基于北斗、GLONASS和GPS系统的中低纬电离层特性联合探测

基于GNSS(Global Navigation Satellite Systems)的发展,我们利用具有北斗、GLONASS和GPS三系统信号接收功能的接收机观测的数据,结合电离层总电子含量(Total Electron Content, TEC)的反演算法,提取出GNSS三系统观测的电离层TEC;同时,将GNSS三系统获取的TEC应用到电离层TEC地图、行进式扰动、不规则体结构和电离层的太阳耀斑响应等方面的研究中,这也是首次使用三种GNSS系统数据对电离层进行联合探测研究.研究结果表明,增加了北斗系统的GNSS三系统在研究中国地区电离层TEC地图、周日变化、逐日变化,行进式扰动以及电离层的实时监测等方面较单系统的GPS具有明显的优势.     

2017年九寨沟M7.0地震前临震电离层异常研究

为研究2017年8月8日四川九寨沟M7.0地震前电离层异常,利用地基GNSS(Global Navigation Satellite System)垂直电子总含量(Vertical Total Electron Content, VTEC)和电离层测高仪F2层临界频率(foF2)观测数据,考察了震前20日内电离层变化,发现震前第4日(8月4日)及地震发生前5小时,震中附近上空出现显著电离层正异常。结合异常对应的日地空间环境分析,认为震前第4日出现的异常由磁暴引起,而发震当日出现的临震电离层异常可能与孕震活动有关。本文表明电离层测高仪具有同GNSS VTEC一致的异常检测结果。相比公布时间滞后的GNSS数据及其产品,测高仪数据的获取更加及时,将两种电离层观测手段结合起来,能实现两种技术优势互补,提高地震电离层监测能力。     

基于载波相位平滑伪距与精密单点定位获取的TEC在GNSS电离层层析中的对比分析

利用GNSS(Global Navigation Satellite System)建立电离层层析(Computerized Ionospheric Tomography, CIT)模型反演电离层的结构,并探测和研究电离层的活动及其变化规律是目前的研究热点,其中相位平滑伪距(Carrier Phase Smoothing Pseudorange, CPSP)和精密单点定位技术(Precise Point Positioning, PPP)是两种主要的电离层电子含量(Total Electron Content, TEC)获取方式,但这两种方法对电离层层析的性能影响,目前尚未有研究进行比较分析.有鉴于此,本文利用欧洲区域2017年9月7、8两日的GNSS数据,分别基于CPSP和PPP获取TEC进行电离层层析反演并分析比较其精度,这两种反演方法分别称为CPSP-CIT和PPP-CIT.其结果显示,CPSP-CIT与测高仪之间的RMSE均值为0.9292×10¹¹ el/m³、PPP-CIT与测高仪之间的RMSE均值为0.6915×10^1...     

基于陆态网络GPS数据的电离层空间天气监测与研究

中国大陆构造环境监测网络(简称陆态网络)是以全球卫星导航定位系统(GNSS)为主,辅以多种空间观测技术,实时动态监测大陆构造环境变化,探求其对资源、环境和灾害的影响的地球科学综合观测网络.基于陆态网络约200个基准站的GPS观测数据,本文探讨了其在电离层空间天气监测与研究方面的应用.包括磁暴期间电离层暴扰动形态,大尺度电离层行进式扰动,太阳耀斑引起的电离层骚扰和低纬电离层不规则体结构等.研究结果表明:陆态网络布局合理,观测数据质量良好,完全可用于中国及周边地区电离层空间天气监测与研究,为进一步开展我国电离层空间天气预警和预报奠定了观测基础.     

中国电离层TEC同化现报系统

数据同化是在基于物理机制的背景模型上,融合时空不规则分布的观测数据的一种现报方法.同化能够有效弥补数据的时空局限和模型的精度偏差,使二者相互匹配从而获得更加合理可信的模拟效果.本研究利用电离层数据同化方法,针对中国及周边区域（15°N-55°N,70°E-140°E）构建了电离层总电子含量（TEC）同化现报系统.系统使用国际参考电离层（IRI）作为背景场,利用中国科学院空间环境监测网和国际GNSS服务组织（IGS）的部分地基GNSS台站数据作为观测值,并采用三维变分与Gauss-Markov卡尔曼滤波相结合的算法进行背景场和观测值的数据同化,生成覆盖中国及周边区域的电离层TEC和GPS单频接收机延迟误差的格点化准实时现报地图,并在中国科学院空间环境预报中心（http：//sepc.ac.cn/TEC_chn.php）网上发布,每15 min进行更新.该系统是我国基于同化算法的电离层现报系统之一,已用于中国及周边区域的电离层环境实时监测,可为卫星导航、雷达成像、短波通信等科学研究和工程应用提供相对及时、准确、有效的电离层TEC和误差修正信息.     

