多普勒系统对历元地球参考框架的影响研究

针对历元地球参考框架在确定站点高频非线性运动和季节性变化方面具有国际地球参考框架不具备的优势问题,该文通过比较两种技术间组合策略建立的多源融合历元地球参考框架的精度,研究DORIS对于多源融合历元地球参考框架的影响。通过基于坐标的法方程叠加方法进行技术内法方程叠加和技术间组合,并利用并置站条件联系不同技术的法方程,从而建立多源融合历元地球参考框架。结果表明,DORIS的引入并不会对多源融合历元地球参考框架的基准定义或其他3种技术站点的点位精度产生较大的影响,同时能够体现4种技术中精度较差的DORIS对于ETRF的精度及稳定性的影响。     

基于我国全球连续监测与评估系统的ERP测定的精度分析

利用GPS观测资料解算地球自转参数,用全球均匀分布的22个IGS跟踪站（IGS05）的连续观测资料估计地球自转参数（ERP）,并与IERSC04（UTC0时）的结果相比较,二者相差很小,均在IERS的ERP估计精度范围之内。基于即将建成的COMPASS全球连续监测与评估系统跟踪站,选择其网的8个IGS跟踪站的资料进行了解算并进行了分析和比对。     

长春国土C级GPS网数据处理与精度分析

从长春国土C级GPS网的数据进行分析,通过高精度GAMIT软件进行解算,为了确定在严格基准下的控制网地心坐标,将控制网纳入到ITRF参考框架中,加上了ITRF参考框架中测站坐标已知的全球站数据一起处理,将吉林省CORS站与IGS跟踪站进行联测,获得控制网某点的瞬时坐标。最后,对整个控制网的精度进行了详细的分析。     

利用VLBI、SLR技术建立我国地球参考框架

本文首先概述了VLBI、SLR数据的特点,给出了建立地球参考框架的模型;通过对模型中参数的协方差分析,得出了利用10～15个良好分布且具有高精度站坐标的VLBI站就可建立和维持精度为苦干厘米的我国最佳地球参考框架的结论;最后,提出了利用VLBI站和国内现有SLR固定站的并置观测建立我国VLBI/SLR地球参考框架的这一途径,并对此框架的作用进行了探讨。     

坐标参考框架长期解内约束模型

地球参考框架是一切测绘活动、地球科学研究的物理基础。目前,地球参考框架常采用长期解的形式,即利用一组全球分布的基准站在某一参考历元的坐标和速度来表示。由于观测有误差,且各基准站又具有非线性变化,故需要对不同历元的瞬时地球参考框架进行累积,形成稳定的长期参考框架。以不同历元观测数据得到的瞬时参考框架成果为输入,构建了一种基于多历元观测数据建立参考框架长期累积解的融合模型。从坐标转换模型和测站坐标的时变模型出发,详细推导了建立长期解的函数模型,依据该函数模型的秩亏数设计了转换参数的内约束基准。采用2010-08—2014-12的国际全球导航卫星系统服务第2次处理结果进行试算,并与国际地球参考框架2014成果进行了对比。结果表明,X、Y、Z方向标准偏差分别为3.45 ?mm、4.04 mm、2.84 mm,速度精度分别为1.53 mm/a、1.46 mm/a、1.21 mm/a,X、Y、Z方向的加权均方根误差优于3 ?mm。     

利用联测IGS跟踪站方法提高GPS控制网起算数据精度

详细讨论了利用联测IGS跟踪站提高GPS区域控制网起算数据精度的方法,并介绍了将区域控制网框架和国际地球参考框架ITRF2000相连的方法,探讨了联测IGS跟踪站时应注意的事项,并根据实例对采用联测IGS跟踪站后对GPS网起算点的精度影响进行分析.     

测站坐标阶跃对参考框架稳定性的影响分析

针对全球卫星导航系统(GNSS)测站坐标阶跃对参考框架稳定性的影响量级尚不明确的问题,该文选取了 340个全球分布的国际GNSS服务(IGS)测站建立长期GNSS参考框架.其中,测站运动模型包含线性速度、周年信号以及震后形变改正.通过迭代增加阶跃的数量,定量分析了测站坐标阶跃对建立的GNSS参考框架稳定性、测站速度及周年振幅的影响.结果表明,340个IGS测站坐标时间序列中存在的阶跃对建立的GNSS参考框架稳定性、测站水平方向速度以及测站周年振幅的影响量级均小于其精度,但是对测站垂直方向速度的影响较为显著.     

