全球定位系统(GPS)技术的最新进展第五讲利用双频GPS观测值建立电离层延迟模型

介绍了电离层的概况，GPS信号在电离层中的传播，电离层改正模型以及利用GPS双频观测值来建立电离层延迟或VTEC模型的原理、方法和结果。     

对利用GPS观测值建立区域VTEC模型的研究

本文根据区域电离层延迟模型的原理与方法，利用载波相位、伪距两种GPS观测值建立了区域VTEC电离层模型，并利用地壳网络观测数据对模型的精度进行了检核。     

顾及高阶电离层延迟的BDS-3/GPS长基线网解精度分析

为了减弱BDS-3/GPS基准站数据处理中电离层延迟的影响,从而提高基准站坐标解算精度,采用BDS-3/GPS双频载波无电离层线性组合消除电离层延迟一阶项的影响,并引入全球垂直总电子含量VTEC文件削弱电离层延迟高阶项的影响.通过设计对比实验对24个MGEX基准站进行解算,分析了BDS-3和GPS解算过程中电离层延迟高...     

港珠澳大桥岛隧工程GNSS数据电离层延迟分析

利用IGS发布的最终电离层数据,分析了在港珠澳大桥岛隧工程区域经度(约E 114°)不同纬度的VTEC分布特征,并以电离层延迟为评价指标,采用TEQC软件对港珠澳大桥岛隧工程实测的GNSS数据进行了数据质量分析,得到结论:北半球沿114°E经线,纬度越低,VTEC日变化量越大,VTEC值越高;低纬度VTEC值在GPS时3~12h显著高于中高纬度;VTEC年变化量季节性特征明显;实测GNSS数据,多颗卫星的电离层延迟峰值超过20m,电离层延迟大于GNSS测量中的一般水平。     

基于JSCORS的区域电离层时空特征分析

本文利用JSCORS中心提供的连续两天的GPS观测数据,以及现有的提取垂直电离层延迟改正VTEC的软件,采用格网技术和常规单层VTEC模型,内插计算出区域格网的时空数据,对所得数据进行处理分析,得出了江苏南京附近大气层中电离层较为明显的特征。文章总结了该区域电离层的时空变化特征,为后续研究电离层更加细化的特征及其在各方面的应用等提供了依据。     

中国区域VTEC模型Kriging算法研究

为了对区域电离层延迟进行实时模型化,利用中国区域GPS实测资料,基于球冠谐函数模型、低阶球谐函数模型、多项式模型和Kriging内插方法,构建了电离层延迟模型。重点讨论了电离层垂直总电子含量(vertical total electron content,VTEC)的空间变异性、相关性的统计计算和Kriging内插估计方法,实现了中国区域VTEC格网实时建模。验证结果表明,高纬度地区VTEC拟合精度优于低纬度地区,Kriging内插估计和多项式模型结果的拟合内符合精度明显优于球冠谐函数模型和低阶球谐函数模型。但多项式拟合的格网,其方差则存在明显的边际效应,拟合区域中央精度较高,区域边缘地带精度明显下降;Kriging算法估计的格网点VTEC方差更符合实际情况,穿刺点多的地方,格网点精度较高。     

利用单基站GPS数据建立电离层VTEC模型

介绍几种常用的电离层VTEC模型.通过利用哈尔滨市CORS观测网络的单基站GPS双频观测数据建立多种电离层VTEC 模型,并对建模成果进行分析与研究.结果表明,模型选择和GPS卫星空间分布对建模有较大影响.     

单频GPS实时定位精度分析

电离层延迟误差是单频GPS实时/事后定位误差的一个重要来源,目前尚无有效的方法来削弱其影响。针对这一状况,该文首先介绍了单频GPS改正电离层延迟误差的常用方法,通过分析说明了电离层格网数据能够有效改善单频GPS实时/事后定位误差。给出了电离层格网数据的建立、预报方法,并详细介绍了刺入点地心经纬度VTEC值的计算方法、四点格网法内插刺入点天顶方向的总电子含量以及单层模型投影函数。结合算例,分析比较了不同类型电离层改正数据与卫星星历数据对单频GPS实时/事后定位精度的影响。实验结果表明,利用电离层格网预报数据能够显著改善单频GPS的实时/事后导航定位精度,对提高单频GPS定位精度具有一定实用价值。     

2010-08-01太阳风暴对电离层及GPS测量的影响分析

利用GPS电离层探测技术分析了2010-08-01太阳风暴对全球电离层VTEC造成的扰动异常影响。受朝向地球的日冕物质抛射影响,08-03首先对北美地区电离层VTEC产生扰动异常,最大值达到15TECu。由于地球自转,发生电离层VTEC异常集中的区域会随太阳直射点向西移动,一般发生于其所在区域的地方时13:00～17:00。另外,还分析了此次太阳风暴对GPS观测数据质量及电离层高阶项误差的影响。结果表明,此次太阳风暴期间,GPS观测数据质量并未受到明显的影响,但使得L1、L2载波的电离层高阶项误差增大,误差影响达到cm级。     

