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1.
GNSS坐标时间序列中季节性信号的振幅表现出明显的时变特性.本文从全球范围内选取了468个GNSS测站的垂向坐标时间序列数据,对周年项振幅的时变特征和原因进行了深入探究.首先坐标时间序列数据在经过带通滤波后,进行分段最小二乘拟合,得到随时间变化的周年项振幅,并在此基础上,分析了振幅变化的量级大小和特点,发现全球测站周年振幅变化的平均幅度在1 mm左右,并且振幅的波动性具有明显的时空分布特征,忽略这种时变特性最大会造成2～3 mm的周年项残留.然后从环境负载和热膨胀效应入手分析了周年项振幅变化的原因及其对周年项振幅变化的贡献,发现环境负载和热膨胀位移与GNSS垂向坐标之间周年振幅变化的平均一致性在60%左右,而且经过两者改正分别有68%和76%的测站周年项振幅波动幅度出现了下降,由此提出环境负载和热膨胀效应是周年项振幅变化的重要原因.同时经过分析发现GNSS数据处理模型和策略也会引起周年项振幅的变化. 相似文献
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本文利用AIM卫星搭载的CIPS云图反照率和冰晶粒径数据,从中提取了2007/08南半球和2008年北半球共6489个小尺度重力波活动(波长5~150km范围)个例,对重力波区域与背景云层冰晶粒径谱进行对比分析,从而研究重力波对冰晶平均半径和谱宽的影响规律.结果表明,北半球重力波区域冰晶的平均半径和谱宽分别比背景云层小2.5nm和6.1nm,南半球则分别减小1.1nm和7.9nm.在随纬度的分布上,小于80°时,南北半球的平均半径扰动值均为负值,绝对值随纬度增大而减小,而大于80°时,负扰动转变为正扰动,且绝对值增加;谱宽扰动的绝对值也随着纬度增加而减小,但均为负值.在季节内随时间的分布上,南北半球重力波对冰晶平均半径和谱宽的扰动在始末阶段以负值为主,且绝对值较大,而在中期阶段正负值相当,且绝对值较小.这一特征与重力波引起冰晶粒径变化的振幅在纬度和时间上的分布趋势一致.重力波的波长均随纬度升高而减小,在季节的始末阶段较大,中期小,且南半球的平均波长和变化幅度都要明显大于北半球的,粒径扰动振幅随波长的变化率为南半球0.207nm·km-1,北半球的0.163nm·km-1.根据分析推断,重力波自身的扰动振幅应与其影响区域内的谱参数相对于背景云层的变化量有直接关系,且振幅越大,平均半径和谱宽的负扰动就越大. 相似文献
3.
GPS高程导出的全球高程振荡运动及季节变化 总被引：20，自引：0，他引：20
对全球分布的GPS连续观测站高程分量时间序列进行了谱分析和小波多分辨分析, 分离了高程信号的平稳和非平稳信号, 用AR模型建立了平稳高程信号的离散模型. 比较表明, GPS高程时间序列相关长度从2天到31天变化, 纠正了随机漫步过程从零时刻积分的不足. 通过分析, 发现地球存在以半周年和周年为周期的整体性扩张与收缩振荡运动, 半周年项的最大值出现在3~4月份和10~11月份, 周年项的最大值出现在9~11月份. 同时南北半球的变化规律存在差异, 南半球相对于北半球正在扩张. 相似文献
4.
利用TOPEX/Poseidon卫星连续12年（1993年1月～2004年12月）对中国大陆及周边地区观测的GDR-M（Merged Geophysical Data Record）数据集,提取Ku波段和C波段的后向散射系数,经平滑、内插处理之后,得到5′×5′的网格数据及其时间序列.对后向散射系数在中国典型地表类型（如湿地、沙漠、山地和农业基地等）的空间分布特征进行了分析与讨论.利用快速Fourier变换（FFT）探测后向散射系数时间序列的周期变化,发现周期以周年为主,部分地区还有半年周期变化.利用最小二乘方法得到周年周期和半年周期的振幅等周期项信息,结果显示周年振幅明显大于半年振幅.分析了后向散射系数时间序列异常与我国环境和气候变化以及严重灾害（如洪水、干旱）的关系.利用SRTM导出的坡度对我国部分地区的后向散射系数的相关性进行了分析,以确定地势对后向散射系数的影响程度,结果显示Ku波段和C波段后向散射系数皆与坡度呈负相关,辽宁和吉林地区的相关性最强为0.56,塔克拉玛干沙漠地区的相关性最弱为0.11,其他地区多为（0.3～0.5）之间,表明地势起伏而引起的坡度对后向散射系数有显著的负相关性. 相似文献
5.
