Comparison of BDS Station Clock Short-term Prediction Models and their Applications in Precise Orbit Determination

BDS (BeiDou Navigation Satellite System) ground tracking stations are equipped with high accuracy atomic clocks, and they are synchronized with the BDS time scale (BDT) via the Precise Orbit Determination (POD) processing. During the periods of satellite maneuver and post-maneuver, station clocks are kept fixed as known values in the POD processing. To improve the real-time POD capability, station clocks need to be predicted. In this paper, the performance of three clock prediction models is evaluated, including quadratic polynomial model (QP), periodical term model (PM), and grey model (GM). The precision of clock fitting and prediction, as well as the performance of the prediction models in POD are compared. Data of six stations are used for test, and the results show that: the mean fitting accuracy of quadratic polynomial model, periodical term model, and grey model is 0.14 ns, 0.05 ns, 0.27 ns, respectively; the 1 h and 2 h prediction precision of the three models is 1.17 ns, 0.88 ns, 1.28 ns, and 2.72 ns, 2.09 ns, 2.53 ns, respectively. Applying the 1 h and 2 h predicted station clocks in the POD, the 3D orbit accuracy reaches the best using the periodical term model, while the radial accuracy of satellite orbit is rather close for the three models with the difference within 3 cm.     

A nonlinear inversion of InSAR-observed coseismic surface deformation for estimating variable fault dips in the 2008 Wenchuan earthquake

Satellite Interferometric Synthetic Aperture Radar (InSAR) is playing an increasingly important role in the observation of coseismic surface deformation caused by earthquakes, and has been used to invert for subsurface fault structure and reveal earthquake source mechanisms. However, the mapping of complex non-planar or curved (e.g., listric-shaped) faults still remains a challenging task due to variable dips along the underground depth and the impenetrability of the deep crust. Here, we develop a set of new inversion algorithms to determine the listric fault geometry with InSAR- and GPS-observed surface deformation as the significant constraints. The fault surface with variable dip angles is discretized into consecutive sub-fault layers along the down-dip direction. A nonlinear iteration algorithm is used to minimize the objective function to determine the dip angle for each sub-fault layer. The proposed method is first tested using synthetic data to show its effectiveness for retrieval of varying fault geometry dips, and then applied to the 2008 Mw 7.9 Wenchuan earthquake that ruptured the Yingxiu-Beichuan fault for over 320 km along the southwest-northeast strike. The inversion shows that the dip angle of the seismogenic fault is up to 76° near the surface layer, and gradually decreases along the down-dip direction. A significant decrease in dip occurs within the depths of 6–15 km with a dip of 32° at a depth of 15 km. The dip angle decreases to 2° at a depth of 20 km, and finally merges with the subparallel PengGuan fault, which is basically consistent with geological investigations and seismic waveform data inversion. Using the inferred fault geometry, the slip model associated with the event is estimated. Five high-slip concentrations along the strike of the Yingxiu-Beichuan fault are recognized. The inversion misfit of InSAR data is reduced to 7.1 cm with a significant improvement compared to previous studies.     

地表质量负载对格陵兰岛区域GPS站点坐标时序特征的影响

选取ITRF2008框架下格陵兰岛区域12个GPS站2013年1月-2016年12月期间的日解坐标时间序列作为研究对象,并利用极大似然估计分析地表质量负载改正前后各站点的噪声特性、速度场及周期项振幅。结果表明：站点最优噪声模型主要为白噪声+幂律噪声与白噪声+闪烁噪声,地表质量负载形变修正GPS坐标时序后,明显增加U方向闪烁噪声的成分,平均降低其速度约0.36 mm/a,对水平方向影响较小;同时分别降低高程方向44.1%、14.2%的1 a项、0.5 a项振幅,相反,却增加了水平方向的周期项振幅。     

逻辑斯蒂增长模型在集装箱运量长期预测中的应用

多因素动态生成系数法是目前集装箱吞吐量预测方法中最为成熟、应用最为广泛的预测方法。该办法首先确定外贸年增长率预测外贸量,然后通过生成系数得到集装箱吞吐量预测值。然而,在进行中长期集装箱吞吐量预测时,未来外贸年增长率的确定经常缺乏依据,导致长期预测结果精度较差。论文通过利用逻辑斯蒂增长模型进行中长期经济增长预测,再利用经济增长与外贸量的回归分析进行外贸量预测来解决这一问题,最终完成了天津港2005~2020年集装箱吞吐量预测的任务。从原理和结果上看,逻辑斯蒂增长模型是更为适宜和先进的方法,可以用来改进多因素动态生成系数法,提高中长期集装箱预测的精度。     

