Analysis of Astrometric Position Time Series for ICRF-2

A. Fey, D. A. Boboltz

Institution:
U.S. Naval Observatory
USA

A second realization of the International Celestial Reference Frame, ICRF-2, is currently underway with a projected completion date concurrent with the 2009 IAU General Assembly. This work is being carried out by two working groups: the IERS/IVS Working Group will generate ICRF-2 from VLBI observations of extragalactic radio sources, consistent with the current realization of the ITRF and EOP data products and the IAU working group will oversee the generation of ICRF-2. Of primary importance to this work is the selection of a set of defining sources to be used to orient the ICRF-2 axes. These sources should be as positionally stable as can be determined with existing data and analysis. It is well known that compact extragalactic sources have variable and unpredictable emission structures on scales larger than the accuracy of their position estimates. Temporal variations of the intrinsic structure of these objects results in apparent motion when astrometric observations are made at several epochs. We present analysis of these variations for sources in the existing astrometric/geodetic database to estimate the position stability of the observed sources. While past performance is not always indicative of future behavior an analysis of this nature can be used to infer position stability which can be used as one criteria for ICRF-2 defining source selection.

Selection of stable radio sources to define a new ICRF

A.-M. Gontier, S. Lambert

Institution:
Paris Observatory - SYRTE, CNRS UMR8630
France

We propose a selection scheme to determine a list of radio sources able to define a stable reference frame. The selection scheme is based on the statistical analysis of ~20-yr long time series of radio source coordinates generated through the analysis of geodetic VLBI observations.

Source positions time series generation and analysis

S. Kurdubov, E. Skurikhina

Institution:
Institute of Applied Astronomy RAS
Russia

Time series for more than 600 sources were calculated with using QUASAR software for VLBI data processing. Source positions for every sources were obtained from single series analyses with fixed coordinates of all another sources. A-priory source positions were used from the ICRF-Ext.2 radio source positions catalogue. Time series analysis is performed with LSM and covariation analyses technique. Information about source structure is used where it is available.

Precessional parameters obtained from biased data of Hipparcos-FK5 proper motion

M.J. Martinez, F.J. Marco, J.A. Lopez

Institution of the first author:
Universidad Politecnica de Valencia
Spain

The Hipparcos catalogue provides a reference frame in optical wavelength for the new ICRS. The differences in the system of proper motions of Hipparcos and the previous materialization of the reference frame, the FK5, are expected to be caused only by the combined effects of the motion of the equinox of the FK5 as well as the Luni-solar and planetary precession, but several authors have signaled the existence of an inconsistency for the proper motion differences of the FK5-Hipparcos with the Delta p values corresponding to the Luni-solar precession as determined from VLBI and LLR The widely employed parametric models do not remove the bias in the random variables. In addition, the introduction of a non parametric method, combined with the inner product in L^2 over S^2 shows the necessity of removing the bias. The precessional formulas should be rearranged to be used in this case.When applying this model, the obtained values for the precession corrections are very consistent with the ones currently adopted by the IAU.

VLBI2010: Progress towards the next generation geodetic VLBI system

A. Niell & VLBI2010 Committee

Institution of the first author:
MIT Haystack Observatory
USA

In order to improve the accuracy of future measurements of the terrestrial and celestial reference frames and of EOP, and to increase reliability while reducing operations costs, Working Group 3 of the IVS recommended the development of a new generation of electronics and antennas, accompanied by advances in data analysis. The main innovation will be the use of multiple radio-frequency bands to resolve phase delays, in contrast to the use of S- and X-bands for group delay in the current system. This technique, in conjunction with the utilization of much higher data record rates, is expected to improve the per-observation accuracy by an order of magnitude, allowing the use of 12m fast-moving antennas. Two areas are being pursued to evaluate the validity of the recommendations. On the analysis side 24-hour sessions with networks of 16 to 32 antennas are being simulated using 12 meter antennas with various slew rates and with observation noise consisting of realistic turbulent atmosphere delays and instrumental noise. Estimated parameters are station positions, EOP including nutation, and atmosphere delays and clock values. On the hardware side prototypes of the equipment that is required to achieve the high phase delay precision will be mounted on two existing antennas. The new components are a wideband feed (2 - 15 GHz), digital backend, and Mark5B+ data recorders. The data record rate for the demonstration will be 8 gigabits per second (gbps), compared to the highest data rate in current use of 1 gbps and the more standard rate of 0.256 gbs. Progress in both of