利用太阳活动高年（2000年）IGS提供的全球TEC数据,采用傅里叶展开的方法,分析了白天电离层TEC周年和半年变化的全球特征.结果显示：电离层TEC周年变化幅度在南北半球中高纬度地区较大、赤道和低纬地区很小.半年变化的幅度在“远极地区”（远离地球南北地磁极点的东北亚和南美地区） 比“近极地区”（靠近地球南北地磁极点的北美和澳大利亚）大得多.进一步的统计显示,全球大部分地区TEC在春秋月份出现最大值,北半球近极地区最大值在冬季出现.南半球的南美和澳大利亚部分地区,最大值出现在夏季.同样,采用傅里叶方法分析了中性大气模式MSIS90计算的全球大气原子分子浓度比值（［O/N2］）的数据,发现在南北半球中高纬度地区,中性成分［O/N2］周年变化幅度较大且有明显的冬季异常现象,依据Rishbeth等提出的理论,我们认为大气成分［O/N2］可能对TEC周年变化的产生有重要作用,并且也是TEC在近极地区出现冬季异常现象的主要原因.TEC半年变化的全球分布特征形成的原因较复杂,我们初步分析可能是由于中性成分［O/N2］、太阳天顶角控制的电离层光化学产生率变化共同作用而产生的. 相似文献
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使用COSMIC掩星提供的NmF2数据,利用傅里叶分析方法,研究全球F2层峰值电子密度的周年和半年分布特征,分析2010年LT12：00 14：00 NmF2周年和半年变化幅度及2008-2011年年平均值变化.结果显示,电离层NmF2周年和半年变化幅度在中高纬地区相对较大;在赤道和低纬地区相对较小,且NmF2以半年变化为主.太阳活动增强期间,NmF2年平均值增大. 相似文献
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本文利用2003年GPS和VLBI组合的站坐标、站速度及它们的误差估计,采用Delaunay算法生成的三角形来逼近地形表面,研究了地球的表面积、体积及它们的变化趋势,并利用板块运动模型插值方法得到的全球分布均匀的台站对检测方法进行了检核.结果表明,实测的和插值后的数据给出的结论是一致的,即若以赤道为界,北半球在压缩,南半球在膨胀;若以0°～180°经线为界,东半球处于挤压变形中,西半球处于扩张变形中;若以90°～270°经线为界,包含太平洋的半球处于压缩状态,而包含大西洋的半球则处于扩张变形中.这种变形证明地球仍处于非对称变形中.根据GPS和VLBI组合的数据解算的体积变化率达到 -15937×1012?m3·a-1,相当于地球半径每年大约缩短3～4 mm,表明地球整体上处于压缩变形中. 相似文献
8.
地球南北半球的非对称性 总被引：12，自引：1，他引：12
依据新的计算分析和空间观测数据,进一步论述了地球南北半球的非对称性. 全球热散失量的计算得出,南半球高出北半球33髎;南半球地幔热散失量是北半球的2倍. 比较南北半球S波速度分布,得出南半球的上地幔为低速、高温,北半球的上地幔为高速、低温. 计算地幔各层的质心位置发现,地球的质心偏于北半球. 计算地球经、纬圈长度的年变化率表明,南半球在扩张,北半球在收缩. 用空间大地测量数据的检测结果证实,南半球处于扩张状态,北半球处于压缩状态. 对地球的非对称性作了初步的动力学解释. 相似文献
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本文利用TIMED卫星搭载的SABER探测仪对全球中间层顶信息进行了研究,包括中间层顶的高度、温度及其季节和纬度变化,并对双中间层顶现象进行了分析.中间层顶的温度约在160～180K之间变化,高度在85～100km内变化,温度和高度都是冬季高夏季低,有着较为一致的变化趋势.中间层顶高纬呈现显著年变化,而低纬和赤道呈现弱的半年变化,南北半球的中间层顶信息有着不对称性.高纬地区的双中间层顶现象十分显著,中间层顶一般会从100km附近迅速降低至85km附近.根据长时间范围内平均的结果显示,北半球的双中间层顶现象在20°N—30°N的中纬范围开始发生,证实了北半球双中间层顶现象不再仅限于极区和中高纬地区.而南半球则仍是在50°S才显著发生双中间层顶现象.我们统计了中高纬地区夏季所有的单个观测剖面并且与当年冬季的平均背景剖面相比较,数据显示,较低的夏季第二中间层顶高度绝大多数比冬季中间层顶低12～16km. 相似文献
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利用GRACE月尺度变化的地球重力场反演了全球水储量变化,并与陆地水文资料、卫星测高资料及海洋模式得到的结果进行了比对.通过对SOURE台站重力变化的陆地水储量变化计算结果和GRACE重力场系数截断为15阶得到的结果比较,发现两者比较接近,且年周期变化特征明显.对于亚马逊流域,当重力场系数截断为15阶且平滑半径使用106 m时,GRACE反演的区域平均水储量厚度的周年变化振幅为15.6×10-2m,小于使用平滑半径为4×105m的23.7×10-2m.在研究长江流域时,本文对水文资料做球谐系数展开,并与GRACE数据做同样的截断和平滑处理,结果发现GRACE反演的水厚度变化与水文资料结果基本上符合.对于纬度±66°之间的海洋区域,GRACE反演的海水质量变化接近于结合卫星测高和海洋模式得到的结果,但对于2°×2°网格,则在一些区域差异明显,最大超过了0.2 m,中误差为3.8×10-2m.可见,当前GRACE卫星时变重力场只能确定出上千公里及以上尺度区域的水储量变化. 相似文献
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Because it can be carried by flowing water, a sand/gravel pit on the river bed could migrate downstream. Consequently, the presence of pits on river beds could pose a safety threat to in-stream hydraulic structures such as bridge piers. A pit migration model can be used to predict progressive changes of pit geometry as it migrates downstream. However, due to the existence of many uncertainties, the maximum pit depth cannot be predicted with certainty. This paper adopted a simple pit migration model and evaluated the uncertainty associated with the calculated maximum pit depth. Such information is essential for evaluating the probability that a migrating pit could pose a safety threat to a downstream hydraulic structure. Three reliability analysis techniques were applied and their performances were compared. 相似文献
13.
