| 1. |
- Bergstrand, Sten, et al.
(författare)
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A gravitational telescope deformation model for geodetic VLBI
- 2019
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Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 93:5, s. 669-680
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.
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| 2. |
- Bergstrand, Sten, 1971, et al.
(författare)
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Geometric Variations of a Geodetic Radio Telescope
- 2017
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Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041104 ; , s. 61-64
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Lindgren, Mikael, 1963-, et al.
(författare)
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CHARACTERIZATION OF REFLECTIVITY AND GEOMETRY FOR SOFT CAR TARGETS
- 2019
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Ingår i: Proceedings of the 29th Session of the CIE. - Wien. - 9783902842749 ; , s. 1753-1767
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper reports on results from a study of characteristics for 3D soft surrogate vehicle targets. Such targets are used extensively for testing and verification of optical sensor systems for Advanced Driver Assistance Systems and Automated Driving. However, the influence of wear-and-tear on the vehicle target is not well known. Consequently, no clear requirement exists on how many collisions a soft target can be exposed to before it no longer performs well.Important characteristics for optical sensor systems are surface reflectance in the relevant wavelength range and geometry of the soft target. We report on measurements of spectral reflectivity and geometry performed before, during and after an accelerated ageing campaign involving 100 rear-end collisions at 50 km/h. The reflectivity was found to change very little while the geometry was strongly affected.
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