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| 2. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Status of the Onsala Twin Telescopes – One Year After the Inauguration
- 2019
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Ingår i: IVS 2018 General Meeting Proceedings "Global Geodesy and the Role of VGOS – Fundamental to Sustainable Development". ; NASA/CP-2019-219039, s. 17-19
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Konferensbidrag (refereegranskat)abstract
- We briefly describe the status of the Onsala twin telescopes and the experience gained since the official inauguration in May 2017.
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| 3. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Status of the Onsala Twin Telescopes – Two Years After the Inauguration
- 2019
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Ingår i: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. - 9788441656345 ; , s. 5-9
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Konferensbidrag (refereegranskat)abstract
- We give a brief overview on the status of the Onsala twin telescopes (OTT), two years after their inauguration. The dierent components of the VGOS systems are briefly described, and the development towards routine operations.
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| 4. |
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| 5. |
- Marti-Vidal, Ivan, 1980, et al.
(författare)
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UVMULTIFIT: A versatile tool for fitting astronomical radio interferometric data
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 563
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Tidskriftsartikel (refereegranskat)abstract
- Context. The analysis of astronomical interferometric data is often performed on the images obtained after deconvolving the interferometer's point spread function. This strategy can be understood (especially for cases of sparse arrays) as fitting models to models, since the deconvolved images are already non-unique model representations of the actual data (i.e., the visibilities). Indeed, the interferometric images may be affected by visibility gridding, weighting schemes (e. g., natural vs. uniform), and the particulars of the (non-linear) deconvolution algorithms. Fitting models to the direct interferometric observables (i.e., the visibilities) is preferable in the cases of simple (analytical) sky intensity distributions. Aims. We present UVMULTIFIT, a versatile library for fitting visibility data, implemented in a Python-based framework. Our software is currently based on the CASA package, but can be easily adapted to other analysis packages, provided they have a Python API. Methods. The user can simultaneously fit an indefinite number of source components to the data, each of which depend on any algebraic combination of fitting parameters. Fits to individual spectral-line channels or simultaneous fits to all frequency channels are allowed. Results. We have tested the software with synthetic data and with real observations. In some cases (e. g., sources with sizes smaller than the diffraction limit of the interferometer), the results from the fit to the visibilities (e. g., spectra of close by sources) are far superior to the output obtained from the mere analysis of the deconvolved images. Conclusions. UVMULTIFIT is a powerful improvement of existing tasks to extract the maximum amount of information from visibility data, especially in cases close to the sensitivity/resolution limits of interferometric observations.
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| 6. |
- Tornatore, Vincenza, et al.
(författare)
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Determination of GLONASS satellite coordinates with respect to natural radio sources using the VLBI technique: preliminary results
- 2011
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Ingår i: Proceedings of the European Test and Telemetry Conference ETTC2011, Toulouse, France.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this manuscript is topresent tests that have been carried out using VLBI (VeryLong Baseline Interferometry) in order to evaluate if thistechnique, primarily a radio astronomical technique, canalso be used to determine positions of Earth orbitingsatellites. A number of GLONASS (Global NavigationSatellite Systems) satellites, usually used for navigationand positioning purposes, were simultaneously trackedwith two European VLBI radio telescopes in geodeticmode. Software, developed for VLBI tracking ofspacecraft, was successfully used for the processing ofthese GLONASS observations. First results are presentedand discussed.
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| 7. |
- Tornatore, Vincenza, et al.
(författare)
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Direct VLBI Observations of Global Navigation Satellite System Signals
- 2014
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Ingår i: International Association of Geodesy Symposia. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0939-9585. ; 139, s. 247-252
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Konferensbidrag (refereegranskat)abstract
- We describe an experiment carried out to observe signals emitted by GLONASS (GLObalNAvigation Satellite System) satellites using the Very Long Baseline Interferometry (VLBI)technique. This test was performed on a single baseline and had as its primary goal toevaluate the capability of the VLBI system to observe GNSS (Global Navigation SatelliteSystem) signals in terms of scheduling, tracking, acquisition, recording, correlation andprocessing of data.
