Relics of the Mozambique Ocean in the central East African Orogen: evidence from the Vohibory Block of southern Madagascar

The Vohibory Block of south‐western Madagascar is part of the East African Orogen, the formation of which is related to the assembly of the Gondwana supercontinent. It is dominated by metabasic rocks, which have chemical compositions similar to those of recent basalts from a mid‐ocean ridge, back‐arc setting and island‐arc setting. The age of formation of protolith basalts has been dated at 850–700 Ma by U–Pb SHRIMP analysis of magmatic cores in zircon, pointing to an origin related to the Neoproterozoic Mozambique Ocean. The metabasic rocks are interpreted as representing components of an island arc with an associated back‐arc basin. In the early stage of the Pan‐African orogeny, these rocks experienced high‐pressure amphibolite to granulite facies metamorphism (9–12 kbar, 750–880 °C), dated at 612 ± 5 Ma from metamorphic rims in zircon. The metamorphism was most likely related to accretion of the arc terrane to the margin of the Azania microcontinent (Proto‐Madagascar) and closure of the back‐arc basin. The main metamorphism is significantly older than high‐temperature metamorphism in other tectonic units of southern Madagascar, indicating a distinct tectono‐metamorphic history.     

Fast error analysis of continuous GPS observations

It has been generally accepted that the noise in continuous GPS observations can be well described by a power-law plus white noise model. Using maximum likelihood estimation (MLE) the numerical values of the noise model can be estimated. Current methods require calculating the data covariance matrix and inverting it, which is a significant computational burden. Analysing 10 years of daily GPS solutions of a single station can take around 2 h on a regular computer such as a PC with an AMD Athlon^TM 64 X2 dual core processor. When one analyses large networks with hundreds of stations or when one analyses hourly instead of daily solutions, the long computation times becomes a problem. In case the signal only contains power-law noise, the MLE computations can be simplified to a process where N is the number of observations. For the general case of power-law plus white noise, we present a modification of the MLE equations that allows us to reduce the number of computations within the algorithm from a cubic to a quadratic function of the number of observations when there are no data gaps. For time-series of three and eight years, this means in practise a reduction factor of around 35 and 84 in computation time without loss of accuracy. In addition, this modification removes the implicit assumption that there is no environment noise before the first observation. Finally, we present an analytical expression for the uncertainty of the estimated trend if the data only contains power-law noise. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

一种GPS多路径反射信号的雪深反演

针对传统雪深测量缺乏必要时空敏感性的不足,该文在分析GPS信号多路径反射模型的基础上,利用GPS信噪比观测数据,通过分离提取多路径反射分量研究其时频特性,探讨GPS多路径信号与雪深及其变化关系并进行反演建模。依据菲涅尔反射区理论,确定了反射区域范围,进一步探讨卫星、波段选择及初始反射高度确定等。对比实验研究表明,反演结果与实测值吻合较好,相关系数为0.93,均方根误差为8.6cm;信噪比多路径反射分量的频率能有效跟踪积雪深度的变化。     

InSAR干涉图滤波方法对比

针对不同滤波算法在InSAR数据处理中去噪效果的差异,该文从滤波理论出发,采用模拟和真实干涉数据进行实验。在各种滤波算法中,均值滤波(多视处理)、Goldstein滤波及其变种滤波应用广泛,本文对4种滤波方法进行了系统分析,深入探讨了经典InSAR滤波和国内外学者算法的优缺点。实验表明:4种滤波均能有效抑制噪声,提升干涉图质量。其中,Goldstein滤波以及两种改进的滤波效果要明显优于均值滤波,且具有更好的自适应性或条纹保持能力,较经典Goldstein滤波而言,变种滤波方法不仅保持了Goldstein滤波的优点,在边缘信息和细节保持能力方面优势更加显著。     

基于国家基准站的北斗数据质量分析

GNSS数据质量可为高精度数据处理提供基础性的参考信息,目前GPS数据质量检查方法成熟且数据资源丰富,而北斗数据质量缺少系统全面的分析。该文介绍北斗观测数据质量检查内容和方法,并基于国家基准站计算了北斗数据多路径效应、周跳、信噪比等质量结果,分析了北斗质量特性和影响因素,并将北斗与GPS进行了对比。结果表明,北斗数据多路径误差、信噪比等质量指标与高度角和信号频率有关,在相同环境下北斗数据质量在多路径误差方面优于GPS数据质量,信噪比方面北斗SN2优于GPS,SN1和SN3较GPS稍差。     

随机镇定与反镇定概述

本文概述了随机镇定与反镇定理论的研究现状.主要回顾了一个微分方程的随机镇定与反镇定普遍理论及其发展,并围绕该理论的应用和扩展从四个方面阐述连续时间系统噪声镇定理论的当前发展概况.此外,本文还概述了离散时间系统随机镇定方面的最新进展.     

