利用重复水准测量及重力测量计算水准面随时间的变化

本文讨论了根据重复水准、重力测量资料利用虚拟质点法计算水准面随时间的变化,提出了虚拟质点位置参数的优化方法(该法克服了司托克斯方法和配置法的缺点)。模拟计算表明,水准面位移的计算精度是很高的。     

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。     

精化区域大地水准面若干问题的探讨

对精化区域大地水准面的一些问题进行了探讨 ,以便有关单位在精化区域大地水准面时进行参考。     

高分辨率厘米级局部大地水准面的典型应用

介绍了香港大地水准面HKGEOID_2 0 0 0和深圳市高分辨率、高精度似大地水准面SZGEOID_2 0 0 0。利用HKGEOID_2 0 0 0和GPS椭球高求得的正常高与香港地区由三角高程测量得到的“正常高 (或本地高 )”进行比较 ,结果表明 ,其差值的均方根为 0 .1 0 2m ,标准差 (STD)为± 3 .4cm。结合HKGEOID_2 0 0 0、SZGEOID_2 0 0 0和这两个大地水准面模型重复覆盖地区的高精度GPS水准数据 ,探测这两个大地水准面模型之间的差异和香港主要高程基准面 (HKPD)与我国 1 95 6黄海高程基准面之间的系统偏差。     

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。     

WHCORS的技术拓展与应用现状

介绍了武汉市连续运行卫星定位服务系统(WHCORS)的基本情况和发展现状;对基于WHCORS技术拓展研究的相关情况和WHCORS的应用推广进行了详述,针对具体的关键技术问题提出了较详细的解决方案,对用户有一定的参考和借鉴作用。     

Sensitivity of GPS and GLONASS orbits with respect to resonant geopotential parameters

The Center for Orbit Determination in Europe (CODE) has been involved in the processing of combined GPS/GLONASS data during the International GLONASS Experiment (IGEX). The resulting precise orbits were analyzed using the program SORBDT. Introducing one satellites positions as pseudo-observations, the program is capable of fitting orbital arcs through these positions using an orbit improvement procedure based on the numerical integration of the satellites orbit and its partial derivative with respect to the orbit parameters. For this study, the program was enhanced to estimate selected parameters of the Earths gravity field. The orbital periods of the GPS satellites are —in contrast to those of the GLONASS satellites – 2:1 commensurable (P _Sid:P _GPS) with the rotation period of the Earth. Therefore, resonance effects of the satellite motion with terms of the geopotential occur and they influence the estimation of these parameters. A sensitivity study of the GPS and GLONASS orbits with respect to the geopotential coefficients reveals that the correlations between different geopotential coefficients and the correlations of geopotential coefficients with other orbit parameters, in particular with solar radiation pressure parameters, are the crucial issues in this context. The estimation of the resonant geopotential terms is, in the case of GPS, hindered by correlations with the simultaneously estimated radiation pressure parameters. In the GLONASS case, arc lengths of several days allow the decorrelation of the two parameter types. The formal errors of the estimates based on the GLONASS orbits are a factor of 5 to 10 smaller for all resonant terms. AcknowledgmentsThe authors would like to thank all the organizations involved in the IGS and the IGEX campaign, in particular those operating an IGS or IGEX observation site and providing the indispensable data for precise orbit determination.     

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.