Abstract
For accurate astronomic and geodetic observations based on radio telescopes, the elevation-dependent deformation of the radio telescopes’ main reflectors should be known. Terrestrial laser scanning has been used for determining the corresponding changes of focal lengths and areal reflector deformations at several occasions before. New in this publication is the situation in which we minimize systematic measurement errors by an improved measurement and data-processing concept: Sampling the main reflector in both faces of the laser scanner and calibrating the laser scanner in situ in a bundle adjustment. This concept is applied to the Onsala Space Observatory 20-m radio telescope: The focal length of the main reflector decreases by 9.6 mm from 85 to 5 elevation angle. Further local deformations of the main reflector are not detected.
Highlights
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 increase the accuracy of geodetic and astronometric measurements performed by a radio telescope, its elevation-dependent deformation should be known very accurately
The present study presents a new measurement and data-processing concept based on a terrestrial laser scanner, applied to the OSO 20-m radio telescope
Summary
Terrestrial laser scanners are widely used in engineering geodesy both for documentation and for deformation monitoring. The Onsala Space Observatory (OSO) 20-m radio telescope is a mm- and cm-wave antenna with a focal length of about 9 m, located about 50 km south of Goteborg, Sweden (Figure 1 left) It consists of 120 solid panels forming the shape of a rotational paraboloid. Changes in focal length of the main reflector or local deformations on the reflector’s surface directly lead to biased signal paths and, biased baseline estimates [22]. Both geometric properties should be known very accurately. This study proposes several general insights in the deformation analysis of large civil infrastructures as well as in the quality assurance when using TLS for such engineering tasks demanding high accuracy
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