Measurement of the solar system acceleration using the Earth scale factor

We propose an alternative method to detect the secular aberration drift induced by the solar system acceleration due to the attraction to the Galaxy centre. This method is free of the individual radio source proper motion caused by intrinsic structure variation. We developed a procedure to estimate the scale factor directly from very long baseline interferometry (VLBI) data analysis in a source-wise mode within a global solution. The scale factor is estimated for each reference radio source individually as a function of astrometric coordinates (right ascension and declination). This approach splits the systematic dipole effect and uncorrelated motions on the level of observational parameters. We processed VLBI observations from 1979.7 to 2016.5 to obtain the scale factor estimates for more than 4,000 reference radio sources. We show that the estimates highlight a dipole systematics aligned with the direction to the centre of the Galaxy. With this method we obtained a Galactocentric acceleration vector with an amplitude of 5.2 $\pm$ 0.2 \mu as/yr and direction $\alpha_G = 281\deg \pm 3\deg$ and $\delta_G = -35\deg \pm 3\deg$.Comment: accepted to A&

Non-linear VLBI station motions and their impact on the celestial reference frame and Earth orientation parameters

© 2015, The Author(s). The increasing accuracy and growing time span of Very Long Baseline Interferometry (VLBI) observations allow the determination of seasonal signals in station positions which still remain unmodelled in conventional analysis approaches. In this study we focus on the impact of the neglected seasonal signals in the station displacement on the celestial reference frame and Earth orientation parameters. We estimate empirical harmonic models for selected stations within a global solution of all suitable VLBI sessions and create mean annual models by stacking yearly time series of station positions which are then entered a priori in the analysis of VLBI observations. Our results reveal that there is no systematic propagation of the seasonal signal into the orientation of celestial reference frame but position changes occur for radio sources observed non-evenly over the year. On the other hand, the omitted seasonal harmonic signal in horizontal station coordinates propagates directly into the Earth rotation parameters causing differences of several tens of microarcseconds

Non-linear VLBI station motions and their impact on the celestial reference frame and Earth orientation parameters

© 2015, The Author(s). The increasing accuracy and growing time span of Very Long Baseline Interferometry (VLBI) observations allow the determination of seasonal signals in station positions which still remain unmodelled in conventional analysis approaches. In this study we focus on the impact of the neglected seasonal signals in the station displacement on the celestial reference frame and Earth orientation parameters. We estimate empirical harmonic models for selected stations within a global solution of all suitable VLBI sessions and create mean annual models by stacking yearly time series of station positions which are then entered a priori in the analysis of VLBI observations. Our results reveal that there is no systematic propagation of the seasonal signal into the orientation of celestial reference frame but position changes occur for radio sources observed non-evenly over the year. On the other hand, the omitted seasonal harmonic signal in horizontal station coordinates propagates directly into the Earth rotation parameters causing differences of several tens of microarcseconds

Non-linear VLBI station motions and their impact on the celestial reference frame and Earth orientation parameters

© 2015, The Author(s). The increasing accuracy and growing time span of Very Long Baseline Interferometry (VLBI) observations allow the determination of seasonal signals in station positions which still remain unmodelled in conventional analysis approaches. In this study we focus on the impact of the neglected seasonal signals in the station displacement on the celestial reference frame and Earth orientation parameters. We estimate empirical harmonic models for selected stations within a global solution of all suitable VLBI sessions and create mean annual models by stacking yearly time series of station positions which are then entered a priori in the analysis of VLBI observations. Our results reveal that there is no systematic propagation of the seasonal signal into the orientation of celestial reference frame but position changes occur for radio sources observed non-evenly over the year. On the other hand, the omitted seasonal harmonic signal in horizontal station coordinates propagates directly into the Earth rotation parameters causing differences of several tens of microarcseconds

Non-linear VLBI station motions and their impact on the celestial reference frame and Earth orientation parameters

© 2015, The Author(s). The increasing accuracy and growing time span of Very Long Baseline Interferometry (VLBI) observations allow the determination of seasonal signals in station positions which still remain unmodelled in conventional analysis approaches. In this study we focus on the impact of the neglected seasonal signals in the station displacement on the celestial reference frame and Earth orientation parameters. We estimate empirical harmonic models for selected stations within a global solution of all suitable VLBI sessions and create mean annual models by stacking yearly time series of station positions which are then entered a priori in the analysis of VLBI observations. Our results reveal that there is no systematic propagation of the seasonal signal into the orientation of celestial reference frame but position changes occur for radio sources observed non-evenly over the year. On the other hand, the omitted seasonal harmonic signal in horizontal station coordinates propagates directly into the Earth rotation parameters causing differences of several tens of microarcseconds

Tropospheric delay modelling and the celestial reference frame at radio wavelengths

Aims. We examine the relationship between Very Long Baseline Interferometry (VLBI) tropospheric delay modelling and source positions. In particular, the effect of a priori ray-traced slant delays on source declination is investigated. Methods. We estimated source coordinates as global positions from 5830 geodetic VLBI sessions incorporating about 10 million group delay measurements. This data set was used for the International Celestial Reference Frame 3 (ICRF3) prototype solutions as of December 2016. Results. We report on a significant bias in source declination of about 50 μas, which can be found between a normal solution and a solution where a priori ray-traced slant delays are used. More traditional tropospheric delay modelling techniques, such as a priori gradients, are tested as well. Significant differences of about 30 μas in declination can only be found when absolute constraints are used for a priori gradient models. Further, we find that none of these models decrease the declination bias between ICRF3 prototype solutions and ICRF2

The Effect of Galactic Aberration on the CRF

International audienceWe compare two Celestial Reference Frame (CRF) solutions made from Very Long Baseline Interferometry (VLBI) group delay observations in S/X band using vector spherical harmonics. In both solutions the same data set was used which consists of almost all observations since 1979 until the beginning of 2018. The same parameterization and models were used with the exception that in one of the solutions the effect of galactic aberration (GA) was corrected. The other solution serves as a reference. We show that the deformation of a CRF estimated with the whole set of VLBI observations can be described by a systematic dipole displacement with an amplitude of about 35 ?as

The Effect of Galactic Aberration on the CRF

International audienceWe compare two Celestial Reference Frame (CRF) solutions made from Very Long Baseline Interferometry (VLBI) group delay observations in S/X band using vector spherical harmonics. In both solutions the same data set was used which consists of almost all observations since 1979 until the beginning of 2018. The same parameterization and models were used with the exception that in one of the solutions the effect of galactic aberration (GA) was corrected. The other solution serves as a reference. We show that the deformation of a CRF estimated with the whole set of VLBI observations can be described by a systematic dipole displacement with an amplitude of about 35 ?as

Improving the S/X Celestial Reference Frame in the South: A Status Update

Catalogs of positions of compact extragalactic radio sources, including the ICRF-3, are generally weaker in the south by factors of 2 or more in both density and precision. In 2018 we started a campaign to improve the S/X celestial reference frame in the South by upgrading existing IVS astrometric observing programmes. Our efforts were mainly focused on the Celestial Reference Frame (CRF) and Celestial Reference Frame Deep South (CRDS) sessions, which are dedicated astrometric observing programmes of sources at mid-and southern declinations. In particular, the data rate of the CRF and CRD