The influence of ionospheric thin shell height on TEC retrieval from GPS observation

We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content（TEC） derived from a small scale Global Positioning System（GPS） network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as～8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of～3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350-500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

Monitoring Seasonal Variations of Ionospheric TEC Using GPS Measurements

The regional ionospheric model is adopted to determine satellite-plus-receiver differential delay. The satellite-plus-receiver differential delay is estimated as constant values for each day. Dual-frequency GPS pseudo-ranges observables are used to compute vertical TEC (VTEC). All the monthly mean VTEC profiles are represented by graphs using GPS data of the Beijing IGS site between 2000 and 2004. The monthly averaged values and amplitudes of VTEC are also represented by graphs. The results indicate that the VTEC has seasonal dependency. The monthly averaged values and amplitudes of VTEC in 2000 are about 2 times larger than that in 2004. The maximum VTEC values are observed in March and April, while the minimum VTEC values are observed in December. The seasonal variations trend is found to be similar after polynomial fitting between 2000 and 2004.

2000年7月和2003年10月大磁暴期间东亚地区中低纬电离层的GPS TEC的响应研究

利用武汉电离层观象台研制的GPSTEC的现报方法及现报系统,对东亚地区GPS台网的观测数据进行处理分析,特别对2000年7月14-18日和2003年10月28日至11月1日两次特大磁暴期间的数据进行了对比考察.文中分析了两次磁暴间的电离层响应,得到对应不同磁暴时段电离层TEC的不同变化情况,着重揭示了TEC赤道异常峰的压缩和移动以及赤道异常随时间的压缩-反弹-恢复的过程,并结合高纬电离层的部分响应机制进行了说明.结果显示,两次磁暴期的电离层响应表现出了各自不同的特点,从而反映出因季节变化引起的高纬电离层暴时能量注入的不同而造成的全球性电离层扰动的不同形态.由此看出,磁暴期间电离层TEC的变化直接与太阳扰动发生的时间及其对高纬电离层的耦合有关.若短时期内连续发生多次磁暴,则电离层反应更加复杂,不能简单地当做单一磁暴叠加处理.

GPS TEC硬件偏差估计方法的有效性

以我国GPS广域差分系统(WAAS)电离层误差改正问题为背景,利用分布在不同纬度上的8个GPS台站2000年2日到60日连续59天的观测数据,评估了典型的GPS TEC硬件偏差求解方法的精度和有效性。结果表明,采用同样的求解方法,处理磁暴期间以及磁纬较低台站的数据得出的结果的稳定性明显下降。因此,在求解 GPS TEC硬件偏差值时,审慎选择所利用的现测数据和方法是十分必要的。

基于GPS TEC的尼泊尔MW7.8地震同震电离层扰动研究

基于GPS数据对2015年尼泊尔M W7.8地震引起的同震电离层扰动进行统计与FFT频谱分析,探究地震电离层TEC扰动传播的时空特性。结果表明,震后5 min起出现明显的TEC扰动异常现象,持续时间超过6 min,呈现增大-减小-增大的变化趋势;扰动由震中向东、东北等方向传播,速率分别为2336.36 m/s和455.52~937.64 m/s;扰动的中心频率为3~7 mHz,符合瑞利波与声波引发的扰动频段。

SAMI2物理模型与东亚扇区GPS TEC数据比较研究

SAMI2(Sami2 is Another Model of the Ionosphere)是美国海军实验室开发的电离层物理模型.利用该物理模型,模拟了东亚扇区不同太阳活动强度、不同纬度地区三个站的电离层电子浓度总含量(TEC).通过模拟结果与GPS观测站TEC数据的比较,检验SAMI2在此扇区的电离层TEC计算精度.结果表明,物理模型输出的电离层TEC具备与观测数据一致的周日变化、季节变化,太阳活动变化.周日分布上,上午时段SAMI2 TEC与观测数据吻合度优于午后时段;季节分布上,SAMI2 TEC在冬季与观测值偏差小于其他季节;SAMI2 TEC与GPS TEC相关系数各站均达到0.87以上,与赤道地区Guam站相关性最好;太阳活动低年计算结果优于太阳活动高年;多数情况下,SAMI2 TEC相对GPS TEC偏大.本文结果为基于SAMI2模型构建背景误差分布特征,开展该区域电离层数值预报研究可行性提供了理论支持.

