arXiv subjects

Zinovy Malkin

Publications and source records attributed to Zinovy Malkin.

63 records · Page 4Linked to original sources

arXiv2009

Empiric Models of the Earth's Free Core Nutation

Free core nutation (FCN) is the main factor that limits the accuracy of the modeling of the motion of Earth's rotational axis in the celestial coordinate system. Several FCN models have been proposed. A comparative analysis is made of the known models including the model proposed by the author. The use of the FCN model is shown to substantially increase the accuracy of the modeling of Earth's rotation. Furthermore, the FCN component extracted from the observed motion of Earth's rotational axis is an important source for the study of the shape and rotation of the Earth's core. A comparison of different FCN models has shown that the proposed model is better than other models if used to extract the geophysical signal (the amplitude and phase of FCN) from observational data.

physics.geo-ph↗

arXiv2009

On comparison of the Earth orientation parameters obtained from different VLBI networks and observing programs

In this paper, a new geometry index of Very Long Baseline Interferometry (VLBI) observing networks, the volume of network $V$, is examined as an indicator of the errors in the Earth orientation parameters (EOP) obtained from VLBI observations. It has been shown that both EOP precision and accuracy can be well described by the power law $σ=aV^c$ in a wide range of the network size from domestic to global VLBI networks. In other words, as the network volume grows, the EOP errors become smaller following a power law. This should be taken into account for a proper comparison of EOP estimates obtained from different VLBI networks. Thus performing correct EOP comparison allows us to accurately investigate finer factors affecting the EOP errors. In particular, it was found that the dependence of the EOP precision and accuracy on the recording data rate can also be described by a power law. One important conclusion is that the EOP accuracy depends primarily on the network geometry and to lesser extent on other factors, such as recording mode and data rate and scheduling parameters, whereas these factors have stronger impact on the EOP precision.

physics.geo-ph↗

arXiv2007

An analysis of celestial pole offset observations in the free core nutation frequency band

In this study, three empirical Free Core Nutation (FCN) models developed to the present time, MHB2000, Malkin's and Lambert's ones, are compared on the basis of representation of variations of the FCN amplitude and phase predicted by these models. It is possible to conclude, that the model of the author provides the most realistic representation of the FCN variations. However, the specified models are based on representation about single FCN rotational mode. At the same time, some results of processing of the VLBI observations made during last years, specify possible presence of two close FCN periods. A theoretical explanation to presence of a second FCN frequency FCN has been given by G. Krasinsky in his theory of rotation of the Earth with two-layer liquid core, ERA2005. In the present work, for more detailed studying this phenomenon, the IVS time series of celestial pole offset, and also those predicted by the ERA2005 theory, have been investigated by means of several statistical methods which confidently show presence of two fluctuations in nutational movement of an Earth's rotation axis with the periods about -452 and -410 solar days.

physics.geo-ph↗

arXiv2007

Systematic errors and combination of individual CRF solutions in the framework of the international pilot project for the next ICRF

A new international Pilot Project for the re-determination of the ICRF was initiated by the International VLBI Service for Geodesy and Astrometry (IVS) in January 2005. The purpose of this project is to compare the individual CRF solutions and to analyze their systematic and random errors with focus on the selection of the optimal strategy for the next ICRF realization. Eight radio source catalogues provided by the IVS Analysis Centers GA, SHAO, DGFI, GIUB-BKG, JPL, MAO NANU, GSFC, USNO were analyzed. In present study, four analytical models were used to investigate the systematic differences between solutions: solid rotation, rotation and deformation (IERS method), and expansion in orthogonal functions: Legendre-Fourier polynomials and spherical functions. It was found that expansions by orthogonal function describe the differences between individual catalogues better than the two former models. Finally, the combined CRF was generated. Using the radio source positions from this combined catalogue for estimation of EOP has shown improvement of the uncertainty of the celestial pole offset time series.

