MGEX广播星历轨道和钟差的精度评估

为了对MGEX提供的广播星历产品进行精度评估，本文推导了广播星历计算卫星在地固坐标系下位置的数学模型，归纳了精密星历对广播星历进行评估的基本原理和方法，借助MGEX系统提供广播星历产品，对比分析了MGEX系统提供的GPS卫星广播星历轨道及钟差的误差平均值和RMS值。试验结果表明：除个别卫星轨道误差RMS超过4 m，钟差误差平均值大于8 ns外，MGEX提供的7 d和27 d的广播星历产品的轨道精度都优于3 m，钟差误差小于6.5 ns。本文为使用MGEX广播星历的用户提供了参考依据。     

Baltic Sea Level project with GPS

In order to study the Baltic Sea Level change and to unify national height systems a two week GPS campaign was performed in the region in Autumn 1990. Parties from Denmark, Finland, Germany, Poland and Sweden carried out GPS measurements at 26 tide gauges along the Baltic sea and 8 VLBI and SLR fiducial stations with baseline lengths ranging from 230 km to 1600 km. The observations were processed in the network mode with the Bernese version 3.3 software using orbit improvement techniques. To get rid of the scale error introduced by the ionospheric refraction from single-frequency data, the local models of the ionosphere were estimated using L4 observations. The tropospheric zenith corrections were also considered. The preliminary results show average root mean square (RMS) errors of about ±3 cm in the horizontal position and ±7 cm in the vertical position relative to the Potsdam SLR station in ITRF89 system. After transformation of the GPS results to geoid heights using the levelled heights, an absolute comparison with gravimetric geoid heights using the least squares modification of Stokes' formula (LSMS), the modified Molodensky and the NKG Scandinavian geoid 1989 (NGK-89) models gives a standard deviation of the difference of ±7cm to ±9cm for the NKG-89 model and of ±9cm to ±30cm for the LSMS and the modified Molodensky model. The Swedish height system is found to be about 8-37cm higher than those of the other Baltic countries for NKG-89 model.     

Swarm系列卫星非差运动学厘米级精密定轨

采用2015年5月24日—30日的Swarm星载GPS双频观测数据,基于Melbourne-Wübbena(MW)和消电离层线性组合,在精密单点定位技术的基础上,采用批处理最小二乘估计法对不同轨道高度的Swarm系列卫星进行非差运动学精密定轨。利用星载GPS相位观测值残差、与欧空局发布的简化动力学轨道对比,以及SLR检核3种方法对Swarm系列卫星非差运动学定轨结果进行精度评估。结果表明:①Swarm系列卫星星载GPS相位观测值残差RMS为6~7 mm;②与欧空局发布的简化动力学轨道进行求差,径向、切向及法向轨道差值RMS为2~4 cm;③与欧空局发布的运动学轨道进行求差,径向、切向及法向轨道差值RMS为1~2 cm;④SLR检核结果表明Swarm-A/B/C卫星轨道精度为3~4 cm。因此,采用非差运动学定轨方法与本文提供的定轨策略进行Swarm系列卫星精密定轨是切实可行的,定轨精度为厘米级。     

广域实时精密定位与时间服务系统

广域实时精密定位与时间服务已成为GNSS应用领域研究热点,目前国内外学者围绕其模型算法已展开大量的研究。本文重点论述广域实时精密定位与时间服务数据的处理方法和服务系统,给出了基于不同基准约束的卫星钟差解算数学模型,提出通过引入外接原子钟测站、标准时间源(UTC/BDT)等不同时间基准,构建卫星拟稳基准、外接原子钟跟踪站拟稳基准及标准时间源等约束下的钟差解算模型,分析了时间基准对精密单点定位和精密单点授时的影响。本文采用实时卫星轨道、钟差、相位偏差、电离层延迟等服务产品及跟踪站实时数据,验证了系统产品可靠性及终端定位与时间服务性能。实测结果表明:GPS轨道径向精度1.8 cm,钟差STD精度约0.05 ns;BDS-3轨道径向精度6.7 cm,钟差STD精度优于0.1 ns;GPS和BDS-2电离层改正精度分别为0.74 TECU与1.03 TECU。基于该产品实现了用户端PPP、PPP-RTK及PPT、PPT-RTK服务,满足了用户实时厘米级定位和优于0.5 ns的单站时间传递服务,当采用GPS+BDS-2 PPP-RTK解算时,平面收敛至5 cm约需要12 min。     

