International VLBI Service for Geodesy and Astrometry

Nothnagel, A.; Artz, Thomas; Behrend, Dirk; Malkin, Zinovy

doi:10.1007/s00190-016-0950-5

Cited by 151 publications

(97 citation statements)

References 26 publications

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“…The catalogs in the SX frequency bands are based on almost the entire archive of VLBI sessions observed and made available by the IVS (Nothnagel et al 2017). The observation time spans from August 1979 to March 2018 and encompasses a total of 6206 sessions, typically of 24 h duration.…”

Section: Sx Bandmentioning

confidence: 99%

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

Karbon

Nothnagel

2019

A&A

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Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of Very Long Baseline Interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Aims. We produce a multifrequency catalog of radio source positions with full variance-covariance information across all radio source positions of all input catalogs. Methods. We combined three catalogs, one observed at 8 GHz (X band), one at 24 GHz (K band) and one at 32 GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog.Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8 Ghz, 824 sources also observed at 24 GHz, and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 µas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

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Section: Sx Bandmentioning

confidence: 99%

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

Karbon

Nothnagel

2019

A&A

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“…The difference in signal arrival time (delay) and its time derivative (delay rate) are the main observables of geodetic VLBI and determined in a correlation process. By observing several different radio sources, one can estimate geodetic target parameters, i.e., station coordinates, EOP and source positions as well as auxiliary parameters (clock behavior, wet part of the troposphere; Haas and Schuh 1996;Behrend et al 2000;Nothnagel et al 2016). In today's geodetic VLBI, observations are carried out at two different frequency bands (X and S).…”

Section: Geodetic Vlbimentioning

confidence: 99%

Geodetic VLBI with an artificial radio source on the Moon: a simulation study

Kłopotek

Hobiger

Haas

2017

J Geod

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We perform extensive simulations in order to assess the accuracy with which the position of a radio transmitter on the surface of the Moon can be determined by geodetic VLBI. We study how the quality and quantity of geodetic VLBI observations influence these position estimates and investigate how observations of such near-field objects affect classical geodetic parameters like VLBI station coordinates and Earth rotation parameters. Our studies are based on today's global geodetic VLBI schedules as well as on those designed for the next-generation geodetic VLBI system. We use Monte Carlo simulations including realistic stochastic models of troposphere, station clocks, and observational noise. Our results indicate that it is possible to position a radio transmitter on the Moon using today's geodetic VLBI with a two-dimensional horizontal accuracy of better than one meter. Moreover, we show that the nextgeneration geodetic VLBI has the potential to improve the two-dimensional accuracy to better than 5 cm. Thus, our results lay the base for novel observing concepts to improve both lunar research and geodetic VLBI.

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“…To demonstrate this, we use the data from CONT14 1 observations (Nothnagel, 2015) at X band. CONT14, as a campaign of continuous VLBI observations conducted by the International VLBI Service for Geodesy and Astrometry (IVS) over 15 days with 17 globally distributed stations, was intended to acquire state-of-the-art VLBI data with the highest accuracy that the then existing VLBI system was capable of.…”

Section: Calculations and Datamentioning

confidence: 99%

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

Mei-ling

Heinkelmann

Anderson

et al. 2017

J Geod

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Abstract. 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.

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International VLBI Service for Geodesy and Astrometry

Cited by 151 publications

References 26 publications

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

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

Geodetic VLBI with an artificial radio source on the Moon: a simulation study

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

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