载波相位差分技术在馈源舱动态定位中的应用

针对ＦＡＳＴ项目馈源舱扫描跟踪设计,作者根据ＧＰＳ载波相位差分精密动态定位原理,讨论了馈源舱位置和姿态的ＧＰ动态检测系统的组成,按照我国贵州ＫＡＲＳＴ地形的地理位置给出了动态检测时需要使用的馈源舱位姿转换矩阵和求解方程,与ＧＰＳ动态定位系统相结合就可以完成对馈源舱位姿的跟踪检测,实现舱体的闭环控制。     

利用中心差分法进行GPS定速时最佳点数的选取

分析了利用中心差分法进行GPS定速时的主要误差来源,证明了当数据采样率一定时,增加中心差分法的点数可减少微分过程中的截断误差,但同时会放大导出相位率的观测误差,得出中心差分法的最佳点数应使这两种误差之和最小的结论。实验结果表明,当数据采样间隔为1s、载体平均速度和加速度为20m.s-1和0.2m.s-2时,9个点的中心差分法定速精度最高。     

The impact of accelerometry on CHAMP orbit determination

 The contribution of the STAR accelerometer to the CHAMP orbit precision is evaluated and quantified by means of the following results: orbital fit to the satellite laser ranging (SLR) observations, GPS reduced-dynamic vs SLR dynamic orbit comparisons, and comparison of the measured to the modeled non-gravitational accelerations (atmospheric drag in particular). In each of the four test periods in 2001, five CHAMP arcs of 2 days' length were analyzed. The mean RMS-of-fit of the SLR observations of the orbits computed with STAR data or the non-gravitational force model were 11 and 24 cm, respectively. If the accelerometer calibration parameters are not known at least at the few percent level, the SLR orbit fit deteriorates. This was tested by applying a 10% error to the along-track scale factor of the accelerometer, which increased the SLR RMS-of-fit on average to 17 cm. Reference orbits were computed employing the reduced-dynamic technique with GPS tracking data. This technique yields the most accurate orbit positions thanks to the estimation of a large number of empirical accelerations, which compensate for dynamic modeling errors. Comparison of the SLR orbits, computed with STAR data or the non-gravitational force model, to the GPS-based orbits showed that the SLR orbits employing accelerometer observations are twice as accurate. Finally, comparison of measured to modeled accelerations showed that the level of geomagnetic activity is highly correlated with the atmospheric drag model error, and that the largest errors occur around the geomagnetic poles. Received: 7 May 2002 / Accepted: 18 November 2002 Correspondence to: S. Bruinsma Acknowledgments. The TIGCM results were obtained from the CEDAR database. This study was supported by the Centre National d'Etudes Spatiales (CNES). The referees are thanked for their helpful remarks and suggestions.     

Geoid determination using adapted reference field, seismic Moho depths and variable density contrast

 The traditional remove-restore technique for geoid computation suffers from two main drawbacks. The first is the assumption of an isostatic hypothesis to compute the compensation masses. The second is the double consideration of the effect of the topographic–isostatic masses within the data window through removing the reference field and the terrain reduction process. To overcome the first disadvantage, the seismic Moho depths, representing, more or less, the actual compensating masses, have been used with variable density anomalies computed by employing the topographic–isostatic mass balance principle. In order to avoid the double consideration of the effect of the topographic–isostatic masses within the data window, the effect of these masses for the used fixed data window, in terms of potential coefficients, has been subtracted from the reference field, yielding an adapted reference field. This adapted reference field has been used for the remove–restore technique. The necessary harmonic analysis of the topographic–isostatic potential using seismic Moho depths with variable density anomalies is given. A wide comparison among geoids computed by the adapted reference field with both the Airy–Heiskanen isostatic model and seismic Moho depths with variable density anomaly and a geoid computed by the traditional remove–restore technique is made. The results show that using seismic Moho depths with variable density anomaly along with the adapted reference field gives the best relative geoid accuracy compared to the GPS/levelling geoid. Received: 3 October 2001 / Accepted: 20 September 2002 Correspondence to: H.A. Abd-Elmotaal     

