共查询到20条相似文献,搜索用时 78 毫秒
1.
郭俊义 《武汉大学学报(信息科学版)》2000,25(5):393-395
通过引进章动坐标系相对惯性参照系的转动角速度随时间的变化 ,导出了一个可同时解出章动和极移的地球自转方程 ,用这个方程可同时研究地球的强迫和自由转动。与现行研究地球自转的惯用方法相比 ,该方法综合性强 ,易于理解。 相似文献
2.
The determination of baseline lengths from certain space techniques is based on the derived coordinates of the terminal stations.
As such, the estimated baselines are susceptible to systematic errors that affect the relative coordinates. One source of
error is in the set of parameters which describes the continuously changing relative orientation of the Conventional Terrestrial
(CTS) and Inertial (CIS) Reference frames. Due to these errors, the coordinates of each terminal station may in fact refer
to a slightly different coordinate svstem, and, therefore, when used for computing the length between the stations, errors
will result. The expected magnitudes of such errors and their possible presence in current solutions are investigated.
In conclusion, we find that the present level of accuracy and stability of the available parameters connecting the CTS and
CIS (e.g., the ERP series) is unsatisfactory for centimeter level baseline length determinations. The available options are
either the use of strictly simultaneous SLR data sets (similar to the VLBI data sets) or the improvement of the parameters
connecting the CTS and the CIS. The first long-range step in the latter direction is the support of the IAG/IAU Joint Working
Group COTES proposal [CSTG Bulletin, 1982], endorsed by both the IAG and IAU in various resolutions [IAU, 1983; IAG, 1982].
Presented at the Annual Fall Meeting of the American Geophysical Union, San Francisco, December 7–15, 1982, and at the Fifth
Annual NASA Geodynamics Program Conference and Crustal Dynamics Project Review, Washington, D.C., January 24–28, 1983. 相似文献
3.
Very Long Baseline Interferometry (VLBI) plays a unique and fundamental role in the maintenance of the global (terrestrial
and celestial) reference frames, which are required for precise positioning in many research areas such as the understanding
and monitoring of global changes, and for space missions. The International VLBI Service for Geodesy and Astrometry (IVS)
coordinates the global VLBI components and resources on an international basis. The service is tasked by the International
Association of Geodesy (IAG) and International Astronomical Union (IAU) to provide products for the realization of the Celestial
Reference Frame (CRF) through the positions of quasars, to deliver products for the maintenance of the terrestrial reference
frame (TRF), such as station positions and their changes with time, and to generate products describing the rotation and orientation
of the Earth. In particular, VLBI uniquely provides direct observations of nutation parameters and of the time difference
UT1-UTC. This paper summarizes the evolution and current status of the IVS. It points out the activities to improve further
on the product quality to meet future service requirements. 相似文献
4.
GUO Junyi 《地球空间信息科学学报》2001,4(3):6-8
1 IntroductionInmodernEarthrotationtheory ,threereferenceframesareusuallyused ,i.e .,thespatial (inertial)frameOξ1 ξ2 ξ3,theterrestrialframeOx1 x2 x3andthenutationframeOx01 x02 x03.Thenutationframedefinesacelestialephemerispole .Themotionofthiscelestialephemerispolew… 相似文献
5.
Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations 总被引:3,自引:3,他引:0
A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry
(VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination
was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series
with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day
nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that
the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints
were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However,
this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement
can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is
defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall,
the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In
terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models
below 4 μas in PM and 0.25 μs in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μas for diurnal PM and 0.07 μs for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy. 相似文献
6.
The impact of errors in polar motion and nutation on UT1 determinations from VLBI Intensive observations 总被引:2,自引:2,他引:0
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. 相似文献
7.
Combined Earth orientation parameters based on homogeneous and continuous VLBI and GPS data 总被引:1,自引:3,他引:1
Daniela Thaller Manuela Krügel Markus Rothacher Volker Tesmer Ralf Schmid Detlef Angermann 《Journal of Geodesy》2007,81(6-8):529-541
The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic
techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network.
Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined
station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique-
specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison
and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for
polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation
between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides
a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to
get a deeper understanding of this singularity. With a rigorous combination of UT1–UTC and length of day (LOD) from VLBI and
GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived
LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same
holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential
role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial
measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies propagate into the combined
EOP solution. 相似文献
8.
The purpose of this paper is to develop a canonical formulation of the rotational motion for an elastic Earth model. We have
obtained the canonical equations for the precession and nutation motion in an inertial frame, and from this we have deduced
the equations in an Earth-fixed frame. The linearized equations deduced for polar motion are equivalent to those obtained
using Liouville's equations. 相似文献
9.