基于星载GPS数据的Jason-3卫星简化动力学和运动学法精密定轨

利用Jason-3星载GPS观测数据,采用简化动力学方法和运动学方法对Jason-3卫星进行精密定轨研究. 通过载波相位残差、重叠轨道对比、参考轨道对比和卫星激光测距(SLR)轨道检核四种方式评定轨道精度. 计算相位残差均方根(RMS)值,简化动力学轨道的RMS值在0.7～0.8 cm,运动学轨道的RMS值在0.50～0.55 cm;简化动力学轨道重叠部分径向RMS值达到0.32 cm,运动学轨道重叠部分径向RMS值达到1.12 cm;与国际DORIS服务(IDS)官方提供的参考轨道对比,简化动力学轨道径向精度达到1.47 cm,运动学轨道径向精度达到4.36 cm;利用SLR观测数据进行核验,简化动力学轨道精度整体优于2.1 cm,运动学轨道精度整体优于3.3 cm. 通过实验证明:Jason-3卫星的简化动力学轨道和运动学轨道的精度均达到cm级.      

SWARM卫星简化动力学厘米级精密定轨

联合星载GPS双频观测值与简化的动力学模型,在卫星运动方程中引入适当的伪随机脉冲参数,对SWARM卫星进行精密定轨。采用星载GPS相位观测值残差、重叠轨道以及与外部轨道对比等3种方法对SWARM卫星简化动力学定轨结果进行检核。结果表明:SWARM星载GPS相位观测值残差RMS为7~10mm;径向、切向以及法向6h重叠轨道差值RMS均在1cm左右,3个方向均无明显的系统误差。通过与欧空局(ESA)发布的精密轨道进行对比分析,径向轨道差值RMS为2~5cm,切向轨道差值RMS为2~5cm,法向轨道差值RMS为2~4cm,3D轨道差值RMS为4~7cm;SWARM-B定轨精度优于SWARM-A与SWARM-C。因此,采用简化动力学法与本文提供的定轨策略进行SWARM卫星精密定轨是切实可行的,定轨结果良好且稳定,定轨精度达到厘米级。     

HY2A卫星的GPS/DORIS/SLR数据精密定轨

采用HY2A卫星2013年2月的实测数据,研究了GPS、星载多谱勒无线电定轨定位系统(DORIS)及卫星激光测距(SLR)三种观测数据的单独和联合定轨问题。通过与法国CNES的精密轨道数据比较发现:分别采用GPS、DORIS和SLR数据进行单独定轨,GPS数据确定轨道的径向平均精度为1.3cm,三维位置约为6.2cm;DORIS定轨的径向平均精度为1.6cm,比GPS结果略差;SLR确定轨道的径向平均精度为2.3cm。用GPS、DORIS和SLR三种数据联合定轨,确定轨道的径向平均精度为1.2cm,三维位置约为6.5cm。与星载GPS定轨结果比较,三种观测数据的联合定轨在提高卫星轨道确定精度上不明显,但联合定轨有利于保持计算轨道精度相对稳定。用站星间高度角大于60°的SLR数据检验GPS/DORIS联合确定的轨道,两者在测距方向的均方差为2.5cm,可见基于HY2A的观测数据可以实现cm级的定轨需求。     

Galileo status: orbits,clocks, and positioning

The European Global Navigation Satellite System Galileo is close to declaration of initial services. The current constellation comprises a total of 12 active satellites, four of them belonging to the first generation of In-Orbit Validation satellites, while the other eight are Full Operational Capability (FOC) satellites. Although the first pair of FOC satellites suffered from a launch anomaly resulting in an elliptical orbit, these satellites can be used for scientific applications without relevant limitations. The quality of broadcast orbits and clocks has significantly improved since the beginning of routine transmissions and has reached a signal-in-space range error of 30 cm. Precise orbit products generated by the scientific community achieve an accuracy of about 5 cm if appropriate models for the solar radiation pressure are applied. The latter is also important for an assessment of the clock stability as orbit errors are mapped to the apparent clock. Dual-frequency single point positioning with broadcast orbits and clocks of nine Galileo satellites that have so far been declared healthy already enables an accuracy at a few meters. Galileo-only precise point positioning approaches a precision of 2 cm in static mode using daily solutions.     

GPS导航电文核心定位参数发展演变分析

文章总结了GPS空间信号接口控制文件的发展历程,对比了现有3种导航电文类型的电文结构及播发方式, 详细分析了星历参数、钟差参数及完好性参数等核心定位参数的发展演变特点和改进效果. 结果表明:GPS新型导航电文采用增加核心定位参数和减小量化单位的方法,提高了广播星历和钟差产品的精度. 增加两个参数后,地面星历拟合位置误差均方根(RMS)平均值由0.137 m减小为0.025 m. 为适应高精度星历拟合模型,距离量化单位也减小至毫米量级. 通过减小卫星钟差参数的量化单位,预报1 h钟差误差RMS由0.097 m减小至0.042 m.      

