Performance Analysis of the QDaedalus Astrogeodetic Measurement System
by CODIAC parallel Observations at the Zimmerwald Observatory in
Switzerland
Abstract
The astrogeodetic or Helmert deflection of the vertical (DoV) data, as
opposed to data obtained through other geodetic instruments (e.g., GNSS
(geodetic coordinates), levelling (normal or orthometric heights) and
gravimeters (gravity data)), cannot be readily obtained by astrogeodetic
instruments. In order to obtain these data, geodetic and astronomical
latitude and longitude information is required. Currently, geodetic
latitude and longitude (φ, λ) are measured with GNSS receivers, while
astronomical latitude and longitude (Φ, Λ) are observed with Digital
Zenith Camera Systems (DZCSs) or the QDaedalus system. The result of
these observations are the astrogeodetic North-South (ξ=Φ-φ) and
East-West (η=(Λ-λ)cosφ) DoV components. This study investigates the
precision and accuracy of the newly installed tachymeter-based (multi
station (MS) 60) QDaedalus astrogeodetic measurement system’s DoV data
with the aid of promising DoV data from the Compact Digital Astronomical
Camera (CODIAC) DZCS. For this study, we used the CODIAC (accuracy of
∼0.05″) and QDaedalus (accuracy of ~0.20″) systems to
conduct parallel measurements over 2 nights (measurement duration of
more than 20 hours) at the Zimmerwald Observatory in Switzerland. Both
the CODIAC and QDaedalus systems were developed at ETH Zurich. CODIAC
has the standard DZCS components seen in other DZCSs in Germany, Latvia,
Turkey and China: telescope, charge-coupled device (CCD) camera,
tiltmeters, focuser, single frequency GNSS receiver and antenna, laptop,
and substructure. While each DZCS has a unique design, CODIAC has
upgraded hardware components (such as the use of four tiltmeters-two
Wyler and two Lipmann High-Resolution Tiltmeters) as well as advanced
software and processing technology. The key components of the QDaedalus
which differ from the DZCS are tachymeter, interface box, and mountable
meniscus lens. Also, the measurement principle and data evaluation
processes of these two systems differ; therefore, we also describe the
data evaluation methods for both the CODIAC and QDaedalus systems.
Finally, we discuss the results of the parallel measurements and their
implications for further astrogeodetic work.