A Study of VLBI2010 Potential for Source Structure Corrections

W. Petrachenko, P. Charlot, A. Collioud, T. Hobiger, A. Niell

Institution of the first author:
Natural Resources Canada
Canada

In October 2003, the International VLBI Service for Geodesy and Astrometry (IVS) installed Working Group 3 'VLBI2010' to examine current and future requirements for geodetic/astrometric VLBI including all components from antennas to analysis, and to create recommendations for a new generation of VLBI systems. Some important recommendations include: the use of larger networks; the use of smaller faster slewing antennas; the use of very high data rates; and, the use of multiple (~4) widely spaced bands to resolve RF phase ambiguities. When taken together, these recommendations result in a many-fold increase in the number of observations per session. UV coverage improves to the point where precise VLBI images of the ICRF sources can be constructed on a daily basis directly from the geodetic observations, therefore enabling source structure corrections to be calculated. Simulations are currently underway to evaluate the potential of this approach.

Connecting the dynamical frame to the ICRF by use of NEA's observations and the historical phenomenon of "fictitious equinox motion"

E. Yagudina

Institution:
IAA RAS
Russia

ICRF is now adopted as the fundamental celestial frame in astronomy. It is based on the positions of extragalactic radio sources obtained by VLBI observations. In order to provide continuity in the changing of the reference systems, the main plane of the ICRF was chosen in such way that its orientation in space coincides (in the range of the errors of the ground-based observations) with that of the "dynamical" equator of the FK5 catalogue at J2000.0. The origin of the old systems was given by the position of the equinox. The old reference catalogues were not free of a small residual rotation of the system as a whole, that was given by a significant motion of the equinox (non-precessional motion of the equinox). The historical analysis of that phenomenon is given in the paper. In spite of the fact that the ICRF is a quasi-inertial system, there are a large quantities of problems associated with the usage of the ICRF, the main of which is the connection between ICRF and dynamical systems. It is known with insufficient accuracy and it is necessary to continue to work at the problem of mutual orientation of these systems at the new level of accuracy using the various new observations of the different solar system oblects. For this purpose, the new radar and optical observations of the asteroids (mainly Near Earth asteroids-NEA's) have been used. The combined solution gave us six orientation parameters which are in good agreement with those obtained by other authors.

Korean VLBI Network and its plan for VLBI metrology

B. W. Sohn

Institution:
KVN/KASI
Korea

Korea's new VLBI project to construct the Korean VLBI Network (KVN) began in 2001 as a 7-year project that is fully funded by Korean government. We plan to build three new high-precision radio telescopes of 21-m diameter at three sites in Korea. We will install the 2/8, 22 and 43-GHz HEMT receivers by 2008, and we will expand the receiving frequency range up to 129 GHz. With its high performance at high frequency, we expect that KVN will contribute to the VLBI metrology, especially for the future realization of ICRF and the related source structure study at high frequency.

Better proper motions accuracy for stars with Hipparcos satellite and ground-based observations

G. Damljanovic

Institution:
Astronomical Observatory
Serbia

About 15 years elapsed since the HIPPARCOS ESA satellite mission observations (the epoch of Hipparcos Catalogue is 1991.25). The errors of the Hipparcos stars proper motions were close to 1 mas/year, and because of it nowadays the error of apparent places of these stars is more than 15 mas. It exceeds the error of Hipparcos stars positions (which is about 1 mas) by one order of magnitude. Also, some parts of the sky (presented via Hipparcos stars data) are with bigger errors than mentioned ones, the shortness of the Hipparcos observations (less than four years) yields bigger proper motions errors of double or multiple stars than the single ones, etc. At the other hand, there are numerous astrometric ground-based observations of some stars referred to Hipparcos Catalogue, made at many observatories during the last century. Here, the data of latitude variations are used (covering the period 1899.7-1992.0) to improve the Hipparcos proper motions in declination of stars observed in line with the Earth orientation programmes. The method and results are presented here.

