BDS-3多频点伪距单点定位性能研究     

张乾坤  刘小生  何琦敏 《测绘通报》2020,(1):71-75

针对目前有关北斗三号系统伪距单点定位研究较少，未对三号系统多个频点的定位性能进行对比分析的现状，本文利用实测数据对三号系统多个频点的定位性能进行了研究，并联合BDS-2、Galileo进行了同频伪距单点定位试验，统计分析了组合定位多个频点的同频定位结果。试验结果表明：目前三号系统单独定位能力有限，不适合单独定位；BDS-3/Galileo同频组合定位可以弥补BDS-3新频点单频定位时卫星个数不足、数据不完整导致的定位精度过差的情况，同时能够提高Galileo的定位精度；BDS-2/3的B3I频点与BDS/Galileo组合的B2b频点的定位精度均与GPS的L1频点的定位精度相当。  相似文献   

Application of a cascading filter implemented using morphological filtering and time–frequency peak filtering for seismic signal enhancement     

Yanping Liu  Zhengguo Yan 《Geophysical Prospecting》2020,68(6):1727-1741

Inspired by the idea of the iterative time–frequency peak filtering, which applies time–frequency peak filtering several times to improve the ability of random noise reduction, this article proposes a new cascading filter implemented using mathematic morphological filtering and the time–frequency peak filtering, which we call here morphological time–frequency peak filtering for convenience. This new method will be used mainly for seismic signal enhancement and random noise reduction in which the advantages of the morphological algorithm in processing nonlinear signals and the time–frequency peak filtering in processing nonstationary signals are utilized. Structurally, the scheme of the proposed method adopts mathematic morphological operation to first preprocess the signal and then applies the time–frequency peak filtering method to ultimately extract the valid signal. Through experiments on synthetic seismic signals and field seismic data, this paper demonstrates that the morphological time–frequency peak filtering method is superior to the time–frequency peak filtering method and its iterative form in terms of valid signal enhancement and random noise reduction.  相似文献   

杭州湾中部实测波浪特性分析   总被引：1，自引：0，他引：1  

杨斌  杨忠良  叶钦  张俊彪  施伟勇 《海洋工程》2018,36(3):96-103

利用杭州湾中部一年实测波浪资料,分析该地区的波参数统计变化特性,采用最小二乘法拟合得出相关参数之间的关系式,并统计分析了频谱特性。结果表明:杭州湾中部以小浪和轻浪为主,在各月分布较为均匀,年平均周期为2.97 s;最大一次波浪过程为冷空气影响所致,影响强度大于台风莫拉克;常浪向分布在东北至东南向,其中又以小浪出现较多,对应的波周期以2~4 s为主;强浪向主要分布在西北和东北方向,对应的波周期主要分布在3~5 s;多数特征波参数之间相关关系较好;由谱分析得知风浪占多数,且以单峰为主。研究结果可为相关工程和理论研究提供基础资料。  相似文献   

Analysis of nonstationarity in low flow in the Loess Plateau of China          下载免费PDF全文

Kun‐xia Yu  Lars Gottschalk  Xiang Zhang  Peng Li  Zhanbin Li  Lihua Xiong  Qian Sun 《水文研究》2018,32(12):1844-1857

An approach for nonstationary low‐flow frequency analysis is developed and demonstrated on a dataset from the rivers on the Loess Plateau of China. Nonstationary low‐flow frequency analysis has drawn significant attention in recent years by establishing relationships between low‐flow series and explanatory variables series, but few studies have tested whether the time‐varying moments of low flow can be fully described by the time‐varying moments of the explanatory variables. In this research, the low‐flow distributions are analytically derived from the 2 basic explanatory variables—the recession duration and the recession coefficient—with the assumption that the recession duration and recession coefficient variables follow exponential and gamma distributions, respectively; the derived low‐flow distributions are applied to test whether the time‐varying moments of explanatory variables can explain the nonstationarities found in the low‐flow variable. The effects of ecosystem construction measures, that is, check dam, terrace, forest, and grassland, on the recession duration and recession coefficient are further discussed. Daily flow series from 11 hydrological stations from the Loess Plateau are used and processed with a moving average technique. Low‐flow data are extracted following the pit under threshold approach. Six of the 11 low‐flow series show significant nonstationarities at the 5% significance level, and the trend curves of the moments of low flow are in close agreement with the curves estimated from the derived distribution with time‐dependent moments of the recession duration and time‐constant moments of the recession coefficient. It is indicated that the nonstationarity in the low‐flow distribution results from the nonstationarity in the recession duration in all 6 cases, and the increase in the recession duration is resulted from large‐scale ecosystem constructions rather than climate change. The large‐scale ecosystem constructions are found to have more influence on the decrease in streamflow than on the increase in watershed storage, thus resulting in the reduction of low flow. A high return period for the initial fixed design value decreases dramatically with an increasing recession duration.  相似文献   

