大地震前震中上空电离层全电子含量异常研究

采用IGS(International GPS Service)网站提供的电离层垂直全电子含量(vertical total elearon content,记为VTEC),分析研究了1998—2006年发生在中国大陆地区的30个M_s≥6.0的地震.采用统计处理的方法,讨论了地震前后15d内电离层全电子含量的变化,分别对震中上空电离层全部TEC资料进行了分析.     

CSES GNSS ionospheric inversion technique,validation and error analysis

With the increased number of low Earth orbit (LEO) satellites equipped with global navigation satellite system (GNSS) receiver, the LEO based GNSS slant total electron content (TEC) and electron density profile (EDP) data play an increasingly important role in space weather and ionospheric research due to improved global coverage. China Seismo-Electromagnetic Satellite (CSES), which was launched in February 2018, is equipped with GNSS receiver for either precise orbit determination (POD) and ionospheric inversion. The purpose of the present paper is to validate CSES GNSS ionospheric inversion technique based on the real observations and verify the accuracy of TEC and EDP retrieval based on the simulated data. The following conclusions can be drawn: the epoch difference inversion (EDI) derived from CSES can successfully retrieve the EDPs without non-occultation side measurements; the technique of EDI and the calibrated TEC inversion (CTI) have similar behaviors in inversion errors, however, the retrieved NmF2 and hmF2 have a larger systematic error surrounding the equatorial ionization anomaly (EIA) where the assumption of spherical symmetry is often invalid; the precision and accuracy of retrieved TEC have been investigated in the paper based on the simulated data, and it is found that the accuracy of the retrieved TEC is relative to solar activity: the lower the F10.7 index, the higher the accuracy of retrieved TEC.     

桂林地区L-波段电离层闪烁初步统计分析

利用2007年1月至2008年6月桂林地区GPS电离层闪烁监测仪的数据,分析L-波段电离层闪烁的特征,包括夜间幅度闪烁的逐日变化和闪烁活动随地方时的变化.初步统计分析结果表明:2007年1月至2008年6月期间,桂林地区的夜间闪烁活动比较平静,S4>O.2的闪烁很少发生;2008年上半年的白天幅度闪烁活动比较频繁,其持续时间可达效小时.     

Research on regional ionospheric TEC modeling using RBF neural network

Machine learning techniques which are about the construction and study of system that can learn from data are combined with many application fields.A method on ionospheric total electron content(TEC)mapping is proposed based on radical basis function(RBF)neural network improved by Gaussian mixture model(GMM).Due to the complicated ionospheric behavior over China,GMM is used to determine the center of basis function in the unsupervised training process.Gradient descent is performed to update the weights function on a sum of squared output error function in the supervised learning process.The TEC values from the center for orbit determination in Europe(CODE)global ionospheric maps covering the period from 2007to 2010 are used to investigate the performance of the developed network model.For independent validation,the simulated TEC values at different latitudes(20°N,30°N and 40°N)along 120°E longitude are analyzed and evaluated.The results show that the simulated TEC from the RBF network based model has good agreement with the observed CODE TEC with acceptable errors.The theoretical research indicates that RBF can offer a powerful and reliable alternative to the design of ionospheric TEC forecast technologies and thus make a significant contribution to the ionospheric modeling efforts in China.     

电离层总电子含量建模的最优观测值选择

观测量的精度对区域电离层总电子含量建模至关重要.介绍电离层总电子含量(TEC)的概念,讨论利用GPS双频观测数据反演TEC的方法和原理.通过对几种TEC计算方法的精度进行研究和分析,提出一种电离层总电子含量建模最优观测值的选取方法.     

电离层闪烁条件下GNSS信号质量对比

为了监测桂林(25.29°N,110.33°E;地磁坐标:15.04°N,181.98°E)L波段电离层闪烁,利用桂林的电离层闪烁与TEC监测仪2011年9月至2013年7月的观测数据,在相同的电离层闪烁环境下对GPS和GLONASS卫星的信号质量进行了对比。结果表明:GPS和GLONASS卫星的L2信号的幅度闪烁强度均比L1信号大;GPS卫星L2信号的幅度闪烁强度比GLONASS卫星L2信号大;GPS和GLONASS卫星的L1信号的幅度闪烁特征相同。在电离层闪烁条件下,GPS和GLONASS卫星的L1信号质量相当,可联合使用GPS和GLONASS的观测研究桂林的L波段电离层闪烁特征。     

利用Klobuchar模型和载波平滑伪距观测值模型分析电离层变化

在GPS测量中,电离层延迟是一个比较重要的误差来源.对于单频接收机,由广播星历中提供Klobuchar模型参数进行电离层延迟改正;对于双频接收机,采用载波平滑伪距观测值计算电离层延迟改正.利用深圳市连续运行卫星定位参考站系统的双频观测数据,分别用Klobuchar模型和载波平滑伪距观测值两种方法计算深圳市5个CORS站上的电离层延迟值,对两种模型计算的电离层延迟值进行比较,分析深圳市电离层延迟的周日变化规律.     

