The determination of the reference point of the VLBI antenna in Ny-Alesund (scientific note)

• Main Authors: Tomasi,Paolo, Sarti,Pierguido, Rioja,Maria
• Format: Report
• Language: English
• Published: Istituto di Radioastronomia, CNR/Istituto di Radioastronomia, CNR/Istituto di Radioastronomia, CNR 2001
• Subjects: Ny-Ålesund; Pillar; Memoirs of National Institute of Polar Research; Ny Ålesund; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2386; http://id.nii.ac.jp/1291/00002386/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2386&item_no=1&attribute_id=18&file_no=1

We present here, the results of a campaign of measures carried on between August 25th and September 8th, 1999,in Ny-Ålesund, to tie the reference point of the VLBI antenna on the ground marks. A number of Leica retro-targets has been attached (glued) all over the structure of the antenna, and their positions determined (horizontal and vertical angles, along with distance whenever it was possible) with respect to a local reference network. The positions of two points at opposite edges of the elevation axis have also been pinpointed and measured (only horizontal and vertical angles. in this case), to determine the vertical component of the reference point and to measure the offset between the elevation and azimuth axes. The local reference network has been measured using direct and inverse intersection depending on different position and mutual visibility of pillars. Occasionally some pillars have been measured using both methodologies. Furthermore, trigonometric levelling has been performed for connecting the levelling bolts of the six closest pillars to the 3-D network adjustment results and therefore obtain an univocal determination of the height of the VLBI reference point tight to the altimetric control network. The positions of several markers on the antenna have been measured for 8 antenna azimuth angles, uniformly spread along 360 degrees, in steps of 45 degrees, with the VLBI antenna at the same elevation angle, nearly at the zenith direction. In order to test the position of the elevation axis, we did similar measures on a selected number of markers at different antenna elevation angles, in the range from 90 to 45 degrees, in steps of 15 degrees, for a fixed azimuth angle. The analysis of these measures provide both coordinates for the position of the reference point of the VLBI antenna, and an estimate of the offset between the elevation and azimuth axes in the antenna of Ny-Ålesund. The offset vector from the reference pillar selected (marker 91) is X=21.830±0.001m and Y=18.787±0.001m, while the height ...