Monitoring Gravitational Deformations of the Wettzell 20 m Radio Telescope’s Main Reflector Using a Leica RTC360

Abstract

Quasars are nowadays the basis to determine the world’s absolute orientation in space by radio interferometry (VLBI). The global network of baselines measured by the used radio telescopes, which vary greatly in size, is subject to various influences that have an impact on the International Terrestrial Reference Frame. Among others, those influences are imperfections of individual panels of the dishes, a possible elevation dependent deformation of the whole dish and a shift of the reference point due to gravitational influences. In this study, we monitor the elevation dependent deformation of the main reflector of the 20 m radio telescope of the Geodetic Observatory Wettzell by a Leica RTC360 laser scanner. For this task, we mount the terrestrial laser scanner overhead near the subreflector to capture the surface of the moving dish at each elevation angle. This study focusses on 1) introducing further redundancy in the measurement and processing strategy to gain a reliable and accurate result even the used scanner is a no high-end one. This furthermore leads to 2) investigations whether there are differences in the results between in related work used high-end scanners and the RTC360 and thus 3) whether the RTC360 proves to be capable to detect deformations at a radio telescope’s main reflector. Using these three foci, we show that deformations in the main reflector between elevations can be reliably determined areal and in focal length by redundant measurements with the RTC360. It is also shown that the results are less sensitive to axis errors compared to those obtained with high-end scanners. However, the compensations also show that the application scanner has certain systematics, which must be investigated in further steps.