双向相位平滑伪距的硬件延迟解算研究

针对利用GPS观测数据提取TEC过程中最主要的误差来源硬件延迟问题,该文为了获取高精度TEC,在对双频观测数据处理时,改进了基于Hatch滤波的相位平滑伪距算法的使用方法,即双向平滑,取得较好的效果。研究采用了VTEC多项式和球冠谐分析模型来进行区域电离层建模及硬件延迟解算,经比较模型解算的硬件延迟与IGS发布值最大差异不超过1ns,其中VTEC多项式模型解80%差异值小于0.5ns,球冠谐函数模型解所有差异值均小于0.5ns。     

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.     

利用GPS监测电离层总电子含量的季节性变化

利用Georgiadiou电离层模型计算了GPS系统硬件延迟，从而由双频伪距观测值获取绝对电离层总电子含量值。利用北京IGS站的GPS观测数据分别计算了2000年和2004年各个不同月份的总电子含量值，对两年各月份的总电子含量进行多项式拟合，发现总电子含量的季节性变化趋势一致。     

Anomalies in broadcast ionospheric coefficients recorded by GPS receivers over the past two solar cycles (1992–2013)

The anomaly phenomenon of broadcast ionospheric model coefficients of the Global Positioning System (GPS) is revealed after analyzing the navigation file data collected from all the IGS (International GNSS Service) stations worldwide over a 22-year period (1992–2013). GPS broadcast ionospheric coefficients widely used by many single-frequency users to correct the ionosphere errors for numerous GPS applications are usually believed to have only one set/version per day. However, it is found that GPS receivers from the IGS network can report as many as eight sets/versions of ionospheric coefficients in a day. In order to investigate the possible factors for such an anomalous phenomenon, the relationship between the number of coefficient sets and solar cycle, the receiver geographic locations, and receiver types/models are analyzed in detail. The results indicate that most of the coefficients show an annual variation. During the active solar cycle period from mid-1999 to mid-2001, all of the coefficients extracted from IGS navigation files behaved anomalously. Our analysis shows that the anomaly is also associated with GPS receiver types/models. Some types/models of GPS receivers report one set/version of ionospheric coefficients daily, while others report multiple sets. Our analysis also suggests that the ionospheric coefficient anomaly is not necessarily related to ionospheric scintillations. No correlation between the anomaly and geographic location of GPS receivers has been found in the analysis. Using the ionospheric coefficient data collected from 1998 to 2013, the impact of ionospheric coefficient anomaly on vertical total electron content (VTEC) calculation using the Klobuchar model has been evaluated with respect to the Global Ionospheric Maps generated by the Center for Orbit Determination in Europe. With different sets of coefficients recorded on the same day, the resulting VTEC values are dramatically different. For instance on June 1, 2000, the largest VTEC at one of our test stations can be as large as 153.3 TECu (total electron content unit) using one set of coefficients, which is 16.36 times larger than the smallest VTEC of 9.37 TECu computed from using another set of coefficients.     

Accurate ionospheric delay model for real-time GPS-based positioning of LEO satellites using horizontal VTEC gradient estimation

Ionospheric delays compensation is a mandatory step for precise absolute and relative positioning of Low Earth Orbit Satellites (LEO) by GPS measurements. The most frequently used ionosphere model for real-time GPS-based navigation in LEO is an isotropic model proposed by Lear, which uses the Vertical Total Electron Content (VTEC) above the receiver and a mapping function for TEC evaluation along a given ray path. Based on significant assessed results available for ground-based GPS receivers, we propose the use of a different model relying on the thin shell assumption and a bilinear horizontal variation of the VTEC as a function of latitude and longitude in the shell. It is expected that this model is capable of better describing horizontal gradients in the ionosphere, thus improving ionospheric delay estimation, especially in intense ionospheric conditions. This model is referred to as Linear Thin Shell (LTS). LTS performance in estimating undifferenced and double-differenced ionospheric delays is checked by comparing measured and predicted delays computed using flight data from the GRACE mission. Results show that the LTS always outperforms the isotropic model, especially in case of high solar activity. Moreover, the LTS model provides a higher performance uniformity over a wide range of ionospheric delays, thus ensuring good performance in different conditions. The results obtained demonstrate that the LTS model improves the ionosphere delays estimation accuracy by 20 and 40% for undifferenced and double-differenced delays, respectively. This suggests the LTS model can effectively contribute to improving precision in LEO positioning applications.     