地球参考框架联合解算方法

地球参考框架是地球坐标系统的实现,本文系统介绍了地球参考框架的确定方法,结合ITRF2005参考框架,详细介绍了地球参考框架联合解算的方法,并对地球参考框架的质量分析方法进行了探讨。     

GNSS连续站阶跃修复及其对数据处理的影响

近年来,由于仪器更换和强震影响,一些长期稳定的GNSS连续站出现了阶跃,严重地影响了参考框架的稳定性和解算精度,理论上这些测站不能再选为参考框架点。针对GNSS连续站阶跃修复及其对数据处理的影响进行了分析,结果表明：1）如果选用未修复阶跃的测站为框架点,将会扭曲解算结果;2）QOCA能够较为便捷地修复测站阶跃;3）修复测站阶跃能够保证参考框架点的稳定性,并能一定程度提高解算精度。     

利用SDCORS数据建立山东区域动态坐标参考框架

为了将SDCORS基准站的坐标纳入到ITRF2008坐标框架中,满足CORS基准站网的建设要求。本文使用GAMIT/GLOBK精密GPS数据处理软件,并考虑对流层延迟和地球固体潮、海潮、大气潮和极潮等的影响,对78个SDCORS基准站2012年全年的观测数据进行解算。最终,得到SDCORS基准站在ITRF2008坐标框架下毫米级精度的三维坐标和速度,并对该年度SDCORS基准站的站坐标变化特征进行了分析,建立了适用于山东省地区的区域动态坐标参考框架。     

利用北斗系统建立和维持国家大地坐标参考框架的方法研究

2000中国大地坐标系统（China Geodetic Coordinate System 2000,CGCS2000）的建立和维持主要依赖于GPS技术,不利于保障国家时空信息安全。中国北斗卫星导航系统（BeiDou navigation satellite system,BDS）提供亚太区域服务,可满足中国及周边地区高精度定位导航应用需求,对建立和维持国家大地坐标参考框架具有重要意义。研究利用已建成的北斗基准站网观测数据,实现基于BDS技术、并与国际地球参考框架（International Terrestrial Reference Frame,ITRF）一致的国家大地坐标参考框架,为今后国家级和全球性北斗坐标参考框架（BeiDou Terrestrial Reference Frame,BTRF）的建立和维持提供理论基础和方法支撑。初步计算结果表明,积累2 a以上的观测数据,利用单独BDS数据可以获得与GPS精度相当的水平速度场,精度约为2~3 mm/a。基于单独BDS数据,测站残差平面和高程的重复性分别可优于0.8 cm和1.7 cm。利用BDS数据已可监测到测站高程方向的季节性变化。此外,还对单独BDS与GPS数据计算的坐标可能存在的与经纬度相关的系统误差进行了分析。总体来说,目前的北斗系统可满足建立和维持中国cm级大地坐标框架的需求。     

Precise relative positioning using real tracking data from COMPASS GEO and IGSO satellites

China completed a basic COMPASS navigation network with three Geostationary and three Inclined Geosynchronous satellites in orbit in April 2011. The network has been able to provide preliminary positioning and navigation functions. We first present a quality analysis using 1-week COMPASS measurements collected in Wuhan. Satellite visibility and validity of measurements, carrier-to-noise density ratio and code noise are analyzed. The analysis of multipath combinations shows that the noise level of COMPASS code measurements is higher than that of GPS collected using the same receiver. Second, the results of positioning are presented and analyzed. For the standalone COMPASS solutions, an accuracy of 20 m can be achieved. An accuracy of 3.0 m for the vertical, 1.5 m for the North and about 0.6–0.8 m for the East component is obtained using dual-frequency code only measurements for a short baseline. More importantly, code and phase measurements of the short baseline are processed together to obtain precise relative positioning. Kinematic solutions are then compared with the ground truth. The precision of COMPASS only solutions is better than 2 cm for the North component and 4 cm for the vertical. The standard deviation of the East component is smaller than 1 cm, which is even better than that of the East component of GPS solutions. The accuracy of GPS/COMPASS combination solutions is at least 20 % better than that of GPS alone. Furthermore, the geometry-based residuals of double differenced phase and code measurements are analyzed. The analysis shows that the noise level of un-differenced phase measurements is about 2–4 mm on both B1 and B2 frequencies. For the code measurements, the noise level is less than 0.45 m for B1 CA and about 0.35 m for B2 P code. Many of the COMPASS results presented are very promising and have been obtained for the first time.     