On the consistent definition of EOPs in relation to the observed ITRF-ICRF transformation

A. Dermanis, D. Tsoulis

Institution:
Aristotle University of Thessaloniki
Greece

Practical Earth rotation determination utilizes a theory-provided precession-nutation and diurnal rotation, which is updated and augmented by polar motion by means of infinitesimal rotations derived via the analysis of spatial observations. Infinitesimal rotations enjoy two properties: they commute and there exist interrelated equivalent left and right infinitesimal corrections to a non-infinitesimal rotation matrix. Based on these properties it is demonstrated that the separation of precession-nutation from polar motion using observational data is a highly unstable problem. This suggests the derivation of the direction and magnitude of the rotation vector, and hence the separation of Earth rotation into precession-nutation, diurnal rotation and polar motion, directly from the observed total Earth rotation matrix on the basis of mathematical consistency. Calculations of the mathematically induced "Compatible Celestial Pole" show a significant systematic deviation from the IERS-provided "Celestial Intermediate Pole" dominated by two periodic terms with semi-annual and 13.5 day periods.

Geopotential of a triaxial Earth with rigid inner core in Andoyer canonical variables

A. Escapa, J. Getino, J. M. Ferrándiz

Institution of the first author:
Dpto. MAtemática Aplicada. Escuela Politécnica Superior. Universidad de Alicante
Spain

In this research we derive analytical expressions for the geopotential of a three-layer Earth model composed by a triaxial rigid mantle, a triaxial fluid outer core and a triaxial rigid inner core, extending previous works performed on the basis of an axial-symmetric three-layer Earth. In order to consider these expressions within the framework of the Hamiltonian theory of the rotation of the non-rigid Earth, we work out the problem in terms of a set of canonical variables arising from associating an Andoyer-like variables to each layer of the Earth (Escapa, Getino and Ferrándiz, J. Geophys. Res., 106, 11387-11397, 2001). With the help of Wigner theorem (e.g. Kinoshita, PASJ, 24, 423-457, 1972), we obtain the development of the geopotential of this Earth model in a mantle attached reference frame. Finally, we analyze the dependence of each geopotential coefficient of the second degree on the triaxiality and figure axis of the rigid inner core.

Estimation of the topographic torque at the core-mantle boundary on the nutation

M. Folgueira, V. Dehant

Institution of the first author:
Ínstituto de Astronomía y Geodesia
Spain

In this paper, we study analytically the effect of the existence of CMB (core-mantle boundary) topography on the Earth’s nutation. For this purpose, we have considered an Earth model with a rigid mantle, a homogeneous and incompressible fluid core, and a slightly non-hydrostatic core-mantle boundary in the same way as Wu and Wahr (Geophys. J. Int., 1997). This work is also the first in a series of aims carrying out the progress of the European DESCARTES Sub-project entitled: “Computation of the topographic coupling at the core-mantle boundary and its effect on the nutation”. The first part of the paper contains a brief report of the mentioned project as a whole, featuring the background work that motivated the project, its aims and objectives and the general research design. Then, we describe the methodology and the strategy to obtain analytical expressions for the topographic coupling and finally we show some preliminary results which will be compared to those obtaining by Wu and Wahr (1997) using a numerical technique.