QZSS L6E增强服务改正数支持的PPP性能评估

准天顶卫星系统目前利用QZS-2~QZS-43颗卫星播发L6E信号,为东亚和大洋洲地区用户提供实时的增强服务。该文分析了L6E信号结构及轨道和钟差的计算模型,研究了目前L6E信号的覆盖范围和可用性,评估了L6E改正数恢复的卫星轨道和钟差及其用于动态PPP的精度水平。结果表明:我国用户在使用15°截止高度角时L6E信号仍有100%的可用性;L6E改正数恢复的GPS和GLONASS卫星轨道的3D RMS平均值分别为5.3和13.9 cm,卫星钟差的STD平均值分别为0.14和0.22 ns,利用GPS卫星的轨道和钟差进行的动态PPP可以获得水平优于10 cm、高程优于15 cm的精度,在加入GLONASS卫星后,东方向和高程方向定位误差和收敛时间均有明显改善。     

Precise orbit determination of the Fengyun-3C satellite using onboard GPS and BDS observations

The GNSS Occultation Sounder instrument onboard the Chinese meteorological satellite Fengyun-3C (FY-3C) tracks both GPS and BDS signals for orbit determination. One month’s worth of the onboard dual-frequency GPS and BDS data during March 2015 from the FY-3C satellite is analyzed in this study. The onboard BDS and GPS measurement quality is evaluated in terms of data quantity as well as code multipath error. Severe multipath errors for BDS code ranges are observed especially for high elevations for BDS medium earth orbit satellites (MEOs). The code multipath errors are estimated as piecewise linear model in \(2{^{\circ }}\times 2{^{\circ }}\) grid and applied in precise orbit determination (POD) calculations. POD of FY-3C is firstly performed with GPS data, which shows orbit consistency of approximate 2.7 cm in 3D RMS (root mean square) by overlap comparisons; the estimated orbits are then used as reference orbits for evaluating the orbit precision of GPS and BDS combined POD as well as BDS-based POD. It is indicated that inclusion of BDS geosynchronous orbit satellites (GEOs) could degrade POD precision seriously. The precisions of orbit estimates by combined POD and BDS-based POD are 3.4 and 30.1 cm in 3D RMS when GEOs are involved, respectively. However, if BDS GEOs are excluded, the combined POD can reach similar precision with respect to GPS POD, showing orbit differences about 0.8 cm, while the orbit precision of BDS-based POD can be improved to 8.4 cm. These results indicate that the POD performance with onboard BDS data alone can reach precision better than 10 cm with only five BDS inclined geosynchronous satellite orbit satellites and three MEOs. As the GNOS receiver can only track six BDS satellites for orbit positioning at its maximum channel, it can be expected that the performance of POD with onboard BDS data can be further improved if more observations are generated without such restrictions.     

GNSS广播星历轨道和钟差精度分析

为了对多个全球导航卫星系统（global navigation satellite system, GNSS）当前的广播星历精度进行一个全面的分析,对比了2014—2018年共5 a的GNSS广播星历与精密星历,并对全球定位系统（global positioning system, GPS）、格洛纳斯卫星导航系统（global navigation satellite system, GLONASS）、伽利略卫星导航系统（Galileo satellite navigation system, Galileo）、北斗卫星导航系统（BeiDou navigation satellite system, BDS）、准天顶卫星系统（quasi-zenith satellite system, QZSS）等5个系统的广播星历长期精度变化进行了分析。结果表明:5 a中GPS的广播星历轨道及钟差精度最稳定;GLONASS的广播星历轨道精度稳定性较好,但其钟差精度存在较大的离散度;Galileo得益于具备全面运行能力（full operational capability, FOC）卫星的大量发射及运行,其广播星历轨道、钟差精度大幅度变好,切向轨道、法向轨道与钟差精度已赶超GPS;BDS的广播星历轨道精度离散度较大,钟差精度出现不稳定现象;QZSS的广播星历轨道与钟差精度的稳定性与离散度相对最差。以2018年1 a的广播星历与精密星历为例分析了各个系统当前的广播星历精度,结果表明,当前GPS、GLONASS、Galileo、BDS、QZSS的考虑轨道误差与钟差误差贡献的空间信号测距误差（signal-in-space ranging error,SISRE）分别为0.806 m、2.704 m、0.320 m、1.457 m、1.645 m,表明Galileo广播星历整体精度最高,GPS次之,其次分别是BDS、QZSS和GLONASS。只考虑轨道误差贡献的SISRE分别为0.167 m、0.541 m、0.229 m、0.804 m、0.675 m,表明GPS广播星历轨道精度最高,其次分别是Galileo、GLONASS、QZSS和BDS。GPS卫星广播星历中新型号卫星的钟差精度总体要优于旧型号卫星。     