利用GPS计算TEC的方法及其对电离层扰动的观测

在总结用ＧＰＳ研究电离层电子总量ＴＥＣ的数据处理方法基础上,分析了利用伪距观测量和载波相位观测量计算电离层ＴＥＣ的特点及误差来源．在处理过程中考虑了卫星的硬件延迟偏差,分析了应用ＩＲＩ模型进行接收机硬件延迟偏差修正的可能性,发现利用少量ＧＰＳ数据和ＩＲＩ模型修正接收机硬件延迟偏差有一定的困难．最后,利用一些ＧＰＳ观测数据有针对性地研究了电离层对若干次扰动事件的响应．包括一次大的太阳耀斑期间的电离层ＴＥＣ变化、一次较典型的电离层行扰以及日食期间的电离层ＴＥＣ的相对变化等电离层物理问题．结果表明,利用该方法计算ＴＥＣ的精度可满足电离层扰动现象的研究．     

地基GNSS VTEC约束的大气掩星电离层误差修正方法

介绍了一种考虑电离层沿GNSS掩星射线路径分布不对称且兼顾一阶和二阶项的大气掩星电离层误差修正新方法,它综合地基GNSS VTEC的水平变化信息和电离层模式的垂直变化信息,在沿"入射线"与"出射线"双边局部球对称假设下,估算GNSS掩星射线路径上的电子密度;进而计算一阶和二阶项弯曲角电离层误差廓线.采用太阳活动低年的2008年7月15日和太阳活动较高年的2013年7月15日两天的MetOp-A和GRACE掩星观测资料和IGS的GNSS VTEC数据,计算了GNSS大气掩星弯曲角一阶和二阶项电离层误差廓线.对比分析表明：新方法经验模型和理论模型的二阶项弯曲角电离层残差,以及经验模型与实测数据的一阶和二阶项弯曲角电离层误差均具有良好的一致性,因此该方法可用于L2信号数据质量较差或L2信号中断的掩星事件,同时修正大气掩星一阶和二阶电离层误差,从而提高弯曲角精度和掩星观测资料的利用率.     

利用GPS观测数据和IRI模型对比分析太阳活动低年广州地区电离层TEC变化

电离层TEC是描述电离层特性的一个重要参量,利用GPS观测数据（包括广州站接收的GPS-TEC数据和国际GNSS提供的IGS-TEC数据）与IRI-2007模型计算的TEC预测值对太阳活动低年2008年的广州地区TEC周日和季节变化以及年变化特征等进行了多方面的对比分析。结果表明：TEC观测值白天较高且变化迅速,夜间较低且变化缓慢,同时表现出明显的季节依赖性和半年变化特性,全年在春秋分季节出现两次峰值,IRI-TEC预测值能较好地反映GPS观测值,但局部上也存在着一些偏差,并对其中的物理机制和产生差异的原因给出了合理的分析和解释。     

电离层GPS掩星观测反演技术

在电离层局部地区球对称假设下,推导了利用双频和单频无线电掩星观测数据,反演电离层电子密度剖面的两种方法. 双频反演的误差来自于载波相位的观测误差,单频反演误差则主要由伪距的观测精度决定. 由于载波相位测量精度比伪距测量精度高两个量级,因此双频反演的精度一般比单频反演的高些. 不过,两载波信号L1和L2之间的传播路径差异会给双频方法带来误差. 利用三维射线追踪的程序模拟的无线电掩星数据来评估这些方法,结果表明,反演出的电离层剖面与给定的模式电离层非常吻合,验证了两种方法的可靠性和准确性. 将这两种反演方法应用于处理实测的GPS/MET掩星观测数据,均能获取合理的电离层剖面信息. 且单频方法得到的反演剖面与双频方法相当一致, 这为利用LEO星载单频GPS接收机进行电离层掩星观测提供了理论基础.     

