A gravitational telescope deformation model for geodetic VLBI

Bergstrand, Sten; Herbertsson, Magnus; Rieck, Carsten; Spetz, Jörgen; Svantesson, Claes-Göran; Haas, Rüdiger

doi:10.1007/s00190-018-1188-1

Cited by 12 publications

(14 citation statements)

References 17 publications

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“…In general, a single position close to the sub-reflector is chosen, which allows observing nearly the full reflector surface and avoiding glancing intersections (cf. Holst et al 2017;Bergstrand et al 2019).…”

Section: Surface Measurement Methodsmentioning

confidence: 99%

“…Due to structural deformations induced by gravity, the focal length F of the radio telescope may change when it rotates around the elevation axis (e.g., Sarti et al 2009;Nothnagel et al 2013;Bergstrand et al 2019). According to Artz et al (2014), two deformation patterns can exist.…”

Section: Double-elliptic Ring-focus Paraboloidmentioning

confidence: 99%

“…This geometrical behavior is experimentally confirmed by direct measurements of R (cf. Nothnagel et al 2013;Bergstrand et al 2019). It should be mentioned that the struts may be affected by further gravitational effects, e.g., an elevation-dependent bending (e.g., Sarti et al 2009).…”

Section: Sub-reflector Variationsmentioning

confidence: 99%

“…Depending on the pointing direction, different structural loads may occur. For large conventional radio telescopes, variations of the focal length between several millimeters up to the centimeter level have been detected (e.g., Sarti et al 2009;Nothnagel et al 2013;Bergstrand et al 2019). The Global Geodetic Observing System (GGOS) calls for high-accuracy station positions at the millimeter level for deriving a reliable global geodetic reference frame (e.g., Rothacher et al 2009).…”

Section: Introductionmentioning

confidence: 99%

“…An important point in this context is that the telescopes in general show individual deformation behavior (cf. Sarti et al 2009;Nothnagel et al 2013;Bergstrand et al 2019), and thus each type of telescope has to be measured and modeled individually.…”

Section: Introductionmentioning

confidence: 99%

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Gravitational deformation of ring-focus antennas for VGOS: first investigations at the Onsala twin telescopes project

Lösler

Haas

Eschelbach

et al. 2019

J Geod

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The receiving properties of radio telescopes used in geodetic and astrometric very long baseline interferometry (VLBI) depend on the surface quality and stability of the main reflector. Deformations of the main reflector as well as changes in the sub-reflector position affect the geometrical ray path length significantly. The deformation pattern and its impact on the VLBI results of conventional radio telescopes have been studied by several research groups using holography, laser tracker, close-range photogrammetry and laser scanner methods. Signal path variations (SPV) of up to 1 cm were reported, which cause, when unaccounted for, systematic biases of the estimated vertical positions of the radio telescopes in the geodetic VLBI analysis and potentially even affect the estimated scale of derived global geodetic reference frames. As a result of the realization of the VLBI 2010 agenda, the geodetic VLBI network is currently extended by several new radio telescopes, which are of a more compact and stiffer design and are able to move faster than conventional radio telescopes. These new telescopes will form the backbone of the next generation geodetic VLBI system, often referred to as VGOS (VLBI Global Observing System). In this investigation, for the first time the deformation pattern of this new generation of radio telescopes for VGOS is studied. ONSA13NE, one of the Onsala twin telescopes at the Onsala Space Observatory, was observed in several elevation angles using close-range photogrammetry. In general, these methods require a crane for preparing the reflector as well as for the data collection. To reduce the observation time and the technical effort during the measurement process, an unmanned aircraft system (UAS) was used for the first time. Using this system, the measurement campaign per elevation angle took less than 30 min. The collected data were used to model the geometrical ray path and its variations. Depending on the distance from the optical axis, the ray path length varies in a range of about ± 1 mm. To combine the ray path variations, an illumination function was introduced as weighting function. The resulting total SPV is about − 0.5 mm. A simple elevation-dependent SPV model is presented that can easily be used and implemented in VLBI data analysis software packages to correct for gravitational deformation in VGOS radio telescopes. The uncertainty is almost 200 µm (2σ) and is derived by Monte Carlo simulations applied to the entire analysis process. Keywords Ring-focus paraboloid • Radio telescope • Antenna deformation • VLBI • VGOS • Signal path variation • SQP • Reverse engineering • Photogrammetry • Unmanned aircraft system B Michael Lösler

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Section: Surface Measurement Methodsmentioning

confidence: 99%

Section: Double-elliptic Ring-focus Paraboloidmentioning

confidence: 99%

Section: Sub-reflector Variationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gravitational deformation of ring-focus antennas for VGOS: first investigations at the Onsala twin telescopes project

Lösler

Haas

Eschelbach

et al. 2019

J Geod

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Baseline vector repeatability at the sub-millimeter level enabled by radio interferometer phase delays of intra-site baselines

Mei-ling¹,

Savolainen²,

Bolotin³

et al. 2021

Preprint

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The technique of very-long-baseline interferometry (VLBI) combines the signal of a radio source recorded by a pair of radio antennas to provide the delay, both phase delay and group delay, of the arrival times at the two antennas. It was initially developed for astronomy in the late 1960s to derive high angular resolution images for celestial objects and was later also used for geodesy to determine the orientation of the Earth in space and the positions of the antennas on the Earth with a high precision (see, Sovers et al., 1998, and the references therein). In astronomy, the highest accuracy is obtained by making use of the full precision of phase delays for relative

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Baseline vector repeatability at the sub-millimeter level enabled by radio interferometer phase delays of intra-site baselines

Mei-ling

Savolainen

Bolotin³

et al. 2022

Preprint

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We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very-long-baseline interferometry (VLBI) observations rather than dedicated short-baseline experiments. An analysis of phase delay observables from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24-hour VLBI sessions since 2019 yields weighted root-mean-square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N-WETTZELL enable an investigation of sources of error at the sub-millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the up estimates of this baseline vector when atmospheric delays were estimated. Although the sub-millimeter repeatability has been achieved for the baseline vector WETTZ13N-WETTZELL, we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step towards the goal of global geodesy at the 1 mm level.

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A gravitational telescope deformation model for geodetic VLBI

Cited by 12 publications

References 17 publications

Gravitational deformation of ring-focus antennas for VGOS: first investigations at the Onsala twin telescopes project

Gravitational deformation of ring-focus antennas for VGOS: first investigations at the Onsala twin telescopes project

Baseline vector repeatability at the sub-millimeter level enabled by radio interferometer phase delays of intra-site baselines

Baseline vector repeatability at the sub-millimeter level enabled by radio interferometer phase delays of intra-site baselines

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