Two-step method for the determination of the differential code biases of COMPASS satellites

The differential code bias (DCB) in satellites of the Global Navigation Satellite Systems (GNSS) should be precisely corrected when designing certain applications, such as ionospheric remote sensing, precise point positioning, and time transfer. In the case of COMPASS system, the data used for estimating DCB are currently only available from a very limited number of global monitoring stations. However, the current GPS/GLONASS satellite DCB estimation methods generally require a large amount of geographically well-distributed data for modeling the global ionospheric vertical total electron content (TEC) and are not particularly suitable for current COMPASS use. Moreover, some satellites with unstable DCB (i.e., relatively large scatter) may affect other satellite DCB estimates through the zero-mean reference that is currently imposed on all satellites. In order to overcome the inadequacy of data sources and to reduce the impact of unstable DCB, a new approach, designated IGGDCB, is developed for COMPASS satellite DCB determination. IGG stands for the Institute of Geodesy and Geophysics, which is located in Wuhan, China. In IGGDCB, the ionospheric vertical TEC of each individual station is independently modeled by a generalized triangular series function, and the satellite DCB reference is selected using an iterative DCB elimination process. By comparing GPS satellite DCB estimates calculated by the IGGDCB approach based on only a handful (e.g., seven) of tracking stations against that calculated by the currently existing methods based on hundreds of tracking stations, we are able to demonstrate that the accuracies of the IGGDCB-based DCB estimates perform at the level of about 0.13 and 0.10?ns during periods of high (2001) and low (2009) solar activity, respectively. The iterative method for DCB reference selection is verified by statistical tests that take into account the day-to-day scatter and the duration that the satellites have spent in orbit. The results show that the impact of satellites with unstable DCB can be considerably reduced using the IGGDCB method. It is also confirmed that IGGDCB is not only specifically valid for COMPASS but also for all other GNSS.     

VLBI-derived troposphere parameters during CONT08

Time-series of zenith wet and total troposphere delays as well as north and east gradients are compared, and zenith total delays (ZTD) are combined on the level of parameter estimates. Input data sets are provided by ten Analysis Centers (ACs) of the International VLBI Service for Geodesy and Astrometry (IVS) for the CONT08 campaign (12?C26 August 2008). The inconsistent usage of meteorological data and models, such as mapping functions, causes systematics among the ACs, and differing parameterizations and constraints add noise to the troposphere parameter estimates. The empirical standard deviation of ZTD among the ACs with regard to an unweighted mean is 4.6?mm. The ratio of the analysis noise to the observation noise assessed by the operator/software impact (OSI) model is about 2.5. These and other effects have to be accounted for to improve the intra-technique combination of VLBI-derived troposphere parameters. While the largest systematics caused by inconsistent usage of meteorological data can be avoided and the application of different mapping functions can be considered by applying empirical corrections, the noise has to be modeled in the stochastic model of intra-technique combination. The application of different stochastic models shows no significant effects on the combined parameters but results in different mean formal errors: the mean formal errors of the combined ZTD are 2.3?mm (unweighted), 4.4?mm (diagonal), 8.6?mm [variance component (VC) estimation], and 8.6?mm (operator/software impact, OSI). On the one hand, the OSI model, i.e. the inclusion of off-diagonal elements in the cofactor-matrix, considers the reapplication of observations yielding a factor of about two for mean formal errors as compared to the diagonal approach. On the other hand, the combination based on VC estimation shows large differences among the VCs and exhibits a comparable scaling of formal errors. Thus, for the combination of troposphere parameters a combination of the two extensions of the stochastic model is recommended.     

IGS Tide Gauge Benchmark Monitoring Pilot Project (TIGA): scientific benefits

The establishment of a long-term stable global reference frame is important for studying sea level records for, e.g., climate-related studies. GPS stations connected to the tide gauge benchmarks provide the necessary technique. However, the analysis of existing GPS solutions showed inconsistencies within the time series especially for the height component. To solve related issues, in 2001 the IGS Tide Gauge Benchmark Monitoring Pilot Project was established. The aim is the processing and re-processing of GPS data of stations at or near tide gauges in order to provide homogeneous and high-quality estimates of the vertical motion. A second objective is the establishment, maintenance and expansion of existing network of GPS stations at tide gauges. During the recent years six different analysis centers have processed overlapping GPS at tide gauge networks and are providing individual solutions allowing now to provide a combined solution. The ansatz for the combination is explained and quality measures are given. In addition, on the basis of the reconstruction of sea level anomalies, the benefit of using the combined TIGA solution is demonstrated.     

