Ocean tidal parameters from starlette data

Starlette was launched in 1975 in order to study temporal variations in the Earth’s gravity field; in particular, tidal and Earth rotation effects. For the period April 1983 to April 1984 over12,700 normal points of laser ranging data to Starlette have been sub-divided into49 near consecutive 5–6 day arcs. Normal equations for each arc as obtained from a least-squares data reduction procedure, were solved for ocean tidal parameters along with other geodetic and geodynamic parameters. The tidal parameters are defined relative to Wahr’s body tides and Wahr’s nutation model and show fair agreement with other satellite derived results and those obtained from spherical harmonic decomposition of global ocean tidal models.     

A catalog of station coordinates for GEOS-C orbit determination

Center-of-mass coordinates for 57 tracking sites participating in the GEOS-C mission are given in a unified system having a common origin and scale. The positions were obtained either directly from analyses of satellite observations or from survey ties to colocated sites with coordinates previously determined by various investigators from optical, laser of doppler data. The uncertainty of the positions in nearly all cases is 5 m in each coordinate. Data reductions show that station coordinates of this quality introduce a rapidly changing error into the altitude of a satellite unless global tracking constrains the orbit.     

Computing geodetic coordinates from geocentric coordinates

A closed-form algebraic method to transform geocentric coordinates to geodetic coordinates has previously been proposed. The validity domain of latitude and height formulae in the vicinity of the Earths core is specified. A new expression of longitude is proposed, excluding indetermination and sensitivity to round-off error around the ±180 degrees longitude discontinuity.     

A new combined European permanent network station coordinates solution

The EUREF [International Association of Geodesy (IAG) Reference Frame Sub-Commission for Europe] network of continuously operating GPS stations (EPN) was primarily established for reference frame maintenance, and also plays an important role for geodynamical research in Europe. The main objective of this paper is to obtain an independent homogeneous time series of the EPN station coordinates, which is also available in SINEX format. A new combined solution of the EPN station coordinates was computed. The combination was performed independently for every week, in three steps: (1) the stated constraints on the coordinates were removed from the individual solutions of the Analysis Centers; (2) the de-constrained solutions were aligned to ITRF2000; (3) the resulting solutions were combined using the Helmert blocking technique. All the data from GPS weeks 900 to 1302 (April 1997–December 2004) were used. We investigated in detail the behavior of the transformation parameters aligning the new combined solution to ITRF2000. In general, the time series of the transformation parameters show a good stability in time although small systematic effects can be seen, most likely caused by station instabilities. A comparison of the new combined solution to the official EUREF weekly combined solution is also presented.     

Monitoring the quality of GPS station coordinates in real time

This paper evaluates various statistical process control algorithms for monitoring the quality of GPS station coordinates in real-time kinematic applications. Real-time detection of small but persistent shifts in GPS coordinates is critical for applications requiring automatic and reliable results in deformation monitoring. Examples include monitoring of dams, high-rise buildings, bridges, tectonic movements, landslides and so on. The conventional cumulative sums (Cusums), the robustified and self-starting Cusums, the adaptive Cusum and the exponential weighted moving average are some of the control charts applied to real-time-kinematic (RTK) data in field experiments. All control charts have been evaluated for their effectiveness in detecting an actual but intentional deformation shift of at least 0.5 standard deviations from a target mean. The observations used in testing these control charts had initially been assumed to be independent and follow a normal distribution, but later, their serial correlation was taken into consideration. These results show that the self-starting but robustified Cusums as well as the exponentially weighted moving average charts are suitable and efficient tools in monitoring quality in the RTK data. All presented control charts are implemented as modules in a software package being developed by the Technical University of Crete.     

The IGS-combined station coordinates, earth rotation parameters and apparent geocenter

