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.     

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。     

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.     

Validation results of NmF2 and hmF2 derived from ionospheric density profiles of GNOS on FY-3C satellite

The first Global Navigation Satellite System Occultation Sounder(GNOS) which is compatible of both Bei Dou System(BDS)and Global Positioning System(GPS) was successfully launched into orbit onboard the Feng Yun 3 C satellite(FY-3 C) on September 23, 2013, and it has already gathered a large amount of ionosphere radio occultation(RO) data so far. However, the detailed analysis and validation of GPS ionosphere RO data have not been done up to now. Therefore, this paper discusses the configuration of the FY-3 C GNOS, the methods and results of GPS ionosphere occultation processment, the quality analysis of the GPS ionosphere RO products, and the precision consistency between the GNOS GPS ionosphere RO product and ionosonde data. The peak electron density(Nm F2) correlation coefficient is 0.97, the corresponding standard deviation is 16.08%. The peak value altitude(hm F2) correlation coefficient is 0.89, and the corresponding standard deviation is 23.79 km. The in-orbit operation of GNOS provides a basis data set for the monitoring, forecasting and research of ionosphere's space weather.     

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。     

电离层延迟改正实例分析

介绍了利用双频GPS观测值建立电离层模型的原理和方法;利用某地的双频GPS观测资料分析了VTEC的变化。     

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.     

TEQC和QCVIEW32在GPS观测数据预处理中的应用

为了得到比较＂干净＂的观测数据或者提高整体观测数据的质量,通常需要对GPS（Global Positio-ning System）观测数据进行预处理。一般的随机处理软件会因为GPS接收机型号的不同而不能对任意的GPS观测数据进行预处理,而TEQC（Translation,Editing and Quality Checking）和QCVIEW32（QualityChecking VIEW32）可以对任意的GPS观测数据进行格式转换,去除噪音等预处理操作。本文分析了GPS观测数据预处理的现状,总结了TEQC和QCVIW32在GPS观测数据预处理中应用的优点和缺点,介绍了TE-QC和QCVIW32的用法,利用VB6.0（Visual Basic 6.0）,结合TEQC和QCVIW32的优点,针对TEQC和QCVIEW32依赖dos环境,人机交互性差等缺点,编写了GPS观测数据预处理可视化程序TEQCAST。通过实例分析,证明该程序操作简便,并且能够使预处理后的数据质量得到显著改善。     

GPS电离层改正模型的评价

讨论了单频接收机的电离层延迟的改正和有关电离层的概况及对GPS信号的影响．对电离层的物理概况作了归纳，并就GPS信号在电离层的传播及其影响进行了探讨，总结了几种电离层延迟改正模型．最后集中讨论了克罗布歇的模型构建及其解算，对模型的优缺点进行了总结，并对电离层延迟改正模型作了评价与展望．     

The variation of the estimated GPS instrumental bias and its possible connection with ionospheric variability

Based on the analysis of the satellite DCB data estimated by our method and the Center for Orbit Determination in Europe(CODE)from 1999 to 2011,the features of the temporal variation of differential code biases(DCB)are studied.Summarily,there are three types of variations in DCB on different time scales.The first one is the day-to-day variation that exhibits more obviously in solar maximum years.The second one is the variation with about one year periodic variation that behaves more obviously from 1999 to 2004.The last one is the monotonously descending tendency from 1999 to 2010.Considering the basic ionospheric approximation in DCB estimation method,the features of the variability of the ionospheric morphology from 1999to 2010 are also displayed based on the ionospheric characteristic parameters.It can be concluded that the day-to-day and annual variation of the estimated global positioning system(GPS).DCB is related to the ionospheric variability.The variation of DCBs on solar cycle time scale includes the real hardware DCBs and pseudo-DCBs induced by ionospheric variation.No doubt,these kinds of"pseudo"variations of DCB will affect the precision of ionospheric total electron content(TEC)derived from the GPS data.In addition,this study is helpful for evaluating the influence of ionospheric weather on TEC derivation and is also useful for developing one estimation method of DCB with more stability and precision through introducing a more practical ionospheric model.     