基于陆态网络GNSS数据的2013年和2015年磁暴期间中国地区电离层特性研究

2013年3月和2015年3月爆发了2次相似的地磁暴,引起了全球不同地区电离层的变化。本文利用中国大陆构造环境监测网络260余个基准站在中国地区的GNSS电离层TEC观测数据,结合电离层测高仪和电离层甚高频相干散射雷达观测,对2次磁暴期间中国地区的电离层变化特性进行了对比分析。结果显示,2013年3月磁暴期间,中国不同地区电离层变化较弱或不明显,而2015年3月磁暴期间中国地区电离层变化整体表现为大范围的强负相暴,中国地区不同程度的电离层响应主要受到不同的磁暴强度和磁暴期间不同的能量输入影响。2次磁暴期间电离层F层不均匀体的发生受到不同程度的影响,可能由不同种类的暴时电场导致。陆态网络数据空间覆盖范围广、时间分辨率高,在研究中国地区磁暴期间的电离层变化特性方面具有优势。     

Automated daily process for global ionospheric total electron content maps and satellite ocean altimeter ionospheric calibration based on Global Positioning System data

The accuracy of single-frequency ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite. Data from a global network of Global Positioning System (GPS) receivers provides timely, continuous, and globally well-distributed measurements of ionospheric electron content. For several months we have been running a daily automatic Global Ionospheric Map process which inputs global GPS data and climatological ionosphere data into a Kalman filter, and produces global ionospheric TEC maps and ocean altimeter calibration data within 24 h of the end-of-day. Other groups have successfully applied this output to altimeter data from the GFO satellite and in orbit determination for the TOPEX/Poseidon satellite. Daily comparison of the global TEC maps with independent TEC data from the TOPEX altimeter is performed as a check on the calibration whenever the TOPEX data are available. Comparisons of the global TEC maps against TOPEX data will be discussed. Accuracy is best at mid-to-high absolute latitudes (∣latitude∣>30°) due to the better geographic distribution of GPS receivers and the relative simplicity of the ionosphere. Our highly data-driven technique is relatively less accurate at low latitudes and especially during ionospheric storm periods, due to the relative scarcity of GPS receivers and the structure and volatility of the ionosphere. However, it is still significantly more accurate than climatological models.     

GPS接收机仪器偏差的短期时变特征提取与建模

卫星和接收机仪器偏差(Differential Code Biases,DCB)是利用GPS(Global Positioning System)研究电离层的两类主要误差源.由于所处的空间环境恒定,且可被全球跟踪站连续观测,GPS卫星的DCB具备长期稳定性和较高的估计精度.但针对各类型接收机而言,受测站环境、硬件设施等影响,其DCB可能会呈现明显的短期变化.精确地模型化接收机DCB的短期变化特征,将有助于提高GPS电离层产品的可靠性,以及基于这些产品反演空间和地球科学现象的准确性.采用零/短基线GPS数据,本文改进了提取和分析接收机DCB变化的现有方案.随后,本文推导了一种能直接估计接收机DCB的函数模型.当检验出接收机DCB的短期变化服从随机游走时,通过对比接收机DCB的直接估值与间接提取值之间的符合程度,可"试探出"过程噪声标准差的最优经验值.实验分析选用4台双频接收机(共形成1条零基线和2条短基线,间距最大为15m)多天的观测数据,主要结论包括:1)改进的接收机DCB提取方案能较好地克服低频伪距噪声和多路径效应的影响;2)针对零基线,其接收机DCB在各天内的变化量级小于1TECu,变化趋势则可采用过程噪声标准差为1.0~1.5mm的随机游走加以描述;3)对应于某短基线的接收机DCB在某天内的变化可达12TECu,当采用随机游走描述其趋势时,过程噪声标准差的经验值超过2mm.     