磁暴期间南极South Pole站和McMurdo站电离层闪烁与GPS TEC时空变化相关性研究

目前,对电离层闪烁特性的研究大多集中在低纬度地区,而在极区,特别是在南极地区,由于测量数据稀少,所以研究十分有限。借助安装在南极South Pole站和Mc Murdo站的GPS闪烁监测仪,获取到实测的电离层闪烁数据,同时结合IGS网站提供的同址GPS观测数据,分析了2011年9月24—25日磁暴发生前,9月26日磁暴发生时以及9月27日磁暴发生后GPS L波段信号电离层相位闪烁和GPS TEC时空变化特征。分析显示,这次磁暴对电离层的一个重要的影响是在电离层扰动剧烈期间,相位闪烁活动及其强度在时间和空间分布上都显著增强。研究结果发现,在强电离层闪烁期间,实测的相位闪烁指数σ_Φ与由GPS观测数据推算的TEC变化率指数(ROTI)的变化非常相似,两者之间呈现出良好的相关性。从而证明,在如南极等缺乏独立电离层闪烁观测值的地区,GPS ROTI可以作为表征电离层闪烁的重要可选参数,进而可以借助全球分布的GPS观测数据来分析和研究电离层闪烁特性。

利用GPS TEC探测2015年尼泊尔地震激发的电离层扰动

利用尼泊尔周边区域6个IGS GPS跟踪站数据,对2015-04-25尼泊尔地震激发的电离层扰动进行分析。结果表明,地震发生后,尼泊尔上空电离层总电子含量(total electron content,TEC)存在不同频率的电离层扰动,扰动中心频率约为3mHz和4mHz。前者发生在震中附近1 000km左右的范围,后者范围达2 000km,推断其分别为地震破裂产生的声重波信号以及瑞利波向上传播到电离层所激发的异常扰动信号。联合两个频率扰动信号,根据观测的扰动位置以及经验扰动速度反演震中位置,结果与实际情况符合较好。

Ionospheric disturbances following the March 2015 geomagnetic storm from GPS observations in China

When strong solar activities and geomagnetic storms happen, satellite communications and navigation system will be strongly disturbed. It is of great significance to monitor ionospheric disturbances,because empirical models cannot capture ionospheric anomalous disturbances well. Nowadays, dualfrequency GPS(Global Positioning System) observations can be used to estimate the ionospheric total electron content, correct the ionospheric delay and analyze the response of the ionosphere to geomagnetic storms. In this paper, the ionospheric response to the geomagnetic storm occurred in March 2015 is investigated using GPS observations provided by Crustal Movement of Observation Network of China. The result shows that this storm increases the electron density in the ionosphere quickly and disrupts the structure of the northern equatorial anomaly region at the beginning. In the main process stage, compared with that in the quite periods, the VTEC(Vertical Total Electron Content)around the longitude of 120°E decreases by 50% and the amount of depletion is larger in the high latitude region than that in the low latitude region. We also find the height of the peak electron density in F2 layer increases during the geomagnetic storm from the electron density profiles derived from GPS occultation mission.

基于GPS技术实时监测2009年7月22日日全食期间长三角区域电离层TEC变化

2009年7月22日上午发生的日全食是21世纪持续时间最长的日全食,其全食带覆盖了中国中部的长江流域,为研究日全食对电离层的影响提供了一次难得的机会.为此本文通过卡尔曼滤波算法实现了实时求解TEC和GPS系统硬件延迟,为实时监测日全食期间电离层变化提供了绝对的电离层TEC.采用上海和浙江区域内GPS网的观测数据,建立了实时区域电离层延迟模型,进而计算出了实时的VTEC和TEC变化率.同时考虑太阳和地磁活动参数,综合上述方法详细分析和讨论了长三角区域在此次日全食期间的TEC变化的电离层异常现象.