利用双频GPS观测量对高原地区（昆明）电离层TEC的研究

采用双频GPS观测值,在顾及GPS系统硬件延迟情况下,通过伪距与载波相位观测值联合解出TEC,并将其投影至高原（昆明地区）上空约350km的某一假想薄层上,从而导出接收站附近垂直TEC。这种方法得到的垂直TEC为天顶周围一锥角内的平均值,通过离散度的统计,并结合昆明站采集得到的高精度数据计算了该地区电离层2007年6～8月的电离层电子浓度总含量的逐日时间序列值,在此基础上对照昆明市连续运行参考站CORS描绘出了对于处在双驼峰区里该地区TEC日变化的特性。     

方差-协方差分量的验后估计与分析

目的对观测值的方差-协方差分量进行验前及验后估计与分析;探求正确评定观测结果精度的途径.方法通过全球定位系统双观测值实测数据,假设是非差观测值相互独立,用常规的基线处理方法,由协方差传播定律求得先验协方差阵;在历元之间相互独立的条件下,分别用最小二乘和MINQUE方法对观测值的方差-协方差矩阵进行验后估计,计算方差-协方差阵的所有元素.结果两种方法估计的方差-协方差阵都与常用的先验协方差阵有明显区别;两种方法估计计算结果非常接近.结论说明对全球定位系统双观测值有必要进行方差-协方差分量估计;两种方法估计计算结果非常接近说明了方差-协方差分量验后估计的严密性,对用方差-协方差分量验后估计进行新型测量数据的处理提供了可靠的理论依据.     

Global ionospheric TEC response to a strong magnetic storm

The global characteristics of the ionospheric storm and irregularities as well as propagation of TEC (total electron content) disturbances during the strong magnetic storm occurring in November 2004 were investigated by using the data of the IGS network. For the response of the global ionospheric TEC to this strong magnetic storm, the following features are noticeable: 1) the maximum of the ionospheric storm phase occurred around the main phase maximum of the magnetic storm; 2) the TEC response in equatorial and low latitudes was more remarkable than that in mid-high latitudes; 3) as a whole, the storm phase in the northern hemisphere was mainly positive, and it was negative in the southern hemisphere; 4) during the whole magnetic storm from November 7 to 11, the locations where the maxima of the positive and negative ionospheric storm phases occurred were nearly invariant to the Sun at low and equatorial latitudes, i.e. the 24-h recurrence. Analyzing results of TEC rate and its standard deviation showed that the ionospheric irregularities and disturbances in the global mainly occurred around the main phase maximum of the storm, and they distributed in a large longitudinal region for both day and night in mid-high latitudes and they generated and developed only after the sunset, and lasted out to the midnight in equatorial and low latitudes. The disturbance propagation parameters were also estimated by using the wavelet reconstruction and cross-correlation technologies for a set of spaced stations in the Northern America. Supported by the National Natural Science Foundation of China (Grant Nos. 40474055, 40504019)     

陕西省北斗三号区域电离层TEC建模与精度评估

基于陕西省北斗地基增强监测站数据,利用4阶球谐函数建立了陕西区域电离层总电子含量(TEC)模型,生成区域TEC格网产品.实验结果表明：以欧洲定轨中心(CODE)全球电离层图(GIM)产品作为参考,利用BDS-3数据获得的陕西区域北斗电离层产品精度为2.54 TECu,与CODE产品标称精度相当.在单频精密单点定位(SF-PPP)性能方面,BDS-3区域电离层产品可以提升定位精度35%,优于CODE全球电离层产品改正效果(27%).综合而言,BDS-3单系统在区域电离层建模方面具备较为优异的性能水平.     

Relationship between air temperature oscillations and solar variability on short and medium time scales

The contemporary science of climate change is increasingly focusing on the temporal and spatial characteristics of temperature oscillations and determining possible underlying causes.In particular,the effect of variations in solar irradiance on the variability of the climate remains a hot topic of debate.Most studies focus on the effects of solar variation on the Earth's climate on long time scales.This study presents the responses of regional climates to solar variations on shorter time scales using two da...     

