基于DDS技术的Loran—C信号源的杂散信号抑制的分析与实现     

皇甫江  华宇  李实锋 《时间频率学报》2014,(1):41-48

采用直接数字频率合成（DDS）技术设计的Loran—C信号源,具有输出杂散多且难以预测的缺点。基于对DDS基本原理的研究分析,针对DDS输出信号存在的相位舍位杂散问题,对其关键部位的相位累加模块进行优化设计,并基于FPGA技术,在QuartusII环境下完成了对Loran．C信号源的实现与仿真验证。结果表明,通过优化的设计算法能够产生失真小,稳定度好的输出波形,从而验证了该方法抑制杂散的有效性与可行性。  相似文献   

Ground-based electromagnetic studies combined with remote sensing based on Demeter mission: A way to monitor active faults and volcanoes   总被引：2，自引：0，他引：2  

J. Zlotnicki  J.L. Le Mouël  P. Yvetot  P. Menny 《Planetary and Space Science》2006,54(5):541-557

The identification of magnetic, electric and electromagnetic (EM) precursory signals related to volcanic activities and earthquakes is still a matter of debate. Some examples are now well established, but they are often based on a few parameters recorded on sparse equipments and with no multi-disciplinary approach. Demeter program takes into account a more complete approach of EM phenomena related to volcanic eruptions and earthquakes, by combining both ground-based and satellite EM monitoring, from direct current to several kilohertz, i.e. from ULF, ELF to VLF frequency domains.The research program stands in two parts: one is the identification of EM signals at the satellite altitude and the other consists in detailed studies in a few pilot sites on the ground. Two main test sites have been considered: La Fournaise volcano in Réunion Island and the seismogenic Corinth rift in Greece. Both sites allow for performing EM studies in a multi-disciplinary environment.La Fournaise volcano erupts on average two times a year. The self-recording Demeter EM station is composed of three modules measuring the components of the magnetic and electric fields in three different frequency domains: DC to 0.5 Hz, 0.0033-160 Hz and 8-10 kHz. Preliminary observations made during the May 2003 eruption show that electric and magnetic signals appeared before the eruption. Some signals present sharp step-like variations, with amplitudes up to several hundreds mV per km and a few hour duration, followed by periods with a higher spectral frequency content. The frequency of these signals can be of several tens of Hz.The Corinth rift is a highly seismic area, frequently affected by seismic swarms. In 2004 the region has experienced tens of earthquakes of magnitude less than 4.6. A Demeter station has been set up on the Trizonia Island along the northern mainland coast, where a 30 km long seismic gap has been identified. The station is composed of two modules recording the three components of the magnetic field and the two horizontal components of the electric field in the ULF and ELF-VLF frequency bands. The audiomagnetotelluric soundings show that the station is close to a regional conductive fault connected to the sea. The first 4 months of observation clearly show that 29 earthquakes, even of low magnitude (M?2.8), occurring at less than 140 km of distance of the station, have generated electric signals when the seismic waves have passed the EM station. For a given magnitude of the earthquake, the energy of the electric signal is independent of the distance between the focal source and the EM station, which points out local electric source mechanisms. The greater the magnitude of the earthquake, the greater is the energy of the electric signal is. The co-seismic electric signals have the same morphology as that of the passing seismic wave, and there is no noticeable time delay between the electric and the seismic signals. This simultaneity between the seismic and the electric signal is best explained by the generation of an electrokinetic effect due to the passage of the seismic wave through the seawater-saturated ground.  相似文献   

VLBI相位校正信号提取的软件实现方法     

杨艳  郑为民 《中国科学院上海天文台年刊》2006,(1):107-117

从VLBI相关处理结果中提取的延迟值包括了天线、终端等设备的时延,必须对其加以修正,最终结果才能达到精度要求。提取相位校正信号,可以消除这些设备引入的时延,从而校正同一波前信号到达基线两端的几何时延。该文介绍了提取相位校正信号的原理、算法及软件实现方法。软件采用多线程和SSE技术,具备4台站多通道全部相位校正信号提取能力。  相似文献   

被动型氢钟波谱信号观测装置的设计     

邵艳丽  张军海  林传富 《时间频率学报》2005,28(1):1-6

简单介绍了被动型氢钟的量子系统,阐述了波谱信号观测装置的设计。该装置采用标准10MHz晶振产生被动型氢钟的微波激射信号(1.420406GHz),然后将该信号输入氢钟的脉泽振荡器中。脉泽振荡器输出的信号经过低噪声放大、两次混频及滤波后所得的谱线包含了量子系统的信息,通过分析最终的谱线即可得知量子系统的优劣。该装置已用于对两台被动型氢钟的测试,并根据测试结果对量子系统进行了改进。  相似文献   

Generalized Born inversion of seismic reflection data     

Douglas J. Foster  Philip M. Carrion 《Geophysical Journal International》1986,85(2):329-347

Summary . Born inverse methods give accurate and stable results when the source wavelet is impulsive. However, in many practical applications (reflection seismology) an impulsive source cannot be realized and the inversion needs to be generalized to include an arbitrary source function. In this paper, we present a Born solution to the seismic inverse problem which can accommodate an arbitrary source function and give accurate and stable results. It is shown that the form of the generalized inversion algorithm reduces to a Wiener shaping ***filter, which is solved efficiently using a Levinson recursion algorithm. Numerical examples of synthetic and real field data illustrate the validity of our method.  相似文献   

