利用空间技术建立绝对板块运动模型

利用欧拉定律和ITRF2005的速度场,给出了全球板块运动模型ITRF2005VEL,并计算了全球地壳旋转总角动量之和。采用离散的Tisserand条件对实测的全球台站运动速度进行约束,建立了一个新的基于NNR参考框架的实测的绝对板块运动模型NNR-ITRF2005,并与地学模型NNR-NUVEL1A和ITRF其他序列建立的NNR模型进行了比较和分析。结果表明,从整体上来看,NNR-ITRF2005比较接近于NNR-NU-VEL1A,但个别板块由于测站较少、分布不均或者测站观测时间短对板块的约束不够等原因,使得这些板块的欧拉极与地学模型的偏差较大。     

Results of the VLBI experiments conducted with Syowa Station, Antarctica

The first successful geodetic Very Long Baseline Interferometry (VLBI) observations to Antarctica were made on baselines from Syowa Station (Antarctica) to Tidbinbilla (Australia) and to Kashima (Japan) in January 1990. Regular geodetic experiments started in 1998 with the installation of a permanent VLBI terminal at Syowa Station. These observations are conducted at the standard geodetic VLBI frequencies of 2.3 and 8.4 GHz, S- and X-Bands. In the first year, the 11-m multipurpose antenna at Syowa Station observed together with the 26-m radio telescope of the University of Tasmania in Australia and the 26-m radio telescope of the Hartebeesthoek Radio Astronomy Observatory in South Africa. From 1999, the experiments were expanded to also include the O’Higgins Station in Antarctica, Fortaleza in Brazil and Kokee on Hawaii. From 1999 until the end of 2003, 25 observing sessions have been reduced and analyzed using the CALC/SOLVE geodetic VLBI data reduction package. The results show that the horizontal baseline of Syowa-Hobart is increasing at the rate of 57.0±1.9 mm/year. The baseline Syowa-Hartebeesthoek is also increasing, but at the lower rate of 9.8±1.9 mm/year. The VLBI result of 2.0±3.1 mm/year and the GPS result of −1.9±0.7 mm/year for the Syowa-O’Higgins horizontal baseline support the hypothesis of one rigid Antarctic plate without intra-plate deformation, which is consistent with the NNR-NUVEL-1A global plate motion model. The location of the Euler pole of the Antarctic plate by VLBI is estimated as 59.7°S and 62.6°E with a rotation rate of 0.190 deg/Myr, while that by GPS in our study is estimated as 60.6°S and 42.2°E with a rotation rate of 0.221 deg/Myr. These pole positions are slightly different to that implied by the NNR-NUVEL-1A model of 63.0°S and 64.2°E with a rotation rate of 0.238 deg/Myr. VLBI observations over a longer time span may resolve small discrepancy of current plate motion from the NNR-NUVEL-1A model. The consistency of the VLBI coordinates with the GPS coordinates at Syowa Station, after correction for the local tie vector components between the two reference markers, is also discussed.     

Contemporary crustal motion and deformation of South America plate

This paper presents the contemporary motion and active deformation of South America plate and relative motion of Nazca-South America plate using space geodetic data. The South America plate is moving at average 14.5 mm/a with an azimuth of 15.2° and shrinking in the west-east at 10.9 mm/a. The geodetic deformations of sites with respect to the South America plate are in quite good agreement with the estimated deformations from NNR-NUVEL1A, but the deformation of the western South America regions is very large.     

Transformation between SLR/VLBI and WGS-84 reference frames

In geodetic and geophysical applications of GPS, it is important to realize the ephemerides of the GPS satellites and the coordinates of station positions in a consistent reference system. At present, more than one reference system is being used by various GPS users depending on their specific applications. The WGS-84 and various reference frames based on satellite laser ranging (SLR), very long baseline interferometry (VLBI), or a combination of SLR and VLBI are the most commonly used in high precision geophysical applications. The WGS-84 is widely used in applications which rely on the GPS broadcast ephemeris. Station coordinates estimated in one system may have to be transformed to another for further use or for evaluation/comparison purposes. This paper presents a seven-parameter transformation between the WGS-84 and SLR/VLBI reference frames. The GPS double-differenced phase measurements for two consecutive weeks from a set of five Defense Mapping Agency (DMA) sites (defined in the WGS-84 frame) and from an augmented set of fifteen CIGNET sites (defined in the SLR/VLBI frame) were processed in a least squares estimation scheme to determine station coordinates, from which the transformation parameters were determined. A scale difference of about 0.2 ppm and an orientation difference in longitude of about 31 milliarcseconds were found to be the only parameters of significance between the adopted SLR/VLBI and the WGS-84 frames. Transformation between WGS-84 and the ITRF90 is also included, in which the scale difference is the same as before but the longitude rotation is about 16 mas.     

