南极电离层特征的球冠谐分析

针对国际GNSS服务(IGS)各电离层分析中心发布的全球电离层图(GIM)在南极地区精度有限的问题,该文在收集IGS、极地对地观测网络(POLENET)计划和中国南极测绘研究中心(CACSM)的GPS数据的基础上,采用球冠谐分析理论建立了南极地区电离层电子总含量(TEC)模型。通过球冠谐分析的零阶项系数表示的日均值与实测TEC日均值的对比,表明二者具有很强相关性,验证了球冠谐分析具有良好的物理意义,可以有效提取南极电离层的周期特征。利用球冠谐函数模型对全南极电离层在2012年季节变化、空间分布和10月地磁暴期间的响应特征进行了分析。实验结果表明,基于球冠谐分析构建的电离层模型更适用于探测南极电离层的特征。     

利用GPS三频观测值监测电离层TEC及其变化率

三频观测数据为监测电离层总电子含量提供了更多的观测值选择。在双频观测值估算电离层总电子含量的原理基础上,利用不同纬度地区的三频GPS观测资料计算获得了电离层总电子含量值及其变化率。分析结果表明：由于GPS接收机码间偏差的影响,不同频率间组合获得的电离层总电子含量结果出现较大的系统差异,使用不同频率组合获得的电离层TEC变化率有很好的一致性。     

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。     

利用球冠谐函数和时间序列分析预报南极地区电离层

利用球冠谐函数和时间序列分析实现了南极地区电离层预报。首先,通过南极地区的GPS实测数据提取高精度的电离层总电子含量,并建立了极区球冠谐函数模型;然后,对不同时间段形成的模型系数时间序列进行了谱分析得到周期项,利用傅里叶三角级数拟合并预报趋势项;最后,利用时间序列分析理论中的ARMA(p,q)模型对剔除了趋势项的随机信号部分进行预报。结果表明,一天内电离层预报精度在1TECU,三天内在1.5TECU。     

利用GPS观测值监测电离层的时空变化

研究电离层时空变规律对卫星导航、航空航天和通讯等具有重要价值。文中利用IGS站提供的GPS双频观测数据,采用区域电离层模型估计GPS系统硬件延迟,从而计算绝对电离层总电子含量。在时间尺度上,选择COR1站的2012年、2015年和2017年的数据进行时间变化分析,结果表明,电离层总电子含量在时间上呈现出周日变化、月变化和季节性变化。在空间方面,选择了经度相差较小、纬度方向分布均匀的CRO1、BRMU、UNBJ和QIKI四个IGS站进行分析,结果表明在纬度方向具有明显的单峰效应,随着纬度的增大电离层总电子含量呈现减小趋势。      

利用单站地基GPS数据反演电离层电子密度

利用单站GPS观测数据对GPS硬件系统延迟作出修正,得到较精确的电离层总电子含量。根据Chapman电离层理论,建立电离层模型,利用遗传算法优化选择电离层关键参量,反演得到接收机上空电子密度剖面,结果表明：该方法用于太阳活动高年白天电子密度剖面反演效果优于国际参考电离层。     

NeQuick2电离层改正模型的性能评估

NeQuick2电离层改正模型是在NeQuick1模型基础上改进而来的。利用GPS实测观测值在不同卫星截止高度角情况下获得的斜路径总电子含量作为参考,对该电离层模型性能进行评价,并与常用的国际参考电离层和Klobuchar电离层模型进行比较。结果表明,NeQuick2模型获得的斜向总电子含量与实测差值的标准差保持在15TECU以内,其稳定性显著优于国际参考电离层和Klobuchar模型。     

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...     

基于GPS电离层测量的SAR成像补偿技术

本文在总结电离层中信号传播时延特性的基础上,提出了一种使用基于GPS电离层测量总电子含量(TEC)改进SAR成像的方法。由模拟的低频SAR经过电离层后的成像情况证明,电离层的影响十分严重。当使用GPS测量的路径TEC进行校正后,可以重新得到比较理想的成像效果。      

基于GPSTk的区域电离层TEC地图重构

电离层是影响卫星导航系统传输时延的重要因素之一,电离层总电子含量(TEC)地图重构是消除电离层传输时延的重要手段。GPSTk作为GPS数据处理的重要软件之一,可以满足区域电离层TEC地图的重构要求。本文针对GPSTk的特点,深入研究了GPSTk的电离层TEC计算原理、数据处理流程及具体的软件操作方法,该研究对基于GPS数据的电离层数据处理软件的研制具有一定的参考意义。     