Computation of GPS P1–P2 Differential Code Biases with JASON-2

GPS Differential Code Biases (DCBs) computation is usually based on ground networks of permanent stations. The drawback of the classical methods is the need for the ionospheric delay so that any error in this quantity will map into the solution. Nowadays, many low-orbiting satellites are equipped with GPS receivers which are initially used for precise orbitography. Considering spacecrafts at an altitude above the ionosphere, the ionized contribution comes from the plasmasphere, which is less variable in time and space. Based on GPS data collected onboard JASON-2 spacecraft, we present a methodology which computes in the same adjustment the satellite and receiver DCBs in addition to the plasmaspheric vertical total electron content (VTEC) above the satellite, the average satellite bias being set to zero. Results show that GPS satellite DCB solutions are very close to those of the IGS analysis centers using ground measurements. However, the receiver DCB and VTEC are closely correlated, and their value remains sensitive to the choice of the plasmaspheric parametrization.     

Joint estimation of vertical total electron content (VTEC) and satellite differential code biases (SDCBs) using low-cost receivers

Vertical total electron content (VTEC) parameters estimated using global navigation satellite system (GNSS) data are of great interest for ionosphere sensing. Satellite differential code biases (SDCBs) account for one source of error which, if left uncorrected, can deteriorate performance of positioning, timing and other applications. The customary approach to estimate VTEC along with SDCBs from dual-frequency GNSS data, hereinafter referred to as DF approach, consists of two sequential steps. The first step seeks to retrieve ionospheric observables through the carrier-to-code leveling technique. This observable, related to the slant total electron content (STEC) along the satellite–receiver line-of-sight, is biased also by the SDCBs and the receiver differential code biases (RDCBs). By means of thin-layer ionospheric model, in the second step one is able to isolate the VTEC, the SDCBs and the RDCBs from the ionospheric observables. In this work, we present a single-frequency (SF) approach, enabling the joint estimation of VTEC and SDCBs using low-cost receivers; this approach is also based on two steps and it differs from the DF approach only in the first step, where we turn to the precise point positioning technique to retrieve from the single-frequency GNSS data the ionospheric observables, interpreted as the combination of the STEC, the SDCBs and the biased receiver clocks at the pivot epoch. Our numerical analyses clarify how SF approach performs when being applied to GPS L1 data collected by a single receiver under both calm and disturbed ionospheric conditions. The daily time series of zenith VTEC estimates has an accuracy ranging from a few tenths of a TEC unit (TECU) to approximately 2 TECU. For 73–96% of GPS satellites in view, the daily estimates of SDCBs do not deviate, in absolute value, more than 1 ns from their ground truth values published by the Centre for Orbit Determination in Europe.     

GNSS电离层延迟模型的数学统一与方法扩展

总结了当前广泛研究的利用GNSS观测数据建立电离层延迟模型的基本理论,并从数学上利用第一类算子方程统一现有的模型。着重分析了电离层VTEC的数学模拟和逼近方法,提出了建立模型的方法上的一系列扩展,从数学角度分析模型各种处理方式上的潜在问题,并给出了简单的单站模型计算实例,实证了理论的正确性。     

基于GPS的2003年10月28日太阳耀斑的电离层响应研究

本文利用VTEC(the Vertical Total Electron Contents)增量和VTEC变化率分析了电离层在2003年10月28日太阳耀斑期间中国的四个IGS跟踪站的响应情况.通过分析比较说明用VTEC变化率似更适合探测电离层对太阳耀斑的响应,并有望发现耀斑期间电离层的一些扰动现象,但在能得到高精度的绝对离层延迟的情况下,利用VTEC增量能准确全面地反映电离层对耀斑响应的整体变化情况.     

不同NeQuick电离层模型参数的应用精度分析

Galileo采用NeQuick作为全球广播电离层模型,其实际应用中以有效电离水平因子Az代替太阳活动指数作为NeQuick的输入参数,并利用二次多项式拟合得到广播星历中播发的3个电离层参数。本文在总结和讨论NeQuick模型参数估计方法及其变化特征的基础上,分别以全球电离层格网、GPS基准站及JASON-2测高卫星提供的电离层TEC为参考,分析不同NeQuick模型参数(包括以太阳活动参数F10.7为输入的NeQuick2、以本文解算参数为输入的NeQuickC和以Galileo广播电离层参数为输入的NeQuickG)在全球大陆及海洋地区的应用精度,并与GPS广播的Klobuchar模型对比。结果表明,NeQuickG在全球范围内的修正精度为54.2%~65.8%,NeQuickC的修正精度为71.1%~74.2%,NeQuick2的修正精度与NeQuickG相当,略优于GPS广播星历中播发的Klobuchar模型。