COMPASS三频数据线性组合优化选取分析

以北斗卫星1支路频点为例,从消除或减弱电离层影响、对流层影响和观测噪声与多路径误差3个方面分析COMPASS三频数据线性组合的优化选取问题,并通过MATLAB模拟,给出一些典型的组合,分析它们可能的应用,为COMPASS三频数据线性组合的优化选取提供一些借鉴。     

全球IGS站数据与GPS区域网数据的联合处理

为了使区域GPS网建立的参考框架与国际地球参考框架（ITRF）更加接近,利用全球IGS站观测数据无疑是一条最佳途径。本文对处理大尺度GPS网数据时如何利用全球分布均匀的IGS站观测数据以及如何选择全球基准站的问题进行了研究。给出了利用全球IGS站数据的数学模型,分析了国内专家选择基准站时存在的一些问题,提出了选择基准站的新方法,这一方法适合于建立我国新的地心参考框架。实测数据计算结果表明,这种方法计算的未知站地心坐标精度相对于ITRF96参考框架约±2 cm。     

Adding source positions to the IVS combination—First results

The consistent estimation of terrestrial reference frames (TRF), celestial reference frames (CRF) and Earth orientation parameters (EOP) is still an open subject and offers a large field of investigations. Until now, source positions resulting from Very Long Baseline Interferometry (VLBI) observations are not routinely combined on the level of normal equations in the same way as it is a common process for station coordinates and EOPs. The combination of source positions based on VLBI observations is now integrated in the IVS combination process. We present the studies carried out to evaluate the benefit of the combination compared to individual solutions. On the level of source time series, improved statistics regarding weighted root mean square have been found for the combination in comparison with the individual contributions. In total, 67 stations and 907 sources (including 291 ICRF2 defining sources) are included in the consistently generated CRF and TRF covering 30 years of VLBI contributions. The rotation angles \(A_1\), \(A_2\) and \(A_3\) relative to ICRF2 are ?12.7, 51.7 and 1.8 \({\upmu }\) as, the drifts \(D_\alpha \) and \(D_\delta \) are ?67.2 and 19.1 \(\upmu \) as/rad and the bias \(B_\delta \) is 26.1 \(\upmu \) as. The comparison of the TRF solution with the IVS routinely combined quarterly TRF solution shows no significant impact on the TRF, when the CRF is estimated consistently with the TRF. The root mean square value of the post-fit station coordinate residuals is 0.9 cm.     

Multi-technique comparison of troposphere zenith delays and gradients during CONT08

CONT08 was a 15 days campaign of continuous Very Long Baseline Interferometry (VLBI) sessions during the second half of August 2008 carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, VLBI estimates of troposphere zenith total delays (ZTD) and gradients during CONT08 were compared with those derived from observations with the Global Positioning System (GPS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and water vapor radiometers (WVR) co-located with the VLBI radio telescopes. Similar geophysical models were used for the analysis of the space geodetic data, whereas the parameterization for the least-squares adjustment of the space geodetic techniques was optimized for each technique. In addition to space geodetic techniques and WVR, ZTD and gradients from numerical weather models (NWM) were used from the European Centre for Medium-Range Weather Forecasts (ECMWF) (all sites), the Japan Meteorological Agency (JMA) and Cloud Resolving Storm Simulator (CReSS) (Tsukuba), and the High Resolution Limited Area Model (HIRLAM) (European sites). Biases, standard deviations, and correlation coefficients were computed between the troposphere estimates of the various techniques for all eleven CONT08 co-located sites. ZTD from space geodetic techniques generally agree at the sub-centimetre level during CONT08, and??as expected??the best agreement is found for intra-technique comparisons: between the Vienna VLBI Software and the combined IVS solutions as well as between the Center for Orbit Determination (CODE) solution and an IGS PPP time series; both intra-technique comparisons are with standard deviations of about 3?C6?mm. The best inter space geodetic technique agreement of ZTD during CONT08 is found between the combined IVS and the IGS solutions with a mean standard deviation of about 6?mm over all sites, whereas the agreement with numerical weather models is between 6 and 20?mm. The standard deviations are generally larger at low latitude sites because of higher humidity, and the latter is also the reason why the standard deviations are larger at northern hemisphere stations during CONT08 in comparison to CONT02 which was observed in October 2002. The assessment of the troposphere gradients from the different techniques is not as clear because of different time intervals, different estimation properties, or different observables. However, the best inter-technique agreement is found between the IVS combined gradients and the GPS solutions with standard deviations between 0.2 and 0.7?mm.