不同海潮模型对东南极沿海地区GPS基线解算的影响

在高精度GPS数据处理中,海潮的影响是一个不可忽略的因素。利用GAMIT软件解算2011年东南极沿海地区中国中山站及其周边6个IGS站的GPS数据,对比分析了FES2004、DTU10、EOT11a、GOT4.7、HAMTIDE11a、OSU12以及TPXO7.2等7个全球海潮模型在不同测站的海潮负荷差异,比较了海潮负荷对于GPS基线解的影响。结果表明,海潮负荷对GPS基线解的影响与测站所处位置及基线方位有关,达到cm级,相对影响达到10-8,因此,在高精度的GPS基线解算中必须考虑海潮的影响;但选用不同海潮模型对东南极沿海地区GPS基线解算的差异可忽略不计。     

FORMOSAT-3/COSMIC observations of the ionospheric auroral oval development

The ionospheric radiance and electron density observed by the tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) payloads on FORMOSAT-3/COSMIC satellites are applied to determine the boundaries of the auroral oval and its width in the winter nighttime ionosphere for both hemispheres. The TIP collects ionospheric emission at 135.6 nm due to electron impact excitation, while the GOX offers ionospheric electron density profiles with radio occultation (RO) technique. Comparison between them shows similar patterns of the plasma structure in the polar caps. The mean width of the auroral bands ranges between about 2 and 11° latitude in the winter nighttime and it varies with longitudes. The comparison by month suggests that the mean radius of the auroral ovals varies with the intensity of the auroral radiance.     

Improving the estimation of fractional-cycle biases for ambiguity resolution in precise point positioning

Ambiguity resolution dedicated to a single global positioning system (GPS) station can improve the accuracy of precise point positioning. In this process, the estimation accuracy of the narrow-lane fractional-cycle biases (FCBs), which destroy the integer nature of undifferenced ambiguities, is crucial to the ambiguity-fixed positioning accuracy. In this study, we hence propose the improved narrow-lane FCBs derived from an ambiguity-fixed GPS network solution, rather than the original (i.e. previously proposed) FCBs derived from an ambiguity-float network solution. The improved FCBs outperform the original FCBs by ensuring that the resulting ambiguity-fixed daily positions coincide in nature with the state-of-the-art positions generated by the International GNSS Service (IGS). To verify this improvement, 1?year of GPS measurements from about 350 globally distributed stations were processed. We find that the original FCBs differ more from the improved FCBs when fewer stations are involved in the FCB estimation, especially when the number of stations is less than 20. Moreover, when comparing the ambiguity-fixed daily positions with the IGS weekly positions for 248 stations through a Helmert transformation, for the East component, we find that on 359 days of the year the daily RMS of the transformed residuals based on the improved FCBs is smaller by up to 0.8?mm than those based on the original FCBs, and the mean RMS over the year falls evidently from 2.6 to 2.2?mm. Meanwhile, when using the improved rather than the original FCBs, the RMS of the transformed residuals for the East component of 239 stations (i.e. 96.4% of all 248 stations) is clearly reduced by up to 1.6?mm, especially for stations located within a sparse GPS network. Therefore, we suggest that narrow-lane FCBs should be determined with ambiguity-fixed, rather than ambiguity-float, GPS network solutions.     

GPS tomography in the polar cap: comparison with ionosondes and in situ spacecraft data

Tomographic 4D reconstructions of ionospheric anomalies appearing in the high-latitude polar cap region are compared with plasma density measurements by digital ionosonde located near the north magnetic pole at Eureka station and with in situ plasma measurements on-board DMSP spacecraft. The moderate magnetic storm of 14–17 October 2002 is taken as an example of a geomagnetic disturbance which generates large-scale ionospheric plasma anomalies at mid-latitudes and in the polar cap region. Comparison of the GPS tomographic reconstructions over Eureka station with the ionosonde measurements of the F layer peak densities indicates that the GPS tomography correctly predicts the time of arrival and passage of the ionospheric tongue of ionization over the magnetic pole area, although the tomographic technique appears to under-estimate the value of F peak plasma density. Comparison with the in situ plasma measurements by the DMSP SSIES instruments shows that the GPS tomography correctly reproduces the large-scale spatial structure of ionospheric anomalies over a wide range of latitudes from mid-latitudes to the high-latitude polar cap region, though the tomographic reconstructions tend to over-estimate the density of the topside ionosphere at 840 km DMSP orbit. This study is essential for understanding the quality and limitations of the tomographic reconstruction techniques, particularly in high-latitude regions where GPS TEC measurements and other ionospheric data sources are limited.     