用于远距离差分GPS的电离层误差分析与补偿

采用差分工作方式的全球定位系统(DGPS)有助于满足许多航空、航天的导航、进场、着陆应用中的精度要求.随着参考站到用户间距离的增大,差分GPS的定位精度很快下降。本文研究了其中一种最重要的系统误差——电离层时间滞后.首先用Bent方法和Klobuchar方法建立了电离层滞后模型,根据该模型用卫星发布的数据计算的结果与接收机的测量结果进行了比较.为远距离的差分GPS建立了一个有效的修正模型.理论分析结果表明,当参考站距用户1000km时,由电离层滞后引起的差分后定位误差可达12m,与卫星数据模拟的结果吻合.     

广西区C级GPS网整体平差探讨

讨论了广西区C级GPS网整体平差几个问题，GPS控制网布设和子网划分原则和方法；GPS控制网子网粗差向量检测方案及子网无约束平差方案，相邻GPS子网无约束平差及粗差向量检测方案；GPS控制网整体无约束平差和整体约束平差方案，不同子网间定权及方差分量估计的应用和C级GPS控制网序贯平差方案。     

基于递归抗差估计的高精度GPS动态定位方法

GTP短基线动态定位中,单个历元求解时多余观测较少,求解精度不高,可以用后面历元的观测来增加多余观测,这就形成块模型。由于观测存在粗差,本文采用抗差估计递归求解块模型的浮点解,并且基于抗差估计的方差协方差矩阵,用LAMBDA方法搜索整周模糊度,然后固定基线向量,就可得到当前及以前历元较精确的基线向量的估计。最后利用块模型设计阵的结构特点改进算法提高抗差估计的计算效率。大量数值试验表明本文方法是有效的。     

Using the GPS observations to reconstruct the ionosphere three-dimensionally with an ionospheric data assimilation and analysis system (IDAAS)

Using an international reference ionosphere (IRI) model as a background ionosphere and applying the Kalman filter to update the state with observations, we develop an ionosphere data assimilation analysis system (IDAAS) to reconstruct a three-dimensional (3D) ionosphere with the GPS slant TEC and ionosonde data over east-south Asia. The preliminary results with the GPS data collected over east-south Asia on 30 June 2005 showed that inversed slant TEC has very good correlation with the observations both for the GPS sites being and not being involved in reconstruction. The inversed NmF2 and vertical TEC both demonstrate great improvement of agreement with those observed from ionosondes and TOPEX satellite independently.     

GPS精密定位数据分析和大气建模回顾与展望

归纳了用于GPS数据分析的大气建模方法。由于大气分布不均和不断的变化,尤其是大气中的水汽影响,使建立无线电信号路径延迟的精确模型在GPS高精度定位中非常必要。目前的路径延迟模型是参数估计及外部修正法。建议应用数值天气预报及其分析模型,以及空间探测仪器取代映射函数直接完成静水力学路径延迟修正。Raman激光雷达可用在各种天气条件下,作更精确的湿路径延迟的外部修正,其校准可用混合GPS数据分析法解决。     

遗传算法最优拟合抑制GPS多径研究

在多径时延较短的情况下,传统全球定位系统抑制多径算法无法对短时延多径信号进行有效的抑制,从而导致无法提高全球定位系统的定位精度．提出了一种基于遗传算法的多径逼近方法,将多径信号估计转换为最优拟合问题,采用遗传算法进行优化逼近,避免了逼近模型陷入局部最小值．得出了实际信号中直达信号和多径信号各自的表达式,相当于消除多径干扰,在短时延多径情况下提高了伪距测量精度．给出了遗传算法估计多径的具体步骤．仿真结果表明,这种方法可以将全球定位系统接收机的伪距测量精度提高一倍左右．     

SINS/GPS组合导航系统初始对准的可观测度分析

针对SINS/GPS组合导航系统的误差传递模型进行了可观测度分析,确定了卡尔曼滤波器对系统各个状态的估计效果.在飞行器处于不同飞行姿态下,通过对相应的状态估计误差协方差阵的特征值及特征向量的比较,发现在动基座对准时,对飞行器引入线加速度可显著提高方位角的估计精度,并且在相同的条件下,拐弯运动的方位角估计速度更快、精度更高.此外,拐弯运动能够估计出加速度计零位偏置.此方法可以为飞行器在初始对准时选择最佳机动方案提供依据.     

高斯粒子滤波的惯性／GPS紧组合算法

为提高组合导航系统的可靠性,针对以伪距、伪距率残差为量测信息的紧组合算法会带来线性化误差的缺点,推导了基于伪距、伪距率的非线性紧组合模型.针对紧组合系统状态维数高导致粒子滤波实时性差的问题,提出基于线性非线性结构分解的高斯粒子滤波算法,对状态方程中的非线性和线性部分利用高斯粒子滤波和经典卡尔曼滤波分别进行递推,有效降低了系统的运算量.仿真结果表明,使用改进的紧组合滤波算法系统定位精度相比线性化紧组合算法提高一倍.