Considerations about some problems on functional parametrical models implementation from a discrete set of data

F. J. Marco, M.J. Martinez, J.A. Lopez

Institution of the first author:
Universidad Jaume I
Spain

The least squares method is widely used in Fundamental Astronomy in the determination of some parameters, especially on a discrete set of points. The parameters to determine are usually coefficients of functional developments based on certain regularity hypothesis about the developed function. This hypothesis of regularity in the working domain, together with the spatial distribution of the discrete data in the domain and the statistical properties of the data to be adjusted should be carefully treated if we want to obtain reliable results. As initial hypothesis of the present paper, we shall take data coming from a normal distribution. Then, we shall assign to the spatial distribution a punctual measure which could be extended to the whole domain. This fact will define a kernel with respect to the searched function will be of integrable square in the definition domain. The discrete initial problem may be described now in terms of the search of a continuous basis; and the discretization of the generalized problem, in numerical terms, the usual least-squares statistical treatment.

Non-rigid Earth rotation Series

V. Pashkevich

Institution:
Central (Pulkovo) Astronomical Observatory of Russian Academy of Sciences
Russia

The last years a lot of attempts to derive a high precision theory of the non-rigid Earth rotation was carried out. For these purposes used the different transfer functions, which usually applied to the nutation in longitude and in obliquity of the rigid Earth rotation with respect to the ecliptic of date. The aim of the research is the construction of the new high-precision Non-Rigid Earth Rotation Series (SN9000), dynamically adequate to the DE404/LE404 ephemeris over 2000 year time interval, which expressed in the function of the three Euler angles with respect to the fixed ecliptic plane and equinox J2000.0.

Analytical theory for an asteroid in the gravitational field of a migrating planet

I. Tupikova

Institution:
Lohrmann-observatory, TU Dresden
Germany

The slow migration of planets introduces a second natural time-dependent small parameter in the description of the dynamics of a mass-less body (the first one being as usual the mass ratio of the perturbing body to the mass of the central body) . We have developed a special modification of the Lie-transform method allowing to solve the time-dependent Hamilton-Jacobi equation with two different small parameters . The approximate analytical solution for the non-resonant case is splitted into three transformations. The first one eliminates the mean anomalies from the equations of motion. After this transformation the algorithm looses the first natural small parameter. As small parameters for the further transformations necessary to eliminate the longitudes of perihelia and nodes we can only choose the eccentricities and inclinations of the bodies involved. As a consequence, the different terms of the expansions of the perturbing function of the problem need a different number of approximations to get the solution correct up to given degrees in the small parameters. This feature of the analytical solution in the asteroid problem seems to be unavoidable even in the case of only one perturbing planet without migration. The second transformation eliminates nodes, and the third one the longitudes of perihelion. The solution obtained so far allows one to calculate the proper elements of a perturbed body before sweeping through resonance up to any desired degree of eccentricities and inclinations.

The use of LLR observations (1969-2006) for the determination of the GCRS coordinates of the pole

W. Zerhouni, N. Capitaine, G. Francou

Institution:
Observatoire de Paris
France

Analysis of Lunar Laser ranging observations allows to determine a number of parameters related to the dynamics of the Earth-Moon system. It also contributes to the determination of the Earth Orientation Parameters (EOP) such as precession nutation, polar motion and UT1. Here, we focus on the determination of the precession nutation corrections DX,DY to the conventional model for the coordinates X and Y of the CIP (Celestial Intermediate Pole) in the GCRS (Geocentric Celestial Reference System) instead of the classical parameters determined in previous works .

Combination of different space geodetic techniques: algorithm of parameters estimation

O. Bolotina

Institution:
Main astronomical observatory of the National academy of sciences of Ukraine
Ukraine

Combined analysis of observations that are acquired by different space geodetic techniques on a level of conditional equations system, is a very interesting scientific task. Such analysis makes it possible to determine the celestial and the terrestrial reference frames, the Earth orientation parameters as well as other geophysical quantities in one solution based on a common set of models, algorithms and an analysis strategy. One of the problems which arises in the combined solution is a treatment of parameters which are estimated. Each of space geodetic techniques has its own peculiarity in management of observations, therefore, the same physical value is estimated on different time intervals which are usually overlapping. For example, the Earth orientation parameters are estimated on a 3-days arcs from the analysis of the SLR observations, a 1-day intervals from the GPS and VLBI sessions, but for the two latest techniques the beginning of each session could differ by six to ten hours. In this work we present an algorithm of parameter estimation which is developed to overcome such problems. The algorithm is based on the Square Root Information Filter and allows a combination of the different types of parameters in a common solution.