A Global Terrestrial Reference Frame from simulated VLBI and SLR data in view of GGOS

In this study, we assess the impact of two combination strategies, namely local ties (LT) and global ties (GT), on the datum realization of Global Terrestrial Reference Frames in view of the Global Geodetic Observing System requiring 1 mm-accuracy. Simulated Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data over a 7 year time span was used. The LT results show that the geodetic datum can be best transferred if the precision of the LT is at least 1 mm. Investigating different numbers of LT, the lack of co-located sites on the southern hemisphere is evidenced by differences of 9 mm in translation and rotation compared to the solution using all available LT. For the GT, the combination applying all Earth rotation parameters (ERP), such as pole coordinates and UT1-UTC, indicates that the rotation around the Z axis cannot be adequately transferred from VLBI to SLR within the combination. Applying exclusively the pole coordinates as GT, we show that the datum can be transferred with mm-accuracy within the combination. Furthermore, adding artificial stations in Tahiti and Nigeria to the current VLBI network results in an improvement in station positions by 13 and 12%, respectively, and in ERP by 17 and 11%, respectively. Extending to every day VLBI observations leads to 65% better ERP estimates compared to usual twice-weekly VLBI observations.     

Continental hydrology loading observed by VLBI measurements

Variations in continental water storage lead to loading deformation of the crust with typical peak-to-peak variations at very long baseline interferometry (VLBI) sites of 3–15 mm in the vertical component and 1–2 mm in the horizontal component. The hydrology signal at VLBI sites has annual and semi-annual components and clear interannual variations. We have calculated the hydrology loading series using mass loading distributions derived from the global land data assimilation system (GLDAS) hydrology model and alternatively from a global grid of equal-area gravity recovery and climate experiment (GRACE) mascons. In the analysis of the two weekly VLBI 24-h R1 and R4 network sessions from 2003 to 2010 the baseline length repeatabilities are reduced in 79 % (80 %) of baselines when GLDAS (GRACE) loading corrections are applied. Site vertical coordinate repeatabilities are reduced in about 80 % of the sites when either GLDAS or GRACE loading is used. In the horizontal components, reduction occurs in 70–80 % of the sites. Estimates of the annual site vertical amplitudes were reduced for 16 out of 18 sites if either loading series was applied. We estimated loading admittance factors for each site and found that the average admittances were 1.01 \(\pm \) 0.05 for GRACE and 1.39 \(\pm \) 0.07 for GLDAS. The standard deviations of the GRACE admittances and GLDAS admittances were 0.31 and 0.68, respectively. For sites that have been observed in a set of sufficiently temporally dense daily sessions, the average correlation between VLBI vertical monthly averaged series and GLDAS or GRACE loading series was 0.47 and 0.43, respectively.     

GPS、SLR、VLBI联合处理站坐标

采用了GPS、VLBI、SLR三种技术的并置站坐标,计算了三种技术实现的参考框架的转换参数,联合处理得到并置站的坐标并与IERS公布的坐标进行了比较。     

VLBI、卫星网和地面网联合平差的数学模型

本文同时顾及地面网尺度系统误差和卫星网尺度系统误差对各自网点坐标的影响,对联合平差中常用的两种7参数转换模型:Bursa模型和Molodensky模型进行了分析比较,在此基础上,提出了一种新的7参数转换模型;建立了甚长基线(VLBI)、卫星网和地面网联合平差的数学模型,并用模拟数据进行了数值分析,得到了一些有益结论。     

A comparison of GPS, VLBI and model estimates of ocean tide loading displacements