一种能实现单频PPP-RTK的GNSS局域参考网数据处理算法

全球范围内大量布设的GNSS(Global Navigation Satellite System)参考网为精密定位、导航和授时等应用提供了丰富的数据资源.基于局域参考网,先后发展了若干侧重实现双频精密定位的技术,如NRTK(Network Real Time Kinematic),PPP(Precise Point Positioning)和PPP-RTK等.其中,PPP-RTK融合了NRTK和PPP的技术优势,是目前相关研究的热点.本文改进了利用局域参考网提取各类改正信息的算法,以便于实现单频PPP-RTK,具体步骤包括:1)逐参考站实施非组合PPP,并固定已知站星距和卫星钟差,预估电离层延迟、浮点模糊度等参数;2)联合所有参考站的PPP模糊度预估值,通过重新参数化,形成一组双差整周模糊度和接收机、卫星相位偏差;3)固定双差整周模糊度,精化求解卫星相位偏差和各参考站PPP电离层延迟.基于网解中用到的卫星轨道和钟差,以及网解所提供的卫星相位偏差和(内插的)电离层延迟,参考网内的单频流动站即可实施PPP-RTK.基于澳大利亚某连续运行参考站网和流动站的实测数据,考察了:1)参考网数据处理中,双差模糊度的固定成功率(98.89%)和卫星相位偏差估值的时间稳定性(各连续弧段优于0.2周);2)流动站处电离层延迟的内插精度(优于10cm);3)单天内任一历元起算,固定静态(动态)单频PPP整周模糊度所需时长(均不超过10min);4)模糊度固定前后,单频动态PPP的定位精度(模糊度固定后,平面和天顶RMS分别优于5cm和10cm;模糊度固定前,相应RMS仅为28~53cm).     

COSMIC低轨卫星GPS接收机差分码偏差估计

GPS接收机差分码偏差（Differential Code Bias,DCB）是利用COSMIC低轨卫星观测值反演电离层总电子含量TEC的一项重要误差源.本文将COSMIC卫星轨道高度以上的电离层作为一个单层,采用球谐函数来参数化电离层TEC值,并利用最小二乘法同时估算电离层球谐系数和DCB参数.运用这种方法对2012年12月份的所有COSMIC卫星GPS接收机DCB进行了解算,并与COSMIC数据分析与档案中心CDAAC提供的产品进行了比较.实验结果表明：在2012年12月期间,估计的接收机DCB与CDAAC结果符合的较好,二者DCB变化趋势相近,DCB差值的RMS值在2 TECU以内,且最大绝对差值小于3 TECU;此外,本文计算的接收机DCB估计误差主要分布在0.2~0.4 TECU之间,具有较高的内符合精度.     

Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method

A homing-in method is presented for determining ionospheric reflected or transionospheric paths between fixed transmitter and receiver locations in the presence of ionospheric gradients or ripples. Both initial elevation and azimuth are automatically adjusted to find the path that arrives exactly at the receiver. The method can be used for any 3D ionospheric model to find precise ray paths and phase and group delays for both magneto-ionic modes. The method takes full account of path location, geomagnetic field orientation and the bending of the ray path resulting from horizontal as well as vertical gradients of electron density. It can also find multiple paths e.g. low and high angle, 1- and 2-hops for both ordinary and extraordinary modes. Examples of its use are given for both terrestrial HF links and Earth to Satellite paths. For paths reflected from the ionosphere, the effect of gradients of both critical frequency and height of maximum electron density are determined and the comparative effect of gradients on high and low angle and 1- and 2-hops paths for both magneto-ionic modes investigated. Path variation with frequency for a fixed link is also studied and the bandwidth of the ionospheric background channel (dispersive bandwidth) and its reciprocal (the pulse rise time), important for wideband digital HF broadcasting or spread spectrum HF communications, is estimated for a range of frequencies, for high- and low-angle rays and 1- and 2-hop paths. For Earth–satellite paths, the effect of the ionosphere and horizontal ionospheric gradients is determined for a range of frequencies and elevation angles. It is shown that the method can also enable the determination of second-order errors in satellite navigation methods, such as GPS, due to ionospheric gradients and the effect of the geomagnetic field.     