Correlation between the solar activity cycles and the Earth rotation

Ya. Chapanov, D. Gambis

Institution of the first author:
Central Laboratory for Geodesy at Bulgarian Academy of Sciences
Bulgaria

The correlation between the solar activity cycles and the Earth rotation is investigated by means of UT1 series from the solution C04 of the IERS. The different oscillations of the Earth rotation are separated by an approximation of the difference UT1-TAI for the period 1962-2006, which includes power polynomials of degree up to 3, main oscillations with periods 22a, 18.6a, 12a, 6.75a, 1a and their harmonics. The UT1-TAI oscillations at solar activity frequencies are approximated with step-variable periods as follow: 11.1a for UT1 data before 1977.5; 10.3a for data between 1977.5 and 1987.8; 9.7a for data between 1987.8 and 1997.4; and 10.0a for data after 1997.4. The step-variable periods yield better approximation of the Earth rotation response to different solar activity cycles. The estimated UT1-TAI oscillations at solar activity frequencies are highly-correlated with the smoothed values of the Wolf’s numbers with mean delay about 1a.

Estimation of the short-term zonal tides from UT1 observations

Ya. Chapanov, C. Ron, J. Vondrák

Institution of the first author:
Central Laboratory for Geodesy at Bulgarian Academy of Sciences
Bulgaria

Short-term zonal tides with periods shorter than 35d, according to the latest IERS model, are estimated by means of UT1-TAI series from the solution C04 of the IERS. All of the Earth rotation oscillations with periods above 35 days are removed by application of Fourier approximation to the UT1-TAI time series for the period 1962.0-2007.5. The total number of used harmonics is equal to 474. The accuracy of the estimated amplitudes of the short-term zonal tides is about 4microseconds. Some of these amplitudes are significantly greater than their theoretical values, due to strong disturbing influence of the atmospherical angular momentum. After removing the estimated short-term zonal tides from UT1-TAI variations, the residual time series contain significant oscillations with periods below 35d. The possible tidal origin of these residual oscillations is discussed.

Use of Atmospheric Angular Momentum forecasts for UT1 predictions

D. Gambis, J.Y. Richard, D. Salstein

Institution of the first author:
Observatoire de Paris
France

Real-time orbitography and interplanetary navigation require accurate predictions of Universal Time UT1. Below 10 days, variations in Earth rotation are mostly due to atmospheric effects. As a result, the axial Atmospheric Angular Momentum (AAM) series can be used as a proxy index to predict UT1. The forecasts of weather centers are based on advancing the equations of motion of the atmosphere according to physical principles, and so the sophistication of the various models contained within the weather forecast systems are of paramount importance to the quality of the forecasts. For example for the National Centres for Environmental Prediction latest improvements, new radiation schemes are available for the model physics, a three dimensional variational approach is now used, an improved vertical coordinate system is in place, and new observing systems are available. We will mention the relevance of such developments to the predictions related to AAM. We are been using AAM forecasts derived by three independent centres, i.e. U.S. National Centres for Environmental Prediction (NOAA/NCEP, formerly NMC), Japanese Meteorological Agency (JMA) and the United Kingdom Meteorological Office (UKMO). Using these three series and their combination, we have made a series of simulations based on an adaptive method to predict UT1. We give the statistics concerning the performances we obtain and characterize the stochastic content of the 6-hour AAM forecasts. The Prediction Comparison Campaign is a good opportunity to check the performance of the procedure on real

Meteorological interpretation of transient LOD changes

Y. Masaki

Institution:
Geographical Survey Institute
Japan

The Earth's spin rate is mainly changed by zonal winds. For example, seasonal changes in global atmospheric circulation and episodic changes accompanied with El Ninos are clearly detected in the Length-of-day (LOD). Sub-global to regional meteorological phenomena can also change the wind field, however, their effects on LOD are uncertain because these signals are expected to be subtle and transient. In our previous study, we introduced atmospheric pressure gradients in the upper atmosphere in order to obtain a rough picture of the meteorological features that change the LOD. In this presentation, we compare a one-year LOD signal with meteorological elements (winds, temperature, pressure, etc.) and make an attempt to link transient LOD changes with sub-global meteorological phenomena.