强震临震微波动现象初步研究(二)   总被引：1，自引：0，他引：1  

杨立明  郝臻  王建军  张淑珍  姚家俊  董蕾 《中国地震》2018,34(2):234-243

为了验证和检验强震临震微波动现象及其主要特征,利用甘、青、川、滇、藏等区域台网200余个宽频带数字地震台站的波形资料,建立了实时监控技术系统。通过对2012~2014年间青藏块体发生的24次5级以上地震及部分无震区域台站观测的全程实时跟踪、动态监控,检验和验证了临震微波动现象的重现性和客观性,验证了临震微波动现象的频谱、时间、空间、方向性等特征,进一步得出了临震微波动现象可能与地震强度有关,且震级越大,震前出现持续临震微波动的可能性越大的结论。  相似文献   

基于全球分布的地震观测数据估计0S0模态的特征频率及品质因子     

周丰森  王迪晋  旦增 《大地测量与地球动力学》2019,39(10):1013-1016

选取2011-03-11日本MW9.3地震后全球地震台站记录的约220 h波形数据，基于一定的判断准则，筛选出质量较高的448个垂向观测数据，采用频域AR方法对0S0模态的特征频率和品质因子进行估值，并以信噪比为权重进行加权平均，得到特征频率f=0.814 658 4±5.3×10-7，品质因子Q=5 586±12。该结果与已有研究成果相比精度更高，有助于约束现有地球介质密度和衰减模型，使其更接近真实地球。  相似文献   

深厚软土场地基岩地震动反演——以天津波为例          下载免费PDF全文

梁建文  张萍  何颖 《世界地震工程》2020,(3):001-11

根据天津波地表加速度记录和相应实测场地钻孔资料，采用等效线性化方法模拟土体非线性，进行了深厚软土场地基岩地震动反演，研究了频率截断对深厚软土场地基岩地震动反演的影响，为天津波地表加速度记录提供了相应的基岩地震动输入。研究表明:不同截断频率情况下，反演得到的基岩地震动峰值和反应谱曲线形状均相差悬殊，但反演后再正演所得到的地面运动与原地表记录相比，加速度时程曲线形状和峰值大小、反应谱曲线形状和峰值大小均非常接近；可根据工程需要对地表加速度记录进行不同频率的截断，反演得到所需强度的基岩地震动。  相似文献   

Forests and floods: Using field evidence to reconcile analysis methods     

James C. Bathurst  Barry Fahey  Andrés Iroumé  Julia Jones 《水文研究》2020,34(15):3295-3310

The extent to which forests, relative to shorter vegetation, mitigate flood peak discharges remains controversial and relatively poorly researched, with only a few significant field studies. Considering the effect purely of change of vegetation cover, peak flow magnitude comparisons for paired catchments have suggested that forests do not mitigate large floods, whereas flood frequency comparisons have shown that forests mitigate frequencies over all magnitudes of flood. This study investigates the apparent inconsistency using field-based evidence from four contrasting field programmes at scales of 0.34–3.1 km². Repeated patterns are identified that provide strong evidence of real effects with physical explanations. Magnitude and frequency comparisons are both relevant to the impact of forests on peak discharges but address different questions. Both can show a convergence of response between forested and grassland/logged states at the highest recorded flows but the associated return periods may be quite variable and are subject to estimation uncertainty. For low to moderate events, the forested catchments have a lower peak magnitude for a given frequency than the grassland/logged catchments. Depending on antecedent soil saturation, a given storm may nevertheless generate peak discharges of the same magnitude for both catchment states but these peaks will have different return periods. The effect purely of change in vegetation cover may be modified by additional forestry interventions, such as road networks and drainage ditches which, by effectively increasing the drainage density, may increase peak flows for all event magnitudes. For all the sites, forest cover substantially reduces annual runoff.  相似文献   

A continuous modelling approach for design flood estimation on sub-daily time scale     

B. Winter  K. Schneeberger  N.V. Dung  M. Huttenlau  S. Achleitner  J. Stötter 《水文科学杂志》2019,64(5):539-554

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Improved fuzzy weighted optimum curve-fitting method for estimating the parameters of a Pearson Type-III distribution     

Guan-Jun Lei  Jun-Xian Yin  Hao Wang  Dong-Mei Xu  Jing Tian 《水文科学杂志》2019,64(16):2115-2128

ABSTRACT

The objective of the curve-fitting method is to determine the optimal distribution by parameter estimation. The selection of the parameter estimation methods and the determination of the parameter estimation results may vary according to the different aims of the curve fitting, as well as the different accuracies and positions of the points. To solve the problem, the fuzzy weighted optimum curve-fitting method (FWOCM) was used to deal with the characters. The deficiencies of the original FWOCM were analysed, and it was found that the membership function and nomograph were unable to effectively deal with the curve fitting. An improved method and its indexes were evaluated, using effectiveness and unbiasedness as the assessment criteria, while scoring and percentage methods were chosen to comprehensively assess the statistical results. Compared with FWOCM, the results showed greater effectiveness and unbiasedness in the improved method.  相似文献