A velocity field estimation of the Brazilian portion of the SOAM plate

With the proposition for the adoption of Geocentric Reference System for the Americas (SIRGAS) as a terrestrial reference frame for South America, the need for temporal monitoring of station coordinates used in its materialization has become apparent. This would provide a dynamic characterization of the frame. The Brazilian Network for Continuous Monitoring of GPS (RBMC) has collected high accuracy GPS measurements since 1996. The Brazilian Institute of Geography and Statistics (IBGE) maintains this network in collaboration with several universities and organizations. Most of the stations are also part of the SIRGAS network. The RBMC also contributes data to the International Terrestrial Reference System (ITRS) to densify the global frame. Two of the RBMC stations are also part of the International GPS Service (IGS). This paper reports initial results from these stations. To estimate the velocity field defined by these stations, ten IGS stations located on the border of the South American plate and in adjacent plates, along with nine RBMC stations, were used. Observations covering five groups of 15 days each were used. These groups of observations were at epochs 1997.3, 1997.9, 1998.3, 1998.9 and 1999.2. Seven IGS stations were chosen to have their coordinates constrained to those epochs. IGS products (precise ephemeris and clocks) were used to process the daily solutions, which were carried out with Bernese software. Carrier phase double differences were formed using the ionospheric-delay free observable. The troposphere was modeled using a combination of the Saastamoinen model and the Niell mapping function. A tropospheric parameter was estimated every two hours. The results of the daily baseline solutions were combined using the summation of normal equations technique, in which the final coordinates and velocities were estimated. The results were compared with various models, such as the NNR-NUVEL1 and the APKIM8.80. Velocity vectors estimated for the RBMC stations show good agreement with those two models, with rates approximately equal to 2 cm/year.     

Seasonal and secular positional variations at eight co-located GPS and VLBI stations

Time series of daily position solutions at eight co-located GPS and VLBI stations are used to assess the frequency features in the solutions over various time-scales. This study shows that there are seasonal and inter-annual signals in all three coordinate components of the GPS and VLBI solutions. The power and frequency of the signals vary with time, the station considered and the coordinate components, and between the GPS and VLBI solutions. In general, the magnitudes of the signals in the horizontal coordinate components (latitude and longitude) are weaker than those in the height component. The weighted means of the estimated annual amplitudes from the eight GPS stations are, respectively, 1.0, 0.8 and 3.6 mm for the latitude, longitude and height components, and are, respectively, 1.5, 0.7 and 2.2 mm for the VLBI solutions. The phases of the annual signals estimated from the GPS and VLBI solutions are consistent for most of the co-located stations. The seasonal signals estimated from the VLBI solutions are, in general, more stable than those estimated from the GPS solutions. Fluctuations at inter-annual time-scales are also found in the series. The inter-annual fluctuations are up to ∼5 mm for the latitude and longitude components, and up to ∼10 mm for the height component. The effects of the seasonal and inter-annual variations on the estimated linear rates of movement of the stations are also evaluated.     

遮挡环境下GPS／GLONASS／Galileo组合PPP性能分析

对于城市遮挡环境下单GPS系统精密单点定位(PPP)性能较差的问题,本文采用多系统融合来改善PPP性能,通过不同卫星高度角,将城市四周环境分为正常环境、一般遮挡、较重遮挡等三种环境.分别采用GPS、GPS／GLONASS、GPS／Galileo、GPS／GLONASS／Galileo不同的模式,对香港4个连续运行参考站进行遮挡环境下的静态PPP模拟实验,结果表明:多系统组合能够有效弥补城市四周遮挡环境下卫星的不足,并且GPS／GLONASS、GPS／Galileo、GPS／GLONASS／Galileo组合相对单GPS系统下的PPP性能有着不同程度的改善.      

电离层延迟高阶项对GPS精密单点定位精度影响分析

随着GPS卫星轨道、钟差及各种误差修正模型的不断精化,静态精密单点定位(PPP)定位精度达到mm级,进行电离层延迟高阶项较小量级的误差改正研究,对改进PPP数据处理策略具有重要的参考价值。本文利用分布在不同地理纬度的5个IGS跟踪站3天的观测数据,对比分析了电离层延迟二阶项、三阶项对GPS观测值精度及静态PPP定位精度的影响。分析结果表明,电离层延迟二阶项、三阶项对GPS观测值精度的影响分别为cm级和mm级,对低纬度地区PPP定位精度的影响大于3 mm,但对中高纬度的测站观测值、定位精度的影响比低纬度地区小很多。      

区域性跟踪站地心坐标精化方法及定轨试验分析─中国GIG′91和IGS′92会战数据处理分析

本文介绍了中国GIG’91和Epoch’92二次GPS会战的情况,着重分析了GIG’91和Epoch’92会战数据处理的结果。结果证明,利用1－2星期质量良好的数据（含分布均匀的部分全球跟踪站数据）,解算的未知区域性跟踪站地心坐标的重复性可以达到几个厘米,站间基线分量的重复性可以达到10－8或更好。利用中国国内4个跟踪站的数据,由5天轨道弧解算的卫星星历与全球精密星历之差在1－3米水平,平均差一般小于1米。我们的研究证明,参加GPS国际会战,是迅速提高区域性跟踪站地心坐标精度和建立区域性高精度地心坐标框架的有效途径,利用区域性跟踪站可有效地改进GPS卫星轨道的精度,形成全国范围的大尺度的控制,进一步改进GPS测量的精度。