The polar motion and the draconitic period

G. Morcov

Institution:
Faculty of Geodesy Bucharest
Romania

The paper is trying to bring something new in the field related to the connection between the 2 motions that are underlined by the title. It is followed: 1). The determination of the medium polar motion in light different way than the average of its determinant components (Chandler’s Wobble). This means that the average of the polar motion is determined by setting the dissipation of the synodic periods of its components (the spiral nods) to be minimal. The advantages: - the synodic values of the extreme spires are going to have relative small weights beside the average, while the synodic values of the medium spires (with low deflections) are going to have relative great weights beside the average. - the average of the polar motion that is counted in such a manner is very stabile, remaining unchanged even in the case of the elimination of some terms. Carrying on some practical determinations of the polar motions’ spires between 1962- 2006, it resulted a slightly different accepted period Chandler’s Wobble (433 days), but only with a little over the 435 days value. 2). The connection between the average of the polar motion and the equation of the eclipses that may produce a supplementary accuracy. We know: 1/T=1/T1+1/T2 (1) Bellow, we are introducing within the synodic combination a value of the medium polar motion closed to that of 435.4 days, already found: 1/T1=1/435.4d+3/T2 (2) And: 1/T=1/435.4d+4/T2 (3) If we are dropping (2) and (3) equations we get the known equation of the eclipses (1).

Comparison of hydrological and GRACE-based excitation functions of polar motion in the seasonal spectral band.

J. Nastula, B. Kolaczek, D. A. Salstein

Institution of the first author:
Space Research Centre of the PAS
Poland

Understanding of changes in the global balance of angular momentum due to the mass redistribution of geophysical fluids is needed to explain the observed polar motion. The role of continental hydrologic signals, from land water, snow, and ice, on polar motion excitation (hydrological angular momentum-HAM), is still inadequately known. Although estimates of HAM have been made from several models of global hydrology based upon the observed distribution of surface water, snow, and soil moisture, the relatively sparse observation network and the presence of errors in the data and the geophysical fluid models preclude a full understanding of the HAM influence on polar motion variations. Recently the GRACE mission monitoring Earth’s time variable gravity field has allowed us to determine the mass term of polar motion excitation functions and compare them with the mass term derivable as a residual from the geodetic excitation functions and geophysical fluid motion terms on seasonal time scales. Differences between these mass terms in the years 2004 - 2005.5 are still on the order of 20 mas. Besides the overall mass excitation of polar motion comparisons with GRACE (Rl04-release), we also intercompare the non-atmospheric, non-oceanic signals in the mass term of geodetic polar motion excitation with hydrological excitation of polar motion.

Forecasting irregular variations of UT1-UTC and LOD data caused by ENSO

T. Niedzielski, W. Kosek

Institution:
Space Research Centre, Polish Academy of Sciences
Poland

Variations of Universal Time (UT1-UTC) and its first derivative Length-of-Day (LOD) are driven by various geophysical processes and contain oscillations ranging from decades to hours. There are irregular fluctuations, which are directly associated with El Nino/Southern Oscillation (ENSO). El Nino events are always preceded by weakening of zonal winds, which causes the increase of the atmospheric angular momentum and LOD. Thus, extreme irregular variations of zonal winds preceding ENSO decreases the accuracy of LOD predictions. The research focuses on prediction of LOD and UT1-UTC time series up to one-year in the future with the particular emphasis on the prediction improvement during El Nino or La Nina events. The polynomial-harmonic least-squares model is applied to fit the deterministic function to LOD data (oscillations: annual, semi-annual, 18.6 years, 9.3 years; trends: linear). This model describes main properties of the time series, hoverer – being deterministic – cannot describe stochastic variation. The stochastic residuals – computed as the difference between LOD data and the polynomial-harmonic model – reveal the extreme values driven by ENSO. These peaks are modeled by the combination of extrapolation of the above-mentioned deterministic model and the stochastic bivariate autoregressive prediction. This approach focuses on the auto- and cross-correlations between LOD and the axial component of the atmospheric angular momentum. The technique in question allows to derive more accurate predictions than the purely univariate forecasts. This can be inferred from bot

