Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning

Abstract

The main re ectors of radio telescopes deform due to gravitation when changing their elevation angle. This can be analyzed by scanning the paraboloid surface with a terrestrial laser scanner and by determining focal length variations and local deformations from best-t approximations.For the E elsberg radio telescope, both groups of deformations are estimated from seven points clouds measured at di erent elevation angles of the telescope: the focal length decreases by . mm when tilting the telescope from deg to . deg elevation angle. Variable deformations of ± mm are detected as well at certain areas. Furthermore, a few surface panels seem to be misaligned. Apart from these results, the present study highlights the need for an appropriate measurement concept and for preprocessing steps when using laser scanners for area-based deformation analyses. Especially, data reduction, object segmentation and laser scanner calibration are discussed in more detail. An omission of these steps would signicantly degrade the deformation analysis and the signicance of its results. This holds for all sorts of laser scanner based analyses.

Terrestrial Laser Scanner Two-Face Measurements for Analyzing the Elevation-Dependent Deformation of the Onsala Space Observatory 20-m Radio Telescope’s Main Reflector in a Bundle Adjustment

“…This can only be achieved if the scanner is mounted on the radio telescope itself so that it moves together with the main reflector when changing the elevation angle. Similar to previous studies at the Effelsberg 100 m radio telescope [ 18 ], positioning the laser scanner at the subreflector would have been preferable. However, since the Onsala 20 m radio telescope is of smaller size, a station could only be realized by a support that was fixed to one of the four beams holding the subreflector ( Figure 2 ).…”

“…Terrestrial laser scanning has also been used for determining changes of focal lengths and areal reflector deformations of radio telescopes at several occasions before [ 14 , 15 , 16 , 17 , 18 , 19 ]. New in this publication is the situation that we adopt and enhance the findings of laser scanner calibration to the deformation analysis of radio telescopes’ main reflectors.…”

“…Hence, the parameters describing the potential mechanical misalignment of the laser scanner are estimated as part of the common deformation analysis leading to an in situ self-calibration. This approach has been introduced for the deformation analysis of the Effelsberg 100-m radio telescope’s main reflector by [ 9 , 18 ] including also a sensitivity analysis. However, deviating from the present study, the Effelsberg radio telescope was not scanned in two cycles or faces, respectively.…”

“…The data pre-processing includes the steps of data reduction, object segmentation and outlier removing that have been introduced for an accurate deformation analysis of radio telescopes [ 18 ]. To avoid repetitions, the necessity and implementation of these steps is only briefly recapitulated here.…”

A Framework Based on Reference Data with Superordinate Accuracy for the Quality Analysis of Terrestrial Laser Scanning-Based Multi-Sensor-Systems

“…Sensor-specific influences like axis deviations [ 9 , 10 , 11 , 12 , 13 ], object-specific influences like material, colour and reflectance [ 14 ] and distance and incidence angle-caused influences are investigated separately and documented in the literature [ 15 , 16 , 17 ]. Approaches to combine all influences in one model are made in the context of forward modelling based on Monte Carlo Simulations in [ 18 ].…”