共查询到20条相似文献，搜索用时 31 毫秒
1.
J. Höpfner 《Journal of Geodesy》2000,74(3-4):335-358
Recently, effective atmospheric-angular-momentum (AAM) functions as calculated from National Centers for Environmental Prediction
(NCEP) (formerly National Meteorological Center, NMC) and National Center for Atmospheric Research (NCAR) Reanalyses have
become available for the years 1958 to 1998. Concerning the wind terms, the top level in the atmosphere used here is 10 hPa.
Compared with earlier NMC model versions, which incorporate wind fields up to 100 hPa since 1976 and up to 50 hPa since 1981,
the reanalyses have produced improved data series over a longer period than before. The axial AAM component χ3 is associated with changes in length of day (LOD). Motivated by better quality and continuity of the series AAM (NCEP) Reanalysis,
the problem of the seasonal imbalances in the solid Earth–atmosphere axial angular momentum budget is re-examined. To assess
better the estimates of the annual and semiannual oscillations in LOD and AAM and of the residual oscillations derived as
difference series between LOD and AAM, the series of LOD data from three analysis centers [International Earth Rotation Service
(IERS), GeoForschungZentrum Potsdam (GFZ) and Jet Propulsion Laboratory Pasadena (JPL)] and of AAM data in terms of χ3(W), χ3(P) and χ3(P+IB) from four meteorological centers [NCEP, Japan Meteorological Agency (JMA), European Centre for Medium-Range Weather
Forecasts (ECMWF) and the UK Meteorological Office (UKMO)] are used in this study. The main analysis steps were removing gaps,
filtering out the seasonal oscillations, calculating optimal estimates of the parameters of the oscillations and calculating
the difference series between the LOD and AAM systems as well as the residuals in the axial angular momentum budget in the
LOD–AAM systems. The results derived as difference series between the different LOD, AAM and LOD–AAM systems show to what
extent the variations reflect systematic differences and significant signals, respectively, which is important for future
activities in this field.
Received: 2 February 1999 / Accepted: 30 November 1999 相似文献
2.
Earth orientation parameters (EOPs) [polar motion and length of day (LOD), or UT1–UTC] were predicted by artificial neural
networks. EOP series from various sources, e.g. the C04 series from the International Earth Rotation Service and the re-analysis
optical astrometry series based on the HIPPARCOS frame, served for training the neural network for both short-term and long-term
predictions. At first, all effects which can be described by functional models, e.g. effects of the solid Earth tides and
the ocean tides or seasonal atmospheric variations of the EOPs, were removed. Only the differences between the modeled and
the observed EOPs, i.e. the quasi-periodic and irregular variations, were used for training and prediction. The Stuttgart
neural network simulator, which is a very powerful software tool developed at the University of Stuttgart, was applied to
construct and to validate different types of neural networks in order to find the optimal topology of the net, the most economical
learning algorithm and the best procedure to feed the net with data patterns. The results of the prediction were analyzed
and compared with those obtained by other methods. The accuracy of the prediction is equal to or even better than that by
other prediction methods.
Received: 6 February 2001 / Accepted: 23 October 2001 相似文献
3.
IGS Earth Rotation Parameters 总被引：1，自引：0，他引：1
Since its official start in January 1994, the International GPS Service (IGS) has been distributing, as part of its product
combination, two distinct Earth rotation parameter (ERP) series: the IGS Rapid series and the IGS Final series. Initially,
the IGS Rapid ERP values were interpolations of the International Earth Rotation Service (IERS) Bulletin A, whereas the IGS
Final ERP series was based on the IERS Bulletin B. Since June 1996, the IGS has been generating its own Final ERP series consistent
with the IGS combined orbit products and based on weighted means of individual IGS analysis center (AC) solutions. At first,
only the polar motion (PM) coordinates and their rates were combined. Length of Day (LOD) and Universal Time (UT) solutions,
also based on separate weighted mean combinations, followed in March 1997. Currently, the IGS Rapid and Final combinations
are produced and made available within 17 hours and 11 days, respectively, after the last observation. Both IGS and the best
AC series are consistent and precise at the 0.1-milliarcsecond (mas) level for PM and at about 30 μs for LOD. Biases in some
AC solutions may exceed these consistency levels. Comparisons of both IGS ERP series with external standards, such as the
IERS multitechnique Bulletins and atmospheric angular momentum series, confirm the estimated precisions. ? 1999 John Wiley
& Sons, Inc. 相似文献
4.