Fragility curves constitute the cornerstone in seismic risk evaluations and performance-based earthquake engineering. They describe the probability of a structure to experience a certain damage level for a given earthquake intensity measure, providing a relationship between seismic hazard and vulnerability. In this paper a numerical approach is applied to derive fragility curves for tunnel shafts built in clays, a component that is found in several critical infrastructure such as urban metro networks, airport facilities or water and waste water projects. The seismic response of a representative tunnel shaft is assessed using tridimensional finite difference non-linear analyses carried out with the program FLAC3D, under increasing levels of seismic intensity. A hysteretic model is used to simulate the soil non-linear behavior during the seismic event. The effect of soil conditions and ground motion characteristics on the soil-structure system response is accounted for in the analyses. The damage is defined based on the exceedance of the concrete wall shaft capacity due to the developed seismic forces. The fragility curves are estimated in terms of peak ground acceleration at a rock or stiff soil outcrop, based on the evolution of damage with increasing earthquake intensity. The proposed fragility models allows the characterization of the seismic risk of a representative tunnel shaft typology and soil conditions considering the associated uncertainties, and partially fill the gap of data required in performing a risk analysis assessment of tunnels shafts. 相似文献
14.
Analysis of data characterizing the chemical composition of atmospheric precipitation was presented, with an emphasis on components responsible for neutralization of rain acidity. For this purpose, chemometric methods were applied. Based on a principal component analysis (PCA) a strong correlation between precipitation pH and potassium and ammonium ions in the heating period (October–March) and potassium and sodium ions in the non‐heating period (April–September) was observed. Additionally, a classification of eight variables, i.e., Na+, K+, Mg2+, Ca2+, , , Cl?, and according to their similarities was made using a cluster analysis. Based on this study, two ions, potassium and ammonium, together with the pH value were classified into one group (cluster) in the heating period while in the non‐heating period ions of potassium and sodium were clustered together with the pH. The results of the cluster analysis indicated that the selected ions contributed the most to the neutralization of the atmospheric precipitation acidity. This relationship was confirmed by a discriminant analysis in which potassium and ammonium ions were selected as components of the highest potential for precipitation classification according to its acidity degree. The relationship between the precipitation pH and the number of non‐precipitation days preceding the precipitation was also analyzed. It was found that although the observed an increase of the pH value was not very high, nevertheless, the effect of the duration of the period preceding the precipitation on the pH value recorded on the day of the precipitation occurrence was quite evident. 相似文献
15.
Y-K. Tung K. -C. Yeh 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(2):131-145
Because it can be carried by flowing water, a sand/gravel pit on the river bed could migrate downstream. Consequently, the presence of pits on river beds could pose a safety threat to in-stream hydraulic structures such as bridge piers. A pit migration model can be used to predict progressive changes of pit geometry as it migrates downstream. However, due to the existence of many uncertainties, the maximum pit depth cannot be predicted with certainty. This paper adopted a simple pit migration model and evaluated the uncertainty associated with the calculated maximum pit depth. Such information is essential for evaluating the probability that a migrating pit could pose a safety threat to a downstream hydraulic structure. Three reliability analysis techniques were applied and their performances were compared. 相似文献
16.