非差虚拟观测值的网络RTK实现

网络RTK是利用多基准站观测值实现流动站附近的误差建模,其中包括对流层、电离层延迟和卫星轨道等误差。讨论了利用VRS技术实现网络RTK中的几个关键技术,包括将多基准站插值所得的双差大气延迟添加到非差模式的VRS观测值中,利用IGS的超快速星历中的预报部分改正广播星历误差和利用恒星日滤波改正VRS的伪距多路径效应。24 ...     

SBAS星历改正数及UDRE参数生成算法分析

星基增强系统(satellite based augmentation system,SBAS)通过地球同步轨道卫星实时播发导航卫星星历改正数和完好性参数,以提升用户定位精度和完好性。采用最小方差法解算GPS星历改正数,利用卡方统计进行改正数完好性检核,并依据星历改正数方差-协方差信息计算SBAS用户差分距离误差(user differential range error,UDRE)和信息类型28(message type 28, MT28)等完好性参数。利用中国区域27个监测站的实测数据,首先以国际GNSS服务组织的精密轨道和钟差产品为参考解算星历改正数,结果表明,钟差改正精度优于0.1 m,轨道改正精度优于0.4 m;然后解算广播星历改正数,并生成UDRE和MT28参数,广播星历残余误差卡方检验值均小于告警门限,保证了改正数的完好性;最后利用生成的改正数进行SBAS定位解算,得到定位结果的水平精度优于0.7 m,垂直精度优于1.0 m,对比GPS单点定位,所提算法的水平和垂直方向精度分别提升了30%和40%。     

GPS+BDS中长距离RTK定位算法及结果分析

GPS/BDS中长距离RTK定位因为电离层和对流层残余误差的影响,其性能相对于常规RTK有所降低。将GPS/BDS卫星双差电离层误差和对流层误差作为参数,采用卡尔曼滤波进行实时估计。为了验证算法的有效性,利用武汉地区103 km静态基线24 h双频观测数据,分析了GPS和BDS单系统以及二者组合双系统中长距离RTK定位性能。实验结果表明,精确估计的双差电离层残余误差达到米级、对流层误差达到分米级;经过改正后,GPS/BDS单系统的定位精度在1 cm左右,组合双系统则实现了中长距离基线毫米级的高精度定位。     

单基站差分GPS定位精度的分析与检验

分析了影响单基站差分GPS测量的主要误差因素，研究了不同基线长情况下广播星历、电离层和对流层延迟等误差对单基站差分GPS数据精度的影响程度及规律，通过设立双基站测量、与精密单点定位软件处理比较等方法检验了单基站差分GPS数据精度，得出了在用单基站差分GPS测量系统满足一定精度要求的结论。     

海洋二号A与资源三号卫星星载GPS自主轨道确定

系统研究了基于海洋二号A（HY2A）与资源三号（ZY3）卫星国产星载GPS接收机双频数据的自主定轨问题,模拟在轨实时处理的结果表明,HY2A与ZY3卫星伪距自主定轨的位置精度可达1.3 m,速度精度可达1.2 mm/s;而HY2A卫星相位自主定轨位置精度可达38 cm,其中径向精度约10 cm,速度精度可达0.36 mm/s;ZY3卫星相位定轨位置精度可达54 cm,速度精度可达0.54 mm/s。自主定轨的相关成果可以应用于我国后续对地观测计划的实时服务。     

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。      

Analyses and Solutions of Errors on GPS／GLONASS Positioning

This paper focuses mainly on the major errors and their reduction approaches pertaining to combined GPS/GLONASS positioning.To determine thd difference in the time reference systems,different receiver clock offsets are introduced with respect to GPS and GLONASS system time.A more desirable method for introducing a independent unknown parameter of fifth receiver,which can be canceled out when forming difference measurements,is discussed.The error of orbit integration and the error of transformation parameters are addressed in detail.Results of numerical integration are give.To deal with the influence of ionospheric delay,a method for forming dual-frequency ionospheric free carrier phase measurements is detailed.     

Single GPS receiver time-relative positioning with loop misclosure corrections

Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about 40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under 20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the horizontal components and 29 cm for the vertical component with dual frequency data.