arXiv subjects

Zinovy Malkin

Publications and source records attributed to Zinovy Malkin.

At least 55 records · Page 3Linked to original sources

arXiv2011

The impact of celestial pole offset modelling on VLBI UT1 Intensive results

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 microarcseconds. It has been also found that using different CPO models causes the differences in UT1 estimates reaching 10 microarcseconds. Obtained results are applicable to the satellite data processing as well.

physics.geo-ph↗

arXiv2011

CPO prediction: accuracy assessment and impact on UT1 intensive results

The UT1 Intensives results heavily depend on the celestial pole offset (CPO) model used during data processing. Since accurate CPO values are available with delay from two to four weeks, CPO predictions are necessarily applied to the UT1 intensive data analysis, and errors in predictions can influence the operational UT1 accuracy. In this papers the real accuracy of CPO prediction is assessed using the actual IERS and PUL predictions made in 2007-2009. Also, results of operational processing was analyzed to investigate the actual impact of EOP prediction errors on the rapid UT1 results. It was found that the impact of CPO prediction errors is at a level of several microseconds, whereas the impact of the inaccuracy in the polar motion prediction may be about one order larger for ultra-rapid UT1 results. The situation can be amended if the IERS Rapid solution will be updated more frequently.

physics.geo-ph↗

arXiv2011

Forthcoming occultations of astrometric radio sources by planets

Astrometric observations of the radio source occultations by solar system bodies may be of large interest for testing gravity theories, dynamical astronomy, and planetary physics. In this paper, we present an updated list of the occultations of astrometric radio sources by planets expected in the nearest years. Such events, like the solar eclipses, generally speaking, can be only observed in a limited region. The map of the shadow path is provided for the events occurred in regions with several VLBI stations and hence the most interesting for radio astronomy experiments.

astro-ph.CO↗

arXiv2011

On Estimate of Real Accuracy of EOP Prediction

To estimate real accuracy of EOP prediction real-time predictions made by the IERS Subbureau for Rapid Service and Prediction (USNO) and at the Institute of Applied Astronomy (IAA) EOP Service are analyzed. Methods of a priory estimate of accuracy of prediction are discussed.

physics.geo-ph↗

arXiv2011

SLR Contribution to Investigation of Polar Motion

SLR technique has being used for determination of ERP during over twenty years. Most of results contributed to IERS are based on analysis of observations of Lageos 1&2 satellites collected at the global tracking network of about 40 stations. Now 5 analysis centers submit operative (with 2-15 days delay) solutions and about 10 analysis centers yearly contribute final (up to 23 years) ERP series. Some statistics related to SLR observations and analysis is presented and analyzed. Possible problems in SLR observations and analysis and ways of its solution are discussed.

physics.geo-ph↗

arXiv2011

Length Variations of European Baselines Derived from VLBI and GPS Observations

Results of VLBI and GPS observations were analyzed with goal to investigate differences in observed baseline length derived from both techniques. VLBI coordinates for European stations were obtained from processing of all available observations collected on European and global VLBI network. Advanced model for antenna thermal deformation was applied to account for change of horizontal component of baseline length. GPS data were obtained from re-processing of the weekly EPN (European Permanent GPS Network) solutions. Systematic differences between results obtained with two techniques including linear drift and seasonal effects are determined.

physics.geo-ph↗

arXiv2011

5,000,000 Delays -- Some Statistics

5,000,000 VLBI delays are stored now in the IVS data base and available for scientific analysis. This is a remarkable result of more than 20 years of geodetic VLBI history. This paper presents some statistics related to the VLBI observations during almost 25 years of geodetic VLBI.

physics.geo-ph↗

arXiv2010

Analysis of the Accuracy of Prediction of the Celestial Pole Motion

VLBI observations carried out by global networks provide the most accurate values of the precession-nutation angles determining the position of the celestial pole; as a rule, these results become available two to four weeks after the observations. Therefore, numerous applications, such as satellite navigation systems, operational determination of Universal Time, and space navigation, use predictions of the coordinates of the celestial pole. In connection with this, the accuracy of predictions of the precession- nutation angles based on observational data obtained over the last three years is analyzed for the first time, using three empiric nutation models---namely, those developed at the US Naval Observatory, the Paris Observatory, and the Pulkovo Observatory. This analysis shows that the last model has the best of accuracy in predicting the coordinates of the celestial pole. The rms error for a one-month prediction proposed by this model is below 100 microarcsecond.

physics.geo-ph↗

arXiv2009

Determination of Redshifts for Selected IVS Sources. I

From observations with the 6-m BTA telescope at SAO RAS, we have determined spectroscopic redshifts of seven optical objects whose coordinates coincide with those of radio sources from the list of IVS (International VLBI Service for Geodesy and Astrometry). When compared to radio data, the obtained spectra and redshifts provide evidence for reliable identification of four observed objects; the other three require further study. The distances to the sources derived from our measurements will make it possible to refine the current estimates for parameters of cosmological models based on proper motions of these objects, which are determined from geodetic VLBI observations.

astro-ph.CO↗

arXiv2009

UT1 prediction based on long-time series analysis

A new method is developed for prediction of UT1. The method is based on construction of a general harmonic model of the Earth rotation using all the data available for the last 80-100 years, and modified autoregression technique. A rigorous comparison of UT1 predictions computed at SNIIM with the prediction computed by IERS (USNO) in 2008-2009 has shown that proposed method pro-vides substantially better accuracy.

physics.geo-ph↗

arXiv2009

Improving short-term EOP prediction using combination procedures

A well known problem with EOP prediction is that a prediction strategy proved to be the best for some testing period and prediction length may not remain as such for other period of time. In this paper we consider possible strategies to combine EOP predictions made using different analysis technique to obtain a final prediction with the best accuracy corresponding to the least prediction error between input predictions. This approach can be used to improve the short-term real-time EOP forecast.