GPS系统硬件延迟估计方法及其在TEC计算中的应用

给出了用于估计GPS系统硬件延迟的卡尔曼滤波的状态方程和观测方程 ,在卫星和接收机相对硬件延迟计算方法的基础上 ,进一步给出了滤波器初值的计算方法 ,然后给出了GPS系统硬件延迟和卫星相对于平均值的硬件延迟的计算结果 ,并对GPS系统硬件延迟及卫星和接收机硬件延迟的稳定性进行了评价 ,结果表明 ,在两个半月的时间里 ,它们是非常稳定的 ,最后通过TEC的计算结果及其与滤波估计的比较证明了本文方法的正确性 .

利用GPS对磁暴期间极区TEC变化与极区碎片(Polar Patches)的研究

利用2004年11月6-10日磁暴发生期间南极区域内的中国中山站GPS常年跟踪站（ZHON）和国际GPS服务站（CAS1,MCM4,SYOG,MAW1）的GPS观测数据,计算了可观测卫星传播路径上的TEC和ROT值,进而依据TEC的波动频率和幅度推估出极区碎片的个数,分析了极区磁暴期间电离层响应及其极区碎片特性.最终所得TEC和ROT结果与极区地磁场Dst和Kp指数信息相吻合,如实地反映了磁暴事件和极区碎片的出现.本文所做工作在国内尚未开展,因此所用方法和结论为将来这一方向的研究提供了一定的参考.

基于GPS数据的地震前电离层TEC异常研究

选取印度洋区域7个IGS站,运用2004年12月26日印度洋地震前后共计25 d的GPS观测数据,计算出高时空分辨率的VTEC。综合考虑了太阳和地磁活动参数,运用统计分析的方法,详尽阐释了地震发生前TEC减小的电离层异常现象。

电离层GPS掩星观测改正TEC反演方法

电离层掩星观测中,当低轨卫星(LEO)轨道高度较低时,轨道以上的电离层电子总含量(TEC)对掩星反演的影响不能忽略.目前,一般采用指数函数等外推方法来处理该问题,对反演结果可能引起较大误差.为提高电离层掩星反演精度,本文研究利用LEO处于非掩星一侧GPS观测数据的改正TEC新反演方法.用三维射线追踪程序计算出电离层掩星观测模拟数据,分别应用改正TEC方法和外推方法进行反演,将反演结果与所用模式值进行比较.结果表明:对于轨道高度约800km的GPS MET掩星模拟数据,外推方法和改正TEC方法反演结果都与模式值基本一致;对于轨道高度约400km的CHAMP掩星模拟数据,外推方法误差较大,改正TEC方法反演结果与模式值相符得较好.将改正TEC方法应用于GPS MET实测数据的反演,取得了合理的结果.这些说明,改正TEC算法是一种有效的电离层掩星反演方法,尤其是对于轨道较低的LEO的电离层掩星观测反演特别有用.

用GPS观测研究电离层TEC水平梯度

双频GPS用户能自动修正电离层总电子含量(TEC)引起的延时误差,但是对于电离层中的不规则体造成的信号闪烁而引起的误差则不能消除.即使是差分GPS系统,电离层误差仍然是其主要的误差源,其中电离层TEC梯度将会影响到系统的定位精度和性能.本文用GPS方法研究了电离层TEC的水平梯度问题,用处于赤道异常区NTUS台站的GPS观测数据作了具体计算.结果表明,在日落以后到子夜前后电离层垂直TEC出现了大的涨落,电离层中的不规则体导致L波段信号强的闪烁,同时还伴随着大而快速变化的电离层TEC水平梯度.对比发现,ROTI指数、电离层TEC水平梯度和电离层垂直TEC三者之间有很好的对应关系,它们的变化特征均由电离层中的不规则体引起.我们认为研究电离层闪烁,特别是在缺乏S_4指数时,电离层TEC梯度也可以作为一个重要的可选参数.

