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- Haas, Rüdiger, 1966, et al.
(författare)
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GLONASS-VLBI: Onsala-Wettzell test observations
- 2015
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Ingår i: Proceedings of the 22nd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789892061917 ; , s. 107-111
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Hellerschmied, Andreas, et al.
(författare)
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Scheduling VLBI observations to satellites with VieVS
- 2017
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Ingår i: International Association of Geodesy Symposia. - Cham : Springer International Publishing. - 0939-9585. - 9783319456287 ; 146, s. 59-64
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Konferensbidrag (refereegranskat)abstract
- © Springer International Publishing Switzerland 2016.Observations of satellites with Very Long Baseline Interferometry (VLBI) radio telescopes provide a variety of new possibilities such as the integration of different geodetic techniques, which is one of the main goals of GGOS, the Global Geodetic Observing System of the IAG. Promising applications can be found, among others, in the field of inter-technique frame ties. With the standard geodetic VLBI scheduling software not being prepared to use satellites as radio sources so far, such observations were complicated due to the need to carefully prepare the required interchange files. The newly developed Satellite Scheduling Module for the Vienna VLBI Software (VieVS) offers a solution to this. It allows the user to prepare VLBI schedule files in a standardized format, providing the possibility to carry out actual satellite observations with standard geodetic antennas, e.g. of the IVS network. First successful observations of GLONASS satellites, based on schedules created with the new VieVS module, took place on the baseline Wettzell-Onsala in January 2014.
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| 5. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
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Position determination of the Chang’e 3 lander with geodetic VLBI
- 2019
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 71:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present results from the analysis of observations of the Chang’e 3 lander using geodetic Very Long Baseline Interferometry. The applied processing strategy as well as the limiting factors to our approach is discussed. We highlight the current precision of such observations and the accuracy of the estimated lunar-based parameters, i.e., the lunar lander’s Moon-fixed coordinates. Our result for the position of the lander is 44.1219 3 ∘ N , -19.51159∘E and -2637.3 m, with horizontal position uncertainties on the lunar surface of 8.9 m and 4.5 m in latitude and longitude, respectively. This result is in good agreement with the position derived from images taken by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter. Finally, we discuss potential improvements to our approach, which could be used to apply the presented concept to high-precision lunar positioning and studies of the Moon.[Figure not available: see fulltext.].
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| 6. |
- Litvinov, D. A., et al.
(författare)
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RadioAstron gravitational redshift experiment: Status update
- 2018
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Ingår i: 14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, Proceedings. - : WORLD SCIENTIFIC. - 9789813226593 ; , s. 3569-3575
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Konferensbidrag (refereegranskat)abstract
- A test of a cornerstone of general relativity, the gravitational redshift effect, is currently being conducted with the RadioAstron spacecraft, which is on a highly eccentric orbit around Earth. Using ground radio telescopes to record the spacecraft signal, synchronized to its ultra-stable on-board H-maser, we can probe the varying flow of time on board with unprecedented accuracy. The observations performed so far, currently being analyzed, have already allowed us to measure the effect with a relative accuracy of 4 × 10−4. We expect to reach 2.5 × 10−5 with additional observations in 2016, an improvement of almost a magnitude over the 40-year old result of the GP-A mission.
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| 7. |
- Litvinov, Dmitry, et al.
(författare)
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Probing the gravitational redshift with an Earth-orbiting satellite
- 2018
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Ingår i: Physics Letters, Section A: General, Atomic and Solid State Physics. - : Elsevier BV. - 0375-9601. ; 382:33, s. 2192-2198
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Tidskriftsartikel (refereegranskat)abstract
- We present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10−5, a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle.
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| 8. |
- Sun, Jing, et al.
(författare)
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VLBI observations to the APOD satellite
- 2018
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Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 61:3, s. 823-829
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Tidskriftsartikel (refereegranskat)abstract
- The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10 cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1 s integration time of the correlator output is on the level of 0.1 ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.
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