Daniel Gambis 《Journal of Geodesy》2006,80(8-11):649-656
DORIS (Détermination d’Orbite et Radiopositionnement Intégrés par Satellite) is a system used for precise orbit determination (POD) and ground-station positioning. It has been implemented on-board various satellites: the SPOT (Système pour l’Observation de la Terre) remote sensing satellites SPOT-2, SPOT-3, SPOT-4, SPOT-5, TOPEX/Poseidon and more recently on its successors Jason-1 and ENVISAT. DORIS is also a terrestrial positioning system that has found many applications in geophysics and geodesy; in particular, it contributes to the realization of the International Terrestrial Reference Frame, ITRF2000 and the forthcoming ITRF2005. Although not its primary objective, DORIS can bring information on Earth orientation monitoring, mainly polar motion and length of day (LOD) variations that complement other astrogeodetic techniques. In this paper, we have analyzed various recent polar motion solutions derived from independent analysis centers using different software packages and applying various analysis strategies. Comparisons of these solutions to the International Earth Rotation and Reference Systems Service (IERS) C04 solution are performed. Depending on the solutions, the accuracy of DORIS polar components are in the range of 0.5–1 mas corresponding to a few centimeters on the Earth’s surface. This is approximately ten times larger than results derived from GPS, which are typically 0.06 mas in both components. This does not allow DORIS results to be taken into account in the IERS–EOP combinations. A gain in the precision could come from technical improvements to the DORIS system, in addition to improvement of the orbit, tropospheric, ionospheric and Earth gravity field modeling. 相似文献
5.
The edge effect in the wavelet time–frequency spectrum of a time series is treated. The time series is first extended on
both ends by applying a non-linear model, namely the leap-step time series analysis (LSTSA) model, prior to the wavelet transform.
The results of a series of simulation experiments and an application to the observed length-of-day (LOD) series demonstrate
that the edge effect is effectively reduced this way. Thus, the application of the LSTSA model improves the wavelet time–frequency
spectrum, especially enhancing the ability to detect the low-frequency signals.
Received: 15 September 1998 / Accepted: 4 October 1999 相似文献
6.
The analysis of lunar laser ranging (LLR) data enables the determination of many parameters of the Earth–Moon system, such
as lunar gravity coefficients, reflector and station coordinates which contribute to the realisation of the International
Terrestrial Reference Frame 2000 (ITRF 2000), Earth orientation parameters [EOPs, which contribute to the global EOP solutions
at the International Earth Rotation Service (IERS)] or quantities which parameterise relativistic effects in the solar system.
The big advantage of LLR is the long time span of lunar observations (1970–2000). The accuracy of the normal points nowadays
is about 1 cm.
The capability of LLR to determine tidal parameters is investigated. In principle, it could be assumed that LLR would contribute
greatly to the investigation of tidal effects, because the Moon is the most important tide-generating body. In this respect
some special topics such as treatment of the permanent tide and the effect of atmospheric loading are addressed and results
for the tidal parameters h
2 and l
2 as well as values for the eight main tides are given.
Received: 14 August 2000 / Accepted: 15 October 2001 相似文献
7.
Comparison of polar motion with oceanic and atmospheric angular momentum time series for 2-day to Chandler periods 总被引：2，自引：0，他引：2
J. Kouba 《Journal of Geodesy》2005,79(1-3):33-42
During a 4-year period starting in July 1996 and using intervals ranging from 3 days to 4 years, four precise polar motion (PM) series have been compared to excitation by atmospheric angular momentum (AAM) augmented with oceanic angular momentum (OAM) data. The first three series (C03, C04 and Bulletin A) are multi-technique combinations generated by the International Earth Rotation and Reference Systems Service (IERS) and the fourth combined series (IGS00P02) is produced by the International GPS Service (IGS) using only GPS data. The IGS PM compared the best with the combined excitations of atmosphere and oceans (AAM+OAM) at all intervals, showing high overall correlation of 0.8–0.9. Even for the interval of only three days, the IGS PM gave a significant correlation of about 0.6. Moreover, during the interval of February 1999 – July 2000, which should be representative of the current precision of the IGS PM, a significant correlation (>0.4) extended to periods as short as 2.2 days and 2.5 days for the xp and yp PM components, respectively. When using the IERS Bulletin B (C04) PM and an interval of almost 6 years, starting in November 1994, the combined OAM+AAM accounted for practically all the annual, semi-annual and Chandler wobble (CW) PM signals. When only AAM was used, either the US National Centers for Environment Prediction reanalysis data, which were used throughout this study, or the Japanese Meteorological Agency data, two large and well-resolved amplitude peaks of about 0.1 mas/day, remained at the retrograde annual and CW periods. 相似文献
8.
