Astrogeodetic Observation Campaigns of Summer 2021: Repeated and Parallel Observations Using the QDaedalus and CODIAC Systems

The total station-based QDaedalus system has been used to observe astrogeodetic deflections of the vertical (DoV) since 2014. DoV observations have been made to determine the precision and accuracy of various QDaedalus systems based on comparison with repeated measurements or previously obtained values from the Digital Zenith Camera Systems (e.g., TZK2-D, DIADEM and CODIAC). More recently, simultaneous parallel observations using two QDaedalus systems or one QDaedalus together with one CODIAC to check the precision or accuracy of the system under identical conditions have also been made.

In the summer 2021 campaign, the MS60 MultiStation-based QDaedalus system was tested to ensure that the QDaedalus has no bias during observations. We previously found biases for QDaedalus in the winter 2021 observation campaigns to determine the precision and accuracy. The precision was determined at the first HEIG-VD test station over 13 nights (in a 44-day observation period from February-April 2021) and the accuracy was determined by simultaneous parallel measurements with the CODIAC at the Zimmerwald Observatory over two days (February-March 2021). From these results, the precision and accuracy of both DoV components were determined as 0.1″. However, we found biases during both campaigns: at the HEIG-VD test station, the N-S DoV component has a large systematic trend (0.008″/day); and, at the Zimmerwald Observatory, we observed a bias with the CODIAC results. To further investigate the cause of both biases, we conducted a new observation campaign in summer 2021 where we changed the HEIG-VD station from a ground mark to the top of the HEIG-VD building's portable survey pillar. We conducted several QDaedalus observations at this pillar before removing the pillar to install the CODIAC, which cannot be installed on a pillar. The CODIAC was deployed over five nights, and on the last night, we did parallel measurements with the MS60-based QDaedalus. During this summer 2021 campaign, we did not encounter biases in either QDaedalus or CODIAC. We conclude, therefore, that the identified bias for QDaedalus in winter could be explained by large temperature variations; however, further investigation is required. These observation campaigns have confirmed that the QDaedalus is able to observe highly accurate DoVs.