The International GNSS Service (IGS) routinely generates a number of weekly, daily and sub-daily products. Station coordinates and velocities, earth rotation parameters (ERPs) and apparent geocenter are among these products generated weekly by the IGS Reference Frame Coordinator. They have been determined since 1999 by combining independent estimates from at least seven IGS Analysis Centers (ACs). Two Global Network Associate Analysis Centers (GNAACs) also provide independent combinations using the same AC weekly solutions and they are currently used to quality control the IGS combination. The combined solutions are aligned to an IGS realization (IGS05) of the ITRF2005 using a carefully selected set of the IGS Reference Frame (RF) stations (nominally 132). During the combination process, the contributing solutions are compared and outliers are removed to ensure a high level of consistency of the estimated parameters. The ACs and the weekly combined solution are consistent at the 1–2 and 3–4 mm levels for the horizontal and vertical components. Similarly, the excess Length of Day (LOD), the pole positions and pole rates are consistent at the 10μs, 0.03–0.05 mas and 0.10–0.20 mas/day levels, respectively. The consistency of the apparent geocenter estimate is about 5 mm in the X and Y components and 10 mm in the Z component. Comparison of the IGS-combined ERP estimates with the IERS Bulletin A suggests a small bias of the order of ?0.04 mas and + 0.05 mas (both ±0.05 mas) in the x and y components.     

高阶电离层延迟对不同区域测站坐标的影响

针对如何有效控制、改正甚至消除不同区域与时段的电离层高阶项延迟对全球导航卫星系统定位结果产生的影响,该文选取了不同区域内有代表性的IGS基准站1999—2003年的观测数据进行解算,并详细分析了各测站坐标受高阶电离层延迟影响的规律。在此基础上,总结出测站的高阶项改正与测站区域地理位置的关系,并探究产生这种影响的原因。最后从全球的角度研究了电离层高阶项改正对基准站坐标的影响。结果表明,要获得高精度的定位结果,需要顾及高阶电离层延迟的影响,尤其是在赤道以及地球两极区域的精密定位,此外,需要顾及电离层变化活跃期的影响。     

南宁CORS系统基准站地心大地坐标精确测定的方法与实践

采用地心坐标系已成为国际测量界的总趋势,而利用GPS连续运行参考站建立地心坐标框架最为普遍。利用GAM IT软件,采用有基准算法对南宁市全球导航连续运行参考站网络系统(NNCORS)的南宁基准站NANN的观测资料进行了归算,结果表明该基准站观测资料的质量是可靠的,并获得了该站在ITRF2000中毫米级精度的地心大地坐标。     

GPS站坐标时间序列的南极地壳运动监测

为了进一步研究南极地壳运动的监测方法,文章提出直接利用GARNER网站公布的长时段测站坐标时间序列进行南极地壳运动监测的方法;直接利用GARNER网站提供的站坐标时间序列保证了站坐标的正确性,避免了对原始观测数据进行处理时步骤繁琐或处理结果不可靠等问题。研究结果表明该方法正确、可行。     

On the significance of periodic signals in noise analysis of GPS station coordinates time series

Each of the GPS-derived time series consists of the deterministic (functional) and stochastic part. We propose that the deterministic part includes all periodicities from 1st to 9th harmonics of residual Chandler, tropical and draconitic periods and compare it with commonly used calculations of the annual and semi-annual tropical curve. Then, we address the issues of whether all residual periodicities, as proposed here, need to be taken into consideration when performing noise analysis. We use the position time series from 180 International GNSS Service stations obtained at the Jet Propulsion Laboratory using the GIPSY-OASIS software in a Precise Point Positioning mode. The longest series has 22.1 years of GPS daily solutions. The spectral indices range from –0.12 to –0.92, while the median values of “global” spectral indices are equal to: –0.41 ± 0.15, –0.38 ± 0.12 and –0.33 ± 0.18 for North, East and Up components, respectively. All non-modelled geophysical processes or non-included artificial effects in time series lead to an underestimation of errors of velocities, but also to changes in the velocity values themselves. The proposed assumption of seasonals subtraction caused the Akaike information criterion values to show a decrease in the median value of 30 %, which in fact means that all the seasonals mentioned here must be taken into account when analyzing noises. Finally, we noticed that there are some of the GPS stations that improved their velocity uncertainty even of 56 %.     

Fast transform from geocentric to geodetic coordinates

 A new iterative procedure to transform geocentric rectangular coordinates to geodetic coordinates is derived. The procedure solves a modification of Borkowski's quartic equation by the Newton method from a set of stable starters. The new method runs a little faster than the single application of Bowring's formula, which has been known as the most efficient procedure. The new method is sufficiently precise because the resulting relative error is less than 10⁻¹⁵, and this method is stable in the sense that the iteration converges for all coordinates including the near-geocenter region where Bowring's iterative method diverges and the near-polar axis region where Borkowski's non-iterative method suffers a loss of precision. Received: 13 November 1998 / Accepted: 27 August 1999     

