基于连续小波变换的大地电磁信号谱估计方法   总被引：16，自引：5，他引：11  

徐义贤  王家映 《地球物理学报》2000,43(5):677-683

在基于连续小波变换的大地电磁信号谱估计方法中 ,通过引入整体平均、小波系数收缩和显著性检验等统计技术 ,以提高谱估计的精度 .文中同时讨论了连续小波变换中各种参数的选取问题 ,给出了Morlet小波函数中尺度与傅里叶频率之间转换的经验公式 ,并给出了谱估计的具体算法 .结果表明 ,本文方法可有效压制较强的白噪声和局部相关噪声 .与FFT谱估计方法相比 ,该方法大大降低了对信号记录长度的要求 ,因而对大地电磁信号的处理有实际意义 .  相似文献   

Continuous chemical monitoring of volcanic gas in Izu-Oshima volcano, Japan     

Y. Shimoike  K. Notsu 《Journal of Volcanology and Geothermal Research》2000,101(3-4)

A new continuous monitoring system has been developed for the measurement of volcanic gas from the steam well located 3 km north from the summit of Izu-Oshima volcano, Japan. After removing the water vapor using three sequential dehydration methods, CO₂ and SO₂ contents are measured using IR sensors, and O₂ and H₂ using a zirconia sensor and a semiconductor sensor, respectively. This system has been in operation without any significant trouble for 3 years.The dehydrated volcanic gas from the well consists of a mixture of CO₂, O₂ and N₂. A decreasing trend of the CO₂ content was observed from 1995 to 1998 together with a decrease of volcanic activity. Seasonal changes have also been observed in CO₂ and O₂ contents, CO₂ being higher and O₂ lower in summer, which suggests larger contribution of magmatic components in summer. While changes in short-term variation in CO₂ and O₂ are influenced by atmospheric pressure changes; the CO₂ content correlates inversely with atmospheric pressure unlike O₂ with some hours delay. In contrast, the H₂ content increased intermittently up to 1200 ppm one to several hours after a sudden drop in the atmospheric pressure and without any apparent correlation with seasonal changes.This system allows us to study temporal variation in chemical composition of volcanic gas during quiescent periods of volcanic activity of Izu-Oshima volcano, and might help us detect anomalous changes before future eruptive events.  相似文献   

Adaptive filtering of continuous GPS results   总被引：2，自引：0，他引：2  

L. Ge  H.-Y. Chen  S. Han  C. Rizos 《Journal of Geodesy》2000,74(7-8):572-580

 An adaptive finite-duration impulse response filter, based on a least-mean-square algorithm, has been used to mitigate multipath effects, and to derive tectonic and fault movement signals from continuous global positioning system (CGPS) data. By applying the filter on both pseudo-range and carrier-phase multipath sequences from CGPS observations on consecutive days, multipath models have been reliably derived. The standard deviations of residual time series are reduced to about one-quarter on pseudo-range and to about one-half on carrier phase. The adaptive filter is then used to process baseline solutions from a five-station array. Tectonic and fault movements have been resolved, which are in good agreement with previous studies involving many more CGPS stations. Received: 11 February 2000 / Accepted: 28 June 2000  相似文献   

CORS主要理论方法的比较分析     

何玉晶 《测绘与空间地理信息》2011,34(2):70-72

主要介绍了CORS的理论基础、基本概念以及国内外发展现状,对其主要理论方法进行了深入的分析比较,为我国各地的CORS建设提供了理论参考和技术借鉴.  相似文献   

2009年冬季至2010年春季黑龙江省气温持续偏低成因     

宋丽华  李永生  张健 《辽宁气象》2011,(2):14-18

利用常规观测温度资料和中国国家气候中心提供的环流特征量、NCEP／NCAR再分析资料及美国气候预测中心（CPC）提供的AO指数等,分析了2009年11月至2010年4月中高纬大气环流异常特征,探讨了AO与同期气温的关系。结果表明：黑龙江省冬春气候异常与500hPa大尺度环流背景有关。冬春持续偏冷,对应北半球欧亚中高纬地区呈“-＋-”的波列分布,90°-180°E呈现出“北正南负”的环流形势;北半球极涡面积偏大,冬季东亚大槽位置偏西,春季东亚大槽强度偏强,冬春AO指数持续异常偏强,显著负位相。  相似文献   