Integrated precise orbit determination of Shenzhou Ⅳ unmanned spacecraft

Considering the characteristic orbit of Shenzhou Ⅳ spacecraft and the advantages and disadvantages of several types of domestic orbit measurements, a scheme of IPOD is determined, which uses GPS, SLR and USB observation data jointly plus precise ionosphere corrections to GPS observation data. IPOD system and mathematic models of OD are introduced. The results of different joint OD are analyzed using true observation data, and show that radial accuracy is better than 2 m.     

Integrated precise orbit determination of Shenzhou IV unmanned spacecraft

On Dec. 30, 2002, Shenzhou IV unmanned spacecraft was launched successfully. The orbital module of Shenzhou IV carries a radar altimeter for ocean dynamic research. In order to get valid and high precision sea surface topography (SST), errors including altimeter, propagation and orbit should be reduced or eliminated. The error budgets of main international oceanographic satellites show that the root-mean-square error (RMS) of orbit error accounts for 70% of the total error. So, orbit acc…     

基于GPS掩星观测的全球偶发E形态学研究

利用COSMIC和GRACE系统提供的2009年12月至2010年2月(南半球夏季)、2010年6月至8月(北半球夏季)的GPS掩星观测数据,通过分析电离E层高度范围内C/A码信噪比扰动情况,研究偶发E随地理位置、高度和地方时变化的月平均特征,研究结果表明,较强的信噪比扰动主要出现在距地面90～110 km高度范围;在南纬、北纬15°～45°,信噪比扰动有明显的半日变化;在南纬15°至北纬15°,信噪比扰动以周日变化为主.统计结果与已知的全球偶发E形态学特征较一致,说明利用GPS掩星观测技术可以有效地监测全球偶发E的形态学特征.     

GPS地基与掩星观测结合的时变三维CIT重建公式

基于地基平行束投影定理和掩星平行束投影定理,导出了GPS地基与掩星观测结合的时变三维电离层层析重建公式,讨论了有限视角和有限接收机孔径对重建图像的影响.根据重建公式,在这些非理想条件下,对一个脉冲源函数进行了CT重建.重建结果的比较表明,结合GPS地基与掩星观测数据进行重建,电子密度整体图像的重建质量特别是其垂直结构的重建质量得到明显改善,表明结合GPS地基与掩星观测数据重建电离层电子密度的时变三维电离层层析是可行的.     

TIME-IGGCAS model validation: Comparisons with empirical models and observations

The TIME-IGGCAS (Theoretical Ionospheric Model of the Earth in Institute of Geology and Geophysics, Chinese Academy of Sciences) has been developed recently on the basis of previous works. To test its validity, we have made comparisons of model results with other typical empirical ionospheric models (IRI, NeQuick-ITUR, and TItheridge temperature models) and multi-observations (GPS, Ionosondes, Topex, DMSP, FORMOSAT, and CHAMP) in this paper. Several conclusions are obtained from our comparisons. The modeled electron density and electron and ion temperatures are quantitatively in good agreement with those of empirical models and observations. TIME-IGGCAS can model the electron density variations versus several factors such as local time, latitude, and season very well and can reproduce most anomalistic features of ionosphere including equatorial anomaly, winter anomaly, and semiannual anomaly. These results imply a good base for the development of ionospheric data assimilation model in the future. TIME-IGGCAS underestimates electron temperature and overestimates ion temperature in comparison with either empirical models or observations. The model results have relatively large deviations near sunrise time and sunset time and at the low altitudes. These results give us a reference to improve the model and enhance its performance in the future. Supported by the KIP Pilot Project of CAS (Grant No. kzcx2-yw-123), National Natural Science Foundation of China (Grant Nos. 40636032 and 40725014), and National Key Basic Research Project of China (Grant No. 2006CB806306)     

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.     

