延时参数对地震信号信噪比的改善

当测区噪声很强,采用组合震源工作仍然不能得到高质量地震数据,为进一步提高地震信号的信噪比,引入能形成定向地震波的相控震源.相控震源产生的地震波方向可由延时参数控制,因此延时参数是影响相控地震效果的重要参数.理论分析表明,定向地震波技术可提高反射波信号信噪比,以含3个激震器的相控震源为例,信噪比可提高6.53~9.54 dB.针对延时参数分别为0,0.802,0.384,0.241,0.174,0.123 ms的情况,完成了野外地震实验.根据原始地震记录,得到了反射波信号功率谱,在此基础上定量地计算了不同延时参数下目标层反射信号的信噪比.结果表明,与单震源情况相比,在6种延时参数下,反射波信噪比分别提高了3.3150,8.0150,6.0547,5.0278,4.5383,4.0364 dB;与组合震源情况相比,信噪比分别提高了0,4.7000,2.7397,1.7128,1.2233,0.7214 dB.综合理论分析及野外实验结果,我们可以得到这样的结论：定向地震波技术能够提高反射波信号信噪比,延时参数变化对信噪比有很大影响,采用合理的延时参数能得到更高的信噪比.     

Spatial characterization of catchment dispersion mechanisms in an urban context

Previous studies have examined in-depth the dispersion mechanisms in natural catchments. In contrast, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. This has the ability to modify the variance of the catchment’s travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. The U-McIUH computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment in France as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2–3 km², after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion in the catchment, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further study with other catchments is needed to asses if the latter is a general feature of urban drainage networks.     

基于垂直剖面函数式的全球对流层天顶延迟模型的建立

对流层延迟是无线电导航定位的主要误差源之一,其值对目标高程的变化敏感.在动态导航定位中,由于目标高程变化随机性强,延迟改正实时性需求高,已有的对流层延迟模型难以满足应用需求.本文利用2005到2006年ERA-Interim再分析气象资料积分方法计算的对流层天顶总延迟(ZTD)、天顶静力学延迟(ZHD)以及天顶非静力学延迟(ZWD)的垂直剖面研究了ZTD随高程变化的最佳拟合形式,并以此为基础建立了全球ZTD改正模型SHAO-H.该模型以大气中水汽的垂直分布规律为依据,将ZTD表示为高程的分段函数,进而再模制每段函数中各参数随时间的变化.精度评估显示:与积分ZTD相比,SHAO-H模型计算的ZTD在不同等压层上的平均bias大部分在±1 mm以内,随着高度的上升,平均RMS由39 mm减小至不足1 mm;与IGS (International GNSS Service)实测ZTD相比,SHAO-H模型的精度(bias为7.02 mm,RMS为38.50 mm)优于UNB3m模型(bias为14.67 mm, RMS为51.95 mm).SHAO-H模型具有精度稳定、计算简便等优点,适宜任意高度的用户使用.     

Variations of shear wave splitting in the 2013 Lushan Ms7.0 earthquake region

In this paper, variations of shear wave splitting in the 2013 Lushan Ms7.0 earthquake sequence were studied. By analyzing shear wave particle motion of local events in the shear wave window, the fast polarization directions and the delay time between fast and slow shear waves were derived from seismic recordings at eight stations on the southern segment of the Longmenshan fault zone. In the study region, the fast polarization directions show partition characteristics from south to north. And the systematic changes of the time delays between two split shear waves were also observed. As for spatial distribution, the NE fast polarization directions are consistent with the Longmenshan fault strike in the south of focal region, whereas the NW fast direction is parallel to the direction of regional principal compressive stress in the north of focal region. Stations BAX and TQU are respectively located on the Central and Front-range faults, and because of the direct influence of these faults, the fast directions at both stations show particularity. In time domain, after the main shock, the delay times at stations increased rapidly, and decreased after a period of time. Shear-wave splitting was caused mostly by stress-aligned microcracks in rock below the stations. The results demonstrate changes of local stress field during the main shock and the aftershocks. The stress on the Lushan Ms7.0 earthquake region increased after the main shock, with the stress release caused by the aftershocks and the stress reduced in the late stage.     