A wavelet based method for estimating the damping ratio in statnamic pile load tests     

Pei-hsun Tsai  Zheng-yi Feng  Shang-yuh Lin 《Computers and Geotechnics》2011

A wavelet based method is proposed to evaluate the time-dependent damping ratio in statnamic load tests by the continuous wavelet transform and half-power bandwidth method. The displacement along the pile during a statnamic test is described by a linear shape function, although the pile is assumed to be a single degree of freedom system (SDOF). The damping ratio is calculated by the half-power bandwidth method from the time–frequency spectra of continuous wavelet transform for the statnamic pile load test. A numerical simulation and two field statnamic tests were analyzed to verify the applicability of the proposed method, and the outcomes were compared with the results obtained using the unloading point method (UPM) and a method in literature. The damping ratio obtained with the proposed method is satisfactory and provides an additional interpretation measure for statnamic load tests.  相似文献   

关于在中国构建全球导航卫星国家级连续运行站系统的思考   总被引：18，自引：0，他引：18  

陈俊勇  张鹏  武军郦  张全德 《测绘学报》2007,36(4):366-369

全球导航卫星连续运行站系统可以维持相应地区的高精度、3维、地心、动态坐标框架,提供集约化的定位和导航服务,成为当前国际和国内发展迅速的一项基础设施建设。该系统可以广泛服务于国家大地基准、气象、地球动力学、地学灾害监测以及位置服务等领域。对在中国构建全球导航卫星国家级连续运行站系统提出了方案,并从建设目的、建设原则以及建设方案等方面进行了讨论。  相似文献   

Marine Plankton Functional Groups Variation and Ecosystem Change     

Sun Song  Sun Xiaoxia 《地球科学进展》2014,29(7):854-858

Marine ecosystem plays a vital role in the economy and society because of its service and production function. Marine ecosystem always changes under the pressure of climate change and human activities. We concern about the status and future of the ecosystem, but it is very difficult to assess and predict the ecosystem health condition. Marine biodiversity is one of the very important indicators of the marine ecosystem change. We focus not only on species composition and quantity change of marine organisms. It is important to determine which are the main contributors to the structure and function of the ecosystem. According to the function of various plankton species in an ecosystem, they can be divided into different functional groups based on the similarity of their ecological roles. By studying the changes of the functional groups, we can enhance our ability to understand the structure and function of ecosystem, and to predict the trend of ecosystem change and the resultant effect on marine biological resource and environment under the multiple pressures of global climate change and human activities. This will help us to establish the marine ecosystem based management.  相似文献   

四川秋季连阴雨的变化特征和时空分布   总被引：2，自引：1，他引：1  

江益  范广洲  周定文  吴泽 《气象科学》2013,33(3):316-324

利用1961-2007年四川省38个站9-11月的日降水资料,从发生次数、降水量和持续天数三方面资料,应用现代气候统计诊断方法,对四川秋季连阴雨的变化特征和时空分布进行了分析.结果表明:四川秋雨量约占四川全年降水量的四分之一,其中秋季连阴雨量约占全年降永的五分之一、约占秋雨量的80％;四川秋季连阴雨的发生次数、降水量和持续天数总体上均呈减少趋势,这种减少是一种突变现象,发生在1980s中后期;从地域上来看,四川秋季连阴雨总体上呈西部增多、东部减少的趋势;EOF分析结果表明四川秋季连阴雨最主要的特征为东西反相型分布.  相似文献   

高速铁路大跨连续梁桥地震反应分析及抗震校核          下载免费PDF全文

张永亮  孙建飞  徐家林 《地震工程学报》2013,35(2):226-231

针对高速铁路大跨连续梁桥的结构特点,结合三水准的抗震设防目标,给出了各水准下桥梁的抗震验算指标.采用反应谱法及弹塑性时程反应分析法对一实桥进行了地震反应分析及抗震性能评价.结果表明固定墩控制该桥的抗震设计.在多遇地震作用下固定墩处于弹性状态;在罕遇地震作用下固定墩纵向进入塑性,但位移延性系数小于规范容许值,结构具有较高的延性储备.该桥的抗震能力满足三水准抗震设防目标.  相似文献