Estimation of elevation-dependent satellite antenna phase center variations of GPS satellites

A method for the estimation of the phase center variations of GPS satellite antennas using global GPS data is presented. First estimations have shown an encouraging repeatability from day to day and between satellites of the same block. Thus, two different satellite antenna patterns for Block II/IIA and for Block IIR with a range of about 4 cm and an accuracy of less than 1 mm could be found. The present approach allows the creation of a consistent set of receiver and satellite antenna patterns and phase center offsets. Thereby, it is possible to switch from relative to absolute phase center variations without a scale problem in global networks. This changeover has an influence on troposphere parameters, reduces systematic effects due to uncorrect antenna modeling and should diminish the elevation dependence of GPS results. AcknowledgmentsThe authors thank Prof. G. Seeber (University of Hannover) and Dr. G. Wübbena (Geo++ GmbH) and their groups for their kindness in making available the absolute field calibration results derived from robot measurements.     

Group delay variations of GPS transmitting and receiving antennas

GPS code pseudorange measurements exhibit group delay variations at the transmitting and the receiving antenna. We calibrated C1 and P2 delay variations with respect to dual-frequency carrier phase observations and obtained nadir-dependent corrections for 32 satellites of the GPS constellation in early 2015 as well as elevation-dependent corrections for 13 receiving antenna models. The combined delay variations reach up to 1.0 m (3.3 ns) in the ionosphere-free linear combination for specific pairs of satellite and receiving antennas. Applying these corrections to the code measurements improves code/carrier single-frequency precise point positioning, ambiguity fixing based on the Melbourne–Wübbena linear combination, and determination of ionospheric total electron content. It also affects fractional cycle biases and differential code biases.     

Absolute phase center corrections of satellite and receiver antennas

Results of the estimation of azimuth-dependent phase center variations (PCVs) of GPS satellite antennas using global GPS data are presented. Significant variations of up to ±3–4 mm that are demonstrated show excellent repeatability over eight years. The application of the azimuthal PCVs besides the nadir-dependent ones will lead to a further reduction in systematic antenna effects. In addition, the paper focuses on the benefit of a possible transition from relative to absolute PCVs. Apart from systematic changes in the global station coordinates, one can expect the GPS results to be less dependent on the elevation cut-off angle. This, together with the significant reduction of tropospheric zenith delay biases between GPS and VLBI, stands for an important step toward more consistency between different space geodetic techniques.     

GPS天线相位中心变化及测试

对GPS天线相位中心随卫星变化的情况及减小和消除天线相位中心误差的方法进行了阐述 ,并详细介绍了对两种型号GPS天线相位中心变化进行比较和测试的结果     

Estimation of phase center corrections for GLONASS-M satellite antennas

Driven by the comprehensive modernization of the GLONASS space segment and the increased global availability of GLONASS-capable ground stations, an updated set of satellite-specific antenna phase center corrections for the current GLONASS-M constellation is determined by processing 84 weeks of dual-frequency data collected between January 2008 and August 2009 by a worldwide network of 227 GPS-only and 115 combined GPS/GLONASS tracking stations. The analysis is performed according to a rigorous combined multi-system processing scheme providing full consistency between the GPS and the GLONASS system. The solution is aligned to a realization of the International Terrestrial Reference Frame 2005. The estimated antenna parameters are compared with the model values currently used within the International GNSS Service (IGS). It is shown that the z-offset estimates are on average 7 cm smaller than the corresponding IGS model values and that the block-specific mean value perfectly agrees with the nominal GLONASS-M z-offset provided by the satellite manufacturer. The existence of azimuth-dependent phase center variations is investigated and uncertainties in the horizontal offset estimates due to mathematical correlations and yaw-attitude modeling problems during eclipse seasons are addressed. Finally, it is demonstrated that the orbit quality benefits from the updated GLONASS-M antenna phase center model and that a consistent set of satellite antenna z-offsets for GPS and GLONASS is imperative to obtain consistent GPS- and GLONASS-derived station heights.     

Improvement in PWV estimation from GPS due to the absolute calibration of antenna phase center variations

Climatology of column-integrated atmospheric water vapor over Spain has been carried out by means of three techniques: soundings, sun photometers and GPS receivers. Comparing data from stations equipped with more than one of these instruments, we found that a large discontinuity occurred on November 6, 2006, in the differences between the data series from GPS receivers and those from the other two techniques. Prior to that date, the GPS data indicate a wet bias of 2–3 mm for all stations when compared with sounding or photometer data, whereas after that date this bias practically reduces to zero. The root mean square error also decreases about half of its value. On November 6, 2006, the International GNSS Service adopted an absolute calibration model for the antennas of the GPS satellites and receivers instead of the relative one. This change is expected to be an improvement, increasing the accuracy of station position determination and consequently benefiting post-processing products such as zenith total delay from which the atmospheric water vapor content is calculated.     

