CMAP降水资料探讨了亚澳季风各夏季风子系统(南亚夏季风、东亚夏季风、北澳夏季风)水汽输送的气候学特征及其与夏季降水的关系。分析表明:各夏季风子系统水汽输送通量主要取决于低层季风气流,南亚夏季风和北澳夏季风以纬向水汽输送为主,而东亚夏季风有很强的经向水汽输送。分析也证实,亚澳季风区的夏季风降水主;要源于水汽输送的辐合,而且ERA-40资料对夏季风水汽输送辐合的描述能力强于NCEP/NCAR资料。此外,受低层季风气流结构的影响,三夏季风子系统水汽输送辐合的动力机理存在明显差异,南亚夏季风和北澳夏季风的水汽输送辐合主要由低层西风气流的风场辐合所造成,而东亚夏季风的水汽输送辐合则由低层南风气流的风场辐合和季风湿平流共同作用造成。因此,东亚夏季风降水有别于南亚夏季风降水和北澳夏季风降水。  相似文献   

基于k阶Voronoi多边形划分的k阶数据场拟合   总被引：2，自引：1，他引：2  

韩元利  胡鹏  黄雪莲  张立华 《武汉大学学报(信息科学版)》2007,32(4):353-357

讨论了k阶Voronoi图的离散点集的生成算法，挖掘了k阶Voronoi图的性质并加以证明；参照k阶Voronoi图的定义提出了k阶空间数据场的定义，并结合参考点利用其影响因子给出了低阶空间数据场的拟合函数通式；利用k阶Voronoi图对平面空间的平面区域最近邻近划分实现了对空间数据场的分割，从而将大量参考点集数据场化解为多个单元数据场的低阶拟舍，有效地降低了数据场拟舍的难度；提出了合并拟合和叠加拟合策略，实现了将单元数据场综合为完整的空间数据场。  相似文献   

一种面向对象的多层次公交数据模型     

黄正东  于卓  汪斌 《武汉大学学报(信息科学版)》2007,32(4):358-361

基于面向对象的建模工具，设计了满足复杂环境需求的多层次公交数据模型。该模型将公共交通实体纳入一个三层的统一体系，能够满足公交系统多尺度的应用需求。  相似文献   

GPS信号载噪比研究   总被引：2，自引：0，他引：2  

黄劲松  刘峻宁  刘成宝  田辉 《武汉大学学报(信息科学版)》2007,32(5):427-431

介绍了GPS接收机所接收信号的栽噪比；提出了载噪比方向图的概念，导出了栽噪比方向图与天线增益方向图的关系；初步评估了大气损耗的时空差异；指出可利用栽噪比异常方向图确定被动式干扰源的方位。  相似文献   

GPS单点测速的误差分析及精度评价   总被引：6，自引：0，他引：6  

王甫红张小红  黄劲松 《武汉大学学报(信息科学版)》2007,32(6):515-519

首先从理论和实测数据模拟两方面分析了SA取消后各类误差源对GPS测速的影响,推导并计算了GPS单点测速可能达到的精度水平。然后用静态数据模拟动态测速试验和实测动态数据测速与同步高精度惯导测速的动态试验进行验证。结果表明,采用载波相位导出的多普勒观测值使用静态数据模拟动态测速,其精度可以达到mm/s级;用接收机输出的多普勒观测值进行测速时,其精度为cm/s级。在动态测速试验中,GPS单点测速方法（即多普勒观测值测速与导出多普勒观测值测速）间的符合精度达到cm/s级,与高精度的惯导测速结果的符合精度为dm/s级,而且和运动载体的动态条件（如加速度和加速度变化率的大小）具有很强的相关性。  相似文献