Modernizing and Upgrading the Astrogeodetic Camera System for Determining Vertical Deflections

The geoid is the equipotential surface of the Earth. Modeling the geoid with high accuracy is one of the critical issues in Geodesy. Development of geoid modeling is based on geodetic, gravimetric and astrogeodetic techniques. In order to reach the intended accuracy, deflection of the vertical (VD) components, which is obtained by the astrogeodetic techniques, can be used. VD is also very important for providing valuable information on the structure of Earth's gravity field. For this reason, astrogeodetic observations were essential gravity field observables and used for astrogeodetic geoid determinations. Scientists in several countries have developed modern instruments to measure vertical deflections. One of those instruments, namely Astro-geodetic Camera System (ACSYS) was developed in Turkey in 2015. The system components include a telescope, a Charged Coupled Device (CCD), two tiltmeters with the accuracy of 0.01 milliradians, a focuser, a single frequency GPS receiver and a substructure. The first version of the ACSYS is capable of determining astronomical coordinates with an accuracy of 0.2-0.3 arc sec, yet it has some limitations in observation duration. Because of the semi-automated mechanical design, leveling the system towards zenith was a time-consuming process. Since the beginning of 2016, the ACSYS has been modernized through the upgrade of the system with new technological components, hardware and software which is supported by The Scientific and Research Council of Turkey. Upgrade process includes the installation of a high-resolution tiltmeter with an accuracy of 1 nano-radians, implementation of a temperature compensating focuser and fully automatized substructure system. The components of the system are controlled by specially designed and integrated software. In the scope of the modernization studies, the project team has also been working on a unified real-time processing and control software for the ACSYS.v2. This study introduces the modernization process of the first digital zenith camera system of Turkey, and discuss the new strategy for the tests and calibrations with the new substructure.