physics.geo-ph↗

arXiv2009

Using the Singular Spectrum Analysis for Investigation of Troposphere Parameters

In this paper, the method of Singular Spectrum Analysis (SSA) is applied for investigation of the zenith troposphere delay time-series derived from VLBI observations. With the help of this method we can analyze the structure of time-series and separate the harmonic and irregular (trend) components. Combined IVS time-series of zenith wet and total troposphere delays obtained in IGG were used for analysis. For this study, several VLBI stations with the most long time series of troposphere zenith delays were selected, also taking into consideration the geographic region where the station is located. The investigations were carried out using SSA mode. As a result, trends and seasonal components (with annual and semiannual periods) were obtained for all the stations. Using of SSA enabled us to determine nonlinear trends in zenith delay, and also to study variations in the amplitude and the phase of the seasonal components with time.

physics.geo-ph↗

arXiv2009

Optical Characteristics of the Astrometric Radio Sources

A new list of physical characteristics of 3914 astrometric radio sources, including all 717 ICRF-Ext.2 sources, observed during IVS and NRAO VCS sessions have been compiled. The list includes source type, redshift and visual magnitude (if available). In case of doubt detailed comment is provided. The list of sources with their positions was taken from the Goddard VLBI astrometric catalog with addition of two ICRF-Ext.2 sources. At this stage the source characteristics were mainly taken from the NASA/IPAC Extragalactic Database (NED). 667 sources from our list are included into the IERS list. Comparison has shown a significant difference in characteristics for about half of these 667 common sources. We compiled a list of frequently observed sources without known physical characteristics for urgent optical identification and spectrophotometric observations with large optical telescopes. This presented list of physical characteristics can be used as a supplement material for the ICRF-2, as well as a database for kinematic studies of the Universe and other related works, including scheduling of dedicated IVS programs.

astro-ph.CO↗

arXiv2009

Effect of asymmetry of the radio source distribution on the apparent proper motion kinematic analysis

A new list of physical characteristics of 4261 astrometric radio sources, including all 717 ICRF-Ext.2 sources has been compiled. Comparison of our data of optical characteristics with the official International Earth Rotation and Reference Systems Service (IERS) list showed significant discrepancies for about half of 667 common sources. We also found that asymmetry in the radio sources distribution between hemispheres could cause significant correlation between the vector spherical harmonics, especially if the case of sparse distribution of the sources with high redshift. We identified radio sources having many-year observation history and lack redshift. This sources should be urgently observed at large optical telescopes. The list of optical characteristics created in this paper is recommended for use as a supplement material for the next International Celestial Reference Frame (ICRF) realization. It can be also effectively used for cosmological studies and planning of observing programs both in radio and optics.

astro-ph.CO↗

arXiv2009

Influence of the Cut-off Elevation Angle and Elevation-Dependent Weighting on Parameter Estimates: A Case of CONT05

In this paper, results are presented on studies which have been performed to investigate the impact of the cut-off elevation angle (CEA) and elevation-dependent weighting (EDW) on the EOP estimates and baseline length repeatability. For this test, CONT05 observations were processed with different CEA and EDW, keeping all other options the same as used during the routine processing. Uncertainties and biases, as well as correlations between estimated parameters have been investigated. It has been shown that small CEA, up to about 8--10 degrees does not have large impact on the results, and applying EDW allows us to get better result (smaller errors). However, this result has been proven with standard geodetic VLBI observations, where rather few observations were made at low elevations. Perhaps, special R&D sessions with more uniform distribution of observations over elevation may be useful for more detailed study on the subject.

physics.geo-ph↗

arXiv2009

On Construction of ICRF-2

In this paper, several issues are considered, related to the construction of the next ICRF generation, ICRF-2. Between them, the following points are touched: ICRF-2 structure, ICRF Core sources selection, and some expected user's requirements.

astro-ph.CO↗

arXiv2009

Comparison and Combination of CRF Catalogues

In 2007, a joint IERS/IVS Working Group has been established to consider practical issues of creating the next ICRF generation, ICRF-2. The goal of the WG is to seek after ways to improve the existing ICRF. In this study we investigate a possibility of ICRF improvement by means of using combined ICRF catalogue instead of a catalogue computed in a single analysis centre, even though using most advanced models and software. In this work, we present a new version of Pulkovo combined catalogue of radio source positions computed using the method proposed in \cite{SokMal07}. Radio source catalogues that were submitted in 2007 in the framework of the WG activity were used as input for mutual comparison and combination. Four combined catalogues have been calculated: Two first of them provide a stochastic improvement of the ICRF, and last two of them allow us to account also for systematic errors in the current ICRF version.

astro-ph.CO↗

arXiv2009

Chandler wobble: two more large phase jumps revealed

Investigations of the anomalies in the Earth rotation, in particular, the polar motion components, play an important role in our understanding of the processes that drive changes in the Earth's surface, interior, atmosphere, and ocean. This paper is primarily aimed at investigation of the Chandler wobble (CW) at the whole available 163-year interval to search for the major CW amplitude and phase variations. First, the CW signal was extracted from the IERS (International Earth Rotation and Reference Systems Service) Pole coordinates time series using two digital filters: the singular spectrum analysis and Fourier transform. The CW amplitude and phase variations were examined by means of the wavelet transform and Hilbert transform. Results of our analysis have shown that, besides the well-known CW phase jump in the 1920s, two other large phase jumps have been found in the 1850s and 2000s. As in the 1920s, these phase jumps occurred contemporarily with a sharp decrease in the CW amplitude.

physics.geo-ph↗