In recent years, ocean tide loading displacements (OTLD) have been measured using the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI). This study assesses the accuracy of GPS measurements of OTLD by comparison with VLBI measurements and estimates derived from numerical ocean tide models. A daily precise point positioning (PPP) analysis was carried out on ∼11 years of GPS data for each of 25 sites that have previous OTLD estimates based on data from co-located VLBI sites. Ambiguities were fixed to integer values where possible. The resulting daily estimates of OTLD, at eight principal diurnal and semi-diurnal tidal frequencies, were combined to give GPS measurements of OTLD at each site. The 3D GPS and VLBI measurements of OTLD were compared with estimates computed (by convolution with Green’s functions) from five modern ocean tide models (CSR4.0, FES2004, GOT00.2, NAO99b and TPXO6.2). The GPS/model agreement is shown to be similar to the VLBI/model agreement. In the important radial direction, the GPS/model misfit is shown to be smaller than the VLBI/model misfit for seven of the eight tidal constituents; the exception being the K2 constituent. Fixing of GPS carrier-phase ambiguities to integer values resulted in a marginal improvement to the GPS/model agreement. Statistically, it is shown there is no significance to the difference between the fit of the GPS and VLBI measurements of OTLD to modelled values. Equally, differences in fit of either the complete set of GPS or VLBI estimates to the five sets of model-derived values cannot be identified with statistical significance. It is thus concluded that, overall, we cannot distinguish between GPS and VLBI measurements of OTLD, and that at the global scale, present ocean tide models are accurate to within the current measurement noise of these techniques.     

Contemporary crustal motion and deformation of South America plate

1　IntroductionSouthAmericaplate (SOAM )liesamongtheCaribbeanSea ,Peru Chileseagouge ,Nazca ,Cocos ,CaribbeanplateandAtlantic .Ithasapeculiartectonicfeature ,andisastrongdeformationregionoftectonicmovementintheSouthHemi sphere .Especially ,theAndesMountaininthewestedgeofSouthAmericacameintobeingduetothedeformationofear lyCenozoic[1 ] .Aroundthisregionthetectonicplateactivities ,suchasearthquakes ,volcaniceruption ,occurfrequently(Fig .1 ) .Ontheotherhand ,becauseofaforcefuleastwardpus…     

A geodetic approach for the recovery of global kinematic plate parameters

Modern techniques of precise geodetic positioning are capable of monitoring global tectonic movements. We can avoid the tremendous effort of observing those point motions at every place on the earth, if we accept the model of rigid tectonic plates, which allows us to extrapolate from discrete point observations to the appertaining plates. The target of describing plate kinematics is the determination of its kinematic parameters, which are the coordinates of the rotation pole and the rotational velocity of each tectonic plate. A mathematical model is presented, which is capable of including geodetic observations (point coordinate shifts, distance changes) as well as geophysical quantities (sea floor spreading rates, earthquake slip vectors). The parameter estimation procedure is derived and demonstrated in simulated examples. Finally a global geodetic network for space techniques is designed, which provides an optimum parameter estimation.     

Effect of the selection of reference radio sources on geodetic estimates from VLBI observations

This paper evaluates the effect of the accuracy of reference radio sources on the daily estimates of station positions, nutation angle offsets, and the estimated site coordinates determined by very long baseline interferometry (VLBI), which are used for the realization of the international terrestrial reference frame (ITRF). Five global VLBI solutions, based on VLBI data collected between 1979 and 2006, are compared. The reference solution comprises all observed radio sources, which are treated as global parameters. Four other solutions, comprising different sub-sets of radio sources, were computed. The daily station positions for all VLBI sites and the corrections to the nutation offset angles were estimated for these five solutions. The solution statistics are mainly affected by the positional instabilities of reference radio sources, whereas the instabilities of geodetic and astrometric time-series are caused by an insufficient number of observed reference radio sources. A mean offset of the three positional components (Up, North, East) between any two solutions was calculated for each VLBI site. From a comparison of the geodetic results, no significant discrepancies between the respective geodetic solutions for all VLBI sites in the Northern Hemisphere were found. In contrast, the Southern Hemisphere sites were more sensitive to the selected set of reference radio sources. The largest estimated mean offset of the vertical component between two solutions for the Australian VLBI site at Hobart was 4 mm. In the worst case (if a weak VLBI network observed a limited number of reference radio sources) the daily offsets of the estimated height component at Hobart exceeded 100 mm. The exclusion of the extended radio sources from the list of reference sources improved the solution statistics and made the geodetic and astrometric time-series more consistent. The problem with the large Hobart height component offset is magnified by a comparatively small number of observations due to the low slewing rate of the VLBI dish (1°/ s). Unless a minimum of 200 scans are performed per 24-h VLBI experiment, the daily vertical positions at Hobart do not achieve 10 mm accuracy. Improving the slew rate at Hobart and/or having an increased number of new sites in the Southern Hemisphere is essential for further improvement of geodetic VLBI results for Southern Hemisphere sites.     