astro-ph↗

arXiv2007

On accuracy assessment of celestial reference frame VLBI realizations

In this paper, we propose to use the scatter of celestial pole offset (CPO) series obtained from VLBI observations as a measure of the accuracy of the celestial reference frame (CRF) realizations. Several scatter indices (SIs) including those proposed for the first time are investigated. The first SI is based on analysis of residuals of CPO series w.r.t. Free Core Nutation (FCN) model. The second group of SIs includes Allan deviation and its extensions, which allow one to treat unequal and multidimensional observations. Application of these criteria to several radio source catalogues showed their ability to perform a preliminary assessment of the quality of radio source catalogues, and 2D Allan deviation estimate seems to be a most sensitive measure. However, in common case, the sensitivity of tested criteria is yet not sufficient to distinguish between radio source catalogues of the highest quality. Proposed extensions of Allan deviation, weighted and multidimensional, can be effectively used also for statistical analysis of astro-geodetic and other time series.

physics.geo-ph↗

arXiv2006

On Computation of Combined IVS EOP Series

Three topics related to computation of the combined IVS EOP series are discussed. The first one is the consistency of the VLBI EOP series with the IERS reference frames ITRF and ICRF. Not all IVS analysis centers use ITRF/ICRF as reference system for EOP solutions. Some of them realize global solution for simultaneous determination of CRF, TRF and EOP with no-net-rotation constrains w.r.t. ITRF/ICRF. Analysis shows that such a method can hardly provide consistency of computed EOP series with the IERS reference frames with sufficient accuracy. Direct use of ITRF and ICRF for computation of EOP series submitted to the IERS seems preferable. Second problem is the long-time stability of the IVS EOP series. Analysis of yearly biases w.r.t. C04 and NEOS is presented. A possible ways are proposed to save long time stability of the combined IVS EOP series. At last, various strategies of computation of weighted mean value are considered. It's shown that usual methods used for this purpose do not provide satisfactory result for the error of the mean. A new method is proposed.

physics.data-an↗

arXiv2004

Detection of Phase Jumps of Free Core Nutation of the Earth and their Concurrence with Geomagnetic Jerks

We detected phase jumps of the Free Core Nutation (FCN) of the Earth directly from the analysis of the Very Long Baseline Interferometer (VLBI) observation of the Earth rotation for the period 1984-2003 by applying the Weighted Wavelet Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function (SPG) method. During the period, the FCN had two significant phase jumps in 1992 and 1998. These epochs coincide with the reported occurrence of geomagnetic jerks.

physics.geo-ph↗

arXiv2004

A New Free Core Nutation Model with Variable Amplitude and Period

Three most long and dense VLBI nutation series obtained at the Goddard Space Flight Center, Institute of Applied Astronomy, and U.S. Naval Observatory were used for investigation of the Free Core Nutation (FCN) contribution to the celestial pole offset. Some recent studies have showed that the FCN period or/and phase does not remain constant, but varies in a rather wide range of about 410--490 days (for equivalent period). To implement this result in the practice, a new FCN model with variable amplitude and period (phase) is developed. Comparison of this model with observations shows better agreement than existing one. After correction of the differences between observed VLBI nutation series and the IAU2000A model, they decreased to a level about 100 microarcseconds.

physics.geo-ph↗

arXiv2004

Computation of a homogeneous coordinate time series for European GPS stations by reprocessing of the weekly EPN solutions

Weekly coordinate time series for the all EPN (European Permanent GPS Network) stations for the period of observations beginning from GPS week 834 was obtained by a reprocessing of the official EPN solutions. Comparison of this series with EPN Central Bureau (EPN CB) and the previous IAA two-year solution for selected EPN stations obtained by reprocessing of the original observations is performed. Results of comparison show that new solution based on fiducial-free strategy is most likely free of seasonal errors. Now the new IAA EPN solution is being computed regularly (on availability of the official EPN solution) and is available to any interested group.

physics.geo-ph↗