The impacts of source structure on geodetic parameters demonstrated by the radio source 3C371

Closure quantities measured by very long baseline interferometry (VLBI) observations are independent of instrumental and propagation instabilities and antenna gain factors, but are sensitive to source structure. A new method is proposed to calculate a structure index based on the median values of closure quantities rather than the brightness distribution of a source. The results are comparable to structure indices based on imaging observations at other epochs and demonstrate the flexibility of deriving structure indices from exactly the same observations as used for geodetic analysis and without imaging analysis. A three-component model for the structure of source 3C371 is developed by model-fitting closure phases. It provides a real case of tracing how the structure effect identified by closure phases in the same observations as the delay observables affects the geodetic analysis, and investigating which geodetic parameters are corrupted to what extent by the structure effect. Using the resulting structure correction based on the three-component model of source 3C371, two solutions, with and without correcting the structure effect, are made. With corrections, the overall rms of this source is reduced by 1 ps, and the impacts of the structure effect introduced by this single source are up to 1.4 mm on station positions and up to 4.4 microarcseconds on Earth orientation parameters. This study is considered as a starting point for handling the source structure effect on geodetic VLBI from geodetic sessions themselves.Comment: 5 figures, 15 pages, accepted by Journal of Geodesy at 19 Dec., 201

An Improved Empirical Harmonic Model of the Celestial Intermediate Pole Offsets from a Global VLBI Solution

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable of measuring all the Earth orientation parameters (EOP) accurately and simultaneously. Modeling the Earth's rotational motion in space within the stringent consistency goals of the Global Geodetic Observing System (GGOS) makes VLBI observations essential for constraining the rotation theories. However, the inaccuracy of early VLBI data and the outdated products could cause non-compliance with these goals. In this paper, we perform a global VLBI analysis of sessions with different processing settings to determine a new set of empirical corrections to the precession offsets and rates, and to the amplitudes of a wide set of terms included in the IAU 2006/2000A precession-nutation theory. We discuss the results in terms of consistency, systematic errors, and physics of the Earth. We find that the largest improvements w.r.t. the values from IAU 2006/2000A precession-nutation theory are associated with the longest periods (e.g., 18.6-yr nutation). A statistical analysis of the residuals shows that the provided corrections attain an error reduction at the level of 15 μas. Additionally, including a Free Core Nutation (FCN) model into a priori Celestial Pole Offsets (CPOs) provides the lowest Weighted Root Mean Square (WRMS) of residuals. We show that the CPO estimates are quite insensitive to TRF choice, but slightly sensitive to the a priori EOP and the inclusion of different VLBI sessions. Finally, the remaining residuals reveal two apparent retrograde signals with periods of nearly 2069 and 1034 days.This work was funded and realized in the framework of the project AYA2016-79775-P (AEI/FEDER, UE) and APOSTD/2026/079

Realization of a multifrequency celestial reference frame through a combination of normal equation systems

International audienc

Impact of the parameterization of the source positions on the Free Core Nutation

International audienceThe positions of the radio sources in the ICRF3 catalog, representing the newest realization of the Celestial Reference Frame (CRF), are given as time invariant coordinate pairs. <P />Failing to acknowledge systematics within the source positions leads to a deterioration in the quality of the frame, and thus in all derived variables, such as the Earth orientation parameters (EOP). <P />A proven approach to overcome these shortcomings is to extend the parameterization of source positions using the multivariate adaptive regression splines (MARS). They allow a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. <P />Here we present first results on the impact of the parameterization of the source positions on the EOP and the estimation of the free core nutation

Kinematics of a mass movement constrained by sparse and inhomogeneous data

On 12 February 2008, a landslide occurred along a 50 m high bank of the Danube river near Dunaszekcsö, Hungary. The initial state is only incompletely documented and the geodetic data acquired after the mass movement are sparse. A generalized 3-D topographic model of the landslide and its surrounding area was assembled and a representative longitudinal profile extracted. The reconstruction of the original surface is based on an orthophoto as well as on morphological considerations. Recorded observations include the locations of the outcrops of basal sliding surfaces, displacements at the main scarp and in the lower part of the slide, and a value to describe the total mass transport. Such sparse and inhomogeneous data were insufficient to derive a comprehensive documentation of the landslide or obtain adequate constraints for an accurate numerical analysis. Therefore, slider block models were fitted to the field data, which have only a small number of free parameters. A general view on the morphology of the mass movement justifies its classification as a rotational slide. A double slider block model fits all observational parameters within their error margin and supplies valuable information on the geometry of the slide. Estimates of the residual friction angles were derived and the question of reactivation was addressed. Finite Difference (FD) modelling and the application of conventional stability analysis support the geometry of the slider blocks and the computed average residual friction angles. Generally, the results are assumed to represent preliminary information, which could only be attained by the combination of the thinly distributed geodetic data with qualitative morphological observations and the implementation of a model. This type of information can be gained quickly and may be valuable for preliminary hazard mitigation measures or the planning of a comprehensive exploration and monitoring program

Impact of the parameterization of the source positions on the Free Core Nutation

International audienceThe positions of the radio sources in the ICRF3 catalog, representing the newest realization of the Celestial Reference Frame (CRF), are given as time invariant coordinate pairs. <P />Failing to acknowledge systematics within the source positions leads to a deterioration in the quality of the frame, and thus in all derived variables, such as the Earth orientation parameters (EOP). <P />A proven approach to overcome these shortcomings is to extend the parameterization of source positions using the multivariate adaptive regression splines (MARS). They allow a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. <P />Here we present first results on the impact of the parameterization of the source positions on the EOP and the estimation of the free core nutation

New Earth orientation parameters by combination of GNSS and VLBI

International audienceWe present the combined processing of GNSS and VLBI normal equations produced at the IERS technique centers. The DYNAMO sofware allows to obtain the combined solution for EOP and station coordinates, along with the corresponding intra-technique VLBI and GNSS solutions. <P />The combined GNSS/VLBI solution seems to be more robust than the intratechnique ones. First the EOP are better decorrelated, second sub-monthly nutation and UT1 have a better stability