GPS天线相位模型变化对高精度GPS测量解算的影响研究

GPS天线存在相位中心偏差,在高精度测量中必须对其进行补偿改正。本文针对GPS天线的两种改正模型:相对改正模型和绝对改正模型,在讨论了它们所具有的相同改正办法的基础上,分析了它们在测定方法上存在区别,最后通过一个算例分别研究了这两种模型对GPS测量解算精度的影响,得出了一些有意义的结论。     

Phase center modeling for LEO GPS receiver antennas and its impact on precise orbit determination

Most satellites in a low-Earth orbit (LEO) with demanding requirements on precise orbit determination (POD) are equipped with on-board receivers to collect the observations from Global Navigation Satellite systems (GNSS), such as the Global Positioning System (GPS). Limiting factors for LEO POD are nowadays mainly encountered with the modeling of the carrier phase observations, where a precise knowledge of the phase center location of the GNSS antennas is a prerequisite for high-precision orbit analyses. Since 5 November 2006 (GPS week 1400), absolute instead of relative values for the phase center location of GNSS receiver and transmitter antennas are adopted in the processing standards of the International GNSS Service (IGS). The absolute phase center modeling is based on robot calibrations for a number of terrestrial receiver antennas, whereas compatible antenna models were subsequently derived for the remaining terrestrial receiver antennas by conversion (from relative corrections), and for the GNSS transmitter antennas by estimation. However, consistent receiver antenna models for space missions such as GRACE and TerraSAR-X, which are equipped with non-geodetic receiver antennas, are only available since a short time from robot calibrations. We use GPS data of the aforementioned LEOs of the year 2007 together with the absolute antenna modeling to assess the presently achieved accuracy from state-of-the-art reduced-dynamic LEO POD strategies for absolute and relative navigation. Near-field multipath and cross-talk with active GPS occultation antennas turn out to be important and significant sources for systematic carrier phase measurement errors that are encountered in the actual spacecraft environments. We assess different methodologies for the in-flight determination of empirical phase pattern corrections for LEO receiver antennas and discuss their impact on POD. By means of independent K-band measurements, we show that zero-difference GRACE orbits can be significantly improved from about 10 to 6 mm K-band standard deviation when taking empirical phase corrections into account, and assess the impact of the corrections on precise baseline estimates and further applications such as gravity field recovery from kinematic LEO positions.     

Absolute calibration of GPS antennas: laboratory results and comparison with field and robot techniques

A critical assessment of the accuracy of GPS antenna calibration is most effectively done by comparison between different calibration methods. We present new chamber calibrations of five different GPS receiver antenna types in an anechoic chamber and a comparison of an individual antenna calibrated by the absolute field calibration technique with robot mount of IfE/GEO++. The accuracy is described using standard error parameters which allow the characterization of the quality of different antennas. The results validate the absolute calibration methods at the 1-mm level and confirm the presence of significant variations in quality between antennas of different design. For the antenna pattern we directly use the measured phase variations and do not have to fit any functions for the chamber calibrations. We include the results of an earlier test made with a set of identical antennas calibrated at five different institutions: two using the absolute field technique with robot mount and three others applying the standard field calibration with reference antenna.     

天线相位中心改正对GPS精密单点定位的影响

GPS卫星与接收机由于自身特性以及机械加工等原因,导致其质量中心与相位中心不重合而产生相位中心误差,进而对GPS精密单点定位产生一定影响。介绍GPS天线相位中心偏移(PCO)、变化(PCV)的原理,并分析PCO、PCV,以及不同模型改正对GPS精密单点定位的影响。结果表明,在GPS精密单点定位中,天线相位中心改正不容忽略:在平面方向上,天线相位中心改正对定位影响较小,仅为毫米级;在高程方向上,天线相位中心改正对定位影响较大,可达厘米级;与相对中心改正模型相比,绝对相位中心改正模型精度更高。     

GPS扼流圈天线相位中心修正效果的实验分析

针对高精度GPS测量中天线相位中心的修正效果问题,该文对GPS扼流圈天线相位中心修正在不同长度基线解算中的影响进行了实验分析。根据不同类型天线间的高程测量受相位中心修正影响较为显著的实验结果,提出利用超短基线水准比对法对相位中心改正模型的修正效果进行评价,开展了相关理论分析,并利用该方法对两种相位中心改正模型的修正效果进行了实验研究。实验结果表明,超短基线水准比对法可以作为天线相位中心校准工作中检验校准结果的新手段。     

Time transfer using GPS carrier phase: error propagation and results

 A joint time-transfer project between the Astronomical Institute of the University of Berne (AIUB) and the Swiss Federal Office of Metrology and Accreditation (METAS) was initiated to investigate the power of the time transfer using GPS carrier phase observations. Studies carried out in the context of this project are presented. The error propagation for the time-transfer solution using GPS carrier phase observations was investigated. To this purpose a simulation study was performed. Special interest was focussed on errors in the vertical component of the station position, antenna phase-center variations and orbit errors. A constant error in the vertical component introduces a drift in the time-transfer results for long baselines in east–west directions. The simulation study was completed by investigating the profit for time transfer when introducing the integer carrier phase ambiguities from a double-difference solution. This may reduce the drift in the time-transfer results caused by constant vertical error sources. The results from the present time-transfer solution are shown in comparison to results obtained with independent time-transfer techniques. The interpretation of the comparison benefits from the investigations of the error propagation study. Two types of solutions are produced on a regular basis at AIUB: one based on the rapid orbits from CODE, the other on the CODE final orbits. The rapid solution is available the day after the observations and has nearly the same quality as the final solution, which has a latency of about one week. The differences between these two solutions are below the nanosecond level. The differences from independent time-transfer techniques such as TWSTFT (two-way satellite time and frequency transfer) are a few nanoseconds for both products. Received: 15 November 2001 / Accepted: 6 September 2002 Correspondence to:R. Dach     

