Investigating the Function of the Star Trails to Improve the Determination of Gravity Field

Recently Geodetic Astronomy provides high precision deflection of the vertical (DoV) data through Digital Zenith Camera Systems (DZCS), which contribute to the accurate geoid modelling studies. The DZCSs process the star images which are captured near the zenith direction, and combine the solutions with GNSS data to calculate DoV components. The DoV components can be used to derive the slope of the geoid, and can be performed as profiles or as network solutions. Thus, it can be possible to produce geoid undulations using astronomical levelling technique, and can be compared and combined with GNSS/Levelling data. Between 2014 and 2018 several observations were performed in Istanbul-Turkey to improve local geoid model that produce vast amount of observation data. The data was collected as star images in various exposure time in order to test the best solution to acquire accurate coordinates. Therefore, the quality of the star images is directly correlated with the results which need to be investigated with the help of the astrometric image processing techniques. This study investigates the effect of the star number and image quality using star trail functions and introducing a mathematical model to improve the accuracy of the image reduction process. Thus, it investigates the possible model function to produce more accurate astronomical coordinates, to obtain precise DoV components that can be used in geoid determination.