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| 8. |
- Tornatore, Vincenza, et al.
(författare)
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Single baseline GLONASS observations with VLBI: data processing and first results
- 2011
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Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 162-165
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The VLBI technique, in geodetic mode, was used to observe signals emitted by three GLONASS (GLObal NAvigationSatellite System) satellites. The baseline observing simultaneously satellites had at its ends the Medicina (32 m) and Onsala85 (25 m) radio telescopes, both equipped with L-band receivers. Several preparatory tests were necessary for obtaining good data that could be processed. In this paper we report on the observations performed on August 16, 2010 data processing and results of the experiment. The natural radio source 3c286 was observed also as a calibrator before and after satellite observing sessions. A narrow band approach using software primarily developed for astronomical and space applications, was applied to extract the narrow band carrier. Differential frequency on the baseline Medicina-Onsala was also evaluated to compute differential phase which was then adopted to determine satellite coordinate corrections with respect to ITRFvalues. Broad-band correlation was performed on the calibrator data using the DiFX software. The SFXC correlation of satellite data was performed testing near field delay model at extreme nearness; obtained results are described.
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| 9. |
- Tornatore, Vincenza, et al.
(författare)
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Tracking of GLONASS satellites by VLBI radio telescopes
- 2010
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Ingår i: Proc. of the 5th ESA International Workshop on Tracking, Telemetry and Command Systems for Space Applications, TTC 2010, ESA-ESTEC.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Several tests to observe signals transmitted by GLONASS (GLObal NAvigation Satellite System) satellites have been performed using the VLBI (Very Long Baseline Interferometry) technique. The radio telescopes involved in these experiments are Medicina and Onsala. The satellites transmit artificial radio signals that were considered in a similar way as natural radio signal that are emitted by natural radio sources. The signal strength of satellite signals is much stronger than the signal strength of natural radio signals, so in order to avoid overload of the telescope frontends, corresponding signal attenuation was applied. Observations at the stations were performed using the standard Mark4 VLBI data acquisition rack and Mark5A disk-based recorders. The goals of the observations were to develop and test the scheduling, signal acquisition and processing routines to verify the full tracking pipeline, foreseeing the cross-correlation of the recorded data on the baseline Onsala-Medicina. The natural radio source 3C454.3 was used as a calibrator before the beginning of the satellite observation sessions.We present results of a detailed analysis of the signal recorded at the Onsala telescope together with a first attempt of cross-correlation of data recorded on the baseline Onsala–Medicina.Further plans to perform new GNSS observations are in preparation, and a study to develop the VLBI delay model for GNSS observations with astronomical VLBI telescopes is in progress.
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| 10. |
- Tuccari, G., et al.
(författare)
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DBBC3 development
- 2014
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- The RadioNet3 JRA project named 'DBBC3' is progressing as planned. The first units of the 4 GHz bandwidth samplers are available as well as the CORE3 processing elements. The first functional mode for both of them has been successfully tested and the construction of two further DBBC3 units is under way. The main parts of the system are shown together with their performance, and an overview of the implementation is presented for data-rates of 32 and 64 Gbps with two examples of their application: a) astronomical for the EVN and for millimetre VLBI with the EHT (Event Horizon Telescope), and b) geodetic for the VGOS broadband network.
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| 11. |
- Tuccari, G., et al.
(författare)
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DBBC3: VLBI at 32 Gbits per second
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)abstract
- The project to develop the third generation of a digital backend system (DBBC3) for VLBI and other applications is presented, including an overview of the evolution of this system. The initial development started about ten years ago and evolved in the course of time by improving all its components: hardware, firmware and software going from DBBC1 to DBBC2. The latest, now third generation will be able to fully implement digitally all the functionality required of a complete 32 Gbps VLBI backend for the EVN and VLBI2010. The architecture and adopted methods are described. The implementation of the astronomical version is financially supported by RadioNet3.
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