GPS接收机噪声对天线相位中心检测的影响分析

利用四天的零基线观测数据，截取不同时间长度的数据段，解算出北方向、东方向、高程方向的偏差量△N、△E、△U，对这些偏差量进行统计分析和误差分析。     

北斗天线相位中心偏差改正对精密单点定位的影响

利用厂商模型、MGEX模型和ESA模型对BDS卫星天线相位中心偏差进行改正,结果表明,3种模型对BDS精密单点定位精度均有所提升,其中,水平方向提升1～2 cm,高程方向定位精度由1 dm提升为厘米级,ESA模型优于另外两种模型。利用GPS接收机天线相位中心偏差改正值对BDS接收机天线相位中心偏差进行改正,其精度改善情况随天线类型的不同而存在差异,水平方向精度影响为毫米级,高程方向与天线类型有关,精度影响最大可达厘米级。     

天线相位中心改正模型对南极GPS基线解算的影响

针对南极地区全球定位系统(GPS)数据解算结果精度较差的问题,该文通过选取合适的解算策略来得到高精度的解算结果。采用GAMIT软件对我国南极地区的长城站、中山站及周边的11个IGS站进行数据处理,对比分析了不使用天线相位中心改正模型以及相对和绝对天线相位中心改正模型对基线解算的影响。结果表明,在南极地区进行高精度GPS数据处理时应考虑天线相位中心的影响,绝对相位中心改正模型比相对相位中心改正模型得到的结果更为精确。     

GPS基线边长与全站仪边长的检验分析

分析了GPS基线边长、全站仪边长、投影变形三者的概念,提出了工程实践中GPS基线边长与全站仪边长检验的正确方法,用实例验证了检验方法的正确性,并提出了检验过程中应注意的问题。     

Adaptive filtering of continuous GPS results

 An adaptive finite-duration impulse response filter, based on a least-mean-square algorithm, has been used to mitigate multipath effects, and to derive tectonic and fault movement signals from continuous global positioning system (CGPS) data. By applying the filter on both pseudo-range and carrier-phase multipath sequences from CGPS observations on consecutive days, multipath models have been reliably derived. The standard deviations of residual time series are reduced to about one-quarter on pseudo-range and to about one-half on carrier phase. The adaptive filter is then used to process baseline solutions from a five-station array. Tectonic and fault movements have been resolved, which are in good agreement with previous studies involving many more CGPS stations. Received: 11 February 2000 / Accepted: 28 June 2000     

Generation of a consistent absolute phase-center correction model for GPS receiver and satellite antennas

The development and numerical values of the new absolute phase-center correction model for GPS receiver and satellite antennas, as adopted by the International GNSS (global navigation satellite systems) Service, are presented. Fixing absolute receiver antenna phase-center corrections to robot-based calibrations, the GeoForschungsZentrum Potsdam (GFZ) and the Technische Universität München reprocessed more than 10 years of GPS data in order to generate a consistent set of nadir-dependent phase-center variations (PCVs) and offsets in the z-direction pointing toward the Earth for all GPS satellites in orbit during that period. The agreement between the two solutions estimated by independent software packages is better than 1 mm for the PCVs and about 4 cm for the z-offsets. In addition, the long time-series facilitates the study of correlations of the satellite antenna corrections with several other parameters such as the global terrestrial scale or the orientation of the orbital planes with respect to the Sun. Finally, completely reprocessed GPS solutions using different phase-center correction models demonstrate the benefits from switching from relative to absolute antenna phase-center corrections. For example, tropospheric zenith delay biases between GPS and very long baseline interferometry (VLBI), as well as the drift of the terrestrial scale, are reduced and the GPS orbit consistency is improved.     

Monitoring Seasonal Variations of Ionospheric TEC Using GPS Measurements

The regional ionospheric model is adopted to determine satellite-plus-receiver differential delay. The satellite-plus-receiver differential delay is estimated as constant values for each day. Dual-frequency GPS pseudo-ranges observables are used to compute vertical TEC (VTEC). All the monthly mean VTEC profiles are represented by graphs using GPS data of the Beijing IGS site between 2000 and 2004. The monthly averaged values and amplitudes of VTEC are also represented by graphs. The results indicate that the VTEC has seasonal dependency. The monthly averaged values and amplitudes of VTEC in 2000 are about 2 times larger than that in 2004. The maximum VTEC values are observed in March and April, while the minimum VTEC values are observed in December. The seasonal variations trend is found to be similar after polynomial fitting between 2000 and 2004.