Hydrogeological and Gasgeochemical Earthquake Precursors – A Review for Application     

Jens?HartmannEmail author  Jason?K.?Levy 《Natural Hazards》2005,34(3):279-304

Even if earthquake precursory signals can be identified, how can they be useful? This paper investigates relationships among the attributes of 229 proposed earthquake related gasgeochemical and hydrogeological precursory signals, and applies these results to improve future earthquake prediction strategies. Sub-groups of these reported signals and relationships between sub-groups are established using parameters, including earthquake magnitude, signal duration, precursory time, and epicentral distance to the monitoring site (original studies are used wherever possible to improve data quality). A strong correlation (r=0.86) between signal duration and precursory time was identified. This suggests a relationship between the investigated precursory signals and tectonic processes related to the referenced earthquakes. Moreover, these signals are categorized into four groups, reflecting differences in monitoring station densities, measurement methods and physical processes related to signal occurrence: (a) radon exhalation from the earth’s crust, (b) exhalation of other gases (helium, argon and others), (c) temporal variation in water level or discharge of springs and (d) temporal variation in temperature and dissolved ions in the water of the monitoring sites. In addition, boundary functions are used to separate signal group subsets. Finally, it is shown how these boundary functions can be used in the context of an earthquake prediction strategy by identifying potential minimum magnitudes and maximum epicentral distances from the monitoring site.  相似文献   

数字化地震波形资料的时频分析方法及应用   总被引：1，自引：1，他引：0       下载免费PDF全文

刘希强  沈萍  山长仑  季爱东  李红  蔡明军 《地震工程学报》2004,26(2):118-125

信号的时频分布具有比时间尺度分布更高的描述和刻画非稳态地震波信号的能力,进一步提高信号的时频聚集性和尽可能减小交叉项干扰是时频分析发展的方向。基于高阶矩时频分布理论,本首次提出了将其应用于数字化地震波形资料分析和处理的技术途径和方法。通过对仿真信号的Choi-Willams各阶矩时频分布与Wigner各阶矩时频分布的对比和交叉项干扰的理论分析,认为Choi-willams高阶矩时频分布具有时频聚集性高和交叉干扰项小的特点,在提高处理数字化地震波特性参数精度和地震应急技术系统的智能化程度等方面具有潜在应用前景。  相似文献   

遥感信源色彩信号的提取与复现   总被引：13，自引：13，他引：0  

陈春  王冬  马克玲 《测绘科学》2006,31(1):27-28

提出遥感信源色彩信号的提取及复现理论,给出了可操作的技术路线,设计了提取与复现程序,用MODIS(中等分辨率航天成像光谱仪)数据提取并复现了色彩信号,生成了色彩信号图像。未进行大气校正的色彩信号图像等效于太空对地摄影,从图像可看出,地物被笼罩在瑞利散射形成的蓝色“云雾”下。经瑞利散射纠正后的色彩信号图像接近于地面真彩色摄影,非专业人员能根据地物颜色及阴影判读出常见地物。理论可用于遥感信源地面真彩色图像重建、色彩信号不完整信源彩色仿真、航天对地真彩色摄影、信源质量评价。  相似文献   

基于星座图改进的QAM盲均衡算法     

张艳萍  薛全琪 《南京气象学院学报》2012,4(5):447-451

针对多模辅助算法均方误差高的缺点,提出了两种基于星座图改进的盲均衡算法.首先利用16QAM星座图信息,增加多模辅助算法代价函数中信号点的均衡数目,得到改进的多模辅助算法,与多模辅助算法相比,改进后的算法稳态均方误差更低,而且收敛速度略有提高;其次将改进的多模辅助算法和判决引导算法相结合,根据均方误差调整两种算法的比例,得到的混合算法进一步降低了稳态均方误差.水声信道仿真结果表明:提出的两种算法都可以有效地降低均方误差,适用于对精度要求较高的场合.  相似文献   

基于地闪数据的雷电流幅值累积频率公式探讨   总被引：2，自引：0，他引：2  

冯志伟  肖稳安  马金福  虞进 《气象科技》2012,40(1):137-140

利用2007年和2008年浙江省气象部门闪电定位系统的地闪监测数据,应用Matlab数学软件中的曲线拟合工具箱,以最小二乘法原理对IEEE推荐公式和我国规程推荐公式进行最优化拟合,得出前者拟合效果优于后者的结论。通过分析IEEE推荐公式计算结果与实际值之间的相对误差,发现正闪雷电流幅值累积频率在(1kA,270kA)范围内相对误差绝对值较小,最大不超过10%;而负闪雷电流幅值累积频率在(-1kA,-300kA)范围内相对误差绝对值较大,最大值约为38%。针对上述情况,利用数学软件拟合出负闪(-1kA,-300kA)相对误差曲线的近似函数,修正了原累积频率公式,大幅度减小了其相对误差。其适用范围也从原来的(2kA,200kA)放宽至正闪(1kA,270kA)、负闪(-1kA,-300kA)。  相似文献