GPS网络RTK中对流层延迟分析

分析了网络RTK中基准站和流动站间气象元素、基线长度、高程差异和模型差异等因素对对流层延迟误差的影响,得出气象元素的大小和基线长度等与单差对流层延迟之间存在线性关系,由基准站和流动站的对流层模型差异造成的差值与高差之间也存在线性关系,且利用网络RTK内插法只可消除其中大部分的误差.这对利用网络RTK算法生成流动站的误差改正数具有重要的参考价值.     

利用不同气候类型的GPS可降水量比较研究

利用高精度定位定轨软件GAMIT对2000～2004年的中国地壳运动监测网络数据进行了处理,获得各测站的可降水量时间序列,并以不同气候类型将各测站的可降水量进行了分类比较。在不同气候类型的可降水量的比较中,青藏高原高寒地区的可降水量最低,温带大陆性气候的可降水量次之,温带季风气候的可降水量居中,热带季风气候的可降水量最高,亚热带季风气候的可降水量为次高。在可降水量的图形变化比较中,不同气候类型的可降水量序列的波形变化也不相同,对可降水量峰值时间进行了量化比较。     

地基GPS遥感大气水汽总量中的"静力延迟"和"湿延迟"

介绍了静力延迟和湿延迟概念的由来,推导了由对流层延迟计算水汽总量的一般公式;与李延兴等提出的新模型进行了对比,对其相应的观点提出讨论意见.认为国际上通用的AN模型比较严密地求解了对流层大气水汽总量,不存在与"真值"相比偏小的问题.     

浅海海底表层速度建模技术及其应用研究

浅海海底起伏和速度变化对OBC资料成像质量产生较大影响。建立浅海海底表层速度模型不仅能够解决OBC资料的静校正问题,也可用于海底反射系数计算、双检资料合并、多次波压制等,但是,目前针对浅海海底表层速度建模的研究还不多。文中提出了针对浅海地区OBC资料的海底表层速度建模的三维初至走时反演技术,主要包括:(1)震源位置校正技术。根据地震波在海水中传播特征,把在海水中激发的震源位置校正至海底,使震源和接收点都位于海底,利于初至走时反演计算;(2)快速三维初至走时反演方法。利用回折波走时和射线方程,形成了高效率初至走时反演方法。将该技术应用于胜利油田莱州湾浅海区海底OBC资料的处理中,建立了三维海底表层速度模型,用此速度模型进行静校正,取得了良好的应用效果。     

GNSS对流层延迟推算可降水量的季节转换模型研究

利用台湾桃园（TWTF）站气象数据和对流层延迟数据开展可降水量和对流层延迟序列的相关性分析,显示两者存在显著正相关特性。利用回归分析建立季节和全年转换模型,并利用各季节降水和无降水期间的数据对模型进行检验。结果显示,各季节GNSS可降水量与线性回归可降水量的RMS值小于1.5 mm,最大误差不超过3.3 mm,满足GNSS气象学的基本要求。     

Characteristics of S-wave Envelope Broadening in the Changbaishan Tianchi Volcano

High-frequency S-wave seismogram envelopes of microearthquakes broaden with increasing travel distance,a phenomenon known as S-wave envelope broadening. Multiple forward scattering and diffraction for the random inhomogeneities along the seismic ray path are the main causes of S-wave envelope broadening,so the phenomenon of S-wave envelope broadening is used to study the inhomogeneity of the medium. The peak delay time of an S-wave,which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope,is accepted to quantify S-wave envelope broadening. 204 small earthquake records in Changbaishan Tianchi volcano were analyzed by the S-wave envelope broadening algorithm. The results show that S-wave envelope broadening in the Changbaishan Tianchi volcano is obvious,and that the peak delay time of S-wave has a positive correlation with the hypocenter distance and frequency of the S-wave. The relationships between the S-wave peak delay time and the hypocenter distance for different frequency bands were obtained using the statistics method. The results are beneficial to the understanding of the S-wave envelope broadening phenomena and the quantitative research on the inhomogeneities of the crust medium in the Changbaishan Tianchi volcano region.