Assessment of local GNSS baselines at co-location sites

As one of the major contributors to the realisation of the International Terrestrial Reference System (ITRS), the Global Navigation Satellite Systems (GNSS) are prone to suffer from irregularities and discontinuities in time series. While often associated with hardware/software changes and the influence of the local environment, these discrepancies constitute a major threat for ITRS realisations. Co-located GNSS at fundamental sites, with two or more available instruments, provide the opportunity to mitigate their influence while improving the accuracy of estimated positions by examining data breaks, local biases, deformations, time-dependent variations and the comparison of GNSS baselines with existing local tie measurements. With the use of co-located GNSS data from a subset sites of the International GNSS Service network, this paper discusses a global multi-year analysis with the aim of delivering homogeneous time series of coordinates to analyse system-specific error sources in the local baselines. Results based on the comparison of different GNSS-based solutions with the local survey ties show discrepancies of up to 10 mm despite GNSS coordinate repeatabilities at the sub-mm level. The discrepancies are especially large for the solutions using the ionosphere-free linear combination and estimating tropospheric zenith delays, thus corresponding to the processing strategy used for global solutions. Snow on the antennas causes further problems and seasonal variations of the station coordinates. These demonstrate the need for a permanent high-quality monitoring of the effects present in the short GNSS baselines at fundamental sites.     

Rapid GPS ambiguity resolution for short and long baselines

 A method of quick initial carrier cycle ambiguity resolution is described. The method applies to high-quality dual-band global positioning system observations. Code measurements on both frequencies must be available. The rapidity of the method is achieved through smoothing pseudoranges by phase observables and forming linear combinations between the phase observables. Two cases are investigated. Case 1: ionospheric bias is neglected (short distances); and case 2: the bias is taken into account (longer distances, more than, say, 10 km). The method was tested on six baselines, from 1 to 31 km long. In most cases, single-epoch ambiguity resolution was achieved. Received: 6 October 1999 / Accepted: 4 March 2002     

Centimeter repeatability of the VLBI estimates of European baselines

Summary In the last three years, the European Geodetic Very Long Baseline Interferometry (VLBI) Network has grown to a total of six fixed antennas placed in Germany, Italy, Spain and Sweden, all equipped with the standard geodetic VLBI instrumentation and data recording systems. During this period of time, several experiments have been carried out using this interferometer providing data of very high quality due to the excellent sensitivity and performance of the European stations. The purpose of this paper is to study the consistency of the VLBI geodetic results on the European baselines with respect to the different degrees of freedom in the analysis procedure. In order to complete this study we have made use of both real and simulated data sets, two different software packages (OCCAM 3.0 and CALC 7.4/SOLVE) and a variety of strategies in the data analysis. The results we have obtained show that the repeatability of the VLBI estimates of the baseline lengths in the European network is better than one centimeter, independent of the different analysis methods, and is consistent with the formal error levels expected from the data analysis. This consistency should be enough to produce geophysically significant information in Europe from VLBI data within a relatively short time span.     

Transformation from geocentric to geodetic coordinates using Newton's iteration

Summary A new procedure for the transformation from geocentric to geodetic coordinates is introduced and analyzed. This new procedure which contains only one trigonometric function uses the Newton's iteration to solve the root of a non-linear equation. Compared with the well-known Bowring's iterative algorithm which uses a number of trigonometric functions, the new procedure is more efficient in computation. Numeric examples are used to test the two algorithms and the results show that the new procedure converges just as well as Bowring's algorithm but requires less time for completion.     

北斗中长基线静态测量精度初步评估

北斗卫星导航系统已于2012年12月27日开始正式提供区域服务,可为亚太地区用户提供定位、导航、授时和短报文通讯等服务,在精密定位方面有很大潜力。本文通过使用南方测绘GNSS后处理软件对长度范围为13~94km的6条基线的北斗静态测量数据进行处理,并将其解算结果与GPS相应解算结果和已知坐标进行比较,初步评估北斗静态测量精度。试验结果显示,基于广播星历对北斗中长基线(100km)静态测量(4h)数据进行解算的基线精度可达4cm,因此北斗中长基线静态测量已具有很大的研究价值和应用前景。     

S2L-RTK: temporal ionospheric modeling for RTK baselines varying from short to long

GPS Solutions - The multipath effect is well known as one of the dominant error sources in most high-precision GNSS applications, as its site-dependent and fast-changing nature render it...