The Hartebeesthoek Terrestrial Laser Scanning Project – Concept and First Results

In May 2024, gravitational deformation measurements were performed at the 26 m and 15 m radio telescopes ofthe South African Radio Astronomy Observatory at Hartebeesthoek (HARTRAO and HART15M) in cooperationof SARAO, TU München and TU Wien. The method of choice was to use a terrestrial laser scanner (TLS)mounted underneath the sub-reflector with a two-axis gimbal hinge to keep the scanner in a vertical position atall telescope tilts. For a full gravitational VLBI delay model, the 26 m HARTRAO telescope with polar mountwas pointed at about 80 different Hour Angle/Declination positions for the TLS to perform its scans of the mainreflector and the sub-reflector. Here, we present the necessary steps of preparation, the measurements themselves,and first results.