基于双频GPS观测的电离层TEC与硬件延迟反演方法

利用全球定位系统(Global Positioning System,GPS)的双频观测数据反演得到电离层的总电子含量(Total Electron Content,TEC),使得广域甚至全球范围高时空分辨率的电离层观测研究成为可能,但由于GPS卫星和接收机对信号的硬件延迟可导致TEC测量系统偏差,因此,需要探索反演TEC并估测GPS卫星与接收机硬件延迟的有效算法.本文根据电离层电波传播理论,阐述了基于双频GPS观测提取电离层TEC的方法,给出TEC与硬件延迟的基本关系.综合研究了TEC与硬件延迟的反演方法,进行分析与归纳分类,在此基础上提出了有待深入研究的问题.

基于MATLAB-GUI的GPS电离层TEC插值软件设计与实现

本文介绍了由IGS提供的关于电离层总电子含量TEC的数据文件IONEX,其包含的数据在时间和地理位置上是不连续的,利用插值方法计算不连续的时间和地理位置的TEC数值。运用MATLAB图形用户界面(GUI)的设计功能并结合其数据处理和绘图功能,设计关于GPS TEC数据处理的软件,按照区域(包括某特定地理位置)、时间为划分绘制TEC分布图或者变化图。通过实际应用,该软件的各功能界面能够独立运行并实现预期的数据处理和绘图等功能。

GPS-based regional ionospheric models and their suitability in Antarctica

There are a number of ionospheric models available for research and application, such as the polynomial model, generalized trigonometric series function model, low degree spherical harmonic function model, adjusted spherical harmonic function model, and spherical cap harmonic function analysis. Using observations from more than 40 continuously operating stations across Antarctica in 2010, ifve models are compared with regard to their precision and applicability to polar regions. The results show that all the models perform well in Antarctica with 0.1 TECU of residual mean value and 2 TECU of root mean square error.

Manifestation of earthquake preparation zone in the ionosphere before 2021 Sonitpur,Assam earthquake revealed by GPS-TEC data

Global Positioning System(GPS)Continuously Operating Reference Station(CORS)data analysis shows that the ionosphere’s electron density variability is linked to the deformation and stress accumulation in the Earth’s crust.Anomalies in ionosphere total electron content(TEC)variability before 2021 M6.4 Sonitpur,Assam earthquake were detected using L1 and L2 GPS frequencies that showed three distinct abnormalities on April 3,9,10,2021.Pearson’s correlation coefficient(r)of TEC decreases in the CORS that lies away from the earthquake epicenter,indicating the possibilities of a positive relationship between TEC variability and earthquake epicenter.TEC concentration also decreases towards the epicenter within the earthquake preparation zone(EPZ).It is also observed that the Pearson’s correlation coefficient(r)of TEC decreases linearly near the EPZ.The study demonstrates the possibilities of determining the TEC anomalous zone in the ionosphere that coincides with the EPZ in the crustal rocks.The research indicated the possibilities of magnitude estimation of an impending earthquake based on the TEC anomalous zone in the ionosphere using closely spaced dense CORS network data.

Pre-seismic ionospheric anomalies of the 2013 Mw=7.7 Pakistan earthquake from GPS and COSMIC observations

The seismo-ionospheric anomalies may provide some insights about the earthquake.However,preseismic ionospheric anomalies are still challenging.In this paper,seismo-ionospheric anomalies are investigated before the September 24,2013(Mw=7.7)Awaran(Pakistan)earthquake from GPS TEC(Total Electron Content)and COSMIC(Constellation Observing System for Meteorology,Ionosphere and Climate)data.The TEC data are showing anomalies on September 21,2013.The abnormality detected in the temporal data is about 10 TECU beyond the 30-day running median.The percentage deviation of the TEC anomaly on September 21,is 30% above the upper confidence interval.The anomalies prevail 5 in Latitude and 10 in Longitude over the epicenter.The spatial and temporal data of TEC showed anomalies in TEC from UT=08 to UT=12.In addition,the enhancement on September 21,2013 is also very significant in COSMIC data.The results of COSMIC completely agreed with GPS TEC anomalies on September 21,2013.The percentage deviation of the peak plasma frequency on September 21 is 5% of the normal distribution.The storm indices are quiet before and after the earthquake.The pre-sesimic ionospheric anomalies are most probably associated with the 2013 Mw=7.7 Awaran(Pakistan)earthquake.