Spectral analysis of climate data 总被引：2，自引：0，他引：2
The complexity of climate variability on all time scales requires the use of several refined tools to unravel its primary dynamics from observations. Indeed, ideas from the theory of dynamical systems have provided new ways of interpreting the information contained in climatic time series.We review the properties of several modern time series analysis methods. Those methods belong to four main classes: Fourier techniques (Blackman-Tukey and Multi-Taper), Maximum Entropy technique, Singular-spectrum techniques and wavelet analysis. Their respective advantages and limitations are illustrated by numerical experiments on synthetic time series. As climate data can be irregularly spaced in time, we also compare three interpolating methods on those time series. Those tests are aimed at showing the pitfalls of the blind use of mathematical or statistical techniques on climate data.We apply those methods to real climatic data from temperature variations over the last century, and the Vostok ice core deuterium record over the last glacial cycle. Then we show how interpretations on the dynamics of climate can be derived on those time scales. 相似文献
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An overview of the applicability of a typical single‐mode pushover method (the N2 method) and two typical multi‐mode pushover methods (the modal pushover analysis (MPA) and incremental response spectrum analysis (IRSA) methods) for the analysis of single column bent viaducts in the transverse direction is presented. Previous research, which was limited to relatively short viaducts supported by few columns, has been extended to longer viaducts with more bents. The single‐mode N2 method is accurate enough for bridges where the effective modal mass of the fundamental mode is at least 80% of the total mass. The applicability of this method depends on (a) the ratio of the stiffness of the superstructure to that of the bents and (b) the strength of the bents. In short bridges with few columns, the accuracy of the N2 method increases as the seismic intensity increases, whereas in long viaducts (e.g. viaducts with lengths greater than 500 m) the method is in general less effective. In the case of the analyzed moderately irregular long viaducts, which are common in construction design practice, the MPA method performed well. For the analysis of bridges where the modes change significantly, depending on the seismic intensity, the IRSA method is in principle more appropriate, unless a viaduct is torsionally sensitive. In such cases, all simplified methods should be used with care. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
18.
How to improve the representation of hydrological processes in SWAT for a lowland catchment – temporal analysis of parameter sensitivity and model performance 
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下载免费PDF全文 Model diagnostic analyses help to improve the understanding of hydrological processes and their representation in hydrological models. A detailed temporal analysis detects periods of poor model performance and model components with potential for model improvements, which cannot be found by analysing the whole discharge time series. In this study, we aim to improve the understanding of hydrological processes by investigating the temporal dynamics of parameter sensitivity and of model performance for the Soil and Water Assessment Tool model applied to the Treene lowland catchment in Northern Germany. The temporal analysis shows that the parameter sensitivity varies temporally with high sensitivity for three groundwater parameters (groundwater time delay, baseflow recession constant and aquifer fraction coefficient) and one evaporation parameter (soil evaporation compensation factor). Whereas the soil evaporation compensation factor dominates in baseflow and resaturation periods, groundwater time delay, baseflow recession constant and aquifer fraction coefficient are dominant in the peak and recession phases. The temporal analysis of model performance identifies three clusters with different model performances, which can be related to different phases of the hydrograph. The lowest performance, when comparing six performance measures, is detected for the baseflow cluster. A spatially distributed analysis for six hydrological stations within the Treene catchment shows similar results for all stations. The linkage of periods with poor model performance to the dominant model components in these phases and with the related hydrological processes shows that the groundwater module has the highest potential for improvement. This temporal diagnostic analysis enhances the understanding of the Soil and Water Assessment Tool model and of the dominant hydrological processes in the lowland catchment. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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概述四川7.0级以上大震前观测场地的异常情况。在核实2个大震震前异常的基础上,将传统异常判别方法进行汇总。总结近年来针对跨断层监测数据进行分析进而识别异常的方法:原始数据反映的断层活动速率异常以及转折异常。在此基础上,引入小波分析的方法对大震前的异常进行判别。对小波分解得到的两个趋势项进行分析,发现了大震与小波分解项异常的对应性。最后,基于对原始数据和小波分解项的分析,提出利用跨断层数据分析大震前兆的参考意见,为以后的震前异常研究工作提供了基础。 相似文献
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对白银形变观测站2008年以来观测资料的运行、变化和噪声水平做初步分析,结果表明：DSQ 型水管倾斜仪观测资料连续、稳定、可靠具有明确的正常背景---夏高冬低,为今后地震前兆异常的判断打下基础;水管倾斜仪 EW 分量在2013年7月22日 MS 6．6地震前出现破年变变化,说明白银地震台水管倾斜仪具有一定的地震前兆异常监测能力。 相似文献