We compare nutation time series determined by several International VLBI Service for geodesy and astrometry (IVS) analysis centers. These series were made available through the International Earth Rotation and Reference Systems Service (IERS). We adjust the amplitudes of the main nutations, including the free motion associated with the free core nutation (FCN). Then, we discuss the results in terms of physics of the Earth’s interior. We find consistent FCN signals in all of the time series, and we provide corrections to IAU 2000A series for a number of nutation terms with realistic errors. It appears that the analysis configuration or the software packages used by each analysis center introduce an error comparable to the amplitude of the prominent corrections. We show that the inconsistencies between series have significant consequences on our understanding of the Earth’s deep interior, especially for the free inner core resonance: they induce an uncertainty on the FCN period of about 0.5 day, and on the free inner core nutation (FICN) period of more than 1000 days, comparable to the estimated period itself. Though the FCN parameters are not so much affected, a 100 % error shows up for the FICN parameters and prevents from geophysical conclusions. 相似文献
10.
Younghee Kwak Mathis Bloßfeld Ralf Schmid Detlef Angermann Michael Gerstl Manuela Seitz 《Journal of Geodesy》2018,92(9):1047-1061
The Celestial Reference System (CRS) is currently realized only by Very Long Baseline Interferometry (VLBI) because it is the space geodetic technique that enables observations in that frame. In contrast, the Terrestrial Reference System (TRS) is realized by means of the combination of four space geodetic techniques: Global Navigation Satellite System (GNSS), VLBI, Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite. The Earth orientation parameters (EOP) are the link between the two types of systems, CRS and TRS. The EOP series of the International Earth Rotation and Reference Systems Service were combined of specifically selected series from various analysis centers. Other EOP series were generated by a simultaneous estimation together with the TRF while the CRF was fixed. Those computation approaches entail inherent inconsistencies between TRF, EOP, and CRF, also because the input data sets are different. A combined normal equation (NEQ) system, which consists of all the parameters, i.e., TRF, EOP, and CRF, would overcome such an inconsistency. In this paper, we simultaneously estimate TRF, EOP, and CRF from an inter-technique combined NEQ using the latest GNSS, VLBI, and SLR data (2005–2015). The results show that the selection of local ties is most critical to the TRF. The combination of pole coordinates is beneficial for the CRF, whereas the combination of \(\varDelta \hbox {UT1}\) results in clear rotations of the estimated CRF. However, the standard deviations of the EOP and the CRF improve by the inter-technique combination which indicates the benefits of a common estimation of all parameters. It became evident that the common determination of TRF, EOP, and CRF systematically influences future ICRF computations at the level of several \(\upmu \)as. Moreover, the CRF is influenced by up to \(50~\upmu \)as if the station coordinates and EOP are dominated by the satellite techniques. 相似文献
11.
The temporal change of the rotation vector of a rotating body is, in the first order, identical in a space-fixed system and
in a body-fixed system. Therefore, if the motion of the rotation axis of the earth relative to a space-fixed system is given
as a function of time, it should be possible to compute its motion relative to an earth-fixed system, and vice versa. This
paper presents such a transformation. Two models of motion of the rotation axis in the space-fixed system are considered:
one consisting only of a regular (i.e., strictly conical) precession and one extended by circular nutation components, which
are superimposed upon the regular precession. The Euler angles describing the orientation of the earth-fixed system with respect
to the space-fixed system are derived by an analytical solution of the kinematical Eulerian differential equations. In the
first case (precession only), this is directly possible, and in the second case (precession and nutation), a solution is achieved
by a perturbation approach, where the result of the first case serves as an approximation and nutation is regarded as a small
perturbation, which is treated in a linearized form. The transformation by means of these Euler angles shows that the rotation
axis performs in the earth-fixed system retrograde conical revolutions with small amplitudes, namely one revolution with a
period of one sidereal day corresponding to precession and one revolution with a period which is slightly smaller or larger
than one sidereal day corresponding to each (prograde or retrograde) circular nutation component. The peculiar feature of
the derivation presented here is the analytical solution of the Eulerian differential equations. 相似文献
12.
Zinovy Malkin 《Journal of Geodesy》2011,85(9):617-622
Very Long Baseline Interferometry (VLBI) Intensive sessions are scheduled to provide operational Universal Time (UT1) determinations
with low latency. UT1 estimates obtained from these observations heavily depend on the model of the celestial pole motion
used during data processing. However, even the most accurate precession- nutation model, IAU 2000/2006, is not accurate enough
to realize the full potential of VLBI observations. To achieve the highest possible accuracy in UT1 estimates, a celestial
pole offset (CPO), which is the difference between the actual and modelled precession-nutation angles, should be applied.