The standard analytical approach which is applied for constructing geopotential models OSU86 and earlier ones, is based on
reducing the boundary value equation to a sphere enveloping the Earth and then solving it directly with respect to the potential
coefficients
n,m
. In an alternative procedure, developed by Jekeli and used for constructing the models OSU91 and EGM96, at first an ellipsoidal
harmonic series is developed for the geopotential and then its coefficients
n,m
e
are transformed to the unknown
n,m
. The second solution is more exact, but much more complicated. The standard procedure is modified and a new simple integral
formula is derived for evaluating the potential coefficients. The efficiency of the standard and new procedures is studied
numerically. In these solutions the same input data are used as for constructing high-degree parts of the EGM96 models. From
two sets of
n,m
(n≤360,|m|≤n), derived by the standard and new approaches, different spectral characteristics of the gravity anomaly and the geoid undulation
are estimated and then compared with similar characteristics evaluated by Jekeli's approach (`etalon' solution). The new solution
appears to be very close to Jekeli's, as opposed to the standard solution. The discrepancies between all the characteristics
of the new and `etalon' solutions are smaller than the corresponding discrepancies between two versions of the final geopotential
model EGM96, one of them (HDM190) constructed by the block-diagonal least squares (LS) adjustment and the other one (V068)
by using Jekeli's approach. On the basis of the derived analytical solution a new simple mathematical model is developed to
apply the LS technique for evaluating geopotential coefficients.
Received: 12 December 2000 / Accepted: 21 June 2001 相似文献
9.
Monitoring Earth orientation using space-geodetic techniques: state-of-the-art and prospective 总被引：10，自引：10，他引：0
D. Gambis 《Journal of Geodesy》2004,78(4-5):295-303
Earth orientation parameters (EOPs) provide the transformation between the International Terrestrial Reference Frame (ITRF) and the International Celestial Reference Frame (ICRF). The different EOP series computed at the Earth Orientation Centre at the Paris Observatory are obtained from the combination of individual EOP series derived from the various space-geodetic techniques. These individual EOP series contain systematic errors, generally limited to biases and drifts, which introduce inconsistencies between EOPs and the terrestrial and celestial frames. The objectives of this paper are first to present the various combined EOP solutions made available at the EOP Centre for the different users, and second to present analyses concerning the long-term consistency of the EOP system with respect to both terrestrial and celestial reference frames. It appears that the present accuracy in the EOP combined IERS C04 series, which is at the level of 200 as for pole components and 20 s for UT1, does not match its internal precision, respectively 100 as and 5 s, because of propagation errors in the realization of the two reference frames. Rigorous combination methods based on a simultaneous estimation of station coordinates and EOPs, which are now being implemented within the International Earth Rotation Service (IERS), are likely to solve this problem in the future. 相似文献
10.
Analysis of the first year of Earth rotation parameters with a sub-daily resolution gained at the CODE processing center of the IGS 总被引：4，自引：4，他引：0
The solutions of the CODE Analysis Center submitted to the IGS, the International Global Position System (GPS) Service for
Geodynamics, are based on three days of observation of about 80–100 stations of the IGS network. The Earth rotation parameters
(ERPs) are assumed to vary linearly over the three days with respect to an a priori model. Continuity at the day boundaries
as well as the continuity of the first derivatives are enforced by constraints. Since early April 1995 CODE has calculated
a new ERP series with an increased time resolution of 2 hours. Again continuity is enforced at the 2-hours-interval boundaries.
The analysis method is described, particularly how to deal with retrograde diurnal terms in the ERP series which may not be estimated with satellite geodetic methods. The results obtained from the first year of data covered by the time series
(time interval from 4 April 1995 to 30 June 1996) are also discussed. The series is relatively homogeneous in the sense of
the used orbit model and the a priori model for the ERPs. The largest source of excitation at daily and sub-daily periods
is likely to be the effect of the ocean tides. There is good agreement between the present results and Topex/Poseidon ocean
tide models, as well as with models based on Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data.
