Digital Zenith Cameras – State-of-the-Art Astrogeodetic Technology for Australian Geodesy

Over recent years, significant progress has been made in astrogeodetic research with the development of digital zenith camera systems (DZCSs) at ETH Zurich, Switzerland, and the University of Hanover, Germany. The use of charged coupled device (CCD) sensors for star imaging improved the degree of automation, accuracy and efficiency of this modern astrogeodetic instrumentation. With DZCSs, vertical deflection determinations usually take about 20 minutes, including highly-redundant observation and data processing. Depending on the distance between field stations, DZCSs allow collection of vertical deflections at 10 or even more stations per night. This is a considerable improvement over the earlier timeconsuming astrogeodetic techniques (e.g., analogue zenith cameras or astrolabes). Between 2003 and 2008, the Hanover and Zurich DZCSs have been used to observe vertical deflections at about 900 new stations in several European countries. The accuracy of DZCS vertical deflections is 0.1 arc-seconds and better. The main applications of DZCS vertical deflections are local and regional highly-precise geoid/quasigeoid determinations, but they can also be used to connect geometric and natural/astronomic coordinate systems.