A velocity field estimation of the Brazilian portion of the SOAM plate

With the proposition for the adoption of Geocentric Reference System for the Americas (SIRGAS) as a terrestrial reference frame for South America, the need for temporal monitoring of station coordinates used in its materialization has become apparent. This would provide a dynamic characterization of the frame. The Brazilian Network for Continuous Monitoring of GPS (RBMC) has collected high accuracy GPS measurements since 1996. The Brazilian Institute of Geography and Statistics (IBGE) maintains this network in collaboration with several universities and organizations. Most of the stations are also part of the SIRGAS network. The RBMC also contributes data to the International Terrestrial Reference System (ITRS) to densify the global frame. Two of the RBMC stations are also part of the International GPS Service (IGS). This paper reports initial results from these stations. To estimate the velocity field defined by these stations, ten IGS stations located on the border of the South American plate and in adjacent plates, along with nine RBMC stations, were used. Observations covering five groups of 15 days each were used. These groups of observations were at epochs 1997.3, 1997.9, 1998.3, 1998.9 and 1999.2. Seven IGS stations were chosen to have their coordinates constrained to those epochs. IGS products (precise ephemeris and clocks) were used to process the daily solutions, which were carried out with Bernese software. Carrier phase double differences were formed using the ionospheric-delay free observable. The troposphere was modeled using a combination of the Saastamoinen model and the Niell mapping function. A tropospheric parameter was estimated every two hours. The results of the daily baseline solutions were combined using the summation of normal equations technique, in which the final coordinates and velocities were estimated. The results were compared with various models, such as the NNR-NUVEL1 and the APKIM8.80. Velocity vectors estimated for the RBMC stations show good agreement with those two models, with rates approximately equal to 2 cm/year.     

基于已知定向参数影像的光束法区域网平差

从自检校光束法区域网平差模型出发,建立了利用同一地区已知定向参数的影像解求新获取影像外方位元素并进行目标定位的数学模型。以此为基础,对来自某地区相隔两年的三期不同摄影比例尺航空影像两两组合地进行联合光束法区域网平差。结果表明,当两期影像比例尺相近时,所解求的新影像外方位元素和加密点坐标精度基本达到常规光束法区域网平差的精度;当两期影像比例尺不同时,利用已知定向参数的大比例尺影像解求出的小比例尺影像的外方位元素和加密点坐标可满足现行规范精度要求,利用已知定向参数的小比例尺影像去解求大比例尺影像的外方位元素和加密点坐标精度明显下降且不可用。本文的研究证实,就同一地区的多时相航摄影像而言,利用已知定向参数的影像进行新影像的定向方法是可行的。     

Evaluation of co-location ties relating the VLBI and GPS reference frames

We have compared the VLBI and GPS terrestrial reference frames, realized using 5 years of time-series observations of station positions and polar motion, with surveyed co-location tie vectors for 25 sites. The goal was to assess the overall quality of the ties and to determine whether a subset of co-location sites might be found with VLBI–GPS ties that are self-consistent within a few millimeters. Our procedure was designed to guard against internal distortion of the two space-geodetic networks and takes advantage of the reduction in tie information needed with the time-series combination method by using the very strong contribution due to co-location of the daily pole of rotation. The general quality of the available ties is somewhat discouraging in that most have residuals, compared to the space-geodetic frames, at the level of 1–2 cm. However, by a careful selection process, we have identified a subset of nine local VLBI–GPS ties that are consistent with each other and with space geodesy to better than 4 mm (RMS) in each component. While certainly promising, it is not possible to confidently assess the reliability of this particular subset without new information to verify the absolute accuracy of at least a few of the highest-quality ties. Particular care must be taken to demonstrate that possible systematic errors within the VLBI and GPS systems have been properly accounted for. A minimum of two (preferably three or four) ties must be measured with accuracies of 1 mm or better in each component, including any potential systematic effects. If this can be done, then the VLBI and GPS frames can be globally aligned to less than 1 mm in each Helmert component using our subset of nine ties. In any case, the X and Y rotations are better determined, to about 0.5 mm, due to the contribution of co-located polar motion.     