A study on the combination of satellite, airborne, and terrestrial gravity data

Satellite gravity missions, such as CHAMP, GRACE and GOCE, and airborne gravity campaigns in areas without ground gravity will enhance the present knowledge of the Earths gravity field. Combining the new gravity information with the existing marine and ground gravity anomalies is a major task for which the mathematical tools have to be developed. In one way or another they will be based on the spectral information available for gravity data and noise. The integration of the additional gravity information from satellite and airborne campaigns with existing data has not been studied in sufficient detail and a number of open questions remain. A strategy for the combination of satellite, airborne and ground measurements is presented. It is based on ideas independently introduced by Sjöberg and Wenzel in the early 1980s and has been modified by using a quasi-deterministic approach for the determination of the weighting functions. In addition, the original approach of Sjöberg and Wenzel is extended to more than two measurement types, combining the Meissl scheme with the least-squares spectral combination. Satellite (or geopotential) harmonics, ground gravity anomalies and airborne gravity disturbances are used as measurement types, but other combinations are possible. Different error characteristics and measurement-type combinations and their impact on the final solution are studied. Using simulated data, the results show a geoid accuracy in the centimeter range for a local test area.     

一种改进的快速最小高差DEM匹配方法

利用最小高差(LZD)法进行DEM匹配时,当待匹配DEM的分辨率比参考DEM高时,确定的同名点中存在冗余,将导致计算冗余和效率降低。为解决上述问题,对LZD法确定同名点的模型进行改化,提出一种改进的基于最小高差原理的快速DEM匹配方法。该方法根据参考DEM的格网点确定同名点以避免冗余,并通过近似确定同名点及其高差,有效简化了计算过程。实验结果表明,该方法在保证较高的收敛速度和匹配精度的基础上,可有效提高计算效率,且计算效率不随待匹配DEM分辨率提高而降低,DEM间分辨率差异越大,方法的优势越明显。     

BDS轨道完备性监测设计与实现

针对北斗卫星导航系统(BDS)完备性研究较少的现状,该文提出了一种导航星历中轨道观测数据的完备性监测新方法。采用轨道积分方法分析了北斗卫星的轨道残差均方根值;通过概率统计的方法,分别计算所有北斗卫星的轨道残差极限误差值(告警限差),剔除误差超限甚至粗差卫星,实现事后轨道完备性监测。另外通过比较分析剔除监测标记出的误差卫星之前和之后对测站精密单点定位的影响,验证完备性的风险性。最后通过实测数据对该算法进行了验证和分析。实验结果表明:该算法可以实现卫星轨道的监测示警,标记误差卫星,达到轨道完备性监测效果。     

双差精密定轨中地面站的选取方法

针对目前全球的地面测站数量多、测站观测数据质量参差不齐及测站地理分布不均的问题,总结了一种测站选取方法。利用该方法编制的测站选取软件对IGS站进行了选择,并根据选得的测站设计了几种定轨试验。结果显示,利用由本文的测站选取方法得到的70个基准站进行定轨时,得到的卫星位置与IGS精密星历在径向、切向、法向偏差均方根分别为1.11、2.19、1.72cm。验证了本文选站软件的可靠性,避免了选站过程中过多的人为因素,并且在保障精度的前提下提高了定轨效率。     

北斗卫星导航系统实时定轨及SSR改正信息生成方法

随着GNSS应用的不断发展,实时位置服务已经成为国内外研究热点,而北斗卫星导航系统的实时服务尚处于发展阶段。本文基于卫星精密定轨基本原理,讨论了北斗导航卫星实时轨道确定策略;研究了基于北斗卫星质心和天线相位中心的SSR轨道改正值生成方法,并给出了一种适合北斗导航卫星的IODE值表达方式;基于国家基准站和全球MGEX站数据,进行了北斗导航卫星的实时轨道解算测试,结果表明,GEO卫星1D RMS精度优于400 cm,平均精度为223 cm,其径向精度优于20 cm;IGSO卫星精度优于30 cm,平均精度为22 cm,其径向精度优于10 cm;MEO卫星精度优于30 cm,平均精度为15 cm,其径向精度优于10 cm。     

北斗新一代试验星观测数据质量分析

5颗北斗新一代试验星搭载了包括B1C、B2a和B2b的诸多新体制民用信号,并且为了与北斗区域系统平稳过渡而搭载了B1I和B3I两个旧体制信号。采集了来自国内的6个监测站7 d的试验星观测数据,针对信号载噪比和码伪距多路径偏差分析了新一代试验星观测数据质量。结果表明,新一代试验星信号的各项指标整体较北斗区域系统卫星更好。前者载噪比较高,虽然仍发现了部分测站数据微小的多路径波动,但通过实时相位平滑伪距的方法可以很好地消除之;新一代试验星上B3I与B1I频点的载噪比最大,B2a和B2b次之,B1C的载噪比最小,且不同测站的观测结果存在明显差异;新一代试验星各频点的MP基本相同,但B2a、B2b和B3I频点MP的RMS明显小于B1I和B1C频点的结果。