Numerical simulation of the structure of the high-latitude ionospheric <Emphasis Type="Italic">F</Emphasis> region during meridional HF propagation

A previously developed model of the high-latitude ionosphere is used to calculate the distribution of the ionospheric parameters in the polar region. A specific method for specifying input parameters of the mathematical model, using the experimental data obtained by the method of satellite radio tomography, is used in this case. The spatial distributions of the ionospheric parameters characterized by a complex inhomogeneous structure in the high-latitude region, calculated with the help of the mathematical model, are used to simulate the HF propagation along the meridionally oriented radio paths extending from middle to high latitudes. The method for improving the HF communication between a midlatitude transmitter and a polar-cap receiver is proposed.     

Application of predictive regional ionosphere model to medium range RTK positioning

Real Time Kinematic (RTK) GPS positioning over longer distances requires a support of atmospheric (ionospheric and tropospheric) corrections, since the atmospheric errors decorrelate with the growing distances and cannot be completely eliminated by double differencing of the satellite observations. Currently, the most commonly used approach is to derive the atmospheric corrections at the reference station network and provide them in real time to the roving receiver. Another solution, proposed here, is to use predictive atmospheric models in order to derive the atmospheric corrections. This paper presents the test results of the performance assessment of the predictive ionosphere model (UWM-IPM) application to medium-range RTK positioning. The rover data collected within 25 to 67 km from the closest reference station were processed in the kinematic mode with the support of the ionospheric corrections derived from the UWM-IPM model. The RTK solution was derived in both single-and multi-baseline modes, and compared to the two reference solutions obtained without the ionospheric corrections. All numerical tests were carried out using the MPGPS software developed in cooperation with The Ohio State University; a recent extension to the software, developed at the University of Warmia and Mazury in Olsztyn, introduces the predictive ionosphere model to the RTK solution. The test results are very promising, and indicate that predicted ionosphere corrections can effectively support medium-range RTK positioning, and allow for fast ambiguity resolution over distances of several tens of kilometers under moderate ionospheric conditions.     

大功率高频电波加热电离层的非线性物理过程

地基大功率电波加热电离层是通过地基大功率短波发射机向电离层发射无线电波,通过波-粒和波-波的相互作用将无线电波的能量注入电离层.通过这种有目的可操控的方式改变电离层电子密度和温度的分布,可以深入研究电离层中等离子体能量和物质的非线性演化过程,特别是电离层电子的非平衡态分布和加速问题.本文通过对电离层加热中几个比较重要物理过程的评述,对过去20年来我国研究学者在这一研究方向上取得的重要进展进行了介绍.     

Anomalous modification of the ionospheric total electron content prior to the 26 September 2005 Peru earthquake

This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the International GNSS Service (IGS) network. For the analysis of the ionospheric effects of the 26 September 2005 Peru earthquake, Global Ionospheric Maps (GIMs) of TEC were used. The possible influence of the earthquake preparation processes on the main low-latitude ionosphere peculiarity—the equatorial anomaly—is discussed. Analysis of the TEC maps has shown that modification of the equatorial anomaly occurred a few days before the earthquake. In previous days, during the evening and night hours (local time—LT), a specific transformation of the TEC distribution had taken place. This modification took the shape of a double-crest structure with a trough near the epicenter, though usually in this time the restored normal latitudinal distribution with a maximum near the magnetic equator is observed. Additional measurements (CHAMP satellite) have also confirmed the presence of this structure. To compare the vertical TEC measurements obtained with GPS satellite signals (GPS TEC), the International Reference Ionosphere, IRI-2001, was used for calculating the IRI TEC.     

Ionospheric space weather effects monitored by simultaneous ground and space based GNSS signals

Ionospheric space weather effects can degrade the performance of global navigation satellite systems (GNSS), i.e. their accuracy, reliability and availability. However, well established ground based and innovative space based GNSS measurements offer the unique chance for a permanent monitoring of the electron density structure of the global ionosphere–plasmasphere system. In this paper we review various types of perturbations in the ionospheric plasma density and distribution. In order to analyze these space weather effects we use 30 s sampled measurements provided by the global GPS ground tracking network of the IGS. Furthermore, to get a more comprehensive view on the perturbations analyzed also are simultaneously obtained GPS measurements onboard the LEO satellite CHAMP (challenging minisatellite payload). Whereas the ground based measurements show strong horizontal redistribution of plasma during ionospheric storms, the space-borne measurements indicate a severe vertical redistribution of the ionospheric plasma during the selected events. The role of the various dynamical forces such as meridional winds and electric fields is also discussed.