Three CPO models are currently available for users. In this paper, these models have been tested and the differences between
UT1 estimates obtained with those models are investigated. It has been shown that neglecting CPO modelling during VLBI UT1
Intensive processing causes systematic errors in UT1 series of up to 20 μas. It has been also found that using different CPO models causes the differences in UT1 estimates reaching 10 μas. Obtained results are applicable to the satellite data processing as well. 相似文献
13.
14.
Johannes Boehm Robert Heinkelmann Paulo Jorge Mendes Cerveira Andrea Pany Harald Schuh 《Journal of Geodesy》2009,83(11):1107-1113
This paper investigates whether in very long baseline interferometry (VLBI) analysis atmospheric loading corrections should
be applied a priori at the observation level or whether it is sufficient to correct for atmospheric loading effects a posteriori
by adding constant values per session to the estimated station coordinates. Simulated observations at single stations corresponding
to the precise point positioning approach of global navigation satellite systems show that the atmospheric loading effect
can be fully recovered by a posteriori corrections, i.e., the height differences between both approaches stay well below 1 mm.
However, real global VLBI network solutions with sessions from 1984 to 2008 reveal that the effect of neglected atmospheric
loading corrections at the stations is distributed to the other stations in the network, thus resulting in station height
differences between solutions with observation level and with a posteriori corrections which can be as large as 10 mm and
a ‘damping’ effect of the corrections. As soon as the terrestrial reference frame and the corresponding coordinate time series
are determined, it would be conceptually wrong to apply atmospheric loading corrections at the VLBI stations. We recommend
the rigorous application of atmospheric loading corrections at the observation level to all stations of a VLBI network because
the seven parameters for translation, rotation, and in particular the network-scale of VLBI networks are significantly affected. 相似文献
15.
A 29-year time-series of four-times-daily atmospheric effective angular momentum (EAM) estimates is used to study the atmospheric
influence on nutation. The most important atmospheric contributions are found for the prograde annual (77 μas), retrograde
annual (53 as), prograde semiannual (45 as), and for the constant offset of the pole (δψsinɛ0=−86 as, δɛ=77 as). Among them only the prograde semiannual component is driven mostly by the wind term of the EAM function,
while in all other cases the pressure term is dominant. These are nonnegligible quantities which should be taken into account
in the new theory of nutation. Comparison with the VLBI corrections to the IAU 1980 nutation model taking into account the
ocean tide contribution yields good agreement for the prograde annual and semiannual nutations. We also investigated time
variability of the atmospheric contribution to the nutation amplitudes by performing the sliding-window least-squares analysis
of both the atmospheric excitation and VLBI nutation data. Almost all detected variations of atmospheric origin can be attributed
to the pressure term, the biggest being the in-phase annual prograde component (about 30 as) and the retrograde one (as much
as 100200 as). These variations, if physical, limit the precision of classical modeling of nutation to the level of 0.1 mas.
Comparison with the VLBI data shows significant correlation for the retrograde annual nutation after 1989, while for the prograde
annual term there is a high correlation in shape but the size of the atmospherically driven variations is about three times
less than deduced from the VLBI data. This discrepancy in size can be attributed either to inaccuracy of the theoretical transfer
function or the frequency-dependent ocean response to the pressure variations. Our comparison also yields a considerably better
agreement with the VLBI nutation data when using the EAM function without the IB correction for ocean response, which indicates
that this correction is not adequate for nearly diurnal variations.
Received: 10 September 1997 / Accepted: 5 March 1998 相似文献
16.
Elizabeth J. Petrie Matt A. King Philip Moore David A. Lavallée 《Journal of Geodesy》2010,84(8):491-499
This study provides a first attempt at quantifying potential signal bending effects on the GPS reference frame, coordinates
and zenith tropospheric delays (ZTDs). To do this, we homogeneously reanalysed data from a global network of GPS sites spanning
14 years (1995.0–2009.0). Satellite, Earth orientation, tropospheric and ground station coordinate parameters were all estimated.
We tested the effect of geometric bending and dTEC bending corrections, which were modelled at the observation level based,
in part, on parameters from the International Reference Ionosphere 2007 model. Combined, the two bending corrections appear
to have a minimal effect on site coordinates and ZTDs except for low latitude sites. Considering five days (DOY 301–305, 28
October–1 November 2001) near ionospheric maximum in detail, they affect mean ZTDs by up to ~1.7 mm at low latitudes, reducing
to negligible levels at high latitudes. Examining the effect on coordinates in terms of power-spectra revealed the difference
to be almost entirely white noise, with noise amplitude ranging from 0.3 mm (high latitudes) to 2.4 mm (low latitudes). The
limited effect on station coordinates is probably due to the similarity in the elevation dependence of the bending term with
that of tropospheric mapping functions. The smoothed z-translation from the GPS reference frame to ITRF2005 changes by less than 2 mm, though the effect combines positively with
that from the second order ionospheric refractive index term. We conclude that, at the present time, and for most practical
purposes, the geometric and dTEC bending corrections are probably negligible at current GPS/reference frame precisions. 相似文献
17.