Non-oceanic periodic variations are also observed in the series. Their origin is most probably a consequence of the GPS solution
strategy; other possible sources are the atmospheric tides.
Received: 13 July 1999 / Accepted: 21 March 2000 相似文献
11.
12.
R. Dach G. Beutler U. Hugentobler S. Schaer T. Schildknecht T. Springer G. Dudle L. Prost 《Journal of Geodesy》2003,77(1-2):1-14
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 相似文献
13.
Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding
several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient
for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions:
retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly
noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy,
demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded
that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years.
The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above
prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons
with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period
variations in published polar motion time series.
Received: 27 March 2001 / Accepted: 15 October 2001 相似文献
14.
G. Bourda 《Journal of Geodesy》2008,82(4-5):295-305
The temporal variations of the Earth’s gravity field, nowadays routinely determined from satellite laser ranging (SLR) and
GRACE (Gravity Recovery And Climate Experiment), are related to changes in the Earth’s rotation rate through the Earth’s inertia
tensor. We study this connection from actual data by comparing the traditional length-of-day (LOD) measurements provided by
the International Earth Rotation and Reference Systems Service (IERS) to the variations of the degree-2 and order-0 Stokes
coefficient of the gravity field determined from fitting the orbits of the LAGEOS-1 and −2 satellites since 1985. The two
series show a good correlation (0.62) and similar annual and semi-annual signals, indicating that the gravity-field-derived
LOD is valuable. Our analysis also provides evidence for additional signals common to both series, especially at a period
near 120 days, which could be due to hydrological effects. 相似文献
15.
This is a companion paper to earlier comparisons and study of operational polar motion series, published recently in the same journal. In this contribution, four operational, publicly available, length-of-day (LOD) time series have been compared to the atmospheric angular momentum (AAM) augmented with recent oceanic angular momentum (OAM) data during September 1997–July 2000, using several intervals ranging from 3 days to almost 3 years. Additionally, the LOD of the International GNSS Service (IGS) historical series and a new LOD combination (CMB) were also analyzed. All the six LOD series showed an overall correlation exceeding 0.99 for the complete interval of almost 3 years. Even for the shortest interval of only 3 days, the correlation was still higher than 0.60. The combined AAM + OAM series with inverted barometer corrections always gave the best correlation. The Rapid Service LOD of the International Earth Rotation and Reference Systems Service (IERS) compared the best at all intervals but the shortest one, where the CMB LOD was the best with a correlation of 0.73, followed by both IGS series with a correlation of about 0.71. Prior to all the correlation analyses, in addition to the removal of all the known (conventional) LOD tidal variations with periods ranging from 5.6 days to 18.6 years and lunar fortnightly and monthly oceanic tides, small corrections of lunar fortnightly and monthly tides, semi-annual, annual periodical signals, drift and scale had to be estimated with respect to the combined AAM + OAM series. 相似文献
16.
M. Kalarus H. Schuh W. Kosek O. Akyilmaz Ch. Bizouard D. Gambis R. Gross B. Jovanović S. Kumakshev H. Kutterer P. J. Mendes Cerveira S. Pasynok L. Zotov 《Journal of Geodesy》2010,84(10):587-596
Precise transformations between the international celestial and terrestrial reference frames are needed for many advanced geodetic and astronomical tasks including positioning and navigation on Earth and in space. To perform this transformation at the time of observation, that is for real-time applications, accurate predictions of the Earth orientation parameters (EOP) are needed. The Earth orientation parameters prediction comparison campaign (EOP PCC) that started in October 2005 was organized for the purpose of assessing the accuracy of EOP predictions. This paper summarizes the results of the EOP PCC after nearly two and a half years of operational activity. The ultra short-term (predictions to 10 days into the future), short-term (30 days), and medium-term (500 days) EOP predictions submitted by the participants were evaluated by the same statistical technique based on the mean absolute prediction error using the IERS EOP 05 C04 series as a reference. A combined series of EOP predictions computed as a weighted mean of all submissions available at a given prediction epoch was also evaluated. The combined series is shown to perform very well, as do some of the individual series, especially those using atmospheric angular momentum forecasts. A main conclusion of the EOP PCC is that no single prediction technique performs the best for all EOP components and all prediction intervals. 相似文献
17.