The impact of errors in polar motion and nutation on UT1 determinations from VLBI Intensive observations

The earth’s phase of rotation, expressed as Universal Time UT1, is the most variable component of the earth’s rotation. Continuous monitoring of this quantity is realised through daily single-baseline VLBI observations which are interleaved with VLBI network observations. The accuracy of these single-baseline observations is established mainly through statistically determined standard deviations of the adjustment process although the results of these measurements are prone to systematic errors. The two major effects are caused by inaccuracies in the polar motion and nutation angles introduced as a priori values which propagate into the UT1 results. In this paper, we analyse the transfer of these components into UT1 depending on the two VLBI baselines being used for short duration UT1 monitoring. We develop transfer functions of the errors in polar motion and nutation into the UT1 estimates. Maximum values reach 30 [μs per milliarcsecond] which is quite large considering that observations of nutation offsets w.r.t. the state-of-the-art nutation model show deviations of as much as one milliarcsecond.     

组合VLBI和SLR数据估计的全球板块运动参数

本文组合应用ＶＬＢＩ和ＳＬＲ数据导出了一个完全基于空间技术实测数据的现时板块运动模型，称为ＳＧＰＭＭ１。ＳＧＰＭＭ１与地学板块运动模型ＮＵＶＥＬ－１的比较指出：空间大地测量数据估计的板块运动总体上与地学估计值一致。经过地磁极倒转时间尺度修正，并考虑到冰斯后地壳回弹的影响，空间大地测量数据估计的北美，欧亚和澳大利亚板块之间的相对运动速率与地学估计值有极好的一致，但太平洋板块相对于北美、欧亚和澳大利亚     

大角度三维基准转换的解析封闭解

传统大地测量应用中的基准转换往往涉及小角度旋转,可只考虑旋转角的一阶量采用线性化方法求解。现代空间测量技术成果应用的基准转换涉及大角度旋转,通过将旋转矩阵所有元素作为未知数并利用旋转矩阵正交条件采用附约束条件平差法迭代求解。本文以空间三维基准转换为例,采用多元模型的矩阵形式将多点坐标组成矩阵处理,并利用旋转矩阵的正交条件导出了大角度三维基准转换的解析分步解。同时引入两套公共点坐标误差对传统三维基准转换模型扩展,导出了同时顾及两套公共点坐标误差的大角度三维基准转换模型的解析解。试验表明:给出的大角度三维基准转换解析解能在实现与传统迭代解等效转换结果的同时,有效避免复杂耗时的迭代计算,提高计算效果。     

基于全球板块运动模型分析大西洋扩张变化

基于现代空间测量技术SLR、VLBI和GPS实测资料，解算出大西洋中脊海底扩张速率，其中北大西洋的东西向扩张速率平均为35mm/a，赤道大西洋东西向扩张速度分别为20－25mm/a，南大西洋东西向扩张速率为22－28mm/a，证实全球板块运动的存在及大西洋扩张学说，并基于全球几百万年地质模型NNR－NUVEL1A，北大西洋的东西向扩张速率平均为24．3mm/a，基于最新全球板块运动模型ITRF2000VEL，北大西洋的东西向扩张速率平均为20．8mm/a，总体上大西洋实测东西扩张速度与根据地学资料推出的地球板块运动模型和最新ITRF2000VEL模型的结果基本一致。     

一种适用大旋转角的GPS网三维平差方法

在工程测量中往往采用工程坐标系,该坐标系坐标轴可能与GPS采用的WGS84坐标系的相应坐标轴间存在较大的旋转角,此时若仍直接按照一般方法进行三维约束平差计算会给结果带来不利影响,本文给出了一种适用大旋转角的GPS网三维平差方法,该方法能够很好地处理大旋转角时直接采用一般三维平差模型计算带来的不利影响,同时又能够获得平差后工程网中各点的点位精度。工程应用表明该方法非常有效,具有很好的应用价值。