郑州市农村饮用水水质评价

为了解决农村饮水安全问题,郑州市进行了农村饮用水水质评价.全市共布设255个水质取样点,水质检测项目约21项,以生活饮用水卫生标准作为水质评价标准.评价结果为:氟化物超标率为10.20%,主要分布在荥阳市北部、登封市西南、新郑市东南、中牟县南部;溶解性总固体超标率为23.81%,总硬度超标率为43.92%,硝酸盐(以氮计)超标率为21.68%,硫酸盐超标率为14.12%,氯化物超标率为10.20%,郑州市苦咸水、浅层地下水污染区域主要分布在巩义市伊洛河两侧、郑州市区—中牟县贾鲁河两侧、新密市—新郑市双洎河两侧、登封市颍河两侧、巩义市米河—上街区汜水河两侧.     

工程场地浅层剪切波速结构反演

目的反演工程场地浅层剪切波速结构,验证中美联合地脉动台阵观测记录适合应用于实际工程场地的浅层剪切波速结构.方法对唐山地区两个实际场地观测,从地脉动台阵观测竖向记录中提取了Rayleigh波相速度频散曲线,从地脉动台阵3分量记录中提取了Love波相速度频散曲线,采用Haskell矩阵计算理论的Rayleigh波和Love波相速度.结合遗传算法与单纯形结合的反演算法对唐山地区的两个具体场地浅层剪切波速度结构进行了反演,并与实际的钻孔资料进行了对比.结果场地1提取的相速度频散曲线与理论计算结果有一定的差别.场地2提取的相速度频散曲线与理论计算结果符合较好,场地2的剪切波速结构反演结果较好,与钻孔资料的平均误差均在20%以内.结论利用从地脉动记录中提取Rayleigh波和Love波相速度频散曲线,反演场地剪切波速结构效果较好,适用于实际工程场地的浅层剪切波速度结构反演.     

普适型GPS用于黄河盐锅峡水位监测分析

黄河水文变化复杂,现有水位监测方法费时费力且不能很好满足时间分辨率和空间分辨率两个方面的需求.地基GPS-IR技术的出现为水位监测提供了新的手段,但目前大多数地基GPS-IR技术采用的接收机为高精度大地测量型接收机,成本高、时效性差,不适合大范围推广.首先介绍了普适型GPS接收机的组成,并对GPS数据观测质量进行了分析;其次给出了地基GPS-IR技术用于水位监测的基本原理;最后利用黄河盐锅峡GPS实测数据进行GPS-IR水位提取,以兰州水文站水位监测数据为参考分析了普适型GPS接收机反演水位的精度,得到了最佳RMSE为0.21 m的精度.实验结果表明,普适型GPS接收机可用于长时间水位监测.     

BDS/GPS/Galileo多频观测值精度评估及随机模型精化

随机模型的优劣直接影响GNSS精密定位的精度以及可靠性.通过MEGX观测网CUT0、CUT2和CUTA测站连续10d观测数据,基于短基线单差模型方法求解各系统单差残差的时间序列,并推导出BDS/GPS/Galileo卫星观测值噪声.统计观测值噪声随高度角变化的情况,通过最小二乘拟合方法确定精化的随机模型.结果表明:Galileo的4个频点的伪距观测值精度约20~50cm,E5频点的精度最高,E1最低,E5a和E5b基本相当;载波相位观测值精度约1~3mm,E5频点的精度明显高于E1、E5a和E5b.BDS载波观测值精度约1~3mm,B1、B2、B3精度基本相当,其伪距观测值精度约30~50cm,B1精度最低,B2和B3相差不多.GPS L1伪距观测值精度约63cm,L2伪距观测值精度约42cm,载波相位精度约3mm.基于单差模型对各系统观测值进行精度估计,在短基线情况下,BDS/GPS/Galileo载波相位观测值精度基本相当,而Galileo E5伪距观测值精度明显优于其他卫星系统伪距观测值精度.各类型卫星观测值的残差分析可为定位中随机模型的建立提供依据.