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According to the decision of the International Astronomical Union (IAU), since 1998 the International Celestial Reference System has been realized by the ICRF catalogue of extragalactic radio source positions obtained from VLBI observations. Over the past years, the accuracy of the ICRF catalogue data has been increased only through an increase in the number and quality of observations and an improvement in the methods of their processing. Both the first ICRF version and the new ICRF2 version adopted by the IAU in 2009 are based on the catalogues obtained at the same VLBI data processing center. However, the experience of classical astrometry shows that a significant increase in the accuracy of the International Celestial Reference Frame can be achieved by creating combined catalogues, such as the fundamental catalogues of star positions. The same approach was applied to improve the ICRF catalogue. Even the first experience of such a combined solution has shown its high efficiency. Here, a new combined catalogue of radio source positions PUL(2013)C02 is presented. Mainly classical methods based on the expansion of the systematic differences between the input catalogues into series of orthogonal functions with additional improvements have been applied for its creation. Comparison of the combined catalogue obtained with the ICRF2 catalogue has shown that the latter is most likely not devoid of systematic errors at a level of 15–20 μas. 相似文献
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Z. Malkin 《Journal of Geodesy》2008,82(6):325-329
The scatter of the celestial pole offset (CPO) time-series obtained from very long baseline interferometry (VLBI) observations
is used as a measure of the accuracy of celestial reference frame (CRF) realizations. Several scatter indices (SI), including
some proposed for the first time, are investigated. The first SI is based on residual analysis of CPO series with respect
to a free core nutation (FCN) model. The second group of SIs includes Allan deviation and its extensions, which allow the
treatment of unequally weighted and multidimensional observations. Application of these criteria to several radio source catalogues
(RSCs) showed their ability to perform a preliminary assessment of the quality of each RSC. The 2D Allan deviation estimate
seems to be the most sensitive measure. The proposed extensions of Allan deviation, weighted and multidimensional, can also
be used for the statistical analysis of other time-series. 相似文献
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Empiric models of the Earth’s free core nutation 总被引：1，自引：0，他引：1
Z. M. Malkin 《Solar System Research》2007,41(6):492-497
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. 相似文献
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The unique environment of the abyssal plains allows many simplifying assumptions, facilitating the acoustic classification of an animal into one of two groups. The most important assumptions are based on low population densities and available target strength histograms and swim rate histograms. The likelihood ratio is formed from this information and accepted signal processing theory. The likelihood function, a three-dimensional integral, is analytically simplified to one dimension and then solved numerically. A simulation based on this solution and measured data demonstrates that classification using the likelihood ratio approach is accurate, e.g. the sensitivity is ⩾0.8. Although the measured data come from two abyssopelagic genera, the methods presented are more generally applicable. Simulations based on hypothetical animal populations show that under certain conditions, a near perfect classification can be made, e.g. sensitivity and specificity greater than 0.969 相似文献
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Z. M. Malkin 《Astronomy Reports》2013,57(2):128-133
The paper investigates the question of whether or not determinations of the distance between the Sun and the Galactic center R 0 are affected by the so-called “bandwagon effect”, leading to selection effects in published data that tend to be close to expected values, as was suggested by some authors. It is difficult to estimate numerically a systematic uncertainty in R 0 due to the bandwagon effect; however, it is highly probable that, even if widely accepted values differ appreciably from the true value, the published results should eventually approach the true value despite the bandwagon effect. This should be manifest as a trend in the published R 0 data: if this trend is statistically significant, the presence of the bandwagon effect can be suspected in the data. Fifty two determinations of R 0 published over the last 20 years were analyzed. These data reveal no statistically significant trend, suggesting they are unlikely to involve any systematic uncertainty due to the bandwagon effect. At the same time, the published data show a gradual and statistically significant decrease in the uncertainties in the R 0 determinations with time. 相似文献
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Astronomy Reports - As of 2019, the International VLBI Service for Geodesy and Astrometry (IVS) has existed for 20 years. This service is the largest and most prominent organization that... 相似文献
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Z. M. Malkin 《Astronomy Reports》2011,55(9):810-815
The influence of proper motions of sources due to Galactic aberration on precession models based on VLBI data is determined.
Comparisons of the linear trends in the coordinates of the celestial pole obtained with and without taking into account Galactic
aberration indicate that this effect can reach 20 μ as per century, which is important for modern precession models. It is
also shown that correcting for Galactic aberration influences the derived parameters of low-frequency nutation terms. It is
therefore necessary to correct for Galactic aberration in the reduction of modern astrometric observations. 相似文献
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