Status report on the Fennoscandian-Japanese project for near real-time UT1-observations with e-VLBI

M. Poutanen, R. Haas, J. Wagner, J. Ritakari, A. Mujunen, M. Sekido, H. Takiguchi, Y. Koyama, T. Kondo

Institution of the first author:
Finnish Geodetic Institute
Finland

We present the status of the Fennoscandian-Japanese project for near real-time UT1-observations with e-VLBI. The project was started in early 2007 as a collaboration between the VLBI research groups at the Fennoscandian telescopes Onsala (Sweden) and Metsähovi (Finland) and the Japanses telescopes Kashima and Tsukuba. This network provides almost parallel baselines with long east-west extension that are ideal for UT1-observations. Several UT1-sessions were observed during 2007 and the e-VLBI data technology was applied. Observational data from the Fennoscandia telescopes were transferred in real-time with the UDP-based data transfer protocol 'Tsunami' to a software correlator at Kashima in Japan where the data were correlated with the Japanses observational data. After the near real-time correlation, the data were further processed with usual VLBI analysis software. Using this strategy the final UT1 estimate was available already within 30 minutes after the end of a one hour long observing session. This means that the latency of the UT1 measurement could be improved dramatically compared to the regular so-called Intensive sessions of the International VLBI Service for Geodesy and Astrometry (IVS). The accuracy of the derived UT1 value obtained from the Fennoscandian-Japanese e-VLBI experiments has been confirmed to be as accurate as the combined solution of International Earth Rotation Service (IERS) bulletin-A. The developed technology will be transfered in teh near future to the weekly IVS-intensive VLBI sessions, and is expected to contribute to improvements of latency

The influence of variable amplitudes and phases of the most energetic oscillations in the EOP on their prediction errors

A. Rzeszotko, W. Kosek, W. Popinski

Institution:
Space Research Centre, Polish Academy of Sciences
Poland

The Discrete Wavelet Transform (DWT) based on the Morlet mother wavelet was applied to determine the time-variable amplitudes and phases of the dominant oscillations in the Earth Orientation Parameters (EOP). Next, the model data for the EOP were obtained where the amplitudes and phases of the most energetic oscillations were assumed to be time-variable or constant. These model data and the original EOP data were then predicted using forward and backward prediction by the combination of the least-squares extrapolation and the autoregressive prediction techniques. Comparison of the forward and backward predictions of the EOP data and the model data computed at different starting prediction epochs enabled examination of irregular variations in the EOP data as well as the influence of the considered variable oscillations on the EOP prediction errors. It has been shown that the main cause of the increase of the pole coordinates prediction errors is the irregular broadband Chandler + annual oscillation. Concerning LOD or UT1-UTC data, irregular non tidal annual and semi-annual oscillations are responsible for increase of their prediction errors. The greatest prediction errors occur at almost the same moments of time independently of the prediction direction.

Estimation of coefficients of differential equation modeling the polar motion

E. Spiridonov, E. Tsurkis, O. Vinogradova

Institution of the first author:
Shmidt's Institute for Physics of the Earth, RAS, Moscow
Russia

We dealt with Liuville equations which describes the polar motion and presents a system of first-order equations with coefficients depending on T (period of free nutation) and Q (mantle quality factor). The actual problem is to evaluate these coefficients (i.e. T and Q)) by:1) Excitation functions series used for constructing right hand-side of Liouville equations and2) Polar coordinates series which one can interprete as a solution of the equations.Validity of this task which is typical inverse problem is shown. Practically we solved a number of “direct” ones under different meanings of T and Q. The preferred values of parameters to be estimated are: T=425-440 days and Q=20-60.Disagreement between our model based on Liouville equations and data series is conditioned by physical reasons, as far as mathematical problem is valid. Possible causes of such disagreement is discussed.