经验模态分解、数值仿真与形变信号滤波试验

首先介绍了经验模态分解的方法与原理, 给出了由经验模态分解产生的固有模态函数重构特定滤波器的算法, 然后通过对已知数据的仿真检验, 认为该方法在分解与重构滤波器方面具有较高的精度, 最后通过对形变数据中几类典型干扰信号的初步试验与对比分析, 可看出获得了满意的处理效果。 综合分析认为, 经验模态分解及其组合滤波器在干扰消除或某些频率成分滤波与研究中具有重要意义, 可作为形变数据预处理中一种行之有效的数据分解方法。     

2006年9月14日担杆岛海域3.5级地震前兆异常特征研究

通过对珠江三角洲地区前兆监测资料的分析,发现担杆岛海域3.5级地震前部分重力、体应变和水位测项有临震异常显示。研究各测项的异常起止时间、幅度以及异常台项的分布,得到此次地震的临震异常特征。     

西南某电站河床坝基开挖卸荷条件下变形破坏的数值分析

西南某电站河床坝基开挖过程中,在河床底部出现大量表征岩体卸荷的变形破坏现象。开挖卸荷深度与卸荷强度成为大坝建设及其长期稳定性的关键问题。采用三维有限差分程序FLAC3D,分析开挖卸荷条件下坝基岩体变形破坏特征。结合现场卸荷裂隙现象调查资料,综合确定出所研究的河床坝基开挖卸荷影响深度及强度。为坝基综合治理提供必要的参考信息,也为今后此类中等地应力边坡开挖卸荷分析储备可以借鉴的资料。     

公路黄土地基处治前后沉降变形分析

在湿陷性黄土地区,黄土作为高速公路地基的主要原料其强度和变形特性不能满足要求,主要有振动碾压、冲击碾压和强夯3种有效且实用的处治方法。本文根据原位试验和室内试验的数据,进行有限元模拟,在不同高度路堤和不同加载方式情况下,地基沉降变形随着处治能级的增加而减小,路堤本身的沉降保持不变。对于地基处理的深度和沉降变形减小的效果,强夯最好,冲碾次之,振碾最弱。处治前后地表中心沉降变形值与加载路堤高度之间的关系均可用二阶多项式回归拟合。2～4m高的路堤采用振碾的方式处理地基,5～10m高的路堤采用冲碾方法,大于10m的路堤多用强夯或者直接修桥来代替,对于黄土地区高速公路建设与维护具有重要意义。     

褶皱相关断层——以库车坳陷新生界盐上构造层为例

以盐构造解析的方法,综合地震与地质资料,表明库车坳陷新生界中的盐上断层受控于褶皱作用。盐上地层首先发生褶皱变形,随着褶皱作用的加强,然后发生断裂作用,盐上构造层的变形方式为褶皱相关断层,其变形特征不同于断层相关褶皱。从断层成因机制可见:断层相关褶皱理论不适用于库车新生代坳陷盐构造发育区。库车坳陷膏盐层的发育造成盐上构造层与盐下构造层变形有差异,盐上构造层以褶皱作用为主,盐下构造层以冲断作用为主。库车坳陷盐上构造层主要为褶皱相关断层,发育张性断块、后翼突破断层、前翼突破断层及褶皱相关断层组合等构造样式,根据盐上构造层的变形特征总结了褶皱相关断层的演化。     

地震中长期预测研究的进展和方向

综述了地震中长期预测的研究历史和发展现状、存在问题及发展方向。地震中长期预测研究大体可以发为确定性预测研究和概率性预测研究两个主要发展阶段。已有的预测模型和方法在地昨发模式、不确定性分析、断裂之间的相互作用、单一学科面临的资料缺乏等方面存在许多问题。今后一个时期内,地震中长期预测研究的主要发展方向粉：建立地震复发模式、建立大陆板内地震复发间隔的通用概率分布模型、活动断裂定量研究资料的应用,不确定性