夏半年热带太平洋中部型海温异常与热带印度洋海盆模对同期中国东部降水的共同影响

利用1961—2013年NCEP/NCAR再分析资料和Had ISST月平均海表面温度资料,分析了夏半年热带太平洋中部型海温异常与热带印度洋海盆模(Indian Ocean Basin M ode,IOBM)的特征,并研究了不同位相配置时二者对同期中国东部气候的共同影响。结果表明:1)太平洋中部型海温异常指数与印度洋海盆模指数几乎相互独立。太平洋中部型海温异常与IOBM同位相变化(记为PPNN事件)和反位相变化(记为PNNP事件)时,热带印太地区海温异常分别呈三级型和偶极型分布。2)不同位相配置对中国东部地区降水异常的影响及其影响机制存在显著差异:当发生PPNN事件时,水汽从海洋性大陆(Maritime Continent,MC)地区向江淮流域输送;热带海温异常引起大气产生Gill型响应,维持了中国东部的环流异常;M C地区通过经向三圈异常垂直环流引起江淮流域降水异常增多。发生PNNP事件时,Gill型环流响应中心西移,长江流域降水偏少,水汽辐散;同时MC地区对流层低层准定常Rossby波能传播也有利于长江流域扰动的维持。这些结果对深刻认识中国东部地区夏半年降水异常成因和印度洋/太平洋海温异常不同分布的作用具有重要意义。     

黄河GPS站噪声模型初探及稳定性分析

北极黄河科学考察站的GPS站位于挪威斯瓦尔巴群岛,该站对于我国在北极测绘领域的研究具有重要作用。由于极区条件的限制,该站建立在冻土之上,因此需要对其稳定性进行深入研究。本文在利用GAMIT/GLOBK软件处理黄河站及周边IGS站观测数据的基础上,估计了不同噪声模型下的噪声量级、站坐标序列参数和不确定度,分析了黄河GPS观测站与IGS站运动趋势之间的关联性。结果表明,黄河站及周边GPS时间序列不仅存在白噪声,还存在较大量级的闪烁噪声,个别站的一些分量还存在随机游走噪声,仅考虑白噪声会低估总噪声和参数不确定度;黄河GPS站与邻近的NYAL站相比,两者的水平和垂直运动趋势完全一致,仅在垂直方向上有2.15 mm·a~(–1)的差异。     

用深井观测的地震研究东川地区随深度变化的场地放大因子.

采用中日合作，分别布设于东川垂直竖井中地下200ｍ、100ｍ 和地面３个位置的高精度数字化地震仪记录的地方震资料（震中距8.5～95ｋｍ，震级ML1.3～5.1），用频谱比的分析方法计算了东川地区不同深度（－100ｍ 和地面）的场地放大因子．在８个频率（f ＝0.75，1.0，1.5，2，3，4，5和12Ｈｚ）上所对应的在-100ｍ 处的3个分向（N-S，E-W，U-D）的场地放大因子（与-200ｍ 处相比），当0.75Ｈｚ f 2Ｈｚ时，为1.0～1.49；当2Ｈｚ＜ f ＜12Ｈｚ时，为0.47～0.99；在地面，3个分向在8个频率上所对应的场地放大因子（与-200ｍ 处相比）均大于1，其值为1.6～7.63．-100ｍ 处的Ｓ波和尾波场地放大因子与地面的Ｓ波和尾波的场地放大因子的相关系数，当0.75Ｈｚ f 2Ｈｚ频段时，分别为0.82和0.81；当2Ｈｚ＜ f＜12Ｈｚ频段时，分别为0.47和0.45．      

Sea surface heights obtained from Modular Ocean Model simulation and comparison with Topex/Poseidon data for the Indian Ocean

The Modular Ocean Model (MOM) is perhaps the most versatile ocean model available today for the simulation of the large scale circulation of the ocean. The Topex/Poseidon altimeter which has been operating since September 1992 has been providing sea surface heights (SSH) of the accuracy of 5–10 cms with a repeat cycle of 10 days. We examine in this paper, the SSH in the Indian Ocean obtained from a global simulation of MOM with a resolution of 1° in the longitude, 1/3° in the latitude between 30°S and 30°N and 20 levels in the vertical with climatological windforcing and restoring conditions on temperature and salinity. They are compared with the SSH from the Topex/Poseidon altimeter after suitable filtering in the time domain to remove smaller time and length scales. In addition, unfiltered data from both sources are analysed by estimating the cross-spectral density to find the coherence and crossphase at different frequencies. The agreement between the two, over most of the Northern Indian Ocean, especially the Arabian Sea and the Bay of Bengal is quite good.