The impact on EOP predictions of AAM forecasts from the ECMWF and NCEP

T. van Dam, R. Gross, O. de Viron

Institution of the first author:
University of Luxembourg
Luxembourg

A Kalman filter has been used at Jet Propulsion Laboratory (JPL) for nearly two decades to combine independent measurements of the Earth's orientation and to predict its evolution. Changes in the Earth's orientation can be described as a randomly excited stochastic process; between measurements, the uncertainty in our knowledge of the Earth's orientation grows and rapidly becomes much larger than the uncertainty in the measurements. Short-term predictions of the Earth's orientation have been improved using analyses and forecasts of the axial component of atmospheric angular momentum (AAM) as proxy length-of-day measurements and forecasts. Such AAM analyses and forecasts are produced at centers, e.g. the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF). For example, the accuracy of JPL's predictions of the Earth's rotation rate can be improved by nearly a factor of 2 when AAM analysis and forecast data from NCEP are used. We compare results using NCEP forecasts with those using ECMWF forecasts. We find that both NCEP and ECMWF 5-day wind AAM forecasts agree well with LOD during 19-03-04 to 22-07-04, with the ECMWF having a slightly higher correlation with the LOD observations but with the NCEP explaining a bit more of the LOD variance. We find that the 7-day UT1 prediction accuracy is slightly better with the NCEP forecasts. Finally we find that adding oceanic angular momentum from an ocean general circulation model (ECCO/JPL/kf066b) to the AAM forecasts improves the accuracy of the UT1 prediction slightly.

Correspondence of EOP and geomagnetic field

P. Varga, Z. Bus, B Süle, A Schreider, C. Bizouard, D. Gambis

Institution of the first author:
Geodetic and Geophysical Research Institut
Hungary

The connection of EOP with centered and eccentric geomagnetic dipole fields described with the use of Gaussian coefficients derived from global geomagnetic observations is discussed for the epoch 1900-2000. The statistical comparison of temporal variation of earth magnetic and astronomical data shows close correlation of geomagnetic dipole momentum M0 and ΔLOD. It should be mentioned that the time-correlation is closer when the centred geomagnetic dipole is used for statistical modelling. In the same time no relation was found between ΔLOD and the orientation variations of the geomagnetic dipole. Similarly there was no dependence detected between time dependent changes of M0 and PM. The physical meaning of above described results is: the interrelation between the variation of LOD and the geomagnetic field in decadal time-scale is explained commonly with circulation in the liquid outer core which leads to the temporal variations of the core angular momentum. This phenomenon however is not related to the density redistribution within the liquid outer core.As a by-product it was demonstrated by the authors similarly to other investigators that in decadal time-scale a strong reduction of the magnitude of M0 is observed for the whole XXth century. It is shown by use of archeomagnetic data that this attenuation was significantly (12 times) smaller during the last twelve millennium and paleomagnetic data proves that during the lifetime of our planet the intensity of the geomagnetic field on the average was the same as it is in our days.

Frequency Modulation Solution of Earth Rotation

W.-J. Wang, H.-W. Zhang, W.-B.Shen, W. Chen

Institution of the first author:
School of Surveying, Henan Polytechnic University
China

Rotation for triaxial Earth has been better solved as of free polar motion and variations of spinning angular velocity. The exact solution of Euler rotation equations is expressed as elliptic functions. Elliptic functions possess double periods. Especially the spinning angular velocity may be seen as of free fluctuations with periods of 7 month and 14.6 year. The most surprise consequence is obtained from the periodic oscillation of the three angular velocity components with free nutations. The numerical results of the components are waving with the nutation periods and also possess the feature similar to the spinning velocity.