Comparison of geodetic and radio interferometric measurements of the Haystack‐Westford base line vector

Carter, William E.; Rogers, A. E. E.; Counselman, C. C.; Shapiro, I. I.

doi:10.1029/jb085ib05p02685

Cited by 35 publications

(15 citation statements)

References 7 publications

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“…Also, the precise orbits were used by all GPS ACs, reducing orbit error effect on PWV estimates. VLBI is not sensitive to the PWV estimates with changing elevation angle (Niell et al, 2001), and a limit of less than 0.2 mm of PWV can be set on this type of error due to the motion of the antenna, due either to deformation of the antenna itself, or to changes in electrical path length of the cables with antenna orientation (Carter et al, 1980;Herring, 1992). The mapping function causes a dry bias of less than 1 mm in the PWV estimates (Tregoning et al, 1998).…”

Section: Discussionmentioning

confidence: 97%

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

Jin

Luo

Cho

2009

Journal of Atmospheric and Solar-Terrestrial Physics

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Section: Discussionmentioning

confidence: 97%

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

Jin

Luo

Cho

2009

Journal of Atmospheric and Solar-Terrestrial Physics

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“…The most likely cause of such errors is associated with the motion of the antenna, due either to deformation of the antenna itself, or to changes in electrical path length of the cables with antenna orientation. A limit of less than 1 mm of ZWD can be set on this type of error due to the close agreement of the relative positions of the Westford and Haystack antennas (separated by 1.4 km) determined by VLBI and by conventional geodesy (Carter et al 1980;).…”

Section: E Vlbimentioning

confidence: 99%

Comparison of Measurements of Atmospheric Wet Delay by Radiosonde, Water Vapor Radiometer, GPS, and VLBI

Niell¹,

Coster²,

Solheim³

et al. 2001

J. Atmos. Oceanic Technol.

255

185

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The accuracy of the Global Positioning System (GPS) as an instrument for measuring the integrated water vapor content of the atmosphere has been evaluated by comparison with concurrent observations made over a 14-day period by radiosonde, microwave water vapor radiometer (WVR), and Very Long Baseline Interferometry (VLBI). The Vaisala RS-80 A-HUMICAP radiosondes required a correction to the relative humidity readings (provided by Vaisala) to account for packaging contamination; the WVR data required a correction in order to be consistent with the wet refractivity formulation of the VLBI, GPS, and radiosondes. The best agreement of zenith wet delay (ZWD) among the collocated WVR, radiosondes, VLBI, and GPS was for minimum elevations of the GPS measurements below 10Њ. After corrections were applied to the WVR and radiosonde measurements, WVR, GPS, and VLBI (with 5Њ minimum elevation angle cutoff ) agreed within ϳ6 mm of ZWD [1 mm of precipitable water vapor (PWV)] when the differences were averaged, while the radiosondes averaged ϳ6 mm of ZWD lower than the WVR. After the removal of biases between the techniques, the VLBI and GPS scales differ by less than 3%, while the WVR scale was ϳ5% higher and the radiosonde scale was ϳ5% lower. Estimates of zenith wet delay by GPS receivers equipped with Dorne-Margolin choke ring antennas were found to have a strong dependence on the minimum elevation angle of the data. Elevation angle dependent phase errors for the GPS antenna/mount combination can produce ZWD errors of greater than 30 mm over a few hour interval for typical GPS satellite coverage. The VLBI measurements of ZWD are independent of minimum elevation angle and, based on known error sources, appear to be the most accurate of the four techniques.

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“…Moreover, investigations are needed to verify the possible hysteresis of the focal length variations. Furthermore, the Onsala Space Observatory is in the possibility of having the SPV variation model externally validated by comparing the baseline derived by high-precision terrestrial observations and the baseline obtained by the VLBI data analysis (e.g., Carter et al 1980). For this purpose, terrestrial measurement campaigns are planed to derive the local base-line vectors between the hosted space geodetic techniques at Onsala.…”

Section: Resultsmentioning

confidence: 99%

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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Comparison of geodetic and radio interferometric measurements of the Haystack‐Westford base line vector

Cited by 35 publications

References 7 publications

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

Comparison of Measurements of Atmospheric Wet Delay by Radiosonde, Water Vapor Radiometer, GPS, and VLBI

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

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