Analytical versus semi-analytical determinations of the Oppolzer terms for a non-rigid Earth 总被引:1,自引:1,他引:0
Estimations of the Oppolzer terms for the angular momentum and rotation axes of a non-rigid Earth are obtained from two different
approaches and compared. The first approach is an analytical method which relies on the solutions of the Liouville equations
for a two-layer Earth model. The Oppolzer terms are evaluated from analytical expressions. The results are then compared to
those calculated from Wahr's theory of nutation for a non-rigid Earth, which is the second approach used. Results are obtained
for the main nutation frequencies and for the precession case. The differences between the two solutions are generally quite
small (the relative error is most of the time under 8%) and are, for a large part, due to successive approximations and truncation
effects during their determination. Departures of the results from the two methods are significantly larger for frequencies
near the Free Core Nutation (FCN) resonance. This is particularly true for the Oppolzer terms of the angular momentum axis.
The Earth model adopted is a little bit different in each case: for the Liouville system solution, we have limited the model
to a homogeneous elastic mantle and a homogeneous liquid core. Another source of some of the small differences in the results
is the presence of a solid inner core in Wahr's theory. We confirm through the analytical calculation the strong effect of
the core on the Oppolzer terms of the angular momentum axis for a non-rigid Earth at the precession frequency. Finally, an
application is given in the determination of the axes' position at J2000 for a non-rigid Earth.
Received: 23 February 1998 /Accepted: 18 November 1998 相似文献
18.
Strategies to mitigate aliasing of loading signals while estimating GPS frame parameters 总被引:7,自引:5,他引:2
Although GNSS techniques are theoretically sensitive to the Earth center of mass, it is often preferable to remove intrinsic
origin and scale information from the estimated station positions since they are known to be affected by systematic errors.
This is usually done by estimating the parameters of a linearized similarity transformation which relates the quasi-instantaneous
frames to a long-term frame such as the International Terrestrial Reference Frame (ITRF). It is well known that non-linear
station motions can partially alias into these parameters. We discuss in this paper some procedures that may allow reducing
these aliasing effects in the case of the GPS techniques. The options include the use of well-distributed sub-networks for
the frame transformation estimation, the use of site loading corrections, a modification of the stochastic model by downweighting
heights, or the joint estimation of the low degrees of the deformation field. We confirm that the standard approach consisting
of estimating the transformation over the whole network is particularly harmful for the loading signals if the network is
not well distributed. Downweighting the height component, using a uniform sub-network, or estimating the deformation field
perform similarly in drastically reducing the amplitude of the aliasing effect. The application of these methods to reprocessed
GPS terrestrial frames permits an assessment of the level of agreement between GPS and our loading model, which is found to
be about 1.5 mm WRMS in height and 0.8 mm WRMS in the horizontal at the annual frequency. Aliased loading signals are not
the main source of discrepancies between loading displacement models and GPS position time series. 相似文献
19.
Tomás Soler 《GPS Solutions》2001,4(3):27-33
A primary output of Global Positoning System (GPS) post-processed data is a set of non-trivial (independent) vector components
and their full covariance information referred to a specific local Cartesian terrestrial frame (e. g., ITRF, WGS84) and epoch.
It is important to recognize that when GPS-determined vector components are simultaneously combined into 3D geodetic network
adjustments, they should always refer to a common coordinate frame and epoch. This paper uses geometric concepts to formulate
rigorous matrix transformations to correct vector components for changes in coordinate systems, secular displacements due
to plate rotations, and antenna centering and/or height measuring errors. Finally, the associated variance-covariance matrix
of the transformed vector components is derived. ? 2001 John Wiley & Sons, Inc. 相似文献
20.
Foreword The International Earth Rotation Service (IERS) was organized by the International Union of Geodesy and Geophysics and the International Astronomical Union. It started
operation on 1988 January 1. Its responsabilities and activities are described in the Geodesist's Handbook (1988). The Central
Bureau ofIERS is operated by a scientific team established in cooperation by Observatoire de Paris, Institut Géographique National and
Bureau des Longitudes. This team was selected in 1987 on the basis of the present document which describes in some detail
the concepts and methods for establishing and maintaining celestial and terrestrial reference frames for Earth orientation
monitoring (polar motion, universal time, precession/nutation). The work of the Central Bureau is based on these concepts
and methods, not withstanding future evolution made possible by the improvements in observations and theories. 相似文献