Laser scanning of 32-m radio telescope: measurements of main dish geometry and panels alignment (internal)

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Create Date Tuesday January 29th, 2019
Last Updated 2019-04-16

Laser scanning measurements of Toruń 32-m radio telescope are discussed in relation to dish surface accuracy. We compare scanning data from different laser scanners, investigate dish shape, focal lengths and their zenith distance (ZD) dependence. We also model and calculate panel alignment corrections required for improving the dish surface accuracy. We select the most suitable data and seek the most promising method of calculating offsets for each of the screws that control the panel alignment. We provide a list of corrections and calculate anticipated gains in the antenna efficiency after their implementation.

We estimate that the main dish focal length is <1 mm shorter than the design value of 11.2 m and that it is weakly time dependent. We detect the dish has non-zero elongation along axis that is roughly perpendicular to the elevation axis at zenith, however the orientation of the best-fitting elliptical paraboloid rotates as the antenna points at larger ZDs. Assuming circular paraboloid with flexible focal length, we estimate that the current axial/normal dish surface RMS error is at the level of ∼0.62/0.54 mm. After optimizing panel alignments (and without optimizing individual panels’ shapes) we anticipate the axial/normal dish surface RMSrror should improve to ∼0.35/0.31 mm.