Since the beginning of the International Global Navigation Satellite System (GLONASS) Experiment, IGEX, in October 1998,
the Center for Orbit Determination in Europe (CODE) has acted as an analysis center providing precise GLONASS orbits on a
regular basis. In CODE's IGEX routine analysis the Global Positioning System (GPS) orbits and Earth rotation parameters are
introduced as known quantities into the GLONASS processing. A new approach is studied, where data from the IGEX network are
combined with GPS observations from the International GPS Service (IGS) network and all parameters (GPS and GLONASS orbits,
Earth rotation parameters, and site coordinates) are estimated in one processing step. The influence of different solar radiation
pressure parameterizations on the GLONASS orbits is studied using different parameter subsets of the extended CODE orbit model.
Parameterization with three constant terms in the three orthogonal directions, D, Y, and X (D = direction satellite–Sun, Y = direction of the satellite's solar panel axis), and two periodic terms in the X-direction, proves to be adequate for GLONASS satellites. As a result of the processing it is found that the solar radiation
pressure effect for the GLONASS satellites is significantly different in the Y-direction from that for the GPS satellites, and an extensive analysis is carried out to investigate the effect in detail.
SLR observations from the ILRS network are used as an independent check on the quality of the GLONASS orbital solutions. Both
processing aspects, combining the two networks and changing the orbit parameterization, significantly improve the quality
of the determined GLONASS orbits compared to the orbits stemming from CODE's IGEX routine processing.
Received: 10 May 2000 / Accepted: 9 October 2000 相似文献
18.
19.
VLBI terrestrial reference frame contributions to ITRF2008 总被引：6，自引：5，他引：1
In late 2008, the Product Center for the International Terrestrial Reference Frame (ITRF) of the International Earth Rotation
and Reference Systems Service (IERS) issued a call for contributions to the next realization of the International Terrestrial
Reference System, ITRF2008. The official contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to
ITRF2008 consists of session-wise datum-free normal equations of altogether 4,539 daily Very Long Baseline Interferometry
(VLBI) sessions from 1979.7 to 2009.0 including data of 115 different VLBI sites. It is the result of a combination of individual
series of session-wise datum-free normal equations provided by seven analysis centers (ACs) of the IVS. All series are completely
reprocessed following homogeneous analysis options according to the IERS Conventions 2003 and IVS Analysis Conventions. Altogether,
nine IVS ACs analyzed the full history of VLBI observations with four different software packages. Unfortunately, the contributions
of two ACs, Institute of Applied Astronomy (IAA) and Geoscience Australia (AUS), had to be excluded from the combination process.
This was mostly done because the IAA series exhibits a clear scale offset while the solution computed from normal equations
contained in the AUS SINEX files yielded unreliable results. Based on the experience gathered since the combination efforts
for ITRF2005, some discrepancies between the individual series were discovered and overcome. Thus, the consistency of the
individual VLBI solutions has improved considerably. The agreement in terms of WRMS of the Terrestrial Reference Frame (TRF)
horizontal components is 1 mm, of the height component 2 mm. Comparisons between ITRF2005 and the combined TRF solution for
ITRF2008 yielded systematic height differences of up to 5 mm with a zonal signature. These differences can be related to a
pole tide correction referenced to a zero mean pole used by four of five IVS ACs in the ITRF2005 contribution instead of a
linear mean pole path as recommended in the IERS Conventions. Furthermore, these systematics are the reason for an offset
in the scale of 0.4 ppb between the IVS’ contribution to ITRF2008 and ITRF2005. The Earth orientation parameters of seven
series used as input for the IVS combined series are consistent to a huge amount with about 50 μas WRMS in polar motion and
3 μs in dUT1. 相似文献
20.
不同技术、不同分析中心得到的地球自转参数（Earth rotation parameters，ERP）往往是不同的，为提供统一的ERP供用户使用，常需对ERP进行融合处理。提出了一种基于多分析中心ERP结果的附加边界约束和内约束融合模型，即先通过参数变换把各分析中心结果转换到相同时刻，考虑到相邻观测时段边界点处ERP应当一致这一特点，施加边界约束，然后对各分析中心的长期解施加转换参数内约束，最后得到多分析中心ERP的融合解。采用从2005—2011年共6 a的7个全球卫星导航系统（Global Navigation Satellite System，GNSS）分析中心的结果进行融合处理，并与IERS C04（International Earth Rotation and Reference Systems ServiceCombined 04）结果进行比较。结果表明，所提出的融合方法计算结果的精度有明显改善。 相似文献